Measurement of Ξcc++{{\varXi_{cc}^{++}}} production in pp collisions at s=13{\sqrt{ s}=13} TeV

The production of Ξcc ++ baryons in proton-proton collisions at a centre-of-mass energy of √s = 13TeV is measured in the transverse-momentum range 4 < PT < 15 GeV/c and the rapidity range 2.0 < y < 4.5. The data used in this measurement correspond to an integrated luminosity of 1.7 fb-1, recorded by the LHCb experiment during 2016. The ratio of the Ξcc ++ production cross-section times the branching fraction of the Ξcc ++ → Λc + K-π+ π+ decay relative to the prompt Λc + production cross-section is found to be (2.22 ± 0.27 ± 0.29) × 10-4, assuming the central value of the measured Ξcc ++ lifetime, where the first uncertainty is statistical and the second systematic

First observation of the decay Λ 0 b → η c ( 1 S ) p K −

The decay Λ0b→ηc(1S)pK− is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of 5.5  fb−1, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the Λ0b→J/ψpK− decay as a normalization mode, to be B(Λ0b→ηc(1S)pK−)=(1.06±0.16±0.06+0.22−0.19)×10−4, where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the ηc(1S)p mass spectrum is performed to search for the Pc(4312)+ pentaquark state. No evidence is observed and an upper limit of B(Λ0b→Pc(4312)+K−)×B(Pc(4312)+→ηc(1S)p)B(Λ0b→ηc(1S)pK−)<0.24 is obtained at the 95% confidence level

Observation of New Resonances in the Λ 0 b π + π − System

We report the observation of a new structure in the Λ0bπ+π− spectrum using the full LHCb data set of pp collisions, corresponding to an integrated luminosity of 9  fb−1, collected at √s=7, 8, and 13 TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to bemΛb(6146)0=6146.17±0.33±0.22±0.16  MeV,mΛb(6152)0=6152.51±0.26±0.22±0.16  MeV,ΓΛb(6146)0=2.9±1.3±0.3  MeV,ΓΛb(6152)0=2.1±0.8±0.3  MeV,with a mass splitting of Δm=6.34±0.32±0.02  MeV, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λ0b baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λb(1D)0 states

Updated measurement of decay-time-dependent CP asymmetries in D0 → K+K− and D0 → π + π − decays

A search for decay-time-dependent charge-parity (CP) asymmetry in D0→K+K− and D0→π+π− decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4  fb−1. The D0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D0 and ¯D0 mesons are determined to be AΓ(K+K−)=(−4.3±3.6±0.5)×10−4 and AΓ(π+π−)=(2.2±7.0±0.8)×10−4, where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield AΓ(K+K−)=(−4.4±2.3±0.6)×10−4 and AΓ(π+π−)=(2.5±4.3±0.7)×10−4

Measurement of the B − c meson production fraction and asymmetry in 7 and 13 TeV p p collisions

The production fraction of the B−c meson with respect to the sum of B− and ¯B0 mesons is measured in both 7 and 13 TeV center-of-mass (c.m.) energy pp collisions produced by the Large Hadron Collider (LHC), using the LHCb detector. The rate, approximately 3.7 per mille, does not change with energy, but shows a transverse momentum dependence. The B−c−B+c production asymmetry is also measured and is consistent with zero within the determined statistical and systematic uncertainties of a few percent

First observation of the decay B 0 → D 0 ¯ D 0 K + π −

The first observation of the decay B0→D0D¯0K+π- is reported using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb-1 collected by the LHCb experiment in 2011, 2012 and 2016. The measurement is performed in the full kinematically allowed range of the decay outside of the D∗- region. The ratio of the branching fraction relative to that of the control channel B0→D∗-D0K+ is measured to be R=(14.2±1.1±1.0)%, where the first uncertainty is statistical and the second is systematic. The absolute branching fraction of B0→D0D¯0K+π- decays is thus determined to be B(B0→D0D¯0K+π-)=(3.50±0.27±0.26±0.30)×10-4, where the third uncertainty is due to the branching fraction of the control channel. This decay mode is expected to provide insights to spectroscopy and the charm-loop contributions in rare semileptonic decays

Measurement of the electron reconstruction efficiency at LHCb

The single electron track-reconstruction efficiency is calibrated using a sample corresponding to 1.3 fb−1 of pp collision data recorded with the LHCb detector in 2017. This measurement exploits B+→ J/ψ(e+e−)K+ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the B meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching fractions involving single electrons with a systematic uncertainty below 1%

Observation of the Λ0b→χc1 (3872) pK− decay

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9 fb−1 of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay Λ0b→χc1Λb0→χc1(3872)pK− with χc1(3872) → J/ψ π+π− is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that (58 ± 15)% of the decays proceed via the two-body intermediate state χc1(3872)Λ(1520). The branching fraction with respect to that of the Λ0bΛb0 → ψ(2S)pK− decay mode, where the ψ(2S) meson is reconstructed in the J/ψ π+π− final state, is measured to be:β(Λ0b→χc1(3872)pK−)β(Λ0b→ψ(2S)pK−)×β(χc1(3872)→J/ψπ+π−)β(ψ(2S)→J/ψπ+π−)=(5.4±1.1±0.2)×10−2,β(Λb0→χc1(3872)pK−)β(Λb0→ψ(2S)pK−)×β(χc1(3872)→J/ψπ+π−)β(ψ(2S)→J/ψπ+π−)=(5.4±1.1±0.2)×10−2,where the first uncertainty is statistical and the second is systematic

Determination of quantum numbers for several excited charmed mesons observed in B − → D * + π − π − decays

A four-body amplitude analysis of the B−→D*+π−π− decay is performed, where fractions and relative phases of the various resonances contributing to the decay are measured. Several quasi-model-independent analyses are performed aimed at searching for the presence of new states and establishing the quantum numbers of previously observed charmed meson resonances. In particular the resonance parameters and quantum numbers are determined for the D1(2420), D1(2430), D0(2550), D∗1(2600), D2(2740) and D∗3(2750) states. The mixing between the D1(2420) and D1(2430) resonances is studied and the mixing parameters are measured. The dataset corresponds to an integrated luminosity of 4.7  fb−1, collected in proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector

Study of the lineshape of the χ c 1 ( 3872 ) state

A study of the lineshape of the χc1(3872) state is made using a data sample corresponding to an integrated luminosity of 3 fb-1 collected in pp collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate χc1(3872) and ψ(2S) mesons from b-hadron decays are selected in the J/ψπ+π- decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the χc1(3872) and ψ(2S) states, Δm, and the width of the χc1(3872) state, ΓBW, are determined to be Δm=185.598±0.067±0.068 MeV,ΓBW=1.39±0.24±0.10 MeV, where the first uncertainty is statistical and the second systematic. Using a Flatté-inspired model, the mode and full width at half maximum of the lineshape are determined to be mode=3871.69-0.04-0.13+0.00+0.05 MeV,FWHM=0.22-0.06-0.13+0.07+0.11 MeV. An investigation of the analytic structure of the Flatté amplitude reveals a pole structure, which is compatible with a quasibound D0D¯∗0 state but a quasivirtual state is still allowed at the level of 2 standard deviations