LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2024). Measurement of CP Violation Observables in D+ → K- K+ π+ Decays. Phys. Rev. Lett., 133(25), 251801–13pp.
Abstract: A search for violation of the charge-parity (CP) symmetry in the D+ -> K- K+ pi(+) decay is presented, with proton-proton collision data corresponding to an integrated luminosity of 5.4 fb(-1), collected at a center-of-mass energy of 13 TeV with the LHCb detector. A novel model-independent technique is used to compare the D+ and D- phase-space distributions, with instrumental asymmetries subtracted using the D-s(+) -> K- K+ pi(+) decay as a control channel. The p value for the hypothesis of CP conservation is 8.1%. The CP asymmetry observables A(CP vertical bar S)(phi pi+) = (0.95 +/- 0.43(stat) +/- 0.26(syst)) x 10(-3) and A(CP vertical bar S)((K) over bar *0 K+) = (-0.26 +/- 0.56(stat) +/- 0.18(syst)) x 10(-3) are also measured. These results show no evidence of CP violation and represent the most sensitive search performed through the phase space of a multibody decay.
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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. (2024). Measurement of Λ0b, Λ+c, and Λ Decay Parameters Using Λ0b →Λ+c h- Decays. Phys. Rev. Lett., 133(26), 261804–15pp.
Abstract: A comprehensive study of the angular distributions in the bottom-baryon decays Lambda(0)(b) ->Lambda(+)(c)h(-) (h = pi,K) , followed by Lambda(0)(c) ->Lambda h(+) with Lambda -> p pi(-) or Lambda(+)(c)-> pK(S)(0) decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb(-1) collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, Lambda(0)(b) ->Lambda(+)(c)h(-) decay parameters are measured. The most precise measurements of the decay parameters alpha, ss, and are obtained for Lambda(+)(c) decays and an independent measurement of the decay parameters for the strange-baryon Lambda decay is provided. The results deepen our understanding of weak decay dynamics in baryon
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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). Long-lived particle reconstruction downstream of the LHCb magnet. Eur. Phys. J. C, 85(1), 7–30pp.
Abstract: Charged-particle trajectories are usually reconstructed with the LHCb detector using combined information from the tracking devices placed upstream and downstream of the 4 T m dipole magnet. Trajectories reconstructed using only information from the tracker downstream of the dipole magnet, which are referred to as T tracks, have not been used for physics analysis to date. The challenges of the reconstruction of long-lived particles with T tracks for physics use are discussed and solutions are proposed. The feasibility and the tracking performance are studied using samples of long-lived Lambda and K-S(0) hadrons decaying between 6.0 and 7.6 m downstream of the proton-proton collision point, thereby traversing most of the magnetic field region and providing maximal sensitivity to magnetic and electric dipole moments. The reconstruction can be expanded upstream to about 2.5 m for use in direct searches of exotic long-lived particles. The data used in this analysis have been recorded between 2015 and 2018 and correspond to an integrated luminosity of 6 fb(-1). The results obtained demonstrate the possibility to further extend the decay volume and the physics reach of 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., Martinez-Vidal, F., et al. (2025). Search for B(s)*0 → μ+μ- in Bc+ → π+μ+μ- decays. Eur. Phys. J. C, 85(1), 20–16pp.
Abstract: A search for the very rare B-*0 -> mu(+) mu(-) and B-(s)(*0) -> mu(+)mu(-) decays is conducted by analysing the B-c(+) -> pi(+)mu(+) mu(-) process. The analysis uses proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb(-1). The signal signatures correspond to simultaneous peaks in the mu(+) mu(-) and pi(+)mu(+) mu(-) invariant masses. No evidence for an excess of events over background is observed for either signal decay mode. Upper limits at the 90% confidence level are set on the branching fractions relative to that for B-c(+) -> J/psi pi(+) decays, RB*0( mu+ mu-)pi+ / J/psi pi+ < 3.8 x 10(-5) and RBs*0( mu+ mu-)pi+ / J/psi pi+ < 5.0 x 10(-5).
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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). Measurements of ψ(2S) and χc1(3872) production within fully reconstructed jets. Eur. Phys. J. C, 85(5), 562–24pp.
Abstract: This paper presents the first measurement of psi(2S) and chi(c1)(3872) meson production within fully reconstructed jets. Each quarkonium state (tag) is reconstructed via its decay to the J/psi(->mu(+)mu(-))pi(+)pi(-) final state in the forward region using proton-proton collision data collected by the LHCb experiment at the center-of-mass-energy of 13TeV in 2016, corresponding to an integrated luminosity of 1.64 fb(-1). The fragmentation function, presented as the ratio of the quarkonium-tag transverse momentum to the full jet transverse momentum (pT(tag)/pT(jet)), is measured differentially in pT(jet) and pT(tag) bins. The distributions are separated into promptly produced quarkonia from proton-proton collisions and quarkonia produced from displaced b-hadron decays. While the displaced quarkonia fragmentation functions are in general well described by parton-shower predictions, the prompt quarkonium distributions differ significantly from fixed-order non-relativistic QCD (NRQCD) predictions followed by a QCD parton shower.
