Search for H± → tb decay in fully hadronic final state

Abstract

(...μη διαθέσιμη ηλεκτρονική μορφή της περίληψης)

The search of the charged Higgs boson H± is an important topic in experimental particle physics as an indication of its existence will provide irrefutable proof of physics Beyond the Standard Model (BSM). The heavy charged Higgs bosons (mH± > mt) are produced mainly in the gb → t(b)H± process. The most prominent decay mode for the heavy charged Higgs in the mass range mH± = [200, 3000] GeV/c2 is H± → tb. This analysis is the first-ever study of the H± → tb channel in the fully hadronic final state. The LHC RunII data collected in the year 2016 at \sqrt{s} = 13 TeV centre of mass energy corresponding to an integrated luminosity L = 35.9 fb−1 was used for the search. Events with at least three b-tagged jets are selected to obtain a signal event topology and to suppress the dominant but reducible QCD-multijet background. The two top candidates in the event are reconstructed by defining a χ2 based on mass width of W± bosons and Δmt. Events with isolated electrons, muons, or hadronically decaying taus τh are rejected to obtain fully hadronic final state and to ensure orthogonality with other analyses operating with the H± → τντ decay mode. The invariant mass of the charged Higgs boson candidates, reconstructed from the leading in the pT top and the leading in the pT free b-tagged jet, is used to separate the signal from the backgrounds. In this analysis, the QCD background is measured with the data-driven method by defining an inverted region orthogonal to the signal region with tt σ pp→t(b)H± × B H± ( →tb) σ pp→t(b)H± × B H± ( →tb) !8 events failing the requirements on b-tagged jets. The background from all other sources including tt ̄ are estimated from the simulation. A model-independent upper limit is calculated on σpp→t(b)H± . B(H± → tb) for the heavy charged Higgs boson search, using the modified frequentist CLs criterion. 95% C.L. upper limit on σpp→t(b)H± . B(H± → tb) is found to be between 30.5 pb and 0.32 pb in mass range [200, 3000] GeV/c2. No excess is observed, and the events passing the signal selection are found to be compatible with the SM predictions.