Beam Background• Touschek/Beam-gas/Radiative Bhabha• Full-detector GEANT4 simulation• Detector performance, radiation dose
• Synchrotron radiation BG• Other background topics

Hiroyuki NAKAYAMA (KEK)
KEKB ARC(Mar. 4th, 2013)

Belle-II beam background
BG sources at Belle-II/SuperKEKB- Touschek, beam-gas- Radiative Bhabha, 2-photon- Synchrotron radiation- beam-beam, etc…

TaCryostat

Ti or SUS
Be pipeOur objectives are to estimate 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

Collimation (20mm->9mm) to stop SR

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)22

What was reported last year
• Touschek loss in IR can be reduced by horizontal collimators• Beam-gas Coulomb loss in IR can be reduced by very-narrowvertical collimator• Spent e+/e- with large DE from RBB could be lost inside IR• 2-photon BG is confirmed to be safe
• Full detector simulation shows RBB is dangerous• SR full-simulation startedHiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)3

Today’s topic• Latest IR loss rate of each BG• Thick tungsten enclosed inside cryostat for stopping BGshower• Full detector simulation (Detector performance, radiationdose, neutron flux)• Full detector simulation including loss from outside detector• Other topics– Improved SR simulation study– IR loss rate at detuned optics– Injection BG

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)

4

BG loss position

Ver. 2013.3.4(5th campaign)
Loss wattage= loss rate
* energy of loss particle

LER(e+)

HER(e-)

1GeV ,1GHz= 0.16W
LER (4GeV e+)HER (7GeV e-)Rad. Bhabha

0.63 W (eff. 0.98GHz) 0.88W (eff. 0.78GHz)

Touschek

0.16 W (0.25GHz)

0.03 W (0.03 GHz)

Coulomb

0.06 W (0.09GHz)

0.001W (0.001GHz)

Background picture

RBB LER

RBB HER
Touschek HERSR

Coulomb HER
Touschek LER

Neutrons (rad. Bhabha)Ver. 2013.3.4

QCS cryostat geometry
By Dmitri Liventsev

tungsten

QC2RE
QC1RE
QC1RP

QC2RP

tungstenLess EM shower comes out from cryostat (neutrons slightly increased).
Very narrow gap for cabling btw detector and cryostat.

7

Full detector simulation
100nsShowing E>1MeV
Green: neutron
Yellow: gamma
Red: e-, Blue: e+▲: primary loss positioncm

cm
RBB+Touschek+Coulomb
Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)8

Detector performance• Too much beam background could lose data quality– PXD occupancy (limited by readout bandwidth)– SVD occupancy , ECL pile-up noise/fake cluster– CDC wire hit rate
– Particle identification performance– etc..
PXD occupancy

CDC wire hit rate

Assuming design luminosity , estimated BG level is tolerable
Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)

9Radiation dose
• Gy and 1MeV-equivalent neutron flux
• Could damage Si devices (FPGA, readoutchips, HAPD, PIN diodes, etc..), calorimator
crystals, etc..
Assuming design luminosity x 10 years,
estimated BG level is more or less tolerable
except for TOP PMT photocathode lifetime
Neutron flux are almost same levels with requirement.
Further mitigation with additional shields are possible but space issue
for cable assembly should be accessed.
Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)10

TOP PMT photocathode lifetime
Gammas in BG shower reach TOP quartz bar and generate electrons by
Compton scattering and etc.. Those electrons emit Cerenkov photons
and those photons reach PMT photocathode.

Factor x2~3 reduction
is needed, or we needto replace PMTs every
few years at design
luminosity(replaceable TOP
design being accessed )4th campaign. Note that RBB
increases by x1.6 in 5th campaign
Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)11

Beam loss position for TOP BG
4th campaign

QC2RE
QC1RE
QC1RP

QC2RP

Beam loss at |z|<60cm (bet IP and cryostat) is dominant.
Beam pipe aperture is already widened as much as possible to reduce
Touschek loss rate (SR might increase).
Very difficult to add shielding around there because of limited space.
Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)12

Tunnel geometry (|s|>4m)
Photon dump
Photon dump

polyethyren shield(10cm30cm thick)Concrete shield(70cm thick)Assume perfect stopping
power of the last collimator
for Touschek LER

Additional neutrons shield under consideration
surrounding “photon dump”, main loss positionof gammas emitted from radiative Bhabha event
Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)13

BG loss positions
Photon dump
Photon dump

LER (4GeV e+)HER (7GeV e-)Rad. Bhabha

61 W (eff. 96GHz)

23W (eff. 19GHz)

Touschek

20W (30GHz)

1.6W (1.4 GHz)

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)+ gammas emitted fromRad. Bhabha event
14

Event displays (1ns)[cm]

4m<|s|<28m4m<|s|<28mShowing E>1MeV
Green: neutron
Yellow: gamma
Red: e-, Blue: e+▲: primary loss
position4m<|s|<28m

4m<|s|<28m

Need study with realisticcollimator stopping powerOther topics

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)16

SR simulation

Yuri Soloviev- HER SR simulation assuming phase space distribution shows rate on PXD is small- Apply same method on LER, especially to confirm inner shape of collimation- Tip-scattering, back-scattered, miss-alignment/miss-steering etc.. should be studied
13th B2GM (Nov 12-15, 2012)

