Nov. 7, 2005Vertex2005 A. Kibayashi 1 Status of the BELLE Silicon Vertex Detector Vertex2005 Nikko Nov. 7-11, 2005 Atsuko Kibayashi Tokyo Institute of

Nov. 7, 2005 Vertex2005A. Kibayashi

1

Status of the BELLE Status of the BELLE Silicon Vertex DetectorSilicon Vertex Detector

Vertex2005 NikkoVertex2005 NikkoNov. 7-11, 2005Nov. 7-11, 2005

Atsuko Kibayashi

Tokyo Institute of Technology

on behalf of the

Belle SVD Group

- Belle Detector at KEKB- History of SVD at Belle- Trigger Updates- Performance- Future Prospects- Recent Problems- Summary


2

KEKBAsymmetric e+(3.5GeV) e-(8GeV) Collider

Lpeak = 1.581 x 1034 /cm2 /s (May 2005)∫Ldt = 487.3 /fb (Oct 　 20,2005)

KEKB ColliderKEKB ColliderBelle

Detector

3km

World Record !

Tsukuba, Japan


3

B0 or B0 (flavor tag side)

8GeV electron 3.5GeV positron

s)CP eigenstate

z ~ 200mcz

t

Physics MotivationPhysics Motivation

　　　　　

)cos()sin())())((

))())((00

00

tmAtmSftBftB

ftBftBA dd

CPCP

CPCPCP

Measurement of time dependent CP violation

B mesons: c= 460 mboost: = 0.42decay distance~ 200 m

Requires vertex resolution ~ 100 m　


4Silicon Vertex Detector

Central Drift Chamber

Aerogel Cherenkov Counter

Time Of Flight CounterCsI Electromagnetic

Calorimeter

Superconducting Solenoid coil

KL muon detector

8GeV electron beam

3.5GeV positron beam

The Belle DetectorThe Belle Detector


5

SVD HistorySVD History

SVD1.0 VA chips with 1.2m process (usable up to 200kRad) read-out chips damaged by soft X-rays

SVD1.2 a gold foil wrapped on the beam pipe to stop the X-raysSVD1.4 VA chips with 0.8m (function up to 1Mrad)

vacuum leak on the beam pipeSVD1.6 ladders damaged by radiation replaced

1.0 1.2 1.4 1.6 2.0

http://kekb.jp/


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SVD1 vs. SVD2SVD1 vs. SVD2

No. of Layers : 3 4 •　 low momentum tracking

Beam Pipe : 20 mm 15 mm•　 better vertex resolution

Full CDC Coverage

Front-end electronics moved out of acceptance

Outer most layer further away from the interaction point•　more decays inside SVD region


7

SVD1 vs. SVD2 : performanceSVD1 vs. SVD2 : performance

)(~/0.542.19:1

)(~/3.344.17:2

mpSVD

mpSVD

Large improvement at lower momentum region!

SVD1 SVD2

No. of layers 3 4

R of 1st. layer 3 2 cm

pitch size

z 84 75 m

r 25 50 m

Large improvementoverall!

r

z

)(~/3.442.42:1

)(~/9.323.26:2

mpSVD

mpSVD

p

ba ~Impact Parameter Resolutions


8

SVD2 SVD2

3.5 GeV e+ 8 GeV e-

Collaboration

U. Hawaii, JAXA, Jozef Stefan Inst., Kanagawa U, KEK, Krakow I

NP, LBNL, U. Melbourne,

National Taiwan U., Nihon Dental College,

Niigata U., Nova Gorica Polytech., Osaka U., Princeton U., U. Sydney, Tohoku U.,

U. Tokyo, Tokyo Inst. Tech.,

U. Tsukuba, Toyama NCMT,

Vienna IHEP

over 20 institutions~100 peopleVA1TA read-out chip


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VA1TA chip

SVD2 Front-end ReadoutSVD2 Front-end Readout

VA1 Analog readout

•shaping time 0.3~1.0s

•128 channel serial read-out with 5MHz clock

TA SVD L1 Trigger

•faster shaper (75ns or 300ns) + discriminator

•128 wired-or out putL0 trigger: tell VA to hold

L1 trigger: get the held signalFADC start AD conversion


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SVD2 : Radiation HardnessSVD2 : Radiation Hardness

