Experimental Determination of the QCD Effective Charge αg1(Q)

The QCD effective charge alpha(g1)(Q) is an observable that characterizes the magnitude of the strong interaction. At high momentum Q, it coincides with the QCD running coupling alpha(s)(Q). At low Q, it offers a nonperturbative definition of the running coupling. We have extracted alpha(g1)(Q) from measurements carried out at Jefferson Lab that span the very low to moderately high Q domain, 0.14 <= Q <= 2.18 GeV. The precision of the new results is much improved over the previous extractions and the reach in Q at the lower end is significantly expanded. The data show that alpha(g1)(Q) becomes Q-independent at very low Q. They compare well with two recent predictions of the QCD effective charge based on Dyson-Schwinger equations and on the AdS/CFT duality.

Automated summary

The QCD effective charge alpha(g1)(Q) is an observable that characterizes the magnitude of the strong interaction. Measurements carried out at Jefferson Lab have provided improved and expanded results for alpha(g1)(Q) in the low to moderately high momentum range. The data show that alpha(g1)(Q) becomes independent of momentum at very low Q and compare well with recent predictions based on Dyson-Schwinger equations and the AdS/CFT duality.