Master’s Thesis (Academic Year 2018)

A study of beam background from SuperKEKB
on Belle II Silicon Vertex Detector(Belle II シリコン崩壊点位置検出器の受けるSuperKEKB からのビームバックグラウンドの研究)

The University of Tokyo
Department of Physics, Graduate School of Science

Hikaru Tanigawa

January 31, 2019

Abstract
The Belle II experiment plans to start its full operation in March 2019 hosted by KEK in
Tsukuba, Japan. The SuperKEKB accelerator has been upgraded to collide e+ and e− beams at
a rate forty times higher than its predecessor. The Belle II detector detects the decay productsof the particles created after e+ e− annihilations to explore new areas of flavor physics.
This thesis focuses on the silicon vertex detector at the core of the Belle II detector. The
upgrade of SuperKEKB introduces a challenging environment for the silicon vertex detector in
two ways: the high data acquisition rate leads to an unignorable dead time of its readout ASIC
and the intense beam background causes detector performance to deteriorate. We developed afirmware module which emulates the data processing procedure of the readout ASIC and minimizes the dead time by optimal trigger-veto. We investigated the beam background condition
with a subset of the detector in the commissioning phase which ran from March to July of 2018.
Based on our estimation of the beam background level in full operation, the full silicon vertex
detector was installed in the Belle II detector.

iContents
1 Introduction

12 Physics motivation

3

2.1

Quark sector of the Standard Model . . . . . . . . . . . . . . . . . . . . . . . . .

3

2.2

The CKM matrix and Unitarity triangle . . . . . . . . . . . . . . . . . . . . . . .

4

3 The Belle II experiment7

3.1

Operation schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7

3.2

SuperKEKB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7

3.2.1

Main storage ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

3.2.2

Nano-beam scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

3.2.3

Linac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2.4

Beam injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3

3.4

3.5

Belle II detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1

Subdetectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.3.2

Target trigger rate in Belle II . . . . . . . . . . . . . . . . . . . . . . . . . 13

SVD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.4.1

Structure of the SVD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4.2

Readout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4.3

Oﬄine signal reconstruction by basf2 . . . . . . . . . . . . . . . . . . . . . 20

3.4.4

Phase 2 SVD cartridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.4.5

Diamond detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Key research subjects in this thesis . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4 Trigger veto

25

4.1

Issue on trigger-veto for SVD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.2

Design of the APV25-FIFO emulator . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3

4.4

4.2.1

Development test bench for the APV25-FIFO emulator . . . . . . . . . . 26

4.2.2

APV25 data processing model

4.2.3

Clock frequency gap between the FTSW and the APV25 . . . . . . . . . 30

4.2.4

Reset timing gap between the FTSW and the FADC-Ctrl . . . . . . . . . 33

. . . . . . . . . . . . . . . . . . . . . . . . 26

Performance evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3.1

Operation check in the test bench . . . . . . . . . . . . . . . . . . . . . . 36

4.3.2

Trigger loss rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.3.3

High trigger rate test in the Phase 2 setup . . . . . . . . . . . . . . . . . . 37

Further improvement in trigger loss rate due to trigger with good timing resolution 38ii

5 Beam backgrounds
5.1

5.2

5.3

40

Background tolerance of the SVD and purpose of study . . . . . . . . . . . . . . 40
5.1.1

Occupancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.1.2

Radiation damage to silicon sensors . . . . . . . . . . . . . . . . . . . . . 41

5.1.3

Radiation tolerance for Belle II SVD . . . . . . . . . . . . . . . . . . . . . 41

5.1.4

Purpose of Phase 2 beam background study . . . . . . . . . . . . . . . . . 41

Beam background sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2.1

Touschek scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.2.2

Beam-gas scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.2.3

Synchrotron radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.2.4

Luminosity backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.2.5

Injection background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Single-beam background model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

6 Beam background simulation

45

6.1

Beam background simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6.2

Simulation for Phase 2 and Phase 3 design optics . . . . . . . . . . . . . . . . . . 46

6.3

Phase 2 realistic simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

6.4

HER SR simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7 Analysis of the beam background data

58

7.1

Beam background evolution over Phase 2 . . . . . . . . . . . . . . . . . . . . . . 59

7.2

Decomposition of Touschek and beam-gas components . . . . . . . . . . . . . . . 59

7.3

7.4

7.2.1

Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

7.2.2

Beam size scans in Phase 2 . . . . . . . . . . . . . . . . . . . . . . . . . . 61

7.2.3

Pressure correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

7.2.4

Errors of the variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

7.2.5

Noise subtraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

7.2.6

Heuristic analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

7.2.7

Gas composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Synchrotron radiation study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.3.1

Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

7.3.2

Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Luminosity backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.4.1

Sensitivity to the luminosity backgrounds . . . . . . . . . . . . . . . . . . 79

7.4.2

Instability of the single-beam backgrounds . . . . . . . . . . . . . . . . . . 79

7.4.3

SVD-TOP correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

7.4.4

Decomposition of background spatial distributions . . . . . . . . . . . . . 81

iii

7.5

Injection background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

7.6

SVD-Diamond correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

7.7

Estimation of the Phase 3 beam background . . . . . . . . . . . . . . . . . . . . . 89

8 Conclusion

98

8.1

Achievements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

8.2

Remaining studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

A The strip charts during beam background measurements

101

B The result of the Phase 3 beam background simulation

108

C The result of the Phase 3 beam background estimation

144

iv

Chapter 1

Introduction
The Belle II experiment is conducted at the SuperKEKB collider in Tsukuba, Japan. The
center-of-mass energy of the asymmetric-energy e+ e− collider is set at the resonance of Υ(4S)
meson, which predominantly decays into a pair of B and anti-B mesons. The previous Belle experiment measured CP-violating parameters in the B decays to confirm the Kobayashi-Maskawa
theory. One of the physical goals of the Belle II experiment is a high-precision measurement of
the parameters with high-statistics data. To produce more BB pairs, SuperKEKB will achieve
forty-fold higher peak luminosity than its predecessor by introducing a “nano-beam” scheme
and increasing beam currents. Thus, the Belle II detector is required to record data at a muchhigher rate while dealing with much more intense beam backgrounds.
The operation of the SuperKEKB collider and the Belle II detector is separated into threephases. In Phase 1, the accelerator was commissioned without beam collisions. Single-beambackgrounds were studied with several background monitors in the absence of the Belle II detector. In Phase 2, beam collisions were realized and the Belle II detector without the Vertex
Detector (VXD) was installed. Instead of the VXD, a subset of the VXD sensors and anotherset of background monitors were installed at the core of the Belle II detector. The verificationof the nano-beam scheme, the commissioning of the Belle II detector with collision data andthe measurement of the beam backgrounds were performed in Phase 2. In Phase 3, the fulloperation will start with all the subdetectors to accumulate physics data.
The important observables of the Belle II experiment include time-dependent CP asymmetries in the B decays. The BB mesons produced almost at rest in the center-of-mass frame
fly along the beam axis, boosted due to the asymmetric beam energies. The flight lengths aretranslated into decay times to measure the time-dependent CP asymmetries. Here the precise
measurement of the decay vertices with the VXD plays a crucial role. The VXD consists of
two types of silicon detectors, the inner Pixel Detector (PXD) and the outer Silicon Vertex
Detector (SVD). These detectors measure the trajectories of charged particles. The main rolesof the SVD are as follows: determination of the readout region of the PXD by extrapolating
the tracks, vertex reconstruction of long-lived KS0 mesons decaying outside the PXD volume,and measurement of the momenta of low-momentum tracks.
This thesis focuses on two issues related to the SVD arising from the upgrade of the experiment. Firstly, the limited size of the trigger buﬀer in the readout ASIC used in the SVD
causes trigger dead time at the high data acquisition rate in Belle II. We developed a firmware
module that is to be loaded in an FPGA in the trigger distributing system. The firmware is1

optimized for the ASIC and vetoes triggers in a way that minimizes the trigger dead time. The
development and performance of the firmware are reported in this thesis. Secondly, the intense
beam backgrounds lead to deterioration of the tracking performance and radiation damage on
the detector. We report on the beam background studies in Phase 2 conducted with a subset of
the SVD. Based on these studies, we estimate the beam backgrounds in Phase 3 to resolve twopoints: One is if the SVD can start running with good performance at the beginning of Phase
3 and the other is if it can go through the whole Phase 3 without suﬀering serious radiation
damage. We also confirm the correlation between the SVD and the radiation monitor system
in order to ensure the eﬀective protection of the SVD by the radiation monitors.
The remaining chapters in the thesis are as follows. In Chapter 2, we introduce the physics
motivation for the Belle II experiment. In Chapter 3, we describe the properties of the SuperKEKB accelerator and the Belle II detector. In Chapter 4, we explain the issue on thetrigger dead time, and the development and the performance evaluation of the trigger-vetomodule. In Chapter 5, we describe the eﬀect of the beam background on the SVD and thevarious beam background sources in SuperKEKB. In Chapter 6, we focus on the simulationof the beam backgrounds. In Chapter 7, the results of the beam background studies in Phase
2 are discussed. In Chapter 8, we summarize the thesis by describing our achievements andremaining studies.

2Chapter 2

Physics motivation
2.1

Quark sector of the Standard Model

The Standard Model (SM) of elementary particles is a chiral gauge field theory with SU (3)C ×
SU (2)L × U (1)Y symmetry. It contains three generations of up-type and down-type quarks
shown in Tab. 2.1. While the left-handed fields form doublets of the SU (2)L group, the righthanded fields are singlets. The U (1)Y hypercharge Y is also diﬀerent. The quark fields couple
with the Higgs field which is an SU (2)L doublet via the Yukawa interaction. Because the Higgs
field has a nonzero vacuum expectation value v, the Yukawa interaction gives rise to the quark
mass terms:
′
u ′
d ′
(2.1)
uRk − vdLj Yjk
dRk + h.c.
Lm = −v u′Lj Yjk′
are weak eigenstates of the quark fields with generation index j, Y u
Here, u′L,Rj and dL,Rj
and Y d are 3 × 3 complex matrices, h.c. stands for Hermitian conjugate. The terms are
summed over the repeated indices. The Yukawa matrices Y u,d are transformed into diagonal
matrices with real numbers by the unitary rotation of the quark fields in the generation space

Table 2.1: The quantum numbers of the quark fields. uL(R) and dL(R) represent left-handed(right-handed) up-type and down-type quark fields, respectively. The index j = 1, 2, 3 denotes
the generation. T3 is the third component of weak isospin, Y is hypercharge, Q is electric chargeof U (1)EM symmetry.
T3
Y
Q
(
)
+ 12
+ 23
uLj
1
+
3
− 12
− 13
dLj
uRj
dRj

+ 34
− 32

0
0

3

+ 23
− 13

u
d
u′L(R)j = SL(R)jk
uL(R)k , d′L(R)j = SL(R)jkdL(R)k [1]:
u†
d†
u u
d d
Ylm
Ylm
Lm = −vuLj SLjl
SRmk uRk − vdLj SLjl
SRmk d′Rk + h.c.

=ud−uLj Mjk
uRk − dLj MjkdRk + h.c.

= −

∑

(2.2)
(2.3)

mq (q L qR + q R qL )

(2.4)

mq qq

(2.5)

q=u,d,s,c,b,t= −∑

q=u,d,s,c,b,t(2.6)
where M u = S u† Y u S u = diag(mu , mc , mt ) and M d = S d† Y d S d = diag(md , ms , mb ) are diagonal
matrices with quark masses, uL(R)1,2,3 = uL(R) , cL(R) , tL(R) and dL(R)1,2,3 = dL(R) , sL(R) , bL(R)are mass eigenstates, and q = qL + qR denotes the Dirac fields of quarks.
The interactions are described by the gauge symmetry; SU (3)C describes the strong interaction. Because of the nonzero vacuum expectation value of the Higgs field, SU (2)L × U (1)Y
spontaneously breaks to U (1)EM . Consequently, the SU (2)L and U (1)Y gauge bosons are mixed
into photons and weak bosons, which respectively mediate the electromagnetic and weak interaction. By using the weak eigenstates, the charged current of weak interaction is expressed
as
]
g2 [
′
LW = √ u′Lj γ µ d′Lj Wµ+ + dLj γ µ d′Lj Wµ−(2.7)
2where Wµ± denotes the W bosons, γ µ is gamma matrices, and g2 is the coupling constant of
SU (2)L . This is also transformed by the unitary rotation of the left-handed quark fields SLu,d :]g2 [u† µ dd† µ u(2.8)γ SLlk dLk Wµ+ + dLk SLjl
γ Slk dLj Wµ−
LW = √ uLj SLjl
2
]
g2 [
∗ µ
= √ uLj Vjk γ µ dLk Wµ+ + dLk Vjk
γ dLj Wµ−(2.9)
2where V = S u† S d is a 3×3 unitary matrix in the generation space called the Cabibbo-KobayashiMaskawa (CKM) matrix. Therefore, the weak doublets of quarks are redefined as
(
) (
) (
)
u
c
t
(2.10)
d′
s′
b′
L

L

L

where the weak eigenstates of the down-type quarks relate to the mass eigenstates via the CKM
matrix:


  
 
d′
d
Vud Vus Vub
d
 ′ 
  
 
(2.11)
 s  = V  s  =  Vcd Vcs Vcb   s  .
′bb
Vtd Vts Vtbb

2.2

The CKM matrix and Unitarity triangle

Generally, a 3 × 3 unitary matrix is characterized by three rotation angles and six complex
phases. Since the mass terms and kinetic terms of quarks are invariant under the phase rotationof the individual quark Dirac fields, five phases of the CKM matrix are absorbed by rotating

4

Figure 2.1: The unitarity triangle [3].
the relative phases of the six quark fields. Thus, the CKM matrix is parametrized by three
angles θij (ij = 12, 13, 23) and one complex phase δ:
c12 c13s12 c13s13 e−iδV =  −s12 c23 − c12 s23 s13 eiδ c12 c23 − s12 s23 s13 eiδ(2.12)
s23 c13 iδiδs12 s23 − c12 c23 s13 e−c12 s23 − s12 c23 s13 e
c23 c13
where sij = sin θij , cij = cos θij . The complex phase δ potentially causes CP violation in the
weak interaction of quarks. Since it is experimentally known that 1 ≫ s12 ≫ s23 ≫ s13 , theWolfenstein parametrization is often used to explicily show the hierarchy:
1 − λ2 /2λAλ3 (ρ − iη)


4
V =
(2.13)−λ1 − λ2 /2
Aλ2
 + O(λ ).
32
Aλ (1 − ρ − iη)−Aλ1Here, λ ≃ 0.22 and A, ρ, η = O(1).
The unitarity of the CKM matrix is expressed by twelve equations [2]. Among those, thefollowing two equations are suitable for measurements since all the terms on the left hand side
are of equal order, O(Aλ3 ):∗Vud Vub+ Vcd Vcb∗ + Vtd Vtb∗ = 0(2.14)∗∗∗
Vtd Vud+ Vts Vus
+ Vtb Vub
= 0.

(2.15)

They are expressed as triangles in the complex plane. The first triangle shown in Fig. 2.1 iscalled the “unitarity triangle” and their angles are given by)(
Vcd Vcb∗(2.16)
ϕ1 = arg −Vtd Vtb∗()
Vtd Vtb∗
ϕ2 = arg −(2.17)∗
Vud Vub(∗ )Vud Vub
ϕ3 = arg −.
(2.18)
Vcd Vcb∗

5

The triangle of Eq. (2.15) has the equal angles up to corrections of O(λ2 ). ϕ1 , ϕ2 , and ϕ3 are
independent observables that relate to ρ and η, which are not well measured compared to A
and λ. The independent measurents of the three angles lead to the verification of the SM. Thisis one of the physics goals of the Belle II experiment.
Among the three angles, ϕ1 has been most precisely measured by the Belle experimentthrough time-dependent CP asymmetry measurement of B 0 → J/ψKS0 . The determination ofsin 2ϕ1 through b → ccs tree processes is important in the Belle II experiment. One can also
determine sin 2ϕ1 by the time-dependent CP asymmetry of b → sqq penguin processes, which
is suppressed in the SM and hence sensitive to new physics.
The second angle ϕ2 is determined by measuring the time-dependent CP asymmetry ofb → uud transitions. The isospin analyses of B → ππ, ρρ, ρπ decays individually determine
ϕ2 .
Finally, ϕ3 is extracted from the interference of b → cus and b → ucs transitions in B → DK
decays. Since the decay modes include no penguin contribution, they provide theoritically clean
measurement of ϕ3 .

6

Chapter 3

The Belle II experiment
In this chapter, we describe the important features of the Belle II experiment. In particular, we
will devote particular attention to the SVD, which we mainly use for our study.

3.1

Operation schedule

The Belle II experiment is conducted in three phases. During Phase 1 in 2016, the accelerator was commissioned without the Belle II detector and the superconducting magnets for final
focusing of the beams (called “QCS” magnets). Single-beam backgrounds without beam collisions were studied with several types of dedicated background monitors collectively known as
BEAST II [4]. Phase 2 commissioning was conducted from March to July in 2018. In Phase2, the positron damping ring started its operation to improve the emittance of the injected
positron beam, which led to better injection eﬃciency. The beam collisions were realized byfocusing the beams with the QCS magnets. The Belle II detector without the Vertex Detector(VXD) was installed in the interaction region (IR) to record collision data. Instead of the VXD,
a subset of the VXD sensors and dedicated background monitors also called BEAST II detectors were installed in the VXD volume of the Belle II detector. Verification of the nano-beamscheme, commissioning of the Belle II detector with collision data and measurement of beam
backgrounds were performed in Phase 2. Phase 3 operation will start in March 2018 in orderto accumulate physics data, where all the subdetectors including the VXD are installed1 .

3.2

SuperKEKBThe SuperKEKB collider, shown in Fig. 3.1, is an electron-positron collider which consists of alinear accelerator (linac) and the main storage ring. The two rings have asymmetric energies:
the 7 GeV electron ring is called the High Energy Ring (HER), and the 4 GeV positron ring the
Low Energy Ring (LER).

1

The second layer of the PXD lacks ten ladders out of twelve. The installation of the whole PXD is plannedin 2020.

7

Figure 3.1: The SuperKEKB collider [5].

3.2.1

Main storage ring

The main storage ring consists of four arc sections and four straight sections. Dipole andquadrupole magnets are aligned along the circumference of 3016 m to bend and focus the beams.
Together with other correction magnets, these magnets determine how the beam particles propagate along the ring, which is called beam optics. In the middle of the Tsukuba straight section,
there are sets of superconducting quadrupole magnets (QCS) for the final focusing of the beam
before the collision at the interaction point (IP). The IP is surrounded by the Belle II detector.
The radio frequency of the accelerating cavities is 509 MHz. Thus, the ring has 5120 “buckets”,
in which a bunch of beam particles is stably accelerated by the cavities. In the designed situation, where every other bucket is filled by a bunch of the beam particles, the HER and LER
bunches cross each other every 4 ns. The machine parameters of SuperKEKB in Phase 2 and 3
are listed in Tab. 3.1.
The pressures inside the beam pipes are monitored by cold cathode gauges (CCGs). The
CCGs are installed together with the sputter ion pumps located approximately every 10 m along
the ring. The residual gas composition is analyzed by mass spectroscopy with two residual gas
analyzers (RGAs). The vertical and horizontal beam sizes are monitored by X-ray monitorsand synchrotron radiation monitors, respectively. Each ring has a bunch current monitor, a
DCCT (Direct Current Current Transformer) to monitor the beam current, and over 400 beam
position monitors.
For beam background mitigation, movable collimators are installed along the ring. In KEKB,

8

Table 3.1: The machine parameters of SuperKEKB. The Phase 2 parameters are the typicalones achieved in the late Phase 2. The Phase 3 parameters are taken from [6].
Phase 2Phase 3+−
Parameter [unit]
LER (e ) HER (e ) LER (e+ ) HER (e− )Beam energy [GeV]
4.0
7.007
4.0
7.007
Beam current I [mA]
327
279
3600
2600
Number of bunches nb
789
789
2500
2500
Bunch current I/nb [mA]
0.414
0.353
1.44
1.04
Horizontal emittance [nm]
1.7
4.6
3.2
4.6
Vertical emittance [pm]
–
–
8.64
12.9
Horizontal beta function at IP βx∗ [mm]
200
100
32
25
∗
Vertical beta function at IP βy [mm]
3
3
0.27
0.3
∗
Horizontal beam size at IP σx [µm]
–
–
10.1
10.7
Vertical beam size at IP σy∗ [nm]
692
486
48
62
Vertical beam-beam parameter ξy0.02770.0186
0.088
0.081
−2
−1
33
35
Luminosity L [cm s ]2.62 × 10
8 × 10the predecessor of SuperKEKB, the vertical collimators had a jaw only on either the top or bottom side and the horizontal collimators only on the inner side of the main ring. The beams
were not collimated from the outer side to prevent the synchrotron radiation from heating thecollimators. However, eﬀective suppression of the Touschek background requires the beam collimation also from the outer side. Since the Touschek background is enhanced by the nano-beamscheme, new collimators with jaws on both sides were developed for SuperKEKB and wereadded to the existing KEKB collimators. In Phase 2, the HER has sixteen KEKB collimatorsand three new ones, while the LER has five new ones.

3.2.2

Nano-beam scheme

SuperKEKB adopts a nano-beam scheme to achieve high luminosity. This scheme is characterized by a large beam crossing angle and extremely small vertical beam sizes.
The luminosity is given by()σy∗ I± ξy± RL
γ±
1+ ∗
L=
(3.1)
2ere
σx
βy∗ Rξy±Here + and − denote positrons and electrons respectively, γ is the Lorentz factor, re is the∗ are the horizontal and vertical beam sizes at the IP, I is the beamclassical electron radius, σx,y
current, ξy is the vertical beam-beam parameter, βy∗ is the vertical beta function at the IP,
and RL , Rξy are the reduction factors for the luminosity and the beam-beam parameters. We
assume that electron and positron beams have the same beam sizes and beta function at the
IP. According to Eq. (3.1), a smaller beta function leads to a higher luminosity. However, if
the beta function becomes as small as the bunch length, further squeezing does not increase theluminosity due to a beam-beam eﬀect. In the nano-beam scheme, we collide the beams with a9large half crossing angle of 41.5 mrad (=ϕ), resulting in a small eﬀective bunch length.
∗
σz,ef
f =

σx∗
sin ϕ

(3.2)

The small eﬀective bunch length makes it possible to increase the luminosity avoiding the beambeam eﬀect. SuperKEKB squeezes the vertical beta function to 1/20 of that in KEKB. The
beam currents are also doubled to achieve the forty-fold higher luminosity.

3.2.3

Linac

The linac provides a 7 GeV electron beam and a 4 GeV positron beam to the main ring. At
first, the low-emittance electron beam is produced by a photocathode RF gun and accelerated
by the linac. The positrons are produced by colliding 3.5 GeV electrons onto a tungsten target
in the middle of the linac. A thermionic electron gun is used for the production of the primaryelectrons because a high-current electron beam is required instead of a low-emittance one. We
accelerate the positrons to 4 GeV with the same accelerating components for the electrons. En
route, we circulate them in a 1.1 GeV damping ring to lower the emittance of the positronbeam. In Phase 2, the thermionic gun was used for both rings in most cases. The linac iscapable of injecting beam bunches at the frequency of 50 Hz while changing the parameters
bunch by bunch.

3.2.4

Beam injection

We use two diﬀerent injection schemes: “normal injection” and “continuous injection”. Normal
injection is used to accumulate a large amount of beam current. Since we do not turn on the
Belle II detector during normal injections, we can perform wilder injections without risking detector damage. After accumulating beam current by normal injections, we start beam collisions
and record physics data with the Belle II detector turned on. At this stage, continuous injection
is used to continuously accumulate smaller amount of the beam current in parallel with the dataacquisition so that the beam currents are kept at the maximum values. This is also known as“top-up injection” or “trickle charge injection”. Since we turn on the Belle II detector duringcontinuous injections, more delicate injections are needed to protect detectors.
Keeping the maximum luminosity by continuous injection is essential for eﬃcient data accumulation, because the beam lifetime is as short as several minutes at SuperKEKB. In Phase
3 operation, we will perform continuous injection at 50 Hz while alternately switching the beamspecies: thus, 25 Hz injections for each ring. In Phase 2, continuous injection was not performed
during physics runs and the Belle II detector was turned oﬀ at every injection. As an exception,
we once measured background rates during LER injections with the Belle II detector on in order
to confirm the feasibility of continuous injection (see Section 7.5).

3.3

Belle II detector

The Belle II detector is a general-purpose detector surrounding the IP. Figure 3.2 shows the
cross-sectional top view of the detector. It detects final state particles of e+ e− collisions withseven subdetectors: PXD (Pixel Detector), SVD (Silicon Vertex Detector), CDC (Central Drift

10Chamber), TOP (Time of Propagation counter), ARICH (Aerogel Ring Imaging Cherenkov
counter), ECL (Electromagnetic Calorimeter), and KLM (KL0 and µ detector).
We define the Belle II coordinate system as a right-handed Cartesian system whose origin
is at the interaction point. As shown in Fig. 3.3, the z-axis is defined as the median line of
the HER and LER beams, and the +Z direction points toward the HER direction. According
to the direction toward which the center-of-mass system is boosted because of the asymmetricbeam energies, the positive and negative z-directions are called Forward (FWD) and Backward(BWD), respectively. The y-direction points along the vertically upper direction. Consequently,
the x-axis points toward the outside√of the main ring. The polar angle θ and the azimuthal
angle ϕ are defined as θ = arccos√(z/ x2 + y 2 + z 2 ), ϕ = arctan (y/x). In this thesis, we define
the radii of the detectors as r = x2 + y 2 .
Because of the asymmetric beam energies, the structure of the Belle II detector is also
asymmetric in the polar angle acceptance of 17◦ < θ < 150◦ .

3.3.1

Subdetectors

The innermost subdetectors are the PXD and the SVD, forming the Vertex Detector (VXD)
together. The PXD forms the inner two layers with DEPFET (DEpleted P-channel Field Eﬀect
Transistor) pixel sensors, while the SVD forms the outer four layers with double-sided silicon
strip sensors. They measure the positions of the charged tracks to reconstruct their production
vertices. Because of the small beam pipe radius of 10 mm at the IP, the innermost layer is only
14 mm apart from the IP. Being closer to the IP is advantageous for the high-precision vertex
reconstruction, but the background environment becomes severe. Thus, the inner PXD has
finer channels of 8 million pixels in total with a typical pixel size of 50×50–80 µm2 . The SVD
covers much larger volume with 223,744 strips with 50–240 µm pitches. We describe the SVD
in detail in Section 3.4.
The CDC is a drift chamber that has 14,336 sense wires, filled with the gas mixture of 50 %He and 50 % C2 H6 . It measures the trajectories and energy losses of the charged particles forthree purposes: measurement of the momenta of the tracks from their curvatures and polar
angles, trigger generation by using the track information, and particle identification using theenergy-loss rates. The particle identification is important for low-momentum tracks that do notreach the TOP and ARICH.
The TOP and ARICH counters are built for the particle identification of π ± and K ± in thebarrel and the forward endcap, respectively. Both reconstruct Cherenkov ring images from theparticles to measure their velocities. The TOP counter uses quartz bars as the radiator anddetects the Cherenkov photons that propagate to the end of the bars by MCP (Micro-Channel
Plate) PMTs. The timing and position information of the hits on the MCP-PMTs are used
for the reconstruction. The MCP PMTs have timing resolution better than 50 ps, enabling the
TOP to provide good timing triggers. The ARICH counter uses silica aerogel as the radiatorand directly reconstructs the ring images detected by HAPDs (Hybrid Avalanche Photon Detectors).
The ECL consists of CsI(Tl) scintillation crystals and PIN photodiodes. It measures theenergies and angular coordinates of photons and identifies electrons. The information from the
ECL is used for trigger generation and luminosity measurement.
All the detectors up to the ECL are surrounded by a superconducting solenoid. It applies

11

C

Figure 3.2: The cross-sectional top view of the Belle II detector.

