Background es.ma.on• Touschek BG, beam‐gas BG‐ Ver.cal collimators and beam instability• Radia.ve Bhabha BG• Synchrotron radia.on BG• 2‐photon BG• Full‐detector GEANT4 simula.on

Hiroyuki NAKAYAMA (KEK)
KEKB ARC(Feb. 20, 2012)

Belle‐II beam background
BG sources at Belle‐II/SuperKEKB‐ Touschek, beam‐gas‐ Radia.ve Bhabha, 2‐photon‐ Synchrotron radia.on‐ beam‐beam, etc…

Ta
CryostatTi or SUS
Be pipeOur objec.ves are to es.mate eachbackground level and to develop
countermeasures which reduce backgroundto be tolerable for each sub‐detectors.

Heavy metal shield
to stop BG showers

Upstream movable collimators

Collima.on (20mm‐>9mm) to stop SR

Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)22

Expected change on BG
from KEKB to SuperKEKB• x20 smaller beam size
 Touschek sca\ering rate increases dras.cally. Need special care.

• x2 more beam current
 Touschek/Beam‐gas sca\ering rate increases.

• x40 higher luminosity
 Radia.ve Bhabha/2‐photon sca\ering rate increases dras.cally.

• Smaller IR beam pipe aperture sca\ered par.cles are more likely to be lost in IR, not in the tunnel.

• Final focusing scheme Back‐sca\ering SR and over‐bent radia.ve Bhabha can beneﬁt from it
Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)3

Final focusing scheme
θ =22mradIPθ =83mrad

IP
In Belle‐II, thanks to the independent ﬁnal Q magnets for each ring,
downstream orbits pass through the center of Q magnets, which
results in less dispersion and therefore less back‐sca\ering SR BG
and less over‐bent radia.ve Bhabha background.
Hiroyuki Nakayama (KEK)

TIPP2011 (June. 11th, 2011)4

Es.ma.on status of each BG• Touschek BG–

Reduced down to ~0.2GHz(LER/HER) thanks to horizontal/ver.cal collimators (Apr. 2011)• Beam‐gas BG–

Reduced down to ~0.1GHz(LER/HER) thanks to ver.cal collimators. (Nov. 2011)• Synchrotron BG–

Reduced down to few order smaller than PXD requirement thanks to collima.on on incoming beam
pipe (Jul. 2010, toy study) Full detector simula.on has just started. . (Jan. 2012)• Radia8ve Bhabha–

Most of spent electrons/positrons are lost outside detector thanks to independent ﬁnal Q magnet(Aug. 2010). But few GHz are s.ll lost in |s|<4m (Nov. 2011).

• 2‐photon process– Small enough according to KoralW simula.on, which is conﬁrmed with BELLE‐I machine
study (Nov. 2010).

• (Beam‐beam)– Computa.onal study ongoing by accelerator group
Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)

5

History
Coulomb LER
110GHzLoss
rate

Coulomb HER
40GHz
More horizontal
collimators near IP
Coulomb BG foundto be dangerous

Hiroyuki Nakayama (KEK)

0.2 GHzKEKB ARC (Feb. 20, 2012)

0.1 GHz
0.1 GHzNow

IPAC’11

0.2 GHz

Sep. ‘11

1 GHz

RBB LER 0.9GHz eﬀ
RBB HER 0.7GHz eﬀ

Jun. ‘11

Dec. ‘10

Sep. ‘10

Touschek HER

Ver.cal collimators
at small beta_y

Dec. ‘11

15 GHzMar ‘11Extrapola.on frommachine study

Touschek LER

6

Ver. 2012.2.20

Total BG

w/o SR, 2‐photon

HER RBB 1‐turn

R‐
side

L‐
side

LER (4GeV e+)HER (7GeV e‐)Rad. Bhabha

0.55 W (eﬀ. 0.9GHz)

0.76W (eﬀ. 0.68GHz)

Touschek

0.14 W (0.22GHz)

0.10 W (0.09GHz)

Coulomb

0.06 W (0.09GHz)

0.001W (0.001GHz)

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)

1GeV ,1GHz= 0.16W
7

Background picture at Belle‐
II
BKLM

EKLM

RBB HER

ECL
CDC

ARICH

TOP

Touschek HERSR

HER e‐LER e+
Coulomb HER

Coulomb LER

Neutrons (rad. Bhabha)