VA1TA 0.35 m radiation hard upto ~20 Mrad• average accumulated dose in first layer ~240 krad• maximum accumulated dose in first layer ~530 krad

Gain stable


11

SVD2: Signal to Noise RatioSVD2: Signal to Noise Ratio

Degradation

1st & 2nd Layer ~20 %

3rd & 4th Layer ~stable


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L0 Trigger Upgrade : MotivationL0 Trigger Upgrade : Motivation

2005 2008

Luminosity 15/nb/s 45+/nb/s

Background x1 x3+

L0 trigger rate 5kHz 45kHz

SVD Hold Efficiency

96% 86%

Exp41 HadronC

Need to reduce L0 rate, while keeping high efficiency.


13

L0 Trigger Update: what's doneL0 Trigger Update: what's done

new hardware installed• added CDC layers (CDC trigger upgrade in summer)• CDC + small cell CDC + TOF

Hold efficiency ~95% L0 rate reduced to 1/4

• Fast TOF trigger + small cell CDC - SVD TA too slow

• Hold efficiency ~ 96%• L0 trigger rate ~5kHz

Before Summer 2005

Summer 2005

L0 rate can be reduced by coincidence with more layers.


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Trigger Updates : SVD Z triggerTrigger Updates : SVD Z trigger

• Many off-IP background events cause fake triggers.– Z trigger would be a solution.

• SVD provides the best Z resolution

• SVD2 Z triggers– L1T trigger

• fast signal from VA1TA– L1.5 trigger

• digitized strip data from FADC• hardware installed

in Summer 2003


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L1T

Z trigger updatesZ trigger updates

GDL rate reduced by ~10%Detection eff.: ~ 99% (hadron)

　　　 ~ 61% (mupair)

Idea　 - Utilize fast peaking time of TA　 - Combine with CDC r- trigger for better　　　 BG reductionProblem　 - Efficiency too low

Idea　 - Reduce dead time- work with predefined masksProblem　 - Only 2~3 % improvement

BB-pair production

@ 10 Hz @ 15 Hz

Current 85.1% 78.5%

w/ L1.5 86.1% 79.8%

SVDL1T Rate Rejection

off 476 Hz 1.00

on 424 Hz 0.89

include L1T in GDL

probability of not losing any BB-pairs

Terminate

Terminate

L1.5


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installment plan early 2006installment plan early 2006Crab Crossing:Crab Crossing: a new idea for higher luminositya new idea for higher luminosity

Head-on collisions with finite crossing angle (22mrad)!

- avoid parasitic collisions- collisions with highest symmetry

large beam-beam parameter ( 0.057 0.19)　　

Future ProspectsFuture Prospects

Luminosity will be more than doubled!!

Study the effect of x3 luminosityx3 backgrounds

http://kekb.jp/


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SVD2 OccupancySVD2 Occupancy

Current Occupancy• 1st layer : 9 ~10 %• 2nd layer 3~4%• 3rd & 4th layers 1~2%

At high luminosity

~ high background

~ high occupancy(occupancy = % of hit channels)

Study performance under high (~30%) occupancy.


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Intrinsic Resolution vs. OccupancyIntrinsic Resolution vs. Occupancy

Intrinsic Resolution

Occupancy

residual residual

occupancy < 0.04 occupancy 0.3

At high occupancy,

cluster shape is 'distorted'

reconstructed cluster energy to be off

the residual distribution to be widened


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Hit Efficiency vs. OccupancyHit Efficiency vs. Occupancy

Layer1 Layer2

Layer3 Layer4

hit or not?

