Quantum Monte Carlo studies of 3-, 6- and 5-quark states

Recent high-statistics experimental results from Jefferson Lab cast doubt on the existence of the flavor exotic pentaquark state with strangeness +1. After reviewing the status of experimental evidence for and against the pentaquark and some of the recent theoretical treatments, we make a careful study of the strangeness +1 state within a non-relativistic constituent quark model (NRCQM). The many-body Schrodinger equation is solved using the variational Monte Carlo technique. Improvements over previous NRCQM include full antisymmetrization of the state of the four light quarks, sometimes neglected, relaxed assumptions for the spin state of the four light quarks, and the inclusion of correlations between pairs of quarks which depend on their isospin-spin-color state. Masses are calculated for negative and positive parity pentaquark states and found to be considerably higher than 1.5 GeV.