RBB LER

Touschek LER

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)88

Y. Ohnishi
H. Nakayama

Touschek background
Intra‐bunch sca\ering, Rate∝(beam size)‐1,(Ebeam)‐3More dangerous in LERLER horizontal collimators
e+

H4

H1

H2

H3
IP

βx or ηxconverted tocollimatorwidth (mm)Collimator width:10~15mm

e+
H6

H7

H8

d x = Max[d xβ , d xη , d ' xβ ]H5d xβ = nx ε x β xd xη = η x (nzσ δ )IPd ' xβ =β x,mask
rQC2
β x,QC2

Compared to KEKB, we add more collimators (H5‐H8) just before IP (‐200m~‐18m).
Collimators are located where beta func.on or dispersion is large.
Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)10

Ver.cally oscilla.ng Touschek BG
Belle detector
Touschek sca\ered par.cles sca\ered at
Fuji‐area (where ver.cal dispersion exists)
start ver.cal oscilla.on and are eventually
lost in IR QC1 where βy is large.

HER

LER

Ver.cal collimator narrower than QC1 canreduce such Touschek loss. Beam
instability caused by such collimator is an
issue.

In Fuji area, LER ringbends ver8cally , topass under HER ringVer.cal collimatorwidth: few mm
LER

Hiroyuki Nakayama (KEK)

Few GHz e+ loss w/o
ver8cal collimator

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)11

Final Touschek loss in IR
HER

LER

e‐

e+

IP

IP

Within |z|<4m,

Within |z|<4m,‐ loss rate: 0.10 GHz‐ loss wa\age: 0.10 W‐ loss rate: 0.22 GHz‐ loss wa\age: 0.14 W
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)12

H. Nakayama
K. Kanazawa
Y. Funakoshi

Beam‐gas background
Coulomb>> bremsstrahlung
Coulomb BG is naively propor.onal to P x I.
Also depends on beta func.on over the ringand IR physical aperture.
P = 10‐7Pa is assumed

Beam‐gas Coulomb life.me(​𝛽↓𝑦,2 , ​𝜙↓𝑦,2 )(​𝛽↓𝑦,1 , ​𝜙↓𝑦,1 )
s=s1

y2
s=s2

𝜃: Sca\ering angle​𝑦↓2 = 𝜃√⁠​𝛽↓𝑦,1 ⋅​𝛽↓𝑦,2 ​sin⁠(​𝜙↓𝑦,2 −​𝜙↓𝑦,1 )

​𝜃↓𝑐 =​𝑟↓𝑄𝐶1 ∕√⁠​⟨​𝛽↓𝑦 ⟩∙𝛽↓𝑦,𝑄𝐶1

The minimum sca\ering angle ​𝜃↓𝑐to hit QC1 beam pipe
Beam life.me ​𝜏↓𝑅 is
propor.onal to ​𝜃↓𝑐↑ ↑2

s

1

τR

= cnG σ R = cnG

KEKB LER

SuperKEKB LER

QC1 beam pipe radius: rQC1

35mm

13.5mmMax. ver.cal beta (in QC1): βy,QC1

600m

2900m

Averaged ver.cal beta: <βy>

23m

48m

Min. sca\ering angle: θc

0.3mrad0.036mrad

Beam‐gas Coulomb life.me>10 hours 2200sec

Hiroyuki Nakayama (KEK)

H. Nakano
K. Kanazawa

KEKB ARC (Feb. 20, 2012)

4π ∑ Z 2 re

γ2

2

1

θc 2

Rate ∝P x I x <β>
x βQC1 / rQC12
Beam‐gas life.me is only
x1/100 of KEKB, due tolarger ver.cal beta in QC1
and narrower QC1 physicalaperture14
14

Strategy to reduce Coulomb BG
LER

mm

mm

• Larger QC1 physical aperture (r=10.5mm13.5mm)
z‐axisHER

Physical aperturez‐axisPhysical aperturee+beta(85σ)e‐beta(55.5σ)
beta(43.5σ)

beta(66σ)
[m]

[m]

[m]

We widened QC1 aperture without major change in QCS design.
Coulomb life.me improved (LER: 13602240sec, HER: 21003260sec)• Ver.cal collimators!

