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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Caron, S., Dobreva, N., Ferrer Sanchez, A., Martin-Guerrero, J. D., Odyurt, U., Ruiz de Austri, R., et al. (2025). Trackformers: in search of transformer-based particle tracking for the high-luminosity LHC era. Eur. Phys. J. C, 85(4), 460–20pp.
Abstract: High-Energy Physics experiments are facing a multi-fold data increase with every new iteration. This is certainly the case for the upcoming High-Luminosity LHC upgrade. Such increased data processing requirements forces revisions to almost every step of the data processing pipeline. One such step in need of an overhaul is the task of particle track reconstruction, a.k.a., tracking. A Machine Learning-assisted solution is expected to provide significant improvements, since the most time-consuming step in tracking is the assignment of hits to particles or track candidates. This is the topic of this paper. We take inspiration from large language models. As such, we consider two approaches: the prediction of the next word in a sentence (next hit point in a track), as well as the one-shot prediction of all hits within an event. In an extensive design effort, we have experimented with three models based on the Transformer architecture and one model based on the U-Net architecture, performing track association predictions for collision event hit points. In our evaluation, we consider a spectrum of simple to complex representations of the problem, eliminating designs with lower metrics early on. We report extensive results, covering both prediction accuracy (score) and computational performance. We have made use of the REDVID simulation framework, as well as reductions applied to the TrackML data set, to compose five data sets from simple to complex, for our experiments. The results highlight distinct advantages among different designs in terms of prediction accuracy and computational performance, demonstrating the efficiency of our methodology. Most importantly, the results show the viability of a one-shot encoder-classifier based Transformer solution as a practical approach for the task of tracking.
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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). Disentangling Sources of Momentum Fluctuations in Xe plus Xe and Pb plus Pb Collisions with the ATLAS Detector. Phys. Rev. Lett., 133(25), 252301–23pp.
Abstract: High-energy nuclear collisions create a quark-gluon plasma, whose initial condition and subsequent expansion vary from event to event, impacting the distribution of the eventwise average transverse momentum [P([p(T)])]. Disentangling the contributions from fluctuations in the nuclear overlap size (geometrical component) and other sources at a fixed size (intrinsic component) remains a challenge. This problem is addressed by measuring the mean, variance, and skewness of P([p(T)]) in Pb-208 thorn Pb-208 and Xe-129 thorn Xe-129 collisions at root s(NN) = 5.02 and 5.44 TeV, respectively, using the ATLAS detector at the LHC. All observables show distinct features in ultracentral collisions, which are explained by a suppression of the geometrical component as the overlap area reaches its maximum. These results demonstrate a new technique to separate geometrical and intrinsic fluctuations, providing constraints on initial conditions and properties of the quark-gluon plasma, such as the speed of sound.
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Batool, A., Malik Sultan, A., Olmo, G. J., & Rubiera-Garcia, D. (2024). Stellar structure in f(R,T) gravity: Some exact solutions. Phys. Rev. D, 110(6), 064059–6pp.
Abstract: We find some exact solutions for constant-density and quark matter equations of state in stellar structure models framed within the f(R, T) = R + lambda(KT)-T-2 theory of gravity, where R is the curvature scalar, T the trace of the stress-energy tensor, and lambda some constant. These solutions correspond to specific values of the constant lambda and represent different compactness states of the corresponding stars, though only those made of quark matter can be regarded as physical. The latter modify the compactness (Buchdahl) limit of neutron stars upward for lambda > 0 until saturating the one of black holes. Our results show that it is possible to find useful insights on stellar structure in this class of theories, a fact that could be used for obtaining constraints on limiting masses such as the minimum hydrogen burning mass.
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Ferreira, M. N., & Papavassiliou, J. (2024). Nonlinear Schwinger mechanism in QCD, and Fredholm alternatives theorem. Eur. Phys. J. C, 84(8), 835–25pp.
Abstract: We present a novel implementation of the Schwinger mechanism in QCD, which fixes uniquely the scale of the effective gluon mass scale and streamlines considerably the procedure of multiplicative renormalization. The key advantage of this method stems from the nonlinear nature of the dynamical equation that generates massless poles in the longitudinal sector of the three-gluon vertex. An exceptional feature of this approach is an extensive cancellation involving the components of the integral expression that determines the gluon mass scale; it is triggered once the Schwinger-Dyson equation of the pole-free part of the three-gluon vertex has been appropriately exploited. It turns out that this cancellation is driven by the so-called Fredholm alternatives theorem, which operates among the set of integral equations describing this system. Quite remarkably, in the linearized approximation this theorem enforces the exact masslessness of the gluon. Instead, the nonlinearity induced by the full treatment of the relevant kernel evades this theorem, allowing for the emergence of a nonvanishing mass scale. The numerical results obtained from the resulting equations are compatible with the lattice findings, and may be further refined through the inclusion of the remaining fundamental vertices of the theory.
