Observation of Cabibbo-Suppressed Two-Body Hadronic Decays and Precision Mass Measurement of the Ω_{c}

The first observation of the singly Cabibbo-suppressed Ω_{c}^{0}→Ω^{-}K^{+} and Ω_{c}^{0}→Ξ^{-}π^{+} decays is reported, using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb^{-1}, collected with the LHCb detector between 2016 and 2018. The branching fraction ratios are measured to be B(Ω_{c}^{0}→Ω^{-}K^{+})/B(Ω_{c}^{0}→Ω^{-}π^{+})=[6.08±0.51(stat)±0.40(syst)]%,B(Ω_{c}^{0}→Ξ^{-}π^{+})/B(Ω_{c}^{0}→Ω^{-}π^{+})=[15.81±0.87(stat)±0.44(syst)±0.16(ext)]%. In addition, using the Ω_{c}^{0}→Ω^{-}π^{+} decay channel, the Ω_{c}^{0} baryon mass is measured to be M(Ω_{c}^{0})=2695.28±0.07(stat)±0.27(syst)±0.30(ext) MeV, improving the precision of the previous world average by a factor of 4.

Improved Measurement of CP Violation Parameters in B_{s}

The decay-time-dependent CP asymmetry in B_{s}^{0}→J/ψ(→µ^{+}µ^{-})K^{+}K^{-} decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb^{-1}, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 B_{s}^{0} signal decays with an invariant K^{+}K^{-} mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕ_{s} is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B_{s}^{0}-B[over ¯]_{s}^{0} system, ΔΓ_{s}, and the difference of the average B_{s}^{0} and B^{0} meson decay widths, Γ_{s}-Γ_{d}. The values obtained are ϕ_{s}=-0.039±0.022±0.006 rad, ΔΓ_{s}=0.0845±0.0044±0.0024 ps^{-1}, and Γ_{s}-Γ_{d}=-0.0056_{-0.0015}^{+0.0013}±0.0014 ps^{-1}, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕ_{s} is also measured independently for each polarization state of the K^{+}K^{-} system and shows no evidence for polarization dependence.

Measurement of CP Violation in B

A measurement of time-dependent CP violation in the decays of B^{0} and B[over ¯]^{0} mesons to the final states J/ψ(→µ^{+}µ^{-})K_{S}^{0}, ψ(2S)(→µ^{+}µ^{-})K_{S}^{0} and J/ψ(→e^{+}e^{-})K_{S}^{0} with K_{S}^{0}→π^{+}π^{-} is presented. The data correspond to an integrated luminosity of 6 fb^{-1} collected at a center-of-mass energy of sqrt[s]=13 TeV with the LHCb detector. The CP-violation parameters are measured to be S_{ψK_{S}^{0}}=0.717±0.013(stat)±0.008(syst) and C_{ψK_{S}^{0}}=0.008±0.012(stat)±0.003(syst). This measurement of S_{ψK_{S}^{0}} represents the most precise single measurement of the CKM angle ß to date and is more precise than the current world average. In addition, measurements of the CP-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed.

Observation of New Baryons in the Ξ_{b}

The first observation and study of two new baryonic structures in the final state Ξ_{b}^{0}π^{+}π^{-} and the confirmation of the Ξ_{b}(6100)^{-} state in the Ξ_{b}^{-}π^{+}π^{-} decay mode are reported using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb^{-1}. In addition, the properties of the known Ξ_{b}^{*0}, Ξ_{b}^{'-} and Ξ_{b}^{*-} resonances are measured with improved precision. The new decay mode of the Ξ_{b}^{0} baryon to the Ξ_{c}^{+} π^{-} π^{+} π^{-} final state is observed and exploited for the first time in these measurements.

Precision Measurement of CP Violation in the Penguin-Mediated Decay B_{s}

A flavor-tagged time-dependent angular analysis of the decay B_{s}^{0}→ϕϕ is performed using pp collision data collected by the LHCb experiment at the center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb^{-1}. The CP-violating phase and direct CP-violation parameter are measured to be ϕ_{s}^{ss[over ¯]s}=-0.042±0.075±0.009 rad and |λ|=1.004±0.030±0.009, respectively, assuming the same values for all polarization states of the ϕϕ system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using pp collisions at center-of-mass energies of 7 and 8 TeV, yielding ϕ_{s}^{ss[over ¯]s}=-0.074±0.069 rad and |λ|=1.009±0.030. This is the most precise study of time-dependent CP violation in a penguin-dominated B meson decay. The results are consistent with CP symmetry and with the standard model predictions.

Measurement of the Λ_{b}

The branching fraction of the rare decay Λ_{b}^{0}→Λ(1520)µ^{+}µ^{-} is measured for the first time, in the squared dimuon mass intervals q^{2}, excluding the J/ψ and ψ(2S) regions. The data sample analyzed was collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb^{-1}. The result in the highest q^{2} interval, q^{2}>15.0 GeV^{2}/c^{4}, where theoretical predictions have the smallest model dependence, agrees with the predictions.

