The resonant substructure of \(B_s^0 \rightarrow \bar{D}^0 K^- \pi^+\) decays is studied using a data sample corresponding to an integrated luminosity of \(3.0\,{\rm fb}^{-1}\) of \(pp\) collision ...data recorded by the LHCb detector. An excess at \(m(\bar{D}^0 K^-) \approx 2.86 {\rm GeV}/c^2\) is found to be an admixture of spin-1 and spin-3 resonances. Therefore the \(D^*_{sJ}(2860)^-\) state previously observed in inclusive \(e^+e^- \rightarrow \bar{D}^0 K^- X\) and \(pp \rightarrow \bar{D}^0 K^- X\) processes consists of at least two particles. This is the first observation of a heavy flavoured spin-3 resonance, and the first time that any spin-3 particle has been seen to be produced in \(B\) decays. The masses and widths of the new states and of the \(D^*_{s2}(2573)^-\) meson are measured, giving the most precise determinations to date.
The kinematic dependences of the relative production rates, \(f_{\Lambda_b^0}/f_d\), of \(\Lambda_b^0\) baryons and \(\bar{B}^0\) mesons are measured using \(\Lambda_b^0 \rightarrow \Lambda_c^+ ...\pi^-\) and \(\bar{B}^0 \rightarrow D^+ \pi^-\) decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb\(^{-1}\) at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, \(p_T\), and pseudorapidity, \(\eta\), of the beauty hadron, in the studied kinematic region \(1.5 < p_T < 40\) GeV/\(c\) and \(2 < \eta < 5\). Using a previous LHCb measurement of \(f_{\Lambda_b^0}/f_d\) in semileptonic decays, the branching fraction \(\mathcal{B}(\Lambda_b^0 \rightarrow \Lambda_c^+ \pi^-) = \Big( 4.30 \pm 0.03 \,\, ^{+0.12}_{-0.11} \pm 0.26 \pm 0.21 \Big) \times 10^{-3}\) is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of \(f_{\Lambda_b^0}/f_d\) and the fourth is due to the \(\bar{B}^0 \rightarrow D^+ \pi^-\) branching fraction. This is the most precise measurement of a \(\Lambda_b^0\) branching fraction to date.
First observations of the rare decays \(B^+\rightarrow K^+\pi^+\pi^-\mu^+\mu^-\) and \(B^+\rightarrow \phi K^+\mu^+\mu^-\) are presented using data corresponding to an integrated luminosity of ...\(3.0\,{fb}^{-1}\), collected by the LHCb experiment at centre-of-mass energies of \(7\) and \(8\mathrm{\,TeV}\). The branching fractions of the decays are \begin{eqnarray*} \mathcal{B}(B^+\rightarrow K^+\pi^+\pi^-\mu^+\mu^-) &=& (4.36\,^{+0.29}_{-0.27}\,\mathrm{(stat)}\pm 0.21\,\mathrm{(syst)}\pm0.18\,\mathrm{(norm)})\times10^{-7},\\ \mathcal{B}(B^+\rightarrow\phi K^+\mu^+\mu^-) &=& (0.82 \,^{+0.19}_{-0.17}\,\mathrm{(stat)}\,^{+0.10}_{-0.04}\,\mathrm{(syst)}\pm0.27\,\mathrm{(norm)}) \times10^{-7},\end{eqnarray*} where the uncertainties are statistical, systematic, and due to the uncertainty on the branching fractions of the normalisation modes. A measurement of the differential branching fraction in bins of the invariant mass squared of the dimuon system is also presented for the decay \(B^+\rightarrow K^+\pi^+\pi^-\mu^{+}\mu^{-}\).
A search for the lepton flavour violating decay \(\tau^-\to \mu^-\mu^+\mu^-\) is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of ...\(1.0\mathrm{\,fb}^{-1}\) of proton-proton collisions at a centre-of-mass energy of \(7\mathrm{\,Te\kern -0.1em V}\) and \(2.0\mathrm{\,fb}^{-1}\) at \(8\mathrm{\,Te\kern -0.1em V}\). No evidence is found for a signal, and a limit is set at \(90\%\) confidence level on the branching fraction, \(\mathcal{B}(\tau^-\to \mu^-\mu^+\mu^-) < 4.6 \times 10^{-8}\).