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IDS Collaboration(Lica, R. et al), Algora, A., & Nacher, E. (2025). Revealing the Nature of yrast States in Neutron-Rich Polonium Isotopes. Phys. Rev. Lett., 134(5), 052502–7pp.
Abstract: Polonium isotopes having two protons above the shell closure at Z = 82 show a wide variety of lowlying, high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to 210Po (N = 126) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the 8+ level in 214,216,218Po isotopes produced in the beta- decay of 214,216,218Bi at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the 8+1 state in 214Po is nearly 20 times shorter than the value available in the literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding 8+1 states in 216,218Po, respectively. The measured B(E2; 8+1 -> 6+1 ) transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for 216Po. The increase contradicts the previous claims of isomerism for the 8+ yrast states in neutron-rich 214Po and beyond. Together with the other measured yrast transitions, the B(E2) values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H 208 effective interactions and their pairing-modified versions, showing an increase in configuration mixing when moving toward the heavier isotopes.
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King, S. F., Leontaris, G. K., Marsili, L., & Zhou, Y. L. (2024). Leptogenesis in realistic flipped SU(5). J. High Energy Phys., 12(12), 211–18pp.
Abstract: We study thermal leptogenesis in realistic supersymmetric flipped SU(5) x U(1) unification. As up-type quarks and neutrinos are arranged in the same multiplets, they exhibit strong correlations, and it is commonly believed that the masses of right-handed (RH) neutrinos are too hierarchical to fit the low-energy neutrino data. This pattern generally predicts a lightest RH neutrino too light to yield successful leptogenesis, with any lepton-antilepton asymmetry generated from heavier neutrinos being washed out unless special flavour structures are assumed. We propose a different scenario in which the lightest two RH neutrinos N1 and N2 have nearby masses of order 109 GeV, with thermal leptogenesis arising non-resonantly from both N1 and N2. We show that this pattern is consistent with all data on fermion masses and mixing and predicts the lightest physical left-handed neutrino mass to be smaller than about 10-7 eV. The Dirac phase, which does not take the maximal CP-violating value, plays an important role in leptogenesis.
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Duan, M. Y., Bayar, M., & Oset, E. (2024). Precise determination of the ηΛ scattering length and effective range and relationship to the Λ(1670) resonance. Phys. Lett. B, 857, 139003–5pp.
Abstract: We use the Belle data on the K(-)p mass distribution of the Lambda(+)(c)-> pK(-)pi(+) reaction near the eta Lambda threshold to determine the eta Lambda scattering length and effective range. We show that from these data alone we can determine the value of a with better precision than so far determined, and the value of r(0) for the first time. The addition of the K(-)p ->eta Lambda data allows us to improve the precision of these magnitudes, with errors smaller than 15%. We also determine with high precision the pole position of the Lambda(1670).
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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 decays of the Higgs boson into a pair of pseudoscalar particles decaying into b(b)over-barτ+τ- using pp collisions at √s=13 TeV with the ATLAS detector. Phys. Rev. D, 110(5), 052013–34pp.
Abstract: This paper presents a search for exotic decays of the Higgs boson into a pair of new pseudoscalar particles, H -> aa, where one pseudoscalar decays into a b-quark pair and the other decays into a tau-lepton pair, in the mass range 12 <= m(a) <= 60 GeV. The analysis uses pp collision data at root s = 13 TeV collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb(-1). No significant excess above the Standard Model (SM) prediction is observed. Assuming the SM Higgs boson production cross section, the search sets upper limits at 95% confidence level on the branching ratio of Higgs bosons decaying into b (b) over bar tau(+)tau(-), B(H -> aa -> b (b) over bar tau(+)tau(-)), between 2.2% and 3.9% depending on the pseudoscalar mass.
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ANTARES Collaboration(Albert, A. et al), Alves, S., Calvo, D., Carretero, V., Gozzini, R., Hernandez-Rey, J. J., et al. (2024). Constraints on the energy spectrum of the diffuse cosmic neutrino flux from the ANTARES neutrino telescope. J. Cosmol. Astropart. Phys., 08(8), 038–27pp.
Abstract: High-significance evidences of the existence of a high-energy diffuse flux of cosmic neutrinos have emerged in the last decade from several observations by the IceCube Collaboration. The ANTARES neutrino telescope took data for 15 years in the Mediterranean Sea, from 2007 to 2022, and collected a high-purity all-flavour neutrino sample. The search for a diffuse cosmic neutrino signal using this dataset is presented in this article. This final analysis did not provide a statistically significant observation of the cosmic diffuse flux. However, this is converted into limits on the properties of the cosmic neutrino spectrum. In particular, given the sensitivity of the ANTARES neutrino telescope between 1 and 50TeV, constraints on single-power-law hypotheses are derived for the cosmic diffuse flux below 20TeV, especially for power-law fits of the IceCube data with spectral index softer than 2.8.
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