A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago Argonne National Laboratory Office of Science U.S. Department of Energy The HERMES dual-radiator RICH detector Design and operating experience, Options for improved performance H. E. Jackson On behalf of the HERMES Collaboration

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6 RICH operating parameters 2. Optimum aerogel thickness from test beam studies was 5 cm. 3. Pixel size was chosen for a yield of 12 pe’s and p max =15 GeV/c (and budget) to be 23.3 mm !  ¼ 6 mr

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9 RICH online monitoring - wk of 04 Apr ’04 On line performance monitor with single-track e § ’s Measure average angles for aerogel and gas rings for  =1 Measure average yields of photo electrons per track Aver.  aero =244 mr Aver.  gas = 54 mr Performance stable – no detectable change in angles or yields since 1998

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H. E. Jackson, RICH0413 Pentaquark search at HERMES  + identified in pK s reconstructed inv mass spectrum Hadron PID with RICH  : 1-15 GeV p: 4-9 GeV Essential function of RICH is background suppression Reject events from  (1116) decay to p  - with mass cut PL B585 (2004) 213

H. E. Jackson, RICH0414 Background suppression with RICH Use quality factor rQP to require higher probability of assignment relative to alternatives Pion PID is very clean (>98%) Main contamination of identified protons comes from misPID’s K’s rQP > 1.5 gives much cleaner proton sample at acceptable loss in proton PID efficiency rPQ>0 rPQ>1.5

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H. E. Jackson, RICH0416 RICH unfolding procedures Recently completed 1 st flavor decomposition of proton spin. Measured spin asymmetries for  ’s and K’s in SIDIS. Objective – high statistics for each hadron sample. Clean samples of  ’s and K’s obtained by unfolding with standard conditions, ie. rQP>0.

H. E. Jackson, RICH0417 RICH unfolding procedures(con’t) PRD, in press – A.Airapetian, et al.

H. E. Jackson, RICH0418 Summary and Future RICH continues to perform with no detectable deterioration. Improved aerogel options are available – edge effects can be substantially ameliorated. Composite mirror arrays with improved rigidity are available. Improved pixel resolution can be achieved with ½” pmt’s or multi-anode pmt’s Substantially improved performance is possible with same design