Evaluation ofDetector Background2009/2/10
M. Iwasaki (Univ. of Tokyo)
for the s-Belle MDI group(KEK / Tohoku Univ. / Univ. of Tokyo)

Introduction
Super-KEKB  High luminosity experiment
Remarkable features of Super-KEKB- High beam current- Strong dynamic-beam effect… squeezes the beam at IP and increases the emittance( To take care of the dynamic-beam effect, IR design has been changed )- Large beam size at final Q  High power SR emission- Place final Q-magnets closer to IP
 These features directly related to the detector beam BGTo assure the stable detector operation,
IR design based on the beam BG study is importantKEKB

HER e-Current status of the MDI group- SR BG simulation studies (Tokyo / KEK)
With the Super-KEKB design, much higher SR BG is expected
Critical energy is 14keV
SR size at IP is 3-7mm for 5σ size beam
(KEKB : 2keV and <5mm for 10σ size beam) Then we estimate the SR BG first- Other BG sources
Beam-gas, radiative BhaBha, Touschek, … Not yet- HOM / mirror current heating studies (Tohoku / KEK)
Just started!

Based on these studies, we’ll design the IP region

SR BG studies- In this talk, we show
1.Upstream SR
1-1. Design of IP beam-pipe to avoid SR hits from HER
1-2. Study of the energy deposit to the IP beam-pipe
2. Backscattered SR
Estimate # of SR hit in the IR region- For the SR BG study,
we construct the beam line simulation based on GEANT4.
Upstream SR
Simple beam pipe + 1st layer SVD + B-field of Q-magnets
Backscattered SR
Realistic beam pipe + SR data1. Upstream SR BG study
1-1. Design of the IP beam-pipe
to avoid SR direct hit

Beam pipe designSR Mask
Au
Base length 4mm
Height 4mm
Inner diameter 22mm

S.Uno

We put the beam pipe in our simulation
Be partAu 10µmt
Be 2mmt
Inner diameter 30mm

HERLER

302230mrad

IP402080

2055
Au Taper partAu 5mmt
30mrad taper
Length 500mm

Au straight partAu 5mmt
Inner diameter 30mm
Length 20mm

Relationship between s-Belle andSuper-KEKBIn Super-KEKB, crossing angle will be increased : 22mrad  30mrad
e- KEKB / Super-KEKB
HER(e- ) axis will not change

8mrad

22mradHER

e+ KEKB, Belle solenoid
Belle solenoid will not change

LERe+ Super KEKBLER(e+) axis will rotate by 8mrad(QCS magnets will be set parallel to Belle solenoid)

Belle beam pipe (and SVD??) axis at Super-KEKB- Belle solenoid- Center of the LER and HER (7mrad from Belle solenoid)- HER axis (22mrad from Belle solenoid)IR magnet layout

HER beam line simulation
HER simulation with LCBDS
5σ beam / physics process on
QC2R

QC1R

QC1L

Beam pipe

QC2L

QCSR QCSL

e+eγHERbeam

Beam pipe  parallel to HERHER simulation
QCSR

Tapere+eγ

QCSL

Beam pipe
SR mask
QC1L

SVD

HER
beam

LER beam-line simulation
LER beam simulation with LCBDS 5σ beam
Physics process on

QC2L
QC2R
LER
beam

QCSR QCSL

Beam pipe

Beam pipe  parallel to HER (30 mrad from LER)e+eγ

LER simulation
QCSR

Taper

QCSL

SR mask

LER
beam

SVD

e+eγ

Upstream SR energy
SR energy (at IP)
5σ beam
HER

LER

100 keV

100 keV
104

105

Energy(GeV)

Energy (GeV)(Vertical scale: Scaled for 1-bunch beam)

The SR energy from HER is very high ( < ~100keV)
 We don’t want the direct hits from HER SR at first

HER beam line simulation
2ndary particle production position @ IP

5σ beam

Total energy(GeV)
22mrad+ maskmask 

22mradNo mask
No beam pipe hits

 beam pipe

Taper R (cm)
7mrad+ mask0mrad+ maskmask  beam pipe

mask 

 beam pipe

HER beam line simulation
R (cm)SR hit position @ beam pipe

Taper SR mask 

HER Beam direction

IPZ(cm)If we locate the beam pipe parallel to HER (22 mrad from solenoid)
and put a 4mm SR mask, we can avoid direct SR hit from HER
We cannot avoid the SR direct hit if:- Without HER side SR mask,- Put the beampipe parallel to Belle solenoid (0mrad) , nor- Put the beampipe center of the LER and HER (7mrad)1. Upstream SR BG study
1-2. Study of the energy deposit
to the IP beam pipeE (GeV)

Energy deposit from upstream SRHER

SR mask

HERtaperE (GeV)2σ beamLER

HER beam

SR mask
LERtaperLER beamz (cm)

Total E deposit to the IP beam pipe
HER ~18000GeV/bunch  1.4kW
LER ~1400GeV/bunch  110W

Energy deposit from SR
2σ beamHERSR Mask 0.73kW

HER taper 0.69kW

LER
SR Mask 20W

LER taper 75W

IP beam-pipe 15W

We have ~1kW Energy deposit at 4mm height SR mask...
(Max. limit to cool : 10~100(?)W / mm2)
 SR mask may melt??

