A radial time projection chamber for α detection in CLAS at JLab Dupré, R.; Stepanyan, S.; Hattawy, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2018, Volume:
898, Issue:
C
Journal Article
Peer reviewed
Open access
A new Radial Time Projection Chamber (RTPC) was developed at the Jefferson Laboratory to track low-energy nuclear recoils to measure exclusive nuclear reactions, such as coherent deeply virtual ...Compton scattering and coherent meson production off 4He. In 2009, we carried out these measurements using the CEBAF Large Acceptance Spectrometer (CLAS) supplemented by the RTPC positioned directly around a gaseous 4He target, allowing a detection threshold as low as 12 MeV for 4He. This article discusses the design, principle of operation, calibration methods and performances of this RTPC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Quasielastic 12C(e, e′p) scattering was measured at spacelike 4-momentum transfer squared Q2 = 8, 9.4, 11.4, and 14.2 (GeV/c)2, the highest ever achieved to date. Nuclear transparency for this ...reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no Q2 dependence, up to proton momenta of 8.5 GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured Q2 scales in exclusive (e, e′p) reactions. These results impose strict constraints on models of color transparency for protons.
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The electromagnetic calorimeters of the various magnetic spectrometers in Hall C at Jefferson Lab are presented. For the existing High Momentum Spectrometer (HMS) and Short Orbit Spectrometer (SOS), ...design considerations, relevant construction information, and comparisons of simulated and experimental results are included. The energy resolution of the HMS and SOS calorimeters is better than σ/E∼6%/E and pion/electron (π/e) separation of about 100:1 has been achieved in the energy range of 1–5GeV. Good agreement has been observed between the experimental and simulated energy resolutions, but simulations systematically exceed experimentally determined π− suppression factors by close to a factor of two. For the Super High Momentum Spectrometer (SHMS), presently under construction, details on the design and accompanying GEANT4 simulation efforts are given. The anticipated performance of the new calorimeter is predicted over the full momentum range of the SHMS. Good electron/hadron separation is anticipated by combining the energy deposited in an initial (preshower) calorimeter layer with the total energy deposited in the calorimeter.
•Construction and performance of lead glass calorimeters in JLab/Hall C are presented.•∼5%/E resolution, ∼100:1π/e separation is achieved in HMS calorimeter in GeV range.•Simulated resolution of the HMS calorimeter is in good agreement with experiment.•Simulated pion suppression of the HMS calorimeter exceeds experiment, by less than 2.•Pion suppression of ∼400:1 is predicted in projected SHMS calorimeter by simulations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The High-Resolution Spectrometers in Hall A at Jefferson Laboratory have been instrumented with state-of-the-art Vertical Drift Chambers designed and constructed by the Nuclear Interactions Group at ...MITLNS in conjunction with the Physics Division at Jefferson Lab. These chambers rely on a unique, high cell-density design made possible by the absence of field-shaping wires. Each chamber has an inherent per-plane resolution for 5-cell cosmic-ray tracks of 145
μm FWHM when operated on the bench at −4.8
kV with argon–isobutane gas, and 225
μm FWHM for 5-cell electron tracks when operated in the High-Resolution Spectrometer detector stack at −4.0
kV with argon–ethane gas. The design and construction facilitates wire placement and replacement to 50
μm, very low dark current, and no cross-talk. The detectors have been in almost continuous use since April 1996, providing reliable, high-resolution charged-particle tracking data for the Hall A physics program. A complete overview of this project is presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The GEp-III and GEp-2γ experiments, carried out in Jefferson Lab’s Hall C from 2007–2008, consisted of measurements of polarization transfer in elastic electron–proton scattering at momentum ...transfers of Q2=2.5,5.2,6.8, and 8.54 GeV 2. These measurements were carried out to improve knowledge of the proton electromagnetic form factor ratio R=μpGEp∕GMp at large values of Q2 and to search for effects beyond the Born approximation in polarization transfer observables at Q2=2.5GeV2. The final results of both experiments were reported in a recent archival publication. A full reanalysis of the data from both experiments was carried out in order to reduce the systematic and, for the GEp-2γ experiment, statistical uncertainties. This technical note provides additional details of the final analysis omitted from the main publication, including the final evaluation of the systematic uncertainties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Subsequent to the release of our original paper, we discovered in the context of preparing our technical supplement 1 for journal publication that a typographical error had existed in the text file ...that the analysis program used to construct the beam polarization "database" for both the original analysis, published in Ref. 2, and our final analysis. The electron-beam polarization Pe and the analyzing power Ay cancel exactly in the ratio R, which is proportional to the ratio Pt/ Pl of the transferred polarization components. On the other hand, the extraction of the relative e dependence of Pl/ PBornl relies on knowledge of the beam polarization. As such, data taking was interrupted roughly every two days during the GEp - 2γ experiment to perform invasive measurements of the beam polarization using the Hall C Moller polarimeter 3.
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