Thursday, June 6, 2013

1306.1004 (Wenjuan Mao et al.)

Beam Spin Asymmetries of Charged and Neutral Pion Productions in
Semi-inclusive DIS

Wenjuan Mao, Zhun Lu
We present a study on the beam single spin asymmetries $A_{LU}^{\sin\phi_h}$ of $\pi^+$, $\pi^-$ and $\pi^0$ productions in semi-inclusive deep inelastic scatting process. The contributions from the Collins effect and the $g^\perp D_1$ term are taken into consideration simultaneously. We calculate the twist-3 transverse momentum dependent distributions $e(x, \bm k_T^2)$ and $g^\perp(x,\bm k_T^2)$ for the $u$ and $d$ valence quarks inside the proton in a spectator model, with the scalar and the axial-vector diquarks as the spectators. We consider two different options for the form of diquark propagator, as well as two different choices for the model parameters in the calculation. Using the model results, we estimate the beam spin asymmetries $A_{LU}^{\sin\phi_h}$ for the charged and neutral pions and compare the results with the data measured by the HERMES Collaboration. We also make predictions on the asymmetry $A_{LU}^{\sin\phi_h}$ at CLAS with a $E_e=5.5 \,\textrm{GeV}$ beam using the same model results. It is found that the different choices for the diquark propagator will not only lead to different expressions for the parton distribution functions but also result in different sizes of the asymmetries.
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