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Gas-based tracking for SuperBelle. Beam background Upgrade plan Summary. Shoji Uno (KEK) April, 20-22, 2005 2 nd Joint Super B factory WS in Hawaii. Wire chamber. Wire chamber is a good device for the central tracker.

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Gas based tracking for superbelle
Gas-based tracking for SuperBelle

  • Beam background

  • Upgrade plan

  • Summary

Shoji Uno (KEK)

April, 20-22, 2005

2nd Joint Super B factory WS in Hawaii

Wire chamber
Wire chamber

  • Wire chamber is a good device for the central tracker.

    • Less material  Good momentum resolution.

    • Cheap  It is easy to cover a large region.

    • Established technology  Easy construction.

    • Many layers  Provide trigger signals and particle ID information.

  • Wire chamber can survive at Super-KEKB.

  • Our answer does not change after the last WS in 2004.

    • The beam background became smaller even for higher beam current and higher luminosity.

    • We recognize the luminosity term is small, clearly.

Cdc total current
CDC Total Current

  • Maximum current is still below 1.2mA, even for higher stored current and higher luminosity.

  • Vacuum condition is still improving.

    • Thanks KEKB people for hard work.

    • I hope there is still room to improve vacuum condition further.

Hit rate
Hit rate

Apr.-5th ,2005

IHER = 1.24A

ILER = 1.7A

Lpeak = 1.5x1034cm-2sec-1

ICDC = 1mA

Small cell




Luminosity dependences
Luminosity Dependences

Feb, 2004

CDC BG did not change!

Inner most



Hit rate at layer 35
Hit rate at layer 35




IHER = 4.1A Hit rate = 13kHz

ILER = 9.4A Hit rate = 70kHz

Dec., 2003 : ~5kHz

Now : ~4kHz

In total 83kHz

Simulation study for higher beam background
Simulation Study for Higher Beam Background

Detail was reported in the last WS by K.Senyo.

MC +BGx1


Tracking eff with b p p decays
Tracking eff. with Bp+p- decays

With 600ns dead time and under x20 occupancy, CDC keeps about 90% of the single tracking efficiency including geometrical acceptance.

(thus the tracking itself has almost 100% eff.)

B->pp reconstruction eff.

including geometrical acceptance

Square root of recon. eff. of the left

~ single track efficiency of mid/high p

Occupancy Overlay(times)

Occupancy Overlay(times)

Slow p efficiency from b d d p slow p
Slow p efficiency from BD*(Dpslow)p

  • About 80% of efficiency is kept in the slow p efficiency under x20 occupancy.

  • Reconstruction using SVD information is necessary to recover the loss of efficiency.

recon. eff. of the slow pion

~ single track efficiency of slow p

BD*p reconstruction eff.

including geometrical acceptance


Random trigger

x20 Bkgd in Belle CDC ~ x3 Bkgd in Babar DCH

Idea for upgrade
Idea for upgrade

  • In order to reduce occupancy,

    • Smaller cell size

      • A new small cell drift chamber was constructed and installed.

      • It has been working, well.

    • Faster drift velocity

      • One candidate : 100% CH4

        • Results show worse spatial resolution due to a large Lorentz angle.

        • A beam test was carried out under 1.5T magnetic field.

      • So far, no other good candidate.

Xt curve max drift time
XT Curve & Max. Drift Time

Normal cell(17.3mm)

Small cell(5.4mm)

Wire configuration
Wire configuration

  • 9 super-layers : 5 axial + 4 stereo(2U+2V)

    • A 160*8, U 160*6, A 192*6, V 224*6,

    • A 256*6, U 288*6, A 320*6, V 352*6, A 388*8

  • Number of layers : 58

  • Number of total sense wires : 15104

  • Number of total wires : ~60000

Deformation of endplate
Deformation of endplate

  • Number of wires increase by factor 2.

    • Larger deformation of endplate is expected.

    • It may cause troubles in a wire stringing process and other occasions.

  • Number of holes increases, but a chamber radius also enlarges. Cell size is changing as a function of radius to reduce number of wires.

    • The fraction of holes respect to total area is not so different, as comparing with the present CDC.

      • 11.7% for present CDC

      • 12.6% for Super-Belle CDC

  • In order to reduce deformation of endplates,

    • The endplate with a different shape is considered.

    • Wire tension of field wires will be reduced.

  • Anyway, we can arrange the wire configuration and can make a thin aluminum endplate.

Better background
Better background

  • Higher luminosity is not always higher beam background.

    • KEKB Luminosity > PEPII Luminosity

    • Belle background < Babar background

  • Now, we(KEKB-Belle+PEPII-Babar) are discussing a future machine. New machine should be designed to reduce the beam background based on our knowledge.

  • We should make effort to get better background condition in the future machine using present both machines and both detectors.

Smaller background in babar cdc
Smaller background in Babar CDC

  • Only ~0.3% occupancy for LER particle background.

