Compact pentaquark structures

We investigated the possibility that the lightest pentaquark state recently reported by the $LH{C}_b$ Collaboration [R. Aaij et al., Phys. Rev. Lett. 115, 072001 (2015); 117, 082002 (2016); 117, 082003 (2016)], $P_c^{+}(4380)$, could be described as a compact pentaquark state. By using very general arguments, dictated by symmetry considerations, we described the pentaquark states within a group theory approach. A complete classification of all possible states and quantum numbers, which can be useful both to the experimentalists in their search for new findings and to theoretical model builders, is given, without introducing any particular dynamical model. Some predictions are provided by means of a Gürsey-Radicati inspired mass formula. We have reproduced the mass and the quantum numbers of the lightest pentaquark state reported by $LH{C}_b$, $P_c^{+}(4380)$, and have predicted other pentaquark resonances which belong to the same multiplet as the lightest one. Having calculated the masses of these resonances, we suggest possible bottom baryon decay channels which involve the predicted resonances as intermediate states. Finally, we have computed the partial decay widths for all the predicted pentaquark resonances.

Figure 1

Feynman diagram for ${\mathrm{\Lambda }}_b^0\to J/\psi +{\mathrm{\Lambda }}^{*}$ decay, reported in Eq. (1) (figure taken from Ref. [1]; APS copyright).

Figure 2

Feynman diagram for ${\mathrm{\Lambda }}_b^0\to P_c^{+}+K^{-}$ decay, reported in Eq. (2) (figure taken from Ref. [1]; APS copyright).

Figure 3

Octet of the charmonium pentaquark states: each state is labeled as $P^{ij}(M)$, where $i=0$, 1, 2 is the number of strange quarks of a given pentaquark state, $j=-,0,+$ is the pentaquark’s electric charge, and $M$ is the predicted mass.

Figure 4

${\mathrm{\Lambda }}_b$ baryon decay in $P^{00}(4377)$ and ${\overline{K}}^{00}$, where $P^{00}(4377)$ is the neutral pentaquark state, a member of the isospin doublet with $Y=1$.