LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Evidence for B- → D**0τ-(ν)over-barτ Decays. Phys. Rev. Lett., 135(2), 021802–15pp.
Abstract: The first evidence for the decay B- -> D(0)tau(-)(nu) over bar (tau) is obtained using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1), at centre-of-mass energies of 7, 8, and 13 TeV. Here, the D0 meson represents any of the three excited charm mesons D-1(2420)(0), D*(2)(2460)(0), and D'(1)(2400)(0). The B- -> D(0)tau(-)(nu) over bar (tau) signal is measured with a significance of 3.5 sigma, including systematic uncertainties. The combined branching fraction B(B- -> D(0)(1,2) tau(-)(nu) over bar (tau)) x B(D(0)(1,2) -> D*(+) pi(-)), where D(0)(1,2) denotes both D-1(2420)(0) and D*(2)(2460)(0) contributions, is measured to be [0.051 +/- 0.013(stat) +/- 0.006(syst) +/- 0.009(ext)]%, where the last uncertainty reflects that of the branching fraction of the normalization channel B- -> DD-0(1,2)-(*())(s). The ratio between the tauonic and muonic semileptonic B decays, with the latter taken from world average values, is also determined and found to be R(D(0)(1,2)) = 0.13 +/- 0.03(stat) +/- 0.01(syst) +/- 0.02(ext).
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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). First Evidence for Direct CP Violation in Beauty to Charmonium Decays. Phys. Rev. Lett., 134(10), 101801–13pp.
Abstract: The CP asymmetry and branching fraction of the Cabibbo-Kobayashi-Maskawa-suppressed decay B+ -> J/psi pi(+) are precisely measured relative to the favored decay B+ -> J/psi K+ using a sample of protonproton collision data corresponding to an integrated luminosity of 5.4 fb(-1) recorded at a center-of-mass energy of 13 TeV during 2016-2018. The results of the CP asymmetry difference and branching fraction ratio are Delta A(CP)= A(CP)(B+ -> J/psi pi(+))-A(CP)(B+ -> J/psi K+)=(1.29 +/- 0.49 +/- 0.08)x10(-2), R-pi/K [B(B+ -> J/psi pi(+))/ B(B+-> J/psi K+)] = (3.852 +/- 0.022 +/- 0.018)x10(-2), where the first uncertainties are statistical and the second are systematic. A combination with previous LHCb results based on data collected at 7 and 8 TeVin 2011 and 2012 yields Delta A(CP) = (1.42 +/- 0.43 +/- 0.08) x 10(-2) and R pi/K = (3.846 +/- 0.018 +/- 0.018) x 10(-2). The combined Delta A(CP) value deviates from zero by 3.2 standard deviations, providing the first evidence for direct CP violation in the amplitudes of beauty decays to charmonium final states.
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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). Study of Λb0 and Ξb0 Decays to Λh+ h'- – and Evidence for CP Violation in Λb0 → ΛK+ K- Decays. Phys. Rev. Lett., 134(10), 101802–16pp.
Abstract: A study of Lambda(0)(b) and Xi(0)(b) decays to Lambda h(+) h'(-) (h((')) = pi, K) is performed using pp collision data collected by the LHCb experiment during LHC Runs 1-2, corresponding to an integrated luminosity of 9 fb(-1). The branching fractions for these decays are measured using the Lambda(0)(b) -> Lambda pi(+)pi(-) decay as a control channel. The decays Lambda(0)(b) -> Lambda pi(+)pi(-) and and Xi(o)(b) -> pi Lambda K-pi(+)- are observed for the first time. For decay modes with sufficient signal yields, CP asymmetries are measured in the full and localized regions of the final-state phase space. Evidence is found for CP violation in the Lambda(0)(b) -> Lambda K+K- decay, interpreted as originating primarily from an asymmetric Lambda(0)(b) -> N*K-+(-) decay amplitude. The measured CP asymmetries for other decays are compatible with zero.
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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). Test of Lepton Flavor Universality with Bs0 → φl+ l- Decays. Phys. Rev. Lett., 134(12), 121803–15pp.
Abstract: Lepton flavor universality in rare b -> s transitions is tested for the first time using B-s(0) meson decays. The measurements are performed using pp collision data collected by the LHCb experiment between 2011 and 2018, corresponding to a total integrated luminosity of 9 fb(-1). Branching fraction ratios between the B-s(0) -> phi e(+) e(-) and B-s(0) -> phi mu(+) mu(-) decays are measured in three regions of dilepton mass squared, q(2), with 0.1 < q(2) < 1.1, 1.1 < q(2) < 6.0, and 15 < q(2) < 19 GeV2/c(4). The results agree with the standard model expectation of lepton flavor universality.
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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). Angular analysis of B0 → K*0 e+ e- decays. J. High Energy Phys., 06(6), 140–53pp.
Abstract: An angular analysis of B0 -> K*0e+e- decays is presented using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb-1. The analysis is performed in the region of the dilepton invariant mass squared of 1.1-6.0 GeV2/c4. In addition, a test of lepton flavour universality is performed by comparing the obtained angular observables with those measured in B0 -> K*0 mu+mu- decays. In general, the angular observables are found to be consistent with the Standard Model expectations as well as with global analyses of other b -> s & ell;+& ell;- processes, where & ell; is either a muon or an electron. No sign of lepton-flavour-violating effects is observed.
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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 the Bc+→ χc1(3872)π+ decay. J. High Energy Phys., 06(6), 013–28pp.
Abstract: A search for the decay B-c(+)-> chi(c1)(3872)pi(+) is reported using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). No significant signal is observed. Using the decay B-c(+)-> psi(2S)pi(+) as a normalisation channel, an upper limit for the ratio of branching fractions R psi(chi c1(3872))((2s)) = BBc+-> chi c1(3872)pi+/BBc+-> psi(2S)pi+ x B chi c1(3872)-> J/psi pi(+)pi(-)/BB psi(2S)-> J/psi pi+pi- <0.05(0.06), is set at the 90 (95)% confidence level.
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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). Test of Lepton Flavor Universality with B+ → K+ π+ π- l+ l- Decays. Phys. Rev. Lett., 134(18), 181803–13pp.
Abstract: The first test of lepton flavor universality between muons and electrons using B+ -> K+ pi(+) pi(-) l(+) l(-) (l = e, mu) decays is presented. The measurement is performed with data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The ratio of branching fractions between B+ -> K+ pi(+) pi(-) mu(+) mu(-) decays is measured in the dilepton invariant-mass-squared range 1.1 < q(2) < 7.0 GeV2/c(4) and is found to be R-K pi pi(-1) = 1.31(-0.17)(+0.18) (stat)(-0.09)(+0.12) (syst), in agreement with the standard model prediction. The first observation of the B+ -> K+ pi(+) pi(-) e(+) e(-) decay is also reported.
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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). 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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