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A bstract The ϒ (1 S ) μ + μ − invariant-mass distribution is investigated for a possible exotic meson state composed of two b quarks and two b ¯ quarks, X b b ¯ b b ¯ . The analysis is based on a data sample of pp collisions recorded with the LHCb detector at centre-of-mass energies s = 7 , 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb −1 . No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the X b b ¯ b b ¯ state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range [2 . 0 , 5 . 0], and the X b b ¯ b b ¯ state has rapidity in the range [2 . 0 , 4 . 5] and transverse momentum less than 15 GeV/ c .

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb −1 , collected with the LHCb detector between 2011 and 2018, a new narrow charmonium state, the X(3842) resonance, is observed in the decay modes$$ \\mathrm{X}(3842)\\to {D}^0{\\overline{D}}^0 $$X 3842 → D 0 D ¯ 0 and X(3842) → D + D − . The mass and the natural width of this state are measured to be$$ \\begin{array}{l}{m}_{X(3842)}=3842.71\\pm 0.16\\pm 0.12\\ MeV/{c}^2,\\hfill \\\ {}{\\varGamma}_{X(3842)}=2.79\\pm 0.51\\pm 0.35\\ MeV,\\hfill \\end{array} $$m X 3842 = 3842.71 ± 0.16 ± 0.12 M e V / c 2 , Γ X 3842 = 2.79 ± 0.51 ± 0.35 M e V , where the first uncertainty is statistical and the second is systematic. The observed mass and narrow natural width suggest the interpretation of the new state as the unobserved (spin-3 ψ 3 1 3 D 3 ) charmonium state. In addition, prompt hadroproduction of the ψ (3770) and χ 2 (3930) states is observed for the first time, and the parameters of these states are measured to be$$ \\begin{array}{l}{m}_{\\psi (3770)}=3778.1\\pm 0.7\\pm 0.6\\ MeV/{c}^2,\\hfill \\\ {}{m}_{\\chi_2(3930)}=3921.9\\pm 0.6\\pm 0.2\\ MeV/{c}^2,\\hfill \\\ {}{\\varGamma}_{\\chi_2(3930)}=36.6 \\pm 1.9 \\pm 0.9\\ MeV,\\hfill \\end{array} $$m ψ 3770 = 3778.1 ± 0.7 ± 0.6 M e V / c 2 , m χ 2 3930 = 3921.9 ± 0.6 ± 0.2 M e V / c 2 , Γ χ 2 3930 = 36.6 ± 1.9 ± 0.9 M e V , where the first uncertainty is statistical and the second is systematic.

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2 fb - 1 , respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80  GeV / c 2 and lifetimes from 5 to 100 ps are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23–198 GeV/ c 2 range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.

A search is presented for long-lived particles with a mass between 25 and 50 GeV / c 2 and a lifetime between 2 and 500 ps, using proton–proton collision data corresponding to an integrated luminosity of 2.0 fb - 1 , collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125 GeV / c 2 Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.

During 2011 the LHCb experiment at CERN collected 1.0 fb −1 of pp collisions. Due to the large heavy quark production cross-sections, these data provide unprecedented samples of heavy flavoured hadrons. The first results from LHCb have made a significant impact on the flavour physics landscape and have definitively proved the concept of a dedicated experiment in the forward region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

A bstract A search is performed for a spin-0 boson, ϕ , produced in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, using prompt ϕ → μ + μ − decays and a data sample corresponding to an integrated luminosity of approximately 3.0 fb −1 collected with the LHCb detector. No evidence is found for a signal in the mass range from 5.5 to 15 GeV. Upper limits are placed on the product of the production cross-section and the branching fraction into the dimuon final state. The limits are comparable to the best existing over most of the mass region considered and are the first to be set near the ϒ resonances.

A bstract A search for the lepton-flavour violating decays B s 0  →  e ± μ ∓ and B 0  →  e ± μ ∓ is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb −1 , collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the B s 0  →  e ± μ ∓ decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate. The results are @ @ ℬ B s 0 → e ± μ ∓ < 6.3 5.4 × 1 0 − 9 and @ @ ℬ B s 0 → e ± μ ∓ < 7.2 6.0 × 1 0 − 9 at 95% (90%) confidence level, respectively. The upper limit on the branching fraction of the B 0 → e ± μ ∓ decay is also evaluated, obtaining @ @ ℬ B 0 → e ± μ ∓ < 1.3 1.0 × 1 0 − 9 at 95% (90%) confidence level. These are the strongest limits on these decays to date.

A bstract The difference between the CP asymmetries in the decays Λ c +  →  pK − K + and Λ c +  →  pπ − π + is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fb −1 . The Λ c + candidates are reconstructed as part of the Λ b 0  →  Λ c + μ − X decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the Λ c +  →  pπ − π + sample. This alters the definition of the integrated CP asymmetry to A CP wgt ( pπ − π + ). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Λ c + decay phase space. The difference in CP asymmetries is found to be Δ A C P w g t = A C P p K − K + − A C P w g t p π − π + = 0.30 ± 0.91 ± 0.61 % , where the first uncertainty is statistical and the second is systematic.

A bstract The resonant structure of the doubly Cabibbo-suppressed decay D + → 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 ϕ (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.

A search is presented for long-lived particles with a mass between 25 and 50  GeV / c 2 and a lifetime between 1 and 200 ps in a sample of proton–proton collisions at a centre-of-mass energy of s = 7  TeV, corresponding to an integrated luminosity of 0.62  fb - 1 , collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.