Analysis of the resonant components in B¯0→J/ψπ+π−

Le résumé fourni par la source

Interpretation of $CP$ violation measurements using charmonium decays, in both the ${\overline{B}}^{0}$ and ${\overline{B}}_{s}^{0}$ systems, can be subject to changes due to ``penguin'' type diagrams. These effects can be investigated using measurements of the Cabibbo-suppressed ${\overline{B}}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decays. The final state composition of this channel is investigated using a $1.0\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ sample of data produced in 7 TeV $pp$ collisions at the LHC and collected by the LHCb experiment. A modified Dalitz-plot analysis is performed using both the invariant mass spectra and the decay angular distributions. An improved measurement of the ${\overline{B}}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ branching fraction of $(3.97\ifmmode\pm\else\textpm\fi{}0.09\ifmmode\pm\else\textpm\fi{}0.11\ifmmode\pm\else\textpm\fi{}0.16)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ is reported where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty of the branching fraction of the decay ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{\ensuremath{-}}$ used as a normalization channel. Significant production of ${f}_{0}(500)$ and $\ensuremath{\rho}(770)$ resonances is found in the substructure of the $J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ final state, and this indicates that they are viable final states for $CP$ violation studies. In contrast evidence for the ${f}_{0}(980)$ resonance is not found. This allows us to establish the first upper limit on the branching fraction product $\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{f}_{0}(980))\ifmmode\times\else\texttimes\fi{}\mathcal{B}({f}_{0}(980)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})<1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$, leading to an upper limit on the absolute value of the mixing angle of the ${f}_{0}(980)$ with the ${f}_{0}(500)$ of less than 31\ifmmode^\circ\else\textdegree\fi{}, both at 90% confidence level.

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