1

2

KLM

QC2LE

QCSL

30º

3

ø540

QC1LE

3351

13
(20)

4

(4
7)

1490

5

1156.4628(Cryostat)400(SVD)

1930(TOP,ECL-ﬂange)

570

1650(CDC:2650)

B-ECL

7

ø530
ø873
8

QC1RE

2417.52150

700(Gap sensor)

2650(CDC)
2870(ECL ﬂange)

633.5(Cryostat)

IP Chamber

145

QC1RP

PXD(2 layers)

CDC

TOP

535(SVD)

6

1960(E-ECL)

1670(ARICH)
B-ECL1590(CDC
w/o S.C:2325)

Small cell chamber

310

311.7

SVD

1000(CDC)

25

QC1LP

(70)

E-ECL

308.1

End cap shield

QC2LP

E-ECL

735(CDC w/o S.C.)

940(TOP,ECL-ﬂange)

1020(E-ECL)

2980

Super conducting coil

8

KLM

R1145(ARICH)

QC2RP

280

(20)

9

ø1299

257.5

KLM

Forward
OHO

QCSR

KEK

Beam line axis
(After +25.95mrad. rotation )

KLM

12

20130318 R1120120720 R1020120418 R9
20120327 R8
20120302 R7
20120111 R6
20110701 R5
20100808 R4
20100519 R3
20100330 R2
20100310 R1e+e-

TOP VIEW

11

Belle II solenoid axis

QC2RE

10

10

11

12

20160303 R14•Update-QCSL(D5,E5)
DESIGNEDDRAWNCHECKED
Takashi Kohriki
Takashi Kohriki
20160225 R13
20100215
20100215•Updates
FINISHORIGINAL SCALE
SIZE
SHEET
REV.
-CDC,SVD,TOP->minor chages
CLEAN&
DEGREASE-QCS vacuum vessel->QCS20160107
1/10
A1 of R14REMOVE ALL BURRS•Addition-Gap sensor(D4,D8)
TITLE
DRAWING NO.
-End cap shiels(D4,D9,E4,E9)
Belle-ll(Nano beam)
Belle-llTopview±41.5.vwx-RVC(D5,D7,E5,E7) not detailed
IR=±41.5 mrad.(Top view A)
20140213 R12
PROJECTPROJECTION-QCS20131203
MECHANICAL ENGINEERING GROUPINSTITUTE FOR PARTICLE AND NUCLEAR STUDIES-CDC covers
HIGH ENERGY ACCELERATOR RESEARCH ORGANIZATION
Belle II
-B&FWD new pole pieces
OHO 1-1, TSUKUBA, IBARAKI 305-0801, JAPAN10

End cap shield

E-ECL
(22)

3920

KLM

E-ECL

9

17º

H

G

F

E

D

KLM

R160(CDC)

B

Barrel7

Belle II

6

R155(VXD)

5

(155)

4

R1165(CDC IDS)
R1250.4(BECL)

Backward
NIKKO

ø500

3

ø742
ø694
ø734

2

0.0085r

A

1

ø1650.71200(TOP)ø926.8R1133.8(TOP inner most R.)(213.3)

R1130(CDC-SC outer most R.)
R452
(116)

Pre-amp
(88)

ARICH
ARICH
(20)

0.0415r

12R410

0.0415r(24)

0.083r

H

G

F

E

D

C

B

A

Figure 3.3: The top view of the Belle II coordinate system.

Table 3.2: The estimated cross sections and trigger rates from various physics processes at theΥ(4S) resonance. The Bhabha and γγ rates are prescaled by a factor of 1/100. [7]Process
σ [nb] Rate [Hz]
Υ(4S)
1.2
960
2.8
2200
qq
µ+ µ−
0.8
640
+
−
τ τ
0.8
640
◦
44
350
Bhabha (θlab ≥ 17 )γγ (θlab ≥ 17◦ )2.4
19◦∼15000Two-photon (θlab ≥ 17 , pt ≥ 0.1 GeV/c) ∼80
Total
∼130
∼20000the magnetic field of 1.5 T along the z-axis.
The KLM detects KL0 mesons and muons. The endcap sections have a sandwich structureof fourteen iron plates and fourteen plastic scintillator layers. The barrel part has fourteeniron plates and fifteen detector layers of RPCs (Resistive Plate Chambers) and plastic scintillators. Muons are identified with hits in the KLM associated with the CDC tracks. KL0
mesons are detected as isolated KLM hit clusters. The KLM is the only subdetector outside
the superconducting solenoid. The iron plates work as the return yoke of the magnetic field.

3.3.2

Target trigger rate in Belle II

In Belle II, the CDC, ECL, TOP, and KLM provide information for trigger generation [7]. The
entire trigger system consists of the four subdetector trigger inputs and the global decision logic(GDL), which makes the final decision.
One of the requirements for the trigger system is to keep the maximum average trigger rate
less than 30 kHz. The event rates from main physics processes are listed in Tab. 3.2. Since thetotal trigger rate from the physics processes amounts to 2/3 of the maximum rate, backgroundsuppression is essential to meet the requirement.

13

Figure 3.4: The Vertex Detector

Figure 3.5: Schematic view of the SVD ladders. [8]

3.4

SVD

3.4.1

Structure of the SVD

The SVD consists of four cylindrical layers located at 39 mm, 80 mm, 104 mm, and 135 mm fromthe z-axis, respectively. The whole VXD structure is shown in Fig. 3.4. The four SVD layers
are called L3–6 (Layer 3–6). Layers 1 and 2 correspond to the two PXD layers. Each SVD layer
is composed of ladders of 2–5 DSSD (double-sided silicon strip detector) sensors. Ladders in
the outer layers have more sensors to cover the wider acceptance region. The sensors are named
FW, +Z, CE, -Z, or BW according to their positions on the ladder as shown in Fig. 3.5. To
eﬀectively cover the asymmetrically wide acceptance in the forward side, most forward (FW)sensors in L4–6 ladders are slanted. The ladders are placed in a windmill shape to make theedges overlap as shown in Fig. 3.6. Each ladder is labeled by the layer number and laddernumber along the ϕ direction, which is shown in Fig. 3.6.
We apply a bias voltage of 100 V on the sensors to deplete them. When an ionizing particle

14

Figure 3.6: The cross section of the VXD in the X-Y plane [9]. The ladder number is shown
beside each ladder. In the first year of Phase 3, two L2 ladders are installed out of twelve.

15

Figure 3.7: The working principle of the DSSD sensor.
traverses the sensor, it produces electron-hole pairs in the depletion region as shown in Fig. 3.7.
The carriers are separated to each side of the sensor by the electric field and collected in the
strips. The electric signals can be read out from the strips on both sides through Al electrodes.
The strips on each side of the sensor are called P and N strips, according to the types ofsilicon. As shown in Fig. 3.8, P and N strips measure the r-ϕ and z coordinates, respectively. We
define (u,v,w) coordinate on each sensor as shown in Fig. 3.8 so that u- (v-)coordinate increases
along the z- (phi-)direction. P (N) strips are also called U (V) strips since they measure u(v-)coordinates.
Three diﬀerent sensors are used to form the ladders depending on the position (Tab. 3.3).
There are two types of rectangular sensors of diﬀerent sizes and strip pitches. The smaller
sensors are for L3 and the larger ones for L4–6. The other type of sensor is the trapezoidal one
for the slanted forward position.

3.4.2

Readout

Figure 3.9 shows the readout chain for the SVD data. We read out the signals from DSSD
sensors with frontend ASICs named APV25 [10]. For the sensors at the forward and backward
ends of ladders, the APV25 chips are mounted on the rigid printed circuit boards outside theacceptance region. For the other sensors, the APV25 chips are mounted on the flex printed
circuit boards which are glued on the DSSD sensors with insulating material in between.
The FADCs2 control the APV25 and receive the data from them. They are responsible forthe analog-to-digital conversion and low-level data processing such as reordering of the data
samples and zero suppression. Each FADC can handle data from 48 APV25 chips.
2

Flash Analog-to-Digital Converters

16

Figure 3.8: (u,v,w) coordinate system on a barrel sensor.

Table 3.3: The parameters of the three types of DSSD sensors [8].
Parameter
Small
Large
Trapezoidal
LocationL3
L4–6 (except FW)
L4–6 (FW)# P-strips
1535
1535
1535
# Readout P-strips
768
768
768
# N-strips
1535
1023
1023
# Readout N-strips
768
512
512
Pitch (P-side) [µm]2537.5
25–37.5
Readout pitch (P-side) [µm]
50
75
50–75
Pitch (N-side) [µm]
80
120
120
Readout pitch (N-side) [µm]
160
240
240
Length [mm]124.88124.88125.58Width [mm]
40.43
59.6
41.02–60.63
Area [mm2 ]5048.907442.856382.60
2
Active area [mm ]4737.807029.885890.00
Thickness [µm]
320
320
300
Manufacturer
Hamamatsu Photonics
Micron Semiconductor

17

Figure 3.9: The readout chain of the SVD data. Two numbers in parentheses that follow a
module name are the number of modules in phase 3, and the number in phase 2, respectively.
The readout modules are placed on the top of the Belle II detector and in an “electronic hut”
beside the detector.
The electrical signals from the FADCs are transferred with the FTBs3 via high-speed serial
communication over optical data links. They are sent to COPPERs4 , which are the common
interface to the central Belle II DAQ.
The trigger signals issued by the GDL and reset signals at the start of every data acquisition
run are distributed by the FTSW5 , which also provides a 127 MHz clock to the readout system.
We operate the APV25 chips with the system clock of 31.8 MHz which is generated by dividing
the 127 MHz clock by four. The FADC-Ctrl6 encodes the trigger and reset signals to the APV25
format with the 31.8 MHz clock.
The APV25 was originally developed for the CMS silicon strip tracker [10]. The APV25
has 128 input channels, each of which has a preamplifier, a shaper with the shaping time of
50 ns, and an analog pipeline with 192 cells. Figure 3.10 shows the block diagram of analog
signal processing in the APV25. We operate the APV25 chips with 31.8 MHz clock and trigger
signals. After being amplified and shaped, signals from a DSSD are sampled at the clock rate
and recorded in the pipeline. The APV25 outputs three consecutive samples from 192 pipeline
cells for reception of a single trigger pulse. We usually send two trigger pulses per each Belle IItrigger to the APV25 to read out six consecutive samples for a Belle II trigger (6-sample mode).
When the trigger timing resolution is as good as O(ns), three data samples will be good enoughto determine the pulse height and the hit timing. In order to reduce the average event size and3

Finesse Transmitter Boards
COmmon Pipelined Platform for Electronics Readout
5
Frontend Timing SWitch
6
FADC-Controller
418Figure 3.10: Block diagram of the APV25 [11]hence reduce the SVD dead time (see Section 4.4), we plan to implement a mixed mode, inwhich we basically read out six samples, but we read out only three samples for the event when
the trigger timing is determined by the TOP counters. We focus on the 6-sample mode without
explicit expressions from this point and “a trigger” means two trigger pulses that result in areadout of six samples from each strip.
In the zero suppression process in the FADC, we set a threshold to classify the strips into
fired and unfired ones. A strip is classified as unfired if all the six samples on the strip are
below the threshold, or fired if any of the samples are above the threshold. Data samples on theunfired strips are discarded and not recorded, while the samples on the fired strips are regarded
as signal and recorded. The threshold is set to the product of the strip noise and a common
signal-to-noise ratio (SNR) factor. The noise is evaluated for each strip as the fluctuation (RMS)of the pedestal ADC values, and the SNR threshold is common for all the strips of the SVD.
While taking data, monitoring software analyzes a part of the data to monitor variables
such as occupancy and hit map. The online-monitored variable of interest is occupancy, whichis the fraction of fired strips in a sensor. In Phase 2, we record most of the data by the zero
suppression with the SNR threshold of 3, while the online occupancy was calculated with the
SNR threshold of 5.
The APV25 data output for one sample consists of a serialized 12-bit digital header andsequential 128 analog values of 128 DSSD strip signals as shown in Fig. 3.11. The header
contains three high bits, an 8-bit pipeline address and an error bit. Therefore the output of
one sample takes 140 clock cycles in total, corresponding to 4.4 µs. In the 6-sample mode,
one trigger requires 26.4 µs for readout, limiting the maximum trigger rate for the APV25 to37.9 kHz. The pulses seen at the edges of Fig. 3.11 are the synchronization pulses called “tickmarks”. The APV25 issues tick marks every 35 clock cycles7 when no data is pending. The
data output always starts when the tick mark is issued. The length of the data output frame
amounts to four tick mark cycles.
Since the analog pipeline cells are overwritten every clock cycle, the 192-cell pipelines can
7

In the CMS experiment, the APV25 is operated with 40 MHz system clock and 20 MHz readout frequency,
which results in a diﬀerent tick mark period, 70 clock cycles.

19Figure 3.11: Output data frames from the APV25 [8]. The horizontal axis shows time using
31.8 MHz clock as the unit.
only keep the most recent 6.0 µs of data. In order to prevent overwriting samples to be read out
before the completion of the readout, the APV25 contains a 32-depth FIFO (First-In-First-Out
memory). The procedure is the following:
1. When the APV25 receives a trigger, it applies overwrite-protection on the pipeline cells
that contain the triggered samples.
2. The pipeline addresses of the samples are pushed into the FIFO.
3. The samples at the first address in the FIFO are sent out from the APV25.
4. The address is popped out from the FIFO. The cell at the address is released from theprotection.
However, if multiple triggers are sent to the APV25 in a short period, a FIFO overflow canhappen. The FIFO overflow error is informed by the error bit in the data frames. Once theerror occurs, the output data become nonsense unless the chip is reset.

3.4.3

Oﬄine signal reconstruction by basf2

The stored data are analyzed by basf2 (Belle II Analysis Software Framework) [12]. We apply
additional hit selections and form clusters with spatially continuous hits. In Phase 2, we usually
took data with the zero suppression of SNR = 3 in order not to discard too much data, allowing
many noise hits. Thus, oﬄine analysis of the stored data requires additional hit selection to
cut oﬀ the noise. The energy deposit of a cluster is calculated as the sum of the energies of
the contained hits. The typical cluster energy spectrum estimated by Monte Carlo simulation20

Cluster Energy Distribution
Uside
200

EntriesMean
Std Dev

180
160

4397
107.1
51.82

Vside
Entries
4336
Mean
110.8
49.89
Std Dev

140
120
100
80
60
40
20
0
0

50

100

150

200

250

300
350
energy [keV]

Figure 3.12: Simulated cluster energy distributions on L3BW sensor. The red (blue) line denotes
U (V) side clusters. 1 GeV muons from the IP are assumed in the simulation.
is shown in Fig. 3.12. The size of a cluster is defined as the number of the strips contained in
the cluster.

3.4.4

Phase 2 SVD cartridge

In Phase 2, we installed the SVD cartridge shown in Fig. 3.13 instead of the full detector. The
cartridge contains one ladder for each layer. The ladders are aligned up straight in the +X
direction (the outward direction of the SuperKEKB main ring) where the highest backgroundrate is predicted by the MC simulation.

3.4.5

Diamond detector

The radiation monitoring system for the VXD uses (4.5 × 4.5 × 0.5) mm3 single-crystal diamonddetectors. Figure 3.15 shows the diamond detector. The single-crystals are artificially grownby the chemical vapor decomposition (CVD) technique. Diamond is a suitable material fora radiation monitor at Belle II because of its radiation resistivity and negligible temperaturedependence. [13]In Phase 3, 28 diamond sensors in total are installed around the SVD: six sensors each on
the FWD and BWD sides of SVD support structure, four each on the FWD and BWD side of
the beam pipe, and four each on the bellows pipes at the FWD and BWD ends of the beam
pipe. In Phase 2, eight sensors were installed on the beam pipe: four on the FWD side and fouron the BWD side as shown in Fig. 3.14. Each sensor is labeled by the side (FWD or BWD) and21

Figure 3.13: The SVD cartridge for Phase 2 commissioning

Figure 3.14: The diamond sensors are located at ⋄ in Phase 2. Twelve sensors are added on theconical structure supporting the SVD in Phase 3.
by the channel number (ch0–3) or the azimuthal angle where it is located (ϕ = 55, 125, 235,305◦ ). Figure 3.16 shows the positional relations of the Phase 2 VXD sensors and diamonds.
The diamond sensors are responsible for the continuous measurement of the instantaneousand integrated radiation doses. To protect the VXD from severe irradiation, they provide beamabort signals to the accelerator at the moment when the radiation dose amount in a short timeinterval reaches a certain threshold. The measurable radiation range can be selected. Since
providing the abort signal requires a larger range at the sacrifice of precision, we alternately
used the sensors on one side for beam abort and those on the other for precise measurement inPhase 2.

3.5

Key research subjects in this thesis

The Belle II experiment is intended to acquire data of 50 ab−1 integrated luminosity in a decade,which requires a much higher rate of triggers and larger beam backgrounds than the Belleexperiment. For the SVD, this requirement causes two major challenges. Firstly, the required
average trigger rate of 30 kHz is close to the maximum readout rate of the APV25 in the 6-sample
mode, leading to the dead times of the APV25. We describe the issue and countermeasures to it
in Chapter 4. Secondly, the accelerator upgrade increases the beam background particles by a22

Figure 3.15: The diamond detector.
factor of about 30 [8], leading to the deterioration of tracking performance due to fake hits andradiation damage on the detector. In Chapter 5, we explain the eﬀect of the beam backgroundon the SVD and the origins of them. The beam background studies in Phase 2 are described in
Chapters 6 and 7.

23

(a) 3-D view(b) X-Y projection

Figure 3.16: The 3-D view (a) and the projection onto the X-Y plane (b) of the VXD sensors,
the diamonds, and the beam pipe in Phase 2. Only the DSSD sensors and the diamond crystals
are shown out of the SVD and diamond sensors. In (b), the distance from the z-axis is shownin the parenthesis for each detector.

24

Chapter 4

Trigger veto
In order to meet the requirement of the average trigger rate of 30 kHz, we need to deal with the
APV25 dead time. We developed a firmware module named “APV25-FIFO emulator” [14] asa countermeasure. The stability of the module and the resulting dead time are evaluated. We
explain the necessity of the APV25-FIFO emulator in Section 4.1, the concept of the modulein Section 4.2, performance evaluation in Section 4.3, and future prospects in Section 4.4.

4.1

Issue on trigger-veto for SVD

Since the FIFO depth of the APV25 is finite, the FIFO overflow can happen by an instantaneous
increase of the trigger rate.1 If we send 30 kHz trigger without any limitation, the APV25 suﬀers
the FIFO overflow in about 3 ms and needs to be reset for resuming data taking. Since therecovery takes a considerable time in which SVD becomes inactive, the FIFO overflow leads tohuge DAQ ineﬃciency. Therefore, it is essential to prevent the overflow by vetoing the triggers
that would cause the FIFO overflow.
Since the event reconstruction is supposed to be done for every trigger with the data fromall the Belle II subdetectors, vetoing the excessive triggers only in the SVD readout system
would stop the event reconstruction. Therefore, the trigger-veto system should be implemented
in the master FTSW, which distributes triggers to each subdetector.
The easiest way of avoiding the overflow is to apply a veto after every accepted trigger until
its readout is completed (26.4 µs after every trigger). However, we lose 44 % of triggers withthis method if we assume 30 kHz random triggers. A more optimized trigger-veto system isnecessary for high-speed data acquisition in Belle II.
The most optimal trigger-veto is to reject triggers only when they would cause overflow onan almost full FIFO. Such a trigger-veto scheme requires information of the FIFO occupancy
for the veto decision. However, the APV25 does not provide such information until the overflow
actually happens. Thus, we need to estimate the occupancy by using input signals of the
APV25. For that purpose, we investigated the behavior of the APV25 on a test bench toconstruct a model which describes how the APV25 processes data. Here we placed importance1

The FIFO depth is 32 samples while one trigger occupies six samples and one sample takes 4.4 µs to be readout. For example, six triggers (36 samples) coming in 17.6 µs (i.e. before four samples are read out) causes theoverflow.

25

on the simplicity of the model, as it leads to simple implementation and conservation of FPGA
resources.
We developed a trigger-veto firmware module (APV25-FIFO emulator) based on the model,
which emulates the FIFO occupancy to prevent overflow with minimal vetoes.

4.2

Design of the APV25-FIFO emulator

The development of the APV25-FIFO emulator requires the simple model which predicts thetiming and error bits of the APV25 output. We observed the behavior of the APV25 withthe dedicated setup described in Section 4.2.1 to construct the model. In Section 4.2.2, we
introduce the model, based on which the firmware module was developed. The implementationof the module in the FTSW requires two additional features to compensate two gaps between
the FTSW and the FADC-Ctrl about the clock frequency and the reset timing. These features
are described in Sections 4.2.3 and 4.2.4.

4.2.1

Development test bench for the APV25-FIFO emulator

The critical information for the APV25-FIFO emulator is the occurrence condition of the FIFO
overflow. We investigated the condition by observing the output signal sequences to known
input signal sequences on a dedicated setup shown in Fig. 4.1(a). A photograph of the test
bench is shown in Fig. 4.2. The setup contains an FTSW, an FADC-Ctrl, an FADC, and aflexible circuit board designed for L6 +Z sensors with ten APV25 chips on it. We can generate
reset and trigger signals at arbitrary timing with the FADC-Ctrl. The output signals to the
inputs are observed through digitization in the FADC or directly from the flexible board byan oscilloscope. The tick mark timing, the start timing of the data frames, and the error bitsin the data frames are checked. The waveforms of reset, trigger, tick marks and data output
signals which are observed by the oscilloscope are shown in Fig. 4.3.
We can test the functionality of the developed firmware module with the same setup as
shown in Fig. 4.1(b). Triggers are either generated by the FTSW itself, or are generated by an
external trigger generator and sent to the FTSW. The firmware module is loaded in the FTSW,
and the triggers are examined by the module before being sent out from the FTSW. We canmonitor a part of the data digitized by the FADC. By sending high rate triggers and checking
the error bits by the monitoring software, the functionality of the APV25-FIFO emulator wastested (see Section 4.3.1).

4.2.2

APV25 data processing model

The APV25 data processing model aims to predict the FIFO occupancy by emulating the timingof the tick marks and data output with the timing of the input trigger and reset signals. We
assumed the model as below and measured the three parameters in the model at the test bench
shown in Fig. 4.1(a). The model assumes:• The reset signal determines the phase of tick marks which are issued at every 35 clock
cycles. The first tick mark in the new cycle is issued after 18 clock cycles from the reset
signal as shown in Fig. 4.4.

26

(a) Setup for APV25 behavior study(b) Setup for the firmware module test

Figure 4.1: The test bench for the investigation of the APV25 behavior (a) and the performance
evaluation of the APV25-FIFO emulator (b). The setup is a simplified version of the SVD
readout chain shown in Fig. 3.9 without DSSD sensors and COPPERs. The reset and trigger
signals are sent from the FTSW or are generated in the FADC-Ctrl. The data from the APV25
chips are digitized in the FADC and a part of them is read out by the monitoring software.

27

Figure 4.2: The photograph of the test bench. The 9U VME boards in the upper crate of theupper photograph are the FADC-Ctrl and FADC boards. The 6U VME board shown in lower
right is the FTSW.

28

(a) Input trigger line and tick marks(b) Output signal

Figure 4.3: Input and output signals of the APV25 are observed by an oscilloscope. They areread out from the negative lines of the LVDS lines and hence inversely polarized. Since weread them out from the connector of the printed board using the probes of the oscilloscope,
the signals are distorted. (a) shows the input line to the APV25 in blue and the output line inyellow. Reset and trigger signals are transmitted as 3-bit sequences via the single input line,
reset corresponding to “101” and trigger “100”. In (a), a reset and a trigger signal are being
sent. We can see the periodic tick marks on the output line. The output signal is shown in (b).
Tick marks are followed by data output frames, which consist of a 12-bit digital header and128-bit analog strip signals.

29

• When the APV25 receives a trigger, it needs some time to start sending out the data
frames. The data output starts at the first tick mark after a delay of 116 clock cycles fromthe trigger signal as shown in Fig. 4.5, when no earlier data are pending. When there are
pending data, the new data sample is sent out consecutively after the earlier ones.
• When a trigger is sent to the APV25, the pipeline addresses of the triggered 3 or 6 samples
immediately occupy the FIFO. When the output of a data frame starts, the corresponding
pipeline address is dequeued from the FIFO after 24 clock cycles from the start of thedata header. Therefore, when the data sample of 27th address in the FIFO is being readout, the next trigger causes a FIFO overflow only if it comes earlier than 24 clock cycles
after the start of the data output. Figure 4.6 illustrates the timing chart of the FIFO
occupancy and ideal veto signal resulting from this assumption.
The measured parameters are indicated by italic characters in the above assumptions. For
the measurement, we chose the FADC-Ctrl as the trigger source. By scanning the timing oftrigger signals, the delay parameters were found at the critical points where the output signal
drastically changes.
The assumptions above enable us to determine when the trigger should be vetoed as longas we know the input signal sequence, that is, the timing of the reset and trigger signals to the
APV25. According to the first assumption, the reset timing determines the tick mark timing.
Then, based on the second assumption, the trigger timing identifies tick mark cycles in which
the triggered data frames are sent out. By subtracting the number of output data frames fromthat of input triggers times six2 , the number of the pending data samples (the FIFO occupancy)
is obtained. The third assumption determines the exact timing relative to the timing of data
output when the FIFO occupancy is decreased. Triggers are acceptable when the occupancy is
26 or less3 ; otherwise, they would cause a FIFO overflow.

