60 research outputs found
A RICH detector for strangeness physics in Hall A at Jefferson Lab
The high-resolution hypernuclear spectroscopy experiment at Jefferson Lab, Hall A (E94-107), needs unambiguous kaon identification. Due to the huge pion and proton background, the standard Hall A hadron particle identification, based on a time of flight and two aerogel threshold Cherenkov detectors, is not sufficient. For this task a proximity focusing C6F14/CsI RICH has been built. Recently, after some improvements to the mechanical structure of its wire chamber and to its electronics rate capability, the RICH has been tested with cosmic rays. This paper represents a status report of the RICH detector
Quantum efficiency measurement system for large area CsI photodetectors
A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported
Performance and results of the RICH detector for kaon physics in Hall A at Jefferson Lab
Abstract A proximity focusing RICH detector has been constructed for the hadron High Resolution Spectrometer (HRS) of Jefferson Lab Experimental Hall-A. This detector is intended to provide excellent hadron identification up to a momentum of 2.5 GeV / c . The RICH uses a 15 mm thick liquid perfluorohexane radiator in proximity focusing geometry to produce Cherenkov photons traversing a 100 mm thick proximity gap filled with pure methane and converted into electrons by a thin film of CsI deposited on the cathode plane of a MWPC. The detector has been successfully employed in the fixed target, high luminosity and high resolution hypernuclear spectroscopy experiment. With its use as a kaon identifier in the 2 GeV / c region, the very large contribution from pions and protons to the hypernuclear spectrum was reduced to a negligible level. The basic parameters and the resulting performance obtained during the experiment are reported in this paper
High Resolution Spectroscopy of 12B_Lambda by Electroproduction
An experiment measuring electroproduction of hypernuclei has been performed
in Hall A at Jefferson Lab on a C target. In order to increase counting
rates and provide unambiguous kaon identification two superconducting septum
magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A
standard equipment. An unprecedented energy resolution of less than 700 keV
FWHM has been achieved. Thus, the observed \lam{12}{B} spectrum shows for the
first time identifiable strength in the core-excited region between the
ground-state {\it s}-wave peak and the 11 MeV {\it p}-wave
peak.Comment: Paper submitted to Physical Review Letter
Spectroscopy of Lambda-9Li by electroproduction
In the absence of accurate data on the free two-body hyperon-nucleon
interaction, the spectra of hypernuclei can provide information on the details
of the effective hyperon-nucleon interaction. Electroproduction of the
hypernucleus Lambda-9Li has been studied for the first time with sub-MeV energy
resolution in Hall A at Jefferson Lab on a 9Be target. In order to increase the
counting rate and to provide unambiguous kaon identification, two
superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH)
were added to the Hall A standard equipment. The cross section to low-lying
states of Lambda-9Li is concentrated within 3 MeV of the ground state and can
be fitted with four peaks. The positions of the doublets agree with theory
while a disagreement could exist with respect to the relative strengths of the
peaks in the doublets. A Lambda separation energy of 8.36 +- 0.08 (stat.) +-
0.08 (syst.) MeV was measured, in agreement with an earlier experiment.Comment: 14 pages, 8 figure
The HERMES Spectrometer
The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of Il, D, and He-3. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon. (C) 1998 Elsevier Science B.V. All rights reserved
Investigation of the operational stability of plastic streamer tubes after polishing of their graphite cathode
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