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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

Inner

Main

10KHz

luminosity dependences
Luminosity Dependences

Feb, 2004

CDC BG did not change!

Inner most

Middle

Outer

hit rate at layer 35
Hit rate at layer 35

Dec.,2003

LER

HER

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

MC+BGx20

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

occupancy
Occupancy

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
Bestcondition
  • 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?

summary
Summary
  • 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

Bhabha

Mu pair

M.I.P

in Hadronic events

0.35<P<0.88GeV/c

without any PID.

Electron

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

log10P(GeV/c)

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

chamber

2000

Summer

2001

Summer

2002

Summer

20003

Summer

2004

Summer

Pulse height variation

Hokuue

hit rate1
Hit rate

Apr.-5th , 2005

IHER = 1.24A

ILER = 1.7A

Lpeak = 1.5x1034

ICDC = 1mA

Small cell

Inner

Main

10kHz

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

D12

D9

D3

D6

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
effectiveness
Effectiveness
  • 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.
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