RICH status report Transversity Meeting A March 05 -Jlab

1. RICH status report Transversity Meeting A March 05 -Jlab • Detector Performances • Possible upgrade

2. Kaon Identification through Aerogels: The PID Challenge p p k All events p k p AERO1 n=1.015 AERO2 n=1.055 KAONS = AERO1•AERO2 Hypernuclei -> smaller scattering angle -> higher background --> something else is needed • Very forward angle ---> high background of p and p • TOF and 2 aerogel in not sufficient for unambiguous K identification !

3. KAON Id Requirements Signal Vs. Background • Very forward angle  high background of p and p • TOF and 2 threshold Cherenkov aerogel are NOT sufficient for unambiguous K identification • RICH DETECTOR

4. JLAB RICH detector, similar to the ALICE and STAR RICH “MIP” Cherenkov angle resolution Separation power Relevant quantities: NP.E. N. of detected photons AND sq angular uncertainty

6. JLAB Hall A RICH MonteCarlo Simulations N. of detected photoelectrons Separation power p, K Separated by qp – qK = 30 mrad p, K Separated by  6.8 s

7. JLAB Hall A RICH: some components

8. Rich MWPC performance at lower HV HV = 2100 V HV = 1900 V

9. JLAB Hall A RICH OPERATING conditions • Gas: Pure Methane (Minimize Photon Feedback, High Q.E.) • High Voltage: ~ 2100 Volts for a gain of 8x104 • Grid Voltage: 250 - 450 Volts • Optimal trigger to read-out delay: ~400 ns (peaking time of gassiplex response) MIP charge and hit size cluster charge and hit size

10. RICH Performances – key parameters p Cherenkov angle reconstruction Npe for p and P Nclusters Cherenkov average angle (rad) Npep/p ratio : Angular resolution :

11. RICH Performances – PID p/K population ratio Aero Selected p Angular resolution Aero Selected K (!) Aero Selected P Separation power Aero Selected K on a large sample of filtered data This would accept ~ 10-4 pions x p/K ratio 1/100 pion contamination …. But NON GAUSSIAN TAILS GIVE AN IMPORTANT CONTRIBUTION ! Kaon selection:

12. Rich – PID – Kaon selection results : Time of coincidence for Aerogel Selected Kaons w/o and w/ rich : AERO K AERO K && RICH K p P K

13. RICH – PID – Pion rejection factor : Time of coincidence for Aerogel Selected Pions: effect of Rich Kaon selection AERO p && RICH K AERO p p p N.Evts in the peak Backgnd subtr. = 64656 N.Evts in the peak Backgnd subtr. = 63 Pion rejection ~ 1000

14. JLAB Hall Aexp e94-107 PreliminaryResults on12C Target Missing Energy Spectra: Aerogel Kaon selection 12C(e,e’K)12BL RICH Kaon selection Missing energy (MeV)

17. 250 ps

18. p p Pion rejection ~ 1000 K K Possible improvements - MWPC stability for high rates For single rates ≤ 60 KHz HV=2100 V is OK In the range 60 KHz – 100 KHz HV=2075 V is OK Above 100 KHz HV must be reduced further (running at reduced gain with moderately good performance seems to be feasable) - p/K separation for p>2.5 GeV/c Doable “just”replacing the radiator DAQ rate bottleneck (~1 KHz) can be ovecome replacing part of the readout

19. RICH electronics upgrade: The HMPID ALICE RICH DAQ scheme fbD[27..0] fbD[31..0] VME to Local Bus Interface LOC_ADD[11..0] LOC_ADD[3..0] DILO 5 Boards (ADC and DILOGIC) Column Controller (1 to 8) Segment Controller LOC_CS GASSIPLEX LOC_CS LOC_R/Wn LOC_R/Wn RCB BOARD SEGMENT Front end digitization/ multiplexing On board 48 multiplexed channels (instead of 240) Clock rate up to 10 MHz

20. HV = 2100 V HV = 1900 V

22. Rich p/K separation for p > 2.5 GeV/c Radiator C5F12 n=1.24 sCh~ 5mr Radiator C6F14 n=1.29 sCh~ 5mr 4 s separation at ~ 2.5 GeV/c 4 s separation at ~ 3.0 GeV/c

26. Danilyuk, Novosibirsk, RICH2004 aerogel photodetector particles L = 4.4 cm at 400 nm Layer t n n mm desired measured 1 6.0 1.030 1.0297 2 6.3 1.027 1.0268 3 6.7 1.024 1.0234 4 7.0 1.022 1.0213 Produced in May 2004

27. RICH SOFTWARE PRESENT STATUS • PID algorithm is based on: • recognition of the “Clusters” (that is continue spots of fired pads) on the cathode planes. • 2. Identification of the baricenters of the clusters with the Čerenkov photon hits on the cathode planes • 3. Calculation of the Cherenkov photon emission angle through Čerenkov photon hits on the cathode planes. • 4. Calculation of the average of the Cherenkov photon angle distribution and check of the value obtained with the expected emission angle (three checks, one for each hypothesis on the particle to be identified: Pion, Kaon and Proton). • 5. Three c2 tests (one for each hypothesis on the kind of the particle) to check the obtained Čerenkov photon angle distribution with the expected one. • 6. A procedure to cross out the signals from noise. This procedure is based on the c2 test values and is performed when none of the hypothesis on the particle hitting the Rich seems statistically significant. • - The p rejection factor obtained with the algorithm described above is ~ 999/1000 To be done • -A better method to determine the Cherenkov photon hits on the pad plane (so far identified with the baricenters of the clusters) will be used. This method will employ an algorithm (Mathieuson formula) that takes in account more accurately of the charge distribution in the pads. • -The systematic errors in the particle entrance angles in the RICH will be lowered using a new algorithm. The particle entrance angles will be assumed as those that make the Cherenkov photon angle distribution variance minimum (so far particle entrance angles in the RICH are given by the tracking chambers). • An accurate check on RICH parameters (above all the radiator refraction index) will be performed. • -The RICH analysis code is still slow. Some improvements has to be done to make it faster. • - Correction for temperature variation (n())

28. Conclusions • RICH detector : excellent Kaon Identification and clean Kaon signal over a large p and p background for p=2 GeV/c (5 ) • limited speed (~ 1KHz) --> electronic upgrade (~ 2KHz) ongoing • separation @2.4 GeV/c : 3.9 sigma (extrapolated) • possible improvement(s): • Changing radiator and proximity gap • ~ 5sigma @2.4 geV/c • ~3 Sigma at 3 GeV/c • Dual radiator for further improvement ??