• QC1 aperture should not be narrowest over the ring

– Collimator aperture should be narrower than QC1 aperture– Beam instability? (collimators should be very close(few mm) to the beam )Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)15

Where we should put ver.cal collimator?
Collimator aperture should be narrower than QC1 aperture.

d max ∝ β 1/ 2

Collimator posi.on
d[mm]
TMC:

d min ∝ β 2 / 3

Aperture
TMC instability should be avoided.

d max ∝ β 1/ 2

Assuming following two formulae:

beta[m]I thresh =C1 f s E / e> 1.44 mA/bunch (LER)∑ βi k⊥i (σ z ) taken from “Handbook of acceleratoriKick factor

physics and engineering, p.121”k⊥ = 0.215 AZ 0c(in case of rectangular collimator window)θd min ∝ β

2/3

σ zd 3We should put collimator where beta_y is SMALL!
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)16

Collimator width d[mm]Candidate collimator loca.ons
TMC condi.on
r=13.5mm

TMC condi.on(r=10.5mm)(r=10.5mm)

LER

HER

beta_y [m]lerfqlc_1604

V1 collimator @ LLB3R (downstream)(s=‐90‐82m, βy=30146m)
βy=125m, 2.23mm<d<2.81mm

beta_y [m]herfqlc5605

V1 collimator @ LTLB2 (downstream)(s=‐63‐61m, βy=81187m)
βy=123m, 1.74mm<d<2.26mm

Collimator posi.on should sa.sfy beta_y condi.on above,
need space(at least 1.5m), and the phase should be close to IP

Hiroyuki Nakayama (KEK)

r=13.5mm

KEKB ARC (Feb. 20, 2012)17

Ver.cal collimator width
vs. Coulomb loss rate, Coulomb life .me
ler1604, V1=LLB3R downstream
V1 width[mm] IR loss [GHz]Total loss[GHz] Coulomb life[sec]
2.40
0.04
149.5
1513.3
2.50
0.05
137.8
1642.0
2.60
0.09
127.4
1776.0
2.70
0.24
118.1
1915.2
2.80
0.81
110.0
2057.2
2.90
8.48
109.3
2069.6
3.00
18.98
109.3
2069.6

Based on element‐by‐element simula.on
considering causality
the phase diﬀerence(by Nakayama)

her5365,V1=LTLB2 downstream
V1 width[mm] IR loss [GHz] Total loss[GHz] Coulomb life[sec]
2.10
0.001
48.4
3379.4
2.20
0.001
44.1
3709.0
2.30
0.357
40.0
4053.8
2.40
6.862
33.0
4099.1
2.50
12.00427.9
4099.1

IR loss rate is VERY sensi.ve to the ver.cal collimator width.
(Once V1 aperture>QC1 aperture, all beam loss goes from V1 to IR
Typical orbit devia.on at V1 : +‐0.12mm (by iBump V‐angle: +‐0.5mrad@IP )Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)18

Y. Funakoshi

Radia.ve Bhabha background‐ Spent e+/e‐ loss in downstream
Dominant loss posi.on is very far (~10m) from IP, but li\le frac.on
with large ΔE (s.ll dangerous with Lx40) can be lost inside detector.
‐ Gamma emi\ed from IP
They hit downstream (~10m) beam pipe/magnet and generate neutrons
by giant dipole resonance. Neutron shielding inside tunnel will be increased

Radia.ve Bhabha BG
HER

LER

e+

e‐

IP
IP

Within |z|<4m,

loss rate: 6.8 GHz(0~1.4GeV)
loss wa\age: 0.55 W

Within |z|<4m,

loss rate: 5.8 GHz(0~2GeV)
loss wa\age: 0.75 W(Equivalent to 0.86GHz of 4GeV e‐)

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)(Equivalent to 0.68GHz of 7GeV e‐)

20

Radia.ve Bhabha HER (contd.)x‐z planeWy‐z plane

e‐

W

e‐

Horizontally lost at z=1.5m

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)21

Radia.ve Bhabha LER (contd.)x‐z planeWy‐z plane

W

e+
e+

Horizontally lost at z=‐1m

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)22

Addi.onal shields in tunnel(BL0RE)
d
n
e
b
t
s
r
ﬁ
HER
IP+7~11m

n

e‐

e‐ e‐

n

Polyethylene shield(10cm) at KEKB
Hiroyuki Nakayama (KEK)

