2002.8.31 PID meeging @ Nagoya univ 1

The possibility of improving TOP counter

Nagoya university

Yuji Enari

2002.8.31 PID meeging @ Nagoya univ 2

Introduction

• mention about the /K separation of TOP counter,

especially about effect of group velocity of the photon.

• Definition of Separation.

S = ・ Nph

TOP + TOF

t

S1ph = Separation of single photon

TOP,TOF : time difference of pi/K (K-pi)t : Time resolution

Nph : Number of detected Photo-electron

2002.8.31 PID meeging @ Nagoya univ 3

Time difference TOP and TOF

TOFTOP

TOP + TOF = 200ps

TOP counter measures time difference btw /K

2002.8.31 PID meeging @ Nagoya univ 4

Uncertainty of TOP measurement.

If we choose to use bar-TOP, this effect is negligible.

2002.8.31 PID meeging @ Nagoya univ 5

The chromatic effect.

The chromatic effect consists of 2 component.

a. Cherenkov angle Determined by the reflective index

b. Light velocity Determined by ‘Group’ index

a : b = -1 : 2 chromatic (1/n ・ n)These two contribution work oppositely.

b.

a.

2002.8.31 PID meeging @ Nagoya univ 6

The measurement of TOP resolution

• From the Beam test result.

– With improved polishing accuracy of the quartz bar.

– This result is limited by chromatic effect (at large L).

Estimate pi/K separability in the Belle detector

2002.8.31 PID meeging @ Nagoya univ 7

TOP difference and Nph in Belle detector

30° 45° 60° 　 90° 120° 140°

TOP : -3.6 -1.4 14.6 110.0 14.6 　　 2.7

TOF : 62.6 44.2 36.1 31.3 36.1 40.84

Nph : ～ 90 ～ 60 ～ 40 ～ 30 ～ 40 　　 ～ 65

P = 3.5GeV/c, barthick = 20mm

2002.8.31 PID meeging @ Nagoya univ 8

Expected TOP counter’s performance in Belle.

• Separation of single photo-electron and S

mean = 390nm, tts = 75ps

Number of detectedphoton

S1p

h

S

Hard to separate /K around in = 45, p=3.5GeV/c region.

30 45 60 90 140

2002.8.31 PID meeging @ Nagoya univ 9

How we can do?

• Increase photon statistics– Use High Q.E. material (Ga ・ As or APD?)– Use thicker quartz bar. (20mm 40mm)

• Improve time resolution.– Use long wave length region (n get small)– (and) use good photon detector(T.T.S < 50ps)

2002.8.31 PID meeging @ Nagoya univ 10

Correlation between TTS and wave length.

tts = 100ps tts = 50ps

P = 3.5GeV/c, in Belle systemSeparation of single photo-electron

S=3

S=5.5

We have to use long wave length with tts < 50 ps.

S1p

h

2002.8.31 PID meeging @ Nagoya univ 11

• wave length : peak = 490nm with high Q.E.(20%@peak) time resolution : tts=50ps

barthick = 20mm barthick = 40mm

2002.8.31 PID meeging @ Nagoya univ 12

Summary

• The chromatic effect make the largest uncertainty.

• To get good performance in Belle system,– Measure long wave length region.– Use good Photon detector which has TTS of 50 ps.– Need good Q.E. material.(Q.E.×C.E.> ２０％ ?)– Workable in 1.5T magnetic field

Photon detector R&D is very very important.

2002.8.31 PID meeging @ Nagoya univ 13

Silicon Photo-Multiplier

2002.8.31 PID meeging @ Nagoya univ 14

What’s SiPM

• SiPM– a kind of multi pixel Avalanche Photo Diode. – Operate in limited Geiger mode.

pixel size : 42 ×42 mm2

• Merit?– Available in magnetic field.– High Q.E. at long wave length (very at

tractive for TOP counter) ,– High gain.– Good time resolution Etc.etc.

2002.8.31 PID meeging @ Nagoya univ 15

Geiger-mode Avalanche photo diode

• Limited Geiger-mode in SiPM

– Under bias voltage of 10-20% more than break down voltage.

– Geiger discharge is stopped when bias goes down below b.d. voltage.

– Gain :• Qpixel = Cpixel ・ (Vbias – Vbeakdown)

– Cpixel 100fF Qpixel 100pC

Close up view of pixel

All pixel(576pixel) are connected by common Al strip. each pixel operates as a binary device, works as an analogue detector.

Vbias ～　５０ V

2002.8.31 PID meeging @ Nagoya univ 16

Performance of SiPM

• Pulse shape

• Gain

• Linearity and dynamic range.

• Detection efficiency

• Noise – temperature dependence.

• Time resolution

2002.8.31 PID meeging @ Nagoya univ 17

pulse height spectra

SiPM has good energy resolution as long as 2 photons enter in same pixel.

2002.8.31 PID meeging @ Nagoya univ 18

Detection efficiency

2002.8.31 PID meeging @ Nagoya univ 19

Noise

2002.8.31 PID meeging @ Nagoya univ 20

Time resolution

～ 50ps

2002.8.31 PID meeging @ Nagoya univ 21

Comparison to another detector

2002.8.31 PID meeging @ Nagoya univ 22

Summary

• SiPM is very good application for TOP counter.• High Q.E. High gain, single photon sensitive.• Good timing resolution.• Workable in strong magnetic field of 1.5T.

• To be use in TOP counter…– Size. (1mm2 20mm ×200mm?)– Enlarge the effective area in each pixel. ( = 0.3 0.5)– Noise

2002.8.31 PID meeging @ Nagoya univ 23

Reference

1, B.Dolgoshein (Moscow Engineering and Physics Institute)

- An Advanced study of Silicon Photomultiplier

ICFA instrumentation Bulletin

- The silicon photomultiplier and its possible application

transparency of 3rd BEAUNE conference

and its proceeding