Beam Backgroundat Super-KEKB/Belle
Osamu Tajima (KEK, IPNS)
for Belle collaboration
Feb 22, 2005
KEKB review

Outline• Current Status• Expectation & Reduction• SummaryBelle Detector
Detector will be upgrade to work under BGx20
SVD will work under BGx30 (rbp: 1.5  1.0 cm)
Almost same structure

PID

ECL

3.5 GeV (LER)

8.0 GeV (HER)

CDC
SVD

KLM

Beam backgrounds should be concern• Synchrotron Radiation (SR) photons
 generated in upstream magnets
 generated in downstream (QCS) magnet• Shower caused by spent particles
 beam-gas scattering Touschek scattering• Radiative Bhabha origin
 Neutrons from downstream beamline
 Showers caused by over bend beams

SR from upstream magnets

SVD1.0 killer source (1999)

Past trouble is reproduced by SRsim.
tibrolautca

1999 summer

azimuthal angle dist.

T.Abe(KEK)

Steering angle was critical
SR BG killed SVD !!
No more trouble w/ limitation of steering magnet

SR from upstream magnets

BG α IHER
few % of SVD BG
Negligible for others
SVD1.0 killer source (1999)
 Not serious after limitation of steeringSR, downstream magnet (QCS) origin
SR frombackscattering
QCS

SVD ~ 1/3 of bkg
CDC ~ 1/3 of bkg

BG α IHER

1. Downstream final focus magnet (QCS) generate high energy
SR (Ecrit ~ 40 keV)
2. SR photons are scattered at downstream chamber (~9m)
3. Backscattering photons enter to the detector (Eeff ~ 100 keV)Shower caused by Spent Particles
Dominant BG(except for KLM)

due to beam-gas scattering
due to Touschek scattering(intrabeam scattering)BGbeam-gas = a PHER x IHER + b PLER x ILER
BGTouchek α ILER x ILER (σ α E )Toucheck-3Study for Contribution of Touschek

background

Smaller beam-size(larger density)

 larger backgroundIf no Touschek

KEKB Collision

Contribution ~ 20 % of
LER BG from particle showers

SVD BG Extraction
SRParticle-BG

Azimuthal angle dist. of SR
at 1st layer of SVD
Single-Bunch 15 mA (trigger-timing is adjusted)
Total 0.8 A w/ 1284 bunch (random timing)
Simulation for SR-backscattering
simulation
63 kRad/yrHER 1.2A

Azimu. angle dist. of Shower particles
at 1st layer of SVD
HER single beam 0.8 A

data
simulation

LER single beam 1.5 A

data
simulation

Almost consistent with simulation ~40% accuracyBG of SVD at 1st layer
SR20%Particle
HER

56%

Particle SR ~ 1/3Particle ~ 2/3LER
24%

outer side

180 kRad/yr

HER 1.2A
42%

42%

16%

LER 1.6 A
inner side

170 kRad/yr

Radiative Bhabha origin
Main BG source for KLM BG α Luminosity
Negligible for othersKLM : EndCap

rate (Hz/cm2)

rate (Hz/cm2)

Main bkg source is luminosity origin
Luminosity component ~ 75 %Beam current component ~ 25 %

FWD

BWD

LER current (A)HER current (A)FWD
Luminosity (1034/cm2/s)

layer8 layer9 layer10 layer11
innerouterWhat is KLM bkg ?
• Strong correlation with Luminosity• Long attenuation length from outer to inneroutsideinsideFWD EndCap

neutronγ

Not EM showers !
Might be neutron

41…
201

Where is neutron source?
Radiative-Bhabha might be origin
1.8 2.2 1.6

1.5

11489

286

565

00.8

EM showers(counts/sec)

fast neutron(mSv/2weeks)81

γ-ray Rad-Bhabha (?)~5 m

472 534
~10 m

99222

HERLER

152~15 m
Apr, 2003 (by Tawara, Nakamura)Oct 27,2004 (by K.Abe & T.Sarangi)
LER / HER = 1630 / 1160 mA

