Tests of a proximity focusing RICH with aerogel as radiator and flat panel PMT (Hamamatsu H8500) as photon detector Rok Pestotnik Jožef Stefan Institute, Ljubljana Slovenia for the Belle Aerogel RICH R+D group International conference on imaging techniques in subatomic physics, astrophysics, medicine, biology and industry Stockholm, Sweden 24 – 27 June 2003

Collaborators Belle Aerogel RICH R&D group Jožef Stefan Institute, Ljublijana, Slovenia P.Križan, S.Korpar, R.Pestotnik, S.Fratina Tokyo Metropolitan University, Tokyo, Japan T.Sumiyoshi, T.Matsumoto, T.Seki KEK, Tsukuba, Japan I.Adachi, K.Suzuki, S.Saitoh Nagoya University, Nagoya, Japan T.Iijima Chiba University, Chiba, Japan H.Kawai, T.Tabata, R.Ishibashi Toho University, Funakoshi, Japan S.Ogawa, Y.Uchida

Present Belle aerogel threshold Cherenkov K/  separation: K below and  above threshold for a given kinematic region e-e- 8 GeV B(1.5T) (8mx8mx8m) e+e+ 3.5 GeV

Upgrade Motivation of the Belle spectr. Physics motivation for PID upgrade  improve  /K separation in the forward ( high momentum ) region for few body decays of B mesons  good  /K separation b  d  /s  etc.  Low momentum(<1 GeV/c ) e/  /  separation ( B  Kll ) Upgrade:  A proximity focusing RICH with aerogel as radiator is being studied in the forward direction  Two body decay products have momenta of up to 4 GeV/c  Kinematic region 0.7~4 GeV/c,  /K separation>4 

Proximity focusing RICH with aerogel radiator  /K separation at 4 GeV/c, n=1.05   c (  ) = 308 mrad   c (  ) –  c (K) ~ 23 mrad    ~ 12 mrad (single photon)  N pe ~10  ~6  separation Particle identification: Tracking system  p Aerogel RICH   ch and N pe   particle mass m Due to a limited space available  proximity focusing type e-e- 8 GeV B(1.5T) (8mx8mx8m) e+e+ 3.5 GeV

Beam tests 1 st beam test(Nov./Dec. 2001): MAPMT(Hamamatsu R5900-M16) ✔   ~10mrad, N pe /ring ~ 2.7 ✔ Principle of operation understood. Increase N pe : Improve the aerogel transparency Use a detector with larger active area 2 nd beam test(Nov. 2002): 64 ch. Flat panel PMT (Hamamatsu H8500)

Aerogel radiator Aerogel for the Belle threshold Cherenkov detector was optimized for the range n=1.01~1.03 Optimization for n=1.05  Cooperation with Matsushita Co. Ltd. Transmission length was improved: 15mm  45 *Novosibirsk sample : hydrophilic Methyl-silicate-51 from different company Precursor Methyl alcohol  di-methyl- formamide(DMF) Solvent

Flat panel PMT (Hamamatsu H8500) Increase in active area 36% (M16)  84% of the total surface Segmented: 64ch (pixel size = 6 x 6mm 2 ) Photon detector pitch: 52.5 mm ✗ Sensitive to magnetic field * Still under developing… Bialkali photocathode  Large variation among 16 PMTs  peak Q.E. : 16~25% )  Gain : 1~6 x 10 6 Pulse height distribution for single Cherenkov photons * for the best PMT

Beam test – set up Refractive index of aerogel thickness of aerogel Carried out Nov KEK-PS  2 beam line  - beam momentum : (0.5 – 4.0 GeV/c) Main+Reference RICH Tracking: 2 MWPCs Readout for 1024 ch. Serialization: Analog memory (10  s/ch ) 256 ch. buffer VME-ADC A wide range of parameters was investigated: type of aerogel Beam momentum...

Cherenkov angle distribution Single event Accumulated hits Cherenkov angle reconstructed from track direction and hit on the detector Distribution for one event Accumulated distributions: Low level of scattered photons (Rayleigh scattering) Cherenkov angle distribution

Number of detected photons Momentum dependence Transmission length dependence Transmission length : 15mm  45mm  Increase in number of detected photons ~x1.5 For saturated rings : N pe ~ 6

Resolution in the Cherenkov angle Contributions: Emmision point uncertainty in the aerogel Finite pixel size of PMT Cromaticity n=n(  lower momentum region: important contribution of multiple scattering Typical resolution   ~ 13mrad Momentum dependence

 /K separation Measured N pe ~6,   ~13 mrad resolution per track:   /sqrt(N pe ) ~ 5.3 mrad *assuming contribution from bkg. is small   /K GeV/c  ~ 4  N pe for the best PMT N pe ~9 better separation is expected in the near future Cherenkov angle track distribution for  and  4 GeV/c 4GeV/c = 1.1 GeV/c)

e  separation Cherenkov angle distribution for single photons, at p=0.8 GeV/c Another benefit from such a counter: e  separation at low momenta, of importance for B  Kll decays

Summary Proximity focusing Aerogel RICH performed according to expectations  1 st Beam test(Nov.,2001)  the method is feasible.  2 nd Beam test(Nov.,2002) Better Aerogel, PMT with large effective area  enhanced number of photons, promising results The contributions to the resolution are well understood Remaining R&D issues  Development of a multianode photon detector for high magnetic fields (1.5 T)  Mass production of large aerogel tiles