Transversity distribution in spin asymmetries in semi-inclusive DIS and in the Drell-Yan process

TL;DR

The paper surveys single-spin asymmetries in SIDIS and Drell–Yan to access the nucleon transversity distribution $h_1(x)$, focusing on the Collins fragmentation function $H_1^\\perp$ and predictions from the chiral quark–soliton model ($\chi$QSM). It demonstrates that $h_1(x)$ can be probed via SIDIS azimuthal asymmetries and, in Drell–Yan, via polarized $p\bar p$ collisions (PAX) with potentially large asymmetries. The authors show that $\chi$QSM combined with ancillary fragmentation data can describe several SIDIS observables without fit parameters, while also highlighting puzzles in transverse-target Collins asymmetries and in unfavoured fragmentation. They emphasize the Drell–Yan route, especially with antiprotons, as a clean and promising path to constrain transversity, motivating future polarized experiments.

Abstract

A review is given on single spin asymmetries in deep inelastic semi-inclusive scattering (SIDIS) and their possible theoretical understanding in the framework of QCD-induced factorization approach, wherefore predictions for transversity from the chiral quark soliton model are used. Arising difficulties to interpret most recent SIDIS data, and the possibility to access the transversity distribution in the Drell-Yan process are discussed.

Figures (12)

• Figure 1: The squared modulus of the matrix element of the process (\ref{['reaction']}) in the parton model summed over states $X$. The $H_1^\perp(z)$ and $h_1(x)$ are examples of PFF and PDF, respectively.
• Figure 2: Kinematics of the process (\ref{['reaction']}).
• Figure 3: The $\theta_2$-dependence of the value ${}\;\;\;\;\;\;\; P_2={6\over\pi}\left|{\langle H_1^{\perp}\rangle\over\langle D_1\rangle}\right|^2 \overline{C}_{TT}{\sin^2\theta_2\over 1+\cos^2\theta_2}$ (in ppm).
• Figure 4: a) The transversity distribution function $h_1^a(x)$ vs. $x$ from the $\chi$QSM Schweitzer:2001sr. b) Comparison of $h_1^u(x)$ from the $\chi$QSM (solid) to $f_1^u(x)$ (dashed) and $g_1^u(x)$ (dotted) and the Soffer bound $(f_1^u+g_1^u)(x)/2$ (dashed-dotted line) taken or constructed from the parameterizations of Gluck:1994uf.
• Figure 5: Azimuthal asymmetries $A_{0L}^{W(\phi)}(x,\pi)$ weighted by $W(\phi)=\sin\phi$ (solid line) and $\sin 2\phi$ (dashed line) for the production of $\pi^0$, $\pi^+$ and $\pi^-$ as function of $x$. The experimental data are from the Refs. Airapetian:1999tvAirapetian:2001eg. Rhombus (squares) denote the data for $A_{0L}^{\sin\phi}$ ($\;A_{0L}^{\sin2\phi}$).