Rare Higgs decays with ATLAS and CMS

In the summer of 2012 the ATLAS and CMS collaborations discovered a new particle with a mass of approximately 125 GeV via decays to photon, $W$ and $Z$ boson pairs with rates consistent with those of the SM Higgs boson. There are three experimentally accessible channels at the LHC for detecting Higgs boson decays to fermions: $H o bar{b}$ , $H o au^{+} au^{-}$ and $H o mu^{+} mu^{-}$ . The branching ratios for these decays are proportional to the fermion masses with the $bar{b}$ and $ au^{+} au^{-}$ decay modes dominant for $m_H$ = 125 GeV. The $H o mu^{+} mu^{-}$ decay has a clean final-state signature and it is the only channel where a Higgs coupling to the second generation fermions can be measured at the LHC. This is a very challenging measurement due to a small $H o mu^{+} mu^{-}$ branching ratio and high SM backgrounds. The SM branching ratio for the H → μ+μ− decays is of the order of $(28 − 6) imes 10^{−5}$ in the Higgs boson mass range 110–150 GeV. The dominant irreducible SM background is the $Z/gamma^∗ o mu^{+} mu^{-}$ process with a very high production rate compared to an expected Higgs signal. The talk presents an inclusive search for the Standard Model Higgs boson decaying into a muon–antimuon pair has been performed using data collected with the ATLAS and CMS detector in pp collisions at √s = 8 TeV at the Large Hadron Collider.