RICH detector status report - Why How Were we are

E-94-107 - High Resolution 1p shell Hypernuclear Spectroscopy F. Garibaldi, S. Frullani, J. LeRose, P. Markowitz, T. Saito forward angle&very good PID are needed to be able to get reasonable counting rates and unambiguous kaon identification in order to clean up the huge background

p p Kaon Identification through Aerogels: p k p k All events AERO1 KAONS = AERO1•AERO2 Hypernuclei -> smaller scattering angle -> higher background --> something else is needed

RICH Process Rates signal (e,e’K) 10-4 – 10-2 accidentals (e,e’)(e,pi) (e,e’)(e,k) 100 0.1 Contamination of pion and proton on the K signal with different PID systems, for the counting rates of two levels (10-2 Hz and 10-4 Hz) without RICH with RICH

n fixed by the momentum(2GeV/c) Cos q =1/nb Db/b = tg Dq N = p.e. per ring Dq  D q /sqrt(N) n fixed by the momentum(2GeV/c) C6 F14, transparent down to 160 nm - compact (~ 50 cm) relatively thin (18% X0) 310 x 1820 mm2 quarz window 5 mm 15 mm 300 nm

Many parameters affect the detector performances (# p.e.) quartz transparency in the v.w. region of interest (160 - 220 nm) freon purity to not absorb the emitted Cherenkov light freon purity circuit + continuously monitoring CsI photocathode - evaporation + on line QE absolute measurement QE is strongly affected by oxygen and moisture Careful handling of photocathodes after evaporation Continuous monitoring of gas “purity”

3 PD

Probably underestimated 2200 V Jlab Cosmic tests June 03 G~ 2.5 x 105 A0=26 Extrapolating to q=0 and taking into account the geometric inefficiency and false triggers (cosmics): > ~ 12 p.e. (as at CERN) Probably underestimated (protons below threshold, random coincidences etc.)

detector ready end ofJuly The detector has been tested succesfully at CERN Novembre 2000 (12 p.e.(14-15 with CH4)) 2 photocathode evaporated respectively at CERN and ROME ---> same result ! (the best CERN had obtained with the same gas mixture) Neverthless increasing HV (2100 to 2200V) gain back p.e 10-12 (very difficult to estimate with cosmic, conservative) Fixing freon leakage ==> 12-14 p.e. (look at possible moisture contamination!) detector ready end ofJuly spare radiator spare f.e. electronics 3 spare radiators to be evaporated by end of July After trasportation, mechanical problems(a. w. to photocatode distance) lower gain --> lower # p.e. (Difficult to measure, difficult to fix) fixed July 2002 right gain back, but wait for freon Radiator accident Fixed, but still some leak ->quench --> lower gain (lower #p.e.) Slow control status to be checked (kaon meeting should be good (Jlab task) DAQ integration (see Bodo) Software - C++ code written by Guido being tested with CERN data for comparison with CERN (report next kaon mee. - improving the tracking (minimizing the angle error) using FPP?

Conclusions Detector ready to be installed when needed decision driven by Hall A installation schedule (eventual “last” evaporation not to be anticipated) only test missing: hight rate behaviour on Jlab beam the CERN experience (the only one available) says that we should not have problem but no tests are possible with a continuous beam) (type of problem: charging up of photocathode (CsI)) F.Piuz (Pilos proceedings): 24 hours with 6.4X10-10 Coulomb/mm2/s - in our case (Hall A, our experiment at 250 KHz we have 2 x 10-13 coulomb/mm2/s