The BELLE Silicon Vertex Detector present performance and upgrade plans'

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The BELLE Silicon Vertex Detector - present
performance and upgrade plans.

• Geoffrey Taylor
• The University of Melbourne and CERN
• For the Belle SVD Collaboration

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OUTLINE

• The Belle Experiment
• The role and specifications of the Silicon Vertex
  Detector (SVD)
• Early performance
• Radiation damage and first upgrades
• Status of major upgrade to SVD2.0

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KEKB Accelerator

• KEKB Asymmetric ee- collider
• Two separate rings
• e (LER) 3.5 GeV
• e- (HER) 8.0 GeV
• CM energy 10.580 GeV at ?(4S)
• Target luminosity 1034 cm-2s-1
• Parameters
• 3016 m circumference
• 11 mrad crossing angle
• 5120 RF buckets
• History
• First collision Jan. 1999
• Physics run since June 1999

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Belle Collaboration
SVD Group U. Hawaii Kanagawa U. KEK Krakow INP U.
Melbourne National Taiwan U. Niigata U. Osaka
U. Princeton U. U. Sydney U. Tokyo Tokyo Inst.
Tech. Tokyo Metropolitan U. U. Tsukuba

• 300 researchers (50 institutes)
• Australia, China, Germany, India, Korea, Japan,
  Philippines, Poland, Russia, Taiwan, Ukraine and
  USA

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CP Violation in B-sector
Mixing-induced CP Violation in B ? CP eigenstate
(fcp)
?
PDG2000 H. Quinn and A. I. Sanda
Mechanism based on the Cabibbo-Kobayashi-Maskawa
ansatz in the Standard Model
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Experimental Challenges

• Copious B pair production, efficient B
  reconstruction
• Efficient and correct flavor tagging
• Observation of time-dependent CP asymmetry in
  B-decays to a CP eigenstate with good vertex
  resolution

decay rate
?z ? cß??t tBB lifetime
proper time difference ?t (ps)
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Belle Detector

• Silicon Vertex Detector (SVD)
• Impact parameter resolution 55?m for p1GeV/c
  at normal incidence
• Central Drift Chamber (CDC)
• (?Pt/Pt)2 (0.0019Pt)2 (0.0034)2 (Pt in
  GeV/c)2
• K/? separation with
• dE/dx in CDC (?dE/dx 6.9)
• TOF (?TOF 95ps)
• Aerogel Cerenkov (ACC)
• Efficiency 85,
• Fake rate 10 up to 3.5GeV/c
• ?, e? with CsI crystals (ECL)
• ?E 1.5 for E1GeV
• e? efficiency gt 90 with 0.3 fake at p gt
  1GeV/c
• KL and ?? with KLM (RPC chambers)
• ?? efficiency gt 90 with 2 fake at p gt 1GeV/c

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KEKB Luminosity History
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KEKB Luminosity Records

• Peak luminosity 4.49 1033 /cm2/sec
• Integrated luminosity
• Per shift 83.3 /pb
• Per calendar day 229.1 /pb
• Per 24h 241.3 /pb
• Per 7days 1478. /pb
• Per month 4703. /pb

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Requirements on SVD

• Good ?z resolution 100?m
• multiple scattering is dominant
• thin beampipe svd
• z strip pitch of 80?m is sufficient
• good alignment should be pursued

• High efficiency
• good angular coverage (90)
• good S/N ratio (20)
• small occupancy ( lt 5)
• small readout deadtime ( less than 200?s/event )

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B0 ? J/? Ks(???? )
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Belle SVD
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SVD1 Detector Configuration

• Be beampipe
• r20.0mm (inner surface)
• double wall (500?m thick/each wall)
• 20?m gold foil as X-ray absorber
• Three layers of DSSD ladders (300?m thick)
• 1st layer r 30.0 mm, 2 DSSDs in z, 8
  ladders
• 2nd layer 45.5 3
  10
• 3rd layer 60.5 4
  14

