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The Hadron Calorimeter of LHCb (HCAL) is one of the four sub-detectors of the experiment calorimetric system, which also includes: Scintillator Pad Detector (SPD), Pre-Shower Detector (PS), and electromagnetic (ECAL) calorimeter. The main purpose of HCAL is to provide data for Level-0 trigger for selection events with high transverse energy hadrons. It is important to have a precise and reliable calibration system which produces result immediately after the calibration run. LHCb HCAL is equipped with a calibration system based on 137Cs radioactive source embedded into the calorimeter structure. It allows to obtain absolute calibration with good precision and monitor technical condition of the detector.

The paper presents results of the search for new meson decays into charmonium and light hadrons in the final state. Relative branching fractions of the studied processes are measured. The contributions of intermediate resonant structures in light hadron systems are considered. Experimental data and theoretical predictions are compared for various mass combinations. The analysis is based on the data collected by the LHCb experiment in proton—proton collisions at the center-of-mass energies of 7, 8, and 13 TeV in the period from 2011 to 2018.

In the Standard Model of particle physics, the strength of the couplings of the b quark to the u and c quarks, | V ub | and | V cb |, are governed by the coupling of the quarks to the Higgs boson. Using data from the LHCb experiment at the Large Hadron Collider, the probability for the Λ b 0 baryon to decay into the p final state relative to the final state is measured. Combined with theoretical calculations of the strong interaction and a previously measured value of | V cb |, the first | V ub | measurement to use a baryonic decay is performed. This measurement is consistent with previous determinations of | V ub | using B meson decays to specific final states and confirms the existing incompatibility with those using an inclusive sample of final states. The accurate determination of quark mixing parameters is essential for the understanding of the Standard Model. The LHCb collaboration now reports the coupling strength of the b quark to the u quark through the measurement of a baryonic decay mode.

A bstract The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of s = 13 TeV, corresponding to an integrated luminosity of 279 ±11 pb −1 . The measurement is performed for J/ψ mesons with a transverse momentum of less than 10 GeV/ c in the rapidity range 2 . 0 < y < 4 . 5. The production cross-section is measured to be 15 . 2 ± 1 . 0 ± 0 . 9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions.

The production of the η c ( 1 S ) state in proton-proton collisions is probed via its decay to the p p ¯ final state with the LHCb detector, in the rapidity range 2.0 < y < 4.5 and in the meson transverse-momentum range p T > 6.5 GeV / c . The cross-section for prompt production of η c ( 1 S ) mesons relative to the prompt J / ψ cross-section is measured, for the first time, to be σ η c ( 1 S ) / σ J / ψ = 1.74 ± 0.29 ± 0.28 ± 0 . 18 B at a centre-of-mass energy s = 7 TeV using data corresponding to an integrated luminosity of 0.7 fb - 1 , and σ η c ( 1 S ) / σ J / ψ = 1.60 ± 0.29 ± 0.25 ± 0 . 17 B at s = 8 TeV using 2.0 fb - 1 . The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the η c ( 1 S ) and J / ψ decays to the p p ¯ final state. In addition, the inclusive branching fraction of b -hadron decays into η c ( 1 S ) mesons is measured, for the first time, to be B ( b → η c X ) = ( 4.88 ± 0.64 ± 0.29 ± 0 . 67 B ) × 10 - 3 , where the third uncertainty includes also the uncertainty on the J / ψ inclusive branching fraction from b -hadron decays. The difference between the J / ψ and η c ( 1 S ) meson masses is determined to be 114.7 ± 1.5 ± 0.1 MeV / c 2 .

A bstract The differential branching fraction of the rare decay Λ b 0  →  Λμ + μ − is measured as a function of q 2 , the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3 . 0 fb −1 , collected by the LHCb experiment. Evidence of signal is observed in the q 2 region below the square of the J/ψ mass. Integrating over 15 < q 2 < 20 GeV 2 /c 4 the differential branching fraction is measured as d ℬ Λ b 0 → Λ μ + μ − / d q 2 = 1.18 − 0.08 + 0.09 ± 0.03 ± 0.27 × 10 − 7 GeV 2 / c 4 − 1 , where the uncertainties are statistical, systematic and due to the normalisation mode, Λ b 0  →  J / ψΛ , respectively. In the q 2 intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon ( A FB ℓ ) and hadron ( A FB h ) systems are measured for the first time. In the range 15 < q 2 < 20 GeV 2 /c 4 they are found to be A F B ℓ = − 0.05 ± 0.09 stat ± 0.03 syst and A F B h = − 0.29 ± 0.07 stat ± 0.03 syst .

A bstract A study is presented of central exclusive production of Υ( nS ) states, where the Υ( nS ) resonances decay to the μ + μ − final state, using pp collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range 2 < y (Υ) < 4 . 5 where the muons are reconstructed in the pseudorapidity range 2 < η ( μ ± ) < 4 . 5. The data sample corresponds to an integrated luminosity of 2.9 fb −1 and was collected at centre-of-mass energies of 7 TeV and 8 TeV. The measured Υ(1 S ) and Υ(2 S ) production cross-sections are σ pp → p Υ 1 S p = 9.0 ± 2.1 ± 1.7 p b and σ pp → p Υ 2 S p = 1.3 ± 0.8 ± 0.3 p b , where the first uncertainties are statistical and the second are systematic. The Υ(1 S ) crosssection is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95% confidence level for the exclusive Υ(3 S ) production cross-section, including possible contamination from χ b (3 P ) → Υ(3 S )γ decays.

A bstract The production of J/ψ mesons in proton-proton collisions at a centre-of-mass energy of s = 13 TeV is studied with the LHCb detector. Cross-section measurements are performed as a function of the transverse momentum p T and the rapidity y of the J/ψ meson in the region p T < 14 GeV/ c and 2 . 0 < y < 4 . 5, for both prompt J/ψ mesons and J/ψ mesons from b -hadron decays. The production cross-sections integrated over the kinematic coverage are 15 . 30 ± 0 . 03 ± 0 . 86 μb for prompt J/ψ and 2 . 34 ± 0 . 01 ± 0 . 13 μb for J/ψ from b -hadron decays, assuming zero polarization of the J/ ψ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for J/ψ mesons from b -hadron decays is used to extrapolate to a total b b ¯ cross-section. The ratios of the cross-sections with respect to s = 8 TeV are also determined.