LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Tracking of charged particles with nanosecond lifetimes at LHCb. Eur. Phys. J. C, 84(7), 761–16pp.
Abstract: A method is presented to reconstruct charged particles with lifetimes between 10 ps and 10 ns, which considers a combination of their decay products and the partial tracks created by the initial charged particle. Using the Xi(-) baryon as a benchmark, the method is demonstrated with simulated events and proton-proton collision data at root s = 13 TeV, corresponding to an integrated luminosity of 2.0 fb(-1) collected with the LHCb detector in 2018. Significant improvements in the angular resolution and the signal purity are obtained. The method is implemented as part of the LHCb Run 3 event trigger in a set of requirements to select detached hyperons. This is the first demonstration of the applicability of this approach at the LHC, and the first to show its scaling with instantaneous luminosity.
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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). Measurement of the branching fraction of B0→ J/ψ π0 decays. J. High Energy Phys., 05(5), 065–27pp.
Abstract: The ratio of branching fractions between B-0 -> J/psi pi(0) and B+ -> J/psi K*+ decays is measured with proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The measured value is B-B(0) -> -> J/psi pi(0)/B+ -> J/psi K*+ = (1.153 +/- 0.053 +/- 0.048) x 10-2, where the first uncertainty is statistical and the second is systematic. The branching fraction for B-0 -> J/psi pi(0) decays is determined using the branching fraction of the normalisation channel, resulting in B-B(0) -> J/psi pi(0) = (1.670 +/- 0.077 +/- 0.069 +/- 0.095) x 10-5, where the last uncertainty corresponds to that of the external input. This result is consistent with the current world average value and competitive with the most precise single measurement to date.
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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). Observation of the Bc+ → J/ψ π+ π0. J. High Energy Phys., 04(4), 151–28pp.
Abstract: The first observation of the B-c(+) -> J/psi pi(+)pi(0) decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb(-1), collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13TeV. The ratio of its branching fraction relative to the B-c(+) -> J/psi pi(+) channel is measured to be BBc+ -> J/psi pi+pi 0/BBc+ -> J/psi pi+ = 2.80 +/- 0.15 +/- 0.11 +/- 0.16, where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B+ -> J/psi K*(+) and B-c(+) -> J/psi pi(+) decays, which are used to determine the pi(0) detection efficiency. The pi(+) pi(0) mass spectrum is found to be consistent with the dominance of an intermediate rho(+) contribution in accordance with a model based on QCD factorisation.
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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). Amplitude analysis and branching fraction measurement of B+ → D*-Ds+π+ decays. J. High Energy Phys., 08(8), 165–40pp.
Abstract: The decays of the B+ meson to the final state D*D--(s)+pi(+) are studied in proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb(-1). The ratio of branching fractions of the B+ -> D-Ds+pi(+) and B-0 -> D*D--(s)+ decays is measured to be 0.173 +/- 0.006 +/- 0.010, where the first uncertainty is statistical and the second is systematic. Using partially reconstructed D-s*(+) -> D-s*(+)gamma and D-s(+)pi(0) decays, the ratio of branching fractions between the B+ -> D*D--(s)*(+)pi(+) and B+ -> D*D--(s)+pi(+) decays is determined as 1.31 +/- 0.07 +/- 0.14. An amplitude analysis of the B+ -> D*D--(s)+pi(+) decay is performed for the first time, revealing dominant contributions from known excited charm resonances decaying to the D*(-)pi(+) final state. No significant evidence of exotic contributions in the D-s(+)pi(+) or D*D--(s)+ channels is found. The fit fraction of the scalar state T*(c (s) over bar0) (2900)(++) observed in the B+ -> D-Ds+pi(+) decay is determined to be less than 2.3% at a 90% confidence level.
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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). Transverse polarization measurement of Λ hyperons in pNe collisions at √sNN=68.4 GeV with the LHCb detector. J. High Energy Phys., 09(9), 082–18pp.
