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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.