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H1
Abstract:
The strong coupling constant $\alpha_s(M_Z)$ is determined from inclusive jet and dijet cross sections in deep-inelastic $ep$ scattering (DIS) using next-to-next-to-leading order (NNLO) QCD predictions. Several previous measurements performed by the H1 experiment are considered and parts of the data are compared for the first time to NNLO QCD predictions. The dependence of the NNLO predictions and of the resulting value of $\alpha_s(M_Z)$ as a function of the choice of the renormalisation and factorisation scales are studied. The methodology of the $\alpha_s(M_Z)$ determination accounts for the $\alpha_s(M_Z)$-dependence of the perturbatively calculated hard coefficients and also of the parton density functions (PDF). Using inclusive jet and dijet data together, the value of the strong coupling constant is determined to $\alpha_s(M_Z)=0.1155(6)_{\rm exp}(20)_{\rm th}$. The results and the methodology are validated by performing additonally a complementary determination of $\alpha_s(M_Z)$ together with PDF parameters, for which in addition inclusive DIS cross section measurements are employed. Values of the strong coupling constant are further determined at different values of the renormalisation scale and the results are found to be in agreement with the
expectations for the running coupling.
