Discovery seminar - speaker Pavel Jez – University of Copenhagen

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Discovery seminar - speaker Pavel Jez

H->tautau searches at the CMS experiment

Abstract: A resonance consistent with a SM Higgs boson with mass of about 125 GeV has been been discovered by the CMS and ATLAS experiments running at the LHC. At both experiments, the observed excess is driven by the H → gg, H → ZZ and H → WW decay modes. The data collected so far are insufficient to claim observation of the SM-predicted decay into fermions, in particular into the pair of bottom quarks or tau leptons.

Reconstruction of the tau lepton decays in the environment of high-intensity hadron collider is very challenging task: part of the original tau lepton energy is always carried by neutrino(s) invisible to the CMS detector and the visible decay products can be mimicked by the QCD jets.

At CMS, the tau decay products are reconstructed from Particle Flow (PF) objects. In the PF approach, the information from all sub-detectors is combined to identify and reconstruct all particles from collision, namely charged and neutral hadrons, photons, muons and electrons. The tau reconstruction algorithm combines PF electromagnetic particles into strips in order to reconstruct pi0 candidates. Those are combined with charged hadrons to reconstruct visible tau decay products. Several identification criteria are applied to the tau candidates: isolation and rejection against electrons and muons. All discriminators exist in cut- or MVA-based form and have several working points with different values of tau reconstruction efficiency and rejection against fake tau candidates.

 A search for the SM Higgs boson decaying to tau-lepton pairs is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012 at a center-of-mass energy of 7 and 8 TeV respectively. The dataset corresponds to an integrated luminosity of 4.9 fb-1 of data taken at 7 TeV center-of-mass energy and 19.4 fb-1 at 8 TeV. The tau-lepton pair invariant-mass spectrum is studied in several different final states corresponding to the decay modes of the two tau leptons. To enhance sensitivity, presence of 2 forward jets is used to search for events where the scalar boson was produced in vector boson fusion. Additionally, presence of W and Z bosons is used in search for events where the scalar boson was produced in association with them. An excess of events over a broad mass range is observed, compatible with the presence of decays of a standard-model Higgs boson with a mass around 125 GeV to the tau pair.