4.2.3

Clock frequency gap between the FTSW and the APV25

Based on the model described above, the core module of the APV25-FIFO emulator is designed.
This module receives 31.8 MHz clock, trigger, and reset signals as the input and provides thetrigger-veto signal as the output. We show the conceptual diagram of the module in Fig. 4.7.
However, the trigger and reset signals are synchronized with the 127 MHz system clock in
the FTSW. To compensate the clock frequency diﬀerence, the FADC-Ctrl generates 31.8 MHz
clock by counting the input 127 MHz clock and latch the input signals with the divided clock. In
the same way, we need to convert the input signal sequence on the 31.8 MHz clock basis before
using them for the APV25-FIFO emulation. There is a fourfold ambiguity which we have toresolve in the phase of the 31.8 MHz clock generated in the FADC-Ctrl since there is no function
to deliver the clock phase back to the FTSW. If the 31.8 MHz clock phase is diﬀerent between
the APV25-FIFO emulator and the APV25, the timing of the translated 31.8 MHz trigger andreset signals can be diﬀerent as shown in Fig. 4.8, which leads to the wrong emulation.
To deal with the phase ambiguity, we implement four identical emulator submodules whose
input clock phases are diﬀerent from each other as shown in Fig. 4.9. By taking the OR of the23

Six data samples are read out per trigger in 6-sample mode.
The FIFO depth (32) minus the number of data samples per trigger (6).

30

Figure 4.4: Reset signals for the APV25 also reset the tick mark cycle. The first tick mark in
the new cycle is issued after 18 clock cycles from the reset signal. A reset signal is expressed as
101 signal on the input trigger line.

Figure 4.5: After reception of a trigger, the APV25 needs 116 clock cycles to become ready forsending out data frames. After the interval, the output starts at the first timing when the tickmark would stand.

31

Figure 4.6: The FIFO is occupied by pipeline addresses immediately after reception of a trigger.
Once a data frame starts to be sent out, the corresponding pipeline address is dequeued fromthe FIFO after 24 clock cycles. These assumptions enable us to estimate the FIFO occupancy.
When the FIFO occupancy is larger than 26 (the FIFO depth (32) minus the number of data
samples per trigger (6)), accepting another trigger signal causes the FIFO overflow.

32

Figure 4.7: The conceptual diagram of the core module of the APV25-FIFO emulator. It
receives 31.8 MHz system clock, the reset and trigger signals for the APV25 as input. The reset
and trigger signals are latched by the system clock. The module is also reset by the reset signal
for the APV25. It calculates the FIFO occupancy every clock, and asserts veto signal at thenext clock when the occupancy is 27 or more. We apply the veto to the trigger before inputting
it to the module so that the vetoed triggers are not recognized by the module.
four veto signals from these submodules, we can prevent the FIFO overflow no matter whichclock phase is adopted in the FADC-Ctrl. Since 3 out of the 4 veto signals are redundant, thisOR solution increases the trigger dead time. However, as they have almost same veto timing,the increase of the dead time is negligible ∼ O(10−3 %).

4.2.4

Reset timing gap between the FTSW and the FADC-Ctrl

While the trigger signals must be delivered as fast as possible to minimize the trigger latency,
the transfer of the reset signal is not as urgent. For this reason, the propagation times of
the trigger signal (short) and the reset signal (long) from FTSW to FADC-Ctrl are diﬀerent.
Therefore, the reset timing relative to the triggers is diﬀerent between the FTSW and on the
FADC-Ctrl. The APV25-FIFO emulator needs to know the delay diﬀerence.
We implemented counters in the FTSW and the FADC-Ctrl to count the interval between
a reset and the first trigger after the reset. The delay of the reset signal was measured by thecounters and found to be a constant value. Since the emulation should be done with the delayed
reset signal, we implemented a shift register in the APV25-FIFO emulator to delay the reset
signal by the constant value. Figure 4.10 shows the final diagram of the APV25-FIFO emulator.
Based on the concepts described above, we implemented the firmware module for the use in
the FTSW. We left the three delay parameters described in Section 4.2.2 changeable via VME
interface.

4.3

Performance evaluation

The APV25-FIFO emulator firmware module was designed based on the concept described in
Section 4.2. We tested the module with the test bench used for the development and the Phase
2 setup.

33

Figure 4.8: If we divide 127 MHz clock to produce 31.8 MHz clock, there are four possibilities
about the phase of the divided clock. When triggers (blue) synchronized with 127 MHz clock
are latched by four 31.8 MHz clocks with diﬀerent phases, the timing of the latched triggers is
diﬀerent depending on the phase.

Figure 4.9: We use four core modules to deal with the ambiguity of the 31.8 MHz clock phase.
The clock divider (essentially a 2-bit counter) uses input 127 MHz trigger to produce four
31.8 MHz clocks (CLKDIV1–4) whose phases are diﬀerent by 1/4 clock cycle from each other.
The four submodules use the clocks with diﬀerent phases to latch the same trigger and reset
signals, and send out veto signals based on the same logic. By using the OR of the four vetosignals, we can safely veto the potentially excessive triggers.

34

Figure 4.10: The conceptual diagram of the APV25-FIFO emulator. In addition to Fig. 4.9, theinput reset signal is delayed for the compensation of the reset-trigger timing gap between the
FTSW and the FADC-Ctrl. The veto signal from the emulator is OR-ed with the other vetosignals in the FTSW.

35

4.3.1

Operation check in the test bench

The firmware module was tested in the test bench shown in Fig. 4.1(b). In the setup, theAPV25-FIFO emulator is implemented on the FPGA of the FTSW. We can generate pseudorandom triggers of an arbitrary frequency by using 32-bit pseudorandom numbers generated
by the Mersenne Twister [15] (MT triggers). The triggers are sent to the FTSW through theexternal input and examined by the APV25-FIFO emulator module. Triggers which are notvetoed by the emulator module are distributed to the APV25 chips. We read out a part of thedata via the VME bus to check the error bits. The maximum readout rate with the software isabout 1 kHz.
60 kHz MT triggers were generated and sent to the emulator module. The output triggers
from the emulator module were sent to the 6 APV25 chips. The output trigger rate from the
FTSW was about 37 kHz. After 15 hours of operation, we observed four error bits and three
failures of detecting the data header in total. However, we consider that the presence of theerrors does not mean the failure of the trigger veto system for the two reasons below. Firstly,
if errors truly happen, the error bits should remain until they are cleared by reset. In thatcase, the number of error bits increases at every trigger. Considering the trigger rate and theoperation time, the observed number of the error bits is strangely small. Secondly, since thesix APV25 chips are supposed to work in synchronization, the number of error bits should be amultiple of six in principle. The number of the error bits not being a multiple of six, they do not
originate from the designed behavior of the APV25. Therefore, we suspect the observed error
bits are due to bit flips. The header detection failures can also be explained by bit flips. From
the observation, we consider the APV25-FIFO emulator prevented the FIFO overflow error atleast for fifteen hours at the maximum possible rate.
We also tried running the system while changing the input parameters described in Section 4.2.2. Sending 30 kHz MT triggers, we observed that the error bits appeared when theparameters were changed from the designed values to the critical side. This validates the reasonability of the assumed data processing model.

4.3.2

Trigger loss rate

The trigger loss rate, the fraction of the vetoed triggers, is the most important observable thatshows the performance of the trigger-veto module. It is defined as#vetoedTriggers#inputTriggers − #outputTriggers=#inputTriggers#inputTriggers(4.1)

where #inputTriggers is the number of the triggers going into the FTSW, #outputTriggers isthe number of the triggers going out from the FTSW, #vetoedTriggers is the number of thetriggers vetoed by the APV25-FIFO emulator. We measured the trigger loss rate as the function of the input trigger rate in the test bench in Fig. 4.1(b). We sent the MT triggers for ten
minutes to count the triggers before and after the FTSW.
In addition, we wrote a C-program to estimate the trigger loss rate by simulating the APV25FIFO emulator. The program generates triggers by itself with the Mersenne Twister and applies
vetoes to them on the same logic as the APV25-FIFO emulator. The trigger loss rate is calculated by counting the vetoed triggers.
The observed and simulated trigger loss rates are shown in Fig. 4.11. The measured trigger

36

0.150simulation
measurement

0.125
trigger loss

0.100
0.075
0.050
0.025
0.000

10

20
30
input trigger rate [kHz]40

Figure 4.11: The trigger loss rate due to the veto by the APV25-FIFO emulator is shown as
the function of the input trigger rate. The triggers were generated by the Mersenne Twister
individually for the measurement and the simulation. We generated 100,000 triggers in eachsimulation. In each measurement, we took data for about ten minutes.
loss rate shows good agreement with the simulation, which indicates the developed emulator
module works as expected. The loss rate is about 3 % assuming the input trigger rate of 30 kHz
as required in the Belle II experiment. This is a significant improvement compared with theeasiest trigger-veto scheme (see Section 4.1) which loses 44 % of 30 kHz triggers.

4.3.3

High trigger rate test in the Phase 2 setup

Before Phase 2 operation, the stability of the trigger-veto system was tested in the Phase 2
setup shown in Fig. 3.9. All the components were in place for the use in Phase 2. We generated
pseudorandom triggers in the FTSW (FTSW triggers) and sent them to the 144 APV25 chips
on the Phase 2 SVD cartridge. We checked all the error bits in the data from the SVD cartridgeby using the readout PC.
We sent 50 kHz FTSW triggers for ten hours while monitoring the number of the error bits in
the readout PC. The output trigger rate was about 35 kHz. After ten hours, no error bits wereobserved except for one APV25 chip. The chip had eighteen error bits in total, discontinuously
increasing the number as shown in Fig. 4.12. For the same reasons described in Section 4.3.1,
we assume the error bits were caused by bit flips. In other tests with shorter run times, thisphenomenon was observed in several chips.
The stability test was conducted well before the start of Phase 2, and the SVD was readyfor high rate data acquisition in Phase 2. However, the trigger rate during Phase 2 was as37

#(observed error bits)

15
10
5
0

0

100

200 300 400 500
operation time [min]600

Figure 4.12: The time evolution of the error-bit count during the stability test in the Phase 2
setup. The error bits arose from the same APV25 chips.
low as 1 kHz due to limitations from the other subdetector systems and the low luminosity.
Therefore, the APV25-FIFO emulator was not intensively utilized, although it was implemented
and functioning.

4.4

Further improvement in trigger loss rate due to trigger withgood timing resolution

We plan to apply the APV25 data processing model to the mixed mode (see Section 3.4.2)
when the trigger with good timing resolution (3-sample trigger) becomes available. We assume
the fraction of the 3-sample triggers R3 and estimate the trigger loss rate by the C-program.
Figure 4.13 shows the estimated trigger loss rate as the function of the input trigger rate.
Assuming R3 =0.5 as was in the Belle experiment4 , the trigger loss rate becomes less than 1 %for the 30 kHz trigger.

4

In the Belle experiment, the timing of roughly half the triggers was decided by the barrel PID detectors. [16].

38R3=0.0
R3=0.2R3=0.4R3=0.6R3=0.8R3=1.0trigger loss

10−1
10−2
10−3

10

20

30
40
50
input trigger rate [kHz]60

Figure 4.13: The simulated trigger loss rate in the mixed mode is shown as the function of the
input trigger rate. Each simulation assumes a fixed input trigger rate and a fixed fraction of
the 3-sample trigger out of all the input trigger, R3 . For each simulation, 1,000,000 triggers andtheir types (3- or 6-sample) are generated pseudorandomly by the Mersenne Twister based on
the assumed rate and R3 . The legend denotes the assumed R3 .

39

Chapter 5

Beam backgrounds
Beam particles sometimes deviate from the ideal orbit and produce electromagnetic showers
by hitting the wall of the beam pipe. If the beam particles are lost near the detectors, theresulting showers can hit the detectors. They are called beam background and the detectors areaﬀected by fake hits and their associated radiation damage. Fake hits transiently deteriorate thedetector performance such as tracking eﬃciency, momentum resolution, etc. They also cause
dead time by occupying a large amount of the DAQ bandwidth. Furthermore, the accumulationof the radiation damage leads to permanent degradation of the performance. For example, theradiation damage increases noise in semiconductor devices, degrades the quantum eﬃciency ofphotoelectric surfaces of photodetectors, and decreases light output of scintillation crystals.
In Section 5.1, we explain the background tolerance of the SVD and the purpose of the beam
background studies performed in Phase 2. We describe the sources of the beam backgrounds
and their properties in Section 5.2. We introduce a model which describes the single-beambackground rate in Section 5.3.

5.1

Background tolerance of the SVD and purpose of study

We consider the eﬀect of beam backgrounds on the SVD from two aspects: the degradation of
tracking performance due to fake hits, and radiation damage on the sensors. The eﬀect of fakehits is quantified as occupancy, that is, the percentage of fired strips in all the strips. The lattereﬀect is quantified as total ionizing dose (TID) and non-ionizing energy loss (NIEL).

5.1.1

Occupancy

We define the occupancy as the fraction of fired strips in a sensor. Thus, the occupancy isdefined for each side of a DSSD sensor. We classify a strip as fired if it survives the zero
suppression or hit selection with the threshold of SNR=5 in this thesis. Under backgroundconditions which result in occupancy of 3 % for the L3 sensors, the SVD standalone tracking
exhibits a tracking eﬃciency of 94 % and a fake rate of 14 % in Monte Carlo simulation [17].
Since BB events produce 11 tracks on average, the 94 % eﬃciency means a full reconstruction
eﬃciency of 50 %. We define the occupancy of 3 % as the limit for the acceptable degradationof the tracking performance.

405.1.2

Radiation damage to silicon sensors

Radiation incident on silicon sensors interacts with the electron cloud or nuclei in the crystal
lattice [18]. Interactions with nuclei cause displacement of the lattice atoms, generating interstitials (atoms between regular lattice sites) and vacancies (empty lattice sites). These unstabledefects grow into stable defect complexes, which change the electrical properties of the sensor
by the following mechanisms:• They capture and emit electrons and holes as recombination-generation centers. Defects
that introduce energy levels at the center of the band gap can alternatively emit electrons
and holes, which increases the reverse-bias current if it happens in the depletion region.
• They change the charge density in the depletion region. This causes type inversion andeventually increases the full depletion voltage of the sensor.
• They trap the charge carriers and release them after some delay. This prevents eﬃcientcharge collection and leads to signal reduction.
Interactions with nuclei are mainly caused by heavy particles. The eﬀect of the NIEL is evaluatedas the equivalent fluence of 1 MeV neutrons.
In the surface region, the displacement of the atoms does not have a significant eﬀect since
the material structure is already irregular. On the other hand, ionizing radiation in the formof photons and charged particles causes damage to the oxide insulator. Because electrons haveseveral orders of magnitude larger mobility than holes in SiO2 , electrons quickly diﬀuse out of
SiO2 while holes are captured. This ends in the positive charge-up of the insulator, reducing
the high voltage stability of the sensor.

5.1.3

Radiation tolerance for Belle II SVD

From the experience of the Belle experiment, the Belle II SVD is required to tolerate the TIDof 10 Mrad. That value is obtained by scaling the radiation dose in Belle by the luminosity(4.5 Mrad) and multiplying it by a safety factor about two [8].
Beam tests showed that irradiation of 10 Mrad does not significantly degrade the signal-tonoise ratio of the DSSD sensors [19]. Regarding the APV25, they observed almost no degradation after 10 Mrad irradiation [10]. Araldite 2011 [20], the adhesive used in the SVD, is also
confirmed to have enough radiation hardness [21]. We define 10 Mrad as the limit of acceptable
TID over a decade of operation.
The significant eﬀect on the SVD due to the NIEL damage is type inversion, which changes
the n-type bulk substrate of the DSSD into eﬀectively p-type and prevents signal readout fromthe p-type strips. We define the acceptable limit of 1013 cm−2 1 MeV neutron equivalent fluenceas the maximum NIEL damage before type inversion, based on the observation of the ATLASSCT group [22].

5.1.4

Purpose of Phase 2 beam background study

The Monte Carlo simulation of the beam background in the designed SuperKEKB condition
predicts about 1 % occupancy and about 0.1 Mrad/smy1 irradiation on the SVD (see Chapter 6).
1

An approximation of the total operation time in a year. 1 smy (snowmass year) = 107 s

41

These values are within the limits described above. However, we should be careful because thesimulation of the beam-induced backgrounds has a large uncertainty due to the diﬃculty insimulating all the details of the accelerator complex, such as beam dynamics, vacuum pressure
measurements, etc. Indeed, in Phase 1, some BEAST II detectors observed background rates
which are one to three orders of magnitude higher than simulation [4]. Judging from the values
above, keeping good tracking performance is the more pressing issue for the SVD.
For the installation of the full SVD, we aim to verify three points by estimating the background level in Phase 3. Firstly, the occupancy should be low enough for the SVD to achieve
good tracking performance in the first year of Phase 3. Secondly, after the design luminosity
is achieved, the integrated dose over Phase 3 and the occupancy should stay within the limits. Finally, the correlation of the background rates between the SVD and diamonds should be
confirmed so that we can use diamonds as a beam abort sensor to keep the SVD safe.

5.2

Beam background sources

In the SuperKEKB storage ring, it is expected that beam backgrounds arise from the following
sources.

5.2.1

Touschek scattering

Touschek scattering is a scattering process between two beam particles within the same bunch,which causes an energy transfer from one to the other. If the energies get out of the dynamic
aperture of the ring, the beam particles are no longer stable and start to deviate from the design
orbit. After hundreds of turns, they are eventually lost by hitting the beam pipe wall andproduce electromagnetic showers. Showers due to beam losses near the IR, or their secondary
showers might hit the detector.
The Touschek background rate is proportional toI2,
σ y nb E 3(5.1)

where I is the beam current, σy is the vertical beam size, nb is the number of bunches andE is the beam energy [8]. Due to its beam size dependence, it is predicted to be the major
background source at SuperKEKB, which adopts the nano-beam scheme. Also, it is more serious
for the LER due to its beam energy dependence. Touschek background rate also depends on
the horizontal beam size, but we focus on the vertical. In the nano-beam scheme, where verticalbeam size is extremely small, dependence on the vertical beam size is more important. To
reduce the Touschek background, movable collimators are installed along the beam pipes (seeSection 3.2.1). These collimators stop the particles deviating widely from the nominal orbit
before they produce showers near the IR.

5.2.2

Beam-gas scattering

Beam-gas scattering is a process where beam particles are scattered by residual gas molecules,
due to Coulomb scattering. It changes the directions of beam particles and leads to immediate42

beam losses at the beam pipe wall. Bremsstrahlung also happens as a higher order eﬀect.
It reduces the energies of the beam particles, producing beam background similarly to the
Touschek background. Because the bremsstrahlung event rate is low and beam particles withlower energies are stopped by horizontal collimators before hitting the beam pipe, the beam-gas
background is mainly due to Coulomb scattering. The beam-gas scattering rate is proportional
to the beam current and the pressure inside the beam pipe.

5.2.3

Synchrotron radiation

Synchrotron radiation (SR) is a process where beam particles emit photons when they are bent
by magnets. In SuperKEKB, beam particles emit low energy photons ranging from a few keV totens of keV [4]. Its contribution in detector background is predicted to be negligible by Monte
Carlo simulation. Moreover, background particles due to SR are hard to detect for the SVD
because their energy deposits are so small relative to the noise of the SVD. The diﬃculty ofdetecting the SR makes it diﬃcult to evaluate its contribution to the radiation dose. The powerof SR is proportional to beam energy squared and magnetic field strength squared. Thus, theHER mainly contributes to this beam background, and we consider only the SR from HER in
the simulation study described in Section 6.1. The SR background rate is also proportional tothe beam current.

5.2.4

Luminosity backgrounds

We define luminosity backgrounds as the beam background components induced by beam collisions. For the SVD, the largest contribution comes from two-photon process e+ e− → e+ e− e+ e− ,where the e+ e− collisions produce low momentum electron-positron pairs at the interaction
point. The magnetic field by the Belle II solenoid makes these tracks with low momenta spiralinside the SVD volume leaving multiple hits on the sensors. The second largest contribution
is due to radiative Bhabha process, where electrons and positrons scatter with small angles,
producing photons along the beam axis. The emitted photons hit the material downstream toproduce showers and neutrons. The beam particles whose energy are taken by two-photon orradiative Bhabha process are overbent by the magnetic field of the solenoid and QCS magnets
after the interaction point to hit the beam pipe. Bhabha scattering with a small scattering
angle also produces such background. Since the rates of these backgrounds are proportional to
the luminosity, they are predicted to dominate beam backgrounds at the design luminosity ofSuperKEKB (8 × 1035 cm−2 s−1 ). However, they are hard to detect at the luminosity of a few
×1033 cm−2 s−1 in Phase 2.

5.2.5

Injection backgroundAs described in Section 3.2.4, in Phase 3, we will take physics data while repeating continuous
injections at 50 Hz continuously to maintain high luminosity. For a few milliseconds just after an
injection, the SVD suﬀers harsh beam background. In order to not take data during this period,
we apply a trigger veto for several milliseconds after every injection. Therefore, the durationin which the SVD cannot take data due to the injection background should be investigated todetermine the veto duration. Also, since the radiation damage from the injections is accumulated

43

in the SVD, it is important to confirm that the radiation dose is at a safe level for the SVD
operation. We used only the normal and continuous injections in Phase 2.

5.3

Single-beam background model

Most of the beam background measurements in Phase 2 were devoted to the investigation of thesingle-beam backgrounds. We introduce a model which describes the single-beam backgroundrate. If we assume the beam background rate from a single beam is dominated by Touschek
and beam-gas Coulomb scatterings and may ignore other background sources, the backgroundrate is parametrized asI2+ B · PI
(5.2)
O=T ·
σy nb
where O is background rate such as SVD occupancy and dose rate on diamond sensors, I isthe beam current, σy is the vertical beam size at the location of the beam size monitor, nb is
the number of bunches, P is the average pressure over the ring, and coeﬃcients T, B are thequantities of Touschek and beam-gas components, which are independent of other parameters.
The Touschek component also depends on the beam energy, the horizontal beam size, and thebunch length as described in Section 5.2.1. However, since we did not change these parametersin the measurements, we show only the parameters of our interest in Eq. (5.2).
The beam-gas component is also proportional to the second power of the eﬀective atomic
number of the residual gas, but we do not take this dependence into account in this thesis.
Instead, the averaged value is absorbed in B. Empirically, the pressure is approximated by alinear function of the beam current:
P = P0 + k · I(5.3)

where P0 is the base pressure without the beam stored and k is a constant. The backgroundrate in Eq. (5.2) is characterized by a quadratic function of the beam current in a beam study
run because the beam size and the number of bunches do not change significantly during a usual
run.

44

Chapter 6

Beam background simulation
In this chapter, we describe the Monte Carlo simulation of the various beam background sources.
Section 6.1 explains the simulation procedure and introduces the simulation campaigns coveredin this thesis. The following sections describe each simulation campaign.

6.1

Beam background simulation

The beam background rates from following sources are estimated by Monte Carlo simulation:
Touschek, beam-gas Coulomb, HER SR, two-photon, and radiative Bhabha scattering. Injection
background is not included since the simulation is diﬃcult. We consider the SR contribution
only from the HER because the HER dominates the SR background owing to its larger beamenergy.
Radiative Bhabha processes are classified depending on the scattering angles of e± , θe± .
“BHWideLargeAngle” (BHWide LA) events are defined as the event where both of θe± arelarger than 1◦ and at least one of them is larger than 10◦ . The events are classified as “BHWide” events if they are not BHWideLargeAngle events and both of θe± are larger than 0.5◦ .
The other events are classified as “RBB” events.
The event generation of each background is done by diﬀerent methods. For the Touschek
and beam-gas Coulomb scatterings, we use SAD (Strategic Accelerator Design) software [23]to simulate the propagation and loss of beam particles along the ring. The information of thelost particles is recorded. The SR events are simulated by Geant4. The two-photon events are
generated by AAFH [24], RBB by BBBREM [25], BHWide and BHWide LA by BHWIDE [26].
We take these events as the input of detector simulation by Geant4 to calculate energy deposits
in the detectors. The radiation dose and NIEL damage on the SVD are estimated by the energy
deposits. The radiation dose is calculated as the energy deposit per sensor mass. We calculate
the NIEL damage as the equivalent fluence of 1 MeV neutron, assigning a conversion factor toeach particle according to its species and kinetic energy.
Since the background events do not happen in sync with triggers1 , these energy deposits are
randomized in the time axis according to the assumed background rate. The time-randomizedenergy deposits in the SVD are processed by a dedicated digitizer module in basf2 [12] to sim1

In the designed condition, the beam bunch crossing period is 4 ns while the trigger rate is 30 kHz. The bunch
crossing is approximately continuous.

45

ulate the signal propagation inside the sensors. As a result, the hit information equivalent to
the APV25 output is produced for each event. The occupancy and the clusters on the SVD arereconstructed from the information.
There have been several background simulation campaigns. We divide them into three categories: Phase 2 and Phase 3 design simulation, Phase 2 realistic simulation, and HER SR
simulation.
Before Phase 2 started, the Phase 2 and Phase 3 design simulation was done assuming thedesigned machine condition in Phase 2 and 3, respectively. Here, the Touschek and beam-gas
backgrounds are simulated with the design optics and collimator setting which is optimized
for the optics by simulation. The luminosity backgrounds are simulated with the event rate
calculated from the assumed luminosity.
A series of the Phase 2 realistic simulations was made for the reference of the single-beambackground studies in Phase 2. For important beam size scans, we produced the Touschek andbeam-gas background samples by reflecting the beam optics and collimator setting during eachstudy in the SAD simulation.
These campaigns do not include the SR background because the previous simulations predicted negligible SR contribution. The SR simulation was done separately, motivated by an
unexpected peak in the energy distribution measured by some detectors in Phase 2. We consider only the HER SR simulation in this thesis.
In the following sections in this chapter, we describe each simulation campaign.