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DSSD Ladders
DSSD (S6936 manufactured by HPK) p-side (r?)
n-side (z) Active area 53.532.04
54.532.025 (mm2) Strip pitch 25 42
(µm) Readout pitch 50 84(µm)
(ganged) of readout 640 640
Only 2 kinds of half-ladders (short and long)
layer 1 short short layer 2 short
long layer 3 long long
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Readout Electronics
Backend Electronics
Front-end Electronics
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Frontend Electronics
VA1 (IDEAS, Norway) - rad. tolerant up to
200kRad (1.2?m process) - excellent noise
performance 200e- 8e-/pF - Peaking time 1?s
at Belle
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Backend Electronics
FADC (HALNY)

• TTMs (Trigger Timing Modules)
• Firmware-based flexible logic modules
• Provide timing signals to FADCs and Repeaters
• Control VA bias parameters
• Issue (CAMAC-like) commands to repeaters
• Monitoring, Gain measurement etc. etc.

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STRIP YIELD AND NOISE
n-side

• Strip yield1st layer 98.82nd layer 96.33rd
  layer 93.5
• Noisep-side 550e (S/N35)n-side 1000e
  (S/N19)pn 1100e (S/N17)
• Cluster energyp-side 18.8ken-side 19.2ke

p-side
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Track Matching Efficiency

• Probability that a track found in the drift
  chamber has associated SVD clusters
• at least 2 layers
• at least 1 layer with 2dim. information
• Kalman filtering technique
• Matching efficiency
• Data 98.7 (average)
• MC 98.7
• Stable (robust against beam background)

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VERTEX RESOLUTION

• SVD
• 3 layers of Double Sided
• Silicon Detector (DSSD)
• Matching eff. 97

srf 19 ? 50/pbsin2/3q (mm)
sZ 36 ? 42/pbsin2/5q (mm)
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D0 Lifetime
? 414.5 ? 1.7(stat) fs
MKp 1865.0MeV s 5.4MeV
D0 ? K-?
(t 412.6 ? 2.8 fs PDG2k)
MKK 1865.0MeV s 6.5MeV
? 409.8 ? 6.3(stat) fs
D0 ? K-K
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D/Ds Lifetime
?4.4 MeV
D?D p0 ? K? p p
?0.79 MeV
?(D) 1021 ? 13(stat) fs (?(D) 1051 ? 13 fs
PDG2k)
M(K-pp)
M(K-ppp0)-M(K-pp)
s4.6MeV
Ds?f p ? K?K
?(DS) 482 ? 9(stat) fs (?(DS) 496 ? 10 fs
PDG2k)
M(fp)
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B meson lifetime
?(B0)1585?53(stat) fs ?(B-)1679?49(stat) fs
t(B0)1548?32fsPDG2k t(B-)1653?28fsPDG2k
?(B0)1518?45(stat) fs ?(B-)1628?60(stat) fs
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And then . . .
We see a drop in gain over time, which is
consistent with what we expect from the measured
dose. The 1.2-micron VA1s are projected to die
after about 10 fb-1 (c.f. initial goal of 100
fb-1).
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. . . Radiation damage

• Within 1 month of turn-on, sudden decrease in VA
  chip gain experienced, inner layers
• Large flux of low energy X-rays in early beam
  operation.

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. . . Fixes made
Although we could easily solve the x-ray problem,
its hard to anticipate every possible
problem. Greatly improved radiation-hardness is
clearly needed.
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Background Understood

• HER background
• No low energy X-rays
• 1/20 at 30keV
• (Dashed lines July, 99
• Solid lines, October 99)

SVD1.2 Installed
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KEKB Plans for Higher Luminosity

• Present status
• 4.5 x 1033 cm-2sec-1 (peak)
• 0.2fb-1/day x 270 days 54 fb-1/year
• Near future
• more bunch current and shorter bunch length
• by replacing masks, etc
• higher emittance
• Future plan
• (1) reduce photoelectron effect
• Antechambers for positron ring
• Charge swap
• e-(8.0GeV)e(3.5GeV)
• ? e-(3.5GeV)e(8.0GeV)
• (2) Crab collision

