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ATLAS Collaboration(Aad, G. et al), Ahuja, S., Aikot, A., Cabrera Urban, S., Cantero, J., Carrion Martinez, C., et al. (2026). A search for lepton-flavour violating τ → 3μ decays with the ATLAS detector. Phys. Lett. B, 880, 140748–18pp.
Abstract: A search for charged lepton flavour violation in tau -> 3 μdecays is performed in pp collisions at a centre-of-mass energy of 13 TeV using ATLAS data collected between 2016 and 2018, corresponding to an integrated luminosity of 137 fb(-1). The search is optimised for the electroweak W -> tau nu production channel, due to its higher trigger efficiency, but also considers potential signal events from heavy-flavour production. Data are collected using two-muon and three-muon triggers and a multivariate analysis is used to separate the signal from the background. An unbinned likelihood fit is then performed to the resulting three-muon invariant mass spectrum and the data are found to be compatible with the background-only hypothesis. The observed (expected) limit on the branching ratio B(tau -> 3 mu) is found to be 8.7 x 10(-8) (7.5 x 10(-8)) at 90% CL
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2026). Search for Higgs bosons produced in association with a high-energy photon via vector-boson fusion and decaying to a pair of b-quarks in the ATLAS detector. Phys. Lett. B, 877, 140279–20pp.
Abstract: A search for Standard Model Higgs bosons produced in association with a high-energy photon and decaying to b (b) over bar is performed using 133 fb(-1) of root s = 13 TeV pp collision data collected with the ATLAS detector at the Large Hadron Collider at CERN. The photon requirement reduces the multijet background, and the H -> b (b) over bar decay is the dominant decay mode. Event selection requirements target events produced by vector-boson fusion, the dominant production mode in this channel. Several improvements enhance the search sensitivity compared to previous measurements. These improvements include better background modelling and characterization, the use of a neural-network classifier, and an updated signal extraction strategy adopting a direct binned-likelihood fit to the classifier output. With these improvements, the Higgs boson signal strength is measured to be 0.2 +/- 0.7 relative to the Standard Model prediction. This corresponds to an observed significance of 0.3 standard deviations, compared to an expectation of 1.5 standard deviations assuming the Standard Model.
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