the hermes dual-radiator rich detector

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

H. E. Jackson, RICH042

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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

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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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