Amplitude models are constructed to describe the resonance structure of \({D^{0}\to K^{-}\pi^{+}\pi^{+}\pi^{-}}\) and \({D^{0} \to K^{+}\pi^{-}\pi^{-}\pi^{+}}\) decays using \(pp\) collision data ...collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of \(3.0\mathrm{fb}^{-1}\). The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes \(D^{0} \to a_1(1260)^{+} K^{-}\) and \(D^{0} \to K_1(1270/1400)^{+} \pi^{-}\) being prominent in \({D^{0}\to K^{-}\pi^{+}\pi^{+}\pi^{-}}\) and \(D^{0}\to K^{+}\pi^{-}\pi^{-}\pi^{+}\), respectively. Precise measurements of the lineshape parameters and couplings of the \(a_1(1260)^{+}\), \(K_1(1270)^{-}\) and \(K(1460)^{-}\) resonances are made, and a quasi model-independent study of the \(K(1460)^{-}\) resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be \(R_{K3\pi} = 0.459\pm 0.010\,(\mathrm{stat}) \pm 0.012\,(\mathrm{syst}) \pm 0.020\,(\mathrm{model})\), which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle \(\gamma\) and studies of charm mixing and \(C\!P\) violation.
A search for the rare decay \(\Sigma^+ \to p \mu^+ \mu^-\) is performed using \(pp\) collision data recorded by the LHCb experiment at centre-of-mass energies \(\sqrt{s} = 7\) and \(8\) TeV, ...corresponding to an integrated luminosity of \(3 fb^{-1}\). An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured \(\Sigma^+ \to p \mu^+ \mu^-\) branching fraction is \((2.2\,^{+\,1.8}_{-\,1.3})\times 10^{-8}\), where statistical and systematic uncertainties are included, which is consistent with the Standard Model prediction.
The \(\Lambda_b^0\to\Lambda\phi\) decay is observed using data corresponding to an integrated luminosity of 3.0fb\(^{-1}\) recorded by the LHCb experiment. The decay proceeds at leading order via a ...\(b\to s\bar{s}s\) loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of \(5.9\) standard deviations. The value of the branching fraction is measured to be \((5.18\pm1.04\pm0.35\,^{+0.67}_{-0.62})\times10^{-6}\), where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.
A search for the flavor-changing neutral-current decay \(\Lambda_{c}^{+} \to p\mu^+\mu^-\) is reported using a data set corresponding to an integrated luminosity of \(3.0\rm fb^{-1}\) collected by ...the LHCb collaboration. No significant signal is observed outside of the dimuon mass regions around the \(\phi\) and \(\omega\) resonances and an upper limit is placed on the branching fraction of \(\mathcal{B} (\Lambda_{c}^{+} \to p\mu^+\mu^-) < 7.7~(9.6)\times 10^{-8}~{\rm at}~90\%~(95\%)\) confidence level. A significant signal is observed in the \(\omega\) dimuon mass region for the first time.
The ratio of branching fractions \({\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau})/{\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})\) 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\(~\)fb\(^{-1}\). For the first time \({\cal{R}}(D^{*-})\) 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 \({\cal{B}}(B^0\to D^{*-}\tau^+\nu_{\tau})/{\cal{B}}(B^0\to D^{*-}\pi^+\pi^-\pi^+) = 1.97 \pm 0.13 \pm 0.18\), where the first uncertainty is statistical and the second systematic. The value of \({\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau}) = (1.42 \pm 0.094 \pm 0.129 \pm 0.054)\% \) 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 \({\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013\) 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.
The ratio of branching fractions \({\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau})/{\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})\) 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\(~\)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 \({\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau})/{\cal{B}}(B^0 \to D^{*-}\pi^+\pi^-\pi^+)\) 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 \({\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau}) = (1.42 \pm 0.094 \pm 0.129 \pm 0.054) \%\), where the third uncertainty is due to the limited knowledge of \({\cal{B}}(B^0\to D^{*-}\pi^+\pi^-\pi^+)\). A test of lepton flavor universality is performed using the well-measured branching fraction \({\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})\) to compute \({\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013\), where the third uncertainty originates from the uncertainties on \({\cal{B}}(B^0 \to D^{*-}\pi^+\pi^-\pi^+)\) and \({\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})\). This measurement is in agreement with the Standard Model prediction and with previous measurements.
