Mjerenje udarnog presjeka za zajedničku tvorbu Higgsovog bozona i elektroslabog bozona u konačnim stanjima s dva b kvarka i dva leptona u proton proton sudarima na Velikom hadronskom sudarivaču

Abstract

This thesis summarizes the analysis in which we measure the cross-section for the production of the standard model Higss boson of 125 GeV in association with an electroweak boson (W or Z). The analysis is performed in the final state where the Higgs boson decays into a pair of b quarks and the electroweak boson decays leptonically resulting in three channels based on the number of charged leptons in the final state (0, 1 or 2 leptons). The analysis uses data recorded by the CMS experiment from proton-proton collisions at √s= 13 TeV in the LHC during the full Run 2 data taking period (2016-2018). The recorded data corresponds to an integrated luminosity of 138 fb−1. The analysis searches for 2 b-jets produced from b-quarks originating from the Higgs boson along with lepton candidates decaying from the vector boson. The mass of the Higgs boson is reconstructed from the four momenta of the b-jets which are identified using b-tagging algorithms. To account for events with a Lorentz boosted Higgs boson, a single large cone jet is reconstructed which consists of the two b-jets merged together due to the boost. Taking this into account, separate analysis called the boosted analysis is performed along with the nominal resolved analysis to improve sensitivity in high pT phase space. Both resolved and boosted analysis are combined together in the final fit to enhance precision of the measurement. To reduce the dependency on theoretical uncertainties this measurement is performed in the simplified template cross-section (STXS) scheme. This also allows for straightforward comparison of theoretical models using such measurements. Under this scheme, the cross section measurement is done in regions delineated by type of vector boson (W or Z), vector boson transverse momentum (pT ), and the presence of additional jets.Budući da se udarni presjeci mjere u shemi STXS, konačni skup događaja u kanalu i u svakoj regiji (signal ili kontrola) dalje se dijele prema shemi predloška STXS. Prilagodba maksimalne vjerodostojnosti izvodi se istovremeno u signalnim i kontrolnim područjima za svako STXS područje kako bi se dobio modifikator jačine signala (μ) koji označava omjer promatranog broja VHbb događaja u odnosu na onaj koji se očekuje u SM-u. μ=1 predstavlja udarni presjek u skladu s SM-om