Single spin asymmetries in charged kaon production from semi-inclusive deep inelastic scattering on a transversely polarized ${}^3\mathrm{He}$ 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 ${}^3\mathrm{He}$ 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 $0.1<x_{bj}<0.4$ 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.

Figure 1

${}^3\mathrm{He}(e,e^{\prime }{h}^{+})\text{X}$ coincidence timing spectrum after a cut on the aerogel detector to remove pions, where $h$ represents detected hadron. The kaon selection cuts are shown as the two vertical lines. The top right subplot shows only $K^{+}$ and ${\pi }^{+}$ peaks in a relatively small CTOF range.

Figure 2

Correlation between $x_{bj}$ and kinematics variables $(Q^2,P_t,z)$ for $K^{+}$, where $x_{bj}=\frac{Q^2}{2P·q},P_t=\sqrt{{\overrightarrow{P_h}}^2-{\left(\frac{\vec{q}·\overrightarrow{P_h}}{|\vec{q}|}\right)}^2},z=\frac{P·P_h}{P·q},P$ is the four-momentum of the initial nucleon, $q$ is the four-momentum of the virtual photon, $P_h$ is the four-momentum of the detected hadron.

Figure 3

The extracted Collins and Sivers moments on ${}^3\mathrm{He}$ are shown together with their statistical errors and systematic error bands for both $K^{+}$ and $K^{-}$ electro-production. The Sivers moments are compared to theoretical predictions from a phenomenological fit to the world data.