Heat at the synchrotron light mask
T.Tsuboyama (KEK)

SRBeam Pipe

Mask
Material : copper is assumed (because of its good thermal conductivity)

Heat at the synchrotron light mask
T.Tsuboyama (KEK)•The temperature distribution Δt for the center slice after
equilibration (in one second) is shown below.
•The temperature goes up to Δt = ~450 degree.
•The heat dissipation to the mask should be of order 100W.
•Next step: reliable calculation by ANSYS or a similar tool.

SR (1kW)

Mask

Energy deposit from HER SR
Why do we have so high energy deposit?
1. Increase the beam current

effect : x3

2. Change beam optics (QC2L)- x3 Beam size at the Q-magnet ↑- x7 B-field of the Q-magnet ↑- Same magnet length- No-bending component ↓Critical Energy @ QC2L : 2keV for 10σ beam (KEKB)
56keV for 10σ beam (super-KEKB)

effect : x28

 We have 3x28 ~ 100 times higher E deposit at super-KEKB
Current super-KEKB beam optics produces huge power SR

Total SR power produced at Q-magnet- To check our simulation results,
we compare the total SR power at the QC2 magnet
1. GEANT4 simulation(For 2σ beam :corresponds to nominal Gaussian beam core)
Total power = 3.3kW2. Hand calculation (by Y.Funakoshi-san)Total power = 2.9kW- We also check that SR power produced at QC2 in our current
KEKB is about 1/100 of super-KEKB, in GEANT4 simulation

2. Backscattered SR study- SR hit to the beam pipe

Back scattered SR simulation
Clement Ng (U. Tokyo)
By constructing the realistic beam pipe in our simulation,
we have studied the back scattered SR BG effect.

- Beam Pipe material
6mm Cu + 10um Au- Construct ±10m from IP- Input SR data generated
in the upstream SR studies

C.Ng (Tokyo)

HER/LER SR simulation
HER
Hit position z vs x

HER
E deposit

QC1R
QCSR
HER taper200keVIP
HER beamz (mm)
600

10500
400109SR mask

300
200

LER

10Ev
entsx
[mm]

LER

E (keV)

QCSL
108

LER taper
1000- 100

40keV

IP
0LER beam

107
2000

4000

6000

8000

10000
z [mm]z (mm)0510152025303540

E [keV]E (keV)Back scattered photons at IP
HER IP region (ESR>20keV)

C.Ng (Tokyo)

Vertical scale is scaled for 1-bunch beam, Scale factor = 100
Hit position z(mm)Energy (keV)

QC2L
QC1L
QCSR

There are 4 entries which may enter to the detector region (energy ~50keV)
These are caused by SR photons produced at QC1/2L
We cannot evaluate the SVD occupancy because MC statistics is too small.
After increasing the statistics, we’ll study the SVD occupancy

Conclusion
Based on the GEANT4 simulation, SR BG has been studied
1. Upstream SR- Design of the IP beam-pipe to avoid SR from HER
To avoid the SR direct hit, we should
Locate the beam pipe parallel to HER (22mrad from Belle solenoid), andPut a 4mm height SR mask

- Study of the energy deposit to the IP beam-pipe
The energy deposit from HER SR will be ~1kW (SR mask) ~1kW (taper)
1kW deposit to the 4mm mask makes ~500 degree temperature rise It is very hard to cool the beam pipe…

2. Backscattered SR
We need more MC statistics to study in detail.

We try to minimize the BG effect in our beam-pipe design,
but SR power is so high that we cannot cool the beam-pipe

New super-KEKB machine parameters with lower SR power
are highly appreciated See the next slide..

New super-KEKB optics
New super-KEKB optics has just been delivered- Beam size at the Q-magnet
QC1L / QC2L : ½ of the current one- B-field of the Q-magnet
QC1L : x1.6 of the current one
QC2L : same
- Same magnet length

In total, SR power is reduced to80% (QC1L) or 25% (QC2L) of the current one
We’ll re-estimate the SR BG based on the new optics

Back upBeam line simulation
Based on the following programs, we construct
the Super-KEKB beam-line simulation- SAD
To get the geometry / element definition / Twiss parameters.
SAD file with dynamic beam-beam effect from Funakoshi-san(Dynamic effect  5 times higher ε, 10 times smaller β in x)- LCBDS
Beam line simulation based on GEANT4
developed by K.Tanabe and T.Abe of U.Tokyo (for ILC/T2K)
At first, we just align the beam line components, beam pipe,and 1st layer SVD in the simulation

