The measurement of charmonium states produced in proton-neon ($p\text {Ne}$) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of ${{J} ...\hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ and $\psi {(2S)}$ mesons is studied with a beam of 2.5$\mathrm{\,Te\hspace{-1.00006pt}V}$ protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\scriptscriptstyle \text {NN}}} =68.5\mathrm{\,Ge\hspace{-1.00006pt}V} $. The data sample corresponds to an integrated luminosity of $21.7\pm 1.4 $ nb$^{-1}$. The ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ and $\psi {(2S)}$ hadrons are reconstructed in $\mu ^+\mu ^-$ final states. The ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ production cross-section per target nucleon in the centre-of-mass rapidity range $y^\star \in -2.29, 0$ is found to be $506 \pm 8 \pm 46 \text { nb/nucleon}$. The ratio of ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ and $D^0$ cross-sections is evaluated to $(1.06 \pm 0.02 \pm 0.09)\%$. The $\psi {(2S)}$ to ${{J} \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }$ relative production rate is found to be $(1.67 \pm 0.27\pm 0.10)\%$ in good agreement with other measurements involving beam and target nuclei of similar sizes.
A flavor-tagged time-dependent angular analysis of the decay B_{s}^{0}→ϕϕ is performed using pp collision data collected by the LHCb experiment at the center-of-mass energy of 13 TeV, corresponding ...to an integrated luminosity of 6 fb^{-1}. The CP-violating phase and direct CP-violation parameter are measured to be ϕ_{s}^{ssover ¯s}=-0.042±0.075±0.009 rad and |λ|=1.004±0.030±0.009, respectively, assuming the same values for all polarization states of the ϕϕ system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using pp collisions at center-of-mass energies of 7 and 8 TeV, yielding ϕ_{s}^{ssover ¯s}=-0.074±0.069 rad and |λ|=1.009±0.030. This is the most precise study of time-dependent CP violation in a penguin-dominated B meson decay. The results are consistent with CP symmetry and with the standard model predictions.
The first observation and study of two new baryonic structures in the final state Ξ_{b}^{0}π^{+}π^{-} and the confirmation of the Ξ_{b}(6100)^{-} state in the Ξ_{b}^{-}π^{+}π^{-} decay mode are ...reported using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb^{-1}. In addition, the properties of the known Ξ_{b}^{*0}, Ξ_{b}^{'-} and Ξ_{b}^{*-} resonances are measured with improved precision. The new decay mode of the Ξ_{b}^{0} baryon to the Ξ_{c}^{+} π^{-} π^{+} π^{-} final state is observed and exploited for the first time in these measurements.
The branching fraction of the rare decay Λ_{b}^{0}→Λ(1520)μ^{+}μ^{-} is measured for the first time, in the squared dimuon mass intervals q^{2}, excluding the J/ψ and ψ(2S) regions. The data sample ...analyzed was collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb^{-1}. The result in the highest q^{2} interval, q^{2}>15.0 GeV^{2}/c^{4}, where theoretical predictions have the smallest model dependence, agrees with the predictions.
A search for the very rare D^{0}→μ^{+}μ^{-} decay is performed using data collected by the LHCb experiment in proton-proton collisions at sqrts=7, 8, and 13 TeV, corresponding to an integrated ...luminosity of 9 fb^{-1}. The search is optimized for D^{0} mesons from D^{*+}→D^{0}π^{+} decays but is also sensitive to D^{0} mesons from other sources. No evidence for an excess of events over the expected background is observed. An upper limit on the branching fraction of this decay is set at B(D^{0}→μ^{+}μ^{-})<3.1×10^{-9} at a 90% C.L. This represents the world's most stringent limit, constraining models of physics beyond the standard model.