Photon dump
IP ~14m
n
γ
e‐ e‐

n

n

Addi.onal concrete
shield at tunnel exit
KEKB ARC (Feb. 20, 2012)

Addi.onal neutron shieldaround gamma dump232‐photon BG

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)24

2‐photon BG
KoralW
BDK

C. Kiesling, S. Koblitz
E. Nedelkovska
Belle‐II Note #12

Consistency among thevarious generator s

Discrepancy between SuperB
numbers and ours disappeared now.
Documenta.on now
available
KEKB machine study in 2010 is consistent with ourgenerator, and inconsistent with SuperB numbers
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)25

Synchrotron BG
mainly from HER

M.Iwasaki

SR simula.on results in 2010
Y(cm)
1
s

Bend

QC1

0
‐1

HER
QC2

‐2

• Simpliﬁed geometry, no SR sca\ering/reﬂec.on considered• Bending magnets, solenoids, Q magnets, Q leak ﬁeld implemented• Gaussian beam with tail cutoﬀ of 20σ~200/bunch (>5keV) photons hit straight part of beampipe, which is 3‐4 order below PXD requirements.
Stopping power:
O(~10‐6) for <20KeV
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)27

Detailed SR simula.on

Detailed beam pipe geometry implemented.
Only QC1/2 included so far, missing bending magnets upstream
Currently using 2D “cylindrical” solenoid ﬁeld, need to be updated with 3D
Reﬂec.on/sca\ering on Au coa.ng of beam pipe will be considered
Test‐beam study to implement home‐made “.p‐sca\ering” model

x[cm]

•
•
•
•
•

H. Nakayama
K. Itagaki

IP
Be: ‐3.7<z<5.9cm

SR (>5keV)
SR (>0.1keV)z[cm]Hiroyuki Nakayama (KEK)

No direct hit on Be part even in the severest case

KEKB ARC (Feb. 20, 2012)28

J. Murakami
S. Tanaka

X‐ray beam test
Test target

Measuresca\ering angle
distribu.on

Irradiate X‐rays onto Ta .p plated with gold andmeasure angle distribu.on of sca\ered ﬂux.
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)

Analysis ongoing29

Whole geometry ready in GEANT4

PXD

Elements outside detector (|s|>4m) are not yet
implemented (bending magnets, concrete shield etc…)
Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)30

Event display
Sqrt(x*x+y*y)*sign(x)[cm]

Draw trajectories of par.cle with E>1MeV

Magenta: primary par.cle
Red: e+Blue: e‐Green: neutron

RBB+Touschek+Coulombz[cm]‐True event signals are not hidden by fake background hits?
in 100ns‐Our detectors are not severely damaged by radia.on?
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)31

Full simula.on campaign• 1st campaign in Dec. 2011
• 0.9GHz Touschek LER / 2photon• 2nd campaign in Feb. 2012 (for BPAC)• Latest Touschek/Beam‐gas/Rad. Bhabha/ 2photon• Results of 1st campaign– Neutron ﬂux, radia.on dose are OK for most of sub‐detectors• Preliminary results of 2nd campaign– PXD: OK (Touschek/2‐photon dominates)– TOP: photo‐cathode aging seems problema.c– ARICH: OK– ECL: OK– Results from other detector are coming soon

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)32

Summary• Touschek BG is eﬀec.vely reduced by horizontal and ver.cal
collimators• Beam‐gas Coulomb BG can be reduced by ver.cal collimators(but very sensi.ve to the collimator width)• Small βy collima.on is essen.al to avoid beam instability• Radia.ve Bhabha is dominant BG now• 2‐photon BG is conﬁrmed to be safe
• No direct SR hits on Be part of beam pipe found• Full‐detector simula.on is ongoing

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)33

To do•••••Simula.on on 3D solenoid magne.c ﬁeld
Secondary shower study from collimators
Collimator R&D which can survive ~100GHz par.cle hits
Background simula.on “at day 1” or “during injec.on”
Include beam‐beam eﬀect

