Mixing of Pentaquark and Molecular States

Abstract

There are experimental evidences for the existence of narrow states ${\Theta }^{+}$ and ${\Theta }_c$ with the same quantum numbers of $uudd\bar{s}$ and $uudd\bar{c}$ pentaquarks and also $N{K}^{(\ast )}$ and $N{D}^{(\ast )}$ molecular states. Their masses deviate from many theoretical estimates of the pure pentaquark and molecular states. In this work we study the possibility that the observed ${\Theta }^{+}$ and ${\Theta }_c$ are mixtures of pure pentaquark and molecular states. The mixing parameters are in general related to non-perturbative QCD which are not calculable at present. We determine them by fitting data from known states and then generalize the mechanism to ${\Theta }_b$ to predict its mass and width. The mixing mechanism can also naturally explain the narrow width for ${\Theta }^{+}$ and ${\Theta }_c$ through destructive interferences, even if the pure pentaquark and molecular states have much larger decay widths. We also briefly discuss the properties of the partner eigenstates of ${\Theta }^{+}$ and ${\Theta }_c$ and the possibility of experimentally observe them. Moreover, probable consequences of multi-state mixing are also addressed.

Comments: 23 pages, 4 figures. Published version in EPJC