Observation of charmless baryonic decays $B_{(s)}^0\to p\overline{p}{h}^{+}{h}^{\prime -}$

Decays of $B^0$ and $B_s^0$ mesons to the charmless baryonic final states $p\overline{p}{h}^{+}{h}^{\prime -}$, where $h$ and $h^{\prime }$ each denote a kaon or a pion, are searched for using the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. Four-body charmless baryonic $B_s^0$ decays are observed for the first time. The decays $B_s^0\to p\overline{p}{K}^{+}{K}^{-}$, $B_s^0\to p\overline{p}{K}^{\pm }{\pi }^{\mp }$, $B^0\to p\overline{p}{K}^{\pm }{\pi }^{\mp }$ and $B^0\to p\overline{p}{\pi }^{+}{\pi }^{-}$ are observed with a significance greater than 5 standard deviations; evidence at 4.1 standard deviations is found for the $B^0\to p\overline{p}{K}^{+}{K}^{-}$ decay and an upper limit is set on the branching fraction for $B_s^0\to p\overline{p}{\pi }^{+}{\pi }^{-}$. Branching fractions in the kinematic region $m(p\overline{p})<2850\mathrm{MeV}/c^2$ are measured relative to the $B^0\to J/\psi (\to p\overline{p})K^{*}(892{)}^0$ channel.

Figure 1

Invariant mass distributions for $B_{(s)}^0$ candidates in the (top left) $p\overline{p}KK$, (top right) $p\overline{p}K\pi$, (bottom left) $p\overline{p}\pi \pi$ final state and (bottom right) invariant mass distribution of $B^0\to J/\psi K^{*}(892{)}^0$ in the $p\overline{p}K\pi$ final state. The results of the fits are shown with blue solid lines. In the first three figures signals for $B^0$ and $B_s^0$ decays are shown, respectively, with green dotted and red dotted-dashed lines, combinatorial backgrounds are shown with black dashed lines and cross-feed backgrounds are shown with violet dotted-dashed lines. In the bottom right figure the normalization signal is shown with a green dotted line, the $K\pi$ S-wave component is displayed with a red dotted-dashed line and the combinatorial background with a black dashed line.

Figure 2

Efficiency-corrected and background-subtracted (left) $m(h{h}^{\prime })$ and (right) $m(p\overline{p})$ distributions from (top) $B^0\to p\overline{p}K\pi$, (middle) $B_s^0\to p\overline{p}KK$, and (bottom) $B^0\to p\overline{p}\pi \pi$ candidates. Events with entries in the charmonium or $D^0$ mass regions have been removed from the samples. All distributions are normalized to unity.