Measurement of Λb0 , Λc+ , and Λ decay parameters using Λb0→Λc+h− decays

A comprehensive study of the angular distributions in the bottom-baryon decays Λ0 b → Λ c+h−(h = π, K), followed by Λþ c → Λhþ with Λ → pπ− or Λþ c → pK0 S decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb−1 collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, the Λ0 b → Λþ c h− decay parameters are measured. The most precise measurements of the decay parameters α, β, and γ are obtained for Λþ c decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays

Test of Lepton Flavor Universality with B_{s}^{0}→ϕℓ^{+}ℓ^{-} Decays.

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}→ϕe^{+}e^{-} and B_{s}^{0}→ϕμ^{+}μ^{-} 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  GeV^{2}/c^{4}. The results agree with the standard model expectation of lepton flavor universality

First Evidence for Direct CP Violation in Beauty to Charmonium Decays.

The CP asymmetry and branching fraction of the Cabibbo-Kobayashi-Maskawa-suppressed decay B^{+}→J/ψπ^{+} are precisely measured relative to the favored decay B^{+}→J/ψK^{+} using a sample of proton-proton 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 ΔA^{CP}≡A^{CP}(B^{+}→J/ψπ^{+})-A^{CP}(B^{+}→J/ψK^{+})=(1.29±0.49±0.08)×10^{-2}, R_{π/K}≡[B(B^{+}→J/ψπ^{+})/B(B^{+}→J/ψK^{+})]=(3.852±0.022±0.018)×10^{-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 TeV in 2011 and 2012 yields ΔA^{CP}=(1.42±0.43±0.08)×10^{-2} and R_{π/K}=(3.846±0.018±0.018)×10^{-2}. The combined ΔA^{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

Study of the rare decay J/ψ → μ+μ−μ+μ−

Abstract The rare electromagnetic J/ψ → μ+μ−μ+μ− 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/ψ → μ+μ− mode. Using the QED model for the four-muon decay in the efficiency estimation, its branching fraction is determined to be$$\mathcal{B}\left(J/\psi \to {\mu}^{+}{\mu}^{-}{\mu}^{+}{\mu}^{-}\right)=\left(1.13\pm 0.10\pm 0.05\pm 0.01\right)\times {10}^{-6},$$ B J / ψ → μ + μ − μ + μ − = 1.13 ± 0.10 ± 0.05 ± 0.01 × 10 − 6 , where the uncertainties are statistical, systematic and due to the uncertainty on the branching fraction of the J/ψ → μ+μ− decay.</jats:p

Study of the rare decay J/ψ → μ+μ−μ+μ−

Abstract The rare electromagnetic J/ψ → μ+μ−μ+μ− 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/ψ → μ+μ− mode. Using the QED model for the four-muon decay in the efficiency estimation, its branching fraction is determined to be$$\mathcal{B}\left(J/\psi \to {\mu}^{+}{\mu}^{-}{\mu}^{+}{\mu}^{-}\right)=\left(1.13\pm 0.10\pm 0.05\pm 0.01\right)\times {10}^{-6},$$ B J / ψ → μ + μ − μ + μ − = 1.13 ± 0.10 ± 0.05 ± 0.01 × 10 − 6 , where the uncertainties are statistical, systematic and due to the uncertainty on the branching fraction of the J/ψ → μ+μ− decay.</jats:p