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The TORCH time-of-flight detector is designed to provide a 15 ps timing resolution for charged particles, resulting in π /K particle identification up to 10 GeV/c momentum over a 10 m flight path. Cherenkov photons, produced in a quartz plate of 10 mm thickness, are focused onto an array of micro-channel plate photomultipliers (MCP-PMTs) which measure the photon arrival times and spatial positions. A half-scale (660 × 1250 × 10 mm 3 ) TORCH demonstrator module has been tested in an 8 GeV/c mixed proton-pion beam at CERN. Customised square MCP-PMTs of active area 53 × 53 mm 2 and granularity 64 × 64 pixels have been employed, which have been developed in collaboration with an industrial partner. The single-photon timing performance and photon yields have been measured as a function of beam position in the radiator, giving measurements which are consistent with expectations. The expected performance of TORCH for high luminosity running of the LHCb Upgrade II has been simulated.

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 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.

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.

Using decays to $\\phi $ -meson pairs, the inclusive production of charmonium states in ${b} $ -hadron decays is studied with pp collision data corresponding to an integrated luminosity of $3.0 {\\,\\mathrm{fb}}^{-1} $ , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting by ${\\mathcal {B}} _C \\equiv {\\mathcal {B}} ( {{b}} \\!\\rightarrow C X ) \\times {\\mathcal {B}} ( C\\!\\rightarrow \\phi \\phi )$ the inclusive branching fraction of a ${{b}} $ hadron to a charmonium state C that decays into a pair of $\\phi $ mesons, ratios $R^{C_1C_2}\\equiv {\\mathcal {B}} _{C_1} / {\\mathcal {B}} _{C_2}$ are determined as $R^{{\\upchi _{{{c}} 0}}}_{{\\eta _{{c}}} (1S)} = 0.147 \\pm 0.023 \\pm 0.011$ , $R^{{\\upchi _{{{c}} 1}}}_{{\\eta _{{c}}} (1S)} = 0.073 \\pm 0.016 \\pm 0.006$ , $R^{{\\upchi _{{{c}} 2}}}_{{\\eta _{{c}}} (1S)} = 0.081 \\pm 0.013 \\pm 0.005$ , $R^{{\\upchi _{{{c}} 1}}}_{{\\upchi _{{{c}} 0}}} = 0.50 \\pm 0.11 \\pm 0.01$ , $R^{{\\upchi _{{{c}} 2}}}_{{\\upchi _{{{c}} 0}}} = 0.56 \\pm 0.10 \\pm 0.01$ and $R^{{\\eta _{{c}}} (2S)}_{{\\eta _{{c}}} (1S)} = 0.040 \\pm 0.011 \\pm 0.004$ . Here and below the first uncertainties are statistical and the second systematic. Upper limits at 90% confidence level for the inclusive production of X(3872), X(3915) and ${\\upchi _{{{c}} 2}} (2P)$ states are obtained as $R^{X(3872){\\upchi _{{{c}} 1}}} < 0.34$ , $R^{X(3915){\\upchi _{{{c}} 0}}} < 0.12$ and $R^{{\\upchi _{{{c}} 2}} (2P)}_{{\\upchi _{{{c}} 2}}} < 0.16$ . Differential cross-sections as a function of transverse momentum are measured for the ${\\eta _{{c}}} (1S)$ and $\\chi _c$ states. The branching fraction of the decay ${{{B}} ^0_{{s}}} \\!\\rightarrow \\phi \\phi \\phi $ is measured for the first time, ${\\mathcal {B}} ( {{{B}} ^0_{{s}}} \\!\\rightarrow \\phi \\phi \\phi ) = (2.15 \\pm 0.54 \\pm 0.28 \\pm 0.21_{{\\mathcal {B}}}) \\times 10^{-6}$ . Here the third uncertainty is due to the branching fraction of the decay ${{{B}} ^0_{{s}}} \\!\\rightarrow \\phi \\phi $ , which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse $\\phi $ polarization is observed. The measurements allow the determination of the ratio of the branching fractions for the ${\\eta _{{c}}} (1S)$ decays to $\\phi \\phi $ and ${{p}} {\\overline{{{p}}} $ as ${\\mathcal {B}} ( {\\eta _{{c}}} (1S)\\!\\rightarrow \\phi \\phi )/{\\mathcal {B}} ( {\\eta _{{c}}} (1S)\\!\\rightarrow {{p}} {\\overline{{{p}}} ) = 1.79 \\pm 0.14\\pm 0.32$ .

