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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). Rapidity and multiplicity dependence of charged-particle flow in pPb collisions at √sNN=8.16 TeV. J. High Energy Phys., 10(10), 124–38pp.
Abstract: The elliptic and triangular flow of charged particles are measured using two-particle angular correlations in pPb collisions in the pseudorapidity range 2.0 < |eta| < 4.8. The data sample was collected by the LHCb experiment in 2016 at a centre-of-mass energy per nucleon pair of root s(NN) = 8.16 TeV, containing in total approximately 1.5 billion collision events. Non-flow contributions are obtained in low-multiplicity collisions and subtracted to extract the flow harmonics. The results are presented as a function of event multiplicity and hadron transverse momentum. Comparisons with a full (3+1)D dynamic model indicate that it overestimates the measured elliptic flow. A comparison between the forward and backward regions reveals no significant differences in flow parameters, suggesting that final-state effects may dominate over initial-state effects in the origin of flow in small systems.
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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). Coherent photoproduction of ρ0, ω and excited vector mesons in ultraperipheral PbPb collisions. J. High Energy Phys., 11(11), 103–32pp.
Abstract: The invariant-mass distribution for the coherent photoproduction of dipions in ultraperipheral PbPb collisions is measured using data, corresponding to an integrated luminosity of 224.6 +/- 9.6 μb(-1), collected by the LHCb experiment in 2018 at a nucleon-nucleon centre-of-mass energy root s(NN) = 5.02TeV. In the mass range from 400 to 1200MeV, the results are consistent with previous experiments, with the spectrum dominated by the rho(0) meson, which interferes with a nonresonant component, together with a smaller omega meson contribution. In an extended mass range up to 2300MeV, models previously used do not fit the data and a consistent description requires the introduction of two resonances at masses of 1350 +/- 20MeV and 1790 +/- 20MeV with widths of about 300MeV. The cross-section for each meson is measured differentially in twelve bins of rapidity from 2.05 to 4.90. The rho(0) cross-section increases with rapidity from about 400 to 600 mb and is measured with a typical precision of 8%, while the cross-section times branching fraction for the omega, rho' and rho '', with the statistical precision of the data, do not have a pronounced rapidity dependence and are between 0.5 and 1.5mb, with uncertainties up to 30%. A large nuclear suppression is observed for the rho(0) meson compared to expectations based on photoproduction on the proton that use the impulse approximation. Significant suppression is also observed compared to that predicted by elastic scattering described in the Glauber approach, or with the addition of inelastic scattering in a Gribov-Glauber model.
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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). Measurement of the ψ(2S) to J/ψ cross-section ratio as a function of centrality in PbPb collisions at √sNN=5.02 TeV. J. High Energy Phys., 07(7), 235–20pp.
Abstract: The ratio of prompt production cross-sections of psi(2S) and J/psi mesons in their dimuon final state is measured as a function of centrality, using data collected by the LHCb detector in PbPb collisions at root s(NN) = 5.02 TeV, for the first time in the forward rapidity region. The measured ratio shows no dependence on the collision centrality, and is compared to the latest theory predictions and to the recent measurements in literature.
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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). Measurement of φ(1020) meson production in fixed-target pNe collisions at √sNN=68.5 GeV. J. High Energy Phys., 03(3), 151–21pp.
Abstract: The first measurement of phi(1020) meson production in fixed-target pNe collisions at root s(NN) = 68.5 GeV is presented. The phi(1020) mesons are reconstructed in their K+K- decay in a data sample consisting of proton collisions on neon nuclei at rest, corresponding to an integrated luminosity of 21.7 +/- 1.4 nb(-1), collected by the LHCb detector at CERN. The phi(1020) production cross-section in the centre-of-mass rapidity range of -1.8 < y* < 0 and transverse momentum range of 800 < p(T) < 6500MeV/ c is found to be sigma = 182.7 +/- 2.7 (stat.) +/- 14.1 (syst) μb/nucleon. A double-differential measurement of the cross-section is also provided in four regions of rapidity and six regions of transverse momentum of the phi(1020) meson and compared with the predictions from Pythia and EPOS4, which are found to underestimate the experimental values.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2022). Study of coherent J/psi production in lead-lead collisions at root S-NN=5 TeV. J. High Energy Phys., 07(7), 117–19pp.
Abstract: Coherent production of J/psi mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about 10 μb(-1). The J/psi mesons are reconstructed in the dimuon final state and are required to have transverse momentum below 1 GeV. The cross-section within the rapidity range of 2.0 < y < 4.5 is measured to be 4.45 +/- 0.24 +/- 0.18 +/- 0.58 mb, where the first uncertainty is statistical, the second systematic and the third originates from the luminosity determination. The cross-section is also measured in J/psi rapidity intervals. The results are compared to predictions from phenomenological models.
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