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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Vidal, J., et al. (2023). Nuclear Modification Factor of Neutral Pions in the Forward and Backward Regions in p-Pb Collisions. Phys. Rev. Lett., 131(4), 042302–12pp.
Abstract: The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16 TeV with the LHCb detector. The p(0) production cross section is measured differentially in transverse momentum (p(T)) for 1.5 < p(T) < 10.0 GeV and in center-of-mass pseudorapidity (?(c.m.)) regions 2.5 < ?(c.m.) < 3.5 (forward) and -4.0 < ?(c.m.) < -3.0 (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of p(0) production, while the backward measurement shows the first evidence of p(0) enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.
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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. (2023). Measurement of the Prompt D0 Nuclear Modification Factor in p-Pb Collisions at √SNN=8.16 TeV. Phys. Rev. Lett., 131(10), 102301–12pp.
Abstract: The production of prompt D0 mesons in proton-lead collisions in both the forward and backward rapidity regions at a center-of-mass energy per nucleon pair of √SNN= = 8.16 TeV is measured by the sNN LHCb experiment. The nuclear modification factor of prompt D0 mesons is determined as a function of the transverse momentum pT, and the rapidity in the nucleon-nucleon center-of-mass frame y*. In the forward rapidity region, significantly suppressed production with respect to pp collisions is measured, which provides significant constraints on models of nuclear parton distributions and hadron production down to the very low Bjorken-x region of similar to 10-5. In the backward rapidity region, a suppression with a significance of 2.0-3.8 standard deviations compared to parton distribution functions in a nuclear environment expectations is found in the kinematic region of pT 6 GeV/c and -3.25 < y* < -2.5, corresponding to x similar to 0.01.
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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. (2023). Precision Measurement of CP Violation in the Penguin-Mediated Decay B0s → φφ. Phys. Rev. Lett., 131(17), 171802–12pp.
Abstract: A flavor-tagged time-dependent angular analysis of the decay B0s -> phi phi is performed using pp collision integrated luminosity of 6 fb-1. The CP-violating phase and direct CP-violation parameter are measured to s = -0.042 +/- 0.075 +/- 0.009 rad and l lambda l = 1.004 +/- 0.030 +/- 0.009, respectively, assuming the same values for all polarization states of the phi phi system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using pp collisions at center-of-mass energies of 7 and 8 TeV, yielding phi sss over bar s = -0.074 +/- 0.069 rad and l lambda l = 1.009 +/- 0.030. This is the most precise study of time-dependent CP violation in a penguindominated B meson decay. The results are consistent with CP symmetry and 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. (2023). Observation of New Baryons in the Ξb- π+π- and Ξb0π+π- Systems. Phys. Rev. Lett., 131(17), 171901–11pp.
Abstract: The first observation and study of two new baryonic structures in the final state Xi(0)(b)pi(+)pi(-) and the confirmation of the Xi(b)(6100)(-) state in the Xi(-)(b)pi(+)pi(-) decay mode are reported using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). In addition, the properties of the known Xi(b)*(0), Xi(b)'(-) and Xi(b)*(-) resonances are measured with improved precision. The new decay mode of the Xi(0)(b) baryon to the Xi(+)(c) pi(-) pi(+) pi(-) final state is observed and exploited for the first time in these measurements.
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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. (2023). Observation of a J/ψΛ Resonance Consistent with a Strange Pentaquark Candidate in B- → J/ψΛ(p)over-bar Decays. Phys. Rev. Lett., 131(3), 031901–11pp.
Abstract: An amplitude analysis of B- -> J/psi Lambda(p) over bar decays is performed using 4400 signal candidates selected on a data sample of pp collisions recorded at center-of-mass energies of 7, 8, and 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 9 fb(-1). A narrow resonance in the J/psi Lambda system, consistent with a pentaquark candidate with strangeness, is observed with high significance. The mass and the width of this new state are measured to be 4338.2 +/- 0.7 +/- 0.4 MeV and 7.0 +/- 1.2 +/- 1.3 MeV, where the first uncertainty is statistical and the second systematic. The spin is determined to be 1/2 and negative parity is preferred. Because of the small Q-value of the reaction, the most precise single measurement of the B- mass to date, 5279.44 +/- 0.05 +/- 0.07 MeV, is obtained.
