Transverse target single-spin asymmetry in inclusive electroproduction of charged pions and kaons by HERMES

HERMES is a polarized deep inelastic scattering experiment at DESY. It uses 27.6 GeV electron/positron beam at DESY-HERA and internal gas targets. In this talk, recent results from the analyses on azimuthal asymmetry of $\pi^\pm$ and $K^\pm$ production with unpolarized beam on transverselly polarized hydrogen target[1] will be presented. $\pi^+$, $\pi^-$, $K^+$ and $K^-$ are detected in high-statistics inclusive measurements as functions of $P_T$ and $X_F$. $A_{UT}$ is measured and the sin$\psi$ amplitude is extracted for these particles where $\psi$ is the azimuthal angle determined by the beam axis, hadron momentum vector and the target spin direction. The results show clear positive amplitudes for $\pi^+$ and $K^+$ and a slightly negative amplitude for $\pi^-$. The results are interpreted based on the three relative scales, $\Lambda_{QCD}$, $P_T$ and $Q$. The Sivers and Collins mechanisms and twist-three quark-gluon correlation function are relevant in different kinematic regions. Correlations between $P_T$ and $X_F$ can be studied with these data.\\[4pt] [1] A. Airapetian et al. HERMES, Transverse target single-spin asymmetry in inclusive electroproduction of charged pions and kaons, Phys. Lett. B 728 (2014) 183.