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Moon, B. et al, & Morales, A. I. (2026). Commissioning and performance of IDATEN: A large fast-timing γ-ray detector array at the RIBF. Nucl. Instrum. Methods Phys. Res. A, 1084, 171239–7pp.
Abstract: A large fast-timing 1-ray detector array has been newly developed under the International Detector Assembly for fast-Timing measurements of Exotic Nuclei (IDATEN) project. The full IDATEN array comprises 82 LaBr3(Ce) 1-ray detectors, of which 46 and 36 are provided by the KHALA and FATIMA collaborations, respectively. To assess the fast-timing performance of this large-scale system with stopped rare-isotope beams, a commissioning experiment was recently carried out at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. Neutron-deficient rare isotopes near 100Sn were produced via in-flight fragmentation of a 124Xe primary beam. The fast-timing capability was evaluated using 96Pd as the reference nucleus by measuring the half-lives of the 2+1 , 4+1 and 6+1 levels, which were populated through the decay of the long-lived 8+1 isomeric state. These results demonstrate the reliability of our experimental setup, including the readout electronics and data acquisition system, thereby validating its readiness for forthcoming physics experiments at the RIBF. Moreover, the measured half-life values are in agreement with previously reported literature values, with some determinations achieving improved precision.
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Dias, J. M., Li, Y. Y., & Oset, E. (2025). π+ π- and Ds+ π± mass spectra in the Ds1(2536) → Ds+ π+ π- decays. Phys. Rev. D, 112(11), 114018–10pp.
Abstract: We have carried out an evaluation of the pi(+)pi(-) and D-s(+)pi(+) mass distributions in the D-s1(2536) decay to D-s(+)pi(+)pi(-), from the perspective that the D-s1(2536) is a molecular state, mostly made from K*D in I = 0. We are able to obtain not only the mass distributions, but also the branching ratio of this decay. The shape of the mass distributions differs appreciably from those of the analogous reaction D-s1(2460) -> D-s(+)pi(+)pi(-), which has been measured by the LHCb Collaboration and analyzed theoretically from the perspective that the D-s1(2460) is a molecular state of D*K, showing good agreement with the data. In spite of the analogy with the D-s1(2460) decay, the dynamical differences in the decay mechanism are important, since now the f(0)(500) resonance is not generated, while it was the dominant mechanism in the D-s1(2460) -> D-s(+)pi(+)pi(-) decay. Nonetheless, we find striking differences in the mass distributions compared with phase space as a consequence of the decay mechanism. The branching ratio obtained is an order of magnitude bigger than the one of the D-s1(2460) -> D-s(+)pi(+)pi(-) reaction, mostly due to the larger available phase space. We also show that the shape of the distributions obtained from the molecular picture is quite different from those obtained based on a qq picture. We conclude that measuring the shape of the mass distributions and the total strength of the decay mode should be very valuable to learn about the structure of the D-s1(2536).
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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. (2025). First measurement of b-jet mass with and without grooming. Phys. Lett. B, 869, 139854–13pp.
Abstract: The LHCb collaboration presents a novel suite of heavy-flavour jet substructure measurements at forward rapidity in proton-proton collisions at a centre-of-mass energy of root s = 13 TeV. The jet mass is a perturbatively calculable probe of the virtuality of hard-scattered quarks and gluons, connecting small-distance quantum chromodynamics (QCD) with long-distance experimental measurement. The jet mass is dominated by nonperturbative corrections at small values, presenting an excellent test of QCD across a broad range of jet energies. Measuring heavy-flavour jet mass with a theoretically unambiguous flavour definition for the first time probes the gluon splitting mechanism for heavy-flavour production and offers tests of perturbative QCD at new levels of theoretical precision. Utilising the soft drop jet-grooming technique to access the perturbative jet core further enhances constraints on first-principles theory. Measurements of the jet mass for jets containing fully reconstructed B-+/- hadrons are reported with and without grooming. The unique phase space instrumented by LHCb offers a different quarkgluon fraction than at midrapidity. These results offer unparalleled tests of quark flavour and mass dependence in QCD and provide a baseline for future studies of heavy-flavour jet quenching in heavy-ion collisions.
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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. (2025). Precision measurement of the Ξ0b baryon lifetime. Phys. Rev. D, 112, 052012–16pp.
Abstract: A sample of pp collision data, corresponding to an integrated luminosity of 5.4 fb(-1) and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the Xi(0)(b) baryon to that of the Lambda(0)(b) baryon, r(tau) equivalent to tau(Xi 0b)/tau(Lambda 0b). The value r(tau)(Run 2) = 1.004 +/- 0.009 +/- 0.006 is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain r(tau) = 1.004 +/- 0.008 +/- 0.005. Multiplying by the known value of the Lambda(0)(b) lifetime yields tau(Xi 0b) = 1.475 +/- 0.012 +/- 0.008 +/- 0.009 ps, where the last uncertainty is due to the limited knowledge of the Lambda(0)(b) lifetime. This measurement improves the precision of the current world average of the Xi(0)(b) lifetime by about a factor of two, and is in good agreement with the most recent theoretical predictions.
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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. (2025). Inclusive B-meson flavour-tagging algorithm at LHCb. J. High Energy Phys., 11(11), 041–32pp.
Abstract: A new algorithm is developed to identify the flavour of neutral B mesons at production in pp collisions by utilising all tracks from the hadronisation process. The algorithm is calibrated separately for B-0 and B-s(0) mesons using B-0 -> J/psi K+pi(-) and B-s(0) -> D-s(-)pi(+) decays from pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13TeV. This new algorithm improves the tagging power by 35% for B-0 mesons and 20% for B-0 s mesons when compared to the combined performance of the existing LHCb flavour-tagging algorithms.
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