6.2

Simulation for Phase 2 and Phase 3 design optics

MC simulations for beam backgrounds are performed under assumptions of the accelerator settings designed for Phase 2 and Phase 3 individually. The assumed machine parameters are listed
in Tab. 6.1. The collimator setting is optimized by simulation for the background mitigation in
the assumed beam optics. The Touschek, beam-gas and luminosity backgrounds are simulated.
For each background species, we estimate the radiation dose, NIEL damage, and occupancy on
the sensors.
Figures 6.1 and 6.2 show the estimated dose, NIEL, and occupancy averaged over the sensors in each layer. We can see that the main contribution in Phase 3 is from the luminosity
backgrounds, especially the two-photon. In contrast, the single-beam backgrounds are dominant in Phase 2, where forty times smaller luminosity is assumed. The background variables in
Figs. 6.1 and 6.2 do not show the radial dependence of 1/r2 , since the background particles do
not necessarily come from the IP.
The azimuthal angle dependence of the radiation dose in Phase 3 is shown in Fig. 6.3. We
can see that the ladders in the horizontal plane suﬀer more intense background condition. One
reason is that the particles with wrong energies arising from the Touschek scattering are lost in
the horizontal plane. The two-photon and radiative Bhabha backgrounds are also more intensein the +X direction since the center-of-mass system is slightly boosted toward the +X direction
owing to the finite crossing angle. We show the ϕ dependence plots of each background species
in Appendix B. In Phase 2, we cannot study the ϕ dependence because the SVD cartridge covers
only the +X direction.
From the Phase 2 simulation result, we calculate the ratio of the radiation dose to the46

Phase 3

Phase 2
twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

20.0
80

Radiation Dose [krad/smy]

Radiation Dose [krad/smy]

17.5
15.0

60

12.5
10.0

40

20

7.5
5.0
2.5

0

L3

L4
L5
Layer

0.0

L6

L3

L4
L5
Layer

L6

(a) Radiation dose

Phase 3

20.0

NIEL damage [1010 neq/cm2smy]

NIEL damage [1010 neq/cm2smy]

22.5
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0.0

L3

L4
L5
Layer

L6

Phase 2

3.5

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

3.0
2.5
2.0
1.5
1.0
0.5
0.0

L3

L4
L5
Layer

L6

(b) NIEL damage

Figure 6.1: The radiation dose (a) and NIEL damage (b) to the SVD are estimated by thesimulation assuming the accelerator setting designed for Phase 2 and 3. The variables areaveraged over the sensors in each layer. The contributions from diﬀerent background species
are plotted in diﬀerent colors as shown in the legend. The NIEL damage is expressed as theequivalent fluence of 1 MeV neutron.
47

Phase 2

Phase 30.25
Strip Occupancy U [%]Strip Occupancy U [%]

0.8

0.20

0.6

0.15

0.4

0.10

0.2

0.0

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

0.05
L3

L4
L5
Layer

0.00

L6

L3

L4
L5
Layer

L6

(a) Occupancy (U side)

Phase 2Phase 3
1.0

Strip Occupancy V [%]Strip Occupancy V [%]

0.25

0.8

0.20

0.6

0.15

0.4

0.10

0.2
0.0

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

0.05

L3

L4
L5
Layer

0.00

L6

L3

L4
L5
Layer

L6

(b) Occupancy (V side)

Figure 6.2: The SVD occupancies on the U side (a) and the V side (b) are estimated by thesimulation assuming the accelerator setting designed for Phase 2 and 3. The occupancies areaveraged over the sensors in each layer. The contributions from diﬀerent background species
are plotted in diﬀerent colors as shown in the legend.
48

2

Radiation Dose[krad/s y]

200

3

4

Layer 3 Total
5

6

7

FW
BW

1

100
0

0

75

90

Radiation Dose[krad/s y]

2

3

180

4

Layer 4 Total
5

6

7

ϕ [∘]
360

270
8

9

10

1

50

FW
CE
BW

25
0

0

Radiation Dose[krad/s y]

60 2

90
3

4

180

5

Layer 5 Total

6

7

8

9

270

ϕ [∘]
360

10 11 12

1

270

ϕ [∘]
360

40
20
0

0

90

180

Layer 6 Total

Radiation Dose[krad/s y]

40 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
20
0

0

90

180

270

FW
CE
-Z
BW

FW
∘Z
CE
-Z
BW

ϕ [∘]
360

Figure 6.3: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The total dose from all the background components is shown for each sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
49

Table 6.1: Machine parameters in the Phase 2 and Phase 3 designed simulation. The pressure
is assumed to be uniform in the ring. Vertical beam sizes are the ones at the location of thebeam size monitor.
Phase 2Phase 3
Parameter [unit]
LER HER LER HER
Beam current [mA]
1000 800 3600 2600
Number of bunches
1576 1576 2500 2500
Bunch current [mA]
0.63 0.51 1.44 1.04
Horizontal beta function at IP [mm] 128
100
32
25
Vertical beta function at IP[mm]
2.16
2.4
0.27
0.3
Vertical beam size [µm]
42
44
10
24
Pressure [10−8 Pa]
13.3 13.3 13.3 13.3
Luminosity [cm−2 s−1 ]2 × 1034
8 × 1035

occupancy on each SVD sensor. The ratios for each background component and each sensor are
shown in Fig. 6.4. In Fig. 6.4, we categorize the sensors according to their shape (see Tab. 3.3).
The ratios of the same sensor type show similar results even though the background sources are
diﬀerent, except for the radiative Bhabha and HER Touschek backgrounds with poor statistics.
This is assumed to be because the distribution of the energy deposits from each backgroundsource is similar and hence the energy deposit per hit is similar. Therefore, while taking datawith the SVD, we can estimate the radiation dose rate on the SVD from the measured occupancy without distinguishing the background sources. Sensors with diﬀerent shapes show
diﬀerent ratios. This is because signal charges are diﬀerently distributed and zero-suppressedby diﬀerent thresholds owing to the diﬀerence of the capacitance between the strips and diﬀering
noise levels.
The dose rates on the diamond sensors are estimated from the same Phase 2 simulation
sample. We calculate the ratio of radiation dose between the SVD and diamond in Phase 2 asshown in Fig. 6.5. To see the correlation, we focus on the SVD L3 sensors, which are nearest
to the diamond sensors. Although the L3 sensors and diamonds at ϕ=55, 305◦ are only several
centimeters apart, we can see that the ratios from diﬀerent backgrounds do not coincide. This
indicates the spatial distribution is diﬀerent between the background sources. The calculated
ratio enables us to make a very rough estimation of the dose rate on the SVD sensor from thediamond dose rate.

6.3

Phase 2 realistic simulation

In Phase 2, we performed beam size scans to estimate the contributions from the beam-gas andTouschek backgrounds, B and T in Eq. (5.2) (see Section 7.2). We estimate B M C and T M C by
the simulation for comparison. For important beam size scans in Phase 2, we take the beam
optics and collimator setting during each study as the input to produce the Phase 2 realistic
simulation. The machine parameters used in each simulation are listed in Tab. 6.2.
For each simulation, we estimate the SVD occupancy. The beam-gas and Touschek contri-

50

Small sensors

80
60
40
20
0
L3FW

L3BW

100

Radiation Dose / Occupancy(U side) [krad/(smy %)]Radiation Dose / Occupancy(U side) [krad/(smy %)]100

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER
total

80
60
40
20
0L4FW

L5FW

Large sensors

100

Radiation Dose / Occupancy(U side) [krad/(smy %)]Trapezoidal sensors

L6FW

80
60
40
20
0

L4CE

L4BW

L5CE

L5-Z

L5BW L6+Z

L6CE

L6-Z

L6BW

(a) U side

Small sensors

80
60
40
20
0
L3FW

L3BW

Trapezoidal sensors
twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER
total

80
60
40
20
0L4FW

L5FW

Large sensors

100

Radiation Dose / Occupancy(V side) [krad/(smy %)]100

Radiation Dose / Occupancy(V side) [krad/(smy %)]Radiation Dose / Occupancy(V side) [krad/(smy %)]

100

L6FW

80
60
40
20
0

L4CE

L4BW

L5CE

L5-Z

L5BW L6+Z

L6CE

L6-Z

L6BW

(b) V side

Figure 6.4: The ratio of radiation dose to occupancy on the SVD sensors in the simulation
assuming the accelerator setting designed for Phase 2. The plots are made for the U sideoccupancy (a) and the V side (b). The x-axis denotes the sensor names. The ratio is calculated
51
for each background species as shown by the legend. We separate the plot areas by the sensor
shape (see Tab. 3.3).

Radiation Dose : SVDL3FW/Diamond

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER
total

100
10 1
10 2
BWD
=55

BWD
=125

BWD
=235

BWD
=305

FWD
=55

FWD
=125

FWD
=235

FWD
=305

(a) SVD L3FW sensor vs Diamonds

Radiation Dose : SVDL3BW/Diamond

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER
total

100

10 1

10 2

BWD
=55

BWD
=125

BWD
=235

BWD
=305

FWD
=55

FWD
=125

FWD
=235

FWD
=305

(b) SVD L3BW sensor vs Diamonds

Figure 6.5: The ratio of the dose rate between the SVD L3 sensors and diamonds in the simulation assuming the accelerator setting designed for Phase 2. The x-axis denotes the diamond
sensor to which the ratio is taken. The ratio is calculated for each background species shown in
the legend. The HER Touschek is missing in many places since corresponding diamond sensors
had no hits due to poor statistics.

52

Table 6.2: Machine parameters in the Phase 2 realistic simulation. The pressure is assumed
to be uniform in the ring. Vertical beam sizes are the ones at the location of the beam size
monitor. The experiment names are the ones set for each beam size scan in Section 7.2.
Experiment
H-A
H-C
L-A
L-B
Ring
HER
HER
LER
LER
Date
June 11th July 16th June 12th July 16th
Beam current I [mA]
287
251
341
302
Number of bunches nb
789
789
789
789
Bunch current I/nb [mA]
0.36
0.32
0.43
0.38
Horizontal beta function at IP βx∗ [mm]
200
100
200
200
∗
Vertical beta function at IP βy [mm]
3
3
3
3
∗
Vertical beam size σy [µm]
36
36
38
38
−8
Pressure P [10 Pa]
13.3
13.3
13.3
13.3

butions, B M C and T M C , are given by
Obeam-gas = B M C · P I
OT ouschek = T M C ·I2
σ y nb

(6.1)
(6.2)

where Obeam-gas , OT ouschek are the occupancies estimated in the beam-gas and Touschek simulation. The beam parameters are fixed at the values in Tab. 6.2, unlike the actual measurement
where the parameters are scanned for the decomposition of the two background sources. The occupancy and background contributions are estimated for each sensor. We compare B M C , T M C
with the measured B, T in Section 7.2.6.

6.4

HER SR simulation

We consider two patterns of beam tail structure in the HER SR simulation because the beam
tail structure has a large eﬀect on the SR background. Three types of simulation samples
are generated: the Gaussian-distributed core part (BeamCore), the Gaussian-distributed tailpart (GausTail), and the uniformly distributed tail part (FlatTail) [27]. We evaluate the SR
background by summing up the contributions from the common core part and either tail part:
BeamCore+GausTail or BeamCore+FlatTail.
The horizontal (vertical) width of the GausTail Gaussian is 5σx-core (15σy-core ) where σx-core(σy-core ) is the horizontal (vertical) width of the BeamCore Gaussian. FlatTail is distributed
over [−18σx-core , +18σx-core ] in the X direction and [−54σy-core , +54σy-core ] in the Y direction.
The tail distributions are scaled so that the number of particles beyond 10σx-core and 30σy-coreare equal to 10−5 of that of the BeamCore population.
In addition to the occupancy, we formed clusters from the hits (see Section 3.4.3) to evaluate
the cluster energies and cluster sizes. Figure 6.6 shows the estimated SR occupancies from an
HER single beam. L3 FW sensor receives the largest contribution from the SR background.
Scaled by the beam current, the simulated SR occupancy amounts to about 10 % of the total
occupancy measured during the SR study on July 13th (see Section 7.3).

53

BeamCore (U side)
BeamCore (V side)
GausTail (U side)
GausTail (V side)
FlatTail (U side)
FlatTail (V side)

0.025
SVD occupancy [%]

0.020
0.015
0.010
0.005
0.000

E
E Z
Z E Z
L3FWL3BWL4FWL4C L4BWL5FWL5C L5- L5BWL6FWL6+ L6C L6- L6BW
sensorFigure 6.6: Estimated occupancy from the three SR components in the HER SR simulation.
The beam current of 800 mA is assumed. The occupancies are calculated for each sensor basedon the zero suppression cut of SNR=5. The x-axis denotes the sensor names. U and V sideoccupancies adopts diﬀerent markers.
The energy spectra of the reconstructed SR clusters are shown in Fig. 6.7. For comparison,
we show the energy spectra in the HER beam-gas and Touschek simulation in Fig. 6.8. We
can see almost all the SR clusters have the energy deposit below 50 keV unlike the beam-gas
and Touschek backgrounds. This is useful information for extracting the SR contribution fromthe measured background rate. We set the energy threshold of the SR study to 50 keV (seeSection 7.3.1) based on the simulation.
The averaged cluster size on the L3 sensors is close to one, as shown in Tab. 6.3. This is
expected because the low energy photons stop at the surface of the silicon sensor and they do nothave enough energies to make hits over multiple strips. We use the information in Section 7.3
to translate the number of the SR clusters into the occupancy.

54

Cluster energy (SR)L3FW_U
Entries
152
Mean
27.24
RMS
8.349

35

30

L3FW_V
Entries
Mean
RMS

25
20

L3BW_U
Entries
66
Mean
38.83
RMS
10.49
L3BW_V
Entries
66
Mean
26.66
RMS
9.295

15
10

5
0
0

217
30.45
9.574

20

40

60

80

100
energy [keV](a) BeamCore+GausTail

Cluster energy (SR)L3FW_U
Entries
268
Mean
27.1
RMS
8.278

60

L3FW_V
Entries
395
Mean
29.75
RMS
10.37

50

40

L3BW_U
Entries
90
Mean
39.11
RMS
11.47

30

L3BW_V

20

Entries
Mean
RMS

10

0
0

20

40

60

76
27.54
9.737

80
100
energy [keV](b) BeamCore+FlatTail

Figure 6.7: Cluster energy distributions on the L3 sensors in the HER SR simulation. The
clusters from the BeamCore and one of the beam tail components are summed up: BeamCore
and GausTail (a), BeamCore and FlatTail (b). The black line corresponds to the U side of L3
FW sensor, red the V side of L3 FW sensor, green the U side of L3 BW sensor, blue the V sideof L3 BW sensor.

55

Cluster energy (SR)L3FW_U
Entries
1789
Mean
89.86
76.17
RMS

220
200
180

L3FW_V
Entries
2007
Mean
107.4
RMS
79.8
L3BW_U
Entries
1468
Mean
122.9
RMS
85.42
L3BW_V
Entries
1487
Mean
103.8
RMS
75.92

160
140
120
100
80
60
40
20
0
0

50

100

150

200

250

300
350
energy [keV](a) HER beam-gas

Cluster energy (SR)L3FW_U
Entries
264
Mean
86.48
RMS
69.86

30

L3FW_V
Entries
286
Mean
105.3
77.08
RMS

25

20

L3BW_U
Entries
190
Mean
126.7
RMS
89.93
L3BW_V
Entries
180
Mean
109.6
RMS
84.08

15

10

5

0
0

50

100

150

200

250

300
350
energy [keV](b) HER Touschek

Figure 6.8: Cluster energy distributions on the L3 sensors in HER beam-gas (a) and HER
Touschek (b) simulations. The black line corresponds to the U side of L3 FW sensor, red theV side of L3 FW sensor, green the U side of L3 BW sensor, blue the V side of L3 BW sensor.
The y-axis scales are arbitrary.

56

Table 6.3: Cluster sizes on L3 sensors in the SR simulations. Each value is followed by thestandard error. For FlatTail component on the U side of L3 FW (BW) sensor, the 68 % C.L.
upper limit is calculated since all the 33 (25) clusters reconstructed in the simulation are singlestrip clusters. The upper limit calculation assumes that the cluster size is either one or two andfollows the binomial distribution.
sensor side
BeamCore
FlatTail
GausTail
L3FW
U
1.04 ± 0.01 1.00 + 1.03 1.05 ± 0.04
L3FW
V
1.23 ± 0.02 1.19 ± 0.06 1.18 ± 0.05
L3BW
U
1.05 ± 0.03 1.00 + 1.04 1.06 ± 0.04
L3BW
V
1.04 ± 0.03 1.10 ± 0.07 1.09 ± 0.05

57

Chapter 7

Analysis of the beam backgrounddata
During the Phase 2 commissioning, which was held March–July 2018, several beam backgroundmeasurements were done. We list the measurements mentioned in this section in Tab. 7.1.
Regarding the important measurements, the strip charts during the measurements are shownin Appendix A.
Table 7.1: The list of beam background measurements. Beam size scans, SR studies, luminosity
scan, and injection background study are respectively mentioned in Section 7.2, 7.3, 7.4, and
7.5.
date

beam

HER
βx∗ /βy∗ [mm]LERβx∗ /βy∗ [mm]April 30th
May 1stMay 8th
May 10th
May 21st
May 21st
May 24th
May 24th
June 11th
June 12th
July 12th
July 13th
July 13th
July 13th
July 14th
July 16th
July 16th

HER
LER
HER
LER
HER
Collision
HER
LER
HER
LER
Collision
LER
LER
HER
–
LER
HER

200/8
–
200/8
–
200/8
200/8
200/6
–
200/3
–
100/3
–
–
100/3
–
–
100/3

–
200/8
–
200/8
–
200/8
–
200/6
–
200/3
200/3
200/3
200/3
–
–
200/3
–

58

note

Beam size scan (H-A)
Beam size scan (L-A)
Luminosity scan
LER injection background study
Beam size scan (H-B), SR study
HER vacuum leak
Beam size scan (L-B), SR study
Beam size scan (H-C)

In the first section of this chapter, we explain the long-term evolution of the single-beambackground rates. In the following sections, we describe dedicated analyses for the beam background sources introduced in Section 5.2. We close the chapter by confirming the correlation
between the SVD and diamond and estimating the Phase 3 background rate, which are thegoals of our beam background study.

7.1

Beam background evolution over Phase 2

In Phase 2, collision tuning started with the optics of (βx∗ [mm], βy∗ [mm]) = (200, 8) for bothrings. As the beta functions were progressively squeezed in stages, we measured the single-beambackground rate. Figure 7.1 shows the long-term evolution of the beam background seen in the
SVD. The occupancy on the V side of L3 FW (BW) sensor is shown for the HER (LER) because
the sensor suﬀers the largest occupancy from the HER (LER) background.
In general, smaller beta functions make the beams narrower, which leads to more backgrounds due to the Touschek eﬀect. However, it is not always true for Fig. 7.1, because thebackground rate also depends largely on the optics and collimator condition.
• The HER background rate on June 11th (βx∗ = 200 mm) is higher than July 13th and16th (βx∗ = 100 mm) despite its larger βx∗ . We suppose this is because June 11th was rightafter the optics setting was changed to a new one and the collimator setting was not yet
optimized to mitigate the background.
• The higher background rate on July 16th compared to July 13th in both rings is also dueto the collimator setting. Since the study on July 16th was the reference for the luminosity
background study on a diﬀerent day, we opened the collimators to make the collimatorsetting the same as the previous study1 .
• The diﬀerence in the LER background between June 12th and July 13th is also due tothe collimator condition. Since a vertical collimator in LER, which is the only one, wasdamaged at the end of June, the beam background is less mitigated by the collimator in
July.

7.2

Decomposition of Touschek and beam-gas components

7.2.1

MethodTo disentangle the two major backgrounds, Touschek and beam-gas components, we performed
several “beam size scans” in Phase 2. In a beam size scan, we monitor the beam parameters andthe background rates on the detectors via EPICS [28] as shown in Fig. 7.2. They are measured
as the beam current decays and the measurement is repeated with diﬀerent beam sizes σy andalso diﬀerent numbers of bunches nb .
Since only the Touschek component depends on the beam size and the number of bunches,the diﬀerence of the background rates between the measurements arises from Touschek eﬀect
assuming the same beam current. The result of a beam size scan is analyzed by plotting O/IP
1

On July 12th, when we performed the luminosity study, poor injection conditions forced us to open thecollimators widely to allow beam injection, leading to higher background rate from the stored beam59

April 30 (200,8)
May 21 (200,8)
May 24 (200,6)
June 11 (200,3)
July 13 (100,3)
July 16 (100,3)

SVD Occupancy (L3FWV) [%]

0.20
0.15
0.10
0.05
0.00

0

50

100
150
200
HER current [mA]

250

300

(a) HER

0.35

SVD Occupancy (L3BWV) [%]May 1 (200,8)0.30

May 24 (200,6)
June 12 (200,3)

0.25

July 13 (200,3)

0.20

July 16 (200,3)

0.15
0.10
0.05
0.00

0

50

100
150
200
LER current [mA]

250(b) LER

Figure 7.1: The long-term evolution of the single-beam backgrounds of the HER (a) and theLER (b). The SVD occupancy is shown as a function of the beam current. The legend denotes(βx∗ [mm], βy∗ [mm]) together with the dates of the measurements. The background rates aremeasured with the nominal beam size of each optics, and by 1 kHz pseudorandom trigger.

60

Figure 7.2: Strip chart showing SVD occupancy and beam parameters during a beam size scan(L-B). The LER parameters (I, P , σy , nb ) and the SVD occupancy (averaged over L3 sensors)
are shown as function of time. We inject the beam to the maximum current and take data as
the current decays. The procedure is repeated for each beam size setting. The SVD occupancy
is recorded only when the Belle II DAQ is running and the last value is kept when the DAQ is
stopped. It goes to the default value when the system is configured for a new run.
values as a function of I/P σy nb . This “heuristic plot” is a convenient way to confirm the validityof our model described in Section 5.3, because another form of Eq. (5.2)
O
I
=T·
+B
IP
P σ y nb

(7.1)

indicates that O/IP should be a linear function of I/P σy nb with an oﬀset of B and a slope of
T . Only sweeping with the beam current is not enough to determine B and T , since I/P does
not change drastically in Eq. (7.1) due to the linearity of P to I.

7.2.2

Beam size scans in Phase 2

Table 7.2 shows the list of beam size scans performed in Phase 2. Two diﬀerent methods wereused to change the beam size: the vertical steering method and the x-y coupling method. In
the vertical steering method, we locally introduce the vertical shift in the beam orbit withbending magnets. This leads to the vertical dispersion and increases the beam size. In thex-y coupling method, we increase the x-y coupling of the beam by changing the strength of askew quadruple magnet. Since the horizontal beam size is larger than the vertical one, the x-y
coupling increases the vertical beam size. The latter method enables us to increase the beam
size without aﬀecting the beam orbit, and is the preferred method. The beam orbit shift by thevertical steering method might cause an unexpected eﬀect on the beam background rate. The
vertical steering method was used in H-B due to miscommunication between the accelerator

61

Table 7.2: The list of beam size scans. nb is the number of bunches, σy is the vertical beam sizeat the location of the beam size monitor, I is the maximum beam current right after the beam
injection. In L-A, the SVD data are available only for nb =789.
exp

date

ring

methodnb

σy [µm]I [mA]

H-A
L-A
H-B
L-B
H-C

June 11th
June 12th
July 13th
July 16th
July 16th

HER
LER
HER
LER
HER

x-y couplingx-y couplingvertical steering
x-y couplingx-y coupling

789, 1576
789(, 1576)
789
789
789

35, 50, 85
35, 85, 165
40, 50, 80, 135
45, 70, 130
40, 60, 70

285
320
320
320
240

and detector groups.
For H-A, H-C, L-A, and L-B, we prepared the dedicated beam background simulations,which reflect the beam optics and collimator settings during the studies. In this section, we aim
to determine the Touschek and beam-gas contributions in these studies and to compare themwith the simulations.

7.2.3

Pressure correction

Since the CCGs (see Section 3.2.1) are located near the sputter ion pumps outside the beam pipe,
they do not directly measure the pressure in the beam pipe. Because of the finite conductance
between the beam pipe and the pumps, the dynamic pressure becomes lower around the CCGs.
In the Phase 1 analysis [4], the dynamic pressure measured by each CCG is considered to be
three times lower than the one in the beam pipe according to simulations:
PCCG = P0 + k · I(7.2)

Pbeam = P0 + 3k · I(7.3)

where, PCCG and Pbeam are the pressures around the CCGs and inside the beam pipe respectively, P0 is the base pressure, and k·I is the dynamic pressure proportional to the beam current.
In this thesis, we take the factor for the dynamic component to be an unknown parameter c.
Pbeam = P0 + ck · I(7.4)

Therefore, the pressure in the beam pipe is given by
Pbeam = c · PCCG − (c − 1) · P0 .

(7.5)

P0 is determined as the pressure which has become stable after several hours without the beam
stored in the ring. When there is not such a period near the background measurement, we
determined it by fitting the measured pressure and the beam current with a linear function.
For the LER, we optimize c so that the measured diamond dose rates fit the single-beambackground model (see Section 5.3) the best. We use the dose rates on the four BWD diamond
sensors during L-A for the optimization. The LER base pressure is determined to be P0 =1.8 × 10−8 Pa from the pressure measured without the beam as shown in Fig. 7.3. For each

62

Figure 7.3: The LER pressure and current during L-A. The pressure after a few hours without
stored beam is taken as the base pressure P0 = 1.8 × 10−8 Pa.
diamond sensor, we fit the dose rate and the beam parameters with Eq. (5.2) to determine B, T ,and c. Figure 7.4 shows the heuristic plots (see Section 7.2.1) for the diamond sensors with the
optimized c. In contrast to Fig. 7.5 where no or old correction is applied, Fig. 7.4 shows good
linearity and hence good agreement with the model.
The optimized parameter c is listed in Tab. 7.3. The parameter does not agree across thediﬀerent channels of diamonds. We speculate this is because we use the average pressure overthe entire ring in the fit though the pressure is an order of magnitude diﬀerent depending on
the location. The probability that the beam-gas background particles hit each detector also
depends on the beam loss position. In order to take these things into account, we should use
all the pressures measured along the ring and assign the beam-gas contribution B to each ofthem, which corresponds to weighting CCGs according to their contributions as was done in
the Phase 1 analysis [4]. In this thesis, we use only the average pressure to avoid introducing
too many fitting parameters.
The parameter c for the SVD sensors may also diﬀer from the ones for the diamonds, but asan approximation, we use the average of the values in Tab. 7.3, c = 1.7, for the LER pressure
correction from this point. Another BEAST II detector at the same radius as the SVD also
shows c = 1.7 [29].
For the HER, we do not determine c from the data, because the data do not match themodel because of the unknown background component (see Section 7.2.6). Thus, we assume
c = 3 for the HER and estimate the systematic uncertainty from c later.

63

Diamond BWD Ch0μ c=1.55

1.2

Diamond BWD Ch1μ c=1.51

/IP [104mrad⋅ −1mA−1Pa−1]

/IP [104mrad⋅ −1mA−1Pa−1]

1.50

1.0

1.25

0.8
0.6
0.4

b

y

b

y

0.2
0.0

1.00

=35μmμ n =789
σ =85μmμ n =789
σ =165μmμ n =789
σ =35μmμ n =1576
σ =85μmμ n =1576
σ =165μmμ n =1576
σy

0

b

y

b

0.25

b

5

10
4
−1μ m−1]
I/Pσ n [10 mAPa
y

0.50

b

y

y

0.75

0.00

15

0

Diamond BWD Ch2μ c=1.6210[104mAPa−1μ m−1]

15

Diamond BWD Ch3μ c=2.03

/IP [104mrad⋅ −1mA−1Pa−1]

/IP [104mrad⋅ −1mA−1Pa−1]

3.5

4

3.0
2.5

3

2.0

2

1.5
1.0

1

0.5
0.0
0.0

5

/

I Pσy nbb0
0.0

2.5 5.0 7.5 10.0 12.54−1μ m−1]
I/Pσ n [10 mAPa
y

b

2.5
5.0
7.5
10.0
4
−1μ m−1]
I/Pσ n [10 mAPa
y

12.5

b

Figure 7.4: Heuristic plots with the optimized pressure correction for the four BWD diamond
sensors in L-A. The x-axis and y-axis represent I/P σy nb and O/P I respectively, where O is thediamond dose rate, I is the beam current, nb is the number of bunches, σy is the vertical beam
size. The pressure is given by P = c · PCCG − (c − 1) · P0 . The data from six measurementswith diﬀerent σy , nb shown in the legend are plotted. In each plot, c is determined by fitting
data with the single-beam background model. The fitted line is drawn in each plot.
Table 7.3: The optimized pressure correction parameter c for the BWD diamond sensors. c
is determined by fitting the diamond dose rate and beam parameters with the single-beambackground model Eq. (5.2). The minute-by-minute averages of the measured values are usedin the fit and the uncertainties are determined as described in Section 7.2.4.
diamondch0 (ϕ = 55)
ch1 (ϕ = 125)
ch2 (ϕ = 235)
ch3 (ϕ = 305)c
1.54 ± 0.02
1.51+0.02−0.01
1.62+0.01−0.02
2.03 ± 0.02

64

χ2 /ndf
51/15145/15185/15143/151

Diamond BWD Ch0μ c=3.00

/IP [104mrad⋅ −1mA−1Pa−1]

1.50

0.8

1.25
1.00

=35μmμ n =789
σ =85μmμ n =789
σ =165μmμ n =789
σ =35μmμ n =1576
σ =85μmμ n =1576
σ =165μmμ n =1576

0.75
0.50

σy

b

y

b

y

0.25
0.00

/IP [104mrad⋅ −1mA−1Pa−1]

Diamond BWD Ch0μ c=1.00

y

b

y

b

y

0

b

5

b

10
15
4
−1μ m−1]
I/Pσ n [10 mAPa
y

0.6
0.4
0.2
0.0

20

0

2
/

I Pσy nbb

4
6
8
[104mAPa−1μ m−1]

Figure 7.5: Heuristic plots for a BWD diamond sensor (ch0) in L-A, with no or old pressure
correction. The x-axis and y-axis represent I/P σy nb and O/P I respectively, where O is thediamond dose rate, I is the beam current, nb is the number of bunches, σy is the vertical beam
size. The pressure is given by P = c · PCCG − (c − 1) · P0 . The plotted data are same as Fig. 7.4
except for the pressure correction factor c. The left plot assumes c = 1 (no correction) and rightc = 3 (naive correction).

