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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R.:, Cabrera Urban, S., Cantero, J., Carrion Martinez, C., et al. (2026). Search for higgsinos in compressed mass spectra using low-momentum tracks in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 06(6), 094–68pp.
Abstract: This paper presents two searches for the electroweak production of higgsinos with compressed mass spectra using 140 fb(-1) of root s = 13TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. Events are required to feature an energetic jet, large missing transverse momentum, and at least one low-momentum charged particle that serves as a candidate higgsino decay product. In the first search, targeting higgsino mass splittings in the range of 0.3-1 GeV, the higgsinos are expected to predominantly decay into pions that are identified as low-momentum charged particles with large transverse impact parameters due to the long higgsino lifetime (c tau approximate to O(0.1-10mm)), and neural networks are used to discriminate between signal and background processes. The second search targets larger mass splittings in the range of 1-3 GeV, where the higgsinos are expected to decay promptly into low-momentum leptons, one of which is identified by dedicated low-momentum electron or muon taggers based on neural networks utilising tracking and calorimeter information. No significant excess above the Standard Model prediction is observed in either search and the results are interpreted within simplified models, to set lower limits on the masses of the higgsino-like charginos and neutralinos. Together, these searches exclude chargino masses below 126 GeV at 95% confidence level for mass splittings between the chargino and lightest neutralino in the range of 0.3-2 GeV. This represents the first ATLAS constraints in a portion of this parameter space and surpasses the limits previously set by other experiments.
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Mitsou, V. A. (2026). Magnetic monopoles: from Dirac to the Large Hadron Collider. Eur. Phys. J.-Spec. Top., , 41pp.
Abstract: One of the basic properties of magnetism is that a magnet has always two poles, north and south, which cannot be separated into isolated poles, the magnetic monopoles. There are strong theoretical arguments in favour of monopoles' existence, but in spite of extensive searches they are yet to be found. In this review article, after highlighting briefly the theoretical foundations of monopoles, a historical overview of experimental endeavours to observe them is given, with emphasis on the state-of-the-art of searches in cosmic and collider experiments and in particular the Large Hadron Collider at CERN.
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Marchini, N. et al, & Valiente Dobon, J. J. (2026). Shape coexistence in 94Zr from a model-independent analysis. Phys. Lett. B, 879, 140668–7pp.
Abstract: Low-lying states of Zr-94 were investigated via low-energy multi-step Coulomb excitation. From the measured gamma-ray yields, 16 reduced E2 transition probabilities between low-spin states were determined, together with the spectroscopic quadrupole moments of the 2(1,2)+ states. Based on this information, for the first time in the Zr isotopic chain, the shapes of the 0(1,2)(+) states including their deformation softness were inferred in a model-independent way using the quadrupole sum rules approach. The ground state of Zr-94 possesses a rather diffuse shape associated with a spherical configuration, while the 0(2)(+) state is triaxial tending towards oblate and more strongly deformed. The observed features of shape coexistence in Zr-94 are consistent with both Monte-Carlo shell-model predictions and IBM-CM calculations, and provide model-independent constraints on the shape character assigned in the IBM-CM to the intruder configuration in Zr92-96.
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Cole, E., Costantini, M. N., Hammou, E., Mantani, L., Merlotti, F., Morales-Alvarado, M., et al. (2026). Tailored PDFs for new physics searches. J. High Energy Phys., 07(7), 043–52pp.
Abstract: Given the non-negligible interplay between parton distribution functions (PDFs) at large x and potential New Physics (NP) effects in the high-energy tails of hadron collider observables, a central question is which PDFs can be reliably employed in beyond-the-Standard-Model (BSM) analyses. In this work, we examine the fine balance between using PDF sets with small uncertainties in the large-x region – crucial for maximising BSM sensitivity – and adopting conservative PDF fits that exclude high-energy data potentially contaminated by unaccounted NP contributions. We systematically assess a range of conservative PDF fitting strategies designed to mitigate such biases and provide a recommendation for the class of PDFs best suited for robust BSM searches. In addition, we investigate the alternative approach of performing simultaneous fits of Standard Model Effective Field Theory (SMEFT) Wilson coefficients and PDFs, thereby consistently accounting for their mutual correlations. Starting from a toy model to illustrate the underlying mechanisms, we then analyse two realistic NP scenarios: one modifying high-mass Drell-Yan production and another affecting the high-invariant-mass tail of top-quark pair production. Both cases are representative of measurements that will be probed with high precision during the High-Luminosity phase of the LHC.
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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 massive, long-lived particles in events with displaced vertices and displaced muons in pp collisions at √s=13.6 TeV with the ATLAS experiment. Phys. Lett. B, 878, 140509–23pp.
Abstract: A search is presented for massive long-lived particles in events featuring at least one displaced vertex and at least one displaced muon, using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider from 2022 to 2024 at a centre-of-mass energy of 13.6 TeV. The data sample corresponds to an integrated luminosity of 164 fb(-1). The analysis targets scenarios in which long-lived particles decay inside the ATLAS inner detector, resulting in a topology of at least one massive, displaced vertex (DV) with multiple associated tracks, and at least one muon with a large transverse impact parameter relative to the primary interaction point. The muon is not required to be associated with the DV. Two signal regions are defined by the transverse distance of the reconstructed DV from the interaction point. Background contributions are estimated by using fully data-driven techniques. No significant excess above the expected background is observed. Upper limits at 95% confidence level are set on the visible cross-section and on the production cross-sections of several benchmark models of R-parity-violating supersymmetry.
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