LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Search for resonance-enhanced CP and angular asymmetries in the Λc+ → pμ+ μ- decay at LHCb. Phys. Rev. D, 111(9), L091102–14pp.
Abstract: The first measurement of the CP asymmetry of the decay rate (A(CP)) and the CP average (Sigma A(FB)) and CP asymmetry (Delta A(FB)) of the forward-backward asymmetry in the muon system of Lambda(+)(c) -> p mu(+) mu(-) decays is reported. The measurement is performed using a data sample of proton-proton collisions, recorded by the LHCb experiment from 2016 to 2018 at a center-of-mass energy of 13 TeV, which corresponds to an integrated luminosity of 5.4 fb(-1). The asymmetries are measured in two regions of dimuon mass near the.-meson mass peak. The dimuon-mass integrated results are A(CP) = (-1.1 +/- 4.0 +/- 0.5)%, Sigma A(FB) = (3.9 +/- 4.0 +/- 0.6)%, Delta A(FB) = (3.1 +/- 4.0 +/- 0.4)%, where the first uncertainty is statistical and the second systematic. The results are consistent with the conservation of CP symmetry and the Standard Model expectations.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). First observation of Λb0 → Σc(*)+ + D(*) – K- decays. Phys. Rev. D, 110(3), L031104–13pp.
Abstract: The four decays, Λ0b→Σ(∗)++cD(∗)−K−, are observed for the first time using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 6fb−1. By considering the Λ0b→Λ+cD⎯⎯⎯⎯0K− decay as reference channel, the following branching fraction ratios are measured to be
(Λ0b→Σ++cD−K−)(Λ0b→Λ+cD⎯⎯⎯⎯0K−)=0.282±0.016±0.016±0.005,(Λ0b→Σ∗++cD−K−)(Λ0b→Σ++cD−K−)=0.460±0.052±0.028,(Λ0b→Σ++cD∗−K−)(Λ0b→Σ++cD−K−)=2.261±0.202±0.129±0.046,(Λ0b→Σ∗++cD∗−K−)(Λ0b→Σ++cD−K−)=0.896±0.137±0.066±0.018,
where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more data set to become available following the LHCb upgrade.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Observation of strangeness enhancement with charmed mesons in high-multiplicity pPb collisions at √sNN=8.16 TeV. Phys. Rev. D, 110(3), L031105–14pp.
Abstract: The production of prompt D-s(+) and D+ mesons is measured by the LHCb experiment in proton-lead (pPb) collisions in both the forward (1.5 < y* < 4.0) and backward (-5.0 < y* < -2.5) rapidity regions at a nucleon-nucleon center-of-mass energy of root s(NN) = 8.16 TeV. The nuclear modification factors of both D-s(+) and D+ mesons are determined as a function of transverse momentum, p(T), and rapidity. In addition, the D-s(+) to D+ cross section ratio is measured as a function of the primary charged particle multiplicity in the event. An enhanced D-s(+) to D+ production in high-multiplicity events is observed for the whole measured pT range, in particular at low p(T) and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity pPb collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Search for the rare decay of charmed baryon Λc+ into the pμ+ μ- final state. Phys. Rev. D, 110(5), 052007–13pp.
Abstract: A search for the nonresonant Lambda(+)(c) -> p mu(+) mu(-) decay is performed using proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the LHCb experiment, corresponding to an integrated luminosity of 5.4 fb(-1). No evidence for the decay is found in the dimuon invariant-mass regions where the expected contributions of resonances is subdominant. The upper limit on the branching fraction of the Lambda(+)(c) -> p mu(+) mu(-) decay is determined to be 2.9(3.2) x 10(-8) at 90%(95%) confidence level. The branching fractions in the dimuon invariant-mass regions dominated by the eta, rho and omega resonances are also determined.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Precision measurement of the Ξb- baryon lifetime. Phys. Rev. D, 110(7), 072002–16pp.
Abstract: A sample of pp collision data, corresponding to an integrated luminosity of 5.5 fb(-1) and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the Xi(-)(b) baryon to that of the A(b)(0) baryon, r(tau) equivalent to tau(Xi b-)/tau(Ab0). The value r(tau)= 1.076 +/- 0.013 +/- 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)(Rrun 1,2) = 1.078 +/- 0.012 +/- 0.007. Multiplying by the world -average value of the A(b)(0) lifetime yields r(Xi b-)(Rrun 1,2) = 1.578 +/- 0.018 +/- 0.010 +/- 0.011 ps, where the uncertainties are statistical, systematic, and due to the limited knowledge of the A(b)(0), lifetime. This measurement improves the precision of the current world average of the Xi(-)(b) lifetime by about a factor of 2, and is in good agreement with the most recent theoretical predictions.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Search for prompt production of pentaquarks in charm hadron final states. Phys. Rev. D, 110(3), 032001–19pp.
