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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Search for the associated production of charm quarks and a Higgs boson decaying into a photon pair with the ATLAS detector. J. High Energy Phys., 02(2), 045–36pp.
Abstract: A search for the production of a Higgs boson and one or more charm quarks, in which the Higgs boson decays into a photon pair, is presented. This search uses proton-proton collision data with a centre-of-mass energy of root s = 13TeV and an integrated luminosity of 140 fb(-1) recorded by the ATLAS detector at the Large Hadron Collider. The analysis relies on the identification of charm-quark-containing jets, and adopts an approach based on Gaussian process regression to model the non-resonant di-photon background. The observed (expected, assuming the Standard Model signal) upper limit at the 95% confidence level on the cross-section for producing a Higgs boson and at least one charm-quark-containing jet that passes a fiducial selection is found to be 10.6 pb (8.8 pb). The observed (expected) measured cross-section for this process is 5.3 +/- 3.2 pb (2.9 +/- 3.1 pb).
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Saa-Hernandez, A., Gonzalez-Diaz, D., Martin-Albo, J., Tuzi, M., Amedo, P., Baldonedo, J., et al. (2025). On the determination of the interaction time of GeV neutrinos in large argon gas TPCs. Eur. Phys. J. C, 85(5), 549–18pp.
Abstract: Next-generation megawatt-scale neutrino beams open the way to studying neutrino-nucleus scattering using gaseous targets for the first time. This represents an opportunity to improve the knowledge of neutrino cross sections in the energy region between hundreds of MeV and a few GeV, of interest for the upcoming generation of long-baseline neutrino oscillation experiments. The challenge is to accurately track and (especially) time the particles produced in neutrino interactions in large and seamless volumes down to few-MeV energies. We propose to accomplish this through an optically-read time projection chamber (TPC) filled with high-pressure argon and equipped with both tracking and timing functions. In this work, we present a detailed study of the time-tagging capabilities of such a device, based on end-to-end optical simulations that include the effect of photon propagation, photosensor response, dark count rate and pulse reconstruction. We show that the neutrino interaction time can be reconstructed from the primary scintillation signal with a precision in the range of 1-2.5 ns (sigma)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\sigma )$$\end{document} for point-like deposits with energies down to 5 MeV. A similar response is observed for minimum-ionizing particle tracks extending over lengths of a few meters. A discussion on previous limitations towards such a detection technology, and how they can be realistically overcome in the near future thanks to recent developments in the field, is presented. The performance demonstrated in our analysis seems to be well within reach of next-generation neutrino-oscillation experiments, through the instrumentation of the proposed TPC with conventional reflective materials and a silicon photomultiplier array behind a transparent cathode.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). First Determination of the Spin-Parity of Ξc(3055) +,0 Baryons. Phys. Rev. Lett., 134(8), 081901–13pp.
Abstract: The Xi(0(-))(b) -> Xi(c)(3055)(+(0))(-> D+(0)Lambda)pi(-) decay chains are observed, and the spin-parity of Xi(c)(3055)(+(0)) baryons is determined for the first time. The measurement is performed using protonproton collision data at a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1), recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the Xi(c)(3055)(+(0)) baryons is determined to be 3/2(+) with a significance of more than 6.5 sigma (3.5 sigma) compared to all other tested hypotheses. The up-down asymmetries of the Xi(0(-))(b) -> Xi(c)(3055)(+(0))pi(-) transitions are measured to be -0.92 +/- 0.10 +/- 0.05 (-0.92 +/- 0.16 +/- 0.22), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the Xi(c)(3055)(+(0)) baryons correspond to the first D-wave lambda-mode excitation of the Xi(c) flavor triplet.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2025). Measurement of the Branching Fraction Ratios R(D+) and R(D*+) Using Muonic τ Decays. Phys. Rev. Lett., 134(6), 061801–13pp.
Abstract: The branching fraction ratios of (B) over bar (0) -> D+tau(-)(v) over bar (tau) and (B) over bar (0) -> D*(+)tau(-)(v) over bar (tau) decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of 2.0 fb(-1) collected by the LHCb experiment in proton-proton collisions at root s = 13 TeV. The reconstructed final states are formed by combining D+ mesons with tau(-) -> mu(-) (v) over bar (mu)(v) over bar (tau) candidates, where the D+ is reconstructed via the D+ -> K- pi(+) pi(+) decay. The results are R(D+) = 0.249 +/- 0.043 +/- 0.047, R(D*(+)) = 0.402 +/- 0.081 +/- 0.085, where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of -0.39 and are compatible with the standard model.
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Herrero-Garcia, J., Landini, G., & Yanagida, T. T. (2025). Dark matter in the high-scale seesaw leptogenesis paradigm. Phys. Rev. D, 111(7), 075033–9pp.
Abstract: The seesaw mechanism with three heavy Majorana right-handed neutrinos provides an elegant explanation for neutrino masses and, combined with leptogenesis, can generate the baryon asymmetry of the universe (BAU). Naturally embedded in a grand unified theory, this framework stands as one of the best-motivated extensions beyond the Standard Model, but it is very difficult to test it. Moreover, it does not account for dark matter (DM). In this paper, we propose a minimal extension that introduces a dark sector with a singlet Majorana fermion (as the DM candidate) and a complex scalar singlet. The heavy righthanded neutrinos serve another role beyond generating neutrino masses and the BAU: producing the cold DM density through their decays. Interestingly, the model also predicts a subdominant DM component from late scalar decays, which in some cases may be hot or warm at the onset of structure formation, as well as an equal number of nonthermal neutrinos. These components leave distinct signatures in various cosmological observables. Furthermore, electromagnetic energy injection from scalar decays alter predictions from big bang nucleosynthesis and induce spectral distortions in the cosmic microwave background black-body spectrum. In this context, upcoming experiments, such as the Primordial Inflation Explorer (PIXIE), could probe the mechanism of neutrino mass generation.
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