PID Nagoya univ1 The possibility of improving TOP counter Nagoya university Yuji Enari

PID Nagoya univ2 Introduction mention about the  /K separation of TOP counter, especially about effect of group velocity of the photon. Definition of Separation. S = ・ N ph  TOP +  TOF tt S 1ph = Separation of single photon  TOP,TOF : time difference of pi/K (K-pi)  t : Time resolution N ph : Number of detected Photo-electron

PID Nagoya univ3 Time difference  TOP and  TOF TOF TOP  TOP +  TOF = 200ps TOP counter measures time difference btw  /K

PID Nagoya univ4 Uncertainty of TOP measurement.  If we choose to use bar-TOP, this effect is negligible.

PID Nagoya univ5 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.b. a.a.

PID Nagoya univ6 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

PID Nagoya univ7 TOP difference and Nph in Belle detector 30° 45° 60° 90° 120° 140°  TOP :  TOF : Nph : ～ 90 ～ 60 ～ 40 ～ 30 ～ 40 ～ 65 P = 3.5GeV/c, bar thick = 20mm

PID Nagoya univ8 Expected TOP counter’s performance in Belle. Separation of single photo-electron and S mean = 390nm,  tts = 75ps Number of detected photon S 1ph S Hard to separate  /K around  in = 45, p=3.5GeV/c region

PID Nagoya univ9 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)

PID Nagoya univ10 Correlation between TTS and wave length.  tts = 100ps  tts = 50ps P = 3.5GeV/c, in Belle system Separation of single photo-electron S=3 S=5.5  We have to use long wave length with  tts < 50 ps. S 1ph

PID Nagoya univ11 wave length : peak = 490nm with high peak ) time resolution :  tts =50ps bar thick = 20mm bar thick = 40mm

PID Nagoya univ12 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.

PID Nagoya univ13 Silicon Photo-Multiplier

PID Nagoya univ14 What’s SiPM SiPM – a kind of multi pixel Avalanche Photo Diode. –Operate in limited Geiger mode. pixel size : 42 ×42 mm 2 Merit? –Available in magnetic field. –High Q.E. at long wave length (very attractive for TOP counter), –High gain. –Good time resolution Etc.etc.

PID Nagoya univ15 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 : Q pixel = C pixel ・ (V bias – V beakdown ) – C pixel  100fF  Q pixel  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

PID Nagoya univ16 Performance of SiPM Pulse shape Gain Linearity and dynamic range. Detection efficiency Noise – temperature dependence. Time resolution

PID Nagoya univ17 pulse height spectra SiPM has good energy resolution as long as 2 photons enter in same pixel.

PID Nagoya univ18 Detection efficiency

PID Nagoya univ19 Noise

PID Nagoya univ20 Time resolution  ～ 50ps

PID Nagoya univ21 Comparison to another detector

PID Nagoya univ22 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. (1mm 2  20mm ×200mm?) –Enlarge the effective area in each pixel. (  = 0.3  0.5) –Noise

PID Nagoya univ23 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 3 rd BEAUNE conference and its proceeding