Occupancy normalized by readout time window(%)

Brian Petersen’s talk in HL6

Best condition

  • Small SR background (PEPII HER)

    + Small HER particle background (KEKB HER)

    + Small LER particle background (PEPII LER)

    + Small Luminosity term (KEKB)

    + Movable masks (KEKB)

  • Small pixel or striplet (New)

    + Larger SVD (Babar SVT)

    + Larger gas-based CDC (Belle CDC)

    + FADC readout (Babar CDC)

    + Good reconstruction software (Babar?)

    + Lower B field?


  • Our conclusion does not change from the previous WS in the last year.

    • Background became better even for higher stored current and higher luminosity.

    • We recognize the luminosity term is small, clearly.

  • New CDC

    • Smaller cell size for inner most layers.

    • Larger outer radius

      • Better performance is expected.

      • Or lower magnetic field.

Radiation damage test
Radiation Damage Test

Gain degradation

Total accumulated charge on sense wire(C/cm)

a: ’93 Plastic tube d: ’94 SUS tube

b: ’93 Plastic tube + O2 filter e: ’94 SUS tube + O2 filter

c: ’94 Plastic tube f: ’94 Plastic tube

Momentum resolution
Momentum Resolution

  • Thanks for filling He based gas and using Aluminum field wires.

  • The resolution was calculated using cosmic ray events during a normal physics run.

  • BaBar data was obtained from a talk in Vancouver WS.

Momentum resolution1
Momentum Resolution

  • We could obtain a small constant term using He-based gas and aluminum field wires.

  • Slop parameter is not so good as compared with expected value.

    • We had to change the electronics parameters to reduce the cross talk.

    • HV is slightly lower than the original value.

    • Alignment is not perfect.

    • More tuning to reject bad points.

    • Some effects from the beam background.

Transverse Momentum(GeV/c)

De dx resolution


Mu pair


in Hadronic events


without any PID.


dE/dx Resolution

  • Good resolution was obtained.

  • It is useful to identify hadrons and electrons.

De dx measurement
dE/dx Measurement

  • MQT chip (Charge to Time conversion) and multi-hit TDC.

  • 80% truncated mean.

  • Relativistic rise.

    • 1.4 for electron.

  • Good PID performance for lower momentum region.

  • dE/dx information helps to separate high momentum K/p.

Normalized dE/dx


Comparison with babar
Comparison with Babar

  • Momemtum resolution(SVD+CDC)

    • sPt/Pt = 0.19Pt  0.30/b[%] : Belle

    • sPt/Pt = 0.13Pt + 0.45 [%] : BaBar

  • Mass(dE) resolution

    • Mass resolution for inclusive J/y  m+m-

      • 9.6 MeV(Belle) vs 12.3 MeV(BaBar)

    • dE resolution for B0 D-p+, D- K+p-p-

      • 13.8MeV(Belle) vs 19.0MeV(BaBar)

  • We could obtain better resolution than BaBar.

    • BaBar has a CFRP support cylinder with 2mm thickness between SVD and CDC.

  • Tracking efficiency for low momemtum particles is worse than BaBar.

    • D*+D*-yield(slow p eff.) ~0.5(?) x BaBar

    • 3 layers SVD (Belle) vs 5 layers SVD(BaBar)

  • Energy loss measurement

    • 5.6%(Belle)vs 7%(Babar) for Bhabar events

Pulse height variation

Change of

bias voltage

for preamp

Replacing with

new S/QT

for layer 0 & 1

Installation of

small cell












Pulse height variation


Hit rate1
Hit rate

Apr.-5th , 2005

IHER = 1.24A

ILER = 1.7A

Lpeak = 1.5x1034

ICDC = 1mA

Small cell




Photo of small cell chamber
Photo of small cell chamber

Just after wire stringing

Installation in 2003 summer

Curved endplate
Curved Endplate

  • Deformation of endplate due to wire tension was calculated at design stage of present Belle CDC.

Deformation(mm) 35.2 2.03 1.31

Present New

Expected performance
Expected performance

  • Occupancy

    • Hit rate : ~140kHz  ~7Hz X 20

    • Maximum drift time : 80-300nsec

    • Occupancy : 1-4% 140kHz X 80-300nsec = 0.01-0.04

  • Momemtum resolution(SVD+CDC)

    • sPt/Pt = 0.19Pt  0.30/b[%] : Conservative

    • sPt/Pt = 0.11Pt  0.30/b[%] : Possible  0.19*(863/1118)2

  • Energy loss measurement

    • 6.9% : Conservative

    • 6.4% : Possible  6.9*(752/869)1/2

Movable masks





Movable Masks

  • 16 masks in HER and 16 masks in LER.

    • 8 horizontal + 8 vertical for each rings.

  • Location

    • 4(H)+4(V) at D6 and 4(H)+4(V) at D3 for LER

    • 4(H)+4(V) at D9 and 4(H)+4(V) at D12 for HER


  • Usually, the horizontal masks are not effective. Because the horizontal tail is not so large.

  • A few vertical masks are quite effective to reduce the beam background in the both cases for storage and injection and also for LER and HER.

    • By factor two or more.

  • KEKB had movable masks near IR, which were not so effective to reduce the beam background.

    • Those masks in both of LER and HER were removed.