The charmless three-body decays B(s)0 → KS0h+h′ − (where h(′) = π, K) are analysed using a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb−1. The branching fractions are measured relative to that of the B0 → KS0π+π− decay, and are determined to be:ℬB0→KS0K±π∓ℬB0→KS0K+π−=0.123±0.009stat±0.015syst,ℬB0→KS0K+K−ℬB0→KS0π+π−=0.549±0.018stat±0.033syst,ℬBs0→KS0π+π−ℬB0→KS0π+π−=0.191±0.027stat±0.031syst±0.011fs/fd,ℬBs0→KS0K±π∓ℬB0→KS0π+π−=1.70±0.07stat±0.11syst±0.10fs/fd,ℬBs0→KS0K+K−ℬB0→KS0π+π−∈0.008−0.051at90%confidencelevel,where fs/fd represents the ratio of hadronisation fractions of the Bs0 and B0 mesons.

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A test of lepton universality, performed by measuring the ratio of the branching fractions of the B 0 [rarr] K *0 [mu] + [mu] - and B 0 [rarr] K *0 e + e - decays, ..., is presented. The K *0 meson is reconstructed in the final state K + [pi] -, 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 ... The corresponding 95.4% confidence level intervals are [0.52, 0.89] and [0.53, 0.94]. The results, which represent the most precise measurements of ... to date, are compatible with the Standard Model expectations at the level of 2.1-2.3 and 2.4-2.5 standard deviations in the two q 2 regions, respectively. [Figure not available: see fulltext.]

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The decays of B s 0 and ... mesons into the J/ψK + K − final state are studied in the K + K − mass region above the ϕ(1020) meson in order to determine the resonant substructure and measure the CP-violating phase, ϕ s , the decay width, Γ s , and the width difference between light and heavy mass eigenstates, ΔΓ s . A decay-time dependent amplitude analysis is employed. The data sample corresponds to an integrated luminosity of 3 fb−1 produced in 7 and 8 TeV pp collisions at the LHC, collected by the LHCb experiment. The measurement determines ϕ s = 119 ± 107 ± 34 mrad. A combination with previous LHCb measurements using similar decays into the J/ψπ + π − and J/ψϕ(1020) final states gives ϕ s = 1 ± 37 mrad, consistent with the Standard Model prediction. [Figure not available: see fulltext.]

In this paper we describe the history of the LHCb experiment over the last three decades, and its remarkable successes and achievements. LHCb was conceived primarily as a b-physics experiment, dedicated to CP violation studies and measurements of very rare b decays, however the tremendous potential for c-physics was also clear. At first data taking, the versatility of the experiment as a general-purpose detector in the forward region also became evident, with measurements achievable such as electroweak physics, jets and new particle searches in open states. These were facilitated by the excellent capability of the detector to identify muons and to reconstruct decay vertices close to the primary pp interaction region. By the end of the LHC Run 2 in 2018, before the accelerator paused for its second long shut down, LHCb had measured the CKM quark mixing matrix elements and CP violation parameters to world-leading precision in the heavy-quark systems. The experiment had also measured many rare decays of b and c quark mesons and baryons to below their Standard Model expectations, some down to branching ratios of order 10-9. In addition, world knowledge of b and c spectroscopy had improved significantly through discoveries of many new resonances already anticipated in the quark model, and also adding new exotic four and five quark states.

The performance of the ring-imaging Cherenkov detectors at the LHCb experiment is determined during the LHC Run 2 period between 2015 and 2018. The stability of the Cherenkov angle resolution and number of detected photons with time and running conditions is measured. The particle identification performance is evaluated with data and found to satisfy the requirements of the physics programme.

The TORCH time-of-flight detector is designed to provide a 15 ps timing resolution for charged particles, resulting in \\(\\pi\\)/\\(K\\) particle identification up to 10 GeV/c momentum over a 10 m flight path. Cherenkov photons, produced in a quartz plate of 10 mm thickness, are focused onto an array of micro-channel plate photomultipliers (MCP-PMTs) which measure the photon arrival times and spatial positions. A half-scale (\\(660\\times1250\\times10\\) mm\\(^3\\)) TORCH demonstrator module has been tested in an 8 GeV/c mixed proton-pion beam at CERN. Customised square MCP-PMTs of active area \\(53\\times53\\) mm\\(^2\\) and granularity \\(64\\times64\\) pixels have been employed, which have been developed in collaboration with an industrial partner. The single-photon timing performance and photon yields have been measured as a function of beam position in the radiator, giving measurements which are consistent with expectations. The expected performance of TORCH for high luminosity running of the LHCb Upgrade II has been simulated.