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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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Study of charm mixing and CP violation with D0→ K±π∓π±π∓ decays. J. High Energy Phys., 12(12), 153–39pp.
Abstract: A study of charm mixing and CP violation in D0 -> K +/-pi -/+pi +/-pi -/+ decays is performed using data collected by the LHCb experiment in proton-proton collisions from 2015 to 2018, corresponding to an integrated luminosity of 6 fb-1. The ratio of promptly produced D0 -> K+pi-pi+pi- to D0 -> K-pi+pi-pi+ decay rates is measured as a function of D0 decay time, both inclusive over phase space and in bins of phase space. Taking external inputs for the D0-D<overline>0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {D}<^>0-{\overline{D}}<^>0 $$\end{document} mixing parameters x and y allows constraints to be obtained on the hadronic parameters of the charm decay. When combined with previous measurements from charm-threshold experiments and at LHCb, improved knowledge is obtained for these parameters, which is valuable for studies of the angle gamma of the Unitarity Triangle. An alternative analysis is also performed, in which external inputs are taken for the hadronic parameters, and the mixing parameters are determined, including triangle x and triangle y, which are nonzero in the presence of CP violation. It is found that x=0.85-0.24+0.15%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ x=\left(0.{85}{-0.24}<^>{+0.15}\right)\% $$\end{document}, y=0.21-0.27+0.29%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ y=\left(0.{21}{-0.27}<^>{+0.29}\right)\% $$\end{document}, triangle x = (-0.02 +/- 0.04) % and Delta y=0.02-0.03+0.04%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta y=\left(0.0{2}_{-0.03}<^>{+0.04}\right)\% $$\end{document}. These results are consistent with previous measurements and the hypothesis of CP conservation.
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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 observation of the Λb0 → Λc+Ds- K+ K- decay and search for pentaquarks in the Λc+Ds- system. Phys. Rev. D, 112(5), 052013–14pp.
Abstract: The Lambda(0)(b) -> Lambda D-+(c)s(-) K+ K- decay is observed for the first time using the data sample from proton-proton collisions recorded at a center-of-mass energy of 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 6 fb-1. The ratio of branching fraction to that of Lambda(0)(b) -> Lambda D-+(c)s(-) decays is measured as 0.0141 +/- 0.0019 +/- 0.0012, where the first uncertainty is statistical and the second systematic. A search for hidden-charm pentaquarks with strangeness is performed in the Lambda D-+(c)s(-) system. No evidence is found, and upper limits on the production ratio of Pc (c) over bars(4338)(0) and Pc (c) over bars(4459)(0) pentaquarks relative to the Lambda D-+(c)s(-) final state are set at the 95% confidence level as 0.12 and 0.20, respectively.
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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). Angular analysis of the decay Bs0 → φ e+ e-. J. High Energy Phys., 07(7), 69–29pp.
Abstract: An angular analysis of the decay Bs0 -> phi e+e- is presented, using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8 and 13 TeV. The combined dataset corresponds to an integrated luminosity of 9 fb-1. Observables are determined by fitting time-integrated projections of the angular distribution in three bins of dielectron mass squared, q2, corresponding to [0.1, 1.1], [1.1, 6.0] and [15.0, 19.0] GeV2/c4. The results are compatible with predictions based on the Standard Model of particle physics.
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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). Observation of the decay B0s → K0p(p)over-bar and measurement of the B0(s) → K0p(p)over-bar branching fractions. J. High Energy Phys., 07(7), 121–25pp.
Abstract: A study of the charmless baryonic decays B-(s)(0) -> K(0)p (p) over bar is presented, where B-(s)(0) denotes either a B-0 or a B-s(0) meson. The analysis is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The decay B-s(0) -> K(0)p (p) over bar is observed for the first time, with a measured branching fraction of (9.14 +/- 1.69 +/- 0.90 +/- 0.33 +/- 0.20) x 10(-7) and a significance of 5.6 sigma. The uncertainties respectively account for statistical and systematic contributions, the precision of the branching fraction of the normalisation channel B-0 -> K-0 pi(+)pi(-) and the fragmentation fraction ratio f(s)/f(d). The branching fraction determined for B-0 -> K(0)p (p) over bar is (2.82 +/- 0.08 +/- 0.12 +/- 0.10) x 10(-6), which is the most precise measurement to date.
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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). Measurement of the Ωc0 and Ξc0 baryon lifetimes using hadronic b-baryon decays. J. High Energy Phys., 09(9), 157–25pp.
Abstract: The lifetimes of the Omega(0)(c) and Xi(0)(c) baryons are measured using a pp collision dataset collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The charm baryons are produced in the fully reconstructed decay chains Omega(-)(b) -> Omega(0)(c)(-> pK(-)K(-)pi(+))pi(-) and Xi(-)(b) -> Xi(0)(c)(-> pK(-)K(-)pi(+))pi(-). The measurement uses topologically and kinematically similar B- -> D-0(-> K-K+pi(-)pi(+))pi(-) decays for normalisation. The measured lifetimes are tau(Omega c0) = 276.3 +/- 19.4 (stat) +/- 1.8 (syst) +/- 0.7(tau(D0))fs, tau(Xi c0) = 149.2 +/- 2.5 (stat) +/- 0.9 (syst) +/- 0.4(tau(D0))fs, where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the D-0 lifetime. These results are consistent with previous measurements performed by the LHCb experiment.
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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). Three-pion Bose-Einstein correlations measured in proton-proton collisions. J. High Energy Phys., 08(8), 174–27pp.
Abstract: A study on the Bose-Einstein correlations for triplets of same-sign pions is presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of root s = 7TeV, recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb(-1). For the first time, the results are interpreted in the core-halo model. The parameters of the model are determined in regions of charged-particle multiplicity. This measurement provides insight into the nature of hadronisation in terms of coherence, being consistent with the presence of coherent emission of pions.
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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). Measurement of the B0→ ρ(770)0γ branching fraction. J. High Energy Phys., 12(12), 151–21pp.
Abstract: The ratio between the branching fractions of the B0 -> rho(770)0 gamma and B0 -> K*(892)0 gamma decays is measured with proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb-1. The measured value isBB0 ->rho 7700 gamma BB0 -> K & lowast;8920 gamma=0.0189 +/- 0.0007 +/- 0.0005, where the first uncertainty is statistical and the second systematic. The branching fraction for B0 -> rho(770)0 gamma decays is hence obtained asBB0 ->rho 7700 gamma=7.9 +/- 0.3 +/- 0.2 +/- 0.2x10-7, where the last uncertainty is due to the branching fraction of the normalisation mode. This result assumes that both the rho(770)0 and K*(892)0 decays saturate the dihadron mass spectra considered in the analysis. It is consistent with the current world-average value and by far the most precise measurement to date.
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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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