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)34

backup

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)35

Y. Funakoshi

Radia.ve Bhabha background‐ Spent e+/e‐ loss in downstream
Dominant loss posi.on is very far (~10m) from IP, but li\le frac.on
with large ΔE (s.ll dangerous with Lx40) can be lost inside detector.
‐ Gamma emi\ed from IP
They hit downstream (~10m) beam pipe/magnet and generate neutrons
by giant dipole resonance. Neutron shielding inside tunnel will be increased

Radia.ve Bhabha HER
W

e‐

e‐

Within |z|<4m,

loss rate: 5.8 GHz(0~2GeV)
loss wa\age: 0.76 W(Equivalent to 0.68GHz of 7GeV e‐)e‐

Hiroyuki Nakayama (KEK)

Loss wa\age: we assume all energy of beam
par.cle is deposited at the loss posi.on.

KEKB ARC (Feb. 20, 2012)37

Radia.ve Bhabha LER
W

e+
e+

e+

Within |z|<4m,

loss rate: 6.0 GHz(0~1.4GeV)
loss wa\age: 0.55 W(Equivalent to 0.86GHz of 4GeV e‐)
Loss wa\age: we assume all energy of beam
par.cle is deposited at the loss posi.on.

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)38

x : posi.ve=ring outer, y: posi.ve=downward

inner
lower
upper
inner

lower

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)39

x : posi.ve=ring outer, y: posi.ve=downward
lower

upper

inner

upper
inner

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)40

How to reduce RBB background?
• Shield leak ﬁeld
– Leak ﬁeld (dipole component) from LER QC1 into HER
beam pipe is diﬃcult to shield. If we shield dipole
component, Filed inside LER is aﬀected and LER dynamic
aperture is degraded.

• Add Tungsten shield around QCS?
– Space btw QCS and CDC is very limited and many cables
and pipes should sit there. Need further inves.ga.on forthe space le€ for the shield (up to 2cm or less).

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)41

Nakayama

Element‐by‐element simula.on
Ver.calcollimator V1

θ

y2
s=s2

s=s1

QC1

θc: cri.cal angle

θc (s1 → QC1) = rQC1 / β y,s ⋅ β y,QC1 /sin(Δφs →QC1 )11θc (s1 → V1 ) = rV / β y,s ⋅ β y,V /sin(Δφs →V )
1

1

1

1

1

Taking into causality, hit rate on QC1 from element s1 can be calculatedbyI beam Ls1 nGe

σR2

I beam Ls1 nG 4π ∑ Z 2 re 2
2
=
⋅
Δ
1
/
θ
c
e
γ2

(

)

Δ(1 / θc ) = 1 / θc (s1 → QC1) 2 − 1 / θc (s1 → V1 ) 2
Sum up for all element s1 over the ring to obtain total hit rate on
QC1.
Mul.‐turnloss is also simulated in similar way (Δφ+= Nturn*Δφturn),also taking in account the causality

Beta_y and vacuum level

βy
2
τR ∝
⋅ β y ,QC1 / rQC1
P

Beta_y[m]• Vacuum level at large beta_y determines Coulomb life.me
LER

s

βy

νy

‐82m

‐

‐1.75

‐62m

1783m ‐1.25‐25m

1854m ‐0.75‐1m

2905m ‐0.25+1m

2902m 0.25+28m

1564m 0.75+67m

1513m 1.25

Very important to achieve good vacuum
level in these regions
Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)

V1

QC1

νy(1 turn)=44.57

43Turn‐by‐turn loss
ler1604, V1=LLB3R downstream, d_V1=2.6mm#turnLoss @ V1

Loss @ QC1#turn

Loss @ V1

Loss @ QC1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

32.76034.22036.10017.450
3.720
2.300
0.660
0.040
0.030
0.050
0.320
0.330
0.060
0.060
0.030
0.020
0.030
0.750
0.700
0.030

0.090
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000

21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

0.040
0.020
0.010
0.020
0.470
0.410
0.010
0.020
0.010
0.010
0.010
0.140
0.120
0.010
0.010
0.010
0.000
0.010
0.010
0.010

0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000

No loss at nturn>4044

βyav = 50.6m

Conﬁrma.on of TMC condi.ons
with realis.c model
K. Ohmi (KEKB)

Impedance of realis.c collimator

Dedicated collimator design forsmall impedance‐ Round‐shape of collimator head
‐ d=5mm(H), d=2mm(V)Y. Suetsugu(KEKB)

Ith calculated by tracking simula.on
LER σz = 6mm

HER σz = 5mm

TMC instability caused by the LER/HER ver.cal
collimators are tolerable.

