A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago

Argonne National Laboratory

Office of ScienceU.S. Department of Energy

The HERMES dual-radiatorRICH detector

Design and operating experience, Options for improved performance

H. E. Jackson

On behalf of the HERMES Collaboration

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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 pmax=15 GeV/c

(and budget) to be 23.3 mm ! ¼ 6 mr

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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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Pentaquark search at HERMES

+ identified in pKs 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

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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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PLB 585 (2004) 213

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RICH unfolding procedures

Recently completed 1st 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.

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RICH unfolding procedures(con’t)

PRD, in press – A.Airapetian, et al.

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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