LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2024). Observation of muonic Dalitz decays of chib mesons and precise spectroscopy of hidden-beauty states. J. High Energy Phys., 10(10), 122–28pp.
Abstract: The decays of the chi(b1)(1P), chi(b2)(1P), chi(b1)(2P) and chi(b2)(2P) mesons into the Upsilon(1S)mu(+)mu(-) final state are observed with a high significance using proton-proton collision data collected with the LHCb detector and corresponding to an integrated luminosity of 9 fb(-1). The newly observed decays together with the Upsilon(2S) -> Upsilon(1S)pi(+)pi(-) and Upsilon(3S) -> Upsilon(2S)pi(+)pi(-) decay modes are used for precision measurements of the mass and mass splittings for the hidden-beauty 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. (2024). Probing the nature of the χc1(3872) state using radiative decays. J. High Energy Phys., 11(11), 121–31pp.
Abstract: The radiative decays chi(c1)(3872) -> (2S) gamma and chi(c1)(3872) -> J/gamma are used to probe the nature of the chi(c1)(3872) state using proton-proton collision data collected with the LHCb detector, corresponding to an integrated luminosity of 9 fb(-1). Using the B+ -> chi(c1)(3872)K+ decay, the chi(c1)(3872) -> psi(2S) gamma process is observed for the first time and the ratio of its partial width to that of the chi(c1)(3872) -> J/psi gamma decay is measured to be Gamma(chi c1(3872))->psi(2S)gamma/Gamma(chi c1(3872)) -> J/psi gamma = 1.67 +/- 0.21 +/- 0.12 +/- 0.04, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainties on the branching fractions of the psi(2S) and J/psi mesons. The measured ratio makes the interpretation of the chi(c1)(3872) state as a pure D-0(D) over bar (*0) + (D) over bar D-0(*0) molecule questionable and strongly indicates a sizeable compact charmonium or tetraquark component within the chi(c1)(3872) state.
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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 the Λb0→ D+D-Λ decay. J. High Energy Phys., 07(7), 140–22pp.
Abstract: The Lambda(0)(b) -> D+D-Lambda decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb(-1). Using the B-0 -> (D+D-KS0) decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be R = sigma(Lambda b0)/sigma(B0) x B(Lambda(0)(b) -> D+D-Lambda)/B(B-0 -> (D+D-KS0))=0.179 +/- 0.022 +/- 0.014, where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B(B-0 -> (D+D-KS0)), and the cross-section ratio, sigma Lambda(b0)/sigma(B0), previously measured by LHCb are used to derive the branching fraction of the Lambda(0)(b)-> D+D-Lambda decay B(Lambda(0)(b) -> D+D-Lambda) = (1.24 +/- 0.15 +/- 0.10 +/- 0.28 +/- 0.11)x10(-4), where the third and fourth contributions are due to uncertainties of B(B-0 -> (D+D-KS0)) and sigma(Lambda b0)/sigma(B0), respectively. Inspection of the D+Lambda and D+D- invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Lambda(0)(b) -> D*+D-Lambda decay is also observed for the first time as a partially reconstructed component in the D+D-Lambda invariant mass spectrum.
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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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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.
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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 New Charmonium or Charmoniumlike States in B+ → D*±D∓K+ Decays. Phys. Rev. Lett., 133(13), 131902–14pp.
Abstract: A study of resonant structures in B+ -> D*(DK+)-D-+/--K--/+ and B+ -> D*(DK+)-D-+/--K--/+ decays is performed, using proton-proton collision data at center-of-mass energies of root s = 7, 8, and 13 TeV recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). A simultaneous amplitude fit is performed to the two channels with contributions from resonances decaying to D*D-+/-(+) and D*D-+/-(-) states linked by C parity. This procedure allows the C parities of resonances in the D*D-+/-(-/+) mass spectra to be determined. Four charmonium or charmoniumlike states are observed decaying into D*D-+/-(-/+): eta(c)(3945), h(c)(4000), chi(c1)(4010), and h(c)(4300), with quantum numbers J(PC) equal to 0(-+), 1(+-), 1(+-), and 1(+-), respectively. At least three of these states have not been observed previously. In addition, the existence of the T-(c) over bar(s) over bar0*(2870)(0) and T-(c) over bar(s) over bar1*(2900)(0) resonances in the D-K+ mass spectrum, already observed in the B+ -> D+D-K+ decay, is confirmed in a different production channel.
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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). 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.
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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). Study of the rare decay J/ψ → μ+μ-μ+μ-. J. High Energy Phys., 12(12), 062–25pp.
Abstract: The rare electromagnetic J/psi -> mu(+)mu(-)mu(+)mu(-) decay is observed with a significance greatly exceeding the discovery threshold, using proton-proton collision data collected by the LHCb experiment during 2016-2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1). The rate of this decay is measured relative to that of the J/psi -> mu(+)mu(-) mode. Using the QED model for the four-muon decay in the efficiency estimation, its branching fraction is determined to be B(J/psi -> mu(+)mu(-)mu(+)mu(-)) = (1.13 +/- 0.10 +/- 0.05 +/- 0.01) x 10(-6), where the uncertainties are statistical, systematic and due to the uncertainty on the branching fraction of the J/psi -> mu(+)mu(-) 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). Study of b-hadron decays to Λc+h-h′- final states. J. High Energy Phys., 08(8), 132–32pp.
Abstract: Decays of Xi(-)(b) and Omega(-)(b) baryons to Lambda(+)(c)h(-)h(-) final states, with h(-)h '(-) being pi(-)pi(-), K-pi(-) and K-K- meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7 fb(-1) of pp collisions collected at centre-of-mass energies root s = 7, 8 and 13 TeV. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the B- -> Lambda(+)(c)(p) over bar pi(-) mode, are measured, with Xi(-)(b) -> Lambda K-+(c)-pi(-), Xi(-)(b) -> Lambda+cK-K- and Omega(-)(b) -> Lambda+cK-K- decays being observed at over 5 sigma significance. The Xi(-)(b) -> Lambda K-+(c)-pi(-) mode is also used to measure the Xi(-)(b) production asymmetry, which is found to be consistent with zero. In addition, the B- -> Lambda(+)(c)(p) over barK(-) decay is observed for the first time, and its branching fraction is measured relative to that of the B- -> Lambda(+)(c)(p) over bar pi(-) mode.
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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). Search for B+c → π+μ+μ- decays and measurement of the branching fraction ratio B(B+c → ψ(2S)π+)/B(B+c< /i> → J/ψπ+). Eur. Phys. J. C, 84(5), 468–17pp.
Abstract: The first search for nonresonant B-c(+) -> pi(+)mu(+)mu(-) decays is reported. 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). No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio B(B-c(+) -> pi(+)mu(+)mu(-))/B(B-c(+) -> J/psi pi(+)) < 2.1x10(-4) at 90% confidence level. Additionally, an updated measurement of the ratio of the B-c(+) -> psi(2S)pi(+) and B-c(+) -> J/psi pi(+) branching fractions is reported. The ratio B(B-c(+) -> psi(2S)pi+)/B(B-c(+) -> J/psi pi(+)) is measured to be 0.254 +/- 0.018 +/- 0.003 +/- 0.005, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic J/psi and psi(2S) decays. This measurement is the most precise to date and is consistent with previous LHCb results.
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