BG components

1st layer

BG Estimation & Reduction
for Super-KEKB/BelleMachine parameters for BG estimation
KEKB

SuperKEKB

LER

HER

LER

HER

I [A]

1.6

1.2

9.4

4.1

βx*[cm]

33

33

2020

βy*[mm]

101033L [/cm2/sec]

1.3 x 1034

2.5 x 1035σy [um]

331.5

1.5

σl [mm]5533Ave. Vacuum (10-7 Pa)

1.25

1.25

5 (2.5)5 (2.5)φ [mrad]1115

SR power : QCSR (kW)Run time (days/year)

29200

179200Backscattering of QCS-SR• Larger current and critical energy gives
larger QCS-SR wattage  x6 (179 kW)• Assume that scattered position will besame as current KEKB (~9m)
 IR chamber design is not finalized• 6 times higher than current SR-BG
Dose at 1st layer of SVD
 400 kRad/yr at inner side of the ring
 130 kRad/yr at outer side of the ring

Shower of Spent Particles• Beam-Gas scattering origin
 HER / LER currents: 1.2/1.6 A  4.1/9.4 A
 x4 Worse Vacuum : 1~1.5x10-7 Pa  5x10-7 Pa
 x13.6 (HER), x23.6 (LER) higher contribution• Touschek origin
 smaller beam size ~ 1.5um/3um
 shorter bunch length ~ 3mm/5mm
 higher bunch current ~ 1.5 times
 many #bunch ~ 3.9 times
 currently just 10% of total BG
 x97 times higher contribution

Rad. Bhabha : KLM
Lsuper-KEKB / LKEKB = 25 / 1.3 ~ 19 times higher
1.8 2.2 1.6

1.5

11489

286~5 m565

00.8

EM showers(counts/sec)

472 534 222~10 m

fast neutron(mSv/2weeks)

8199HERLER

152~15 m etc.)
Reduced by neutron shield (polyethylene ~0.1/(25cm thickness)

Radiative Bhabha : inner detectors• Actually, BaBar has large BG for innerdetectors while it is negligible at BelleBaBar
DCH

We should consider
because higher lum
gives higher BG

HERRadiative
LER
RadiativeRadiative
BhabhasBhabhasPEP-IIBhabhas
30

2.520
0.5

131
3.

1.5 2

Difference of QCS
position is the reason
Shower caused by overbend particle

3.5eV

4G10cm

9 GeV

066.5
77.5
8

4.5
5 5.5

Pointed out by M.Sallivan
in 6th HLWS (Nov,2004)

9 GeV

-10
0.5

Super
KEKB IR
1330-20

3.