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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. (2023). Measurement of the Ratios of Branching Fractions R(D*) and R(D0). Phys. Rev. Lett., 131(11), 111802–13pp.
Abstract: The ratios of branching fractions R(D*) = B((B) over bar -> D* tau(-) (v) over bar (tau))/B((B) over bar -> D*.mu(-)(v) over bar mu) and R(D-0) = B(B- -> D(0)t-mu(-)(v) over bar mu) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb(-1) of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode tau(-) -> mu(-)v(tau)(v) over bar mu. The measured values are R(D) = 0.281 +/- 0.018 +/- 0.024 and R(D-0) = 0.441 +/- 0.060 +/- 0.066, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is rho = -0.43. The results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the standard model.
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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. (2023). Evidence of a J / ψK0S Structure in B0 → J / ψφK0S Decays. Phys. Rev. Lett., 131(13), 131901–11pp.
Abstract: An amplitude analysis of B0 -> J=psi phi K0S decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 9 fb-1, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. Evidence with a significance of 4.0 standard deviations of a structure in the J=psi K0S system, named T theta psi s1o4000 thorn 0, is seen, with its mass and width measured to be 3991 thorn 12 thorn 9 -10 -17 MeV=c2 and 105 thorn 29 thorn 17 -25 -23 MeV, respectively, where the first uncertainty is statistical and the second systematic. The T theta psi s1 o4000 thorn 0 state is likely to be the isospin partner of the T theta psi s1 o4000 thorn thorn state, previously observed in the J=psi K thorn system of the B thorn -> J=psi phi K thorn decay. When isospin symmetry for the charged and neutral T theta psi s1 o4000 thorn states is assumed, the signal significance increases to 5.4 standard deviations.
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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. (2023). Observation of New Ω0c States Decaying to the Ξc plus K- Final State. Phys. Rev. Lett., 131(13), 131902–11pp.
Abstract: Two new excited states, S2c(3185)0 and S2c(3327)0, are observed in the E thorn c K- invariant-mass spectrum using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb-1. Five previously observed excited S20c states are confirmed, namely S2c(3000)0, S2c(3050)0, S2c(3065)0, S2c(3090)0, and S2c(3119)0. The masses and widths of these seven states are measured with the highest precision to date.
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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. (2023). Evidence for Modification of b Quark Hadronization in High-Multiplicity pp Collisions at √s=13 TeV. Phys. Rev. Lett., 131(6), 061901–11pp.
Abstract: The production rate of B-s(0) mesons relative to B-0 mesons is measured by the LHCb experiment in pp collisions at a center-of-mass energy root s = 13 TeV over the forward rapidity interval 2 < y < 4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4 sigma level is found for an increase of the ratio of B-s(0) to B-0 cross sections with multiplicity at transverse momenta below 6 GeV=c, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from e(+)e(-) collisions implies that the density of the hadronic medium may affect the production rates of B mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.
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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. (2023). Search for Rare Decays of D0 Mesons into Two Muons. Phys. Rev. Lett., 131(4), 041804–13pp.
Abstract: A search for the very rare D^{0}mu^{+}mu^{-} decay is performed using data collected by the LHCb experiment in proton-proton collisions at sqrt[s]=7, 8, and 13TeV, corresponding to an integrated luminosity of 9fb^{-1}. The search is optimized for D^{0} mesons from D^{*+}D^{0}pi^{+} decays but is also sensitive to D^{0} mesons from other sources. No evidence for an excess of events over the expected background is observed. An upper limit on the branching fraction of this decay is set at B(D^{0}mu^{+}mu^{-})<3.1*10^{-9} at a 90% C.L. This represents the world's most stringent limit, constraining models of physics beyond the standard model.
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