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A measurement of the phase difference between the short- and long-distance contributions to the [Formula: see text] decay is performed by analysing the dimuon mass distribution. The analysis is based on collision data corresponding to an integrated luminosity of 3[Formula: see text] collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the [Formula: see text] decay is modelled as a sum of relativistic Breit-Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the [Formula: see text] and [Formula: see text] resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, [Formula: see text] and [Formula: see text], and the branching fraction of the short-distance component is measured.

A measurement of Z → τ ⁺ τ ⁻production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb ⁻¹ , from pp collisions at √s̅=8 TeV collected by the LHCb experiment. The τ ⁺ τ ⁻candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for Z bosons with invariant mass between 60 and 120 GeV/c ² , which decay to tau leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be σ_(pp)_(→ Z→ τ⁺)_(τ⁻)=95.8 ± 2.1 ± 4.6 ± 0.2 ± 1.1 pb, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for Z → τ ⁺ τ ⁻to Z → μ ⁺ μ ⁻(Z → e ⁺ e ⁻ ), determined to be 1.01 ± 0.05 (1.02 ± 0.06), is consistent with the lepton-universality hypothesis in Z decays.

A study ofB⁰_(s) → η_(c) φandB⁰_(s) → η_(c) π⁺π⁻decays is performed usingppcollision data corresponding to an integrated luminosity of 3.0 \\rm fb⁻¹ , collected with the LHCb detector in Run 1 of the LHC. The observation of the decayB⁰_(s) → η_(c) φis reported, where theη_(c)meson is reconstructed in thepp̄ ,K⁺K⁻π⁺π⁻ ,π⁺π⁻π⁺π⁻andK⁺K⁻K⁺K⁻decay modes and theφ(1020)in theK⁺ K⁻decay mode. The decayB⁰_(s) → J/ψ φis used as a normalisation channel. Evidence is also reported for the decayB⁰_(s) → η_(c) π⁺π⁻ , where theη_(c)meson is reconstructed in thepp̄decay mode, using the decayB⁰_(s) → J/ψ π⁺ π⁻as a normalisation channel. The measured branching fractions are eqnarray* B (B⁰_(s) _(c) ) &=& (5.01 0.53 0.27 0.63 ) 10⁻4 , B (B⁰_(s) _(c) ⁺ ⁻) &=& (1.76 0.59 0.12 0.29 ) 10⁻4 , eqnarray* where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.

A search for the rare two-body charmless baryonic decayB⁺ → p Λ̄is performed withppcollision data, corresponding to an integrated luminosity of3\\mbox{ fb}{⁻¹}{} , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess ofB⁺ → p Λ̄candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using theB⁺ → K⁰_(\\mathrm S) π⁺decay for normalisation, is eqnarray B(B⁺ p ) & = & ( 2.4 ⁺1.0₋0.8 0.3 ) 10⁻7 , eqnarray where the first uncertainty is statistical and the second systematic.

A test of lepton universality, performed by measuring the ratio of the branching fractions of the B $^{0}$→ K $^{*0}$μ $^{+}$μ $^{−}$and B $^{0}$→ K $^{*0}$e $^{+}$e $^{−}$decays,$ {R}_{K^{*0}} $, is presented. The K $^{*0}$meson is reconstructed in the final state K $^{+}$π $^{−}$ , which is required to have an invariant mass within 100 MeV/c $^{2}$of the known K $^{*}$ (892) $^{0}$mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb $^{−1}$ , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q $^{2}$ , to be$ {R}_{K^{*0}}=\\left\\{\\begin{array}{l}{0.66_{-}^{+}}_{0.07}^{0.11}\\left(\\mathrm{stat}\\right)\\pm 0.03\\left(\\mathrm{syst}\\right)\\kern1em \\mathrm{f}\\mathrm{o}\\mathrm{r}\\kern1em 0.045<{q}^2<1.1\\kern0.5em {\\mathrm{GeV}}^2/{c}^4,\\hfill \\\ {}{0.69_{-}^{+}}_{0.07}^{0.11}\\left(\\mathrm{stat}\\right)\\pm 0.05\\left(\\mathrm{syst}\\right)\\kern1em \\mathrm{f}\\mathrm{o}\\mathrm{r}\\kern1em 1.1<{q}^2<6.0\\kern0.5em {\\mathrm{GeV}}^2/{c}^4.\\hfill \\end{array}\\right. $

Bose-Einstein correlations of same-sign charged pions, produced in proton-proton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decrease.

Two new algorithms for use in the analysis of [Formula: see text] collision are developed to identify the flavour of [Formula: see text] mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using [Formula: see text] decays from [Formula: see text] collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV . The tagging power of the new pion algorithm is 60% greater than the previously available one; the algorithm using protons to identify the flavour of a [Formula: see text] meson is the first of its kind.

The decays [Formula: see text] and [Formula: see text] are observed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb[Formula: see text], collected by the LHCb experiment in proton-proton collisions at the centre-of-mass energies of 7 and 8[Formula: see text]. The branching fractions relative to that of [Formula: see text] are measured to be [Formula: see text]where the first uncertainties are statistical and the second are systematic.

The production ofWandZbosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98±0.02 fb ⁻¹ . TheWboson is identified using its decay to a muon and a neutrino, while theZboson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios ofW+ jet andZ +jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.

The resonant structure of the doubly Cabibbo-suppressed decay \\(D^+ \\to K^-K^+K^+\\) is studied for the first time. The measurement is based on a sample of pp-collision data, collected at a centre-of-mass energy of 8 TeV with the LHCb detector and corresponding to an integrated luminosity of 2 fb\\(^-1\\). The amplitude analysis of this decay is performed with the isobar model and a phenomenological model based on an effective chiral Lagrangian. In both models the S-wave component in the \\(K^-K^+\\) system is dominant, with a small contribution of the \\(\\phi(1020)\\) meson and a negligible contribution from tensor resonances. The \\(K^-K^+\\) scattering amplitudes for the considered combinations of spin (0,1) and isospin (0,1) of the two-body system are obtained from the Dalitz plot fit with the phenomenological decay amplitude.