Precise determination of the deuteron spin structure at low to moderateQ2with CLAS and extraction of the neutron contribution

Abstract

Precise determination of the deuteron spin structure at low to moderate Q^{2} with CLAS and extraction of the neutron contribution We present the final results for the deuteron spin structure functions obtained from the full data set collected with Jefferson Lab's CLAS in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2 and 5.8 GeV were scattered from deuteron ( 15 ND3) targets, dynamically polarized along the beam direction, and detected with CLAS. From the measured double spin asymmetry, the virtual photon absorption asymmetry A d 1 and the polarized structure function g d 1 were extracted over a wide kinematic range (0.05 GeV 2 < Q 2 < 5 GeV 2 and 0.9 GeV < W < 3 GeV). We use an unfolding procedure and a parametrization of the corresponding proton results to extract from these data the polarized structure functions A n 1 and g n 1 of the (bound) neutron, which are so far unknown in the resonance region, W < 2 GeV. We compare our final results, including several moments of the deuteron and neutron spin structure functions, with various theoretical models and expectations as well as parametrizations of the world data. The unprecedented precision and dense kinematic coverage of these data can aid in future extractions of polarized parton distributions, tests of perturbative QCD predictions for the quark polarization at large x, a better understanding of quark-hadron duality, and more precise values for higher-twist matrix elements in the framework of the Operator Product Expansion.

Updating spin-dependent Regge intercepts

“…That is, we conjecture Second, we assume that the isoscalar deuteron asymmetry A d 1 can be taken as zero in first approximation. The deuteron data on A d 1 are consistent with zero in each experiment in our chosen kinematics [6,7,34,35] (as well as in g d 1 measurements at deep inelastic Q 2 and low x < 0.03 [19]). This means that we set the normalisation factors N (0) i = N g = 0 in Eq.(1).…”

Determination of the proton spin structure functions for 0.05<Q2<5GeV2 using CLAS

“…Additional data from this experiment on the deuteron with similar precision have already been published [14]. Further information will come from the analysis of the completed EG4 experiment with CLAS, which extends the kinematic coverage of the present data set to even lower Q 2 for a more rigorous test of χ PT.…”

Iterative Monte Carlo analysis of spin-dependent parton distributions

“…In fixed-target deep-inelastic scattering (DIS) experiments, new high-precision data from Jefferson Lab on polarized protons [12][13][14][15], deuterons [15,16] and 3 He nuclei [17][18][19] are yielding a wealth of information on nucleon spin structure at lower energies. As well as improving the constraints on the large-x behavior of polarized PDFs, the new results are also providing new insights into nonperturbative quark-gluon interaction effects through higher twist contributions.…”

“…As in the previous JAM analysis [20], we use the measured A and A ⊥ asymmetries, whenever available, instead of the derived A 1 asymmetry or g 1 structure function to avoid uncertainties associated with inconsistent use of spin-averaged structure functions in the extraction of the spin-dependent observables. We include new data sets with high-precision A and A ⊥ asymmetry measurements at Jefferson Lab from the "eg1b" [14,16] and "eg1-dvcs" [15] analyses on the proton and deuteron, and new results from the E06-014 experiment on 3 He from Hall A [17,18]. Also included are the most recent A 1 measurements on the proton from COMPASS [39].…”