Gorkavenko, V., Jashal, B. K., Kholoimov, V., Kyselov, Y., Mendoza, D., Ovchynnikov, M., et al. (2024). LHCb potential to discover long-lived new physics particles with lifetimes above 100 ps. Eur. Phys. J. C, 84(6), 608–15pp.
Abstract: For years, it has been believed that the main LHC detectors can play only a limited role of a lifetime frontier experiment exploring the parameter space of long-lived particles (LLPs)-hypothetical particles with tiny couplings to the Standard Model. This paper demonstrates that the LHCb experiment may become a powerful lifetime frontier experiment if it uses the new Downstream algorithm reconstructing tracks that do not allow hits in the LHCb vertex tracker. In particular, for many LLP scenarios, LHCb may be as sensitive as the proposed experiments beyond the main LHC detectors for various LLP models, including heavy neutral leptons, dark scalars, dark photons, and axion-like particles.
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Heavy Flavor Averaging Group(Amhis, Y. et al), & Oyanguren, A. (2023). Averages of b-hadron, c-handron, and t-lepton properties as of 2021. Phys. Rev. D, 107(5), 052008–365pp.
Abstract: This paper reports world averages of measurements of b-hadron, c-hadron, and τ-lepton properties obtained by the Heavy Flavor Averaging Group using results available before April 2021. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays, and Cabibbo-Kobayashi-Maskawa matrix elements.
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Heavy Flavor Averaging Group(Amhis, Y. et al), & Oyanguren, A. (2017). Averages of b-hadron, c-hadron, and tau-lepton properties as of summer 2016. Eur. Phys. J. C, 77(12), 895–335pp.
Abstract: This article reports world averages of measurements of b-hadron, c-hadron, and tau-lepton properties obtained by the Heavy Flavor Averaging Group using results available through summer 2016. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays, and Cabbibo-Kobayashi-Maskawa matrix elements.
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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). Amplitude analysis of B+ → ψ(2S)K+ π+ π- decays. J. High Energy Phys., 01(1), 054–69pp.
Abstract: The first full amplitude analysis of B+ -> psi(2S)K+pi(+)pi(-) decays is performed using proton-proton collision data corresponding to an integrated luminosity of 9 fb(-1) recorded with the LHCb detector. The rich K+pi(+)pi(-) spectrum is studied and the branching fractions of the resonant substructure associated with the prominent K-1(1270)(+) contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity J(P) = 1(+) in the psi(2S)pi(+) system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the psi(2S)pi(+)pi(-) invariant-mass structure, dominated by X-0 -> psi(2S)rho(770)(0) decays, broadly resembles the J/psi phi spectrum observed in B+ -> J/psi phi K+ decays. Exotic psi(2S)K+pi(-) resonances are observed for the first time.
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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). 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), 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), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2024). Measurement of the effective leptonic weak mixing angle. J. High Energy Phys., 12(12), 026–28pp.
Abstract: Using pp collision data at root s = 13TeV, recorded by the LHCb experiment between 2016 and 2018 and corresponding to an integrated luminosity of 5.4 fb-1, the forward-backward asymmetry in the pp -> Z/gamma* -> mu(+) mu(-) process is measured. The measurement is carried out in ten intervals of the difference between the muon pseudorapidities, within a fiducial region covering dimuon masses between 66 and 116 GeV, muon pseudorapidities between 2.0 and 4.5 and muon transverse momenta above 20 GeV. These forward-backward asymmetries are compared with predictions, at next-to-leading order in the strong and electroweak couplings. The measured effective leptonic weak mixing angle is sin(2) theta(l)(eff) = 0.23147 +/- 0.00044 +/- 0.00005 +/- 0.00023, where the first uncertainty is statistical, the second arises from systematic uncertainties associated with the asymmetry measurement, and the third arises from uncertainties in the fit model used to extract sin(2) theta(l)(eff) from the asymmetry measurement. This result is based on an arithmetic average of results using the CT18, MSHT20, and NNPDF31 parameterisations of the proton internal structure, and is consistent with previous measurements and with predictions from the global electroweak fit.
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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 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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