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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). Observation of the Λb0 → J/ψ Ξ- K+ and Ξb0 → J/ψ Ξ- π+ decays. Eur. Phys. J. C, 85(7), 812–15pp.
Abstract: The first observation of the Xi(0)(b) -> J/psi Xi(-)pi(+) decay and the most precise measurement of the branching fraction of the Lambda(0)(b) -> J/psi Xi K--(+) decay are reported, using proton-proton collision data from the LHCb experiment collected in 2016-2018 at a centre-of-mass energy of 13\,TeV, corresponding to an integrated luminosity of 5.4 fb(-1). Using the Lambda(0)(b) -> J/psi Lambda and Xi(-)(b) -> J/psi Xi(-) decays as normalisation channels, the ratios of branching fractions are measured to be B(Lambda(0)(b) -> J/psi Xi K--(+))/B(Lambda(0)(b) -> J/psi Lambda) =(1.17 +/- 0.14 +/- 0.08) x 10(-2), B(Xi(0)(b) -> J/psi Xi(-)pi(+))/B(Xi(-)(b) -> J/psi Xi(-)) = (11.9 +/- 1.4 +/- 0.6) x 10(-2) where the first uncertainty is statistical and the second systematic.
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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). Search for charge-parity violation in semileptonically tagged D0 → K+ π- decays. J. High Energy Phys., 03(3), 149–30pp.
Abstract: An analysis of the flavour oscillations of the charmed neutral meson is presented. The ratio of D-0 -> K+ pi(-) and D-0 -> K- pi(+) decay rates is measured as a function of the decay time of the D-0 meson and compared with the charge-conjugated system to search for charge-parity violation. The meson flavour at production is double-tagged by the charges of the muon and pion in the preceding (B) over bar -> D*(2010)(+) mu(-) X and D*(2010)(+) -> D-0 pi(+) decays, respectively. These decays are selected from proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13TeV and corresponding to an integrated luminosity of 5.4 fb(-1). The flavour oscillation parameters, relating to the differences in mass and width of the mass eigenstates, are found to be y' = (5.8 +/- 1.6) x10(-3) and (x')(2) = (0.0 +/- 1.2) x10(-4). No evidence for charge-parity violation is seen either in the flavour oscillations or in the decay, where the direct charge-parity asymmetry is measured to be A(D) = (2.3 +/- 1.7)%.
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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 CP asymmetry in Bs0 → Ds∓ K± decays. J. High Energy Phys., 03(3), 139–33pp.
Abstract: A measurement of the CP-violating parameters in B-s(0) -> D-s(-/+) K-+/- decays is reported, based on the analysis of proton-proton collision data collected by the LHCb experiment corresponding to an integrated luminosity of 6 fb(-1) at a centre-of-mass energy of 13TeV. The measured parameters are obtained with a decay-time dependent analysis yielding C-f = 0.791 +/- 0.061 +/- 0.022, A(f)(Delta Gamma) = -0.051 +/- 0.134 +/- 0.058, A((f) over bar)(Delta Gamma) = -0.303 +/- 0.125 +/- 0.055, S-f = -0.571 +/- 0.084 +/- 0.023 and S-(f) over bar = -0.503 +/- 0.084 +/- 0.025, where the first uncertainty is statistical and the second systematic. This corresponds to CP violation in the interference between mixing and decay of about 8.6 sigma. Together with the value of the B-s(0) mixing phase -2 beta s, these parameters are used to obtain a measurement of the CKM angle gamma equal to (74 +/- 12)degrees modulo 180 degrees, where the uncertainty contains both statistical and systematic contributions. This result is combined with the previous LHCb measurement in this channel using 3 fb(-1) resulting in a determination of gamma = (81(-11)(+12))degrees.
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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), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Measurement of CP violation in B0 → D+D- and B0s→ D+ s D- s decays. J. High Energy Phys., 01(1), 061–26pp.
Abstract: A time-dependent, flavour-tagged measurement of CP violation is performed with B-0 -> D+D- and B-s(0)-> D+ (s) D- (s)decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13TeV corresponding to an integrated luminosity of 6 fb(-1). In B-0 -> D+D- decays the CP-violation parameters are measured to be S-D(+) (-)(D) = -0.552 +/- 0.100 (stat) +/- 0.010 (syst), C-D(+) (-)(D) = 0.128 +/- 0.103 (stat) +/- 0.010 (syst). In B-s(0)-> D+ (s) D- (s) decays the CP-violating parameter formulation in terms of phi(s) and |lambda| results in phi s = -0.086 +/- 0.106 (stat) +/- 0.028 (syst) rad, |lambda (+)(D) (-)(s D) (s) | = 1.145 +/- 0.126 (stat) +/- 0.031 (syst). These results represent the most precise single measurement of the CP-violation parameters in their respective channels. For the first time in a single measurement, CP symmetry is observed to be violated in B-0 -> D+D- decays with a significance exceeding six standard deviations.
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