Pentaquark

A pentaquark is an hypothetical subatomic particle consisting of a group of five exotic baryon. Several experiments since 2003 claim to have seen a pentaquark with a mass of about 1540 MeV, presumably composed of two up quarks, two down quarks and an anti-strange quark (uudds). This is the minimal quark composition of an object with baryon number 1, and positive strangeness.