The strong coupling from the IR to the UV extremes: Determination of $\hat{I}{\pm }_s$ and prospects from EIC and JLab at 22 GeV

Abstract

We discuss how the Bjorken sum rule allows access to the QCD running coupling $\hat{I}{\pm }_s$ at any scale, including in the deep infrared IR domain. The Bjorken sum data from Jefferson Lab, together with the world data on $\hat{I}{\pm }_s$ reported by the Particle Data Group, allow us to determine the running of $\hat{I}{\pm }_s(Q)$ over five orders of magnitude in four-momentum $Q$. We present two possible future measurements of the running of $\hat{I}{\pm }_s(Q)$ using the Bjorken sum rule: the first at the EIC, covering the range $1.5<Q<8.7$ GeV, and the second at Jefferson Lab at 22 GeV, covering the range $1.0<Q<4.7$ GeV.

7 pages, 3 figures. Contribution to the proceedings of the "QCD at the Extremes" workshop, Sept. 1-11 2025 (V2: fixed a typo & added missing references)