Charged lepton flavor violation is a clear signal of new physics. Such decays are not allowed in the Standard Model, but highly anticipated in a large class of new physics models. The ATLAS and the CMS experiments at the Large Hadron Collider are only two places where we may discover lepton-flavor-violating decays of the Higgs boson in the near future. With the increase in center-of-mass energy at the Large Hadron Collider, the rate of production of Higgs boson have increased. This makes the present search at the world’s highest energy particle collider to be more interesting than ever.
A direct search for lepton flavor violation in decays of the Higgs boson with the ATLAS detector at the LHC is presented here. The analysis is performed in the H→ℓτ channel, where the leading lepton (ℓ) can be either an electron or a muon, and the tau (τ) lepton decays via the hadronic decay channel.
Preliminary sensitivity of the search is presented based on a data sample of proton–proton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 36 inverse-femto-barns (fb−1) at a center-of-mass energy (√s) of 13 trillion-electron-volts (TeV). The analysis is already found to be three times more sensitive than the previous analysis performed with 20 fb−1 of data collected at √s = 8 TeV during the 2012 data-taking period (Run1). The sources for this improvement are discussed in this presentation. They mainly arise from inclusion of additional phase-phase for the analysis with higher sensitivity to signal, as well as an improved description of the fake-background with a data-driven technique using a transfer factor from control region to signal region.
The plan of the present data-taking condition (Run2) is to accumulate 100 fb−1 of proton-proton collision data by the end of 2018, before 2-year long shutdown is planned at the Large Hadron Collider. The goal of this thesis is to complete analysis of 100 fb−1 of Run 2 data. The final sensitivity is expected to improve by another factor of 1.7 according to naïve luminosity-scaling with respect to the results with 36 fb−1. Further improvements are expected by inclusion of another phase-space corresponding to Vector Boson Fusion production mechanism of the Higgs boson, as well as use of multi-variate signal-to-background discriminants.
This search would strongly constrain lepton flavor violation expected in a wide variety of new physics models or discover signature of new physics.