The fraction of $Z+$jet events that contain a charm jet is measured for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of 6 fb$^{-1}$ collected at a center-of-mass energy
of $13$ TeV with the LHCb detector. The ratio of production cross sections ${sigma(Zc)/sigma(Zj)}$ is determined in intervals of $Z$-boson rapidity in the range $2.0 < y(Z) < 4.5$. A sizable enhancement is observed in the forward-most $y(Z)$ interval, which could be indicative of a valence-like intrinsic-charm component in the proton wave function.
A measurement of the lifetimes of the $Omega^{0}_{c}$ and $Xi^{0}_{c}$ baryons is reported using proton-proton collision data at a centre-of-mass energy of $13text{ TeV}$, corresponding to an integrated luminosity of $5.4text{ fb}^{-1}$ collected by
the LHCb experiment. The $Omega^{0}_{c}$ and $Xi^{0}_{c}$ baryons are produced directly from proton interactions and reconstructed in the $pK^{-}K^{-}pi^{+}$ final state. The $Omega^{0}_{c}$ lifetime is measured to be $276.5pm13.4pm4.4pm0.7text{ fs}$, and the $Xi^{0}_{c}$ lifetime is measured to be $148.0pm2.3pm2.2pm0.2text{ fs}$, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the $D^{0}$ lifetime. These results confirm previous LHCb measurements based on semileptonic beauty-hadron decays, which disagree with earlier results of a four times shorter $Omega^{0}_{c}$ lifetime, and provide the single most precise measurement of the $Omega^{0}_{c}$ lifetime.
The $W$ boson mass is measured using proton-proton collision data at $sqrt{s}=13$ TeV corresponding to an integrated luminosity of 1.7 fb$^{-1}$ recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon $q/p_T$ distribution of
a sample of $W to mu u$ decays and the $phi^*$ distribution of a sample of $Ztomumu$ decays the $W$ boson mass is determined to be begin{equation*} m_{W} = 80354 pm 23_{rm stat} pm 10_{rm exp} pm 17_{rm theory} pm 9_{rm PDF}~mathrm{MeV}, end{equation*} where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.
An exotic narrow state in the $D^0D^0pi^+$ mass spectrum just below the $D^{*+}D^0$ mass threshold is studied using a data set corresponding to an integrated luminosity of 9 fb$^{-1}$ acquired with the LHCb detector in proton-proton collisions at cen
tre-of-mass energies of 7, 8 and 13 TeV. The state is consistent with the ground isoscalar $T^+_{cc}$ tetraquark with a quark content of $ccbar{u}bar{d}$ and spin-parity quantum numbers $mathrm{J}^{mathrm{P}}=1^+$. Study of the $DD$ mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell $D^{*+}$ mesons is confirmed by the $D^0pi^+$ mass distribution. The mass of the resonance and its coupling to the $D^{*}D$ system are analysed. Resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of the $T^+_{cc}$ state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.
Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. The observation of a new type of hadronic state, a doubly charmed tetraquark containing two charm quarks, an anti-$u$ and an ant
i-$d$ quark, is reported using data collected by the LHCb experiment at the Large Hadron Collider. This exotic state with a mass of about 3875 MeV$/c^2$ manifests itself as a narrow peak in the mass spectrum of $D^0D^0pi^+$ mesons just below the $D^{*+}D^0$ mass threshold. The near threshold mass together with a strikingly narrow width reveals the resonance nature of the state.
A data set corresponding to an integrated luminosity of $9 text{fb}^{-1}$ of proton-proton collisions collected by the LHCb experiment has been analysed to search for $B_c^+ to D^{(*)+}_{(s)} overset{scriptstyle (-)}{D}{}^{(*)0}$ decays. The decays a
re fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to $B^+$ decays to final states with similar topologies, are obtained for fourteen $B_c^+$ decay modes. For the decay $B_c^+ to D_s^+ {overline{D}}^0$, an excess with a significance of 3.4 standard deviations is found.
The production cross-sections of $J/psi$ mesons in proton-proton collisions at a centre-of-mass energy of $sqrt{s}=5$ TeV are measured using a data sample corresponding to an integrated luminosity of $9.13pm0.18~text{pb}^{-1}$, collected by the LHCb
experiment. The cross-sections are measured differentially as a function of transverse momentum, $p_{text{T}}$, and rapidity, $y$, and separately for $J/psi$ mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised $J/psi$ mesons, the production cross-sections integrated over the kinematic range $0<p_{text{T}}<20~text{GeV}/c$ and $2.0<y<4.5$ are $8.154pm0.010pm0.283~mutext{b}$ for prompt $J/psi$ mesons and $0.820pm0.003pm0.034~mutext{b}$ for nonprompt $J/psi$ mesons, where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at $sqrt{s}=8$ TeV and $13$ TeV, and are used to update the measurement of the nuclear modification factor in proton-lead collisions for $J/psi$ mesons at a centre-of-mass energy per nucleon pair of $sqrt{s_{text{NN}}}=5$ TeV. The results are compared with theoretical predictions.
