High precision determination of the $Q^2$-evolution of the Bjorken Sum

TL;DR

This paper provides an improved determination of the Bjorken Sum's Q^2 evolution using new precise data, extracting key QCD parameters and reducing uncertainties in the strong coupling constant, thus enhancing tests of Quantum Chromodynamics.

Contribution

It offers the most precise measurement of the Bjorken Sum's Q^2 dependence and extracts the twist-4 coefficient and color polarizabilities with reduced uncertainties.

Findings

Twist-4 coefficient $f_2^{p-n}=-0.064 190.036

Color polarizabilities chi_E^{p-n}=-0.0320.024, chi_B^{p-n}=0.0320.013

Strong coupling alpha_s^{ar{ ext{MS}}}(M_Z^2)=0.11240.0061

Abstract

We present a significantly improved determination of the Bjorken Sum for 0.6$\leq Q^{2}\leq$4.8 GeV$^{2}$ using precise new $g_{1}^{p}$ and $g_{1}^{d}$ data taken with the CLAS detector at Jefferson Lab. A higher-twist analysis of the $Q^{2}$-dependence of the Bjorken Sum yields the twist-4 coefficient $f_{2}^{p-n}=-0.064 \pm0.009\pm_{0.036}^{0.032}$. This leads to the color polarizabilities $\chi_{E}^{p-n}=-0.032\pm0.024$ and $\chi_{B}^{p-n}=0.032\pm0.013$. The strong force coupling is determined to be $\alpha_{s}^{\overline{\mbox{ MS}}}(M_{Z}^{2})=0.1124\pm0.0061$, which has an uncertainty a factor of 1.5 smaller than earlier estimates using polarized DIS data. This improvement makes the comparison between $\alpha_{s}$ extracted from polarized DIS and other techniques a valuable test of QCD.