Search for weakly decaying $b$-flavored pentaquarks

Investigations of the existence of pentaquark states containing a single $b$ (anti)quark decaying weakly into four specific final states $J/\psi K^{+}{\pi }^{-}p$, $J/\psi K^{-}{\pi }^{-}p$, $J/\psi K^{-}{\pi }^{+}p$, and $J/\psi \varphi (1020)p$ are reported. The data sample corresponds to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ in 7 and 8 TeV $pp$ collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the ${\mathrm{\Lambda }}_b^0$.

Figure 1

Leading-order diagrams for pentaquark decay modes into (a) $J/\psi K^{+}{\pi }^{-}p$ or (b) $J/\psi \varphi p$ final states.

Figure 2

Invariant mass distributions above the decay mass thresholds for the indicated modes.

Figure 3

For the $P_{B^{0}p}^{+}\to J/\psi K^{+}{\pi }^{-}p$ decay search (mode I), the invariant mass of $J/\psi K^{+}{\pi }^{-}$ combinations in the (a) region above threshold and in the (b) signal region. The peak in the sideband region results from $B^0$ decays.

Figure 4

(a) Outputs of the BDT classifier for the $J/\psi K^{+}{\pi }^{-}p$ final state. The circles (blue) show the signal training sample, and the triangles (red) show the background training sample, while the shaded (blue) histogram shows the signal test sample, and the diagonal (red) line-shaded histogram the background test sample. (b) Efficiencies of signal, solid (blue) curve, and background, dotted (red) curve, and the value of the $S/(\sqrt{B}+1.5)$, dashed (green) curve, called “significance,” as a function of the BDT output.

Figure 5

Reconstructed mass distributions after the BDT selection for the (a) $J/\psi K^{+}{\pi }^{-}p$, (b) $J/\psi K^{-}{\pi }^{-}p$, (c) $J/\psi K^{-}{\pi }^{+}p$, and (d) $J/\psi \varphi p$ final states.

Figure 6

Upper limits on $R$ at 90% C.L. for (a) $J/\psi K^{+}{\pi }^{-}p$, (b) $J/\psi K^{-}{\pi }^{-}p$, (c) $J/\psi K^{-}{\pi }^{+}p$, and (d) $J/\psi \varphi p$ final states.