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 contextof the ZEUS and CMS groups at DESY. The first measurement of the MS beauty-quarkmass mb (mb ) at an electron-proton collider is presented. The measurement is based ona QCD analysis of beauty production cross sections in deep inelastic (DIS) ep scatteringmeasured by ZEUS at HERA, together with inclusive DIS HERA data, using Next-toLeading-Order QCD predictions. The measured value of the running beauty-quark massin the MS scheme was found to bemb (mb ) = 4.07 ± 0.14 (fit)+0.01 (mod.)+0.05 (param.) +0.08 (theo.) GeV, which is in good−0.07−0.00−0.05agreement with the world average Particle Data Group value and previous measurementsat electron-positron colliders. It is also found to be consistent with the expected runningof mb (µ).A first measurement of the charm-quark mass mc (µ) running in the MS scheme ispresented. The measurement is based on a QCD analysis of the published H1 and ZEUScombination of charm cross section measurements in DIS ep scattering at HERA, togetherwith inclusive DIS HERA data, using Next-to-Leading-Order QCD predictions. Therunning charm-quark mass mc (µ) was measured at different scales µ and is presented ina charm-quark mass running plot with a comparison to the world average Particle DataGroup mc (mc ) evolved to higher scales. The running is found to be consistent with theexpectations from QCD.The uncertainties of the theoretical predictions for Higgs production in associationwith beauty-quarks originating from the beauty-quark mass were studied and reduced formassive 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 shownthat the uncertainty from the beauty-quark mass mb (mb ) in the case of massive calculations for Hb¯ production at LHC can be reduced to 2%. This makes it negligible comparedbto 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 ofthe beauty-quark mass parameter to 0.17 GeV in the case of massless calculations. It wasshown 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 uncertaintiesfor this calculation. This has the potential to improve the expected precision of futuremeasurements of the Yukawa coupling of the beauty quark to the Higgs boson at theLHC.