Reanalysis of Azimuthal Spin Asymmetries of Meson Electroproduction

Abstract

The azimuthal spin asymmetries for pion production in semi-inclusive deep inelastic scattering of unpolarized charged lepton beams on longitudinally polarized nucleon targets, are reanalyzed by taking into account an important sign correction to previous formulas. It is found that different approaches of distribution functions and fragmentation functions may lead to distinct predictions on the azimuthal asymmetries measured in the HERMES experiments, thus the available data cannot be considered as a direct measurement of quark transversity distributions, although they still can serve to provide useful information on these distributions and on T-odd fragmentation functions. Predictions of the azimuthal spin asymmetries for kaon production are also presented, with different approaches of distribution and fragmentation functions. The unfavored fragmentation functions cannot be neglected for $K^-$ and $K^0_S$ production in semi-inclusive deep inelastic processes.

Figures (8)

• Figure 1: The azimuthal asymmetries $A_{UL}^{\sin \phi}$ for semi-inclusive pion production in deep inelastic scattering of unpolarized charged lepton on the longitudinally polarized proton target, with polarization $S=0.86$Kor00. The upper row corresponds to (a) $\pi^{+}$, (b) $\pi^{0}$, and (c) $\pi^-$ production with the distribution functions in the quark diquark model, and the lower row corresponds to (d) $\pi^{+}$, (e) $\pi^{0}$, and (f) $\pi^-$ production with the distribution functions in the pQCD based analysis. The thick dotted, dashed, and solid curves correspond to the calculated results for Leading Approach, Approach 1, and Approach 2, and the thin dashed and solid curves correspond to the calculated results for Approach 1 and Approach 2 with an additional factor 2 in the Collins fragmentation functions. Both the favored and unfavored fragmentation functions for the pions are included in the calculation.
• Figure 2: The same as Fig. \ref{['msy13f1']}, but for the deuteron target with polarization $S=0.75$.
• Figure 3: The same as Fig. \ref{['msy13f1']}, but for the neutron target with polarization $S=0.75$.
• Figure 4: The same as Fig. \ref{['msy13f1']}, but with only favored fragmentation functions for the pions being included.
• Figure 5: The azimuthal asymmetries $A_{UL}^{\sin \phi}$ for semi-inclusive kaon production in deep inelastic scattering of unpolarized charged lepton on the longitudinally polarized proton target, with polarization $S=0.86$. The upper row corresponds to (a) $K^{+}$, (b) $K^{0}_S$, and (c) $K^-$ production with the distribution functions in the quark diquark model, and the lower row corresponds to (d) $K^{+}$, (e) $K^{0}_S$, and (f) $K^-$ production with the distribution functions in the pQCD based analysis. The thick dotted, dashed, and solid curves correspond to the calculated results for Leading Approach, Approach 1, and Approach 2, and the thin dashed and solid curves correspond to the calculated results for Approach 1 and Approach 2 with an additional factor 2 in the Collins fragmentation functions. Both the favored and unfavored fragmentation functions for the kaons are included in the calculation.