Particle Identification at Belle

1
Particle Identification at Belle     Present
status and upgrade plan Takahiro Matsumoto /
Tokyo Metropolitan University

• Belle/KEKB plan
• Belle PID upgrade plan
• TOP counter
• Aerogel RICH counter
• Summary

2
Introduction

• Goal of B-factory project
• Explore variety of B decays
• ? Establish CKM scheme of CP violation
• Discovery of New physics (if possible)
• Brief history
• 1999 KEKB/Belle operation started
• 2001 Establish CP violation in B decay
• 2003 Hint of new physics in B?fKS?
• 2004 Direct CP violation in B?Kp

Upgrade of detector is planned to continue
exciting B physics race (Super-B project).
Particle ID section is one of the
most active area at Belle.
3
International Collaboration Belle
Seoul National U. Shinshu U. Sungkyunkwan U. U.
of Sydney Tata Institute Toho U. Tohoku U. Tohuku
Gakuin U. U. of Tokyo Tokyo Inst. of Tech. Tokyo
Metropolitan U. Tokyo U. of Agri. and
Tech. Toyama Natl College U. of Tsukuba Utkal
U. VPI Yonsei U.
Nagoya U. Nara Womens U. National Central
U. Natl Kaoshiung Normal U. National Taiwan
U. National United U. Nihon Dental
College Niigata U. Osaka U. Osaka City U. Panjab
U. Peking U. U. of Pittsburgh Princeton
U. Riken Saga U. USTC
IHEP, Vienna ITEP Kanagawa U. KEK Korea U. Krakow
Inst. of Nucl. Phys. Kyoto U. Kyungpook Natl U.
EPF Lausanne Jozef Stefan Inst. / U. of
Ljubljana / U. of Maribor U. of Melbourne
Aomori U. BINP Chiba U. Chonnam Natl U. U. of
Cincinnati Ewha Womans U. Frankfurt U. Gyeongsang
Natl U. U. of Hawaii Hiroshima Tech. IHEP,
Beijing IHEP, Moscow
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Belle PID Group (for Upgrade)

• Tokyo Metropolitan U. ( Aerogel RICH,
  electronics )
• T.Sumiyoshi, T.Matsumoto, T.Seki, S.Yamamoto,
  T.Nakagawa
• KEK ( TOP, Aerogel RICH )
• I. Adachi, S.Nishida, H.Ikeda, Y.Uchida
• Ljubliana Institute ( TOP, Aerogel RICH )
• P.Krizan, S.Korpar, M.Staric, A.Gorisek,
  R.Pestonik, S.Fratina
• Nagoya U. ( TOP, Aerogel RICH )
• T. Ohshima, T.Iijima, K.Inami, Y.Kozakai,
  T.Kubota, H.Nakano, K.Aoki, Y.Mazuka
• Chiba U. ( Aerogel RICH, aerogel production)
• H.Kawai, Y.Unno, M.Konishi, T.Fukushima, M.Tabata
• Toho U. ( Aerogel RICH )
• S.Ogawa, S.Ohtake, M.Iwabuchi

5
KEKB Collider
8 GeV e- x 3.5 GeV e
?11mrad crossing
Lpeak 1.39 x 1034 sec-1cm-2
_at_ 1.2A x 1.6A
300 fb-1 on Y(4S) (330 M BB) 30 fb-1 below
Y(4S)
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Continuous Injection
No need to stop run Always at max. currents,
luminosity
CERN courier Jan/Feb 2004
both KEKB PEP-II
30 more ? L dt
continuous injection (new)
normal injection (old)
HER current
LER current
Luminosity
1 fb-1/day ! (1x106 BB)
-
0
12
24
Time
7
(No Transcript)
8
Belle detector
Aerogel Cherenkov cnt.
n1.0151.030
SC solenoid 1.5T
3.5 GeV e
CsI(Tl) 16X0
TOF conter
8 GeV e-
Central Drift Chamber small cell He/C2H5
Si vtx. det. 3(4) lyr. DSSD
m / KL detection 14/15 lyr. RPCFe
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Particle ID at Belle
eff.(K?K) 90
fake(p?K)10
10
Successful of PID (example)
Belle
B0 ? pp- (140/fb)
BaBar
pp- 231.4 Kp 83.3 qq 168.3 total
483
to appear in PRL, hep-ex/0401029
App 0.58 ?0.15(stat) ?0.07(syst) Spp ?1.00
?0.21(stat) ?0.07(syst)
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Super-B factory ( 2008 ? )
Super-KEKB
3.5GeV e- 9.6 A
8GeV e 4.1 A
Aiming L 2.5-5 x 1035 cm-2s-2 1st goal ?L dt
5 ab-1 (long term 50 ab-1 )
Super B Factory at KEK
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B physics Roadmap
Tevatron (m100GeV) ? LHC (m1TeV) KEKB (1034)
? SuperKEKB (1035) Concurrent program
Identification of SUSY breaking mechanism
Anomalous CPV in bgsss
if NPSUSY
sin2f1, CPV in Bgpp, f3, Vub, Vcb, bgsg, bgsll,
new states etc.
Study of NP effect in B and t decays
time or integrated luminosity
Precise test of SM and search for NP
Yes!!
NP discovered at LHC (2010?)
Discovery of CPV in B decays
Now 300 fb-1
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Belle Detector Upgrade
SC solenoid 1.5T ? lower?
PID TOP RICH
CsI(Tl) 16X0

