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 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 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.-5th ,2005IHER = 1.24AILER = 1.7ALpeak = 1.5x1034cm-2sec-1

ICDC = 1mA

Main

Inner

Small cell

Luminosity Dependences

CDC BG did not change!

Feb, 2004

Inner most

Middle

Outer

Hit rate at layer 35　410I**2 + 1400*I + 80

0

200

400

600

800

1000

1200

1400

1600

0 0.2 0.4 0.6 0.8 1

HER Beam Current(A)

Hit

rat

e(H

z)

740I**2 + 470*I + 80

0

500

1000

1500

2000

2500

3000

0 0.5 1 1.5 2

LER Beam Current(A)H

it R

ate

(Hz)

IHER = 4.1A Hit rate = 13kHzILER = 9.4A Hit rate = 70kHz

Dec., 2003 : ~5kHzNow : ~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 +BGx1 MC+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) 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 Slow p efficiency from BBDD*(*(DDppslowslow)p)p Slow p efficiency from Slow p efficiency from BBDD*(*(DDppslowslow)p)p

recon. eff. of the slow pion~ single track efficiency of slow p

BD* reconstruction eff. including geometrical acceptance

Occupancy

Luminosity

1034cm-2sec-1

No. of channel

NTotal

Readout time window

(sec)

Q>0 Q>50

NHit

Belle 1.5 8464 6 - 300

Babar 0.8 7104 2 ~700 ~350

Occ. = NHit/NTotal

(%)

Occ./Time window

(%/sec)

Max. drift time

(sec)

Occ./Time x Max. Drift time (%)

Normalized by Lum.(%)

Belle 3.5 0.58 0.4 0.23 0.15

Babar 4.9 2.45 ~0.6 1.47 1.84

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 sizeA new small cell drift chamber was constructed and installed. It has been working, well.

Faster drift velocityOne 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

Small cell(5.4mm)

Normal cell(17.3mm)

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 for dE/dx measurement (mm) 752 978Gas He-C2H6 He-C2H6

Diameter of sense wire (m) 30 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 : 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.

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 CDC12.6% 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 0.58 0.23

Babar 2.45 0.074

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 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

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)

(%)/ PtPt

% /35.028.0:~ PtonlyCDC

%/30.019.0:~ PtSVDCDC

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

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

2000 Summer

2001 Summer

2002 Summer

20003Summer

2004Summer

Change of bias voltagefor preamp

Installation ofsmall cell chamber

Replacing withnew S/QT for layer 0 & 1

Hokuue

Hit rate

10kHz

Apr.-5th , 2005IHER = 1.24AILER = 1.7ALpeak = 1.5x1034

ICDC = 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) 35.2 2.03 1.31

Present New

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

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 LER4(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.