Nucleon tensor charge from Collins azimuthal asymmetry measurements

TL;DR

This work addresses the nucleon tensor charge by extracting the quark transversity distribution through a global analysis of Collins azimuthal asymmetries in SIDIS and $e^+e^-$ data, incorporating transverse momentum dependent (TMD) evolution at next-to-leading logarithmic (NLL') order within the CSS formalism. The authors jointly fit the Collins fragmentation functions and transversity at an initial scale, using a nonperturbative $S_{ m NP}$ parametrization and a $b_*$ prescription, to constrain the tensor charge in the accessible region $0.0065 \,\le\, x_B \,\le\, 0.35$ at $Q^2=10$ GeV$^2$. The main quantitative result is $δu^{[0.0065,0.35]} = +0.30^{+0.12}_{-0.08}$ and $δd^{[0.0065,0.35]} = -0.20_{-0.11}^{+0.28}$ (90% CL). The study demonstrates that including TMD evolution improves the description of the data and highlights the need for future high-$x_B$ and low-$x_B$ measurements to determine the total tensor charge.

Abstract

We investigate the nucleon tensor charge from current experiments by a combined analysis of the Collins asymmetries in two hadron production in $e^+e^-$ annihilations and semi-inclusive hadron production in deep inelastic scattering processes. The transverse momentum dependent evolution is taken into account, for the first time, in the global fit of the Collins fragmentation functions and the quark transversity distributions at the approximate next-to-leading logarithmic order. We obtain the nucleon tensor charge contribution from up and down quarks as $δu=+0.30^{+0.12}_{-0.08}$ and $δd=-0.20_{-0.11}^{+0.28}$ at 90\% confidence level for momentum fraction $0.0065 \le x_B \le 0.35$ and $Q^2=$ 10 GeV$^2$.

Figures (3)

• Figure 1: Extracted transversity distribution and Collins fragmentation function at two different scales $Q^2 = 10$ (solid lines) and $Q^2 = 1000$ (dashed lines) GeV$^2$.
• Figure 2: Collins asymmetries measured by the BABARTheBABAR:2013yha Collaboration as a function of $P_{h\perp}$ in production of unlike sign "U" over like sign "L" pion pairs at $Q^2 = 110$ GeV$^2$. The solid line corresponds to the full NLL$'$ calculation, the dashed line to the LL calculation, and the dotted to the calculation without TMD evolution. Calculations are performed with parameters from Table \ref{['parameters']}.
• Figure 3: $\chi^2$ profiles for up and down quark contributions to the tensor charge. The errors of points correspond to 90% C.L. interval.