TMC instability

stableIth[mA]*beta[m]Calculated by
impedanceσz = 5mmHER
56

σz = 6mm

I thresh =

LER
57d24

unstableσz = 6mm
Calculated by formulae

C1 f s E / e∑ β i k⊥i (σ z )
i

HER
57

Rect. headθk⊥ = 0.215 AZ 0c
σ zd 3d[mm]Belle‐II focused review (Nov. 11th, 2011)

H.Nakayama (KEK)50

Beam‐gas summary• Coulomb >> bremsstrahlung• Larger <βy> and narrower IR aperture make Coulomb BG muchseverer at SuperKEKB than at KEKB• Ver.cal collimators , placed at small beta_y, can reduce beam‐gas BG down to ~0.1GHz for LER/HER.
• Beam instability for such collimators is conﬁrmed to be
tolerable, performing tracking simula.on with realis.c
collimator shape• Vacuum level at large beta_y aﬀects beam‐gas life.me.
• Simula.on using “SAD” is in prepara.on• R&D ongoing for collimator which can resist ~100GHz loss
Hiroyuki Nakayama (KEK)

Belle‐II/SuperB Joint BG mee.ng (Feb. 9‐10, 2012)51

Rad. Bhabha LER
Sqrt(x*x+y*y)*sign(x)[cm]Show par.cles with E>1MeV

Magenta: primary par.cle
Red: e+Blue: e‐Yellow: gamma
Green: neutronz[cm]464 events in 100ns
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)52

Rad. Bhabha HER
Sqrt(x*x+y*y)*sign(x)[cm]Show par.cles with E>1MeV

Magenta: primary par.cle
Red: e+Blue: e‐Yellow: gamma
Green: neutronz[cm]284 events in 100ns
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)53

Rad. Bhabha HER
Sqrt(x*x+y*y)*sign(x)[cm]Show par.cles with E>1MeV

Magenta: primary par.cle
Red: e+Blue: e‐Yellow: gamma
Green: neutronz[cm]284 events in 100ns
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)54

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)55

Total (w/o SR, 2‐photon)
Sqrt(x*x+y*y)*sign(x)[cm]Show par.cles with E>1MeVz[cm]in 100ns
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)56

Total (w/o SR, 2‐photon)
Sqrt(x*x+y*y)*sign(x)[cm]Show par.cles with E>1MeVz[cm]in 100ns
Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)57

Orbit devia.on
HER
X[m]

Be

Track back from IP, withhorizontal angler devia.on θx

Orbit entering IP with θx/σ’x* = 0, +‐3,+‐6, +‐9, +‐12, +‐15, +‐18
Hiroyuki Nakayama (KEK)

σ’x*= 0.45mrad

KEKB ARC (Feb. 20, 2012)58

Yellow: SR(>0.1keV)
Green: SR(>5keV)
Magenta: beam e‐

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)59

Ver. 2012.2.2

Total BG (for full simula.on campaign)

R‐
side

L‐
side

LER (4GeV e+)HER (7GeV e‐)Rad. Bhabha

0.45 W (eﬀ. 0.7GHz)

0.44W (eﬀ. 0.40GHz)

Touschek

0.10 W (0.16GHz)

0.05 W (0.04GHz)

Coulomb

0.06 W (0.09GHz)

0.001W (0.001GHz)

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)

1GeV ,1GHz= 0.16W
60

Ver. 2012.2.9

Total BG (shown at Vienna)A€er Vienna,
We found 1‐turn canHER
beRBB 1‐turnstopped by collimator

R‐
side

L‐
side

LER (4GeV e+)HER (7GeV e‐)Rad. Bhabha

0.55 W (eﬀ. 0.9GHz)

1.60W (eﬀ. 1.4GHz)

Touschek

0.14 W (0.22GHz)

0.10 W (0.09GHz)

Coulomb

0.06 W (0.09GHz)

0.001W (0.001GHz)

Hiroyuki Nakayama (KEK)

KEKB ARC (Feb. 20, 2012)

0.75W(eﬀ.0.68GHz)

1GeV ,1GHz= 0.16W
61