A new determination of $\alpha_s$ using direct photon production cross sections in $pp$ and $\overline{p}p$ collisions at $\sqrt{s}=24.3$ GeV

Direct photon production cross sections obtained in high statistics $\bar{p}p$ and $pp$ collisions at $\sqrt{s}=24.3$ GeV at the CERN SPS are used in a next-to-leading order QCD analysis. From the ( stat.)~\pm0.0033\,(syst.)~^{+0.0077}_{-0.0034} \,(t cross section difference $\sigma(\bar{p}p~\to~\gamma X)~-~\sigma(pp~\to~\gamma X)$ and quark distributions measured in deep inelastic scattering, a determination of the strong coupling constant, $\alpha_s$, is performed via a measurement of \ms. This measurement yields a value \ms\ = $210 \pm 22 \,(stat.) \pm 44 \,(syst.) ^{+105}_{-36} \,(theo.)$ MeV. The corresponding value of $\alpha_s$ expressed at $M^2_Z$ is $\alpha_s(M^2_Z)=0.1112~\pm0.0016\,