Transcript PowerPoint プレゼンテーション - University of Hawaii

Drift chamber for super-Belle
Shoji Uno (KEK)
Jan-20th, 2003 at Super B-factory WS in Hawaii

Present performance and background
 Idea for upgrade
 Upgrade plan
 Summary
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.

Can the wire chamber survive at S-KEKB?
 Answer is ” Yes”.
 My talk and Senyo’s talk.
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.
dE/dx Resolution
Bhabha
Mu pair

Good resolution
was obtained.

It is useful to
identify hadrons
and electrons.
M.I.P
in Hadronic events
0.35<P<0.88GeV/c
without any PID.
Electron
Hit Rate

~200kHz for inner most layers.
 Chamber itself was working.
 No significant gain degradation
was observed for four years
operation.
 Exceeds 0.2C/cm.

CDC
Exp 27 Run 206
HER 1.1A
LER 1.5A
L=9.6x1033cm-1s-1
5-10KHz for most of layers.
 Quite small.
 The gas chamber can work at 20
times higher beam background.
Inner most part was replaced
with a new chamber in the last
summer.
 At S-KEKB, it will be covered
with a silicon detector.

Cathode
Inner
Main
Layer
Total Current Draw of CDC

Total CDC current(8400 wires)
has kept about 1mA at the
maximum beam current for
each years.

Vacuum condition is improving
from year to year.

Better masking system has
been adopted for fixed masks
near IP and movable masks in
arc section.
Gain degradation
Radiation Damage Test
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
Simulation Study for Higher Beam Background
Detail will be reported by K.Senyo.
MC +BGx1
MC+BGx20
Idea for upgrade

In order to reduce occupancy,
 Smaller cell size
 More wires.  smaller hit rate for each wire.
 Shorter maximum drift length  shorter maximum drift time.
 A new small cell drift chamber was constructed((Maximum drift length is
2.5mm).
 Inner most three layers were replaced with the new chamber in the last
summer.
 Faster drift velocity
 Shorter maximum drift time.
 One candidate : 100% CH4  Drift time simulation shows maximum
drift time is similar to the present gas due to a large Lorentz angle.
More study
Small Cell Drift Chamber
Photo of small cell chamber
Just after wire stringing
Installation in the last summer
XT Curve & Max. Drift Time
Normal cell(17.3mm)
Small
cell(5.4mm)
Drift Velocity

Two candidate gases
were tested.
 CH4 and He-CF4

In case of He-CF4, higher
electric field is necessary
to get fast drift velocity.

In case of CH4, faster drift
velocity by factor two or
more can be obtained,
even in rather lower
electric field.
dE/dx Resolution

The pulse heights for
electron tracks from 90Sr
were measured for
various gases.

The resolutions for CH4
and He(50%)C2H6(50%) are same.

The resolution for HeCF4 is worse than Arbased gas(P-10).
xt curve for 7mm cell
He/C2H6 = 50/50
100nsec
Distance from wire (cm)
Pure CH4
100nsec
Distance from wire (cm)
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

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.

In order to reduce deformation of endplates,
 The endplate with a different shape is considered.
 Wire tension of field wires will be reduced.
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
Baseline design
CDC
SVD
Main parameters
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
Number of total sense wires
Effective radius of dE/dx measurement (mm)
Gas
Diameter of sense wire (mm)
Present
77
Future
160
880
88
863
1140
172
1120
50
8400
752
58
15104
978
He-C2H6 He-C2H6
30
30
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
Summary

Present CDC is working well.
Good momentum resolution is obtained even for low
momentum range.
Energy loss measurement is also good.
Beam background is manageable range.
 Vacuum condition is still improving.

New CDC
Smaller cell size for inner most layers.
New gas with a fast drift velocity is preferred.
Larger outer radius
 Better performance is expected.
Chamber Gas

He(50%)-C2H6(50%)
 Longer radiation length(680m).
 Drift velocity is higher than other He-based gas.
 Average drift velocity : ~3.3cm/msec in the chamber cell.
 Maximum drift time : ~400nsec for 18mm cell size.
 Good dE/dx resolution.

Gas system
 Gas circulation( Flow rate : 3.0 liter/min).
 Fresh gas( Input flow rate : 0.3 liter/min).
 Keeping an absolute pressure constant.
 O2 contamination ~50ppm (with O2 filter)
 H2O contamination ~500ppm ( no control )
Momentum Resolution


We could obtain a small
constant term using Hebased 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.
s Pt / Pt (%)
CDC only :~ 0.28Pt  0.35 / b %
CDC  SVD :~ 0.19Pt  0.30 / b %
Transverse Momentum(GeV/c)
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.
log10P(GeV/c)
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

Total accumulated
charge.
2000
Layer 1
 >0.2 coulomb/cm at inner
most layer for 4 years.

Layer 49
No significant
deterioration, so far.
Layer 3
Layer 49
Layer 1
2002
Layer 3
CH4

Faster drift velocity
Factor two faster than He(50%)-C2H6(50%)

Long radiation length
Same as He(50%)-C2H6(50%)

Good dE/dx resolution
Same resolution is expected from a test using
electron from 90Sr.

Small radiation damage
Similar performance as He(50%)-C2H6(50%)
Electron Drift Simulation

Electron drift simulation in gas volume was done by
A.Sugiyama of Saga Univ., recently.
 He/C2H6=50/50(present gas) and pure CH4 under
1.5 Tesla.
 Small cell size(7mm) and normal cell size(18mm)
Maximum drift time for pure CH4 is not shorter than
the present gas due to large Lorentz angle.
 Simulation shows He/CH4 =50/50 is slightly better
than the present gas.
 Smaller ionization loss  Worse spatial resolution and worse dE/dx
resolution?
Drift line for 7mm cell
He/C2H6 = 50/50
Pure CH4
Wire configuration
Super-layer structure
 6 layers for each super-layer

 at least 5 layers are required for track reconstruction.
 Even number is preferred for preamp arrangement on
support board to shorten signal cable between feedthrough and preamp.

Additional two layers in inner most superlayer and outer super-most layer.
 Higher hit rate in a few layers near wall.
 Inner most layer and outer most layer are consider as
active guard wire.
Problems and Cures

Cross Talk
 Coaxial cable between pin and preamp.
 Better grounding is also effective.
 We replaced all cables with coaxial ones in summer 2003.
 Then, electronics parameter will move back original one.

High background around inner most layer
 Enlarge inner radius : 7.7cm  16cm
 Smaller cell size : 8.6mm(64 in f)  6.8mm (160 in f)
 One inner cylinder  No additional wall
 Inner most layer should be considered as a guard wire(active).

3D Tracking(especially, low momentum tracks)
 6(?) layers SVD
 6 layers in stereo super layer
 Better track reconstruction program.
 Charge division?