1

eV2.5

G

2
1.5

2 1.5
1-5

4

Detector 0.5
10.5

2.5

320-30-7.5

60m

Q1ER2

LER radiative bhabhas

2.5Q2PL

3205

7.52.5

1.5

12M. Sullivan
Feb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

541Detector

6720.50.5

QCSL

QC2RE

QC2LP

10HER radiative bhabhas

5 303-2.5

KEKB Interaction Region

7QCSR
CSL

HER 10gammas

3HER radiative
gammasCSR

LER gammas

cm

QC1RE

0cm

LER radiative
gammas03.5 GeV

-10

RHE

LER

eV

8G

CSL

QC1LE-5-2.5

Q2PR
QCSR

Q1EL

Detector

0m

CSR

QCSL

-20
QC2RP

QC2LE-30-7.5

eV

8G

QCSR

-20

LER
HER

-10
QCSL

3.5 GeV

Detector

2.55 -30-7.5

7.5

M. Sullivan Nov. 13, 2004
B3$_SUPER_KEK_RADBHA-5-2.50m

2.557.5
M. Sullivan Nov. 9, 2004
B3$KEK2_IR_RADBHA

Rad. Bhabha BG at ECL, NOW
BarrelBWD
EndCap

FWD
EndCapData
L=1.39x1034 /cm2/s
HER = 1.19 A
LER = 1.57 A

Simulation~4 % oftotal BG

Asuuming
L=1034 /cm2/s

Rad. Bhabha BG sim. for Super-KEKB
BarrelBWD
EndCap

FWD
EndCapRealistic design
based on discussion
with QCS group

Expected BG
from othersources
L=1034 /cm2/s

L=25x1034/cm2/s

with heavy metal
total ~ 1.5 ton~4 % oftotal BG

Super-KEKB (current) design

Average Vacuum
5x10-7 Pa

1st layer

Average Vacuum
2.5x10-7 Pa
Suppressed byNeutron shield

1st layer

Beampipe radius 1.51cm
BGx33 (several MRad/yr)!?
(sim. for particle shower)

SR from upstream magnets
simulation for SVD 1st layer
QC1L(-3m) during injection~20 kRad/yr

Deposit dose is localizedon 1st layer of SVD
But, still lower than others
QC2L(-7m) at stored~40 kRad/yr~100 kRad/yr

Summary• Backscattering of QCS-SR is not serious, butstrongly depends on IR chamber configuration• Vacuum level is very important Original design (5x10-7 Pa) is serious  BGx25
 w/ further effort (2.5x10-7 Pa)  BGx18-30%• Increasing of Touschek origin BG
 Smaller bunch size & higher bunch currents are reason Might be reduced by further study• Radiative Bhabha origin BG can be suppressed• Beampipe radius 1.5cm  1cm
 Further simulation study of shower particles into SVD is important

backupKLM : Barrelrate (Hz/cm2)

Main bkg source might be luminosity origin
Luminosity component ~ 70%
Beam current component ~ 30 %LER current (A)HER current (A)Luminosity (1034/cm2/s)

layer0 layer1 layer2 layer3
innerouterNow• HER / LER = 1.2 / 1.8 A• Luminosity ~ 13 /nb/sec (1.3x1034 /cm2/sec)• Which is dominant background?
– SVD : SR ~ 1/3, Spent particles ~ 2/3– CDC : SR ~ 1/4, Spent particles ~ 3/4(HER ~ 1/4, LER ~ 2/4)

– KLM EndCap : L ~ 75 %, Spent particles ~ 25 %Barrel : L ~ 70 %, Spent particles ~ 30 %– Others : Spent particles might be dominat

Near Future Prospects of KEKB
Now (2004)
L = 13 /nb/sec
HER / LER = 1.2 / 1.8 A
RF limits beam-current

21IHER (A)

02060

ILER (A)Lumi. (/nb/sec)

300

2004

05

06

07 08

RF repair & minor upgrade (2005)
Assumption
within3~4 years …
LER = 1.5xHER
Beam: x 1.7 higher
L =current
βIHER
Luminosity: 10%x 4.6higherfactor β increase
everyyear
Crab cavity (2006) HER&LER twice luminosity !?
Minor upgrades (2007-2008)
 L = 60/nb/sec
HER / LER = 2 / 3 A

Near Future
SR (α IHER)
Spent particles (α I2)Luminosity origin (α L)
SVD outer x 2.6
inner x 2.3
CDC x 2.5
KLM EndCap x 4.2
Barrel x 4.1
Others x 2.8

If we can keep good vacuum( optimistic case )most of detectors x 1.7
KLMx 3.9
lower limit !?
3 times bkg isgood target value
for near futureSummary2004
13 /nb/s
1.2 A
1.8 A2008Lumi.
60 /nb/s

HER2A
LER
3ABkgSVD
 x 1.7 ~ 2.6
Bkg
CDC x 1.7 ~ 2.5
Bkg
KLM x 3.9 ~ 4.2
Bkg
Others x 1.7 ~ 2.8
Higher bkg study must be needed for ~3 year later
KLM bkg reduction must be start as soon as possible

