LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Search for CP Violation in D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) Decays. Phys. Rev. Lett., 122(19), 191803–11pp.
Abstract: A search for charge-parity (CP) violation in Cabibbo-suppressed D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8 fb(-1), collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored D-(s())+ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by CP violation in the neutral kaon system. The results are A(CP)(D-s(+) -> K-S(0)pi(+)) = (1.3 +/- 1.9 +/- 0.5) x 10(-3), A(CP)(D+ -> (KSK+)-K-0) = (-0.09 +/- 0.65 +/- 0.48) x 10(-3), A(CP)(D+ -> phi pi(+)) = (0.05 +/- 0.42 +/- 0.29) x 10(-3), where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with CP symmetry. A combination with previous LHCb measurements, based on data collected at 7 and 8 TeV, is also reported.
|
LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Observation of CP Violation in Charm Decays. Phys. Rev. Lett., 122(21), 211803–12pp.
Abstract: A search for charge-parity (CP) violation in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb(-1) collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D* (2010)(+) -> D-0 pi(+) decays or from the charge of the muon in (B) over bar -> D-0 mu(-)(nu) over bar X-mu decays. The difference between the CP asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is measured to be Delta A(CP) = [-18.2 +/- 3.2(stat) +/- 0.9(syst)] x 10(-4) for pi-tagged and Delta A(CP) = [-9 +/- 8(stat) +/- 5(syst)] x 10(-4) for mu-tagged D-0 mesons. Combining these with previous LHCb results leads to Delta A(CP) = (-15.4 +/- 2.9) x 10(-4), where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons.
|
LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Observation of a Narrow Pentaquark State, P-c(4312)(+), and of the Two-Peak Structure of the P-c(4450)(+). Phys. Rev. Lett., 122(22), 222001–11pp.
Abstract: A narrow pentaquark state, P-c(4312)(+), decaying to J/psi p, is discovered with a statistical significance of 7.3 sigma in a data sample of Lambda(0)(b) -> J/psi pK(-) decays, which is an order of magnitude larger than that previously analyzed by the LHCb Collaboration. The P-c(4450)(+) pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, P-c(4440)(+) and P-c(4457)(+), where the statistical significance of this two-peak interpretation is 5.4 sigma. The proximity of the Sigma(+)(c)(D) over bar (0) and Sigma(+)(c)(D) over bar (*0) thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.
|
LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Observation of an Excited B-c(+) State. Phys. Rev. Lett., 122(23), 232001–10pp.
Abstract: Using pp collision data corresponding to an integrated luminosity of 8.5 fb(-1) recorded by the LHCb experiment at center-of-mass energies of root s = 7, 8, and 13 TeV, the observation of an excited B-c(+) state in the B-c(+)pi(+)pi(-) invariant-mass spectrum is reported. The observed peak has a mass of 6841.2 +/- 0.6(stat) +/- 0.1(syst) +/- 0.8(B-c(+)) MeV/c(2), where the last uncertainty is due to the limited knowledge of the B-c(+) mass. It is consistent with expectations of the B-c*(2(3)S(1))(+) state reconstructed without the low-energy photon from the B-c*(1(3)S(1))(+) -> B-c(+)gamma decay following B-c*(2(3)S(1))(+) -> B-c*(1(3)S(1))(+)pi(+)pi(-). A second state is seen with a global (local) statistical significance of 2.2 sigma (3.2 sigma) and a mass of 6872.1 +/- 1.3(stat) +/- 0.1(syst) +/- 0.8(B-c(+)) MeV/c(2), and is consistent with the B-c(2(1)S(0))(+) state. These mass measurements are the most precise to date.
|
LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Measurement of the Mass Difference Between Neutral Charm-Meson Eigenstates. Phys. Rev. Lett., 122(23), 231802–10pp.
Abstract: We report a measurement of the mass difference between neutral charm-meson eigenstates using a novel approach that enhances sensitivity to this parameter. We use 2.3 x 10(6) D-0 -> K-S(0)pi(+)pi(-) decays reconstructed in proton-proton collisions collected by the LHCb experiment in 2011 and 2012. Allowing for CP violation in mixing and in the interference between mixing and decay, we measure the CP-averaged normalized mass difference x(cp)= [2.7 +/- 1.6(stat) +/- 0.4(syst)] x 10(-3) and the CP-violating parameter Delta x = [-0.53 +/- 0.70(stat) +/- 0.22(syst)] x 10(-3). The results are consistent with CP symmetry. These determinations are the most precise from a single experiment and, combined with current world-average results, yield the fast evidence that the masses of the neutral charm-meson eigenstates differ.
|
LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2025). Measurement of D0 – (D)over-bar0 mixing and search for CP violation with D0 →K+ π- decays. Phys. Rev. D, 111(1), 012001–25pp.
Abstract: A measurement of the time-dependent ratio of the D-0 -> K+ to (D) over bar (0) pi(-) decay rates is reported. The analysis uses a sample of proton-proton collisions corresponding to an integrated luminosity of 6 fb- 1 recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The D-0 meson is required to originate from a D*(2010)(+) -> D-0 pi(+) decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the K+ pi(-) and K- pi(+) final states, allowing both mixing and CP-violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be R-K pi = (343.1 +/- 2.0) x 10(-5). The mixing parameters are measured to be c(K pi) = (51.4 +/- 3.5) x 10(-4) and c(K pi)(0) = (13 +/- 4) x 10(-6), where root R(K pi)c(K pi) is the linear coefficient of the expansion of the ratio as a function of decay time in units of the D-0 lifetime, and c(K pi)(0) is the quadratic coefficient, both averaged between the K+ pi(-) and K- pi(+) final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for CP violation is found.
|
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.
|
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.
|
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.
|
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.
|