Observation of New Ω_{c}

Two new excited states, Ω_{c}(3185)^{0} and Ω_{c}(3327)^{0}, are observed in the Ξ_{c}^{+}K^{-} invariant-mass spectrum using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb^{-1}. Five previously observed excited Ω_{c}^{0} states are confirmed, namely Ω_{c}(3000)^{0}, Ω_{c}(3050)^{0}, Ω_{c}(3065)^{0}, Ω_{c}(3090)^{0}, and Ω_{c}(3119)^{0}. The masses and widths of these seven states are measured with the highest precision to date.

Evidence of a J/ψK_{S}

An amplitude analysis of B^{0}→J/ψϕK_{S}^{0} decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 9 fb^{-1}, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. Evidence with a significance of 4.0 standard deviations of a structure in the J/ψK_{S}^{0} system, named T_{ψs1}^{θ}(4000)^{0}, is seen, with its mass and width measured to be 3991_{-10}^{+12} _{-17}^{+9} MeV/c^{2} and 105_{-25}^{+29} _{-23}^{+17} MeV, respectively, where the first uncertainty is statistical and the second systematic. The T_{ψs1}^{θ}(4000)^{0} state is likely to be the isospin partner of the T_{ψs1}^{θ}(4000)^{+} state, previously observed in the J/ψK^{+} system of the B^{+}→J/ψϕK^{+} decay. When isospin symmetry for the charged and neutral T_{ψs1}^{θ}(4000) states is assumed, the signal significance increases to 5.4 standard deviations.

Measurement of the Prompt D

The production of prompt D^{0} mesons in proton-lead collisions in both the forward and backward rapidity regions at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=8.16 TeV is measured by the LHCb experiment. The nuclear modification factor of prompt D^{0} mesons is determined as a function of the transverse momentum p_{T}, and the rapidity in the nucleon-nucleon center-of-mass frame y^{*}. In the forward rapidity region, significantly suppressed production with respect to pp collisions is measured, which provides significant constraints on models of nuclear parton distributions and hadron production down to the very low Bjorken-x region of ∼10^{-5}. In the backward rapidity region, a suppression with a significance of 2.0-3.8 standard deviations compared to parton distribution functions in a nuclear environment expectations is found in the kinematic region of p_{T}>6 GeV/c and -3.25

Observation of a Resonant Structure near the D_{s}

An amplitude analysis of the B^{+}→D_{s}^{+}D_{s}^{-}K^{+} decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A near-threshold peaking structure, referred to as X(3960), is observed in the D_{s}^{+}D_{s}^{-} invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width, and the quantum numbers of the structure are measured to be 3956±5±10 MeV, 43±13±8 MeV, and J^{PC}=0^{++}, respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of cc[over ¯]ss[over ¯] quarks. Evidence for an additional structure is found around 4140 MeV in the D_{s}^{+}D_{s}^{-} invariant mass, which might be caused either by a new resonance with the 0^{++} assignment or by a J/ψϕ↔D_{s}^{+}D_{s}^{-} coupled-channel effect.

Measurement of the Branching Fractions B(B

Searches for the rare hadronic decays B^{0}→pp[over ¯]pp[over ¯] and B_{s}^{0}→pp[over ¯]pp[over ¯] are performed using proton-proton collision data recorded by the LHCb experiment and corresponding to an integrated luminosity of 9 fb^{-1}. Significances of 9.3σ and 4.0σ, including statistical and systematic uncertainties, are obtained for the B^{0}→pp[over ¯]pp[over ¯] and B_{s}^{0}→pp[over ¯]pp[over ¯] signals, respectively. The branching fractions are measured relative to the topologically similar normalization decays B^{0}→J/ψ(→pp[over ¯])K^{*0}(→K^{+}π^{-}) and B_{s}^{0}→J/ψ(→pp[over ¯])⁢ϕ(→K^{+}K^{-}). The branching fractions are measured to be B(B^{0}→pp[over ¯]pp[over ¯])=(2.2±0.4±0.1±0.1)×10^{-8} and B(B_{s}^{0}→pp[over ¯]pp[over ¯])=(2.3±1.0±0.2±0.1)×10^{-8}. In these measurements, the first uncertainty is statistical, the second is systematic, and the third one is due to the external branching fraction of the normalization channel.

Measurement of the Time-Integrated CP Asymmetry in D

The time-integrated CP asymmetry in the Cabibbo-suppressed decay D^{0}→K^{-}K^{+} is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb^{-1} collected at a center-of-mass energy of 13 TeV with the LHCb detector. The D^{0} mesons are required to originate from promptly produced D^{*+}→D^{0}π^{+} decays, and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated CP asymmetry is measured to be A_{CP}(K^{-}K^{+})=[6.8±5.4±1.6]×10^{-4} where the first uncertainty is statistical and the second systematic. The direct CP asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, a_{K^{-}K^{+}}^{d} and a_{π^{-}π^{+}}^{d}, are derived by combining A_{CP}(K^{-}K^{+}) with the time-integrated CP asymmetry difference, ΔA_{CP}=A_{CP}(K^{-}K^{+})-A_{CP}(π^{-}π^{+}), and other inputs, giving a_{K^{-}K^{+}}^{d}=(7.7±5.7)×10^{-4},a_{π^{-}π^{+}}^{d}=(23.2±6.1)×10^{-4},with a correlation coefficient corresponding to ρ=0.88. The compatibility of these results with CP symmetry is 1.4 and 3.8 standard deviations for D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, respectively. This is the first evidence for direct CP violation in a specific D^{0} decay.

