Gas-based tracking for SuperBelle Beam background Upgrade plan Summary Shoji Uno (KEK) April, 20-22, nd Joint Super B factory WS in Hawaii

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  The beam background became smaller even for higher beam current and higher luminosity.  We recognize the luminosity term is small, clearly.

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 10KHz Apr.-5 th,2005 I HER = 1.24A I LER = 1.7A L peak = 1.5x10 34 cm -2 sec -1 I CDC = 1mA Main Inner Small cell

Luminosity Dependences CDC BG did not change! Feb, 2004 Inner most Middle Outer

Hit rate at layer 35 I HER = 4.1A Hit rate = 13kHz I LER = 9.4A Hit rate = 70kHz Dec., 2003 : ~5kHz Now : ~4kHz Dec.,2003 In total 83kHz HER LER

Simulation Study for Higher Beam Background Detail was reported in the last WS by K.Senyo. MC +BGx1MC+BGx20

Tracking eff. with B     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.) Occupancy Overlay(times) B->  reconstruction eff. including geometrical acceptance Square root of recon. eff. of the left ~ single track efficiency of mid/high p

About 80% of efficiency is kept in the slow  efficiency under x20 occupancy. Reconstruction using SVD information is necessary to recover the loss of efficiency. Slow p efficiency from B  D*(Dp slow )p recon. eff. of the slow pion ~ single track efficiency of slow p B  D*  reconstruction eff. including geometrical acceptance

Occupancy Luminosity cm -2 sec -1 No. of channel N Total Readout time window (  sec) Q>0Q>50 N Hit Belle Babar ~700 ~350 Occ. = N Hit /N Total (%) Occ./Time window (%/  sec) Max. drift time (  sec) Occ./Time x Max. Drift time (%) Normalized by Lum.(%) Belle Babar ~ x20 Bkgd in Belle CDC ~ x3 Bkgd in Babar DCH Random trigger

at HL6 in KEK

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% CH 4  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 Small cell(5.4mm) Normal cell(17.3mm)

Baseline design CDC SVD

Main parameters Present Future Radius of inner boundary (mm) Radius of outer boundary (mm) Radius of inner most sense wire (mm) Radius of outer most sense wire (mm) Number of layers 5058 Number of total sense wires Effective radius for dE/dx measurement (mm) Gas He-C 2 H 6 Diameter of sense wire (  m) 30

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 : Number of total wires : ~60000

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 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 Only ~0.3% occupancy for LER particle background. Brian Petersen’s talk in HL6 Total LER Belle Babar Occupancy normalized by readout time window(%)

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?

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 a: ’93 Plastic tube d: ’94 SUS tube b: ’93 Plastic tube + O2 filter e: ’94 SUS tube + O 2 filter c: ’94 Plastic tube f: ’94 Plastic tube Total accumulated charge on sense wire(C/cm) Gain degradation

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 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 Good resolution was obtained. It is useful to identify hadrons and electrons. BhabhaMu pair M.I.P in Hadronic events 0.35<P<0.88GeV/c without any PID. Electron

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/ . log 10 P(GeV/c)

Comparison with Babar Momemtum resolution(SVD+CDC)  Pt /Pt = 0.19Pt  0.30/  [%] : Belle  Pt /Pt = 0.13Pt [%] : BaBar Mass(dE) resolution  Mass resolution for inclusive J/       9.6 MeV(Belle) vs 12.3 MeV(BaBar)  dE resolution for B 0  D   +, D   K +     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  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 2000 Summe r 2001 Summer 2002 Summer Summer 2004 Summer Change of bias voltage for preamp Installation of small cell chamber Replacing with new S/QT for layer 0 & 1 Hokuue

Hit rate 10kHz Apr.-5 th, 2005 I HER = 1.24A I LER = 1.7A L peak = 1.5x10 34 I CDC = 1mA Main Inner Small cell

Small Cell Drift Chamber

Photo of small cell chamber Installation in 2003 summerJust after wire stringing

Curved Endplate Deformation of endplate due to wire tension was calculated at design stage of present Belle CDC. Deformation(mm) Present New

Expected performance Occupancy  Hit rate : ~140kHz  ~7Hz X 20  Maximum drift time : nsec  Occupancy : 1-4%  140kHz X nsec = Momemtum resolution(SVD+CDC)  Pt /Pt = 0.19Pt  0.30/  [%] : Conservative  Pt /Pt = 0.11Pt  0.30/  [%] : Possible  0.19*(863/1118) 2 Energy loss measurement  6.9% : Conservative  6.4% : Possible  6.9*(752/869) 1/2

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 D3 D6 D9 D12

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.