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Cho, Y. et al, & Perez-Vidal, R. M. (2026). Regularity of core coupled high-spin structure in neutron-rich 196-202Au isotopes approaching N=126. Phys. Lett. B, 878, 140558–7pp.
Abstract: Excited states built upon long-lived high-spin isomers in hard-to-reach neutron-rich Au (Z = 79) isotopes were populated using multi-nucleon transfer reactions between 136Xe and 198Pt at 7 MeV/u. These states in 196,198-202Au were identified for the first time using the powerful combination of the VAMOS++ spectrometer, the CATLIFE detection system, and the AGATA 1-ray tracking array. Their measured energies exhibit remarkable regularity as a function of neutron number and are seen to be inherited from the energies of yrast-band members in the corresponding Hg (Z = 80) isotope. Large-scale shell-model calculations reproduce the observed regularity and show that these states arise from the unique-parity orbitals 20h11/2 and v0i13/2 coupled to the Hg core. This regularity is due to the dominant proton configurations of the Hg and Au isotopes, where the level energies are almost independent of different neutron-orbital occupancies. The calculated Au wave functions show significant higher-spin components of the corresponding Hg core, unlike what is expected in the conventional interpretation in terms of the weak-coupling/decoupling limits of the particle-core coupling model.
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Ramos, D., Caamaño, M., Farget, F., Rodriguez-Tajes, C., Lemasson, A., Rejmund, M., et al. (2026). Isotopic fission yields of 240Pu as a function of the excitation energy. Phys. Rev. C, 113(5), 054611–10pp.
Abstract: Complete isotopic fission yields distributions of 240Pu have been measured as a function of the initial excitation energy. The 240Pu fissioning system was produced through a two-proton transfer reaction between a 238U beam and a 12C target. The reaction was measured in inverse kinematics at Coulomb barrier energies, allowing for the full distribution of fission fragments to be isotopically identified with the VAMOS + + Spectrometer. The excitation energy of the system was measured on an event-by-event basis by detecting the targetlike recoil 10Be in a segmented silicon telescope. This manuscript reports on the evolution of the fission yields as a function of the excitation energy of the system between 8.2 to 11.9 MeV. The influence of the excitation energy is manifested in the damping of shell effects that feed the yields in the symmetry valley, as well as in a reduction of the neutron content of the fragments. This reduction, however, is observed only in the heavy fragment, while the neutron content of the light fragment remains unaffected. The comparison with previous measurements, models, and evaluations highlights the importance of correlated observables for improving fission models.
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Patel, R. V., Shah, M. A., & Pandya, B. (2026). Singly heavy cascade baryon Ξc0, Ξc′0, Ξb- & Ξb′- spectroscopy in the relativistic framework of independent quark model. Eur. Phys. J. C, 86(6), 608–21pp.
Abstract: In this work, the potential parameters of the independent quark model are systematically reduced using previously determined inputs from a broad range of baryons. The reduced-parameter formulation, developed within the relativistic Dirac formalism and employing a Martin-like potential, is then applied to the spectroscopy of the singly heavy baryons Xi c0 and Xi b- in anti-triplet(3 & strns;) and sextet(6) representations. This enables an explicit verification of the linear relation obtained between the potential parameters. Radially and orbitally excited state masses are calculated accordingly, and the resulting Regge trajectories are used to assign spin-parity of experimentally observed states. The observed states Xi c0(2882), Xi c0(2923), and Xi c0(2970) are interpreted as JP=32- states, where Xi c0(2882) is assigned to the anti-triplet (3 & strns;) configuration, while Xi c0(2923) and Xi c0(2970) are identified as sextet (6) states. In the bottom sector, the Xi b-(6227) state is interpreted either as a 3 & strns; baryon with JP=52+ or as a 6 baryon with JP=32+. To investigate the electromagnetic structure of these baryons, their magnetic moments and radiative decay widths are computed. Additionally, the two-body weak decay branching ratios of Xi c0 are evaluated and compared with experimental data to assess the robustness of the approach. The two-body nonleptonic decays of Xi b '- are also analyzed, providing predictions for branching ratios that may be tested in future experiments. Overall, the results demonstrate the effectiveness of the parameter-reduction procedure and support its applicability in the spectroscopy of heavy flavor baryons.
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Bolton, P. D., Kamenik, J. F., & Novoa-Brunet, M. (2026). Dark light shining on B -> K(*) Emiss. Phys. Rev. D, 113(11), 115001–20pp.
Abstract: Recent Belle II data on B+ -* K+Emiss show an excess consistent with a two-body decay involving a light invisible particle with mass around 2.1 GeV. We present a UV-complete explanation based on a Higgsed U(1)' gauge symmetry with a light vector boson Z' and a vectorlike top partner, which naturally enhances b -* s transitions. While the minimal model can reproduce the required B -* K(*)Z' rate, it is excluded by LHCb searches for resonant dimuon decays due to unavoidable loop-induced couplings of Z' to charged leptons. We show that a minimal extension with an additional light U(1)'-charged singlet fermion allows Z' to decay dominantly invisibly, evades existing constraints coming also from dark photon and collider searches as well as Higgs measurements, and can simultaneously account for the Belle II excess and the observed dark matter abundance through resonant thermal freeze-out.
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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). Observation of a cross-section enhancement near the t(t)over-bar production threshold in √s=13 TeV pp collisions with the ATLAS detector. Rep. Prog. Phys., 89(5), 057801–45pp.
Abstract: A measurement of t (t) over bar production is presented in the invariant-mass region near the pair production threshold, m(t (t) over bar) similar to 345 GeV, in final states with two charged leptons and multiple jets. The measurement is based on 140 fb(-1) of proton-proton collision data collected at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The data are compared to two models of t (t) over bar production: a baseline model including only perturbative quantum chromodynamics (pQCD) predictions for the hard process at approximate next-to-next-to leading order accuracy in the strong coupling, and an extended model that, in addition, incorporates non-relativistic QCD simulations that also include the formation of colour-singlet quasi-bound-states near the t (t) over bar threshold. The agreement between the data and the models is quantified via a profile-likelihood fit to the reconstructed m(t (t) over bar) distributions, in bins of two angular observables sensitive to spin-correlations in the t (t) over bar system. An excess of events is observed over the baseline pQCD prediction, with an observed significance over 8 standard deviations. This excess is consistent with the formation of colour-singlet and spinsinglet S-wave quasi-bound t((t) over bar) states, as predicted by non-relativistic QCD, and corresponds to an observed cross-section of 9.3- (+1.4)(1.3) pb.
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