Duke University, Durham, North Carolina 27708, USA.
Phys Rev Lett. 2011 Aug 12;107(7):072003. doi: 10.1103/PhysRevLett.107.072003. Epub 2011 Aug 10.
We report the first measurement of target single spin asymmetries in the semi-inclusive (3)He(e,e'π(±))X reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.16 < x < 0.35 with 1.4 < Q(2) < 2.7 GeV(2). The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The π(±) Collins moments for (3)He are consistent with zero, except for the π(+) moment at x = 0.35, which deviates from zero by 2.3σ. While the π(-) Sivers moments are consistent with zero, the π(+) Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and measured cross section ratios of proton to (3)He, and are largely consistent with the predictions of phenomenological fits and quark model calculations.
我们报告了在横极化靶上进行的半单举（3）He(e,e'π(±))X 反应中靶自旋单不对称性的首次测量。该实验是在杰斐逊实验室利用 5.9GeV 电子束进行的，覆盖了 0.16 < x < 0.35 的范围，其中 1.4 < Q(2) < 2.7GeV(2)。从测量不对称性的方位角依赖关系中提取了 Collins 和 Sivers 矩。对于（3）He，除了 x = 0.35 处的 π(+)矩外，π(±)Collins 矩都接近于零，该矩偏离零值 2.3σ。虽然 π(-)Sivers 矩接近于零，但 π(+)Sivers 矩倾向于负值。使用核子有效极化和质子与（3）He 的测量截面比提取了中子结果，这些结果与唯象拟合和夸克模型计算的预测基本一致。
