ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Search for single-production of vector-like quarks decaying into Wb in the fully hadronic final state in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 02(2), 075–44pp.
Abstract: A search for T and Y vector-like quarks produced in proton-proton collisions at a centre-of-mass energy of 13 TeV and decaying into Wb in the fully hadronic final state is presented. The search uses 139 fb(-1) of data collected by the ATLAS detector at the LHC from 2015 to 2018. The final state is characterised by a hadronically decaying W boson with large Lorentz boost and a b-tagged jet, which are used to reconstruct the invariant mass of the vector-like quark candidate. The main background is QCD multijet production, which is estimated using a data-driven method. Upon finding no significant excess in data, mass limits at 95% confidence level are obtained as a function of the global coupling parameter, kappa. The observed lower limits on the masses of Y quarks with kappa = 0.5 and kappa = 0.7 are 2.0 TeV and 2.4 TeV, respectively. For T quarks, the observed mass limits are 1.4 TeV for kappa = 0.5 and 1.9 TeV for kappa = 0.7.
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KM3NeT Collaboration(Aiello, S. et al), Alves Garre, S., Bariego-Quintana, A., Calvo, D., Carretero, V., Cecchini, V., et al. (2025). Probing invisible neutrino decay with the first six detection units of KM3NeT/ORCA. J. High Energy Phys., 04(4), 105–24pp.
Abstract: In the era of precision measurements of neutrino oscillation parameters, it is necessary for experiments to disentangle discrepancies that may indicate physics beyond the Standard Model in the neutrino sector. KM3NeT/ORCA is a water Cherenkov neutrino detector under construction and anchored at the bottom of the Mediterranean Sea. The detector is designed to study the oscillations of atmospheric neutrinos and determine the neutrino mass ordering. This paper focuses on the initial configuration of ORCA, referred to as ORCA6, which comprises six out of the foreseen 115 detection units of photosensors. A high-purity neutrino sample was extracted during 2020 and 2021, corresponding to an exposure of 433 kton-years. This sample is analysed following a binned log-likelihood approach to search for invisible neutrino decay, in a three-flavour neutrino oscillation scenario, where the third neutrino mass state nu 3 decays into an invisible state, e.g. a sterile neutrino. The resulting best fit of the invisible neutrino decay parameter is alpha 3=0.92-0.57+1.08x10-4\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\alpha}3={0.92}{-0.57}<^>{+1.08}\times {10}<^>{-4} $$\end{document} eV2, corresponding to a scenario with theta 23 in the second octant and normal neutrino mass ordering. The results are consistent with the Standard Model, within a 2.1 sigma interval.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2025). Search for diphoton resonances in the 66 to 110 GeV mass range using pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 01(1), 053–45pp.
Abstract: A search is performed for light, spin-0 bosons decaying into two photons in the 66 to 110 GeV mass range, using 140 fb(-1) of proton-proton collisions at root s = 13TeV produced by the Large Hadron Collider and collected by the ATLAS detector. Multivariate analysis techniques are used to define event categories that improve the sensitivity to new resonances beyond the Standard Model. A model-independent search for a generic spin-0 particle and a model-dependent search for an additional low-mass Higgs boson are performed in the diphoton invariant mass spectrum. No significant excess is observed in either search. Mass-dependent upper limits at the 95% confidence level are set in the model-independent scenario on the fiducial cross-section times branching ratio into two photons in the range of 8 fb to 53 fb. Similarly, in the model-dependent scenario upper limits are set on the total cross-section times branching ratio into two photons as a function of the Higgs boson mass in the range of 19 fb to 102 fb.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb-1 of pp collision data collected by the ATLAS detector. J. High Energy Phys., 07(7), 250–49pp.
Abstract: This paper presents a search for top-squark pair production in final states with a top quark, a charm quark and missing transverse momentum. The data were collected with the ATLAS detector during LHC Run 2 and correspond to an integrated luminosity of 139 fb(-1) of proton-proton collisions at a centre-of-mass energy of root s = 13TeV. The analysis is motivated by an extended Minimal Supersymmetric Standard Model featuring a non-minimal flavour violation in the second- and third-generation squark sector. The top squark in this model has two possible decay modes, either (t) over tilde (1) -> c (chi) over tilde (0)(1) or (t) over tilde (1) -> t (chi) over tilde (0)(1), where the (chi) over tilde (0)(1) is undetected. The analysis is optimised assuming that both of the decay modes are equally probable, leading to the most likely final state of tc + E-T(miss). Good agreement is found between the Standard Model expectation and the data in the search regions. Exclusion limits at 95% CL are obtained in the m((t) over tilde1) vs . m((chi) over tilde (0)(1)) plane and, in addition, limits on the branching ratio of the (t) over tilde -> t (chi) over tilde (0)(1)1 decay as a function of m((t) over tilde (1)) are also produced. Top-squark masses of up to 800 GeV are excluded for scenarios with light neutralinos, and top-squark masses up to 600 GeV are excluded in scenarios where the neutralino and the top squark are almost mass degenerate.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2024). Search for dark mesons decaying to top and bottom quarks in proton-proton collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 09(9), 005–55pp.
Abstract: A search for dark mesons originating from strongly-coupled, SU(2) dark flavor symmetry conserving models and decaying gaugephobically to pure Standard Model final states containing top and bottom quarks is presented. The search targets fully hadronic final states and final states with exactly one electron or muon and multiple jets. The analyzed data sample corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions collected at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider. No significant excess over the Standard Model background expectation is observed and the results are used to set the first direct constraints on this type of model. The two-dimensional signal space of dark pion masses m(pi D) and dark rho-meson masses m(rho D) is scanned. For m(pi D)/m(rho D) = 0.45, dark pions with masses m(pi D)< 940 GeV are excluded at the 95% CL, while for m(pi D)/m(rho D) = 0.25 masses m(pi D)< 740 GeV are excluded.
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