Background at detuned optics
Touschek_LER,horizontal
verticalY.Ohnishi, Sep. 2012

Important information for BEAST BG study

Injection Background
Dangerous background for PXD with long(20us) readout frame
Injection VETO scheme being developed

A. Phase-space distribution at e+/e- source
B. Phase-space distribution at injection point, after tracking
through DR/LINAC/BT
C. Tracking in KEKB main ring, taking into account:- strong beam-beam effect by horizontal injection oscillation(mitigated if synchrotron injection possible)- damping effect by feedback to suppress coherent oscillation

Phase space distribution at BT exit
4nC

N. Iida, June 2012

Injection survival rate
without beam-beam effectY.Ohnishi, Feb. 2012

with beam-beam effectSummary• BG estimation now includes up to |s|<28m.
• SR full-simulation updated• TOP photocathode lifetime is still the biggest concern

13th B2GM (Nov 12-15, 2012)

plans• Additional neutron shielding vs. cabling spaces• Tunnel shield design (to protect end-cap detectors)• Radiation level in experimental hall (human-safety, FPGAs
around detector)• Collimator study (tip-scattering at the last collimator)• SR simulation– Update with the latest optics, miss-alignment/miss-steering impact– Tip-scattering implementation using beam test data (optimize ridgestructure)

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)23

backup

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)24

Neutron fluxRegion

Simulation

Tolerance[ x1011 eqn/cm2/year][ x1011 eqn/cm2/year]

1MeV equivalent rate

1 year = 107 sec

Current tolerancePXD

DHP,DCD,
Swithers

0.8<10

OK up to 100x1011 eqn/cm2

SVD

Sensors,
chips--

Should be OK,
irradiation test ongoing

CDC

Readout
Boards

2.0<2

OK up to 20x1011 eqn/cm2 (FPGA)
but need to manage SEUs
Optical receiver tested up to 10TOP

Readout
electronics

0.2<1Tested up to 10x1011 eqn/cm2
ASICs not tested yet

ARICH

HAPD

1.4

<1

Tested up to 10x1011 eqn/cm2

ECL

Crystals

1.4<10

OK up to 100x1011 eqn/cm2

ECL

Diodes1.4<1

OK up to 10x1011 eqn/cm2

No hits found-BKLMSiPMs

4th campaign

13th B2GM (Nov 12-15, 2012)(dark=1uA, QE=97.6%)

Note: In 5th campaign
RBB increase by x1.6

1krad=10Gy
10krad=100Gy
100krad=1000Gy
RegionPXD

SensorRadiation dose
Simulation

Tolerance[Gy/year][Gy/year]20k

1 year = 107 sec

Current tolerance-

Tested up to 100kGy(=10Mrad)
200kGy would be also OK
OK up to 100kGy (by Peter)(2MRad/y)
SVD

APV--

CDC

Readout
boards21<100

Tested up to 1000Gy (FPGA and opticalTOP

Readout
electronics

2<300

Tested up to 1000Gy
ASICs not tested yet

ARICH

HAPDs

5<100APD tested up to 1000Gy

ECLCrystals

8<10OK up to 100Gy

12<70

OK up to 700Gy--(f-endcap)
ECL

BKLM

Diodes

SiPMs

4th campaign

13th B2GM (Nov 12-15, 2012)

receiver w/ communication)(light yield -27% at 36Gy)(efficiency drop=1%)-Note: In 5th campaign
RBB increase by x1.6

Detector performance
Simulation

Requirement

PXD occupancy

0.9%

< 2%

SVD occupancy

Safe< ~10%CDC
hit rate

120kHz/wire< 200kHz/wire

TOPK/pi separation

K/pi separation remains goodTOP photocathode aging

Photoelectron flux: 2.2MHz/PMT<1MHz/PMTECL

1.4 fake clusters
2.3 MeV pile up noise in f-endcap

Belle1: 6 fake clusters
Belle1: 0.8 MeV pile up(2nd campaign)

Note: In 5th campaign
RBB increase by x1.6
4th campaign

13th B2GM (Nov 12-15, 2012)Same DE process, smaller cross section than Touschek

Yes, we do have such collimators at each arc positions

Hiroyuki Nakayama (KEK)

KEKB ARC (Mar. 4, 2013)28

Implement Kanazawa-shields
Pole tipと門型の隙間は約12cm

Radiation level測定のための仮想物質（r=4m, dr=10cm,コンクリート）
ポリエチレン(30cm厚)

門型シールド(75cm厚)コンクリート(70cm厚)phi

10us分simulate

uSv/hour

上外
下
内

z[cm]

|z|>8mはさらに2m厚のコンクリシールドで囲われる。

|z|<8mを拡大
phi

uSv/hour

10us分simulate

上外

下

内
数10uSv/hour程度
Cf. 立入禁止管理区域: >200uSv/h, 立入制限管理区域:>20uSv/h,
一般管理区域: >1.5uSv/h, 周辺監視区域: 0.2uSv/hz[cm]