Naive time-reversal odd phenomena in semi-inclusive deep-inelastic scattering from light-cone constituent quark models

TL;DR

The paper investigates leading-twist azimuthal asymmetries in SIDIS arising from naively T-odd TMDs (Sivers and Boer-Mulders) using a light-cone constituent quark model. It employs a one-gluon-exchange mechanism within the LCCQM and a Gaussian Ansatz for transverse momentum, then addresses scale evolution from a low hadronic scale to experimental Q^2 using LO patterns. The study finds good agreement with HERMES and COMPASS data for the Sivers effect and reasonable compatibility for the Boer-Mulders effect, while providing predictions for Jefferson Lab and clarifying the role of p_T-broadening and Cahn-related corrections. Overall, the work demonstrates that the LCCQM can capture essential transverse-momentum dynamics of T-odd TMDs in the valence region and underscores areas where more refined TMD evolution is needed.

Abstract

We present results for leading-twist azimuthal asymmetries in semi-inclusive lepton-nucleon deep-inelastic scattering due to naively time-reversal odd transverse-momentum dependent parton distribution functions from the light-cone constituent quark model. We carefully discuss the range of applicability of the model, especially with regard to positivity constraints and evolution effects. We find good agreement with available experimental data from COMPASS and HERMES, and present predictions to be tested in forthcoming experiments at Jefferson Lab.

Figures (5)

• Figure 1: Kinematics of the SIDIS process $lN\to l^\prime h X$. The azimuthal angles of produced hadron and nucleon polarization vector are $\phi_h$ and $\phi_S$. The transverse momentum of the hadron is $P_{h\perp}\ll Q$ where $Q^2=-q^2=(l-l^\prime)^2$.
• Figure 2: Transverse moments $f_{1T}^{\perp(1)q}(x)$ and $h_{1}^{\perp(1)q}(x)$ in a proton for up (left) and down (right) quark, as function of $x$. The dashed curves show the results at the hadronic scale $\mu_0$ of the model . The solid curves correspond to the results after LO evolution to $Q^2=2.5$ GeV$^2$, using the evolution patterns of the unpolarized parton distribution (transversity) for the Sivers (Boer-Mulders) function.
• Figure 3: The positivity relations involving the Sivers (upper panels) and Boer-Mulders functions (lower panels) from Eqs. (\ref{['Ineq:f1Tperp']}) and (\ref{['Ineq:h1perp']}), respectively, as function of $p^2_T$ at different values of $x$: $x=0.3$ (short-dashed curves), $x=0.4$ (long-dashed curves), and $x=0.5$ (solid curves). The left (right) panels show the results for up (down) quark.
• Figure 4: The single-spin asymmetry $A_{UT}^{\sin(\phi_h-\phi_S)}$ for pion production off proton in SIDIS, as function of $x$. The HERMES data are from Airapetian:2009ti. The theoretical curves are obtained on the basis of the LCCQM predictions for $f_{1T}^{\perp(1)q}(x)$Pasquini:2010af.
• Figure 7: The difference of azimuthal asymmetries $A_{UU}^{\cos(2\phi_h)}$ for negative and positive pions or hadrons, as function of $x$. The experimental points were obtained taking the differences of preliminary $\pi^-$ and $\pi^+$ HERMES data Giordano:2010gq, and preliminary $h^-$ and $h^+$ COMPASS data Sbrizzai. The error bars show the propagation of statistical errors, and do not include systematic errors. The theoretical curves are obtained using $h_1^{\perp(1)q}(x)$ from the LCCQM Pasquini:2010af. Panel (d) shows a prediction for Jefferson Lab.