Observations of exotic structures in the $J/\psi p$ channel, which we refer to as charmonium-pentaquark states, in ${\mathrm{\Lambda }}_b^0\to J/\psi K^{-}p$ decays are presented. The data sample corresponds to an integrated luminosity of $3{\mathrm{fb}}^{-1}$ acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the $J/\psi p$ mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of $4380\pm 8\pm 29\mathrm{MeV}$ and a width of $205\pm 18\pm 86\mathrm{MeV}$, while the second is narrower, with a mass of $4449.8\pm 1.7\pm 2.5\mathrm{MeV}$ and a width of $39\pm 5\pm 19\mathrm{MeV}$. The preferred $J^P$ assignments are of opposite parity, with one state having spin $3/2$ and the other $5/2$.

A measurement of the ratio of the branching fractions of the $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$ and $B^{+}\to K^{+}{e}^{+}{e}^{-}$ decays is presented using proton-proton collision data, corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$, recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range $1<q^2<6{\mathrm{GeV}}^2/c^4$ is measured to be $0.745_{-0.074}^{+0.090}(\text{stat})\pm 0.036(\text{syst})$. This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.

An angular analysis of the B ⁰ → K ^*0(→ K ⁺ π ⁻)μ ⁺ μ ⁻ decay is presented. The dataset corresponds to an integrated luminosity of 3.0 fb⁻¹ of pp collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine CP-averaged observables and CP asymmetries, taking account of possible contamination from decays with the K ⁺ π ⁻ system in an S-wave configuration. The angular observables and their correlations are reported in bins of q ², the invariant mass squared of the dimuon system. The observables are determined both from an unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for q ²-dependent decay amplitudes in the region 1.1 < q ² < 6.0 GeV²/c ⁴, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of CP-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions. Open image in new window

We present a measurement of form-factor-independent angular observables in the decay $B^0\to K^{*}(892{)}^0{\mu }^{+}{\mu }^{-}$. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$, collected by the LHCb experiment in $pp$ collisions at a center-of-mass energy of 7 TeV. Four observables are measured in six bins of the dimuon invariant mass squared $q^2$ in the range $0.1<q^2<19.0{\mathrm{GeV}}^2/c^4$. Agreement with recent theoretical predictions of the standard model is found for 23 of the 24 measurements. A local discrepancy, corresponding to 3.7 Gaussian standard deviations is observed in one $q^2$ bin for one of the observables. Considering the 24 measurements as independent, the probability to observe such a discrepancy, or larger, in one is 0.5%.

An angular analysis and a measurement of the differential branching fraction of the decay B _s ⁰ → ϕμ ⁺ μ ⁻ are presented, using data corresponding to an integrated luminosity of 3.0 fb⁻¹ of pp collisions recorded by the LHCb experiment at \( \sqrt{s}=7 \) and 8 TeV. Measurements are reported as a function of q ², the square of the dimuon invariant mass and results of the angular analysis are found to be consistent with the Standard Model. In the range 1 < q ² < 6 GeV² /c ⁴, where precise theoretical calculations are available, the differential branching fraction is found to be more than 3σ below the Standard Model predictions. Open image in new window

The quantum numbers of the $X(3872)$ meson are determined to be $J^{PC}=1^{++}$ based on angular correlations in $B^{+}\to X(3872)K^{+}$ decays, where $X(3872)\to {\pi }^{+}{\pi }^{-}J/\psi$ and $J/\psi \to {\mu }^{+}{\mu }^{-}$. The data correspond to $1.0{\mathrm{fb}}^{-1}$ of $pp$ collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements $J^{PC}=2^{-+}$ is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the $X(3872)$ state.