We report on measurements of the neutron spin asymmetries A{sub 1,2}{sup n} and polarized structure functions g{sub 1,2}{sup n} at three kinematics in the deep inelastic region, with x=0.33, 0.47, ...and 0.60 and Q{sup 2}=2.7, 3.5, and 4.8 (GeV/c){sup 2}, respectively. These measurements were performed using a 5.7 GeV longitudinally polarized electron beam and a polarized {sup 3}He target. The results for A{sub 1}{sup n} and g{sub 1}{sup n} at x=0.33 are consistent with previous world data and, at the two higher-x points, have improved the precision of the world data by about an order of magnitude. The new A{sub 1}{sup n} data show a zero crossing around x=0.47 and the value at x=0.60 is significantly positive. These results agree with a next-to-leading-order QCD analysis of previous world data. The trend of data at high x agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (PQCD) assuming hadron helicity conservation. Results for A{sub 2}{sup n} and g{sub 2}{sup n} have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d{sub 2}{sup n} was evaluated and the new result has improved the precision of this quantity by about a factor of 2. When combined with the world proton data, polarized quark distribution functions were extracted from the new g{sub 1}{sup n}/F{sub 1}{sup n} values based on the quark-parton model. While results for {delta}u/u agree well with predictions from various models, results for {delta}d/d disagree with the leading-order PQCD prediction when hadron helicity conservation is imposed.
We have measured the neutron spin asymmetry A{sub 1}{sup n} with high precision at three kinematics in the deep inelastic region at x = 0.33, 0.47 and 0.60, and Q{sup 2} = 2.7, 3.5 and 4.8 ...(GeV/c){sup 2}, respectively. Our results unambiguously show, for the first time, that A{sub 1}{sup n} crosses zero around x = 0.47 and becomes significantly positive at x = 0.60. Combined with the world proton data, polarized quark distributions were extracted. Our results, in general, agree with relativistic constituent quark models and with perturbative quantum chromodynamics (pQCD) analyses based on the earlier data. However they deviate from pQCD predictions based on hadron helicity conservation.
Methods for optical calibration of the BigBite hadron spectrometer Mihovilovič, M.; Širca, S.; Allada, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2012, Letnik:
686
Journal Article
Recenzirano
Odprti dostop
The techniques for the optical calibration of Jefferson Lab's large-acceptance magnetic hadron spectrometer, BigBite, have been examined. The most consistent and stable results were obtained using a ...method based on singular value decomposition. In spite of the complexity of the optics, the particles' positions and momenta at the target have been precisely reconstructed from the coordinates measured in the detectors by means of a single back-tracing matrix. The technique is applicable to any similar magnetic spectrometer and any particle type. For 0.55GeV/c protons, we have established a vertex resolution of 1.2cm, angular resolutions of 7mrad and 13mrad (in-plane and out-of-plane, respectively), and a relative momentum resolution of 1.6%.
Color polarizabilities of the neutron are extracted from data on the lowest moment of the spin-dependent g1 structure function. New data in the resonance region from Jefferson Lab at Q2≲1 GeV2, in ...combination with world data at higher Q2, allow a systematic determination of the 1/Q2 corrections, and provide the first constraints on 1/Q4 corrections. The results suggest that higher-twist effects in the neutron are small, and that quark–hadron duality may be approximately valid, even down to Q2∼1 GeV2.
The HERMES Spectrometer Ackerstaff, K.; Akopov, N.; Aschenauer, E.C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1998, Letnik:
417, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and
3He. 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.
The generalized forward spin polarizabilities gamma(0) and delta(LT) of the neutron have been extracted for the first time in a Q2 range from 0.1 to 0.9 GeV2. Since gamma(0) is sensitive to nucleon ...resonances and delta(LT) is insensitive to the Delta resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on delta(LT) show significant disagreement with chiral perturbation theory calculations, while the data for gamma(0) at low Q2 are in good agreement with a next-to-leading-order relativistic baryon chiral perturbation theory calculation. The data show good agreement with the phenomenological MAID model.
A lead–glass hodoscope calorimeter that was constructed for use in the Jefferson Lab Real Compton Scattering experiment is described. The detector provides a measurement of the coordinates and the ...energy of scattered photons in the GeV energy range with resolutions of 5
mm and 6%/
E
γ
GeV
. Features of both the detector design and its performance in the high luminosity environment during the experiment are presented.
We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial ...(full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space.
We have measured the proton recoil polarization in the He-4((e) over right arrow ,e(')(p) over right arrow)H-4 reaction at Q(2)=0.5, 1.0, 1.6, and 2.6 (GeV/c)(2). The measured ratio of polarization ...transfer coefficients differs from a fully relativistic calculation, favoring the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model. In addition, the measured induced polarizations agree reasonably well with the fully relativistic calculation indicating that the treatment of final-state interactions is under control.
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