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Abstract Conventional, hadronic matter consists of baryons and mesons made of three quarks and a quark–antiquark pair, respectively 1,2 . Here, we report the observation of a hadronic state containing four quarks in the Large Hadron Collider beauty experiment. This so-called tetraquark contains two charm quarks, a $$\overline{{{{{u}}}}}$$ u ¯ and a $$\overline{{{{{d}}}}}$$ d ¯ quark. This exotic state has a mass of approximately 3,875 MeV and manifests as a narrow peak in the mass spectrum of D 0 D 0 π + mesons just below the D *+ D 0 mass threshold. The near-threshold mass together with the narrow width reveals the resonance nature of the state. 

Abstract The identification of charm jets is achieved at LHCb for data collected in 2015–2018 using a method based on the properties of displaced vertices reconstructed and matched with jets. The performance of this method is determined using a dijet calibration dataset recorded by the LHCb detector and selected such that the jets are unbiased in quantities used in the tagging algorithm. The charm-tagging efficiency is reported as a function of the transverse momentum of the jet. The measured efficiencies are compared to those obtained from simulation and found to be in good agreement. 

A bstract The production cross-section of the χ c 1 (3872) state relative to the ψ (2 S ) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of $$ \sqrt{s} $$ s = 8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb − 1 , respectively. The two mesons are reconstructed in the J/ψπ + π − final state. The ratios of the prompt and nonprompt χ c 1 (3872) to ψ (2 S ) production cross-sections are measured as a function of transverse momentum, p T , and rapidity, y , of the χ c 1 (3872) and ψ (2 S ) states, in the kinematic range 4 < p T < 20 GeV/ c and 2 . 0 < y < 4 . 5. The prompt ratio is found to increase with p T , independently of y . For the prompt component, the double ratio of the χ c 1 (3872) and ψ (2 S ) production cross-sections between 13 and 8 TeV is observed to be consistent with unity, independent of p T and centre-of-mass energy. 

A bstract The W boson mass is measured using proton-proton collision data at $$ \sqrt{s} $$ 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 → μν decays and the ϕ * distribution of a sample of Z → μμ decays the W boson mass is determined to be $$ {m}_w=80354\pm {23}_{\mathrm{stat}}\pm {10}_{\mathrm{exp}}\pm {17}_{\mathrm{theory}}\pm {9}_{\mathrm{PDF}}\mathrm{MeV}, $$ m w = 80354 ± 23 stat ± 10 exp ± 17 theory ± 9 PDF MeV , 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. 

A bstract Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb − 1 collected with the LHCb detector, seven decay modes of the $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + meson into a J / ψ or ψ(2S) meson and three charged hadrons, kaons or pions, are studied. The decays $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → (ψ(2S) → J / ψπ + π − )π + , $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → ψ(2S)π + π − π + , $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → J / ψK + π − π + and $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → J / ψK + K − K + are observed for the first time, and evidence for the $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → ψ(2S)K + K − π + , decay is found, where J / ψ and ψ(2S) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays. 

A bstract The first search for the rare radiative decay $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − γ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb − 1 . The $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − J/ψ channel is used as normalization. No $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − γ signal is found and an upper limit of $$ \mathcal{B} $$ B ( $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − γ ) < 1 . 3 × 10 − 4 at 95% confidence level is obtained. 

A bstract A data set corresponding to an integrated luminosity of 9 fb − 1 of proton-proton collisions collected by the LHCb experiment has been analysed to search for $$ {B}_c^{+}\to {D}_{(s)}^{\left(\ast \right)+}{\genfrac{}{}{0pt}{}{\left(\hbox{---} \right)}{D}}^{\left(\ast \right)0} $$ B c + → D s ∗ + — D ∗ 0 decays. The decays are 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 sixteen $$ {B}_c^{+} $$ B c + decay modes. For the decay $$ {B}_c^{+}\to {D}_s^{+}{\overline{D}}^0 $$ B c + → D s + D ¯ 0 , an excess with a significance of 3.4 standard deviations is found.