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

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

A highly significant structure is observed in the ${\mathrm{\Lambda }}_c^{+}{K}^{-}{\pi }^{+}{\pi }^{+}$ mass spectrum, where the ${\mathrm{\Lambda }}_c^{+}$ baryon is reconstructed in the decay mode $p{K}^{-}{\pi }^{+}$. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon ${\mathrm{\Xi }}_{cc}^{++}$. The difference between the masses of the ${\mathrm{\Xi }}_{cc}^{++}$ and ${\mathrm{\Lambda }}_c^{+}$ states is measured to be $1334.94\pm 0.72(\text{stat.})\pm 0.27(\text{syst}\mathrm{.})\mathrm{MeV}/c^2$, and the ${\mathrm{\Xi }}_{cc}^{++}$ mass is then determined to be $3621.40\pm 0.72(\text{stat.})\pm 0.27(\text{syst}\mathrm{.})\pm 0.14({\mathrm{\Lambda }}_c^{+})\mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the ${\mathrm{\Lambda }}_c^{+}$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $1.7{\mathrm{fb}}^{-1}$, and confirmed in an additional sample of data collected at 8 TeV.

The ratio of branching fractions $\mathcal{R}(D^{*-})\equiv \mathcal{B}(B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau })/\mathcal{B}(B^0\to D^{*-}{\mu }^{+}{\nu }_{\mu })$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. The $\tau$ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of $b$ hadrons with high purity. Using the $B^0\to D^{*-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$ decay as the normalization channel, the ratio $\mathcal{B}(B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau })/\mathcal{B}(B^0\to D^{*-}{\pi }^{+}{\pi }^{-}{\pi }^{+})$ is measured to be $1.97\pm 0.13\pm 0.18$, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive $\mathcal{B}(B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau })=(1.42\pm 0.094\pm 0.129\pm 0.054)\%$, where the third uncertainty is due to the limited knowledge of $\mathcal{B}(B^0\to D^{*-}{\pi }^{+}{\pi }^{-}{\pi }^{+})$. A test of lepton flavor universality is performed using the well-measured branching fraction $\mathcal{B}(B^0\to D^{*-}{\mu }^{+}{\nu }_{\mu })$ to compute $\mathcal{R}(D^{*-})=0.291\pm 0.019\pm 0.026\pm 0.013$, where the third uncertainty originates from the uncertainties on $\mathcal{B}(B^0\to D^{*-}{\pi }^{+}{\pi }^{-}{\pi }^{+})$ and $\mathcal{B}(B^0\to D^{*-}{\mu }^{+}{\nu }_{\mu })$. This measurement is in agreement with the Standard Model prediction and with previous measurements.

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 ratio of branching fractions $\mathcal{R}(D^{*-})\equiv \mathcal{B}(B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau })/\mathcal{B}(B^0\to D^{*-}{\mu }^{+}{\nu }_{\mu })$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. For the first time, $\mathcal{R}(D^{*-})$ is determined using the $\tau$-lepton decays with three charged pions in the final state. The $B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau }$ yield is normalized to that of the $B^0\to D^{*-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$ mode, providing a measurement of $\mathcal{B}(B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau })/\mathcal{B}(B^0\to D^{*-}{\pi }^{+}{\pi }^{-}{\pi }^{+})=1.97\pm 0.13\pm 0.18$, where the first uncertainty is statistical and the second systematic. The value of $\mathcal{B}(B^0\to D^{*-}{\tau }^{+}{\nu }_{\tau })=(1.42\pm 0.094\pm 0.129\pm 0.054)\%$ is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the $B^0\to D^{*-}{\mu }^{+}{\nu }_{\mu }$ decay, a value of $\mathcal{R}(D^{*-})=0.291\pm 0.019\pm 0.026\pm 0.013$ is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and $B^0\to D^{*-}{\mu }^{+}{\nu }_{\mu }$ modes. This measurement is in agreement with the standard model prediction and with previous results.