SELEX RICH performance and physics results Page: 2 of 5

stream of the charm production tar-
get, with two analysis magnets with
800 MeV/c pt-kick each in-between,
and is surrounded by multi-wire pro-
portional and drift chambers which
provide particle tracking. The aver-
age number of tracks reaching the
RICH is about 5 per event. First re-
sults from this detector can be found
in [5]. A detailed description of the
detector itself is given in [6,7].
In this article we first describe
shortly the main parts of the detector
(vessel, mirrors, photon detector),
after this we will review its stability
during the run and performance for
physics analyses. Finally we report
about physics results obtained with
the help of the RICH up to now.
2 Description of the detector
A detailed description can be
found in [6]. Here we will repeat
the main features only. The SELEX
RICH detector consists of a 10.22m
long vessel with 93 in. diameter, filled
with pure Neon at atmospheric pres-
sure. After initial filling to a slight
(1 psi) overpressure, the vessel was
perfectly tight for a period of more
than 15 months.
At the end of the vessel an ar-
ray of 16 hexagonal spherical mir-
rors is mounted on a low-mass hex-
panel with 3-point mounts to form a
sphere of 19.8 m radius. Each mirror
is 10 mm thick, made out of low-
expansion class, and has a reflectivity
> 85 % at 160 nm. Before evaporat-
ing, the quality of every mirror was
measured [8].
The phototube matrix at the focal
plane consists of 2848 1/2 in. photo-

multipliers in a hexagonal closed
packed matrix of 89 columns in
32 rows. One column of 32 photo-
tubes is connected to one common
high voltage. In the center part, al-
ternating columns of Hamamatsu
R760 and FEU60 tubes are em-
ployed, and in the outer part only
FEU60 tubes are used. Every photo-
tube is connected to a preamplifier-
discriminator-ECL driver hybrid
chip, and the readout of the signals
is performed with a standard wire-
chamber electronics [9] with 170 nsec
integration time.
The whole vessel is tilted by 2.40
so particles are not passing through
the phototubes.
3 Performance of detector
The detector performance over
the 15 month running period was
very stable.
In the central region (mixed R760
and FEU60) we observed on aver-
age 13.6 photons for a # = 1 par-
ticle, corresponding to a figure of
merit [10] No = 104 cm-1, and in the
outside (only FEU60) we obtained
No = 70 cm-1.
The refractive index, measured
in several different ways, was stable
to better than 0.6%, which would
change the ring radius at # = 1 by
less than 10 % of its resolution.
The single photon resolution was
estimated to be 5.5 mm, with the
biggest contribution coming from
the size of the phototubes. The ring
radius resolution for the typical mul-
titrack environment was measured
at 1.56 mm. In fig. 1 we show the dis-
tribution of ring radii for single track

2

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al., Jurgen Engelfried et. SELEX RICH performance and physics results, article, August 28, 2002; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc734669/m1/2/ocr/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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