Beam line simulation setup- Aperture of the Q-magnets ~ 5σ (= 5√εβ)- Beam size 5σ (max = 5σ) or 2σ (max = 2σ)- Beam shape : sqrt(x) shapex (y)5√εβ- The number of particles in a bunch
HER : 4.1A / (1.6*10^-19)/(100kHz)/5000 = 0.5 *1011
LER : 9.4A / (1.6*10^-19)/(100kHz)/5000 = 1.2 *1011

Beam size @ IR Q-magnets
IP

HER Beam

HER

QC2L

QC1L

QCSL

QCSR

QC1R

QC2R

OLD

75.2mm
(5σx)

31.1

11.0

4.4

30.3

74.5

35.4

16.5

14.4

6.3

30.1

69.0

New

LER Beam

LER

QC2L

QC1L

QCSL

QCSR

QC1R

QC2R

OLD

52.1mm
(5σx)

29.0

2.9

15.1

52.2

63.9

34.4

---2.910.7---66.3

NewEnergy deposit from SR- 2σ sqrt-shape beam
HER: SR Mask 0.73kW
QC1 0.30kW
QC2 0.44kW

LER: SR Mask 20W

HER taper 0.69kW
QC1 0.02kW
QC2 0.67kW

LER taper 75W- Gaussian beam (2σ tail cut)
HER: SR Mask 0.52kW HER taper 0.43kW
QC1 0.15kW
QC2 0.37kW

QC1 0.01kW
QC2 0.42kW- Gaussian beam (5σ tail cut)
HER: SR Mask 0.68kW HER taper 1.18kW
QC1 0.32kW
QC2 0.36kW

QC1 0.17kWQC2 1.01kW

x (y)
2√εβ

IP beam-pipe 15W

Heat at the synchrotron light mask
T.Tsuboyama (KEK)HER simulation
QCSR

Taper

QCSL

HER side mask

SVDe+eγ

HERbeamLER beamline simulation
2.5σ beam

SR energy (at IP)
LER

HER

100 keV
100 keV

Energy (GeV)

Energy(GeV)

SR produced position
QCSR
QC2R

(Vertical scale:Scaled for 1-bunch beam)

C.Ng (Tokyo)

HER SR simulation

QCSR
HER taper# event for the simulation ~108 event  We need to scale 2*102 for a bunch

HER SR simulation (IP region)
LER taper

HER taper

C.Ng (Tokyo)

HER SR simulation (IP region:Back-scattered only) C.Ng (Tokyo)

LER taper

HER taper

LER SR simulation

C.Ng (Tokyo)

SR mask
QCSL
LER taper# event for the simulation ~108 event  We need to scale 103 for a bunchBack scattered particlesC.Ng (Tokyo)

HER IP+Taper (ESR>20keV)

Back scattered particles in IR are caused by SR produced at QC1L & QCSR
~2000 particles in IP region Mainly (97%) charged particle  can ignore them?!

Back scattered particlesC.Ng (Tokyo)LER IP+Taper (ESR>1keV)

Back scattered particles in IR are caused by SR produced at QCSL
Energy of back scattered particles is low

Dynamic beam-beam effectY.Funakoshi
at Super-KEKB

Emittance ε (wo dynamic effect)
β (wo dynamic effect)

ε (with dynamic effect)
β (with dynamic effect)

5 times higher ε, 10 times smaller β in x

Dynamic effect at Super-KEKB is very strong

Beam size @ IR Q-magnets ():ν =.505
5σxx

QC1LE

QC2LE

QC1RE

QC2RE

QC2LP

QC2RP

βx*=20cm
QC2RE:元8.2(41)26.9(134.5)

11.6(58)28.8(144)

14.7(73.5)

18.6(93)

βx*=20cm
QC2RE>IP8.4(42)19.0(95)

12.0(60)

20.7(103.5)

5.9(29.5)

13.4(67)

8.5(42.5)

14.6(73)

9.8(49)12.3(61.5)

βx*=40cm
QC2RE>IP{8.1935,26.8558,3.8466,3.7051,.9061,1.3841,1.9202,7.0217,28.8117,11.568
b8}{8.3769,18.9777,3.8942,3.822,.6862,1.0242,1.9233,7.7565,20.6713,12.029}{5.9335,13.4436,3.8125,3.9122,1.1345,.7348,1.8316,5.9383,14.6468,8.5229}{14.7486,.7803,.4297,4.1507,4.1178,18.5996}{9.7761,.9536,.3712,4.2204,3.4765,12.3323}

SR BG studies- SR BG may affect toIncrease the vertex detector occupancy
To keep ~1% occupancy for pixel (readout 10µsec) or~10% occupancy for strip (readout 150nsec)# of SR hits (E>50keV) < ~100hits/bunch

Heat the IP beam pipe
- In this talk, we show
1.Upstream SR
1-1. Design of IP beam-pipe to avoid SR hits from HER
1-2. Study of the energy deposit to the IP beam-pipe

2. Backscattered SR
Estimate # of SR hit in the IR region- For SR BG study,
beam line simulation based on GEANT4 is constructed
Upstream SR
Simple beam pipe + 1st layer SVD + B-field of Q-magnets
Backscattered SR Realistic beam pipe + SR data