Transcript ppt

The HERMES dual-radiator
RICH detector
Design and operating experience,
Options for improved performance
H. E. Jackson
On behalf of the HERMES Collaboration
Argonne National Laboratory
Office of Science
U.S. Department of Energy
A U.S. Department of Energy
Office of Science Laboratory
Operated by The University of Chicago
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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
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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 multianode pmt’s
Substantially improved performance is possible with same design
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