Evidence for the Dimuon Decay of the Higgs Boson in $ pp$ Collisions with the ATLAS Detector

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\text{}\text{}{\mathrm{fb}}^{-1}$ at $ \sqrt{s}=13.6\text{}\text{}\mathrm{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\sigma $ ($ 2.5\sigma $ expected). The best-fit signal strength is $ \mu =1.4\pm 0.4$. This result provides evidence for the $ H\to \mu \mu $ decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions.