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Costantini, M. N., Mantani, L., Moore, J. M., Schütze Sanchez, V., & Ubiali, M. (2026). A new tool for fast-flying PDF fits. Eur. Phys. J. C, 86(1), 22–19pp.
Abstract: We present Colibri, an open-source Python code that provides a general and flexible tool for PDF fits. The code is built so that users can implement their own PDF model, and use the built-in functionalities of Colibri for a fast computation of observables. It grants easy access to experimental data, several error propagation methodologies, including the Hessian method, the Monte Carlo replica method, and an efficient numerical Bayesian sampling algorithm. To demonstrate the capabilities of Colibri, we consider its simplest application: a polynomial PDF parametrisation. We perform closure tests using a full set of DIS data and compare the results of Hessian and Monte Carlo fits with those from a Bayesian fit. We further discuss how the functionalities illustrated in this example can be extended to more complex PDF parametrisations. In particular, the Bayesian framework in Colibri provides a principled approach to model selection and model averaging, making it a valuable tool for benchmarking and combining different PDF parametrisations on solid statistical grounds.
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Estrada, E. J., & Roig, P. (2026). Tensor meson pole contributions to the HLbL piece of aμHLbL within RχT. J. High Energy Phys., 01(1), 070–26pp.
Abstract: We compute the tensor meson pole contributions to the Hadronic Light-by-Light piece of a μin the purely hadronic region, using Resonance Chiral Theory. Given the differences between the dispersive and holographic groups determinations and the resulting discussion of the corresponding uncertainty estimate for the Hadronic Light-by-Light section of the muon g – 2 theory initiative second White Paper, we consider timely to present an alternative evaluation. In our approach, in addition to the lightest tensor meson nonet, two vector meson resonance nonets are considered, in the chiral limit.Disregarding operators with derivatives, only the form factor FT 1 is non-vanishing, as assumed in the dispersive study. All parameters are determined by imposing a set of short-distance QCD constraints, and the radiative tensor decay widths. In this case, we obtain the following results for the different contributions (in units of 10-11): aa2-pole μ= – (1.02(10)stat(+0.00 -0.12) syst), af2-pole μ= – (3.2(3)stat(+0.0 -0.4) syst) and af' 2 -pole μ= -(0.042(13)stat), which add up to aa2+f2+ f' 2 -pole μ= – (4.3+0.3 -0.5), in close agreement with the holographic result when truncated to FT 1 only. However, with an ad-hoc extended Lagrangian, that also generates FT 3, as in the holographic approach, we have found: aa2-pole μ= +0.47(1.43)norm(3)stat(+0.06 -0.00)syst, af2-pole μ= +1.18(4.18)norm(12)stat(+0.24 -0.00) syst and af' 2 -pole μ= +0.040(78)norm(2)stat, summing to aa2+f2+ f' 2 -pole μ= +1.7(4.4), which agree with these recent determinations within uncertainties (dominated by the FT 3 normalization). We point out that R.T generates all five form factors, differently to previous approaches. The contributions to a μof F2,4,5 cannot be evaluated in the current basis, preventing for the moment a complete calculation of aT-poles μwithin our framework.
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n_TOF Collaboration(Perez-Maroto, P. et al), Lerendegui-Marco, J., Domingo-Pardo, C., Babiano-Suarez, V., Balibrea-Correa, J., & Ladarescu, I. (2026). New measurement of 50Cr and 53Cr (n,γ) cross sections at n_TOF: a call for chromium nuclear data revision. Eur. Phys. J. A, 62(1), 5–19pp.
Abstract: Cr-50 and Cr-53 are very relevant in criticality safety benchmarks related to nuclear reactors. The discrepancies of up to 30% between the neutron capture cross section evaluations have an important effect on the k(eff) and k(infinity) in criticality benchmarks particularly sensitive to chromium. In this work, the Cr-50,Cr-53(n,gamma) cross sections are to be determined between 1 and 100 keV with an 8-10% accuracy following the requirements of the NEA High Priority Request List (HPRL) to solve the current discrepancies. We have measured these reactions by the time-of-flight technique at the EAR1 experimental area of the n_TOF facility, using an array of four C6D6 detectors with very low neutron sensitivity. The highly-enriched samples used are significantly thinner than in previous measurements, thus minimizing the multiple-scattering effects. We have produced, and analysed with the R-matrix analysis code SAMMY, capture yields featuring 33 resonances of Cr-50 and 51 of Cr-53 with an accuracy between 5% and 9%, hence fulfilling the requirements made by the NEA. The differential and integral cross sections have been compared to previous data and evaluations. The new measured Cr-50,Cr-53(n,gamma) cross sections provide a valuable input for upcoming evaluations, which are deemed necessary given that the results presented herein do not support the increase in both cross sections proposed in the recent INDEN evaluation.
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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). Amplitude analysis of the Ξc+ → pK- π+ decay and Ξc+ baryon polarization measurement in semileptonic beauty-hadron decays. Phys. Rev. D, 112(9), 092003–23pp.
Abstract: An amplitude analysis of the Xi(+)(c) -> pK(-) pi(+) decay together with a measurement of the Xi(+)(c) polarization vector in semileptonic beauty-hadron decays is presented. The analysis is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. A sizeable. thornc polarization is found. A large sensitivity of the Xi(c) -> pK(-)pi(+) decay to the polarization is seen, making the amplitude model suitable for Xi(+)(c) polarization measurements in other systems.
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Belocchi, V., Barbaro, M. B., De Pace, A., & Martini, M. (2025). Two-particle two-hole excitations in semi-inclusive neutrino-nucleus scattering. Phys. Rev. D, 112(9), 093002–22pp.
Abstract: A calculation of the two-particle two-hole contribution to the semi-inclusive (nu(mu), μN-) cross section on carbon is performed in the framework of the relativistic Fermi gas model. The process is driven by mesonexchange currents encompassing all contributions involving the exchange of a single pion and the excitation of a Delta resonance. The calculation is validated against the inclusive (nu(mu), mu(-)) response functions already existing in the literature, and then extended for the first time to the semi-inclusive channel. Results are presented both at fixed neutrino energy and folded with the T2K neutrino flux.
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