Proximity focusing RICH with TOF capabilities for the Belle upgrade Peter Križan University of Ljubljana and J. Stefan Institute For the Belle Aerogel RICH R&D group EPS HEP 2007, July 19-23 2007, Manchester, UK July 19, 2007 EPS HEP 2007, Manchester

Belle @ KEK-B in Tsukuba Tsukuba-san Belle KEKB ~diameter 1 km July 19, 2007 EPS HEP 2007, Manchester

Belle spectrometer at KEK-B  and KL detection system (14/15 layers RPC+Fe) Aerogel Cherenkov Counter (n=1.015-1.030) 3.5 GeV e+ Silicon Vertex Detector (4 layers DSSD) Electromag. Cal. (CsI crystals, 16X0) 8 GeV e- Central Drift Chamber (small cells, He/C2H6) ToF counter 1.5T SC solenoid Accumulated data sample ~700 M BB-pairs July 19, 2007 EPS HEP 2007, Manchester

PID upgrade in the endcap for the Super B factory improve K/p separation in the forward (high p) region for few-body decays of B mesons good K/p separation for b  dg , b  sg improve purity in fully reconstructed B decays low momentum (<1GeV/c) e/m/p separation (B  Kll) keep high the efficiency for tagging kaons July 19, 2007 EPS HEP 2007, Manchester

BELLE Aerogel RICH group I. Adachi, R. Dolenec, A. Petelin, K. Fujita, A. Gorišek, K. Hara, D. Hayashi, T. Iijima, T. Ikado, H. Kawai, S. Korpar, Y. Kozakai, P. Križan, A. Kuratani, Y. Mazuka, Y. Miyazawa, S. Nishida, I. Nishizawa, S. Ogawa, R. Pestotnik, T. Sumiyoshi, M. Tabata, M. Yamaoka Chiba University, Japan Toho University, Funabashi, Japan High Energy Accelerator Research Organization (KEK), Japan J. Stefan Institute, Ljubljana, Slovenia University of Ljubljana, Slovenia University of Maribor, Slovenia Nagoya University, Nagoya, Japan Tokyo University of Science, Noda Tokyo Metropolitan University July 19, 2007 EPS HEP 2007, Manchester

Contents Introduction, motivation and requirements Radiator with multiple refractive indices Time-of-flight measurement with a RICH Beam tests Photon detector R+D Summary July 19, 2007 EPS HEP 2007, Manchester

Proximity focusing RICH in the forward region Requirements and constraints: ● ~ 5 s K/p separation @ 1-4 GeV/c ● operation in magnetic field 1.5T ● limited available space ~250 mm Proximity focusing aerogel RICH - n = 1.05 - qc(p) ~ 308 mrad @ 4 GeV/c - qc(p)– qc(K) ~ 23 mrad pion threshold 0.44 GeV/c, kaon threshold 1.54 GeV/c - time-of-flight difference (2m): t(K) - t(p) = 180 ps @ 2 GeV/c 45 ps @ 4 GeV/c July 19, 2007 EPS HEP 2007, Manchester

Beam tests Clear rings, little background Photon detector: array of 16 H8500 PMTs July 19, 2007 EPS HEP 2007, Manchester

Beam tests: Cherenkov angle resolution and number of photons Beam test results with 2cm thick aerogel tiles: excellent, >4s K/p separation NIM A521(2004)367 but: Number of photons has to be increased.  July 19, 2007 EPS HEP 2007, Manchester

How to increase the number of photons? What is the optimal radiator thickness? Use beam test data on s0 and Npe s0 Npe Minimize the error per track: Optimum is close to 2 cm July 19, 2007 EPS HEP 2007, Manchester

Radiator with multiple refractive indices How to increase the number of photons without degrading the resolution? NIM A548 (2005) 383 NIM A565 (2006) 457  stack two tiles with different refractive indices: “focusing” configuration normal n1= n2 n1< n2 July 19, 2007 EPS HEP 2007, Manchester focusing radiator

Focusing configuration NIM A548 (2005) 383 4cm single index Npe=7.7 s0= 21 mrad, strack= 6.4 mrad 2+2cm, two indices Npe=7.5 s0= 14 mrad, strack= 4.6 mrad July 19, 2007 EPS HEP 2007, Manchester

Multilayer extensions Number of detected photons Single photon resolution Npe Resolution per track s0 Multiple layer radiators combined from 5mm and 10mm tiles Cherenkov angle resolution per track: ~4.3 mrad p/K separation at 4 GeV: better than 5s July 19, 2007 EPS HEP 2007, Manchester

Photon detector candidate for 1.5 T: MCP-PMT multi-anode PMTs BURLE 85011 microchannel plate (MCP) PMT: multi-anode PMT with two MCP steps good performance in beam and bench tests  very fast (s=50ps, single photons)  R+D: ageing July 19, 2007 EPS HEP 2007, Manchester NIM A567 (2006) 124