7.2.4

Errors of the variables

We use the minute-by-minute averages of the beam parameters and the SVD occupancies provided by EPICS for the decomposition analysis. An example is shown in Fig. 7.6. For eachvariable, we separate all the data points into subsets by timestamp to calculate the average.
The error of the SVD occupancy is estimated as the standard error of the mean x,√∑n2i=1 (xi − x)
σx =
(7.6)
n(n − 1)for each subset xi (i = 1...n). We conservatively assume the errors of σy and P to be 5 % of
the center value. Since the standard deviation of the beam current monitored by the DCCT isnegligibly small2 compared to other variables, we ignore the error of the beam current.

7.2.5

Noise subtraction

When a DSSD sensor does not have particle hits, it still has the finite occupancy of about 10−3 %due to electrical noise (assuming the zero suppression threshold of SNR = 5). We measured
the noise occupancy without the beam stored before or after each beam background study. The
noise is subtracted in our analysis. However, since the occupancy from beam background isO(0.1 %), the noise component does not have a significant eﬀect on the total occupancy.

20.01 mA for the LER and 0.007 mA for the HER [30].

65SVD occupancy [%]

0.08
0.06
0.04
0.02
0.00
11:50

data from EPICS
Average

11:51

11:52

time

11:53

11:54

11:55

Figure 7.6: The occupancy of the U side of L3 FW sensor as the function of time during abeam background measurement. The blue dots show the occupancy which is calculated by themonitoring software and provided via EPICS. The data points are separated on a minute-byminute basis. The average and the standard error of each subset are shown in red.

7.2.6
(1)

Heuristic analysis
HER

Figures 7.7 and 7.8 show the heuristic plots for the HER beam size scans, H-A, H-B, and H-C.
We use the occupancy of the V side of L3 FW sensor in the plots because the sensor has thelargest occupancy from HER. We can see that data points are not in a linear relation indicatedby the single-beam background model represented as Eq. (7.1). As clearly seen in Fig. 7.7(b),when we increase the beam size from the smallest point (the nominal size in the optics), theSVD occupancy slightly decreases at first but increases significantly at larger beam sizes. The
decrease is explained by the Touschek component, but the increase indicates the existence of an
unexpected background component which is not involved in the model. We call this unexpectedcomponent X. The X component positively correlates with the beam size, in contrast to the
Touschek component.
The dependence of the X component on the other beam parameters is seen in Fig. 7.7(a).
On June 11th, we measured the beam background rate with three diﬀerent σy and two diﬀerent
nb . If we group the six datasets into three groups by vertical beam size σy , we can draw threelines each of which goes through each dataset. Figure 7.9 shows the oﬀsets and slopes of theselines. They have similar oﬀsets B as shown in Fig. 7.9(a). Assuming the oﬀsets are common,
Eq. (5.2) can be extended as
O=T·

I2
I2
+ B · P I + X(σy )σ y nbnb(7.7)

where X(σy ) is the function describing the beam size dependence of the X. If σy is fixed, O/P I
is still a linear function of I/P σy nb but the slope of the line is modified as T + σy X(σy ).
As shown in Fig. 7.9(b), the lines for σy = 35, 50 µm in Fig. 7.7(a) have the almost same slope
T + σy X(σy ), which is much diﬀerent from σy = 85 µm. This means that the X contribution

66

6.11 HER beam si e scan (c=3μ5/IP [102/(mAPaμ]43=35 μm, n =789
σ =50 μm, n =789
σ =85 μm, n =789
σ =35 μm, n =1576
σ =50 μm, n =1576
σ =85 μm, n =1576

2
1
0

0

10

20
30
40
4
I/Pσ n [10 mA/(Paμmμ]
y

σy

b

y

b

y

b

y

b

y

b

y

b

50

b

(a) H-A

7.13 HER beam size scan (c=3μ

1.4

=40 m
σ =50 mσ =80 mσ =135 m
σy

1.2

y

1.0

/IP [102/(mAPaμ]

y

y

0.8
0.6
0.4
0.2
0.0

0

5

/

10
15
20
[104mA/(Pa mμ]25

I Pσy nb(b) H-B

Figure 7.7: Heuristic plots for two HER beam size scans: H-A (a), H-B (b). The x-axis andy-axis represent I/P σy nb and O/P I respectively, where O is the occupancy of the V side of
L3 FW sensor, I is the beam current, P is the pressure, nb is the number of bunches, σy isthe vertical beam size. The SVD occupancy was measured by 1 kHz pseudorandom trigger.
The legend denotes rough σy (and nb for (a)) during each measurement. The three lines in (a)respectively fit the data points with σy =35, 50, 85 µm. χ2 /ndf of the fitted lines are 12.2/30,
33.5/45, and 7.9/27, respectively. The line in (b) fits the data points with σy =40, 50 µm. χ2 /ndfof the fitting is 21.2/40.
67

7.16 HER beam size scan (c=3μ2.00=40 μmσ =60 μm
σ =70 μm
σy

1.75

y

1.50

/IP [102/(mAPaμ]

y

1.25
1.00
0.75
0.50
0.25
0.00

0

5

/

10

I Pσy nb

15
20
25
[104mA/(Paμmμ]30

Figure 7.8: Heuristic plots for the HER beam size scan H-C. The x-axis and y-axis represent
I/P σy nb and O/P I respectively, where O is the occupancy of the V side of L3 FW sensor, I isthe beam current, P is the pressure, nb is the number of bunches, σy is the vertical beam size.
The SVD occupancy was measured by 1 kHz pseudorandom trigger. The legend denotes roughσy during each measurement. The line fit the data points with σy =40, 60 µm. χ2 /ndf of thefitting is 28.1/41.

68

offsetμBμ[102/(PaμmA)]

1.8
1.7
1.6
1.5

0

20

40
σy [μm]

60

80

60

80

slopeμT + σyX [10−2μm/mA2](a) oﬀset

0.15
0.10
0.05
0.00

0

20

40

σy [μm](b) slopeFigure 7.9: The oﬀsets (a) and slopes (b) of the three lines drawn in Fig. 7.7(a). Each line fits
the data points with the same beam size in Fig. 7.7(a). The x-axis shows the vertical beam
size that is averaged over the data points used in each fit. The error bar shows the standard
deviation of the beam size. The errors of the oﬀsets and slopes originate from the errors of theparameters used in the fit (see Section 7.2.4).

69

Table 7.4: The uncertainty of the fitted background contributions B, T due to the pressure
correction factor c. For each experiment, B and T are obtained assuming c = 1 or c = 3.
xc=1
xc=3 − 1(x = T, B, BP ) are averaged over the sensors and are listed in the table.
T
B
BP

H-A

H-B

H-C

−0.5 %+62 %−3.4 %+1.0 %+65 %−4.5 %

+15 %
+35 %
−24 %

X(σy ) is small around the nominal beam size but increases drastically when the beam size is
too large. We assume the X contribution is negligible at σy = 35, 50 µm and determine thebeam-gas and Touschek contribution B, T by fitting Eq. (7.1) to these data. Similarly, wechoose σy = 40, 60 µm runs in Fig. 7.8 to determine B, T in H-C. We estimate B, T for eachsensor and compare them with the simulation. Figure 7.10 shows B data /B M C , T data /T M C foreach sensor. The measured background contributions are larger than the simulated ones by twoor three orders of magnitude. Uncertainties originate from the errors of the parameters used in
the fits (see Section 7.2.4) and the statistical error of the simulation.
We have been using c = 3 for the pressure correction so far, but since the smaller value (1.5–
2.0) for c is favored in the LER (see Section 7.2.3), we estimate the systematic uncertainties of
B and T due to c. For that purpose, we compare B and T determined with c = 1 and c = 3.
If we set c smaller, the corrected pressure becomes smaller and the beam-gas contribution B
will be larger. In order to compensate for this obvious eﬀect, we also compare the beam-gas
contributions multiplied by the corrected pressure3 B · P . The Touschek contributions arecompared as they are. The eﬀect of changing c is shown in Tab. 7.4. We can see that theeﬀect on the decomposition is negligible in H-A and H-B, but rather large in H-C. During H-C,
dynamic pressure was almost twice as high as H-B, because of a vacuum leak which happened
between these experiments. We speculate this is the reason why the decomposition of H-C issensitive to c.
(2)

LER

Figure 7.11 shows the heuristic plots for the LER beam size scans, L-A and L-B. The occupancyof the V side of L3 FW sensor, which is most sensitive to the LER background, is used for theplots. The pressure correction factor is set to c = 1.7 as described in Section 7.2.3.
The heuristic plot for L-A Fig. 7.11(a) shows good linearity, indicating that the LER background is explained as the sum of the Touschek and beam-gas components. The X component
that appears in the HER background is not present in the LER or at least not visible. The
beam-gas and Touschek contributions in L-A are determined by simply fitting the model to all
the data.
On the other hand, the result of L-B Fig. 7.11(b) is not easily explained by the model. In
L-B, we measured the background rate at the nominal beam size twice, at the beginning andend of the study. The two measurements show diﬀerent background rates, despite there being
3

The pressure at I = 300 mA is used.

70

B data/B MC, T data/T MC

6.11 HER: Data / Simulation
103

Touschek (U side)
Beam-gas (U side)

Touschek (V side)
Beam-gas (V side)

102
101

E
E Z
Z E Z
L3FWL3BWL4FWL4C L4BWL5FWL5C L5- L5BWL6FWL6+ L6C L6- L6BW(a) H-A

B data/B MC, T data/T MC

7.16 HER: Data / Simulation
103
102
101

Touschek (U)Beam-gas (U)Touschek (V)Beam-gas (V)

E
E Z
Z E Z
L3FWL3BWL4FWL4C L4BWL5FWL5C L5- L5BWL6FWL6+ L6C L6- L6BW(b) H-C

Figure 7.10: The beam-gas and Touschek contributions in the HER background B, T are compared between the measurement and the simulation for each sensor. The comparison was done
individually for H-A (a) and H-C (b). The x-axis denotes the sensor names. The triangles(inverted triangles) denote the Touschek component of the U (V) side occupancy. The squares(diamonds) denote the beam-gas component of the U (V) side occupancy.

71

0.8

6.12 LER beam size scan (c=1.7μ=35 m
σ =85 mσ =165 m
σy

0.7

y

0.6

/IP [102/(mAPaμ]

y

0.5
0.4
0.3
0.2
0.1
0.0
0.0

2.5

5.0

7.5 10.0 12.5
4I/Pσ n [10 mA/(Pa mμ]
y

15.0

b

(a) L-A

3.0

7.16 LER beam size scan (c=1.7μ=45 μm (1stμσ =70 μmσ =130 μm
σ =45 μm (2ndμ
σy

2.5

y

/IP [102/(mAPaμ]

y

2.0

y

1.5
1.0
0.5
0.0
0.0

2.5

5.0

7.5 10.0 12.5 15.0
4
I/Pσ n [10 mA/(Paμmμ]yb(b) L-B

Figure 7.11: Heuristic plots for the LER beam size scans: L-A (a) and L-B (b). The x-axis andy-axis represent I/P σy nb and O/P I respectively, where O is the occupancy of the V side of L3
BW sensor, I is the beam current, P is the pressure, nb is the number of bunches, σy is thevertical beam size. The SVD occupancy was measured by 1 kHz pseudorandom trigger. The
legend denotes rough σy during each measurement. The line in (a) fit all the data points in theplot. In L-B, six measurements where σy =45, 130, 130, 70, 70, 45 µ were done. The two lines in(b) individually fit the data points measured during the first and second halves of L-B. χ2 /ndfof the fitted lines are 32.3/40, 35.6/51, and 11.8/43,
respectively.
72

Table 7.5: The uncertainty of the fitted background contributions B, T due to the pressure
correction factor c. For each experiment, B and T are obtained assuming c = 1.5, 1.7, 2.0.
(BP )c′ =1.5,2.0
Tc′ =1.5,2.0
Tc=1.7 − 1 are averaged over the sensors and are listed in the table.
(BP )c=1.7 − 1 and
L-A
c′

1.5

2.0

beam-gas
Touschek+0.5 %-2.1 %-0.6 %+2.6 %

L-B (1st half)
1.5
2.0

L-B (2nd half)
1.5
2.0-0.3 %-1.5 %-1.3 %+5.3 %+0.4 %+1.9 %+1.6 %-6.2 %

no diﬀerence in accelerator conditions such as the beam current, pressure at each location of
the ring, vertical and horizontal beam sizes, and eﬀective atomic number of the residual gas.
This diﬀerence was also seen in other subdetectors.
The background rate measured on July 12th, four days before L-B shows a similar inexplicable eﬀect (see Section 7.4.2). Considering these observations, we conclude that the LER
background was unstable for an as-yet-undetermined reason. One possible explanation is thevacuum leak that occurred two days before L-B in the HER. Since the leak was found in the
HER beam pipe near the IP, it could have aﬀected the LER vacuum condition near the IP,
where there are no vacuum pumps or CCGs.
Assuming that the LER background follows our model in the short term, we divide L-B into
halves and estimate the beam-gas and Touschek contributions B, T for each half. The halves
show similar beam-gas contributions, whereas the Touschek contribution is doubled in the second half. This result does not support the above hypothesis that the instability was caused by
the vacuum leak.
Figure 7.12 shows the comparison of the beam-gas and Touschek contributions between dataand simulation. Uncertainties originate from the errors of the parameters used in the fits (seeSection 7.2.4). Similarly to the HER, the measured background contributions are larger than
the simulated ones, but the discrepancy is not as large as that seen in the HER. The discrepancy
for the Touschek component is within one order of magnitude, while the beam-gas contributions
diﬀer by one or two orders of magnitude. We can see that B data /B M C and T data /T M C are flatin Fig. 7.12, which means the simulated spatial distribution is consistent with the measured one
for each background species.
We estimate the systematic uncertainties of B and T due to the pressure correction factor c.
Since c for the diamond sensors ranges from 1.5 to 2.0, we use these values to obtain B and T ,and compare them with the ones obtained assuming c = 1.7. The result is shown in Tab. 7.5.
The uncertainty is 6 % at most.

7.2.7

Gas composition

Up to this point, the eﬀective atomic number of the residual gas Zef f has not been discussed.
M C = 7, theSince the measured Zef f (∼ 2) is smaller than the one assumed in the simulation Zeffsimulated beam-gas contribution is overestimated about 9 times as shown in Tab. 7.6. Therefore,taking this into account, B data /B M C estimated above, which is O(102 ) for the HER and O(10)for the LER, becomes 9 times larger (O(103 ) for the HER and O(102 ) for the LER).

73

B data/B MC, T data/T MC

10

2

10

1

10

0

6.12 LER: Data / Simulation

Touschek (U side)
Beam-gas (U side)
Touschek (V side)

10

Beam-gas (V side)
−1

E
E Z
Z E Z
L3FWL3BWL4FWL4C L4BWL5FWL5C L5- L5BWL6FWL6+ L6C L6- L6BW

B data/B MC, T data/T MC(a) L-A

10

2

10

1

10

0

10

7.16 LER: Data / Simulation

Touschek (U)Beam-gas (U)−1Touschek (V)Beam-gas (V)

E
E Z
Z E Z
L3FWL3BWL4FWL4C L4BWL5FWL5C L5- L5BWL6FWL6+ L6C L6- L6BW(b) L-B

Figure 7.12: The beam-gas and Touschek contributions in the LER background B, T are compared between the measurement and the simulation for each sensor. The comparison was done
individually for L-A (a) and L-B (b). The triangles (inverted triangles) denote the Touschek
component of the U (V) side occupancy. The squares (diamonds) denote the beam-gas component of the U (V) side occupancy. In (b), B data (T data ) derived from the first half of themeasurement is plotted in red (blue) markers and the ones derived from the second half areplotted in black markers.

74

Table 7.6: Eﬀective atomic numbers which are measured or assumed in the simulation.
(
)2
data
sim
sim /Z data
exp Zef
Z
Z
f
ef f
ef f
ef f
H-A
L-A
L-B
H-C

2.265
2.265
2.314
2.314

7
7
7
7

9.55
9.55
9.15
9.15

7.3

Synchrotron radiation study

7.3.1

MethodWe evaluate the SR background, which is considered to be a minor background component
hidden by other backgrounds. Background hits from SR can be discriminated from beam-gas
and Touschek backgrounds by their low energies and beam current dependence.
In Phase 2, we measured the background rate from single beams while the beam current
decayed. Figure 7.13 shows the typical cluster energy distribution on the SVD, which was measured during the HER single-beam background measurement. We set a threshold of O(10 keV)for hit energies to separate the background hits into two classes. Since the Touschek, beam-gas,
and SR rates are a quadratic or linear function of I, the background rates above and below thethreshold, H(I) and L(I), are individually represented as quadratic functions.
∫dO
H(I) =(I, e)de = a · I + b · I 2
(7.8)
de
e>e0
∫
dO
L(I) =(I, e)de = c · I + d · I 2
(7.9)
de
e<e0
Here, e is the hit energy and e0 is the threshold. We set the threshold e0 so that the SR
contributes only to the low energy class L(I). We assume that the energy spectra of SR andother backgrounds, fSR (e) and fB+T (e), do not depend on the beam current.
dO(I, e) = OB+T (I)fB+T (e) + OSR (I)fSR (e)de(7.10)

L(I) = k · H(I) + S · I(7.11)

Then, Eq. (7.8) becomes∫∫

where k = e<e0 fB+T (e)de/ e>e0 fB+T (e)de = d/b is a constant and S · I is the SR term
proportional to the beam current. Therefore, the SR quantity S is given by
S =c−a·db(7.12)

where a to d are determined by fitting quadratic functions to measured H(I) and L(I).

7.3.2

ResultWe estimated the SR contribution in the HER and LER backgrounds. The estimated contribution in the HER is compared with simulation. Since the estimated SR backgrounds are75

Cluster Energy Distribution
0.1

0.08

0.06

0.04

0.02

0
0

50

100

150

200

250

300
350
energy [keV]

Figure 7.13: Cluster energy distributions on L3 BW sensor due to the HER beam backgroundparticles. The red (blue) line denotes U (V) side clusters.
Table 7.7: The SR studies. We measured the SVD occupancy with the nominal beam sizeand by the 1 kHz pseudorandom trigger while the beam current decays. nb , σy , and I are thenumber of bunches, the vertical beam size at the location of the beam size monitor, and thebeam current, respectively. We also took noise data before each measurement when no beam isstored in the ring for the noise subtraction.
ring

date

nb

σy [µm]I [mA]

time length [s]

HER
LER

July 13th
July 16th

789
789

40
45

300–217
282–1701020
540

both consistent with zero as described below, the simulation studies are done only for the HER,
which has larger SR background than the LER.
Table 7.7 shows the measurements for the SR studies. The SR contribution is estimated for
the HER and LER individually.
In the oﬄine analysis, we apply a hit selection with a threshold of SNR = 5 and reconstructclusters from the fired strips. The clusters are classified according to an energy threshold of
50 keV, which is determined by the HER SR simulation. Assuming the simulation is true andalso applicable for the LER, the SR contribution is present in only the class of lower energy
clusters.
The data acquisition period is divided into six parts of equal length. For each period theaveraged number of clusters in each class per event is calculated. After subtracting the noise,
we fit the number of clusters with a function of the beam current. Figure 7.14 shows the fit
results. The SR contribution in the number of clusters per event per beam current SR cluster is76

Table 7.8: The SR occupancies in the measurement and simulation are shown for L3 sensors.
The observed occupancy (data) assumes ⟨clsSize⟩ = 1 and scaled to the final beam currentof Phase 3 (I=2.6 [A] for HER, I=3.6 [A] for LER). The simulation was done only for the
HER. The error of the observed occupancy arises from the fit. The simulated occupancy varies
depending on the tail structure.
ring

sensorside

data [10−3 %]simulation [10−3 %]BeamCore+FlatTailsimulation [10−3 %]BeamCore+GausTail

HER
HER
HER
HER
LER
LER
LER
LER

L3FW
L3FW
L3BW
L3BW
L3FW
L3FW
L3BW
L3BW

U
V
U
V
U
V
U
V

-2.6 ± 3.4-0.5 ± 1.5-0.2 ± 3.1-1.1 ± 7.0-6.5 ± 17.0
-49.7 ± 14.4
-8.3 ± 15.2
-82.4 ± 16.6

58.5
102.4
19.5
16.9
–
–
–
–

68.3
114.4
29.3
27.0
–
–
–
–

determined by Eq. (7.12). It is translated into occupancy as
SRoccupancy[%] = SR cluster · I · ⟨clsSize⟩ ·100#strips(7.13)

where I is the beam current of interest, ⟨clsSize⟩ is the averaged number of strips containedin an SR cluster, #strips is the total number of strips on the sensor. Since the SR cluster
size is confirmed to be close to unity in the HER SR simulation, we assume ⟨clsSize⟩ = 1 forsimplicity. The calculated SR occupancies equivalent to I = 800 mA are listed in Tab. 7.8. The
observed SR contributions are consistent with zero within errors for both rings. For the HER,
the estimated contributions are systematically lower than the simulated ones.

7.4

Luminosity backgrounds

The evaluation of luminosity backgrounds requires a series of luminosity background studies.
On July 12th, we performed a luminosity scan, where the HER and LER beams were stored in
the rings and the luminosity was changed by vertically shifting the orbit of one beam at the IP.
The background rate was measured while the beams were colliding and not colliding. However,
only scanning the luminosity is not enough to extract luminosity backgrounds. Because thebeam sizes increase during beam collisions, leading to the mitigation of Touschek backgrounds,
we need to estimate the Touschek contribution separately to evaluate the luminosity component. To estimate the decrease of the Touschek component, beam size scans of each ring were
performed on July 16th, on the same beam optics and collimator setting as the luminosity scan.
Originally, we planned to extract luminosity backgrounds by subtracting single-beam backgrounds estimated by the beam size scans from the background rate during collisions. However,this strategy was found to be not feasible this time because the single-beam background rates
during the beam size scans and during the luminosity scan contradicted each other. Hence,77L3FWU
0.05
0.04

p0

9.411e−06 ± 9.898e−06

p1

5.568e−07 ± 3.904e−08

χ / ndf

0.03

2

8.043 / 4p0

4.441e−14 ± 6.011e−06

p1

4.486e−07 ± 2.964e−09

0.02

L3BWU

3.54 / 4

0.03

0.025

< 50 keV

23.78 / 4

p0

1.204e−06 ± 1.814e−05

p1

3.726e−07 ± 3.688e−08

χ 2 / ndf

0.02

0.015

> 50 keV

0.01

χ 2 / ndf

#SVDClusters per event#SVDClusters per eventχ 2 / ndf

16.79 / 4

p0

1.665e−14 ± 1.496e− 06

p1

1.851e−07 ± 2.409e− 09> 50 keV

0.01< 50 keV

0.005

0
0

50

0.06

χ 2 / ndf

100

150

200

0
0

250
300
Current [mA]

50

100

3.889e−06 ± 1.135e− 05

p1

6.982e−07 ± 4.476e− 08

0.04

χ 2 / ndf

0.03

7.883e−13 ± 1.773e− 06

p1

2.462e−07 ± 2.359e− 09

0.02

0.03

0.025

9.001 / 4p0

χ 2 / ndf

#SVDClusters per event#SVDClusters per event

5.853 / 4

p0

250
300
Current [mA]

20.79 / 4p0

5.94e−13 ± 7.703e− 05

p1

3.735e−07 ± 2.687e− 09

χ 2 / ndf

0.02

3.967 / 43.284e−06 ± 6.218e− 06

p0

9.609e−08 ± 2.434e− 08

p1

0.015

> 50 keV> 50 keV

0.01< 50 keV< 50 keV

0.01

200

L3BWV

L3FWV
0.05

150

0.005

0
0

50

100

150

200

0
0

250
300
Current [mA]

50

100

150

200

250
300
Current [mA](a) HER

L3BWU

0.5
0.4
0.3

#SVDClusters per event#SVDClusters per event

L3FWUχ 2 / ndf

18.47 / 4

p00.0006381 ± 2.803e−05

p1

4.516e−06 ± 1.261e−07

χ 2 / ndf

0.8

50.71 / 4

p00.0004315 ± 2.343e− 05

p1

3.152e−06 ± 1.054e− 07

χ 2 / ndf

0.001011 ± 3.593e− 05

0.7

p1

7.564e− 06 ± 1.617e− 07

0.6

χ 2 / ndf
13.1 / 4
p00.0004043 ± 2.331e− 05
p1
3.157e−06 ± 1.049e− 07

0.5
0.4

0.2

> 50 keV> 50 keV

0.3< 50 keV

16.43 / 4p0

< 50 keV

0.2

0.1

0.1
0
0

50

100

150

0
0

50

0.8

χ 2 / ndf

200
250
Current [mA]

100

0.5
0.4

41.93 / 4

p00.0007998 ± 3.228e− 05

p1

6.24e−06 ± 1.453e− 07

χ 2 / ndf

3.28 / 40.000281 ± 2.161e− 05p0p1#SVDClusters per event#SVDClusters per event

0.6

3.02e− 06 ± 9.733e− 08

0.3> 50 keV

0.2< 50 keV

0.1
0
0

200
250
Current [mA]

L3BWV

L3FWV
χ 2 / ndf

150

0.7

0.0009984 ± 3.526e− 05

p1

7.162e−06 ± 1.586e− 07

0.6

χ 2 / ndf

0.5

p0

0.4
0.3
0.2

17.34 / 4

p0

p1

27.9 / 40.0003393 ± 2.38e− 05

3.694e−06 ± 1.072e− 07> 50 keV< 50 keV

0.1
50

100

150

200
250
Current [mA]

0
0

50

100

150

200
250
Current [mA](b) LER

Figure 7.14: The number of clusters per event is plotted as a function of the beam current.
The clusters are reconstructed from the HER (a) and the LER (b) single-beam backgrounddata. Each plot represents the clusters on one of the four sides of L3 sensors. The clusters are
78 (red) and below 50 keV (blue). The solid linesclassified by the energy threshold: above 50 keV
are the fitting functions p0 · I + p1 · I 2 .

subtracting the single-beam background rates from the rate during collision was no longer
valid. We describe this issue in Section 7.4.2. Instead, we attempted to estimate the luminosity
backgrounds by two diﬀerent methods, described in Sections 7.4.3 and 7.4.4.