• / KL detection
• Scintillator strip/tile

pure CsI (endcap)
Tracking dE/dx small cell longer arm
Si vtx. det.
2 pixel lyrs. 3 lyr. DSSD
14
Requirements for Particle ID

• Further Improvement on K/p separation
• Currently, Slightly worse performance than BaBar
• Missing high momentum PID in the forward endcap
• Present endcap-ACC is used only for flavor
  tagging
• High momentum K/p sep. ? Low momentum m/p sep.
• Also useful for study of AFB in B?K() l l

Belle
BaBar

• Operational under very high bkg. ( x 20 )
• TOF may not survive
• ACC seems to be OK
• Reduction of radiation length
• 30 in total 18 (ACC) 12 (TOF)
• PMTs dominate for ACC

under 10A total current
15
PID upgrade

• Baseline
• Barrel ? TOP Counter
• Endcap ? Aerogel RICH

• Other option
• Focusing DIRC
• TOF w/ finer segmentation ( with Barrel-ACC )

16
TOP Counter Concept

• Quartz-based RICH counter
• detect internally reflected Cherenkov light (like
  DIRC at BaBar)
• Reconstruct the image in (X,TOP) instead of
  (X,Y).
• TOP Time Of Propagation
• Possible if DTOP lt 100ps for each arriving photon.

qC Cherenkov angle F
horizontal emission angle L distance for
light travel vg(l) group velocity of light
NIM A453(2000)331
TOF from IP to quartz bar is also used.
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Bar TOP Counter
Simulation 2GeV/c, q90 deg.

• Proximity focusing in X measurement
• Simplified structure and easier installation.
• Loose requirement for DX (5mm)
• Well polished quartz radiator
• Photodetection by linear-anode PMT
• Flipped images can be resolved by widening the
  bar width (gt20cm).

K p
d-ray, had. int.
18
TOP Counter Design

• Quartz radiator 40cm x 2cm x 255cm
• ? 18 segmentation in r-f
• Photodetection MCP-PMT
• w/ linear anode (5mm)
• Good time resolution lt 40ps/photon
• Single photon sensitive up to 1.5T
• Number of PMTs (channels)
• 15 pcs. (60ch) /module
• 270 pcs. (1080ch) / total
• for 1 read-out plane (LoI design)
• 810 pcs. (3240cn) / total
• for 3 read-out planes (present baseline)

16 x X0
R115125cm Z-72.5182.5cm
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Beam Test w/ Prototype

• Demonstration of principle w/
• 1m(L)x20cm(W)x2cm(T)
• R5900-00-L16

Test counter
_at_ KEK PS p2 line 3 GeV/c p- beam
qinfin90 degree

• Clear ring image
• Reasonable
• time resolution
• Enough bar quality

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Quartz Radiator
s(time) measured w/ beam (Butterfly TOP w/
R5900-L16)
Bar1

• Synthetic fused silica
• Long transmission
• Good polishability
• Radiation hardness
• Shin-etsu, SUPRASIL-P30
• T90 at l 250nm
• Polishing accuracy at Okamoto Kogaku Co.
  (Yokohama)

Bar2
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MCP-PMT (SL10)
Under Development

• 1x4 linear-anode MCP-PMT newly developed for TOP
  readout.

