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.

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 $$ {R}_{K^{*0}}=\left\{\begin{array}{l}{0.66_{-}^{+}}_{0.07}^{0.11}\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right)\kern1em \mathrm{f}\mathrm{o}\mathrm{r}\kern1em 0.045<{q}^2<1.1\kern0.5em {\mathrm{GeV}}^2/{c}^4,\hfill \\ {}{0.69_{-}^{+}}_{0.07}^{0.11}\left(\mathrm{stat}\right)\pm 0.05\left(\mathrm{syst}\right)\kern1em \mathrm{f}\mathrm{o}\mathrm{r}\kern1em 1.1<{q}^2<6.0\kern0.5em {\mathrm{GeV}}^2/{c}^4.\hfill \end{array}\right. $$ 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 \( {R}_{K^{*0}} \) 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. Open image in new window

A narrow pentaquark state, $P_c(4312{)}^{+}$, decaying to $J/\psi p$, is discovered with a statistical significance of $7.3\sigma$ in a data sample of ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ decays, which is an order of magnitude larger than that previously analyzed by the LHCb Collaboration. The $P_c(4450{)}^{+}$ pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, $P_c(4440{)}^{+}$ and $P_c(4457{)}^{+}$, where the statistical significance of this two-peak interpretation is $5.4\sigma$. The proximity of the ${\mathrm{\Sigma }}_c^{+}{\overline{D}}^0$ and ${\mathrm{\Sigma }}_c^{+}{\overline{D}}^{*0}$ thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.