Beam Current dep. of Vacuum
was reproduce by its dep. of BG
Nparticle/NSR α P(Pa)NSR α I(A)
Nparticle α I(A) x P(Pa)
Average Pressure in
upstream of HER

Azimu. angle dist. of Shower particles
88 kRad/yr simulation
at HER 1.1A 106 kRad/yrdatasimulation

HER single beam 0.8 A

86 kRad/yr simulation
at LER 1.6A 42 kRad/yr

data
simulation

LER single beam 1.5 A

Azimu. angle dist. of Shower particles

w/ correction of Touschek
88 kRad/yr simulation
44 86 kRad/yr simulation
at HER 1.1A 106 kRad/yr
at LER 1.6A 42 kRad/yr
36

data
simulation

HER single beam 0.8 A

data
simulation

LER single beam 1.5 A

SVD Cluster Energy Spectrain Single Beam Run (1st layer)
Energy deposition  Radiation doseHER(e-) 0.8 A
SR andParticle-BG

LER(e+) 1.5 A
OnlyParticle-BG

#clusters/keV/event

E-spectrum of HER Particle-BG• Diff. btw vacuum
bump on/off in HER• LER 1.5 A

HER E-spectrumof particle BG issame as LER !!

Can measure SR
and particle-BG
separately

energy (keV)Variation of Pressures at Pump
pressure ( x10-8 Pa )H01A (3.5m)

1.9  3.3 (x1.7)

H02A (7m)

6.7  14 (x2.1)

H03 (15m)

15  35 (x2.4)

H04 (25m)

4.8  13 (x2.7)

H05 (35m)

1*  6.8 (x6.8)

H06-08 (~80m)

1*  13 (x13)

H09-12 (~120m, ARC)

10  259 (x2.6)

H13-15 (~160m)

4.5  107 (x24)monitorlimit *MaximumvalueH13-15

H09-12

H05
H02A
H01A
H06-08H03

H04

CDC Leak Currents
CDC0(inner)
CDC1(middle)+8% +12%+18%

CDC2(outer)

HER current

鉛ブロック(5cm厚)で囲まれたプラスチックシンチレー
ター検出器
Belle

IP

luminosity

background

LER current

ビーム電流だけでなく、ルミノシティーに比例したバックグランド(中性子と思われる)が大量に存在する
SuperKEKBではルミノシティーは50倍になる!!

Super-KEKB Machine Parameters
KEKB

SuperKEKB

Horizontal emittance

24 nm

33 nmx-y coupling

~3%

6.4 %

βx* / βy* (cm)

63 / 0.7

30 / 0.3

Beam current

1.1 A

4.1 A

Crossing angle

22 mrad

30 mrad

HER-beampipe tilt

11 mrad

15 mradHER β Functions
Based on IR_HER6.sadBeampipe in Super-Belle• Scaled to 2/3 ( rbp 1.5  1.0 cm)

 Can we also scale SR-mask height ?

Dose (kRad/107sec)

Discussion for SR-mask (rbp=1cm)

2/3 scale
3.5 MRad/yr !!
350 kRad/yr

Discussion for SR-mask (rbp=1cm)
Mask height should be same as
rbp=1.5 cm case ( ~2.5 mm height)
Dose (kRad/107sec)

Acceptable height

2/3 scale
3.5 MRad/yr !!
350 kRad/yr

Discussion for SR-mask (rbp=1cm)

Dose (kRad/107sec)

outsideinside350 kRad/yr

Discussion for SR-mask (rbp=1cm)

Dose (kRad/107sec)

outsideinsideoutsideinsideIf vertical direction
is higher ?
350 kRad/yr

Discussion for SR-mask (rbp=1cm)
outsideinside

Dose (kRad/107sec)

Dose (kRad/107sec)

outside350 kRad/yr

140 kRad/yr

inside