MCP stage 2
Gain (HV) 2x106 (-3.5KV)
MCP hole dia. 10mm
Geometrical collection eff. 50
pixel /size 1x4 / 5mmx22mm
Effective area/ Total area 64
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RD for Readout ASIC

• Time-to-Analog Converter ? Time resolution
  lt20ps.
• Double overlap gates ? Less dead time (100ns).
• 0.35m CMOS process.
• 2nd batch TAC-IC was submitted to VDEC (U. Tokyo)

TAC-IC Concept
40MHz CLOCK
23
Performance of TOP

• Separation power

Single photon resolution
Light propagation velocity
Npe
24
Efficiency/fake (LoI)

• Large drop around q7080 degree, due to
  chromaticity.
• Need to optimize TOP design (Bar length, width,
  ch. division, etc.)

25
Segmented TOP

• Segmented TOP
• Decreased D(TOP) , but avoid chromatic
  effect
• 3 times more readout
• No need for gluing
• ?much easier construction
• Various version is tested.
• For example,

K/p separation _at_ 3 GeV/c
Belle e(K) 90, fake(p) 10 TOP e(K)
98, fake(p) 2
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Robustness against Beam BG

• Efficiency and fake rate for KID
• Bialkali photo-cathode option
• Estimated background rate
• Based on a simulation w/ spent
• electron generator
• Dominated by g? ee- conversion
• g hit rate 44kHz/counter at L1034
• 6.8 photons/hit/counter
• 900kHz-hit/counter at BG x 20
• 80kHz/ch
• Stable performance even for 10 times more BG rate
  of our estimate

(/counter)
Our estimate
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Aerogel RICH

• Proximity focusing RICH with an aerogel radiator
• Proximity focusing ? Due to limited space
• Target K/? sep. gt 4 s _at_ 0.7 4 GeV/c
• qc(p) qc(K) 23mrad (n1.05)
• ????separation if??qC(meas.) 14 mrad with Npe6
• Key components
• High optical quality aerogel
• with n 1.05
• Photon detector
• Single photon
• Position sensitive
• Strong B field (1.5T)
• ? HPD/HAPD
• Readout electronics
• Mechanical structure

28
Aerogel radiator

• Used as Threshold counter at Belle
• K/p separtion with ON/OFF signal
• Aerogel radiator, n 1.01 1.03
• adequate for a few GeV range
• Hydrophobic aerogel by surface modification
• optical quality is improved
• But not devlopped for n1.05 !
• Because both p/K emits cherenkov photon

29
Aerogel production improvement

• RD in cooperation with Matsushita
• Goal
• better optical quality for n1.05 hydrophobic
  aeogel
• Method
• A new solvent(Di-Methyl-Formamide instead of
  Methyl-alcohol)
• Precursor(Mthyl-silicate-51) from a different
  supplyer
• ? Considerable improvement

30
Beam test with Flat-panel PMT

• Demonstration of principle
• Various aerogel samples
• 44 array of H8500
• 85 effective area
• Analog memory readout
• 64 ch x 16 1024 ch ADC ? pipeline

31
Results

• Chrenkov angle/photon
• s0 14 mrad
• s(em.) 8.6 mrad
• s(pix.) 6.4 mrad
• Trying to understand Rest component 7 mrad,
  (chromatic dispersion, aerogel uniformity,
  surface effects etc.).
• Npe 6
• Naïve estimation of s / track
• s0/sqrt(Npe) 5.7 mrad
• K/p separation _at_ 4 GeV
• 4 s is expected
• Demonstrated by Data!

32
Photo detector

• Requirement on Photodetector
• Sensitive to Single photon
• Position sensitive
• Immune to Magnetic Field (1.5T)
• HPD and HAPD option is studied.
• Developed between HPK and Belle

Package 72x72mm2 72x72mm2
of pixels 12x12(6x6/chip) 12x12(6x6/chip)
Pixel size 5x5mm2 5x5mm2
Effective area 64 64
PD APD
Gain 2000 20000
Cd 10pF 80pF
I(leak) 10nA 30nA
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Performance of HAPD

• Very recently, we could start to test
  12 x 12 HAPD
• Due to problem of out-gas etc.
• Modification on ceramic case was done
• However, 2 dead out of 4 chips
• Single photon can be observed.
  Further studies (Uniformity, crosstalk, incident
  angle dependence etc.) are underway.

