Search for the decay mode $B^0\to pp\overline{p}\overline{p}$

A search is presented for the four-body decay $B^0\to pp\overline{p}\overline{p}$ in a sample of 471 million $B\overline{B}$ pairs collected with the BABAR detector, operated at the SLAC PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The center-of-mass energy is 10.58 GeV. From a fit to the distribution of the energy-substituted mass $m_{\mathrm{ES}}$, the branching fraction $\mathcal{B}(B^0\to pp\overline{p}\overline{p})=(1.1\pm 0.5\pm 0.2)\times {10}^{-7}$ is extracted, where the first uncertainty is statistical and the second is systematic. The significance of the signal, including the systematic uncertainty, is 2.9 standard deviations. The upper limit on the branching fraction is determined to be $2.0\times {10}^{-7}$ at 90% confidence level.

Figure 1

The BDT output distribution for simulated signal (shaded histogram) and background (filled histogram) events. The two background components, from continuum and generic $B\overline{B}$ events, are stacked, with the total background prediction scaled to correspond to the number of selected events in the data. For purposes of visibility, the signal distribution has been multiplied by a factor of 100. The selection on the BDT output is indicated by the black vertical line.

Figure 2

Fit to the data $m_{\mathrm{ES}}$ distribution (dots) in the interval $5.2<m_{\mathrm{ES}}<5.3\mathrm{GeV}/c^2$. The bottom plot shows the pull distribution, which is the bin-by-bin difference between the data and fitted distribution normalized by the corresponding statistical uncertainty from the fit.