Measurement of beauty quark mass at HERA and impact on Higgs production in association with beauty quarks at LHC

Three different, but related topics are the subject of this thesis, performed in the context of the ZEUS and CMS groups at DESY. The first measurement of the MS beauty-quark mass mb(mb) at an electron-proton collider is presented. The measurement is based on a QCD analysis of beauty production cross sections in deep inelastic (DIS) ep scattering measured by ZEUS at HERA, together with inclusive DIS HERA data, using Next-toLeading-Order QCD predictions. The measured value of the running beauty-quark mass in the MS scheme was found to be mb(mb) = 4.07± 0.14 (fit) −0.07 (mod.) −0.00 (param.) +0.08 −0.05 (theo.)GeV, which is in good agreement with the world average Particle Data Group value and previous measurements at electron-positron colliders. It is also found to be consistent with the expected running of mb(μ). A first measurement of the charm-quark mass mc(μ) running in the MS scheme is presented. The measurement is based on a QCD analysis of the published H1 and ZEUS combination of charm cross section measurements in DIS ep scattering at HERA, together with inclusive DIS HERA data, using Next-to-Leading-Order QCD predictions. The running charm-quark mass mc(μ) was measured at different scales μ and is presented in a charm-quark mass running plot with a comparison to the world average Particle Data Group mc(mc) evolved to higher scales. The running is found to be consistent with the expectations from QCD. The uncertainties of the theoretical predictions for Higgs production in association with beauty-quarks originating from the beauty-quark mass were studied and reduced for massive and massless QCD calculations. The beauty-quark mass measurement mb(mb) was used to decrease the variation of the beauty-quark mass to 0.17 GeV. It was shown that the uncertainty from the beauty-quark mass mb(mb) in the case of massive calculations for Hbb̄ production at LHC can be reduced to 2%. This makes it negligible compared to other uncertainties for this calculation. Also, a further QCD analysis of beauty production at HERA was performed to evaluate the impact of the decrease of the variation of the beauty-quark mass parameter to 0.17 GeV in the case of massless calculations. It was shown that the uncertainty from the beauty-quark mass parameter in the massless calculation for Hbb production at LHC, which is a priori one of the dominant uncertainties, can be decreased to 4%, such that it becomes small with respect to other uncertainties for this calculation. This has the potential to improve the expected precision of future measurements of the Yukawa coupling of the beauty quark to the Higgs boson at the LHC.

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