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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). Combination of Measurements of CP Properties of Higgs Boson Interactions with Vector Bosons Using Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 137(2), 021801–22pp.
Abstract: A combination of measurements of the CP properties of Higgs boson interactions with electroweak gauge bosons is presented, using 140 fb(-1) of proton-proton collisions at root s = 13 TeV recorded by the ATLAS detector. Results from vector boson fusion H -> tau tau/WW*/gamma gamma, inclusive H -> ZZ*, and WH, H -> b (b) over bar channels are combined. No evidence of CP violation is observed, and constrains on the CP-violating operators in the Standard Model effective field theory framework (SMEFT) are set in theWarsaw basis. The results from the combination improve by over 40% on previous individual limits on c(H<(W)over tilde) and, for the first time, simultaneous constraints on three coefficients c(H<(W)over tilde>), c(H<(B)over tilde), and c(H<(W)over tildeB) are set. These limits are the most stringent constraints to date on the relevant Wilson coefficients in the SMEFT framework with minimum model dependence.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2026). Observation of CP Violation in B0 → J/ψρ (770)0 Decays. Phys. Rev. Lett., 137(3), 031803–14pp.
Abstract: The time-dependent CP asymmetry in B-0 -> J/psi rho (770)(0) decays is measured using proton-proton collision data corresponding to an integrated luminosity of 6 fb(-1), collected with the LHCb detector at a center-of-mass energy of 13 TeV during the years 2015-2018. The CP-violation parameters for this process are determined to be 2 beta(eff)(c (c) over bard) = 0.710 +/- 0.084 +/- 0.051 rad and vertical bar lambda vertical bar = 1.019 +/- 0.034 +/- 0.024, where the first uncertainty is statistical and the second systematic. This constitutes the first observation of timedependent CP violation in B-0 -> J/psi rho (770)(0) decays. Assuming approximate SU(3) flavor symmetry, these results are combined with the previous consistent LHCb measurement to set the most stringent constraint on the penguin contribution, Delta phi(s), to the CP-violating phase phi(s) in B-0 -> J/psi phi (1020) decays, yielding Delta phi(s) = 5.0 +/- 4.6 mrad.
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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). Missing-mass search in forward-proton-tagged dilepton events with the ATLAS detector. J. High Energy Phys., 07(7), 236–55pp.
Abstract: A search is conducted in proton-proton collisions at the Large Hadron Collider for photon-induced production pp -> pp + gamma gamma, (gamma gamma -> V X) of a visible particle V decaying into a pair of same-flavour charged leptons (e(+)e(-) or mu(+)mu(-)) and an undetected invisible component X. Measurements of the outgoing proton energies by the ATLAS forward proton spectrometer allow the full photon-photon four-momentum to be reconstructed. By subtracting the visible four-momentum of the central system measured with the ATLAS detector, the “missing mass” of any event components not detected in the central region can be reconstructed, enabling the reconstruction of X without knowing its properties, thus allowing the search to be model-independent. A search for a narrow resonance is performed in the missing-mass spectrum between 100 GeV and 900 GeV. The analysis uses data collected in 2017 from proton-proton collisions at a centre-of-mass energy of root s = 13TeV, corresponding to an integrated luminosity of 14.7 fb(-1). No significant excess over the Standard Model expectation is observed and upper limits at 95% confidence level are set on the fiducial cross sections for three different signal models in the range between 128 and 2.5 fb. Additionally, model-independent limits are set on the visible cross section of BSM processes, for two sets of selection criteria. Both individual lepton flavour decay channels of the visible boson and a combination of the two channels are considered.
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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). Search for long-lived charginos and τ-sleptons using final states with a disappearing track in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 152–56pp.
Abstract: This paper reports a search for decays of long-lived charginos or tau-sleptons to final states containing a short disappearing track, a single high-energy jet, and missing transverse momentum. The search uses 137 fb(-1) of data from 13TeV proton-proton collisions recorded by the ATLAS detector during Run 2 of the LHC. Multiple search regions are defined, all requiring the presence of a track reconstructed from either three or four measurements in the innermost layers of the ATLAS detector. Regions with tracks having only three measurements are further characterised by the absence or presence of a low-energy charged pion reconstructed using a dedicated algorithm, leveraging machine learning. Data-driven methods are used to estimate the background contributions in the search regions. No significant excesses are found and 95% CL lower limits are placed on the masses of charginos and tau-sleptons in the lifetime range 0.01-10 ns. Observed (expected) mass limits of up to 225 GeV (250 GeV) are set for pure-higgsino charginos in scenarios with lifetimes below 0.03 ns, where the electroweakino mass splitting is entirely due to loop corrections involving the Standard Model bosons, and up to 720 GeV (840 GeV) for charginos with a lifetime of around 1 ns. For wino production, charginos with masses up to 880 GeV (1020 GeV) are excluded for lifetimes of around 1 ns. For tau-sleptons with lifetimes of around 1 ns, masses are excluded up to 320 GeV (390 GeV) in Constrained Minimal Supersymmetric Standard Model scenarios and 300 GeV (380 GeV) in Gauge-Mediated Supersymmetry-Breaking scenarios.
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ATLAS Collaboration(Aad, G. et al), Ahuja, S., Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., et al. (2026). Constraints on effective field theories via quadruple-differential angular decay rates from t-channel single-top-quark production at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 107–62pp.
Abstract: Events with t-channel single top quarks are used to probe effective field theory operators in root s = 13TeV proton-proton collision data corresponding to 140 fb(-1) recorded by the ATLAS detector at the Large Hadron Collider. To extract a maximum amount of information from these events, the joint fourfold probability distribution for four kinematic angles is simultaneously analysed. A method leveraging Fourier techniques to handle the challenges arising from this approach is employed. The relevant effective field theory operators are those sensitive to top-quark decay and t-channel production vertices. Their Wilson coefficients are tightly constrained, with results compatible with Standard Model predictions.
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