Abstract: A measurement of the transverse polarization of the Lambda and (Lambda) over bar hyperons in pNe fixed-target collisions at root s(NN) = 68.4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Lambda -> p pi(-) together with its charge conjugated process, the integrated values measured are P-Lambda = 0.029 +/- 0.019 (stat) +/- 0.012 (syst), P-(Lambda) over bar = 0.003 +/- 0.023 (stat) +/- 0.014 (syst). Furthermore, the results are shown as a function of the Feynman x variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements.
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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). Comprehensive analysis of local and nonlocal amplitudes in the B0 → K*0μ+μ- decay. J. High Energy Phys., 09(9), 026–60pp.
Abstract: A comprehensive study of the local and nonlocal amplitudes contributing to the decay B-0 -> K-*0(-> K+pi(-))mu(+)mu(-) is performed by analysing the phase-space distribution of the decay products. The analysis is based on pp collision data corresponding to an integrated luminosity of 8.4 fb(-1) collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient C9, responsible for vector dimuon currents, exhibits a 2.1 sigma deviation from the Standard Model expectation. The Wilson Coefficients C-10, C-9 ' and C-10 ' are all in better agreement than <mml:msub>C9 with the Standard Model and the global significance is at the level of 1.5 sigma. The model used also accounts for nonlocal contributions from B-0 -> K-*0[tau(+)tau(-)-> mu(+)mu(-)] rescattering, resulting in the first direct measurement of the bs tau tau vector effective-coupling C-9 tau.
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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). Search for the lepton-flavor violating decay Bs0 → φμ±τ∓. Phys. Rev. D, 110(7), 072014–12pp.
Abstract: A search for the lepton-flavor violating decays B-s(0) -> phi mu(+/-)tau(-/+) is presented, using a sample of proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb(-1). The tau leptons are selected using decays with three charged pions. No significant excess is observed, and an upper limit on the branching fraction is determined to be B(B-s(0) -> phi mu(+/-)tau(-/+)) < 1.0 x 10(-5) at 90% confidence level.
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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). Search for Time-Dependent CP Violation in D0 → π+ π- π0 Decays. Phys. Rev. Lett., 133(10), 101803–12pp.
Abstract: A measurement of time-dependent CP violation in D-0 -> pi(+) pi(-) pi(0) decays using a pp collision data sample collected by the LHCb experiment in 2012 and from 2015 to 2018, corresponding to an integrated luminosity of 7.7 fb(-1), is presented. The initial flavor of each D-0 candidate is determined from the charge of the pion produced in the D*(2010)(+) -> D-0 pi(+) decay. The decay D-0 -> K- pi(+) pi(0) is used as a control channel to validate the measurement procedure. The gradient of the time-dependent CP asymmetry Delta Y in D-0 -> pi(+) pi(-) pi(0) decays is measured to be Delta Y = (-1.3 +/- 6.3 +/- 2.4) x 10(-4), where the first uncertainty is statistical and the second is systematic, which is compatible with CP conservation.
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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. (2024). Measurement of CP Violation in B0 → ψ(→ l+ l-)KS0(→ π+ π-) Decays. Phys. Rev. Lett., 132(2), 021801–12pp.
Abstract: A measurement of time-dependent CP violation in the decays of B-0 and (B) over bar (0) mesons to the final states J/psi(-> mu(+) mu(-))K-S(0), psi(2S)(-> mu(+) mu(-))K-S(0) and J/psi(-> e(+)e(-))K-S(0) with K-S(0) -> pi(+)pi(-) is presented. The data correspond to an integrated luminosity of 6 fb(-1) collected at a center-of-mass energy of root s = 13 TeV with the LHCb detector. The CP-violation parameters are measured to be S-psi KS0 = 0.717 +/- 0.013(stat) +/- 0.008(syst) and C-psi KS0 = 0.008 +/- 0.012(stat) +/- 0.003(syst). This measurement of S-psi KS0 represents the most precise single measurement of the CKM angle beta to date and is more precise than the current world average. In addition, measurements of the CP-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Mazorra de Cos, J., Oyanguren, A., et al. (2024). The LHCb Upgrade I. J. Instrum., 19(5), P05065–213pp.
Abstract: The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all -software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all -software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software.
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