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

2. Kaon Identification through Aerogels: AERO1 n=1.015 AERO2 n=1.055 p k KAONS = AERO1AERO2 p k All events Hypernuclei -> smaller scattering angle -> higher background --> something else is needed The PID Challenge Very forward angle ---> high background of and p -TOF and 2 aerogel in not sufficient for unambiguous K identification !

3. K AON Id Requirements ProcessRates signal(e,eK) bound state 10 -4 – 10- 2 accidentals (e,e)(e, ) (e,e)(e,p) (e,e)(e,k) 100 0.1 Very forward angle high background of p and p TOF and 2 threshold Cherenkov aerogel are NOT sufficient for unambiguous K identification RICH DETECTOR Signal Vs. Background

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

6. N. of detected photoelectrons N. of detected photoelectrons J LAB Hall A RICH M onte C arlo Simulations, K Separated by, K Separated by – K = 30 mrad, K Separated by 6.8, K Separated by 6.8 Separation power

7. J LAB Hall A RICH: some components

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

9. J LAB Hall A RICH OPERATING conditions Gas: Pure Methane (Minimize Photon Feedback, High Q.E.) High Voltage: ~ 2100 Volts for a gain of 8x10 4 Grid Voltage: 250 - 450 Volts Optimal trigger to read-out delay: ~ 400 ns (peaking time of gassiplex response) MIP charge and hit sizecluster charge and hit size

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

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

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

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

14. JLAB Hall A exp e94-107 Preliminary Results on 12 C Target Aerogel Kaon selection RICH Kaon selection 12 C(e,eK) 12 B Missing energy (MeV) Missing Energy Spectra:

17. 250 ps

18. - 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 p K K Pion rejection ~ 1000 Possible improvements

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

20. HV = 2100 VHV = 1900 V

22. R ich /K separation for p > 2.5 GeV/c Radiator C6F14 n=1.29 Ch ~ 5mr Radiator C5F12 n=1.24 Ch ~ 5mr 4 separation at ~ 2.5 GeV/c4 separation at ~ 3.0 GeV/c

26. aerogel photodetector particles Danilyuk, Novosibirsk, RICH2004 Produced in May 2004 = 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

27. PID algorithm is based on: 1.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 Č erenkov photon hits on the cathode planes 3. Calculation of the Cherenkov photon emission angle through Č erenkov 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 tests (one for each hypothesis on the kind of the particle) to check the obtained Č erenkov photon angle distribution with the expected one. 6. A procedure to cross out the signals from noise. This procedure is based on the test values and is performed when none of the hypothesis on the particle hitting the Rich seems statistically significant. - The rejection factor obtained with the algorithm described above is ~ 999/1000 RICH SOFTWARE PRESENT STATUS -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( )) To be done

28. C onclusions RICH detector : excellent Kaon Identification and clean Kaon signal over a large 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 ??