Double Spin Asymmetries of Inclusive Hadron Electroproduction From a Transversely Polarized \u3csup\u3e3\u3c/sup\u3eHe Target

We report the measurement of beam-target double spin asymmetries (ALT) in the inclusive production of identified hadrons, e⃗ + 3He↑→h+X, using a longitudinally polarized 5.9-GeV electron beam and a transversely polarized 3He target. Hadrons (π±,K±, and proton) were detected at 16∘ with an average momentum ⟨Ph⟩=2.35 GeV/c and a transverse momentum (pT) coverage from 0.60 to 0.68 GeV/c. Asymmetries from the 3He target were observed to be nonzero for π± production when the target was polarized transversely in the horizontal plane. The π+ and π− asymmetries have opposite signs, analogous to the behavior of ALT in semi-inclusive deep-inelastic scattering

Measurement of “Pretzelosity” Asymmetry of Charged Pion Production in Semi-Inclusive Deep Inelastic Scattering on a Polarized \u3csup\u3e3\u3c/sup\u3eHe Target

An experiment to measure single-spin asymmetries of semi-inclusive production of charged pions in deep-inelastic scattering on a transversely polarized 3He target was performed at Jefferson Laboratory in the kinematic region of 0.16\u3cx\u3c0.35 and 1.42\u3c2.7 GeV2 Pretzelosity asymmetries on 3He, which are expressed as the convolution of the h⊥1T transverse-momentum-dependent distribution functions and the Collins fragmentation functions in the leading order, were measured for the first time. Under the effective polarization approximation, we extracted the corresponding neutron asymmetries from the measured 3He asymmetries and cross-section ratios between the proton and 3He. Our results show that both π± on 3He and on neutron pretzelosity asymmetries are consistent with zero within experimental uncertainties

Precision Measurements of A\u3csup\u3en\u3c/sup\u3e\u3csub\u3e1\u3c/sub\u3e in the Deep Inelastic Regime

We have performed precision measurements of the double-spin virtual-photon asymmetry A1 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 ≤ 0.548 at an average Q2 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 an An1 zero crossing near x = 0.5. We find no evidence of a transition to a positive slope in ( d + d¯)/(d + d¯) up to x = 0.548

Single Spin Asymmetries in Charged Kaon Production from Semi-Inclusive Deep Inelastic Scattering on a Transversely Polarized He-3 Target

We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized 3He target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of0.1 \u3c xbj \u3c 0.4for K+ and K− production. While the Collins and Sivers moments for K+ are consistent with zero within the experimental uncertainties, both moments for K− favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While the K+ Sivers moments are consistent with the prediction, the K− results differ from the prediction at the 2-sigma level

Single Spin Asymmetries in Charged Kaon Production from Semi-Inclusive Deep Inelastic Scattering on a Transversely Polarized \u3csup\u3e3\u3c/sup\u3eHe Target

We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized 3He target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of 0.1\u3cxbj\u3c0.4 for K+ and K− production. While the Collins and Sivers moments for K+ are consistent with zero within the experimental uncertainties, both moments for K− favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While the K+ Sivers moments are consistent with the prediction, the K− results differ from the prediction at the 2-sigma level

Single Spin Asymmetries of Inclusive Hadrons Produced in Electron Scattering from a Transversely Polarized \u3csup\u3e3\u3c/sup\u3eHe Target

We report the first measurement of target single spin asymmetries (AN) in the inclusive hadron production reaction, e+3He↑→h+X, using a transversely polarized 3He target. The experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons (π±, K±, and proton) were detected in the transverse hadron momentum range 0.54 \u3cpT\u3c 0.74 GeV/c. The range of xF for pions was −0.29 \u3cxF\u3c −0.23 and for kaons was −0.25 \u3cxF\u3c −0.18. The observed asymmetry strongly depends on the type of hadron. A positive asymmetry is observed for π+ and K+. A negative asymmetry is observed for π−. The magnitudes of the asymmetries follow ∣∣Aπ−|\u3c|Aπ+|\u3c|AK+∣∣. The K− and proton asymmetries are consistent with zero within the experimental uncertainties. The π+ and π− asymmetries measured for the 3He target and extracted for neutrons are opposite in sign with a small increase observed as a function of pT

A New Measurement of the π0\pi^0 Radiative Decay Width

High precision measurements of the differential cross sections for $\pi^0$ photoproduction at forward angles for two nuclei, $^{12}$C and $^{208}$Pb, have been performed for incident photon energies of 4.9 - 5.5 GeV to extract the ${\pi^0 \to \gamma\gamma}$ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The ${\pi^0 \to \gamma\gamma}$ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is $\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}$. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.Comment: 4 pages, 5 figure

Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction \u3csup\u3e3\u3c/sup\u3eHe\u3csup\u3e↑\u3c/sup\u3e(\u3cem\u3ee\u3c/em\u3e,\u3cem\u3ee\u3c/em\u3e′)\u3cem\u3eX\u3c/em\u3e

We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction 3He↑(e,e′)X on a polarized 3He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero 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\u3cW\u3c2.9 GeV, 1.0\u3cQ2\u3c4.0 GeV2 and 0.16\u3cx\u3c6.5. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-3He cross-section ratios. The measured neutron asymmetries are negative with an average value of (−1.09±0.38)×10−2 for invariant mass W\u3e2  GeV, which is nonzero at the 2.89σ 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

Deeply Virtual Compton Scattering off the neutron

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$({\vec e},e'\gamma)X$ cross section measured at $Q^2$=1.9 GeV$^2$ and $x_B$=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.Comment: Published in Phys. Rev. Let