Measurement of the shape of the Bs0→Ds∗−μ+νμ {B}_s^0\to {D}_s^{\ast -}{\mu}^{+}{\nu}_{\mu } differential decay rate

International audienceThe shape of the ${B}_s^0\to {D}_s^{\ast -}{\mu}^{+}{\nu}_{\mu }$ differential decay rate is obtained as a function of the hadron recoil parameter using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb$^{−1}$ collected by the LHCb detector. The ${B}_s^0\to {D}_s^{\ast -}{\mu}^{+}{\nu}_{\mu }$ decay is reconstructed through the decays ${D}_s^{\ast -}\to {D}_s^{-}\gamma$ and ${D}_s^{-}\to {K}^{-}{K}^{+}{\pi}^{-}$. The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.[graphic not available: see fulltext

Observation of structure in the J/ψJ /\psi -pair mass spectrum

International audienceUsing proton-proton collision data at centre-of-mass energies of $\sqrt{s} = 7$, $8$ and $13\mathrm{\,TeV}$ recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of $9\mathrm{\,fb}^{-1}$, the invariant mass spectrum of $J/\psi$ pairs is studied. A narrow structure around $6.9\mathrm{\,GeV/}c^2$ matching the lineshape of a resonance and a broad structure just above twice the $J/\psi$ mass are observed. The deviation of the data from nonresonant $J/\psi$-pair production is above five standard deviations in the mass region between $6.2$ and $7.4\mathrm{\,GeV/}c^2$, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow $X(6900)$ structure are measured assuming a Breit--Wigner lineshape

Study of the lineshape of the χc1(3872)\chi_{c1}(3872) state

International audienceA study of the lineshape of the $\chi_{c1}(3872)$ state is made using a data sample corresponding to an integrated luminosity of $3\,$fb$^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7 and 8\,TeV with the LHCb detector. Candidate $\chi_{c1}(3872)$ and $\psi(2S)$ mesons from b-hadron decays are selected in the $J/\psi \pi^+ \pi^-$ decay mode. Describing the {\mbox{lineshape}} with a Breit--Wigner function, the mass splitting between the $\chi_{c1}(3872)$ and $\psi(2S)$ states, $\Delta m$, and the width of the $\chi_{c1}(3872)$ state, $\Gamma_{\mathrm{BW}}$, are determined to be \begin{eqnarray*} \Delta m & = & 185.598 \pm 0.067 \pm 0.068\, \mathrm{MeV} \,, \\ \Gamma_{\mathrm{BW}} & = & \phantom{00}1.39\phantom{0} \pm 0.24\phantom{0} \pm 0.10\phantom{0} \mathrm{MeV} \,, \end{eqnarray*} where the first uncertainty is statistical and the second systematic. Using a Flatt\'e-inspired model, the mode and full width at half maximum of the lineshape are determined to be \begin{eqnarray*} \mathrm{mode} & = 3871.69^{\,+\,0.00\,+\,0.05}_{\,-\,0.04\,-\,0.13} &\mathrm{MeV} \\ \mathrm{FWHM} & = 0.22^{\,+\,0.07\,+\,0.11}_{\,-\,0.06\,-\,0.13}& \mathrm{MeV} . \end{eqnarray*} An investigation of the analytic structure of the Flatt\'e amplitude reveals a pole structure, which is compatible with a quasi-bound $D^0\bar{D}^{*0}$ state but a quasi-virtual state is still allowed at the level of $2$ standard deviations

Measurement of branching fraction ratios for B+→D∗+D−K+B^+\to D^{*+}D^-K^+, B+→D∗−D+K+B^+\to D^{*-}D^+K^+, and B0→D∗−D0K+B^0\to D^{*-}D^0K^+decays

International audienceA measurement of four branching-fraction ratios for three-body decays of B mesons involving two open-charm hadrons in the final state is presented. Run 1 and Run 2 pp collision data are used, recorded by the LHCb experiment at centre-of-mass energies 7, 8, and 13 TeV and corresponding to an integrated luminosity of 9 fb$^{−1}$. The measured branching-fraction ratios are${\displaystyle \begin{array}{c}\frac{\mathcal{B}\left({B}^{+}\to {D}^{\ast +}{D}^{-}{K}^{+}\right)}{\mathcal{B}\left({B}^{+}\to {\overline{D}}^0{D}^0{K}^{+}\right)}=0.517\pm 0.015\pm 0.013\pm 0.011,\\ {}\frac{\mathcal{B}\left({B}^{+}\to {D}^{\ast -}{D}^{+}{K}^{+}\right)}{\mathcal{B}\left({B}^{+}\to {\overline{D}}^0{D}^0{K}^{+}\right)}=0.577\pm 0.016\pm 0.013\pm 0.013,\\ {}\begin{array}{c}\frac{\mathcal{B}\left({B}^0\to {D}^{\ast -}{D}^0{K}^{+}\right)}{\mathcal{B}\left({B}^0\to {D}^{-}{D}^0{K}^{+}\right)}=1.754\pm 0.028\pm 0.016\pm 0.035,\\ {}\frac{\mathcal{B}\left({B}^{+}\to {D}^{\ast +}{D}^{-}{K}^{+}\right)}{\mathcal{B}\left({B}^{+}\to {D}^{\ast -}{D}^{+}{K}^{+}\right)}=0.907\pm 0.033\pm 0.014,\end{array}\end{array}}$where the first of the uncertainties is statistical, the second systematic, and the third is due to the uncertainties on the D-meson branching fractions. These are the most accurate measurements of these ratios to date.[graphic not available: see fulltext