7.4.1

Sensitivity to the luminosity backgrounds

We can estimate the sensitivity to the luminosity backgrounds from the simulation. The sensitivity is defined as the ratio between the expected luminosity component and the total background:
M C · Ldata /LM C
Olumi
.
data
Ototal(7.14)

M C is the simulated occupancy due to the luminosity backgrounds, Ldata,M C is theHere, Olumi
data is the measured occupancy.
luminosity that is measured or assumed in the simulation, Ototal
For the L3 FW sensor, where the luminosity backgrounds have the largest contribution in thesimulation, the sensitivity is estimated to be about 1/40. The luminosity in Phase 2 was low andthe single-beam background rates were unexpectedly high so that the luminosity backgrounds
were hard to detect. Even though the expected sensitivity is low, the luminosity background will
be visible if it shows a huge excess with respect to the simulation. Therefore, it is worthwhile
to confirm it is not visible.

7.4.2

Instability of the single-beam backgrounds

We have problems in estimating both of the HER and LER single-beam backgrounds during theluminosity scan. Firstly, the LER single-beam background rate during the luminosity scan contradicts the one measured during the LER beam size scan on July 16th. Figure 7.15 shows the
background rate measured during the LER beam size scan and non-collision run in the luminosity study. The optics and collimator settings for the LER are the same for both measurements.
We measured the background rate twice with the nominal beam size during the beam size scan,and the results are inconsistent as noted in subsection (2) of section 7.2.6. Since the HER
also contributes, the background rate during the non-collision run should be higher than the
LER single-beam background rate. However, the LER background rates measured on July 16th
exceed the background rate on July 12th. Therefore, the LER background rates are diﬀerent
between the three measurements despite the apparently identical accelerator conditions, which
are three hours or four days apart from each other.
The HER displayed short-term instability. Figure 7.16 is the strip chart during one run ofthe luminosity scan, which shows the background rates measured by various subdetectors andthe beam parameters as functions of time. The background rates show step-like deviation, which
is synchronized with the horizontal betatron tune of the HER. This deviation was observed inboth the collision and non-collision runs of the luminosity scan, but was not present in the beam
size scans. The other parameters such as the horizontal or LER betatron tunes, beam currents,pressures, and horizontal and vertical beam sizes, did not show the deviation synchronized withthe background rates. We suppose that the HER tune was close to an unstable resonance atthat time and any subtle changes of the tune made a large diﬀerence in the background rate.
It is practically impossible to take into account the eﬀect of the unstable tune.

79

L3BWV occupancy [%]July16 07:10-

0.4(

σy=43um)

July16 04:30-

0.3(

σy=43um)

July12 Non-collision(0.2

σy=37um)

0.1
0.0

0

50

100
150
200
beam current [mA]

250

Figure 7.15: The background rates during the luminosity scan (July 12th) and the LER beam
size scan (July 16th) as functions of the LER beam current. Despite including the HER component, the background rate during the luminosity scan is lower than the LER single-beambackground rates.

Figure 7.16: The strip chart during a non-collision run of the luminosity scan. The overlappedlines are the background rates measured by various subdetectors. The background rates show
step-like deviation synchronized with the horizontal tune of the HER (the blue line).

80

7.4.3

SVD-TOP correlation

Instead of the original plan which found to be not feasible, we introduce two diﬀerent methods
to analyze the luminosity scan data. In these two methods, we assume the spatial distributionsof the backgrounds were stable even though the background rate changed over time.
Firstly, we focus on low-momentum charged tracks due to the two-photon process, which
dominates the luminosity backgrounds on the SVD. Due to their small radii, these tracks leave
multiple hits on the SVD, but in contrast, do not reach outer detectors. We choose the TOP
counters as a reference and study the correlation between the SVD and the TOP, with andwithout collisions.4 The low-momentum components are evaluated as the diﬀerence of the SVDTOP correlation between with and without collisions.
When we measure the SVD and TOP rates with and without collisions, the low-momentum
contribution in the SVD, SVD low-pt , is approximately estimated as()
SVD
SVD low-pt = SVD coll −· TOP coll
(7.15)TOP non-coll
where coll (non-coll) denotes the background rate measured with (without) collisions. Here, it isassumed that only the low-momentum component makes diﬀerence between collisions and noncollisions and the ratio SVD/TOP of the total single-beam backgrounds is conserved. However,since the ratio is the weighted sum of the ratio for each background component, it can vary as
the percentage of each background component changes. In our case, the beam collisions makethe beam sizes larger and Touschek backgrounds decrease. Hence the ratio depends on the
beam size in general. In order to validate Eq. (7.15), we study the beam size dependence of theratio.
We measured the ratio for the single beams during the beam size scans on July 16th.
Figure 7.17 shows the ratio between the SVD occupancy averaged over each layer and the TOP
MCP-PMT rate. We can see that the LER background ratio of the SVD L3, 4 and TOP
depends on the beam sizes. The negative correlation indicates that the SVD-TOP ratio of the
LER Touschek background is larger than that of the beam-gas. The presence of the beam size
dependence does not allow us to use the ratio measured in non-collision runs as in Eq. (7.15).
In principle, the low-momentum background enhances the SVD-TOP ratio. The fact that theratio during collisions is not larger than that without collisions implies that the low-momentum
contribution, and hence the luminosity background itself, is small so that it is hidden by the
Touschek eﬀect.

7.4.4

Decomposition of background spatial distributions

The second method uses the spatial distribution of each beam background component to break
down the background rate measured during collisions. We categorize the beam backgrounds into
three components: luminosity backgrounds, HER single-beam backgrounds, and LER singlebeam backgrounds. We estimate the spatial distribution of each component by the simulation
or measurement. Fitting a superposition of the three spatial distributions to the one measured
during collisions, the contribution of each background component is determined.
4

According to simulation, the charged particles due to two-photon process have transverse momenta of pT =4 MeV/c in average, while pT > 500 MeV/c (18 MeV/c) is required to reach the TOP counters (the SVD).

81

SVD L4 / TOP [%/MHz]SVD L3 / TOP [%/MHz]

0.20

0.06

0.15
0.10

40

60

SVD L5 / TOP [%/MHz]

0.06

80 100σy [μm]

0.02

120

0.00

40

60

0.04

80

100

σy [μm]

120

0.03

0.04

0.02

LER single
HER single
Non-Collision
Collision

0.02
0.00

LER single
HER single
Non-Collision
Collision

SVD L6 / TOP [%/MHz]

0.05
0.00

0.04

LER single
HER single
Non-Collision
Collision

40

60

80 100σy [μm]LER single
HER single
Non-Collision
Collision

0.01

120

0.00

40

60

80

100

σy [μm]120

Figure 7.17: The ratio between the SVD and TOP background rates as a function of the beam
size. The averaged occupancy of each SVD layer and the total scaler rate of the TOP MCPPMT are used. The single-beam background rates were measured during the beam size scan on
July 16th, when the same collimator setting was applied as the luminosity scan. Non-collision(Collision) denotes the background rate measured during non-collision (collision) runs in theluminosity scan. The x-axis is the HER vertical beam size for “HER single”, otherwise the LER
vertical beam size.

82

0.125

HER
0.04
LER
Luminosity

0.100

0.03

0.075

0.02

fraction (HER, LER)

occupancy [%] (Luminosity)

0.150

0.050

0.01

0.025
0.000

E
E Z
Z E Z
L3FWL3BWL4FWL4C L4BWL5FWL5C L5- L5BWL6FWL6+ L6C L6- L6BW

0.00

Figure 7.18: The spatial distributions of the single-beam and luminosity backgrounds. The
measured single-beam background rates and simulated luminosity background rate are plottedfor each sensor. △, ×, □ (▽, +, ⋄) denote the U (V) side occupancy. The HER and LER distributions are normalized so that the sum of all the sensors becomes unity, while the luminosity
background shows the absolute occupancy [%] assuming the luminosity of 2 × 1034 cm−2 s−1 .
The HER (LER) distribution was measured on July 13th (16th).

0.14

occupancy during collision (2018-07-12 04:40)

Occupancy (U side)
Ocucpancy (V side)

0.12
occupancy [%]

0.10
0.08
0.06
0.04
0.02
0.00

E
E Z
Z E Z
L 3 F W L 3 B W L 4 F W L 4 C L 4 BW L 5 F W L 5 C L 5 - L 5 BW L 6 F W L 6 + L 6 C L 6 - L 6 BW

Figure 7.19: An occupancy spatial distribution averaged over one minute. □ (⋄) denotes the U(V) side occupancy. Measured during beam collisions.

83

Figure 7.18 shows the spatial distributions of the HER single beam, LER single beam, andluminosity backgrounds. The distribution is defined as the SVD occupancy calculated on eachside of the sensors. The distributions for the single-beam backgrounds are measured during thebeam size scans on July 16th, while the one for the luminosity backgrounds is taken from thesimulation that assumes the designed accelerator settings in Phase 2.
To calculate the spatial distribution, the SVD occupancy measured during collisions is divided into one-minute periods. For each period, the distribution is given by the occupancies
averaged over that period and the error is given by the standard error (see Section 7.2.4). Figure 7.19 shows a typical occupancy distribution during collisions.
The background spatial distributions measured during collisions are fitted by the superposition of the three distributions:i
Ocoll[%] = a · HERi + b · LERi +L
LM C· LUMIi [%](7.16)

where i denotes each sensor, Ocoll is the occupancy measured during collisions, HER, LER,LUMI are the measured single-beam background distributions and the simulated luminosity
background distribution, LM C is the luminosity assumed in the simulation, and a, b, L are thefit parameters. The luminosity during the collision run is estimated as L by the fit. Figure 7.20
shows the fit result of one period. The measured background distribution is well fitted by thesuperposition.
The fitted luminosity is determined in each period as shown in Fig. 7.21. We can see that thesensitivity of the fit is not good enough to see such low luminosity. Since there is not an excessof the fitted luminosity, assuming the simulated distribution is true, the luminosity backgrounds
are not much larger than the simulation. The reasonability of the luminosity background simulation is confirmed within the large error.
We note that the fitted luminosity tends to be negative at the beginning of each run inFig. 7.21. Since the LER lifetime is smaller than the HER, the largest change of the spatial
distribution between the beginning and end of the run would be the fraction of the LER components. Assuming the negative luminosity is explained by the fraction of the LER component, it
appears that the LER distribution used for the fit is slightly wrong and the error is compensatedfor by the negative luminosity component.

7.5

Injection background

In order to confirm the feasibility of continuous injection in Phase 3, we turned on the SVD andmeasured the background rate during LER injections on July 13th. Before the measurement,
the injection background rate was confirmed to be low, judging from the dose rates on the
diamond sensors. We checked the online-monitored SVD occupancy and the oﬄine-analyzed
one to observe the instantaneous increase due to the injection background.
The background rate was not measured with the SVD during the HER injections since thediamond dose rates were too high to ramp up the SVD high voltage. In the middle of July,when the injection background measurement was done, the injection conditions were unstablebecause a large temperature deviation had changed the length of the accelerating tube. Before
that, when the HER injection was well controlled, the HER injection background was observed
to be as low as the LER. Therefore, we consider the background measurement during the HER84

occupanc0 during collision (2018-07-12 04:40)
0.14

fit(all)measured

0.12
occupancy [%]

0.10
0.08
0.06

fit(LUMI)

33 12 11Fitted luminosity = 2.93+2.56−2.58x10 cm s
2
χ /ndf=20.626/25
Mea−/red luminosity = 1.14x1033cm12s11

0.04
0.02
0.00

E
E Z
Z E Z
L 3 F W L 3 B W L 4 F W L 4 C L 4 BW L 5 F W L 5 C L 5 - L 5 BW L 6 F W L 6 + L 6 C L 6 - L 6 BW

Figure 7.20: A fit result of the occupancy spatial distribution. The distribution measured duringcollisions is fitted with the superposition of the distributions of single beam backgrounds and33−2 −1
luminosity background. The luminosity is determined to be 2.93+2.56−2.58 × 10 cm s , while33−2−1
the measured luminosity is 1.14×10 cm s . The contribution from the fitted luminosity
background is plotted in green. △ and □ (▽ and ⋄) denote the U (V) side occupancy.

Luminosity [1033cm −2s −1]

10
5
0
−5
−10

fitted luminosity
measured luminosity−15
12 03:10 12 03:25 12 03:40 12 03:55 12 04:10 12 04:25 12 04:40 12 04:55
time

Figure 7.21: The fitted and measured luminosity during collisions are plotted as functions oftime. The fitted luminosity is estimated by fitting the occupancy spatial distribution on aminute-by-minute basis.

85

injection is also possible under more favorable conditions and should be conducted in Phase 3.
Figure 7.22 is the strip chart describing the LER injection background measurement. During
the measurement, the LER maximum beam current was set to 125 mA and the LER was topped
up as soon as 0.5 % of the current was lost. Accordingly, the injection was performed byalternating between injection periods of about 20 seconds with an injection rate of 0.5 Hz, andnon-injection periods of about 30 seconds. The HER beam current of about 100 mA was also
stored in the ring without injections, though not shown in the chart. The SVD occupancy anddiamond dose rate were measured over the alternating injection and non-injection periods. The
SVD occupancy in the chart is calculated online from part of the data taken by pseudorandom
1 kHz trigger. The diamond dose rate is sampled by 500 MHz clock and averaged every second.
We note that the period of the harsh background condition after each injection lasts fora few milliseconds according to a measurement with a background monitor. Therefore, theeﬀect of the injection background is diluted to about O(10−3 )5 . Despite the dilution, we cansee periodic increases in the diamond dose rate synchronized with the 0.5 Hz injections during
injection periods in Fig. 7.22. On the other hand, the online SVD occupancy does not show
any concurrent increase. Since the SVD time window is as short as O(100 ns), the trigger was
not synchronized with the injection, and the trigger rate was as low as 1 kHz, each injection
background event was rarely captured by the SVD time window. This would be one reason
why the injection background on the SVD is not visible in the strip chart in spite of the same
dilution as the diamonds.
We further investigate the eﬀect of the injection backgrounds on the SVD occupancy in theoﬄine analysis. Figure 7.23 shows the histogram of the occupancy calculated on an event-byevent basis. We can see that high-occupancy events tend to happen in the injection periods andthe average occupancy is about 1 % higher during injections. The eﬀect on the SVD occupancy
is much smaller than the diamond dose rate, which increases by about 10 % in average during
injection as shown in Fig. 7.22.
One possible explanation for the diﬀerence is that the injection background particles are
more likely to hit the diamonds than the SVD because of their spatial distribution. Since thecorrelation between the SVD and diamonds is confirmed for the backgrounds from the storage
beam (see Section 7.6), this is a remarkable feature of the LER injection background.
This observation indicates that at least the background from the 0.5 Hz LER injections has
a negligible eﬀect on the tracking performance, while 25 Hz continuous injection is plannedin Phase 3. The eﬀect of higher injection rates and the HER injection background should be
investigated in Phase 3. Since the SVD cartridge is only installed in the +X direction, attention
should be paid to the injection backgrounds in the other directions in Phase 3.

7.6

SVD-Diamond correlation

A large number of background hits arriving in a short period can destroy the APV25 chips
due to large currents on input channels. Thus, before ramping up the high voltage on the
DSSD sensors, we need to estimate the beam background rate on the SVD. Since the diamond
sensors always monitor the background level on the beam pipe near the SVD, we think about
estimating the SVD background conditions with the diamonds. The correlation between the5

a few milliseconds times the injection rate, 0.5 Hz.

86

Figure 7.22: The strip chart during the LER injection background measurement. The LER
current (red) is topped-up by injections as soon as it loses 0.5 % of the current. The diamonddose rate (magenta) shows instantaneous increases synchronously with the 0.5 Hz injection while
the SVD occupancy (blue) does not.
SVD and diamond background rate is studied for that purpose. The correlation also ensuresthat a beam abort by the diamonds can protect the SVD from the excessive radiations.
The measurements in Phase 2 are separated into three categories according to the stored
beam species: HER, LER, and HER+LER. For each category, we show the correlation between
the SVD L3 occupancy and BWD (FWD) Diamond dose rate in Fig. 7.24 (7.25). Figure 7.25
does not include the HER+LER case because we did not measure the background rate withboth beams while the FWD diamonds had sensitive measurable range. In the plots, only theoccupancy on the U side of the sensors and the dose rate on the diamond sensor at ϕ = 305 (ch3)
are used. This is because the occupancies on the U and V sides of a sensor is well correlated,
and the ch3 diamond sensor is one of the nearest sensors to the SVD and has the largest dose
rate among four diamond sensors on each side.
In each scatter plot, we can see the clear correlation between the SVD and diamond rates.
The correlation is stable even though the measurements are weeks or months apart from eachother. Therefore, it enables us to make robust estimation of the SVD occupancy without
actually ramping up the SVD high voltage.
For each set of SVD sensor and diamond, the scatter plots in Fig. 7.24 and 7.25 are overlaid
and shown in Fig. 7.26. We can see that the correlation largely depends on the positions of
the sensors of interest and which ring stores the beam. This is due to the position distributionof the backgrounds (the HER background is harder on the FWD side, the LER on the BWDside).
Table 7.9 shows the ratio between the SVD occupancy and the diamond dose rate calculated
from Fig. 7.26. For comparison, we show the ratio estimated by the simulation assuming the87

L3FWU1
10−1

InjectionL3FWU
Entries
324917Mean
0.1196RMS
0.3353
NoInjectionL3FWU

10−2

Entries
Mean
RMS

10−3

3119010.11860.3106

L3FWV
1
10−1

10−5

10−5
5 10 15 20 25 30 35 40 45
event-by-event occupancy [%]

L3BWU
1
−1

10

InjectionL3BWU
Entries 324917
Mean 0.08498
RMS
0.1701
NoInjectionL3BWU

10−2

Entries 311901
Mean 0.08369
RMS
0.1474

−3

10

0

1
10

Entries 311901
Mean
0.0812RMS
0.1097

−3

10

10−5
5

NoInjectionL3BWV

10−2

10−5

0

10
15
20
25
event-by-event occupancy [%]InjectionL3BWV
Entries 324917
Mean
0.08209
RMS
0.1261−110−43119010.12060.32155 10 15 20 25 30 35 40 45
event-by-event occupancy [%]

L3BWV

10−4

0

Entries
Mean
RMS

10−3
10−4

0

NoInjectionL3FWV

10−2

10−4

InjectionL3FWV
Entries 324917
Mean
0.1216RMS
0.3453

5

10
15
20
25
event-by-event occupancy [%]Figure 7.23: Histograms of event-by-event occupancy on the L3 sensors. The blue lines are theoccupancies during injection periods, the red lines during non-injection periods.

88

Table 7.9: The ratio between the U side occupancy of L3 sensors and the dose rate on diamond
sensors at ϕ=305 [%/(mrad/s)]. Calculated from the Fig. 7.26. The standard deviation of each
distribution is shown in the parentheses.
SVD / diamond
L3FW / BWD
L3BW / BWD
L3FW / FWD
L3BW / FWD

HER
0.55(16)0.37(12)0.10(2)0.07(1)LER
0.10(2)0.15(3)0.30(4)0.43(6)

HER+LER
0.17(5)0.16(3)––

Table 7.10: The ratio between the U side occupancy of L3 sensors and the dose rate on diamond
sensors at ϕ=305 [%/(mrad/s)]. Estimated by the Phase 2 simulation (see Section 6.2). The
ratio for the single beam backgrounds are shown except for the HER Touschek which has no
hit on the diamond sensors owing to poor statistics.
SVD / diamond
L3FW / BWD
L3BW / BWD
L3FW / FWD
L3BW / FWD

HER
beam-gas Coulomb
0.12(3)0.09(2)0.021(4)0.016(3)LER
beam-gas Coulomb
0.0143(5)0.0158(6)0.056(3)0.062(4)Touschek
0.0308(8)0.0299(7)0.062(2)0.060(2)design optics of Phase 2 in Tab. 7.10. The measured ratios are several times higher than thesimulated ones. This indicates the discrepancy is smaller for the diamonds while the measured
SVD background shows large excess with respect to the simulation.

7.7

Estimation of the Phase 3 beam background

One goal of the Phase 2 beam background studies is to estimate the beam background rate inPhase 3. The diﬃculty is that the simulation of the beam-induced backgrounds is not reliable.
As described in Section 7.2, we assumed the single-beam background model (see Section 5.3)
and estimated the beam-gas and Touschek contributions B and T . However, simply substituting
the obtained B, T and the expected beam parameters in Phase 3 into Eq. (5.2) does not give areasonable result, because B and T will be changed in Phase 3 due to the diﬀerence in the beam
optics and the collimator settings. To take account of both the measured background rate inPhase 2 and the optics and collimators in Phase 3, we correct the result of Phase 3 simulation
by
data
data
Bph2
Tph2
beam-gas
T ouschek+· Oph3M(7.17)
Ocorr = M C · Oph3M
C
C
MC
Tph2
Bph2
data , T M C are the Touschek contributions measured in Phase 2 and calcufor each ring. Here, Tph2
ph2
T ouschek(beam-gas)

lated in Phase 2 simulation, and similarly for the beam-gas contributions. Oph3M C
is the Touschek (beam-gas) background rate in the Phase 3 simulation. By this method, we

89Diamond BWD ch3 rate [mrad/s]

Diamond BWD ch3 rate [mrad/s]

0.5
0.4
0.3

5.21HER
5.24HER
0.2
6.11HER
7.13HER
0.1
7.16HER
0.00.00.1
0.2
SVD L3FWU occupancy [%]

0.5
0.4
0.3

5.21HER
5.24HER
0.2
6.11HER
7.13HER
0.1
7.16HER
0.00.00.1
0.2
SVD L3BWU occupancy [%]Diamond BWD ch3 rate [mrad/s]

Diamond BWD ch3 rate [mrad/s](a) HER

2.5
2.0
1.5
1.0

5.24LER
6.12LER
0.5
7.13LER
7.16LER
0.00.0 0.1 0.2 0.3 0.4
SVD L3FWU occupancy [%]

2.5
2.0
1.5
1.0

5.24LER
6.12LER
0.5
7.13LER
7.16LER
0.00.0 0.1 0.2 0.3 0.4
SVD L3BWU occupancy [%]

1.25
1.00

7.12
5.21

0.75
0.50
0.25
0.000.00 0.05 0.10 0.15 0.20 0.25
SVD L3FWU occupancy [%]Diamond BWD ch3 rate [mrad/s]

Diamond BWD ch3 rate [mrad/s](b) LER

1.25
1.00

7.12
5.21

0.75
0.50
0.25
0.000.00 0.05 0.10 0.15 0.20 0.25
SVD L3BWU occupancy [%](c) HER+LER

Figure 7.24: The correlation between the SVD and the BWD diamond. The x-axis shows theoccupancy on the U side of the SVD L3 FW or BW sensor and the y-axis shows the dose rateon the BWD diamond (ch3). The background is from the HER single beam (a), the LER single
beam (b), or HER and LER beams (c). Each point corresponds to the one-minute averaged
90 of the measurements.
background rates. The legend denotes the dates

0.25

4.30HER
5.8HER

0.20
0.15
0.10
0.05
0.000.00

0.01
0.02
0.03
SVD L3FWU occupancy [%]Diamond FWD ch3 rate [mrad/s]

Diamond FWD ch3 rate [mrad/s]

0.30

0.30
0.25
0.20
0.15
0.10
4.30HER
5.8HER
0.000.00
0.01
0.02
0.03
SVD L3BWU occupancy [%]
0.05

0.3
0.2
0.1

4.30LER
5.10LER
0.00.00
0.05
0.10
0.15
SVD L3FWU occupancy [%]Diamond FWD ch3 rate [mrad/s]

Diamond FWD ch3 rate [mrad/s](a) HER

0.3

4.30LER
5.10LER

0.2
0.1
0.00.00

0.05
0.10
0.15
SVD L3BWU occupancy [%](b) LER

Figure 7.25: The correlation between the SVD and the FWD diamond. The x-axis shows theoccupancy on the U side of the SVD L3 FW or BW sensor and the y-axis shows the dose rateon the FWD diamond (ch3). The background is from the HER single beam (a) or the LER
single beam (b). Each point corresponds to the one-minute averaged background rates. The
legend denotes the dates of the measurements.

91

Diamond BWD ch3 rate [mrad/s]

Diamond BWD ch3 rate [mrad/s]

2.5
2.0
1.5
1.0

LER
HER+LER
HER

0.5
0.00.00.1 0.2 0.3 0.4
SVD L3FWU occupancy [%]

2.5
2.0

LER
HER+LER
HER

1.5
1.0
0.5
0.00.00.1 0.2 0.3 0.4
SVD L3BWU occupancy [%]

0.4

HER
LER

0.3
0.2
0.1
0.00.00

0.05
0.10
0.15
SVD L3FWU occupancy [%]Diamond FWD ch3 rate [mrad/s]

Diamond FWD ch3 rate [mrad/s](a) SVD vs BWD diamond

0.4

HER
LER

0.3
0.2
0.1
0.00.00

0.05
0.10
0.15
SVD L3BWU occupancy [%](b) SVD vs FWD diamond

Figure 7.26: The correlation between the SVD and the BWD diamond (a) or the FWD diamond(b). The x-axis shows the occupancy on the U side of the SVD L3 FW or BW sensor and they-axis shows the dose rate on the FWD or BWD diamond (ch3). The scatter plots in Fig. 7.24
and 7.25 are overlaid for each set of the SVD and diamond sensors. Each point corresponds tothe one-minute averaged background rates. The legend denotes the beams stored during themeasurements.

