Angular Analysis of D

The first full angular analysis and an updated measurement of the decay-rate CP asymmetry of the D^{0}→π^{+}π^{-}µ^{+}µ^{-} and D^{0}→K^{+}K^{-}µ^{+}µ^{-} decays are reported. The analysis uses proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. The dataset corresponds to an integrated luminosity of 9 fb^{-1}. The full set of CP -averaged angular observables and their CP asymmetries are measured as a function of the dimuon invariant mass. The results are consistent with expectations from the standard model and with CP symmetry.

Tests of Lepton Universality Using B

Tests of lepton universality in B^{0}→K_{S}^{0}ℓ^{+}ℓ^{-} and B^{+}→K^{*+}ℓ^{+}ℓ^{-} decays where ℓ is either an electron or a muon are presented. The differential branching fractions of B^{0}→K_{S}^{0}e^{+}e^{-} and B^{+}→K^{*+}e^{+}e^{-} decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb^{-1} . The results are consistent with the standard model and previous tests of lepton universality in related decay modes. The first observation of B^{0}→K_{S}^{0}e^{+}e^{-} and B^{+}→K^{*+}e^{+}e^{-} decays is reported.

Observation of Two New Excited Ξ_{b}

Two narrow resonant states are observed in the Λ_{b}^{0}K^{-}π^{+} mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb^{-1}. The minimal quark content of the Λ_{b}^{0}K^{-}π^{+} system indicates that these are excited Ξ_{b}^{0} baryons. The masses of the Ξ_{b}(6327)^{0} and Ξ_{b}(6333)^{0} states are m[Ξ_{b}(6327)^{0}]=6327.28_{-0.21}^{+0.23}±0.12±0.24 and m[Ξ_{b}(6333)^{0}]=6332.69_{-0.18}^{+0.17}±0.03±0.22 MeV, respectively, with a mass splitting of Δm=5.41_{-0.27}^{+0.26}±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Λ_{b}^{0} mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Γ[Ξ_{b}(6327)^{0}]<2.20(2.56) and Γ[Ξ_{b}(6333)^{0}]<1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Ξ_{b}^{0} resonances.

Measurement of the Nuclear Modification Factor and Prompt Charged Particle Production in p-Pb and pp Collisions at sqrt[s_{NN}]=5 TeV.

The production of prompt charged particles in proton-lead collisions and in proton-proton collisions at the nucleon-nucleon center-of-mass energy sqrt[s_{NN}]=5 TeV is studied at LHCb as a function of pseudorapidity (η) and transverse momentum (p_{T}) with respect to the proton beam direction. The nuclear modification factor for charged particles is determined as a function of η between -4.8<η<-2.5 (backward region) and 2.0<η<4.8 (forward region), and p_{T} between 0.2

Evidence for a New Structure in the J/ψp and J/ψp[over ¯] Systems in B_{s}

An amplitude analysis of flavor-untagged B_{s}^{0}→J/ψpp[over ¯] decays is performed using a sample of 797±31 decays reconstructed with the LHCb detector. The data, collected in proton-proton collisions between 2011 and 2018, correspond to an integrated luminosity of 9 fb^{-1}. Evidence for a new structure in the J/ψp and J/ψp[over ¯] systems with a mass of 4337_{-4}^{+7} _{-2}^{+2} MeV and a width of 29_{-12}^{+26} _{-14}^{+14} MeV is found, where the first uncertainty is statistical and the second systematic, with a significance in the range of 3.1 to 3.7σ, depending on the assigned J^{P} hypothesis.

Analysis of Neutral B-Meson Decays into Two Muons.

Branching fraction and effective lifetime measurements of the rare decay B_{s}^{0}→µ^{+}µ^{-} and searches for the decays B^{0}→µ^{+}µ^{-} and B_{s}^{0}→µ^{+}µ^{-}γ are reported using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a luminosity of 9 fb^{-1}. The branching fraction B(B_{s}^{0}→µ^{+}µ^{-})=(3.09_{-0.43-0.11}^{+0.46+0.15})×10^{-9} and the effective lifetime τ(B_{s}^{0}→µ^{+}µ^{-})=2.07±0.29±0.03 ps are measured, where the first uncertainty is statistical and the second systematic. No significant signal for B^{0}→µ^{+}µ^{-} and B_{s}^{0}→µ^{+}µ^{-}γ decays is found and upper limits B(B^{0}→µ^{+}µ^{-})<2.6×10^{-10} and B(B_{s}^{0}→µ^{+}µ^{-}γ)<2.0×10^{-9} at the 95% C.L. are determined, where the latter is limited to the range m_{µµ}>4.9 GeV/c^{2}. The results are in agreement with the standard model expectations.

Branching Fraction Measurements of the Rare B_{s}

The branching fraction of the rare B_{s}^{0}→ϕµ^{+}µ^{-} decay is measured using data collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to integrated luminosities of 1, 2, and 6 fb^{-1}, respectively. The branching fraction is reported in intervals of q^{2}, the square of the dimuon invariant mass. In the q^{2} region between 1.1 and 6.0 GeV^{2}/c^{4}, the measurement is found to lie 3.6 standard deviations below a standard model prediction based on a combination of light cone sum rule and lattice QCD calculations. In addition, the first observation of the rare B_{s}^{0}→f_{2}^{'}(1525)µ^{+}µ^{-} decay is reported with a statistical significance of 9 standard deviations and its branching fraction is determined.

