The present experiment exploits the interference between the deeply virtual Compton scattering (DVCS) and the Bethe-Heitler processes to extract the imaginary part of DVCS amplitudes on the neutron ...and on the deuteron from the helicity-dependent D(e,e'gamma)X cross section measured at Q2=1.9 GeV2 and xB=0.36. We extract a linear combination of generalized parton distributions (GPDs) particularly sensitive to E_{q}, the least constrained GPD. A model dependent constraint on the contribution of the up and down quarks to the nucleon spin is deduced.
The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a ...negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.
Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized ...deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.
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.
The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a ...negligible residual vector polarization enabled the first measurement of the tensor asymmetry A{sub zz}{sup d} and the tensor structure function b{sub 1}{sup d} for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV{sup 2}<<Q{sup 2}><5 GeV{sup 2}. The quantities A{sub zz}{sup d} and b{sub 1}{sup d} are found to be nonzero. The rise of b{sub 1}{sup d} for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.
A measurement of the proton spin structure function g1p(x,Q{sup 2}) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA ...incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021<x<0.85 and 0.8 GeV{sup 2}<Q{sup 2}<20 GeV{sup 2}.
The CLAS forward electromagnetic calorimeter Amarian, M.; Asryan, G.; Beard, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2001, Letnik:
460, Številka:
2
Journal Article
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The CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab utilizes six iron-free superconducting coils to provide an approximately toroidal magnetic field. The six sectors are instrumented ...individually to form six independent spectrometers. The forward region (8°<
θ<45°) of each sector is equipped with a lead–scintillator electromagnetic sampling calorimeter (EC), 16
radiation lengths thick, using a novel triangular geometry with stereo readout. With its good energy and position resolution, the EC is used to provide the primary electron trigger for CLAS. It is also used to reject pions, reconstruct π° and η decays and detect neutrons. This paper treats the design, construction and performance of the calorimeter.
We have measured the 3He(e,e' pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and ...measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p(tot). For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low p(tot) and rises to approximately 0.5 at large p(tot). This shows the dominance of tensor over central correlations at this relative momentum.
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The ...asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.
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