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A bstract The isospin asymmetries of B → Kμ + μ − and B → K * μ + μ − decays and the partial branching fractions of the B 0 → K 0 μ + μ − , B + → K + μ + μ − and B + → K *+ μ + μ − decays are measured as functions of the dimuon mass squared, q 2 . The data used correspond to an integrated luminosity of 3 fb −1 from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.

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.

Mesons comprising a beauty quark and strange quark can oscillate between particle ( B s 0 ) and antiparticle ( B ¯ s 0 ) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, Δ m s . Here we present a measurement of Δ m s using B s 0 → D s − π + decays produced in proton–proton collisions collected with the LHCb detector at the Large Hadron Collider. The oscillation frequency is found to be Δ m s  = 17.7683 ± 0.0051 ± 0.0032 ps −1 , where the first uncertainty is statistical and the second is systematic. This measurement improves on the current Δ m s precision by a factor of two. We combine this result with previous LHCb measurements to determine Δ m s  = 17.7656 ± 0.0057 ps −1 , which is the legacy measurement of the original LHCb detector. The LHCb collaboration reports an improved measurement of the oscillation frequency of mesons consisting of a bottom quark and strange quark, which is then combined with previous results.

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 .

Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of s√=8TeV. The analysis is based on an integrated luminosity of 2.0fb−1 recorded with the LHCb detector. The bosons are identified in the W→μν and Z→μ+μ− decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0<η<4.5, with transverse momenta pT>20GeV/c and, in the case of the Z boson, a dimuon mass within 60

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