The ratios of the branching fractions of the decays \(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}\), \(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}\), and \(\Lambda_{c}^{+} \rightarrow p \pi^{-} ...K^{+}\) with respect to the Cabibbo-favoured \(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+}\) decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb\(^{-1}\): \begin{align*} \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} & = (7.44 \pm 0.08 \pm 0.18)\,\%, \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &= (1.70 \pm 0.03 \pm 0.03)\,\%, \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} & = (0.165 \pm 0.015 \pm 0.005 )\,\%, \end{align*} where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for \(\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})\), the corresponding branching fractions are \begin{align*} \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}) &= (4.72 \pm 0.05 \pm 0.11 \pm 0.25) \times 10^{-3}, \mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}) &= (1.08 \pm 0.02 \pm 0.02 \pm 0.06) \times 10^{-3}, \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}) &= (1.04 \pm 0.09 \pm 0.03 \pm 0.05) \times 10^{-4}, \end{align*} where the final uncertainty is due to \(\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})\).
The difference between the \(CP\) asymmetries in the decays \(\varLambda_{c}^{+} \to pK^{-}K^{+}\) and \(\varLambda_{c}^{+} \to p\pi^{-}\pi^{+}\) is presented. Proton-proton collision data taken at ...centre-of-mass energies of \(7\) and \(8\,\mathrm{TeV}\) collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of \(3\,\mathrm{fb}^{-1}\). The \(\varLambda_{c}^{+}\) candidates are reconstructed as part of the \(\varLambda_{b}^{0} \to \varLambda_{c}^{+}\mu^{-}X\) 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 \(\varLambda_{c}^{+} \to p\pi^{-}\pi^{+}\) sample. This alters the definition of the integrated \(CP\) asymmetry to \(A_{CP}^{\text{wgt}}(p\pi^{-}\pi^{+})\). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional \(\varLambda_{c}^{+}\) decay phase space. The difference in \(CP\) asymmetries is found to be \begin{align*} \Delta{A^{\text{wgt}}_{CP}} &= A_{CP}(pK^{-}K^{+}) - A_{CP}^{\text{wgt}}(p\pi^{-}\pi^{+})\\ &= (0.30 \pm 0.91 \pm 0.61)\,\%, \end{align*} where the first uncertainty is statistical and the second is systematic.
Measurements of the cross-section for producing \bquark quarks in the reaction \(pp\to b\bar{b} X\) are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity \(\eta\) in ...the range \(2<\eta<5\) covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of \(b\)-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross-sections in the covered \(\eta\) range are \(72.0\pm 0.3\pm6.8~\mu\)b and \(144\pm 1\pm 21~\mu\)b for 7 and 13 TeV. The ratio is \(2.00\pm0.02\pm0.26\), where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross-sections is larger at lower \(\eta\) than the model prediction.
A search for \(C\!P\) violation in the decay \(\Lambda^0_b \to p K^- \mu^+ \mu^-\) is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is ...potentially sensitive to new sources of \(C\!P\) violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of \(3\) \(\mathrm{fb}^{-1}\). The \(\Lambda^0_b \to p K^- \mu^+ \mu^-\) decay is observed for the first time, and two observables that are sensitive to different manifestations of \(C\!P\) violation are measured, \(\Delta\mathcal{A}_{C\!P} \equiv \mathcal{A}_{C\!P}(\Lambda^0_b \to p K^- \mu^+ \mu^-)-\mathcal{A}_{C\!P}(\Lambda^0_b\to pK^- J/\psi)\) and \(a_{C\!P}^{\widehat{T}-odd}\), where the latter is based on asymmetries in the angle between the \(\mu^+\mu^-\) and \(p K^-\) decay planes. These are measured to be \(\Delta\mathcal{A}_{C\!P} = (-3.5 \pm 5.0(stat) \pm 0.2(syst))\times 10^{-2}\), \(a_{C\!P}^{\widehat{T}-odd} = (1.2 \pm 5.0(stat) \pm 0.7(syst))\times 10^{-2}\), and no evidence for \(C\!P\) violation is found.
