Evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons

Abstract

A search for a standard model Higgs boson decaying into a pair of tau leptons is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012. The dataset corresponds to an integrated luminosity of 4.9 inverse-femtobarns at a centre-of-mass energy of 7 TeV, and 19.7 inverse-femtobarns at 8 TeV. Each tau lepton decays hadronically or leptonically to an electron or a muon, leading to six different final states for the tau-lepton pair, all considered in this analysis. An excess of events is observed over the expected background contributions, with a local significance larger than 3 standard deviations for mH values between 115 and 130 GeV. The best fit of the observed H→τ−τ signal cross section for mH = 125 GeV is 0.78 +/- 0.27 times the standard model expectation. These observations constitute evidence for the 125 GeV Higgs boson decaying to a pair of tau leptons

What is the machine learning?

“…(1) by uniformly binning the input events and inverting the histogram, which introduces some finite bin effects as will be apparent below. Note for a different purpose, the experimental collaborations frequently weight events to match the transverse momentum spectrum of different samples (e.g., [18][19][20]). Next, we train a new network on the planed input data.…”

Search for a Higgs boson decaying to a pair of 125 GeV Higgs bosons (hh) or for a Higgs boson decaying to Zh, with tau leptons in the final state

“…1 left). In addition to the ττ selection, each event must contain two b jet candidates that come from h → bb which are ordered by the b-tagging discriminator value, CSV [7], such that the leading and subleading jets are defined as those with the two highest CSV values and are used to reconstruct m bb . Then the events are separated into categories, according to the number of b-jets, which pass the medium CSV working point.…”

“…The Z → ττ process also constitutes an irreducible background but it is greatly reduced thanks to the b-tagging requirements. It is estimated combining Drell-Yan MC sample and data with a dedicated datadriven technique [7]. Another significant source of background comes from QCD multijet events, where one or more jets are misidentified as τ h .…”

“…These proceedings report the results of searches for the decays H → hh → bbττ and A → Zh → ττ (where denotes µ µ or ee), exploiting the same techniques used for the search for the SM Higgs boson at 125 GeV in a τ leptons pair [7]. Several different ττ signatures are studied: for the channel H → hh → bbττ, the µτ h , eτ h , and τ h τ h final states are considered, where τ h denotes a hadronically decaying τ, whereas for the channel A → Zh → ττ, the µτ h , eτ h , τ h τ h , and eµ final states are selected.…”

Identification of hadronic tau decays in CMS

“…Tau leptons constitute an important experimental signature for physics analyses at the LHC, such as the analysis of standard model (SM) Higgs → ττ production [1] searches for supersymmetry, for leptoquarks, Z' and W' bosons and for non-SM Higgs bosons.…”