Observation of the Decay Λ_{b}

The first observation of the semileptonic b-baryon decay Λ_{b}^{0}→Λ_{c}^{+}τ^{-}ν[over ¯]_{τ}, with a significance of 6.1σ, is reported using a data sample corresponding to 3 fb^{-1} of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ^{-} lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λ_{b}^{0}→Λ_{c}^{+}τ^{-}ν[over ¯]_{τ})/B(Λ_{b}^{0}→Λ_{c}^{+}π^{-}π^{+}π^{-}) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λ_{b}^{0}→Λ_{c}^{+}τ^{-}ν[over ¯]_{τ})=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λ_{b}^{0}→Λ_{c}^{+}π^{-}π^{+}π^{-}. The ratio of semileptonic branching fractions R(Λ_{c}^{+})≡B(Λ_{b}^{0}→Λ_{c}^{+}τ^{-}ν[over ¯]_{τ})/B(Λ_{b}^{0}→Λ_{c}^{+}µ^{-}ν[over ¯]_{µ}) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λ_{b}^{0}→Λ_{c}^{+}µ^{-}ν[over ¯]_{µ} contributes to the last term. This result is in agreement with the standard model prediction.

Study of Z Bosons Produced in Association with Charm in the Forward Region.

Events containing a Z boson and a charm jet are studied for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of 6 fb^{-1} collected at a center-of-mass energy of 13 TeV with the LHCb detector. In events with a Z boson and a jet, the fraction of charm jets is determined in intervals of Z-boson rapidity in the range 2.0

Angular Analysis of the B

We present an angular analysis of the B^{+}→K^{*+}(→K_{S}^{0}π^{+})µ^{+}µ^{-} decay using 9 fb^{-1} of pp collision data collected with the LHCb experiment. For the first time, the full set of CP-averaged angular observables is measured in intervals of the dimuon invariant mass squared. Local deviations from standard model predictions are observed, similar to those in previous LHCb analyses of the isospin-partner B^{0}→K^{*0}µ^{+}µ^{-} decay. The global tension is dependent on which effective couplings are considered and on the choice of theory nuisance parameters.

Observation of the Mass Difference between Neutral Charm-Meson Eigenstates.

A measurement of mixing and CP violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb^{-1}. A total of 30.6 million D^{0}→K_{S}^{0}π^{+}π^{-} decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for CP violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be x_{CP}=[3.97±0.46(stat)±0.29(syst)]×10^{-3} and y_{CP}=[4.59±1.20(stat)±0.85(syst)]×10^{-3}, respectively. The CP-violating parameters are measured as Δx=[-0.27±0.18(stat)±0.01(syst)]×10^{-3} and Δy=[0.20±0.36(stat)±0.13(syst)]×10^{-3}. This is the first observation of a nonzero mass difference in the D^{0} meson system, with a significance exceeding seven standard deviations. The data are consistent with CP symmetry and improve existing constraints on the associated parameters.

Evidence for an η c ( 1 S ) π - resonance in B 0 → η c ( 1 S ) K + π - decays.

A Dalitz plot analysis of B 0 → η c ( 1 S ) K + π - decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of s = 7 , 8 and 13 Te V , corresponding to a total integrated luminosity of 4.7 fb - 1 . A satisfactory description of the data is obtained when including a contribution representing an exotic η c ( 1 S ) π - resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096 ± 20 - 22 + 18 Me V and 152 ± 58 - 35 + 60 Me V , respectively. The spin-parity assignments J P = 0 + and J P = 1 - are both consistent with the data. In addition, the first measurement of the B 0 → η c ( 1 S ) K + π - branching fraction is performed and gives B ( B 0 → η c ( 1 S ) K + π - ) = ( 5.73 ± 0.24 ± 0.13 ± 0.66 ) × 10 - 4 , where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.

Measurement of the [Formula: see text] production cross-section in proton-proton collisions via the decay [Formula: see text].

The production of the [Formula: see text] state in proton-proton collisions is probed via its decay to the [Formula: see text] final state with the LHCb detector, in the rapidity range [Formula: see text] and in the meson transverse-momentum range [Formula: see text]. The cross-section for prompt production of [Formula: see text] mesons relative to the prompt [Formula: see text] cross-section is measured, for the first time, to be [Formula: see text] at a centre-of-mass energy [Formula: see text] using data corresponding to an integrated luminosity of 0.7 fb[Formula: see text], and [Formula: see text] at [Formula: see text] using 2.0 fb[Formula: see text]. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the [Formula: see text] and [Formula: see text] decays to the [Formula: see text] final state. In addition, the inclusive branching fraction of [Formula: see text]-hadron decays into [Formula: see text] mesons is measured, for the first time, to be [Formula: see text], where the third uncertainty includes also the uncertainty on the [Formula: see text] inclusive branching fraction from [Formula: see text]-hadron decays. The difference between the [Formula: see text] and [Formula: see text] meson masses is determined to be [Formula: see text].