Next-to-leading order QCD predictions for H → b ̄b and Z →b ̄b at √s=7 TeV and mH =125 GeV, using the parton-level generator MCFM
MetadataShow full item record
In this thesis, the QCD next-to-leading order predictions for the transverse momentum (pT) distribution of the H → b ̄b and Z → b ̄b cross-sections were made using the parton- level generator MCFM. The predictions form a contribution to the search for the Higgs boson in the boosted H → b ̄b channel, where Z → b ̄b forms the main background. As an extension to the WH/ZH (VH) production channel, previously expected to be the most dominant at high pT, the gluon-gluon fusion (ggH) and vector boson fusion (VBF) channels are added. The total cross-sections agree within scale uncertainty to the results from the LHC Higgs Cross Section Working Group. The cross-section pT distributions for the considered processes are shown, along with their respective k-factors (NLO/LO). It is shown that ggH forms the most dominant contribution over the whole Higgs pT range. At higher pT , the H → b ̄b cross section is shown to increase relatively to the Z → b ̄b cross section and is 1 : 3 at pT ≈ 450 GeV. Additionally, the cross-section pT distributions are generated with different PDFs (MSTW08, CT10 and NNPDF2.1) and their corresponding PDF and strong coupling uncertainties are calculated. The ratio of the results of CT10 and NNPDF2.1 with respect to MSTW08 are compared to gg and qq luminosity plots. The central predictions including uncertainties of all PDFs are combined into envelope plots including scale variations that account for missing higher-order corrections. The band is constructed by analyzing the variation of the renormalization and factorization scales independently in a certain range. From the envelope plots, it is apparent there are improvements that can be made on the PDFs. Specifically, for gluon fusion the PDF+αs uncertainty becomes more dominant than the scale uncertainty at high pT, because the gluon has not yet been measured accurately at high values of x.