Transverse Quark Spin Effects and the Flavor Dependence of the Boer-Mulders Function

TL;DR

This paper investigates the flavor dependence of the Boer-Mulders function for up and down quarks within a diquark spectator model, revealing negative moments for both flavors and predicting azimuthal asymmetries in SIDIS and Drell-Yan processes.

Contribution

It provides a new calculation of the Boer-Mulders function showing both flavors have negative moments, contrasting previous models, and predicts related azimuthal asymmetries in SIDIS and Drell-Yan.

Findings

Both u- and d-quark Boer-Mulders functions have negative moments.

Predicted cos(2φ) asymmetries for π+ and π− in SIDIS.

Calculated the single spin asymmetry A_UL^{sin(2φ)} for longitudinally polarized targets.

Abstract

The naive time reversal odd (``T-odd'') parton distribution $h_{1}^{\perp}$, the so-called Boer-Mulders function, for both up ($u$) and down ($d$) quarks is considered in the diquark spectator model. While the results of different articles in the literature suggest that the signs of the Boer-Mulders function in semi-inclusive DIS for both flavors $u$ and $d$ are the same and negative, a previous calculation in the diquark-spectator model found that $h_{1}^{\perp(u)}$ and $h_{1}^{\perp(d)}$ have different signs. The flavor dependence is of significance for the analysis of the azimuthal $\cos(2\phi)$ asymmetries in unpolarized SIDIS and DY-processes, as well as for the overall physical understanding of the distribution of transversely polarized quarks in unpolarized nucleons. We find substantial differences with previous work. In particular we obtain half and first moments of Boer-Mulders function that are negative over the full range in Bjorken $x$ for both the $u$- and $d$- quarks. In conjunction with the Collins function we then predict the $\cos(2\phi)$ azimuthal asymmetry for $\pi^{+}$ and $\pi^{-}$ in this framework. We also find that the Sivers $u$- and $d$- quark are negative and positive respectively. As a by-product of the formalism, we calculate the chiral-odd but ``T-even'' function $h_{1L}^{\perp}$, which allows us to present a prediction for the single spin asymmetry $A_{UL}^{\sin(2\phi)}$ for a longitudinally polarized target in SIDIS.