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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 LHCb detector has undergone a major upgrade for LHC Run 3. This Upgrade I detector facilitates operation at higher luminosity and utilises full-detector information at the LHC collision rate, critically including the use of vertex information. A new vertex locator system, the VELO Upgrade, has been constructed. The core element of the new VELO are the double-sided pixelated hybrid silicon detector modules which operate in vacuum close to the LHC beam in a high radiation environment. The construction and quality assurance tests of these modules are described in this paper. The modules incorporate 200 \\mum thick, n-on-p silicon sensors bump-bonded to 130 \\nm technology ASICs. These are attached with high precision to a silicon microchannel substrate that uses evaporative CO\\(_2\\) cooling. The ASICs are controlled and read out with flexible printed circuits that are glued to the substrate and wire-bonded to the chips. The mechanical support of the module is given by a carbon fibre plate, two carbon fibre rods and an aluminium plate. The sensor attachment was achieved with an average precision of 21 \\(\\mathrm{\\mu m}\\), more than 99.5\\% of all pixels are fully functional, and a thermal figure of merit of 3 \\mathrm{Kcm^{2}W^{-1}}$ was achieved. The production of the modules was successfully completed in 2021, with the final assembly and installation completed in time for data taking in 2022.

Precision sound velocity measurements can simultaneously determine binary gas composition and flow. We have developed an analyzer with custom electronics, currently in use in the ATLAS inner detector, with numerous potential applications. The instrument has demonstrated ~0.3% mixture precision for C3F8/C2F6 mixtures and < 10-4 resolution for N2/C3F8 mixtures. Moderate and high flow versions of the instrument have demonstrated flow resolutions of +/- 2% F.S. for flows up to 250 l.min-1, and +/- 1.9% F.S. for linear flow velocities up to 15 ms-1; the latter flow approaching that expected in the vapour return of the thermosiphon fluorocarbon coolant recirculator being built for the ATLAS silicon tracker.

An upgrade to the ATLAS silicon tracker cooling control system may require a change from C3F8 (octafluoro-propane) evaporative coolant to a blend containing 10-25% of C2F6 (hexafluoro-ethane). Such a change will reduce the evaporation temperature to assure thermal stability following radiation damage accumulated at full LHC luminosity. Central to this upgrade is a new ultrasonic instrument in which sound transit times are continuously measured in opposite directions in flowing gas at known temperature and pressure to deduce the C3F8/C2F6 flow rate and mixture composition. The instrument and its Supervisory, Control and Data Acquisition (SCADA) software are described in this paper. Several geometries for the instrument are in use or under evaluation. An instrument with a pinched axial geometry intended for analysis and measurement of moderate flow rates has demonstrated a mixture resolution of 3.10-3 for C3F8/C2F6 molar mixtures with 20%C2F6, and a flow resolution of 2% of full scale for mass flows up to 30gs-1. In mixtures of widely-differing molecular weight (mw), higher mixture precision is possible: a sensitivity of <5.10-5 to leaks of C3F8 into part of the ATLAS tracker nitrogen envelope (mw difference 160) has been seen. An instrument with an angled sound path geometry has been developed for use at high fluorocarbon mass flow rates of around 1.2 kgs-1 - corresponding to full flow in a new 60kW thermosiphon recirculator under construction for the ATLAS silicon tracker. Extensive computational fluid dynamics studies were performed to determine the preferred geometry (ultrasonic transducer spacing and placement, together with the sound crossing angle with respect to the vapour flow direction). A prototype with 45deg crossing angle has demonstrated a flow resolution of 1.9% of full scale for linear flow velocities up to 15 ms-1. The instrument has many potential applications.