Evidence of a J/ψΛJ/\psi\Lambda structure and observation of excited Ξ−\Xi^- states in the Ξb−→J/ψΛK−\Xi^-_b \to J/\psi\Lambda K^- decay

First evidence of a structure in the $J/\psi{\Lambda}$ invariant mass distribution is obtained from an amplitude analysis of $\Xi_b^-{\rightarrow}J/\psi{\Lambda}K^-$ decays. The observed structure is consistent with being due to a charmonium pentaquark with strangeness with a significance of $3.1\sigma$ including systematic uncertainties and look-elsewhere effect. Its mass and width are determined to be $4458.8\pm2.9^{+4.7}_{-1.1}$ MeV and $17.3\pm6.5^{+8.0}_{-5.7}$ MeV, respectively, where the quoted uncertainties are statistical and systematic. The structure is also consistent with being due to two resonances. In addition, the narrow excited $\Xi^-$ states, $\Xi(1690)^-$ and $\Xi(1820)^-$, are seen for the first time in a $\Xi^-_b$ decay, and their masses and widths are measured with improved precision. The analysis is performed using $pp$ collision data corresponding to a total integrated luminosity of 9 fb$^{-1}$, collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV

Study of the ψ2(3823)\psi_2(3823) and χc1(3872)\chi_{c1}(3872) states in B+→(Jψπ+π−)K+B^+ \rightarrow \left( J\psi\pi^+\pi^-\right)K^+ decays

International audienceThe decays B$^{+}$→ J/ψπ$^{+}$π$^{−}$K$^{+}$ are studied using a data set corresponding to an integrated luminosity of 9 fb$^{−1}$ collected with the LHCb detector in proton-proton collisions between 2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate ψ$_{2}$(3823), χ$_{c1}$(3872) and ψ(2S) states are reported. The values are {\displaystyle \begin{array}{c}\frac{{\mathcal{B}}_{{\mathrm{B}}^{+}\to {\uppsi}_2(3823){\mathrm{K}}^{+}}\times {\mathcal{B}}_{\uppsi_2(3823)\to \mathrm{J}/{\uppsi \uppi}^{+}{\uppi}^{-}}}{{\mathcal{B}}_{{\mathrm{B}}^{+}\to {\upchi}_{\mathrm{c}1}(3872){\mathrm{K}}^{+}}\times {\mathcal{B}}_{\upchi_{\mathrm{c}1}(3872)\to \mathrm{J}/{\uppsi \uppi}^{+}{\uppi}^{-}}}=\left(3.56\pm 0.67\pm 0.11\right)\times {10}^{-2},\\ {}\frac{{\mathcal{B}}_{{\mathrm{B}}^{+}\to {\uppsi}_2(3823){\mathrm{K}}^{+}}\times {\mathcal{B}}_{\uppsi_2(3823)\to \mathrm{J}/{\uppsi \uppi}^{+}{\uppi}^{-}}}{{\mathcal{B}}_{{\mathrm{B}}^{+}\to \uppsi \left(2\mathrm{S}\right){\mathrm{K}}^{+}}\times {\mathcal{B}}_{\uppsi \left(2\mathrm{S}\right)\to \mathrm{J}/{\uppsi \uppi}^{+}{\uppi}^{-}}}=\left(1.31\pm 0.25\pm 0.04\right)\times {10}^{-3},\\ {}\frac{{\mathcal{B}}_{\mathrm{B}+\to {\upchi}_{\mathrm{c}1}(3872){\mathrm{K}}^{+}}\times {\mathcal{B}}_{\upchi_{\mathrm{c}1}(3872)\to \mathrm{J}/{\uppsi \uppi}^{+}{\uppi}^{-}}}{{\mathcal{B}}_{{\mathrm{B}}^{+}\to \uppsi \left(2\mathrm{S}\right){\mathrm{K}}^{+}}\times {\mathcal{B}}_{\uppsi \left(2\mathrm{S}\right)\to \mathrm{J}/{\uppsi \uppi}^{+}{\uppi}^{-}}}=\left(3.69\pm 0.07\pm 0.06\right)\times {10}^{-2},\end{array}} where the first uncertainty is statistical and the second is systematic. The decay of B$^{+}$→ ψ$_{2}$(3823)K$^{+}$ with ψ$_{2}$(3823) → J/ψπ$^{+}$π$^{−}$ is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the ψ$_{2}$(3823), χ$_{c1}$(3872) and ψ(2S) states are measured to be {\displaystyle \begin{array}{c}{m}_{\upchi_{\mathrm{c}1}(3872)}-{m}_{\uppsi_2(3823)}=47.50\pm 0.53\pm 0.13\;\mathrm{MeV}/{c}^2,\\ {}{m}_{\uppsi_2(3823)}-{m}_{\uppsi_2\left(2\mathrm{S}\right)}=137.98\pm 0.53\pm 0.14\;\mathrm{MeV}/{c}^2,\\ {}{m}_{\upchi_{\mathrm{c}1}(3872)}-{m}_{\uppsi_2\left(2\mathrm{S}\right)}=185.49\pm 0.06\pm 0.03\;\mathrm{MeV}/{c}^2,\end{array}} resulting in the most precise determination of the χ$_{c1}$(3872) mass. The width of the ψ$_{2}$(3823) state is found to be below 5.2 MeV at 90% confidence level. The Breit-Wigner width of the χ$_{c1}$(3872) state is measured to be {\Gamma}_{\upchi_{\mathrm{c}1}(3872)}^{\mathrm{BW}}={0.96}_{-0.18}^{+0.19}\pm 0.21\;\mathrm{MeV} which is inconsistent with zero by 5.5 standard deviations.[graphic not available: see fulltext