Drift chamber for super-Belle

Present performance and background Idea for upgrade Upgrade plan Summary

Shoji Uno (KEK)　　　Jan-20th, 2003 at Super B-factory WS in Hawaii

Wire chamber Wire chamber is a good device for the centr

al 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

Good resolution was obtained.

It is useful to identify hadrons and electrons.

Bhabha Mu pair

M.I.P in Hadronic events

0.35<P<0.88GeV/cwithout any PID.

Electron

Hit Rate ~200kHz for inner most layers.

Chamber itself was working. No significant gain degradation wa

s observed for four years operation.

Exceeds 0.2C/cm.

5-10KHz for most of layers. Quite small. The gas chamber can work at 20 ti

mes 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.

Layer

Hit

rat

e/w

ire (

k Hz)

CDC

Exp 27 Run 206

HER 1.1ALER 1.5AL=9.6x1033cm-1s-1

MainInner

Cathode

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.

Radiation Damage Test

a: ’93 Plastic tube d: ’94 SUS tubeb: ’93 Plastic tube + O2 filter e: ’94 SUS tube + O2 filterc: ’94 Plastic tube f: ’94 Plastic tube

Total accumulated charge on sense wire(C/cm)

Gai

n de

grad

atio

n

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 sizeMore 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 velocityShorter 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

Installation in the last summerJust after wire stringing

XT Curve & Max. Drift Time

Small cell(5.4mm)

Normal cell(17.3mm)

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 He-CF

4 is worse than Ar-based

gas(P-10).

xt curve for 7mm cell

Distance from wire (cm)

Pure CH4

100nsec

Distance from wire (cm)

Dri

ft ti

me

(se

c)

Dri

ft ti

me

(se

c )

He/C2H6 = 50/50

100nsec

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 ot

her 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

Present FutureRadius of inner boundary (mm) 77 160Radius of outer boundary (mm) 880 1140Radius of inner most sense wire (mm) 88 172Radius of outer most sense wire (mm) 863 1120Number of layers 50 58Number of total sense wires 8400 15104Effective radius of dE/dx measurement (mm) 752 978Gas He-C2H6 He-C2H6

Diameter of sense wire (m) 30 30

Expected performance

OccupancyHit 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) Pt/Pt = 0.19Pt 0.30/[%] : Conservative Pt/Pt = 0.11Pt 0.30/[%] : Possible 0.19*(863/1118)2

Energy loss measurement 6.9% : Conservative6.4% : 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 CDCSmaller 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/sec in the chamber cell. Maximum drift time : ~400nsec for 18mm cell size.

Good dE/dx resolution.

Gas systemGas 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 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)

(%)/ PtPt

% /35.028.0:~ PtonlyCDC

%/30.019.0:~ PtSVDCDC

dE/dx Measurement MQT chip (Charge to T

ime 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/.

log10P(GeV/c)

Comparison with Babar

Momemtum resolution(SVD+CDC) Pt/Pt = 0.19Pt 0.30/[%] : Belle

Pt/Pt = 0.13Pt + 0.45 [%] : BaBar

Mass(dE) resolution Mass resolution for inclusive J/

9.6 MeV(Belle) vs 12.3 MeV(BaBar)

dE resolution for B0 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

Total accumulated charge.>0.2 coulomb/cm at inner

most layer for 4 years.

No significant deterioration, so far.

2000

2002

Layer 49

Layer 49

Layer 1

Layer 1

Layer 3

Layer 3

CH4

Faster drift velocityFactor two faster than He(50%)-C2H6(50%)

Long radiation lengthSame as He(50%)-C2H6(50%)

Good dE/dx resolutionSame resolution is expected from a test using electro

n from 90Sr.

Small radiation damageSimilar 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 feed-through and preamp.

Additional two layers in inner most super-layer 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 ) 6.8mm (160 in ) 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?