Observation of New Resonances Decaying to J/ψK

The first observation of exotic states with a new quark content cc[over ¯]us[over ¯] decaying to the J/ψK^{+} final state is reported with high significance from an amplitude analysis of the B^{+}→J/ψϕK^{+} decay. The analysis is carried out using proton-proton collision data corresponding to a total integrated luminosity of 9 fb^{-1} collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The most significant state, Z_{cs}(4000)^{+}, has a mass of 4003±6_{-14}^{+4} MeV, a width of 131±15±26 MeV, and spin parity J^{P}=1^{+}, where the quoted uncertainties are statistical and systematic, respectively. A new 1^{+} X(4685) state decaying to the J/ψϕ final state is also observed with high significance. In addition, the four previously reported J/ψϕ states are confirmed and two more exotic states, Z_{cs}(4220)^{+} and X(4630), are observed with significance exceeding 5 standard deviations.

Observation of a New Excited D_{s}

Using pp collision data corresponding to an integrated luminosity of 5.4 fb^{-1} collected with the LHCb detector at a center-of-mass energy of 13 TeV, the B^{0}→D^{-}D^{+}K^{+}π^{-} decay is studied. A new excited D_{s}^{+} meson is observed decaying into the D^{+}K^{+}π^{-} final state with large statistical significance. The pole mass and width, and the spin parity of the new state are measured with an amplitude analysis to be m_{R}=2591±6±7 MeV, Γ_{R}=89±16±12 MeV, and J^{P}=0^{-}, where the first uncertainty is statistical and the second systematic. Fit fractions for all components in the amplitude analysis are also reported. The new resonance, denoted as D_{s0}(2590)^{+}, is a strong candidate to be the D_{s}(2^{1}S_{0})^{+} state, the radial excitation of the pseudoscalar ground-state D_{s}^{+} meson.

Measurement of CP Violation in the Decay B

A measurement of CP violation in the decay B^{+}→K^{+}π^{0} is reported using data corresponding to an integrated luminosity of 5.4 fb^{-1} collected with the LHCb experiment at a center-of-mass energy of sqrt[s]=13 TeV. The CP asymmetry is measured to be 0.025±0.015±0.006±0.003, where the uncertainties are statistical, systematic, and due to an external input. This is the most precise measurement of this quantity. It confirms and significantly enhances the observed anomalous difference between the direct CP asymmetries of the B^{0}→K^{+}π^{-} and B^{+}→K^{+}π^{0} decays, known as the Kπ puzzle.

Observation of Multiplicity Dependent Prompt χ_{c1}(3872) and ψ(2S) Production in pp Collisions.

The production of χ_{c1}(3872) and ψ(2S) hadrons is studied as a function of charged particle multiplicity in pp collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2 fb^{-1}. For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of χ_{c1}(3872) to ψ(2S) cross sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the χ_{c1}(3872) structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the χ_{c1}(3872) state are discussed.

First Observation of the Decay B_{s}

The first observation of the suppressed semileptonic B_{s}^{0}→K^{-}µ^{+}ν_{µ} decay is reported. Using a data sample recorded in pp collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of 2 fb^{-1}, the branching fraction B(B_{s}^{0}→K^{-}µ^{+}ν_{µ}) is measured to be [1.06±0.05(stat)±0.08(syst)]×10^{-4}, where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay B_{s}^{0}→D_{s}^{-}µ^{+}ν_{µ}, where D_{s}^{-} is reconstructed in the final state K^{+}K^{-}π^{-}, is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the B_{s}^{0}→K^{-} and B_{s}^{0}→D_{s}^{-} transitions are employed to determine the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements |V_{ub}|/|V_{cb}| at low and high B_{s}^{0}→K^{-} momentum transfer.

Observation of Enhanced Double Parton Scattering in Proton-Lead Collisions at sqrt[s_{NN}]=8.16 TeV.

A study of prompt charm-hadron pair production in proton-lead collisions at sqrt[s_{NN}]=8.16 TeV is performed using data corresponding to an integrated luminosity of about 30 nb^{-1}, collected with the LHCb experiment. Production cross sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.

Observation of New Ξ_{c}

The Λ_{c}^{+}K^{-} mass spectrum is studied with a data sample of pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb^{-1} collected by the LHCb experiment. Three Ξ_{c}^{0} states are observed with a large significance and their masses and natural widths are measured to be m[Ξ_{c}(2923)^{0}]=2923.04±0.25±0.20±0.14 MeV, Γ[Ξ_{c}(2923)^{0}]=7.1±0.8±1.8 MeV, m[Ξ_{c}(2939)^{0}]=2938.55±0.21±0.17±0.14 MeV, Γ[Ξ_{c}(2939)^{0}]=10.2±0.8±1.1 MeV, m[Ξ_{c}(2965)^{0}]=2964.88±0.26±0.14±0.14 MeV, Γ[Ξ_{c}(2965)^{0}]=14.1±0.9±1.3 MeV, where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λ_{c}^{+} mass. The Ξ_{c}(2923)^{0} and Ξ_{c}(2939)^{0} baryons are new states. The Ξ_{c}(2965)^{0} state is in the vicinity of the known Ξ_{c}(2970)^{0} baryon; however, their masses and natural widths differ significantly.

Model-Independent Study of Structure in B

The only anticipated resonant contributions to B^{+}→D^{+}D^{-}K^{+} decays are charmonium states in the D^{+}D^{-} channel. A model-independent analysis, using LHCb proton-proton collision data taken at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb^{-1}, is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the D^{+}D^{-} pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the D^{-}K^{+} channel with masses around 2.9 GeV/c^{2}.