Abstract: A search for hidden-charm pentaquark states decaying to a range of Sigma(c)(D) over bar and Lambda(+)(c)(D) over bar final states, as well as doubly charmed pentaquark states to Sigma D-c and Lambda D-+(c), is made using samples of proton-proton collision data corresponding to an integrated luminosity of 5.7 fb(-1) recorded by the LHCb detector at root sp = 13 TeV. Since no significant signals are found, upper limits are set on the pentaquark yields relative to that of the Lambda(+)(c) baryon in the Lambda(+)(c) -> pK(-)pi(+) decay mode. The known pentaquark states are also investigated, and their signal yields are found to be consistent with zero in all cases.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Search for the lepton-flavor violating decay Bs0 → φμ±τ∓. Phys. Rev. D, 110(7), 072014–12pp.
Abstract: A search for the lepton-flavor violating decays B-s(0) -> phi mu(+/-)tau(-/+) is presented, using a sample of proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb(-1). The tau leptons are selected using decays with three charged pions. No significant excess is observed, and an upper limit on the branching fraction is determined to be B(B-s(0) -> phi mu(+/-)tau(-/+)) < 1.0 x 10(-5) at 90% confidence level.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Measurement of the D* longitudinal polarization in B0 → D*- τ+νt decays. Phys. Rev. D, 110(9), 092007–18pp.
Abstract: The longitudinal polarization fraction of the D* meson is measured in B-0 -> D*(-) tau(+)nu(t) decays, where the tau lepton decays to three charged pions and a neutrino, using proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV and corresponding to an integrated luminosity of 5 fb(-1). The D* polarization fraction F-L(D)* is measured in two q(2) regions, below and above 7 GeV2/c(4), where q(2) is defined as the squared invariant mass of the tau nu(tau) system. The F-L(D)*L values are measured to be 0.52 +/- 0.07 +/- 0.04 and 0.34 +/- 0.08 +/- 0.02 for the lower and higher q(2) regions, respectively. The first uncertainties are statistical and the second systematic. The average value over the whole q(2) range is F-L(D)* = 0.41 +/- 0.06 +/- 0.03. These results are compatible with the Standard Model predictions.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Production of η and η' mesons in pp and pPb collisions. Phys. Rev. C, 109(2), 024907–20pp.
Abstract: The production of eta and eta' mesons is studied in proton -proton and proton -lead collisions collected with the LHCb detector. Proton -proton collisions are studied at center -of -mass energies of 5.02 and 13 TeV and proton -lead collisions are studied at a center -of -mass energy per nucleon of 8.16 TeV. The studies are performed in center -of -mass (c.m.) rapidity regions 2.5 < y(c.m.) < 3.5 (forward rapidity) and -4.0 < y(c.m.) < -3.0 (backward rapidity) defined relative to the proton beam direction. The eta and eta' production cross sections are measured differentially as a function of transverse momentum for 1.5 < p(T) < 10 GeV and 3 < p(T) < 10 GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for eta and eta' mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of eta mesons are also used to calculate eta/pi 0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass -dependent nuclear effects in heavy -ion collisions, as well as eta and eta' meson fragmentation.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Measurement of Ξc+ production in pPb collisions at √sNN=8.16 TeV at LHCb. Phys. Rev. C, 109(4), 044901–14pp.
Abstract: A study of prompt Xi(+)(c) production in proton-lead collisions is performed with the LHCb experiment at a centerof-mass energy per nucleon pair of 8.16 TeV in 2016 in pPb and Pbp collisions with an estimated integrated luminosity of approximately 12.5 and 17.4 nb(-1), respectively. The Xi(+)(c) roduction cross section, as well as the Xi(+)(c) to Lambda(+)(c) production cross-section ratio, are measured as a function of the transverse momentum and rapidity and compared to the latest theory predictions. The forward-backward asymmetry is also measured as a function of the Xi(+)(c) ransverse momentum. The results provide strong constraints on theoretical calculation and are a unique input for hadronization studies in different collision systems.
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