• Delivered sample
• QE 11.3 at 420nm
• Max high voltage -8KV
• Max bias voltage 335V

Muliti Photoelectron
Single Photoelectron
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Readout Electronics

• Aerogel RICH readout
• Total 100k channel!
• Readout scheme ? pipeline
• Only record hit information
• Basic parameters for the ASIC
• CMOS-FET
• Gain10V/pc
• Shaping time0.15?sec
• VGA1.2520
• 18 channels/chip
• Power consumption 5 m W/channel
• 3rd batch was submitted to VDEC (More protection
  to noise was done )

?4.93mm
Shaper
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Mechanical design
Aerogel
Photo detector

• Aerogel radiator
• Hexegonal tiling to minimize aerogel boundary
• side length, 125 mm
• Photo detector
• Total PD 564, 6 sectors
• Cover 89.0 of area

36
Aerogel RICH, performance

• Based on Simulation study, likelihood approach
• K/p efficiency by keeping fake rate 5
• ? gt 95 up to 4 GeV/c

37
Dual-(Multi-) radiator Scheme

• Focusing defocusing schemes
• Solve a dilemma thicker radiator for more Npe
  deteriorates an angle resolution
• Advantage from manageable refractive index

n1ltn2
n1gtn2
n1
n2
n1
n2
Defocusing type
Focusing type
1.056
1.051
1.061
1.034
1.051
1.029
1.046
1.056
38
Beam test results(1)
single photon resolution
of Npe
Improved !!
Increased !!
D
?
conventional dual multiple
B
C
D
?
A

C
B
A
A
B
C
D
40mm
1.056
1.046
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Beam test results(2)
Comparison of angle resolution per track
Optimal values
resolution thickness
conventional 6.7 mrad 20mm
dual 6.2 mrad 40mm
multiple 5.2 mrad 30mm
D
A
C
B
optimal
5.2 mrad
Separation power at 4GeV/c 4.2? for K/?
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Summary

• We are developing new types of RICH detector for
  the upgrade of the Belle detector.
• Barrel ?TOP counter
• Internally reflected Cherenkov light with (X,T)
  readout.
• Endcap ? Aerogel RICH
• Proximity focusing with aerogel radiator(s).
• Target performance gt4s K/p separation up to 4
  GeV/c
• Target date 2008?
• Photo-detection is most key issue for the
  development.
• MCP-PMT for TOP
• Also trying to test GaAsP photocathode for the
  improvement.
• H(A)PD for Aerogel-RICH

41
Backup slides
42
dE/dx

• He C2H6 50 50
• Low Z gas to avoid multiple scattering
• Keeping good dE/dx resolution
• With higher composition of hydro-carbons
• dE/dx resolution 6
• 80 truncated mean
• 50 layers in total

43
Time Of Flight Counter
PID for Plt 1.2 GeV/c

• Measure b ( L/t ), and obtain m with p from
  tracking
• Dt 100ps with
• Fast scintillator, BC408
• Long att. Length 4m
• Larger photon coverage with FM-PMT (R6680) (under
  1.5T)

44
Aerogel Cherenkov Counter (1)

• Threshold counter
• K/p separtion with ON/OFF signal
• Aerogel radiator, n 1.01 1.03
• adequate for a few GeV range
• Hydrophobic aerogel by surface modification
• optical quality is improved

45
Aerogel Cherenkov Counter (2)

• ACC
• K/p in 1.5ltplt3.5 GeV/c
• Barrel 960 modules
• in 60 f-segments
• n 1.010 1.028
• FWD endcap 228 modules
• in 5 layers
• n 1.030

Npe 10 20
46
Combined performance
Efficiency/fake rate for Barrel, prob gt 0.6

• Typical performance
• Eff (K?K) 88
• Fake (p?K) 810
• up to 4 GeV/c

47
Segment TOP Performance

• Target gt4s K/p _at_ 4GeV/c over q35-135deg.

2.5s m/p _at_ 0.6GeV/c
TOP performance (base design)
DIRC performance (from RICH2002)
Want improvement to achieve the target !