The first observation of \(Z\) boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of \(\sqrt{s_{NN}}=5~\text{TeV}\) is presented. The data sample ...corresponds to an integrated luminosity of \(1.6~\text{nb}^{-1}\) collected with the LHCb detector. The \(Z\) candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above \(20~\text{GeV}/c\). The invariant dimuon mass is restricted to the range \(60-120~\text{GeV}/c^2\). The \(Z\) production cross-section is measured to be \begin{eqnarray*} \sigma_{Z\to\mu^+\mu^-}(\text{fwd})&=&13.5^{+5.4}_{-4.0}\text{(stat.)}\pm1.2\text{(syst.)}~\text{nb} \end{eqnarray*} in the direction of the proton beam and \begin{eqnarray*} \sigma_{Z\to\mu^+\mu^-}(\text{bwd}) & =&10.7^{+8.4}_{-5.1}\text{(stat.)}\pm1.0\text{(syst.)}~\text{nb} \end{eqnarray*} in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.
A search for the rare decays \(B_s^0 \to \pi^+\pi^-\mu^+\mu^-\) and \(B^0 \to \pi^+\pi^-\mu^+\mu^-\) is performed in a data set corresponding to an integrated luminosity of 3.0 fb\(^{-1}\) collected ...by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3 GeV/\(c^2\) and with muon pairs that do not originate from a resonance are considered. The first observation of the decay \(B_s^0 \to \pi^+\pi^-\mu^+\mu^-\) and the first evidence of the decay \(B^0 \to \pi^+\pi^-\mu^+\mu^-\) are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be \(\mathcal{B}(B_s^0 \to \pi^+\pi^-\mu^+\mu^-)=(8.6\pm 1.5\,({\rm stat}) \pm 0.7\,({\rm syst})\pm 0.7\,({\rm norm}))\times 10^{-8}\) and \(\mathcal{B}(B^0 \to \pi^+\pi^-\mu^+\mu^-)=(2.11\pm 0.51\,({\rm stat}) \pm 0.15\,({\rm syst})\pm 0.16\,({\rm norm}) )\times 10^{-8}\), where the third uncertainty is due to the branching fraction of the decay \(B^0\to J/\psi(\to \mu^+\mu^-)K^*(890)^0(\to K^+\pi^-)\), used as a normalisation.
Measurements of the effective lifetimes in the \(B_{s}^{0} \rightarrow K^{+}K^{-}\), \(B^{0} \rightarrow K^{+}\pi^{-}\) and \(B_{s}^{0} \rightarrow \pi^{+}K^{-}\) decays are presented using ...\(1.0~\mathrm{fb^{-1}}\) of \(pp\) collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are \(\tau_{B_{s}^{0} \rightarrow K^{+}K^{-}}\) = \(1.407~\pm~0.016~\pm~0.007~\mathrm{ps}\), \(\tau_{B^{0} \rightarrow K^{+}\pi^{-}}\) = \(1.524~\pm~0.011~\pm~0.004~\mathrm{ps}\), \(\tau_{B_{s}^{0} \rightarrow \pi^{+}K^{-}}\) = \(1.60~\pm~0.06~\pm~0.01~\mathrm{ps}\). This is the most precise determination to date of the effective lifetime in the \(B_{s}^{0} \rightarrow K^{+}K^{-}\) decay and provides constraints on contributions from physics beyond the Standard Model to the \(B_{s}^{0}\) mixing phase and the width difference \(\Delta\Gamma_{s}\).
Measurements are presented of the \(CP\) violation observables \(S\) and \(C\) in the decays of \(B^0\) and \(\overline{B}{}^0\) mesons to the \(J/\psi K^0_S\) final state. The data sample ...corresponds to an integrated luminosity of \(3.0\,\text{fb}^{-1}\) collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of \(7\) and \(8\,\text{TeV}\). The analysis of the time evolution of \(41500\) \(B^0\) and \(\overline{B}{}^0\) decays yields \(S = 0.731 \pm 0.035 \, \text{(stat)} \pm 0.020 \,\text{(syst)}\) and \(C = -0.038 \pm 0.032 \, \text{(stat)} \pm 0.005\,\text{(syst)}\). In the Standard Model, \(S\) equals \(\sin(2\beta)\) to a good level of precision. The values are consistent with the current world averages and with the Standard Model expectations.