Photon detector candidate: H(A)PD -10kV 15~25mm e- Multialkali photocathode Pixel PD or APD 12 x 12 channels 65% effective area (59x59mm2) R&D project in collaboration with HPK After a considerable R&D effort we finally have two full size prototypes to study July 19, 2007 EPS HEP 2007, Manchester

Photon detector candidate: SiPM immune to magnetic field high single photon detection efficiency up to 70% good timing properties (~300ps FWHM) no high voltage low material budget high noise rate ~ 1MHz/mm2 radiation damage - increase of dark noise scan with single photons 1 mm e(K) @ 4 Gev/c  Increase signal to noise ratio by using narrow time (<10ns) window and light guides. July 19, 2007 EPS HEP 2007, Manchester

Additional feature: time-of-flight measurement Make use of fast photon detectors: measure time-of-flight with Cherenkov photons from aerogel radiator and PMT window Cherenkov photons from PMT window from aerogel MCP-PMT aerogel track START STOP Beam test: 50ps per single ph. (~20ps per track) ~35ps per track Cherenkov photons from the window can be used to positively identifiy particles below the threshold in aerogel July 19, 2007 EPS HEP 2007, Manchester

Summary A proximity focusing RICH with ~ 20 cm radiator to photon detector distance and ~ 6x6mm2 pads is being developed for the upgrade of the Belle forward PID. Single refractive index radiator has an optimal radiator thickness of ~ 2 cm; increasing the thickness results in degradation of Cherenkov angle resolution per track. Way out: use of multi layer radiator with varying refractive index Expected performance of the focusing configuration: excellent p/K separation up to 4 GeV/c More studies are needed to decide which photon detector to use for the Belle PID upgrade Such a counter can also be used for TOF measurement → extend PID capabilities into low momentum region July 19, 2007 EPS HEP 2007, Manchester

Back-up slides July 19, 2007 EPS HEP 2007, Manchester

Aerogel production R&D Going to thicker radiators: advantage only if aerogels have a high transmission length -> R+D Improved optical quality for n~1.05 hydrophobic aerogel with a new solvent and precursor 100x100x20mm3 n=1.050 Transmission length vs refractive index NIM A553 (2006) 146 No cracks July 19, 2007 EPS HEP 2007, Manchester

Optimisation of radiator parameters upstream aerogel: d=11mm, n=1.045 downstream aerogel layer: vary refractive index measured resolution in good agreement with prediction wide minimum allows some tolerance in aerogel production NIM A565 (2006) 457 Single photon resolution refractive index difference July 19, 2007 EPS HEP 2007, Manchester

Focusing configuration – low momentum Matching of indices: done for high momentum tracks (4GeV/c) How is the overlapping of rings at lower momenta? Good overlapping down to 0.6 GeV/c July 19, 2007 EPS HEP 2007, Manchester

Focusing configuration – momentum scan single photon resolution: dual radiator ~same as single (of half the thickness) for the full momentum range number of detected hits: dual radiator has a clear advantage Overlapp optimized at 4GeV/c-> OK at low momenta as well July 19, 2007 EPS HEP 2007, Manchester

Focusing configuration - inclined tracks 2+2cm aerogel angle 20o 2+2cm aerogel angle 30o Works as well! July 19, 2007 EPS HEP 2007, Manchester

PID capability - MC results simulation of the test setup with the level of background expected for Super Belle 3cm single radiator compared to 2x1.5cm focusing radiator (n~1.05) focusing radiator improves PID for momenta above ~3GeV July 19, 2007 EPS HEP 2007, Manchester

Photon detector: MCP-PMT multi-anode PMTs BURLE 85011 MCP-PMT: multi-anode PMT with two MCP steps 25 mm pores bialkali photocathode gain ~ 0.6 x 106 collection efficiency ~ 60% box dimensions ~ 71mm square 64(8x8) anode pads pitch ~ 6.45mm, gap ~ 0.5mm active area fraction ~ 52% Tested in combination with multi-anode PMTs sJ~13 mrad (single cluster) number of clusters per track N ~ 4.5 sJ~ 6 mrad (per track) -> ~ 4 s p/K separation at 4 GeV/c 10 mm pores required for 1.5T collection eff. and active area fraction should be improved aging study should be carried out July 19, 2007 EPS HEP 2007, Manchester

Time-of-flight with photons from the PMT window Benefits: Čerenkov threshold in glass (or quartz) is much lower than in aerogel. Cherenkov angle aerogel, n=1.05 Aerogel: kaons (protons) have no signal below 1.6 GeV (3.1 GeV): identification in the veto mode. Threshold in the window: K p Window: threshold for kaons (protons) is at ~0.5 GeV (~0.9 GeV):  positive identification possible. July 19, 2007 EPS HEP 2007, Manchester