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3 4

Layer No.

0% 30%Occupancy

1.0

0.6

Efficiency

Higher Occupancy ~ Lower Hit Efficiency

• Signal + background hitswider 'distorted' cluster

• Wrongly associated background cluster


20

Vertex Resolutions vs. OccupancyVertex Resolutions vs. Occupancy

3xBGMC

Impact Parameter Resolution

OccupancyZ Resolution

Degradation• Impact parameter resolutionsfor higher momentum tracks ~10%

• Z resolution for lower momentum clusters ~17%

J/Ks

Use correlations between - cluster detected charge from both sides of a DSSD (wrongly associated clusters)- cluster size and track incident angle ( BG induced hits)

Software efforts in progress.


21

Recent Problems: How we sawRecent Problems: How we saw

Oct. 5After HER beam abort, at the beginning of the next run, noise monitor showed some chips havegone null..

Oct. 17 After an earthquake (M5.1),some more hybrids seemedto have gone dead, but later recovered .


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Recent Problems: Initial investigationRecent Problems: Initial investigation

LV monitor shows 0 current.

• LV supplied to the repeater system inside of the endcap.

• Checked power supply cables, relay cable connector pins No problems

• Checked resistance in each power cable.

• Some are found to be very large. Open endcap


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Recent Problems: Where it happened?Recent Problems: Where it happened?

In the front-end repeater system. - receives the analog signals from the VA1TA chips, amplifies them, and sends to the backend electronics (FADCs) .- accepts control signals from the backend timing modules, converts and sends to VA1TA chips. - provides detector bias voltages

located just outside of the CDC end wall

5 forward, 5 backward


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Recent Problems: Power connectorRecent Problems: Power connector

Connector pins can handle ~3A according to the spec.

Our operation <3A.

Pins made of phosphorusbronze, tin-plated.

Housing made ofnylon.


25

Recent Problems: Burnt connectorsRecent Problems: Burnt connectors

FW1

Power supply connectors.forward 2/5 badly burnt, 1 1pinbackward 1/5 slightly

FW4

Cause

still under

investigation!


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Recent Problems: A quick fixRecent Problems: A quick fix FW x5: Avoid using the connector.Solder wire directly.

BW x5: Polished pins.Confirmed R not high.Installed temperature monitor. Keep monitoring temp. & R.

Resume KEKB/Belle operation

10/20 ~8am stopped normal run, opened endcap11/1 endcap closed, 11/4 start taking data


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SummarySummary

• SVD2 Operation – No serious problems for 2 years– Performance within expectations

• Trigger Updates– L0 trigger updated to cope with higher background – L1T, L1.5 trigger activities have been terminated

• Next Year : Expect x3 Higher Luminosity– L0 trigger upgraded– Software works in progress

• Problem in Oct.– A quick fix finished– Cause still under investigation


28

backupsbackups


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AlignmentAlignment

Move each DSSD so that the track is a straight line matching the position of the

signal hit on the DSSD.

– Shift : x, y, z – Rotation : x, y, z – 246 DSSDs

1,476 parameters total

222 )( tracksignal xx

y

x

z

Double-Sided Silicon Detector(DSSD)

Track

signal

Use cosmic ray tracks with the mag. field off.


30

SVD2 Performance SVD2 Performance

dr 　 < 20 m,

dz < 30 m

IP resolution stable at ~10% fluctuation

a

b p

ba ~

Summer03

Summer04

Summer05


31

Signal and NoiseSignal and Noise

Cluster Energy Noise


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Leak CurrentLeak Current


33

SVD1 vs. SVD2SVD1 vs. SVD2

Documents

Nov. 7, 2005Vertex2005 A. Kibayashi 1 Status of the BELLE Silicon Vertex Detector Vertex2005 Nikko Nov. 7-11, 2005 Atsuko Kibayashi Tokyo Institute of