Measurement of Single Spin Asymmetries in Semi-Inclusive Deep Inelastic Scattering Reaction n↑(e, éπ+)X at Jefferson Lab

What constitutes the spin of the nucleon? The answer to this question is still not completely understood. Although we know the longitudinal quark spin content very well, the data on the transverse quark spin content of the nucleon is still very sparse. Semi-inclusive Deep Inelastic Scattering (SIDIS) using transversely polarized targets provide crucial information on this aspect. The data that is currently available was taken with proton and deuteron targets. The E06-010 experiment was performed at Jefferson Lab in Hall-A to measure the single spin asymmetries in the SIDIS reaction n↑(e,éπ±/K±)X using transversely polarized 3He target. The experiment used the continuous electron beam provided by the CEBAF accelerator with a beam energy of 5.9 GeV. Hadrons were detected in a high-resolution spectrometer in coincidence with the scattered electrons detected by the BigBite spectrometer. The kinematic coverage focuses on the valence quark region, x = 0.19 to 0.34, at Q2 = 1.77 to 2.73 (GeV/c)2. This is the first measurement on a neutron target. The data from this experiment, when combined with the world data on the proton and the deuteron, will provide constraints on the transversity and Sivers distribution functions on both the u and d-quarks in the valence region. In this work we report on the single spin asymmetries in the SIDIS n↑(e,éπ+)X reaction

Measurements of \u3cem\u3ed\u3csup\u3en\u3c/sup\u3e\u3c/em\u3e\u3csub\u3e2\u3c/sub\u3e and \u3cem\u3eA\u3csup\u3en\u3c/sup\u3e\u3c/em\u3e\u3csub\u3e1\u3c/sub\u3e: Probing the Neutron Spin Structure

We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element d2 of the neutron (dn2) was conducted. The quantity dn2 represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the 3He spin structure functions, g1 and g2, after nuclear corrections had been applied to these moments. The structure functions were obtained from a measurement of the unpolarized cross section and of double-spin asymmetries in the scattering of a longitudinally polarized electron beam from a transversely and a longitudinally polarized 3He target. The measurement kinematics included two average Q2 bins of 3.2  GeV2 and 4.3  GeV2, and Bjorken-x 0.25 ≤ x ≤ 0.90 covering the deep inelastic and resonance regions. We have found that dn2 is small and negative for ⟨Q2⟩ = 3.2  GeV2, and even smaller for ⟨Q2⟩ = 4.3  GeV2, consistent with the results of a lattice QCD calculation. The twist-4 matrix element fn2 was extracted by combining our measured dn2 with the world data on the first moment in x of gn1, Γn1. We found fn2 to be roughly an order of magnitude larger than dn2 . Utilizing the extracted dn2 and fn2 data, we separated the Lorentz color force into its electric and magnetic components, Fy,nE and Fy,nB, and found them to be equal and opposite in magnitude, in agreement with the predictions from an instanton model but not with those from QCD sum rules. Furthermore, using the measured double-spin asymmetries, we have extracted the virtual photon-nucleon asymmetry on the neutron An1, the structure function ratio gn1/Fn1, and the quark ratios (Δu + Δu¯)/(u + u¯) and (Δd + Δd¯)/(d + d¯). These results were found to be consistent with deep-inelastic scattering world data and with the prediction of the constituent quark model but at odds with the perturbative quantum chromodynamics predictions at large x

Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction 3He↑(e,e′)X^{3}\mathrm{He}^{\uparrow}(e,e')X

We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction $^3$He$^{\uparrow}\left(e,e' \right)X$ on a polarized $^3$He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be non-zero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of $1.7 < W < 2.9$ GeV, $1.0<Q^2<4.0$ GeV$^2$ and $0.16<x<0.65$. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-$^3$He cross section ratios. The measured neutron asymmetries are negative with an average value of $(-1.09 \pm 0.38) \times10^{-2}$ for invariant mass $W>2$ GeV, which is non-zero at the $2.89\sigma$ level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering.Comment: This is the final edited version as published in PR

Probing the Repulsive Core of the Nucleon-Nucleon Interaction via the 4He(e,e'pN) Triple-Coincidence Reaction

We studied simultaneously the 4He(e,e'p), 4He(e,e'pp), and 4He(e,e'pn) reactions at Q^2=2 [GeV/c]2 and x_B>1, for a (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum in a region where the nucleon-nucleon force is expected to change from predominantly tensor to repulsive. Neutron-proton pairs dominate the high-momentum tail of the nucleon momentum distributions, but their abundance is reduced as the nucleon momentum increases beyond ~500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum in the range we studied. Our data are compared with ab-initio calculations of two-nucleon momentum distributions in 4He.Comment: 6 pages, 2 figure

Precision measurements of A1N in the deep inelastic regime

We have performed precision measurements of the double-spin virtual-photon asymmetry A1A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277≤x≤0.5480.277≤x≤0.548 at an average Q2Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of anA1n zero crossing near x=0.5x=0.5. We find no evidence of a transition to a positive slope in(Δd+Δd¯)/(d+d¯) up to x=0.548x=0.548

Semi-inclusive DIS Experiments Using Transversely Polarized Targets in Hall-A: Current Results and Future Plans

Measurement of single (SSA) and double spin asymmetries (DSA) in semiinclusive DIS reactions using polarized targets provide a powerful method to probe transverse momentum dependent parton distribution functions (TMDs). In particular, the experimentally measured SSA on nucleon targets can help in extracting the transversity and Sivers distribution functions of u and d-quarks. Similarly, the measured DSA are sensitive to the quark spin-orbital correlations, and provide an access to the TMD parton distribution function (g1T). A recent experiment conducted in Hall-A Jefferson Lab using transversely polarized 3He provide first such measurements on “effective” neutron target. The measurement was performed using 5.9 GeV beam from CEBAF and measured the target SSA/DSA in the SIDIS reaction 3He↑(e, e′π±)X. The kinematical range, x = 0.19 ~ 0.34, at Q2 = 1.77 ~ 2.73 (GeV/c)2, was focused on the valence quark region. The results from this measurement along with our plans for future high precision measurements in Hall-A are presented

Single spin asymmetries of inclusive hadrons produced in electron scattering from a transversely polarized [superscript 3]He target

We report the first measurement of target single spin asymmetries (A[subscript N]) in the inclusive hadron production reaction, e + [superscript 3]He[superscript ↑] → h + X, using a transversely polarized [superscript 3]He target. The experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons (π[superscript ±], K[superscript ±], and proton) were detected in the transverse hadron momentum range 0.54 < p[subscript T] < 0.74 GeV/c. The range of x[subscript F] for pions was −0.29 < x[subscript F] < −0.23 and for kaons was −0.25 < x[subscript F] < −0.18. The observed asymmetry strongly depends on the type of hadron. A positive asymmetry is observed for π[superscript +] and K[superscript +]. A negative asymmetry is observed for π[superscript −]. The magnitudes of the asymmetries follow ∣∣A[superscript π−] |<| A[superscript π+] |<| A[superscript K+]∣∣. The K[superscript −] and proton asymmetries are consistent with zero within the experimental uncertainties. The π[superscript +] and π[superscript −] asymmetries measured for the [superscript 3]He target and extracted for neutrons are opposite in sign with a small increase observed as a function of p[subscript T].National Science Foundation (U.S.)United States. Dept. of Energy (Contract DE-AC05-06OR23177