Measurement of the Ratios of Branching Fractions R(D

The ratios of branching fractions R(D^{*})≡B(B[over ¯]→D^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]→D^{*}µ^{-}ν[over ¯]_{µ}) and R(D^{0})≡B(B^{-}→D^{0}τ^{-}ν[over ¯]_{τ})/B(B^{-}→D^{0}µ^{-}ν[over ¯]_{µ}) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ^{-}→µ^{-}ν_{τ}ν[over ¯]_{µ}. The measured values are R(D^{*})=0.281±0.018±0.024 and R(D^{0})=0.441±0.060±0.066, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is ρ=-0.43. The results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the standard model.

Evidence for Modification of b Quark Hadronization in High-Multiplicity pp Collisions at sqrt[s]=13 TeV.

The production rate of B_{s}^{0} mesons relative to B^{0} mesons is measured by the LHCb experiment in pp collisions at a center-of-mass energy sqrt[s]=13 TeV over the forward rapidity interval 2

Test of Lepton Universality in b→sℓ

The first simultaneous test of muon-electron universality using B^{+}→K^{+}ℓ^{+}ℓ^{-} and B^{0}→K^{*0}ℓ^{+}ℓ^{-} decays is performed, in two ranges of the dilepton invariant-mass squared, q^{2}. The analysis uses beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb^{-1}. Each of the four lepton universality measurements reported is either the first in the given q^{2} interval or supersedes previous LHCb measurements. The results are compatible with the predictions of the Standard Model.

Observation of a J/ψΛ Resonance Consistent with a Strange Pentaquark Candidate in B

An amplitude analysis of B^{-}→J/ψΛp[over ¯] decays is performed using 4400 signal candidates selected on a data sample of pp collisions recorded at center-of-mass energies of 7, 8, and 13 TeV with the LHCb detector, corresponding to an integrated luminosity of 9 fb^{-1}. A narrow resonance in the J/ψΛ system, consistent with a pentaquark candidate with strangeness, is observed with high significance. The mass and the width of this new state are measured to be 4338.2±0.7±0.4 MeV and 7.0±1.2±1.3 MeV, where the first uncertainty is statistical and the second systematic. The spin is determined to be 1/2 and negative parity is preferred. Because of the small Q-value of the reaction, the most precise single measurement of the B^{-} mass to date, 5279.44±0.05±0.07 MeV, is obtained.

First Observation of a Doubly Charged Tetraquark and Its Neutral Partner.

A combined amplitude analysis is performed for the decays B^{0}→D[over ¯]^{0}D_{s}^{+}π^{-} and B^{+}→D^{-}D_{s}^{+}π^{+}, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb^{-1}. Two new resonant states with masses of 2.908±0.011±0.020 GeV and widths of 0.136±0.023±0.013 GeV are observed, which decay to D_{s}^{+}π^{+} and D_{s}^{+}π^{-} respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content [cs[over ¯]ud[over ¯]], and the latter state is a neutral tetraquark composed of [cs[over ¯]u[over ¯]d] quarks. Both states are found to have spin-parity of 0^{+}, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.

Nuclear Modification Factor of Neutral Pions in the Forward and Backward Regions in p-Pb Collisions.

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16 TeV with the LHCb detector. The π^{0} production cross section is measured differentially in transverse momentum (p_{T}) for 1.5

Search for Rare Decays of D

A search for the very rare D^{0}→µ^{+}µ^{-} decay is performed using data collected by the LHCb experiment in proton-proton collisions at sqrt[s]=7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb^{-1}. The search is optimized for D^{0} mesons from D^{*+}→D^{0}π^{+} decays but is also sensitive to D^{0} mesons from other sources. No evidence for an excess of events over the expected background is observed. An upper limit on the branching fraction of this decay is set at B(D^{0}→µ^{+}µ^{-})<3.1×10^{-9} at a 90% C.L. This represents the world's most stringent limit, constraining models of physics beyond the standard model.

First Measurement of the Z→µ

The first study of the angular distribution of µ^{+}µ^{-} pairs produced in the forward rapidity region via the Drell-Yan reaction pp→γ^{*}/Z+X→ℓ^{+}ℓ^{-}+X is presented, using data collected with the LHCb detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.1 fb^{-1}. The coefficients of the five leading terms in the angular distribution are determined as a function of the dimuon transverse momentum and rapidity. The results are compared to various theoretical predictions of the Z-boson production mechanism and can also be used to probe transverse-momentum-dependent parton distributions within the proton.