Evidence for the dimuon decay of the Higgs boson in pp collisions with the ATLAS detector

Abstract

A search for the dimuon decay of the Higgs boson is presented based on pp collision data recorded by ATLAS during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of 165 fb$^{-1}$ at $\sqrt{s} = 13.6$ TeV. To enhance the sensitivity, the results are combined with those from Run 2. An excess of events over the background is observed with a significance of $3.4 σ$ ($2.5 σ$ expected). The best-fit signal strength is $μ= 1.4\pm0.4$. This result provides evidence for the $H \to μμ$ decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions.

Figures (2)

• Figure 1: Observed dimuon invariant mass spectrum combining all of the Run-3 categories. The events and probability density functions (pdf) are weighted by $\ln(1 + S/B)$, where $S$ and $B$ are the signal and background yields, respectively, evaluated in the $m_{\mu\mu}\xspace = 120-130\,\,\text{Ge V}$ window. These yields are extracted from the fit performed in the mass range $m_{\mu\mu}\xspace = 110-160~\,\text{Ge V}$, providing a signal strength of $\mu = 1.6 \pm 0.6$. The background and signal pdfs are obtained from the fit to the data. The lower panel shows the data with the background model subtracted, and the fitted signal pdf, normalized to the signal best-fit value. Error bars represent the data statistical uncertainties.
• Figure 2: Best-fit values of the signal-strength parameters for the analysis of the Run-3 data and the full Run-2 dataset. Results are first shown for Run 3 by grouping the signal strength parameters into six major categories ($t\bar{t}H$, $VH$, VBF, 2-jet, 1-jet, and 0-jet), where the systematic uncertainties reported in the legend are symmetrized. In the lower part of the plot, the full Run-2 and Run-3 results are given, as well as their combination.