92

Table 7.11: The scale factors used for the estimation of the Phase 3 single-beam backgrounds.
HER
LER

Touschek
1700
4.6

Coulomb
610
39

scale the Phase 3 simulation results by the observed discrepancy between measurements andsimulations in Phase 2, assuming the actual background rate in Phase 3 will show a similar
discrepancy from the simulation as observed in Phase 2.
So far, we have simulated the beam backgrounds in Phase 2 and Phase 3 (see Section 6.2),
and compared the single-beam backgrounds between the measurements and simulation in Phase
2 (see Section 7.2.6).
The estimated Phase 3 beam background rates on the L3 sensors
are shown in Figs. 7.27, 7.29, and 7.31.6 In these plots, we scale the Touschek and beam-gas
Coulomb backgrounds according to Eq. (7.17), while the luminosity backgrounds are not scaled
because no large excess is found in the luminosity background study (see Section 7.4.4). The
SR background is not included because the observed SR contribution was consistent with zero(see Section 7.3). The shown errors include only the statistical error of the Phase 3 simulation
result and the errors of the scale factors are not considered. The background rates averaged
over the sensors in each layer are shown in Figs. 7.28, 7.30, and 7.32. The occupancies exceed
the limit from tracking performance. Assuming the luminosity backgrounds are irreducible, themitigation of the beam backgrounds by an order of magnitude is required to take good-quality
data within the limit. The radiation dose rate is still within the limit of 10 Mrad in a decade
for all the L3 sensors, but we note that the injection backgrounds are not included in the plot.
The estimated NIEL damage exceeds the limit for some L3 sensors in the horizontal plane.
It will reach acceptable level after the background mitigation required from the viewpoint ofoccupancy.
In the first year of Phase 3, the plan is to keep the beam currents less than half of the designed
values. This will make the single-beam backgrounds roughly four times smaller than the final
condition. Since the planned beam sizes in the period are also 7–9 times larger, the Touschek
backgrounds will be even smaller and the luminosity will be 1/20 of the design. Considering the
reduction, the occupancy due to the backgrounds will be acceptable at the beginning of Phase
3 and the SVD will be operational with good performance. In order to proceed with Phase 3,
we will mitigate the backgrounds by tuning the beam optics and collimator settings, improving
the vaccum condition, and adding collimators.

6

The background rates on the other layers are shown in Appendix C.

93Phase 3 L3 occupancy, Uside (ZS SNR=5)

occupancy (U side) [%]12

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

10
8
6
4
2
0

FW BW FW BW FW BW FW BW FW BW FW BW FW BW
L3.1 L3.1 L3.2 L3.2 L3.3 L3.3 L3.4 L3.4 L3.5 L3.5 L3.6 L3.6 L3.7 L3.7(a) U side

Phase 3 L3 occupancy, Vside (ZS SNR=5)

occupancy (V side) [%]12

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

10
8
6
4
2
0

FW BW FW BW FW BW FW BW FW BW FW BW FW BW
L3.1 L3.1 L3.2 L3.2 L3.3 L3.3 L3.4 L3.4 L3.5 L3.5 L3.6 L3.6 L3.7 L3.7(b) V side

Figure 7.27: The estimated occupancies on U sides (a) and V sides (b) of the L3 sensors in the
final Phase 3 condition. The result of the Phase 3 simulation is rescaled considering the Phase 2
observation. The contributions from diﬀerent background sources are plotted in diﬀerent colors
denoted by the legend. The x-axis denotes the sensor names. The red dotted line is the detector
limit of 3 % from tracking performance (see Section 5.1.1). The errors of the scale factors are
not considered.

94

Strip Occupancy U [%]Phase 3 Strip Occupancy U side (ZScut 5)
twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

6
4
2
0

L3

L4

L5
Layer(a) U side

L6

Phase 3 Strip Occupancy V side (ZScut 5)

Strip Occupancy V [%]8

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

6
4
2
0

L3

L4

L5
Layer
(b) V side

L6

Figure 7.28: The estimated occupancies on U sides (a) and V sides (b) in the final Phase 3
condition. The occupancy is averaged over the sensors in each layer. The result of the Phase
3 simulation is rescaled considering the Phase 2 observation. The contributions from diﬀerent
background sources are plotted in diﬀerent colors denoted by the legend. The x-axis denotes
the layer number. The red dotted line shows the limit of 3 % from tracking performance (seeSection 5.1.1). The errors of the scale factors are not considered.

95

Phase 3 Radiation Dose Rate (Rescaled MC)

Radiation Dose Rate
[krad/smy]

1000

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

800
600
400
200
0

FW BW FW BW FW BW FW BW FW BW FW BW FW BW
L3.1 L3.1 L3.2 L3.2 L3.3 L3.3 L3.4 L3.4 L3.5 L3.5 L3.6 L3.6 L3.7 L3.7

Radiation Dose [krad/smy]

Figure 7.29: The estimated radiation dose on the L3 sensors in the final Phase 3 condition.
The result of the Phase 3 simulation is rescaled considering the Phase 2 observation. The
contributions from diﬀerent background sources are plotted in diﬀerent colors denoted by thelegend. The red dotted line shows the limit of 1 Mrad/smy (see Section 5.1.3). The errors of
the scale factors are not considered.

Phase 3 Radiation Dose

1000

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

750
500
250
0

L3

L4

Layer

L5

L6

Figure 7.30: The estimated radiation dose rate on the SVD in the final Phase 3 condition.
The dose rate is averaged over the sensors in each layer. The result of the Phase 3 simulationis rescaled considering the Phase 2 observation. The contributions from diﬀerent backgroundsources are plotted in diﬀerent colors denoted by the legend. The x-axis denotes the layer
number. The red dotted line shows the limit of 1 Mrad/smy (see Section 5.1.3). The errors of
the scale factors are not considered.

96

NIEL damage [1010 neq/cm2smy]

Phase 3 NIEL damage (Rescaled MC)

175

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

150
125
100
75
50
25
0

FW BW FW BW FW BW FW BW FW BW FW BW FW BW
L3.1 L3.1 L3.2 L3.2 L3.3 L3.3 L3.4 L3.4 L3.5 L3.5 L3.6 L3.6 L3.7 L3.7

NIEL damage[1010 neq/cm2smy]

Figure 7.31: The estimated NIEL damage on the L3 sensors in the final Phase 3 condition.
The result of the Phase 3 simulation is rescaled considering the Phase 2 observation. The
contributions from diﬀerent background sources are plotted in diﬀerent colors denoted by thelegend. The red dotted line shows the limit of 1012 cm−2 smy−1 1 MeV neutron equivalent fluence(see Section 5.1.3). The errors of the scale factors are not considered.

Phase 3 NIEL damage

100

twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

75
50
25
0

L3

L4

Layer

L5

L6

Figure 7.32: The estimated NIEL damage on the SVD in the final Phase 3 condition. The
NIEL damage is averaged over the sensors in each layer. The result of the Phase 3 simulationis rescaled considering the Phase 2 observation. The contributions from diﬀerent backgroundsources are plotted in diﬀerent colors denoted by the legend. The x-axis denotes the layer
number. The red dotted line shows the limit of 1012 cm−2 smy−1 1 MeV neutron equivalent
fluence (see Section 5.1.3). The errors of the scale factors are not considered.

97Chapter 8

Conclusion
8.1

Achievements

Although the SM successfully explains most of the phenomena in the particle physics, there
remain many unexplained mysteries: the matter-antimatter asymmetry in the universe, thenumber of the fermion generations, the source of the neutrino mass, the existence of dark matter, the fine-tuning of the Higgs mass, etc. Many new physics models beyond the SM aresuggested to explain these mysteries. The Belle II experiment, an intensity frontier experiment,
probes the new physics scenarios by precisely measuring the deviations from SM predictions.
The essence of the Belle II experiment is to accumulate 50 times more data than its predecessor with more intense beam collisions and a higher DAQ rate. For these improvements, theSVD faces two challenges: the harsh beam background environment resulting from the intense
beam collisions and the dead time of the readout ASIC due to the high trigger rate.
The APV25, the readout ASIC for the SVD, needs a trigger-veto system to prevent FIFO
overflow. However, the conventional trigger-veto scheme results in a large dead time of the
APV25 at the trigger rate of 30 kHz. Therefore there is a need for a more sophisticated triggerveto system (the APV25-FIFO emulator) that prevents the FIFO overflow with minimal deadtime.
At a test bench setup, we investigated how the APV25 reacts to given input signals. Basedon the observation, we constructed a simple model to estimate the FIFO occupancy, in orderto develop the APV25-FIFO emulator which provides the most eﬃcient trigger-veto. We implemented the developed APV25-FIFO emulator in the FTSW firmware. We confirmed thattrigger loss rates due to the APV25-FIFO emulator are consistent with expectations from simulation at various input trigger rates. The trigger loss rate for 30 kHz input triggers is about 3 %,which is a significant improvement from the conventional trigger-veto scheme. We verified its
performance to prevent the FIFO overflow at high trigger rate by using the Phase 2 setup. The
development of the APV25-FIFO emulator was an essential achievement for the 30 kHz DAQof the SVD.
Since the harsh beam background environment leads to the degradation of the detector performance and radiation damage, it is necessary to confirm that the background level in Phase
3 is appropriate for SVD operation. The installation of the full SVD should happen after theconfirmation of the following three items: The strip occupancy on every SVD sensor should98be low enough to achieve good tracking performance; the radiation dose rate should be low
enough to ensure acceptable levels of radiation damage on the SVD when accumulated for a
decade; the diamond sensors should be well correlated to the SVD for eﬀective protection frominstantaneous excessive background.
We had several simulation campaigns of the beam backgrounds in Phase 2 and 3, and several
beam background measurements during Phase 2 operation. We decomposed the measured beam
backgrounds according to their beam parameter dependency, energy distribution, and spatial
distribution. For each background species, we compared the measurement and simulation. We
confirmed large excesses of the observed Touschek and beam-gas backgrounds especially in the
HER, while there was no measurable excess of the observed synchrotron radiation and luminosity backgrounds. Considering the observed excess of beam backgrounds, we scaled the Phase 3
simulation results to make a realistic estimation of the background rate in Phase 3. We concluded that the background level is low enough to allow for acceptable tracking performance
assuming moderate accelerator conditions in the first years of Phase 3, but long-term operation
requires the mitigation of single-beam backgrounds by an order of magnitude. We also observed
a good correlation between the diamond dose rate and the SVD occupancy. Based on theseresults, the installation of the SVD in the Belle II detector was finally completed in Novemberof 2018, anticipating the background will be mitigated in the first years of Phase 3.

8.2

Remaining studies

In order to achieve the design performance of the Belle II experiment, some topics in the SVD
remain to be studied in the Phase 3 operation. We list them below:• We have already confirmed that the APV25-FIFO emulator functions for short periods in
the Phase 3 setup1 . The long-term stability of the trigger veto system with the APV25FIFO emulator should be confirmed in the Phase 3 operation with a high rate trigger.
• The mixed mode of the APV25-FIFO emulator should be implemented and tested.
• In the first year of Phase 3, beam background mitigation by tuning the accelerator andcollimator settings will be the first priority. We should perform beam size scans to update
the estimate of the final Phase 3 background. This will be an important input to decide
the operation plan.
• The properties of the unknown background X in the HER should be investigated. In
addition to the beam size scans, scanning the number of bunches will be an important
approach to disentangle it from other backgrounds.
• We should investigate the source of the discrepancy between the measured and simulated single-beam background rates. By correcting the simulation, we should make theestimation for the final Phase 3 more reliable.
• The beam-gas background model is approximated in this thesis. We should consider thegas composition and local diﬀerence of pressure to make the model more realistic.
• Since the SVD is not sensitive to the SR background, it can damage the SVD without
being recognized. Therefore, the SR background should be carefully estimated. We should
1

The data from the full SVD were read out without the FIFO overflow for at least 50 minutes with 10 kHz
FTSW pseudorandom trigger, and at least 27 minutes with 30 kHz pseudorandom trigger.

99

investigate it with a more sensitive approach to the low energy photons.
• In Phase 2, the machine luminosity was too low to measure the luminosity backgrounds,
which are predicted to be dominant in the Phase 3 simulation. We should redo theluminosity background study in stable accelerator condition with higher luminosity.
• The LER continuous injection background was barely visible to the SVD in Phase 2,
unlike the diamonds. The reason and the background from the HER injections should be
investigated.
• In Phase 3, the full SVD covering the entire azimuthal angle will be available. The ϕ distribution of the beam backgrounds should be investigated and utilized for the comparison
to the simulation.

100Appendix A

The strip charts during beam
background measurements
In this chapter, we show the strip charts for important beam background measurements, thebeam size scans and luminosity scan. In each chart, the beam parameters (current, pressure,vertical beam size, number of bunches, and luminosity) and the background rates (SVD occupancy averaged over the L3 sensors, diamond dose rate averaged over the BWD diamond
sensors, and total PMT rate of the TOP counters) are shown as functions of time.
While pseudorandom trigger was used in the most of the measurements, we took data by“physics trigger” during some runs in the beam size scans H-A and L-A. Due to the short time
window of the SVD, the SVD occupancy measured by the physics trigger is biased to be higher
than pseudorandom trigger. The bias can be seen by comparing the SVD occupancy with the
diamond and TOP background rate which are measured independently of the trigger.
In the physics data taking, the physics trigger should be sensitive to only the collision events andbeam background events are observed as random events superimposed on the collision events.
Therefore, we are interested in the beam background rate measured by the pseudorandom trigger. Physics trigger runs are not included in the analysis in this thesis.

101

102
Figure A.1: HER beam size scan on June 11th, H-A.

103
Figure A.2: HER beam size scan on July 13th, H-B.

104
Figure A.3: HER beam size scan on July 16th, H-C.

105
Figure A.4: LER beam size scan on June 12th, L-A.

106
Figure A.5: LER beam size scan on July 16th, L-B.

107

Figure A.6: Luminosity scan on July 12th. The number of bunches is 789 for both rings.

Appendix B

The result of the Phase 3 beam
background simulation
We show the detailed result of the Phase 3 background simulation in this chapter. The following
plots show the background rate (occupancy on U and V sides, radiation dose, and NIEL damage)on each SVD sensor due to various background sources (two-photon, RBB, BHWide, BHWide
LA, HER Coulomb, LER Coulomb, HER Touschek, LER Touschek, and total of them), in
addition to Fig. 6.3. Each plot is separated by the layers. The x-axis shows the azimuthal angleof the center of the sensor.1 The ladder numbers are shown above the data points. Markers
denote the sensor position on the ladder.

1

In the plots, the FW sensors are adjusted to the azimuthal angle and the other sensors are slightly shiftedfor visibility.

108

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

2

1.0

Layer
3 two-photon
4
5
6

3

7

FW
BW

1

0.5
0.0 0

90

0.4

2

3

180

4

Layer
4 two-photon
5
6
7
8

270

360
9

10

[ ]
FW
CE
BW

1

0.2
0.0 0
0.6

90
2

3

4

180

5

270

360

[ ]

Layer
5 two-photon
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.4
0.2
0.0 0

90

180

Layer 6 two-photon

270

360

[ ]
FW
+Z
CE
Z
BW

0.2 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.1
0.0 0

90

180

270

360

[ ]

Figure B.1: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from two-photon background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
109

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

2

0.2

3

4

Layer 53 RBB 6

7

FW
BW

1

0.1
0.0 0

90
2

0.2

3

180

Layer64 RBB7

4

5

270
8

360
9

10

[ ]
FW
CE
BW

1

0.1
0.0 0
0.2

90
2

3

4

180

5

6

270

360

[ ]

Layer
5 RBB
7 8 9 10 11 12 1

FW
CE
Z
BW

0.1
0.0 0

0.10

90

180

Layer 6 RBB

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.05
0.00 0

90

180

270

360

[ ]

Figure B.2: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from RBB background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
110

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]2

0.3

Layer 3 5BHWide6

3

4

7

FW
BW

1

0.2
0.1
0.0 0

90
2

0.2

3

180

4

Layer
46BHWide
5
7
8

270

360
9

10

[ ]
FW
CE
BW

1

0.1
0.0 0
0.2

90
2

3

4

180

5

270

360

[ ]

Layer
5 BHWide6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.1
0.0 0

0.10

90

180

Layer 6 BHWide

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.05
0.00 0

90

180

270

360

[ ]

Figure B.3: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from BHWide background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
111

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

0.04

2

Layer
3 BHWide
LA
4
5
6

3

7

FW
BW

1

0.02
0.00 0

90
2

0.02

3

180

4

Layer
4 BHWide
LA 8
5
6
7

270

360
9

10

[ ]
FW
CE
BW

1

0.01
0.00 0
0.02

90
2

3

4

180

5

270

360

[ ]

Layer
5 BHWide LA
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.01
0.00 0

0.010

90

180

Layer 6 BHWide LA

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.005
0.000 0

90

180

270

360

[ ]

Figure B.4: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from BHWide LA background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
112

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

0.010

2

Layer
3 HER
Coulomb
4
5
6

3

7

FW
BW

1

0.005
0.000 0
0.004

90
2

3

180

Layer5 4 HER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.002
0.000 00.004 2

90
3

4

180

270

360

[ ]

Layer
5 HER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.002
0.000 0

90

180

270

360

[ ]

6 HER Coulomb
0.0015 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

0.00100.00050.0000 0

90

180

270

360

[ ]

Figure B.5: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from HER Coulomb background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
113

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

0.2

2

Layer
3 LER5 Coulomb
4
6

3

7

FW
BW

1

0.1
0.0 0

90

0.2

2

3

180

Layer5 4 LER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.1

0.0 0
0.15

90
2

3

4

180

5

270

360

[ ]

Layer
5 LER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.10
0.05
0.00 0
0.10

90

180

Layer 6 LER Coulomb

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.05
0.00 0

90

180

270

360

[ ]

Figure B.6: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from LER Coulomb background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
114

Layer3 HER5 Touschek
4
6

3

7

FW
BW

1

0.000500.000250.00000 0

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]U side Occupancy [%]20.000759020.00153

180

Layer54 HER
Touschek
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.00100.00050.0000 0
0.002

90
2

3

4

180

270

360

[ ]

Layer
5 HER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.001
0.000 0

90

180

270

360

[ ]

6 HER Touschek
0.002 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

0.001
0.000 0

90

180

270

360

[ ]

Figure B.7: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from HER Touschek background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
115

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

2

0.3

Layer
3 LER5 Touschek
4
6

3

7

FW
BW

1

0.2
0.1
0.0 0
0.2

90
2

3

180

Layer5 4 LER6 Touschek
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.1
0.0 0

90

0.10 2

3

4

180

270

360

[ ]

Layer
5 LER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.05
0.00 0
0.06

90

180

Layer 6 LER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.04
0.02
0.00 0

90

180

270

360

[ ]

Figure B.8: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The U side occupancy from LER Touschek background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
116

U side Occupancy [%] U side Occupancy [%] U side Occupancy [%] U side Occupancy [%]

2

1.5

3

4

Layer 53 total 6

7

FW
BW

1

1.0
0.5
0.0 0

90

1.0

2

3

180

4

Layer
4 total7
5
6

270
8

360
9

10

[ ]
FW
CE
BW

1

0.5
0.0 0

0.75

90
2

3

4

180

5

270

360

[ ]

Layer
5 total
7 8 9 10 11 12 1

FW
CE
Z
BW

6

0.50
0.25
0.00 0
0.4

90

180

Layer 6 total

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.2
0.0 0

90

180

270

360

[ ]

Figure B.9: The azimuthal angle dependence of the U side occupancy in the Phase 3 simulation.
The total U side occupancy is plotted for each SVD sensor. The plots are separated by thelayers. For each layer, the x-axis shows the azimuthal angle of the center of the sensor. The
ladder numbers are shown above the data points. Markers denote the sensor position on theladder.
117

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

2

1.0

Layer
3 two-photon
4
5
6

3

7

FW
BW

1

0.5
0.0 0

90
2

0.4

3

180

4

Layer
4 two-photon
5
6
7
8

270

360
9

10

[ ]
FW
CE
BW

1

0.2
0.0 0
0.4

90
2

3

4

180

5

270

360

[ ]

Layer
5 two-photon
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.2
0.0 0
0.2

90

180

Layer 6 two-photon

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.1
0.0 0

90

180

270

360

[ ]

Figure B.10: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from two-photon background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
118

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

0.2

2

3

4

Layer 53 RBB 6

7

FW
BW

1

0.1
0.0 0

90
2

0.3

3

180

Layer64 RBB7

4

5

270
8

360
9

10

[ ]
FW
CE
BW

1

0.2
0.1
0.0 0

90

0.2 2

3

4

180

5

6

270

360

[ ]

Layer
5 RBB
7 8 9 10 11 12 1

FW
CE
Z
BW

0.1

0.0 0
0.15

90

180

Layer 6 RBB

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.10
0.05
0.00 0

90

180

270

360

[ ]

Figure B.11: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from RBB background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
119

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]0.4

2

Layer 3 5BHWide6

3

4

7

FW
BW

1

0.2
0.0 0

90
2

0.3

3

180

4

Layer
46BHWide
5
7
8

270

360
9

10

[ ]
FW
CE
BW

1

0.2
0.1
0.0 0
0.3

90
2

3

4

180

5

270

360

[ ]

Layer
5 BHWide6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.2
0.1
0.0 0

90

180

Layer 6 BHWide

270

360

[ ]
FW
+Z
CE
Z
BW

0.15 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.10
0.05
0.00 0

90

180

270

360

[ ]

Figure B.12: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from BHWide background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
120

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

0.04

2

Layer
3 BHWide
LA
4
5
6

3

7

FW
BW

1

0.02
0.00 0
0.03

90
2

3

180

4

Layer
4 BHWide
LA 8
5
6
7

270

360
9

10

[ ]
FW
CE
BW

1

0.02
0.01
0.00 00.03 2

90
3

4

180

5

270

360

[ ]

Layer
5 BHWide LA
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.02
0.01
0.00 090180Layer 6 BHWide LA

270

360

[ ]
FW
+Z
CE
Z
BW

0.015 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.010
0.005
0.000 0

90

180

270

360

[ ]

Figure B.13: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from BHWide LA background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
121

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

2

0.010

Layer
3 HER
Coulomb
4
5
6

3

7

FW
BW

1

0.005
0.000 0

90

0.004

2

3

180

Layer5 4 HER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.002
0.000 0
0.004

90
2

3

4

180

270

360

[ ]

Layer
5 HER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.002
0.000 00.001590

180

Layer 6 HER Coulomb

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.00100.00050.0000 0

90

180

270

360

[ ]

Figure B.14: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from HER Coulomb background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
122

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

0.2

2

Layer
3 LER5 Coulomb
4
6

3

7

FW
BW

1

0.1
0.0 0
0.2

90
2

3

180

Layer5 4 LER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.1
0.0 0

0.15 2

90
3

4

180

5

270

360

[ ]

Layer
5 LER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.10
0.05
0.00 0

90

180

270

360

[ ]

6 LER Coulomb
0.10 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

0.05
0.00 0

90

180

270

360

[ ]

Figure B.15: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from LER Coulomb background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
123

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]0.00102

Layer
3 HER5 Touschek
4
6

3

7

FW
BW

1

0.00050.0000 0

90
2

0.002

3

180

Layer54 HER
Touschek
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.001
0.000 00.003 2
0.002

90
3

4

180

270

360

[ ]

Layer
5 HER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.001
0.000 0
0.002

90

180

Layer 6 HER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.001
0.000 0

90

180

270

360

[ ]

Figure B.16: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from HER Touschek background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
124

V side Occupancy [%] V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

2

0.3

Layer
3 LER5 Touschek
4
6

3

7

FW
BW

1

0.2
0.1
0.0 0

90
2

0.2

3

180

Layer5 4 LER6 Touschek
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.1
0.0 0

0.10

90
2

3

4

180

270

360

[ ]

Layer
5 LER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.05
0.00 0
0.06

90

180

Layer 6 LER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.04
0.02
0.00 0

90

180

270

360

[ ]

Figure B.17: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The V side occupancy from LER Touschek background is plotted for each SVD sensor. The
plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of thecenter of the sensor. The ladder numbers are shown above the data points. Markers denote thesensor position on the ladder.
125V side Occupancy [%]V side Occupancy [%] V side Occupancy [%] V side Occupancy [%]

2

2

3

4

Layer 53 total 6

7

FW
BW

1

1
00

1.0

90
2

3

180

4

Layer
4 total7
5
6

270
8

360
9

10

[ ]
FW
CE
BW

1

0.5
0.0 0
1.0 2

90
3

4

180

5

270

360

[ ]

Layer
5 total
7 8 9 10 11 12 1

FW
CE
Z
BW

6

0.5
0.0 0

90

180

Layer 6 total

270

360

[ ]
FW
+Z
CE
Z
BW

0.6 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.4
0.2
0.0 0

90

180

270

360

[ ]

Figure B.18: The azimuthal angle dependence of the V side occupancy in the Phase 3 simulation.
The total V side occupancy is plotted for each SVD sensor. The plots are separated by thelayers. For each layer, the x-axis shows the azimuthal angle of the center of the sensor. The
ladder numbers are shown above the data points. Markers denote the sensor position on theladder.
126

Radiation Dose[krad/smy]

Radiation Dose[krad/smy]

Radiation Dose[krad/smy]

Radiation Dose[krad/smy]

100

2

Layer
3 two-photon
4
5
6

3

7

FW
BW

1

50
00

90
2

20

3

180

4

Layer
4 two-photon
5
6
7
8

270

360
9

10

[ ]
FW
CE
BW

1

10
00
20

90
2

3

4

180

5

270

360

[ ]

Layer
5 two-photon
6 7 8 9 10 11 12 1

FW
CE
Z
BW

10
00
15

90

180

Layer 6 two-photon

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

10
5
00

90

180

270

360

[ ]

Figure B.19: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from two-photon background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
127

Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]

30

2

3

4

Layer 53 RBB 6

7

FW
BW

1

20
10
00
10

90
2

3

180

Layer64 RBB7

4

5

270
8

360
9

10

[ ]
FW
CE
BW

1

5
00
15 2

90
3

4

180

5

6

270

360

[ ]

Layer
5 RBB
7 8 9 10 11 12 1

FW
CE
Z
BW

10
5
00

90

180

Layer 6 RBB

270

360

[ ]
FW
+Z
CE
Z
BW

10 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
5
00

90

180

270

360

[ ]

Figure B.20: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation. The radiation dose from RBB background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
128

Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]

30

Layer 3 5BHWide6

3

4

7

FW
BW

1

20
10
00

90
2

20

3

180

4

Layer
46BHWide
5
7
8

270

360
9

10

[ ]
FW
CE
BW

1

10
00

90

15 2

3

4

180

5

270

360

[ ]

Layer
5 BHWide6 7 8 9 10 11 12 1

FW
CE
Z
BW

10
5
00

10
Radiation Dose[krad/smy]

2

90

180

Layer 6 BHWide

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

5
00

90

180

270

360

[ ]

Figure B.21: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from BHWide background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
129

Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]

4

2

Layer
3 BHWide
LA
4
5
6

3

7

FW
BW

1

2
00
2

90
2

3

180

4

Layer
4 BHWide
LA 8
5
6
7

270

360
9

10

[ ]
FW
CE
BW

1

1
00
2 2

90
3

4

180

5

270

360

[ ]

Layer
5 BHWide LA
6 7 8 9 10 11 12 1

FW
CE
Z
BW

1
00

90

180

270

360

[ ]

6 BHWide LA
1.0 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

0.5
0.0 0

90

180

270

360

[ ]

Figure B.22: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from BHWide LA background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
130

Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]

0.75

2

Layer
3 HER
Coulomb
4
5
6

3

7

FW
BW

1

0.50
0.25
0.00 0
0.15

90
2

3

180

Layer5 4 HER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.10
0.05
0.00 00.15 2

90
3

4

180

270

360

[ ]

