Gasbased tracking for SuperBelle

1
Gas-based tracking for SuperBelle
Shoji Uno (KEK) April, 20-22,
2005 2nd Joint Super B factory WS in
Hawaii

• Beam background
• Upgrade plan
• Summary

2
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.

3
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.

4
Hit rate
Apr.-5th ,2005 IHER 1.24A ILER 1.7A Lpeak
1.5x1034cm-2sec-1 ICDC 1mA
Small cell
Inner
Main
10KHz
5
Luminosity Dependences
Feb, 2004
CDC BG did not change!
Inner most
Middle
Outer
6
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
7
Simulation Study for Higher Beam Background
Detail was reported in the last WS by K.Senyo.
MC BGx1
MCBGx20
8
Tracking eff. with B??pp- decays
B-gtpp 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)

• 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.)

9
Slow p efficiency from B?D(Dpslow)p
recon. eff. of the slow pion single track
efficiency of slow p
B??Dp reconstruction eff. including geometrical
acceptance

• 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.

10
Occupancy
Random trigger
x20 Bkgd in Belle CDC x3 Bkgd in Babar DCH
11
at HL6 in KEK
12
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.

13
XT Curve Max. Drift Time
Small cell(5.4mm)

• Normal cell(17.3mm)

14
Baseline design
CDC
SVD
15
Main parameters
16
Wire configuration

• 9 super-layers 5 axial 4 stereo(2U2V)
• A 1608, U 1606, A 1926, V 2246,
• A 2566, U 2886, A 3206, V 3526, A 3888
• Number of layers 58
• Number of total sense wires 15104
• Number of total wires 60000

17
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.

18
Better background

• Higher luminosity is not always higher beam
  background.
• KEKB Luminosity gt PEPII Luminosity
• Belle background lt Babar background
• Now, we(KEKB-BellePEPII-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.

19
Smaller background in Babar CDC

• Only 0.3 occupancy for LER particle background.

Occupancy normalized by readout time window()
Brian Petersens talk in HL6
20
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?

21
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.

22
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
23
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.

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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)
25
dE/dx Resolution

• Good resolution was obtained.
• It is useful to identify hadrons and electrons.

26
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)
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Comparison with Babar

• Momemtum resolution(SVDCDC)
• sPt/Pt 0.19Pt ? 0.30/b Belle
• sPt/Pt 0.13Pt 0.45 BaBar
• Mass(dE) resolution
• Mass resolution for inclusive J/y ? mm-
• 9.6 MeV(Belle) vs 12.3 MeV(BaBar)
• dE resolution for B0? D-p, D- ?Kp-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.
• DD- 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

28
Pulse height variation
Hokuue
29
Hit rate
Apr.-5th , 2005 IHER 1.24A ILER 1.7A Lpeak
1.5x1034 ICDC 1mA
Small cell
Inner
Main
10kHz
30
Small Cell Drift Chamber
31
Photo of small cell chamber
Installation in 2003 summer
Just after wire stringing
32
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
33
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(SVDCDC)
• 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

34
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

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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.