Abstract
Searches for the Higgs boson decays H→ee and H→eμ are performed using data corresponding to an integrated luminosity of 139fb−1 collected with the ATLAS detector in pp collisions at s=13 TeV at the LHC. No significant signals are observed, in agreement with the Standard Model expectation. For a Higgs boson mass of 125 GeV, the observed (expected) upper limit at the 95% confidence level on the branching fraction B(H→ee) is 3.6×10−4 (3.5×10−4) and on B(H→eμ) is 6.2×10−5 (5.9×10−5). These results represent improvements by factors of about five and six on the previous best limits on B(H→ee) and B(H→eμ) respectively.
Highlights
The discovery of a heavy scalar particle by ATLAS and CMS [1, 2] provided experimental confirmation of the Englert–Brout–Higgs mechanism [3,4,5,6,7,8], which spontaneously breaks electroweak (EW)gauge symmetry and generates mass terms for the W and Z gauge bosons
The observed dielectron mass spectra are divided into 200 mee bins in each of the seven categories and signal yields are obtained in a simultaneous maximum-likelihood fit
The Higgs boson production cross sections are assumed to be as predicted in the Standard Model
Summary
The discovery of a heavy scalar particle by ATLAS and CMS [1, 2] provided experimental confirmation of the Englert–Brout–Higgs mechanism [3,4,5,6,7,8], which spontaneously breaks electroweak (EW). This Letter presents the first ATLAS searches for H → ee and for the lepton-flavour-violating decay H → eμ using the full Run. 2 datase√t of proton–proton ergy of s = 13 TeV, with (pp) collisions an integrated at a centre-of-mass enluminosity of 139 fb−1. There are strong indirect constraints on the off-diagonal Yeμ coupling, the strongest derived from limits on the branching fraction of μ → eγ and the electric dipole moment of the electron [19]. These indirect constraints assume SM values for the as yet unmeasured Yee and Yμμ. The production of top quarks, dibosons (mainly through W W → eνeμνμ), W +jets and multijet events, with jets misidentified as leptons, are more important than in the ee search
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