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BELLE Upgrade

• SVD2
• New Beam Pipe for IP
• Small Cell Chamber

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Performance Improvements

• Better impact parameter resolution
• Rbp 2.0 cm? 1.5 cm ? sDz 100 mm ? 75 mm
• Larger acceptance for SVD
• Ladder length 22 cm ? 46 cm ? 23º lt q lt 139º ?
  17º lt q lt 150º
• Better tracking efficiency
• RSVD-outermost 6.0 cm? 8.8 cm ? eff. of slow p
  54 ? 77
• More radiation hardness for SVD
• VA1?0.8 mm ? VA1?0.35 mm ? 1 MRad ? gt5 MRad
• Better trigger capability
• VA1 ? VA1TA (VA1 with trigger)
• Introduction of Level?1.5 trigger in SVD FADC
  system
• Introduction of Small cell chamber
• Faster SVD / CDCsmallcell electronics
• ? trigger rate _at_ design current 1400 Hz ? 500?
  Hz
• Installation in Summer 2002

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Inner Tracker Upgrade
Beam pipe Rin 2.0 cm SVD1 R 3.0, 4.5, 6.0
cm CDC 3 layers of Cathode part
Beam pipe Rin 1.5 cm SVD2 R 2.0, 4.35,
7.0, 8.8 cm CDC 2 layers of small cell chamber
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Improved Acceptance
23 º lt q lt 139 º
17 º lt q lt 150 º
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New Beam Pipe

• Simulation study on beam background

• Rbp1.5 cm for SVD2 (Rbp1.0 cm is too risky)
• Better cooling capability (He ? PF200)

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Radiation Tolerant DSSD

• Ionization induced leakage currentArea of
  unimplanted region
• But increasing strip width raises interstrip
  capacitance and associated noise.
• Prototype measurements
• Cinterstrip 11.4pF (ohmic side) 400e
  noise
• 2.6pF (junction side)
  100e noise
• Expect leakage current (25oC) after 2Mrad 900e
  for 3 DSSDs
• maximise strip width!
• Significant temperature dependence to Total
  noise
• Leakage current reduced by 50, Total noise by
  25 with reduction 25oC ? 15oC
• 940 e noise (S/N 20) ? 740 e noise (S/N 27)

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SVD2 DSSD Specs.
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SVD2
Electronics
Ladder
Hybrid
DSSD
FLEX
Support structure
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SVD2 Upgrade Status

• DSSD
• delivered for 1st, 2nd and 3rd layers
• designed for 4th layer and will be delivered from
  Oct. 2001
• FLEX
• prototype delivered and
• tested with DSSD/VA1
• VA1TA/Hybrid
• Ladder assembly (KEK/Melbourne)
• under prototyping and final design
• Ladders will be assembled by Apr. 2002
• Support structure (KEK)
• under prototyping and final design

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Front-end Electronics

• VA1-0.35 tested with DSSDFLEX to 5 Mrad

• VA1TA
• Fast shaper and discriminator
• Radiation hardness up to 10 MRad confirmed
• 2 or 4 analog output from a hybrid
• will be delivered and tested end of June

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Thin Oxide. . . Rad. Tolerance
depends on ionization
Reducing the oxide thickness by half is
equivalent to cutting the dose by four.
From Dan Marlowe
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Process Comparison
In the range of interest to BELLE, the noise
performance dramatically improves with decreasing
feature size, as expected.
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AMS Process Comparison
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Backend Electronics

• Repeater system under final design
• DC level shift for 2 or 4 analog signals from a
  hybrid
• 4 trigger signals from a hybrid
• FADC and Trigger under final design

• PC farm for SVD DAQ under test

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Level 1.5 Trigger

• Makes use of ADC information picked off at time
  of the serial scan.
• Virtual trigger trips with an effective width
  equal to 16 strips, quickly processed with
  massively parallel system of FPGAs.
• Logic provides z-vertex, discriminates against
  beam-gas events.

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Trigger Information Extraction
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Trigger Logic
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CDC Small Cell Drift Chamber

• Prototype is being tested.
• Final one will be fabricated by Dec. 2001.

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Summary

• Belle / KEKB has been a great success during
  initial running and analysis.
• SVD has provided the crucial vertexing required
  for the CP measurements (after rapid replacement
  of radiation damaged detectors!).
• Current SVD will survive though 2002 (assuming no
  accidents)
• KEKB continually improving luminosity with plans
  to reach or exceed the 1034 cm2s-1 design value.
• Radiation Tolerance, Detector Hit Occupancy
  Rates, Improved Trigger - drive major upgrade.
• SVD2, Small Drift Chamber to be installed in
  Summer 2002 in preparation for the expected
  luminosity targets.