Layer
5 HER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.10
0.05
0.00 0

90

180

270

360

[ ]

6 HER Coulomb
0.10 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

0.05
0.00 0

90

180

270

360

[ ]

Figure B.23: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from HER Coulomb background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
131

Radiation Dose[krad/smy]
Radiation Dose[krad/smy]

2

Layer
3 LER5 Coulomb
4
6

3

7

FW
BW

1

10
5
00

90
2

10

3

180

Layer5 4 LER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

5
00

90

7.5 2

3

4

180

5

270

360

[ ]

Layer
5 LER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5.0
2.5
0.0 0

Radiation Dose[krad/smy]

Radiation Dose[krad/smy]

15

4

90

180

Layer 6 LER Coulomb

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

2
00

90

180

270

360

[ ]

Figure B.24: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from LER Coulomb background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
132

Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]
Radiation Dose[krad/smy]

0.10

2

Layer
3 HER5 Touschek
4
6

3

7

FW
BW

1

0.05
0.00 0

90
2

0.10

3

180

Layer54 HER
Touschek
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.05
0.00 0
0.10

90
2

3

4

180

270

360

[ ]

Layer
5 HER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.05
0.00 0
0.10

90

180

Layer 6 HER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

0.05
0.00 0

90

180

270

360

[ ]

Figure B.25: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from HER Touschek background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
133

Radiation Dose[krad/smy]

20

Layer
3 LER5 Touschek
4
6

3

7

FW
BW

1

10
00

90
2

10

Radiation Dose[krad/smy]

Radiation Dose[krad/smy]

Radiation Dose[krad/smy]

2

3

180

Layer5 4 LER6 Touschek
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

5
00

90

6 2

3

4

180

270

360

[ ]

Layer
5 LER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

4
2
00
3

90

180

Layer 6 LER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

2
1
00

90

180

270

360

[ ]

Figure B.26: The azimuthal angle dependence of the radiation dose in the Phase 3 simulation.
The radiation dose from LER Touschek background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
134

NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]

2

Layer
3 two-photon
4
5
6

3

7

FW
BW

1

10
00

NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

20

6

90
2

3

180

4

Layer
4 two-photon
5
6
7
8

270

360
9

10

[ ]
FW
CE
BW

1

4
2
00

15 2

90
3

4

180

5

270

360

[ ]

Layer
5 two-photon
6 7 8 9 10 11 12 1

FW
CE
Z
BW

10
5
00

90

180

270

360

[ ]

6 two-photon
15 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1
10

FW
+Z
CE
Z
BW

5
00

90

180

270

360

[ ]

Figure B.27: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from two-photon background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
135

NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]

2

30

3

4

Layer 53 RBB 6

7

FW
BW

1

20
10
00

90
2

10

3

180

Layer64 RBB7

4

5

270
8

360
9

10

[ ]
FW
CE
BW

1

5
00
15

90
2

3

4

180

5

6

270

360

[ ]

Layer
5 RBB
7 8 9 10 11 12 1

FW
CE
Z
BW

10
5
00

90

180

Layer 6 RBB

270

360

[ ]
FW
+Z
CE
Z
BW

20 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
10
00

90

180

270

360

[ ]

Figure B.28: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from RBB background is plotted for each SVD sensor. The plots are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
136

NIEL damage[1010 neq/cm2smy]

2Layer 3 5BHWide6

3

4

7

FW
BW

1

5
00

7.5

90
2

3

180

4

Layer
46BHWide
5
7
8

270

360
9

10

[ ]
FW
CE
BW

1

5.0
2.5
0.0 0

NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

10

10 2

90
3

4

180

5

270

360

[ ]

Layer
5 BHWide6 7 8 9 10 11 12 1

FW
CE
Z
BW

5
00

90

180

270

360

[ ]

6 BHWide10 2 3 4 5 6 7 Layer
8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

5
00

90

180

270

360

[ ]

Figure B.29: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from BHWide background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
137

NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]

1.0

2

Layer
3 BHWide
LA
4
5
6

3

7

FW
BW

1

0.5
0.0 0

90
2

0.4

3

180

4

Layer
4 BHWide
LA 8
5
6
7

270

360
9

10

[ ]
FW
CE
BW

1

0.2
0.0 0
0.6

90
2

3

4

180

5

270

360

[ ]

Layer
5 BHWide LA
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.4
0.2
0.0 0

90

180

Layer 6 BHWide LA

270

360

[ ]
FW
+Z
CE
Z
BW

0.3 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.2
0.1
0.0 0

90

180

270

360

[ ]

Figure B.30: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from BHWide LA background is plotted for each SVD sensor. The plots are
separated by the layers. For each layer, the x-axis shows the azimuthal angle of the center ofthe sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
138

NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]

0.10

Layer
3 HER
Coulomb
4
5
6

3

7

FW
BW

1

0.05
0.00 0

90
2

0.02

3

180

Layer5 4 HER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.01

0.00 0
0.020
0.015

90
2

3

4

180

270

360

[ ]

Layer
5 HER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.010
0.005
0.000 0NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

2

90

180

Layer 6 HER Coulomb

270

360

[ ]
FW
+Z
CE
Z
BW

0.02 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.01
0.00 0

90

180

270

360

[ ]

Figure B.31: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from HER Coulomb background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
139

NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]

1.0

2

Layer
3 LER5 Coulomb
4
6

3

7

FW
BW

1

1.0
0.5
0.0 0

90
2

3

180

Layer5 4 LER
Coulomb
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.5
0.0 0

0.75 2

90
3

4

180

5

270

360

[ ]

Layer
5 LER Coulomb
6 7 8 9 10 11 12 1

FW
CE
Z
BW

0.50
0.25
0.00 0NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

1.5

90

180

270

360

[ ]

6 LER Coulomb
0.4 2 3 4 5 6 Layer
7 8 9 10 11 12 13 14 15 16 1

FW
+Z
CE
Z
BW

0.2
0.0 0

90

180

270

360

[ ]

Figure B.32: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from LER Coulomb background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
140

Layer3 HER5 Touschek
4
6

3

7

FW
BW

1

0.005
0.000 0
0.06

90
2

3

180

Layer54 HER
Touschek
6
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.04
0.02
0.00 0

0.015

90
2

3

4

180

270

360

[ ]

Layer
5 HER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.010
0.005
0.000 0NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

2

0.010

NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

0.015

90

180

Layer 6 HER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

0.02 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.01
0.00 0

90

180

270

360

[ ]

Figure B.33: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from HER Touschek background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
141

NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]
NIEL damage[1010 neq/cm2smy]

3

2

Layer
3 LER5 Touschek
4
6

3

7

FW
BW

1

2
1

00
1.0

90
2

3

180

Layer5 4 LER6 Touschek
7
8

270

4

360
9

10

[ ]
FW
CE
BW

1

0.5
0.0 0
0.3

90
2

3

4

180

270

360

[ ]

Layer
5 LER Touschek
6 7 8 9 10 11 12 1

FW
CE
Z
BW

5

0.2
0.1
0.0 0

90

180

Layer 6 LER Touschek

270

360

[ ]
FW
+Z
CE
Z
BW

0.75 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0.50
0.25
0.00 0

90

180

270

360

[ ]

Figure B.34: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The NIEL damage from LER Touschek background is plotted for each SVD sensor. The plots
are separated by the layers. For each layer, the x-axis shows the azimuthal angle of the centerof the sensor. The ladder numbers are shown above the data points. Markers denote the sensor
position on the ladder.
142

NIEL damage[1010 neq/cm2smy]

2

3

4

Layer 53 total 6

7

FW
BW

1

40
20
00
30

90
2

3

180

4

Layer
4 total7
5
6

270
8

360
9

10

[ ]
FW
CE
BW

1

20
10
00
3

4

180

5

270

360

[ ]

Layer
5 total
7 8 9 10 11 12 1

NIEL damage[1010 neq/cm2smy]

90

30 2

NIEL damage[1010 neq/cm2smy]

NIEL damage[1010 neq/cm2smy]

60

40 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1

FW
CE
Z
BW

6

20
10
00

90

180

Layer 6 total

270

360

[ ]
FW
+Z
CE
Z
BW

20
00

90

180

270

360

[ ]

Figure B.35: The azimuthal angle dependence of the NIEL damage in the Phase 3 simulation.
The total NIEL damage is plotted for each SVD sensor. The plots are separated by the layers.
For each layer, the x-axis shows the azimuthal angle of the center of the sensor. The laddernumbers are shown above the data points. Markers denote the sensor position on the ladder.
143

Appendix C

The result of the Phase 3 beam
background estimation
We show the result of the Phase 3 background estimation described in Section 7.7 about theL4–6 sensors. In the following figures, the background rates (U and V side occupancy, radiationdose, and NIEL damage) are plotted for each sensor, which name is denoted by the x-axis. The
contributions from diﬀerent background sources are plotted in diﬀerent colors denoted by thelegend. The shown errors do not include the errors of the scale factors and originate from only
the statistical errors of the Phase 3 simulation. The red dotted lines denote the acceptablebackground rates.

144

L5.1 FW
L5.1 CE
L5.1 1Z
L5.1 BW
L5.2 FW
L5.2 CE
L5.2 1Z
L5.2 BW
L5.3 FW
L5.3 CE
L5.3 1Z
L5.3 BW
L5.4 FW
L5.4 CE
L5.4 1Z
L5.4 BW
L5.5 FW
L5.5 CE
L5.5 1Z
L5.5 BW
L5.6 FW
L5.6 CE
L5.6 1Z
L5.6 BW
L5.7 FW
L5.7 CE
L5.7 1Z
L5.7 BW
L5.8 FW
L5.8 CE
L5.8 1Z
L5.8 BW
L5.9 FW
L5.9 CE
L5.9 1Z
L5.9 BW
L5.10 FW
L5.10 CE
L5.10 1Z
L5.10 BW
L5.11 FW
L5.11 CE
L5.11 1Z
L5.11 BW
L5.12 FW
L5.12 CE
L5.12 1Z
L5.12 BWocc.panc0 (U side) [%]0

L4.1 FW
L4.1 CE
L4.1 BW
L4.2 FW
L4.2 CE
L4.2 BW
L4.3 FW
L4.3 CE
L4.3 BW
L4.4 FW
L4.4 CE
L4.4 BW
L4.5 FW
L4.5 CE
L4.5 BW
L4.6 FW
L4.6 CE
L4.6 BW
L4.7 FW
L4.7 CE
L4.7 BW
L4.8 FW
L4.8 CE
L4.8 BW
L4.9 FW
L4.9 CE
L4.9 BW
L4.10 FW
L4.10 CE
L4.10 BWoccupancy (U side) [%]Phase 3 L4 occupancy (U side)

12

10

twoPhoton
RBB
BHWideBHWide_LA

1210

twoPhoton
RBB
BHWideBHWide_LA

145

Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

8

6

4

2

Figure C.1: The Phase 3 U side occupancy in the L4 sensors. The Phase 3 simulation iscorrected by the Phase 2 observation.

Phase 3 L5 occupancy (U side)
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

8

6

4

2

0

Figure C.2: The Phase 3 U side occupancy in the L5 sensors. The Phase 3 simulation iscorrected by the Phase 2 observation.

146

0

2

4

6

8

10

12

+ccup nc1 (U −ide) [%].0+P%+.+n
RBB
BHWideBHWide_LA
C+u(+)b_HER
C+u(+)b_LER
T+u−c%ek_HER
T+u−c%ek_LER

Figure C.3: The Phase 3 U side occupancy in the L6 sensors. The Phase 3 simulation is corrected by the Phase 2 observation.

P% −e 3 L6 +ccup nc1 (U −ide)

L6.1 FW
L6.1 +Z
L6.1 CE
L6.1 −Z
L6.1 BW
L6.2 FW
L6.2 +Z
L6.2 CE
L6.2 2Z
L6.2 BW
L6.3 FW
L6.3 +Z
L6.3 CE
L6.3 2Z
L6.3 BW
L6.4 FW
L6.4 +Z
L6.4 CE
L6.4 2Z
L6.4 BW
L6.5 FW
L6.5 +Z
L6.5 CE
L6.5 2Z
L6.5 BW
L6.6 FW
L6.6 +Z
L6.6 CE
L6.6 2Z
L6.6 BW
L6.7 FW
L6.7 +Z
L6.7 CE
L6.7 2Z
L6.7 BW
L6.8 FW
L6.8 +Z
L6.8 CE
L6.8 2Z
L6.8 BW
L6.9 FW
L6.9 +Z
L6.9 CE
L6.9 2ZL6.9 BW
L6.10 FW
L6.10 +Z
L6.10 CE
L6.10 2Z
L6.10 BW
L6.11 FW
L6.11 +Z
L6.11 CE
L6.11 2Z
L6.11 BW
L6.12 FW
L6.12 +Z
L6.12 CE
L6.12 2Z
L6.12 BW
L6.13 FW
L6.13 +Z
L6.13 CE
L6.13 2Z
L6.13 BW
L6.14 FW
L6.14 +Z
L6.14 CE
L6.14 2Z
L6.14 BW
L6.15 FW
L6.15 +Z
L6.15 CE
L6.15 2Z
L6.15 BW
L6.16 FW
L6.16 +Z
L6.16 CE
L6.16 2Z
L6.16 BW

L5.1 FW
L5.1 CE
L5.1 1Z
L5.1 BW
L5.2 FW
L5.2 CE
L5.2 1Z
L5.2 BW
L5.3 FW
L5.3 CE
L5.3 1Z
L5.3 BW
L5.4 FW
L5.4 CE
L5.4 1Z
L5.4 BW
L5.5 FW
L5.5 CE
L5.5 1Z
L5.5 BW
L5.6 FW
L5.6 CE
L5.6 1Z
L5.6 BW
L5.7 FW
L5.7 CE
L5.7 1Z
L5.7 BW
L5.8 FW
L5.8 CE
L5.8 1Z
L5.8 BW
L5.9 FW
L5.9 CE
L5.9 1Z
L5.9 BW
L5.10 FW
L5.10 CE
L5.10 1Z
L5.10 BW
L5.11 FW
L5.11 CE
L5.11 1Z
L5.11 BW
L5.12 FW
L5.12 CE
L5.12 1Z
L5.12 BWocc.panc0 (V side) [%]0

L4.1 FW
L4.1 CE
L4.1 BW
L4.2 FW
L4.2 CE
L4.2 BW
L4.3 FW
L4.3 CE
L4.3 BW
L4.4 FW
L4.4 CE
L4.4 BW
L4.5 FW
L4.5 CE
L4.5 BW
L4.6 FW
L4.6 CE
L4.6 BW
L4.7 FW
L4.7 CE
L4.7 BW
L4.8 FW
L4.8 CE
L4.8 BW
L4.9 FW
L4.9 CE
L4.9 BW
L4.10 FW
L4.10 CE
L4.10 BWoccupancy (V side) [%]Phase 3 L4 occupancy (V side)

12

10

twoPhoton
RBB
BHWideBHWide_LA

1210

twoPhoton
RBB
BHWideBHWide_LA

147

Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

8

6

4

2

Figure C.4: The Phase 3 V side occupancy in the L4 sensors. The Phase 3 simulation iscorrected by the Phase 2 observation.

Phase 3 L5 occupancy (V side)
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

8

6

4

2

0

Figure C.5: The Phase 3 V side occupancy in the L5 sensors. The Phase 3 simulation iscorrected by the Phase 2 observation.

148

0

2

4

6

8

10

12

+ccup nc1 (V −ide) [%].0+P%+.+n
RBB
BHWideBHWide_LA
C+u(+)b_HER
C+u(+)b_LER
T+u−c%ek_HER
T+u−c%ek_LER

Figure C.6: The Phase 3 V side occupancy in the L6 sensors. The Phase 3 simulation is corrected by the Phase 2 observation.

P% −e 3 L6 +ccup nc1 (V −ide)

L6.1 FW
L6.1 +Z
L6.1 CE
L6.1 −Z
L6.1 BW
L6.2 FW
L6.2 +Z
L6.2 CE
L6.2 2Z
L6.2 BW
L6.3 FW
L6.3 +Z
L6.3 CE
L6.3 2Z
L6.3 BW
L6.4 FW
L6.4 +Z
L6.4 CE
L6.4 2Z
L6.4 BW
L6.5 FW
L6.5 +Z
L6.5 CE
L6.5 2Z
L6.5 BW
L6.6 FW
L6.6 +Z
L6.6 CE
L6.6 2Z
L6.6 BW
L6.7 FW
L6.7 +Z
L6.7 CE
L6.7 2Z
L6.7 BW
L6.8 FW
L6.8 +Z
L6.8 CE
L6.8 2Z
L6.8 BW
L6.9 FW
L6.9 +Z
L6.9 CE
L6.9 2ZL6.9 BW
L6.10 FW
L6.10 +Z
L6.10 CE
L6.10 2Z
L6.10 BW
L6.11 FW
L6.11 +Z
L6.11 CE
L6.11 2Z
L6.11 BW
L6.12 FW
L6.12 +Z
L6.12 CE
L6.12 2Z
L6.12 BW
L6.13 FW
L6.13 +Z
L6.13 CE
L6.13 2Z
L6.13 BW
L6.14 FW
L6.14 +Z
L6.14 CE
L6.14 2Z
L6.14 BW
L6.15 FW
L6.15 +Z
L6.15 CE
L6.15 2Z
L6.15 BW
L6.16 FW
L6.16 +Z
L6.16 CE
L6.16 2Z
L6.16 BW

L5.1 FW
L5.1 CE
L5.1 .Z
L5.1 BW
L5.2 FW
L5.2 CE
L5.2 .Z
L5.2 BW
L5.3 FW
L5.3 CE
L5.3 .Z
L5.3 BW
L5.4 FW
L5.4 CE
L5.4 .Z
L5.4 BW
L5.5 FW
L5.5 CE
L5.5 .Z
L5.5 BW
L5.6 FW
L5.6 CE
L5.6 .Z
L5.6 BW
L5.7 FW
L5.7 CE
L5.7 .Z
L5.7 BW
L5.8 FW
L5.8 CE
L5.8 .Z
L5.8 BW
L5.9 FW
L5.9 CE
L5.9 .Z
L5.9 BW
L5.10 FW
L5.10 CE
L5.10 .Z
L5.10 BW
L5.11 FW
L5.11 CE
L5.11 .Z
L5.11 BW
L5.12 FW
L5.12 CE
L5.12 .Z
L5.12 BW

Radiation dos [krad/sm−]
0

L4.1 FW
L4.1 CE
L4.1 BW
L4.2 FW
L4.2 CE
L4.2 BW
L4.3 FW
L4.3 CE
L4.3 BW
L4.4 FW
L4.4 CE
L4.4 BW
L4.5 FW
L4.5 CE
L4.5 BW
L4.6 FW
L4.6 CE
L4.6 BW
L4.7 FW
L4.7 CE
L4.7 BW
L4.8 FW
L4.8 CE
L4.8 BW
L4.9 FW
L4.9 CE
L4.9 BW
L4.10 FW
L4.10 CE
L4.10 BW

Radiation dose [krad/smy]

Phase 3 L4 Radiation dose

1000

800

twoPhoton
RBB
BHWideBHWide_LA

1000

800

twoPhoton
RBB
BHWid
BHWid _LA

149

Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

600

400

200

Figure C.7: The Phase 3 radiation dose in the L4 sensors. The Phase 3 simulation is correctedby the Phase 2 observation.

Phas 3 L5 Radiation dos
Coulomb_HER
Coulomb_LER
Tousch k_HER
Tousch k_LER

600

400

200

0

Figure C.8: The Phase 3 radiation dose in the L5 sensors. The Phase 3 simulation is correctedby the Phase 2 observation.

150

Phase 3 L6 Radiation dose
twoPhoton
RBB
BHWideBHWide_LA
Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

Figure C.9: The Phase 3 radiation dose in the L6 sensors. The Phase 3 simulation is corrected by the Phase 2 observation.

0

200

400

600

800

1000

Ra ia+ion ose [kra /smy]
L6.1 FW
L6.1 +Z
L6.1 CE
L6.1 −Z
L6.1 BW
L6.2 FW
L6.2 +Z
L6.2 CE
L6.2 −Z
L6.2 BW
L6.3 FW
L6.3 +Z
L6.3 CE
L6.3 −Z
L6.3 BW
L6.4 FW
L6.4 +Z
L6.4 CE
L6.4 −Z
L6.4 BW
L6.5 FW
L6.5 +Z
L6.5 CE
L6.5 −Z
L6.5 BW
L6.6 FW
L6.6 +Z
L6.6 CE
L6.6 −Z
L6.6 BW
L6.7 FW
L6.7 +Z
L6.7 CE
L6.7 −Z
L6.7 BW
L6.8 FW
L6.8 +Z
L6.8 CE
L6.8 −Z
L6.8 BW
L6.9 FW
L6.9 +Z
L6.9 CE
L6.9 −Z
L6.9 BW
L6.10 FW
L6.10 +Z
L6.10 CE
L6.10 −Z
L6.10 BW
L6.11 FW
L6.11 +Z
L6.11 CE
L6.11 −Z
L6.11 BW
L6.12 FW
L6.12 +Z
L6.12 CE
L6.12 −Z
L6.12 BW
L6.13 FW
L6.13 +Z
L6.13 CE
L6.13 −Z
L6.13 BW
L6.14 FW
L6.14 +Z
L6.14 CE
L6.14 −Z
L6.14 BW
L6.15 FW
L6.15 +Z
L6.15 CE
L6.15 −Z
L6.15 BW
L6.16 FW
L6.16 +Z
L6.16 CE
L6.16 −Z
L6.16 BW

L5.1 FW
L5.1 CE
L5.1 1Z
L5.1 BW
L5.2 FW
L5.2 CE
L5.2 1Z
L5.2 BW
L5.3 FW
L5.3 CE
L5.3 1Z
L5.3 BW
L5.4 FW
L5.4 CE
L5.4 1Z
L5.4 BW
L5.5 FW
L5.5 CE
L5.5 1Z
L5.5 BW
L5.6 FW
L5.6 CE
L5.6 1Z
L5.6 BW
L5.7 FW
L5.7 CE
L5.7 1Z
L5.7 BW
L5.8 FW
L5.8 CE
L5.8 1Z
L5.8 BW
L5.9 FW
L5.9 CE
L5.9 1Z
L5.9 BW
L5.10 FW
L5.10 CE
L5.10 1Z
L5.10 BW
L5.11 FW
L5.11 CE
L5.11 1Z
L5.11 BW
L5.12 FW
L5.12 CE
L5.12 1Z
L5.12 BW

NIEL damage [1010 neq/ m2sm0]0

L4.1 FW
L4.1 CE
L4.1 BW
L4.2 FW
L4.2 CE
L4.2 BW
L4.3 FW
L4.3 CE
L4.3 BW
L4.4 FW
L4.4 CE
L4.4 BW
L4.5 FW
L4.5 CE
L4.5 BW
L4.6 FW
L4.6 CE
L4.6 BW
L4.7 FW
L4.7 CE
L4.7 BW
L4.8 FW
L4.8 CE
L4.8 BW
L4.9 FW
L4.9 CE
L4.9 BW
L4.10 FW
L4.10 CE
L4.10 BW

NIEL damage [1010 neq/cm2smy]

Phase 3 L4 NIEL damage

175

150

twoPhoton
RBB
BHWideBHWide_LA

175

150

−/oPho−on
RBB
BHWideBHWide_LA

151

Coulomb_HER
Coulomb_LER
Touschek_HER
Touschek_LER

125

100

75

50

25

Figure C.10: The Phase 3 NIEL damage in the L4 sensors. The Phase 3 simulation is correctedby the Phase 2 observation.

Phase 3 L5 NIEL damage
Co.lomb_HER
Co.lomb_LER
To.s hek_HER
To.s hek_LER

125

100

75

50

25

0

Figure C.11: The Phase 3 NIEL damage in the L5 sensors. The Phase 3 simulation is correctedby the Phase 2 observation.

152

NIEL damage [1010 neq/cm2−m1].0+Ph+.+n
RBB
BHWideBHWide_LA
C+/l+m _HER
C+/l+m _LER
T+/−chek_HER
T+/−chek_LER

Figure C.12: The Phase 3 NIEL damage in the L6 sensors. The Phase 3 simulation is corrected by the Phase 2 observation.

0

25

50

75

100

125

150

175

Pha−e 3 L6 NIEL damage

L6.1 FW
L6.1 +Z
L6.1 CE
L6.1 −Z
L6.1 BW
L6.2 FW
L6.2 +Z
L6.2 CE
L6.2 2Z
L6.2 BW
L6.3 FW
L6.3 +Z
L6.3 CE
L6.3 2Z
L6.3 BW
L6.4 FW
L6.4 +Z
L6.4 CE
L6.4 2Z
L6.4 BW
L6.5 FW
L6.5 +Z
L6.5 CE
L6.5 2Z
L6.5 BW
L6.6 FW
L6.6 +Z
L6.6 CE
L6.6 2Z
L6.6 BW
L6.7 FW
L6.7 +Z
L6.7 CE
L6.7 2Z
L6.7 BW
L6.8 FW
L6.8 +Z
L6.8 CE
L6.8 2Z
L6.8 BW
L6.9 FW
L6.9 +Z
L6.9 CE
L6.9 2ZL6.9 BW
L6.10 FW
L6.10 +Z
L6.10 CE
L6.10 2Z
L6.10 BW
L6.11 FW
L6.11 +Z
L6.11 CE
L6.11 2Z
L6.11 BW
L6.12 FW
L6.12 +Z
L6.12 CE
L6.12 2Z
L6.12 BW
L6.13 FW
L6.13 +Z
L6.13 CE
L6.13 2Z
L6.13 BW
L6.14 FW
L6.14 +Z
L6.14 CE
L6.14 2Z
L6.14 BW
L6.15 FW
L6.15 +Z
L6.15 CE
L6.15 2Z
L6.15 BW
L6.16 FW
L6.16 +Z
L6.16 CE
L6.16 2Z
L6.16 BWAcknowledgment
I would first like to thank my supervisor, Prof. Yutaka Ushiroda, for oﬀering me the opportunity
to participate in the Belle II experiment and encouragement for my work.
I would also like to thank Dr. Katsuro Nakamura, Dr. Toru Tsuboyama, Dr. Koji Hara,
Dr. Takeo Higuchi, Dr. Yoshiyuki Onuki and all the collegues in the SVD group, for spending
their precious time to help me with their knowledge and experience.
I am deeply grateful to Dr. Hiroyuki Nakayama and the BEAST group for fruitful discussions
about the beam background studies. I am also grateful to Prof. Mikihiko Nakao and the DAQ
group for their cooperation which was essential for the development of the trigger veto module.
I would like to acknowledge Dr. Taku Gunji and Dr. Yasuyuki Okumura as the vicecommittees of this thesis and I am gratefully indebted to them for their valuable comments on
the thesis. Also I would like to thank Dr. Zachary Liptak for kindly proofreading my poor
English.
I would like to thank K. Nakamura, T. Tsuboyama, K. Hara, Yuma Uematsu, Ryohei
Sugiura, and Nobuhiko Sato, who all have made my life in Tsukuba comfortable.
Finally, I would like to thank my family for their endless support.

153

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155