Search for the Standard Model Higgs boson decay to $μ^{+}μ^{-}$ with the ATLAS detector

TL;DR

ATLAS searches for the Standard Model Higgs boson decay to μ^+μ^- using 24.8 fb^{-1} of pp collision data at 7 and 8 TeV. The analysis employs seven categories, including a VBF-hadronic signature, and analytic signal/background models to fit the dimuon mass spectrum in 110–160 GeV, aiming to observe a narrow H→μμ resonance. No excess over background is found; for m_H=125.5 GeV the observed (expected) signal strength upper limit is 7.0 (7.2) times the SM expectation, corresponding to BR(H→μμ) < 1.5×10^{-3}. This result constrains the Higgs coupling to second-generation fermions and demonstrates the sensitivity of dimuon final states for precision Higgs couplings.

Abstract

A search is reported for Higgs boson decay to $μ^{+}μ^{-}$ using data with an integrated luminosity of $24.8~\rm{fb}^{-1}$ collected with the ATLAS detector in $pp$ collisions at $\sqrt{s}$=7 and 8 TeV at the CERN Large Hadron Collider. The observed dimuon invariant mass distribution is consistent with the Standard Model background-only hypothesis in the 120-150 GeV search range. For a Higgs boson with a mass of 125.5 GeV, the observed (expected) upper limit at the 95 % confidence level is 7.0 (7.2) times the Standard Model expectation. This corresponds to an upper limit on the branching ratio BR($H \rightarrow μ^+μ^-$) of $1.5\times10^{-3}$.

Figures (4)

• Figure 1: The distribution of the dimuon invariant mass (top) and dimuon momentum (bottom) for 7 TeV and 8 TeV data with all the selection requirements described in Section \ref{['sec:event']}. The expected signal is shown for $m_{H}=125$Ge V.
• Figure 2: The background model fits to the $m_{\mathrm{\mu^+ \mu^-}}$ distribution for the central medium $p_{\rm T}^{\mu^{+}\mu^{-}}$ category for 7 TeV (top) and 8 TeV (bottom) data. The statistical uncertainties are given for the data points. The expected signal is shown for $m_{H}=125$Ge V and is scaled by a factor of 50.
• Figure 3: The signal model fit to the $m_{\mathrm{\mu^+ \mu^-}}$ distribution for the central (top) and non-central (bottom) simulated Higgs boson events for $m_{H}=125$ GeV in the medium $p_{\rm T}^{\mu^{+}\mu^{-}}$ category for $\sqrt{s}=8$ TeV.
• Figure 4: Observed (solid) and expected (dashed) 95% CL upper limits on the $H \rightarrow \mu^+\mu^-$ signal strength as a function of $m_H$ over the mass range $120\hbox{--}150~\rm{GeV}$. The dark- and light-shaded regions indicate the $\pm 1\sigma$ and $\pm2\sigma$ uncertainty bands on the expected limit, respectively.