Lattice study of exotic S=+1 baryon

TL;DR

This study uses lattice QCD to explore the mass spectrum of exotic S=+1 baryons, proposing new operators based on diquark models, and finds the lowest state likely has quantum numbers (1/2)^-, with the charm analog being significantly heavier.

Contribution

Introduces novel lattice QCD operators for S=+1 baryons based on diquark-antiquark structures and computes their mass spectrum, providing new insights into their quantum numbers and mass hierarchy.

Findings

The lowest $ heta$ state likely has $J^P = (1/2)^-$.

The charm analog $ heta_c$ is much heavier than the $DN$ threshold.

Mass spectrum results differ from some model predictions.

Abstract

We propose S=+1 baryon interpolating operators, which are based on an exotic description of the antidecuplet baryon like diquark-diqaurk-antiquark. By using one of the new operators, the mass spectrum of the spin-1/2 pentaquark states is calculated in quenched lattice QCD at $\beta=6/g^2=6.2$ on a $32^3\times48$ lattice. It is found that the $J^P$ assignment of the lowest $\Theta(uudd \bar s)$ state is most likely $(1/2)^-$. We also calculate the mass of the charm analog of the $\Theta$ and find that the $\Theta_c(uudd \bar c)$ state lies much higher than the $DN$ threshold, in contrast to several model predictions.