LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Study of Bc(1P)+ states in the B+cγ mass spectrum. Phys. Rev. D, 112(11), 112003–18pp.
Abstract: The study of a wide peaking structure in the B-c(+)gamma mass spectrum is reported using a data sample of proton-proton collisions collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The observed structure is consistent with the lowest excited P-wave B-c(+) states and exhibits a statistical significance exceeding 7 standard deviations relative to the background-only hypothesis. A two-peak model serves as an effective description of the data, with various theory-constrained models further explored to provide physical interpretation. Based on the predictions for the B-c(1P)(+) spectrum, the relative production cross section of the overall B-c(1P)(+) states with respect to the B-c(+) ground state with the transverse momentum p(T) and rapidity y of B-c(+) mesons in the regions p(T) < 20 GeV/c and 2.0 < y < 4.5 at root s = 13 TeV is measured to be 0.20 +/- 0.03 +/- 0.02 +/- 0.03, where the uncertainty terms represent statistical, systematic, and uncertainties related to the choice of theoretical models, respectively. The results provide a test of theoretical models and deepen our understanding of quantum chromodynamics.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Measurement of the Lund plane for light- and beauty-quark jets. Phys. Rev. D, 112(7), 072015–22pp.
Abstract: The substructure of jets in quantum chromodynamics (QCD) has garnered significant attention with the advent of infrared- and collinear-safe clustering algorithms and observables. A key question emerging from these studies is how in-jet emissions at soft and hard energy scales, across collinear and wide angles relative to the emitter, differ with the mass of the emitting parton. The Lund jet plane (LJP) is a perturbatively well-defined substructure observable that maps the radiation pattern of jets onto a plane, visually distinguishing emissions with different kinematic properties. Comparing LJP for jets containing hadrons of low versus high mass enables the testing of QCD splitting functions from first-principles calculations across both soft and hard regimes and at different radiation angles. This article presents the first measurement of the LJP for light-quark-enriched and beauty-initiated jets at a center-of-mass energy of 13 TeV at LHCb. This marks the first direct observation of the dead-cone effect in beauty-quark jets, measured in the collinear region of the LJP.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Measurement of transverse Λ and (Λ)over-bar hyperon polarization in pPb collisions at √sNN=5.02 TeV. Phys. Rev. D, 112(11), 112022–15pp.
Abstract: The transverse polarization of Lambda and (Lambda) over bar hyperons is measured in pPb collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The polarization is averaged over hyperon transverse momentum in the range 0.15 < p(T) < 6.00 GeV/c, and Feynman-x in the ranges 0.005 < x(F) < 0.040 (forward region) and -0.10 < x(F) < -0.01 (backward region) defined relative to the proton beam direction. The transverse polarization is found to be compatible with zero for both Lambda and and (Lambda) over bar hyperons. The results are also measured as a function of p(T) and x(F) with no significant dependence on these variables observed. The results are compared with previous experimental measurements at different centerof-mass energies and collision environments.
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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. (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.
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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 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), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Study of light-meson resonances decaying to KS0Kπ in the B → (Ks0Kπ) channels. Phys. Rev. D, 111(9), 092009–32pp.
Abstract: A study is presented of B+ -> (KSK-)-K-0 pi K-+(+) and B+ -> (KSK+)-K-0 pi K--(+) decays based on the analysis of proton-proton collision data collected with the LHCb detector at center-of- mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The (KSK)-K-0 pi invariant-mass distributions of both Bthorn decay modes show, in the m((KSK)-K-0 pi) < 1.85 GeV mass region, large activity which is resolved using an amplitude analysis. A simple model, where J(PC) amplitudes are described by multiple Breit-Wigner functions with appropriate angular distributions, provides a good description of the experimental data. In this approach a complex mixture of J(PC) = 0(-+), 1(++) and 1(-+) amplitudes is observed that is dominated by eta(1405), eta(1470), eta(1760), f 1o1285THORN, f(1)(1420) and h(1)(1405) resonances. The (KSK)-K-0 pi Dalitz plots are dominated by asymmetric crossing K*(K) over bar bands which are different for the two Bthorn decay modes. This is due to a different interference pattern between the 1(++) and 1(+-) amplitudes in the two channels. Branching fractions are measured for each resonant contribution.
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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 asymmetries in Λb0 → ph- decays. Phys. Rev. D, 111(9), 092004–15pp.
Abstract: A search for CP violation in Lambda(0)(b) -> pK(-) and Lambda(0)(b) -> p pi(-) decays is presented using the full Run 1 and Run 2 data samples of pp collisions collected with the LHCb detector, corresponding to an integrated luminosity of 9 fb(-1) at center-of-mass energies of 7, 8, and 13 TeV. For the Run 2 data sample, the CPviolating asymmetries are measured to be A(CP)(pK-) = (-1.4 +/- 0.7 +/- 0.4)% and A(CP)(p pi-)= (0.4 +/- 0.9 +/- 0.4)%, where the first uncertainty is statistical and the second is systematic. Following significant improvements in the evaluation of systematic uncertainties compared to the previous LHCb measurement, the Run 1 dataset is reanalyzed to update the corresponding results. When combining the Run 2 and updated Run 1 measurements, the final results are found to be A(CP)(pK-) = (-1.1 +/- 0.7 +/- 0.4)% and A(CP)(p pi-) = (0.2 +/- 0.8 +/- 0.4)%, constituting the most precise measurements of these asymmetries to date.
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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). Branching fraction measurement of the decay B+ → ψ(2S) φ(1020)+. Phys. Rev. D, 111(9), 092008–15pp.
Abstract: The branching fraction of the decay B+ ->psi(2S)phi(1020)K+, relative to the topologically similar decay B+ -> J psi phi(1020)K+, is measured using proton-proton collision data 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 is found to be 0.061 +/- 0.004 +/- 0.009, where the first uncertainty is statistical and the second systematic. Using the world-average branching fraction for B+ -> J psi phi(1020)K+, the branching fraction for the decay B+ ->psi(2S)phi(1020)K+ is found to be (3.0 +/- 0.2 +/- 0.5 +/- 0.2) x 10(-6), where the first uncertainty is statistical, the second systematic, and the third is due to the branching fraction of the normalization channel.
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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 D0 meson decays to π+π- e+e- and K+K- e+e- final states. Phys. Rev. D, 111, L091101–13pp.
Abstract: A search for D-0 meson decays to the pi(+)pi(-) e(+)e(-) and K(+)K(-)e(+)e(-) final states is reported using a sample of proton-proton collisions collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb(-1). The decay D-0 -> pi(+)pi(-) e(+)e(-) is observed for the first time when requiring that the two electrons are consistent with coming from the decay of a phi or rho(0)/omega meson. The corresponding branching fractions are measured relative to the D-0 -> K-pi(-) [e(+)e(-)](rho 0/omega) decay, where the two electrons are consistent with coming from the decay of a rho(0) or omega meson. No evidence is found for the D-0 -> K(+)K(-)e(+)e(-) decay and world-best limits are set on its branching fraction. The results are compared to, and found to be consistent with, the branching fractions of the D-0 -> pi(+)pi(-)mu(+)mu(-) and D-0 -> K+K-mu(+)mu(-) decays recently measured by LHCb and confirm lepton universality at the current precision.
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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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