Five-Quark Particle Found

By Katherine Redding & Kathleen M. Wong, California Academy of Sciences
July 2, 2003

Evidence of a new type of subatomic particle has the physics world abuzz. Known as the pentaquark, it consists of five of the fundamental particles called quarks that themselves make up protons and neutrons. Though squeezed close in the buzzing heart of an atom, quarks remain grouped into distinct trios within protons and neutrons. In 25 years of experiments, these clannish bits of matter haven't seemed to mingle with their already-grouped neighbors. The new discovery, reported in the journal Physical Review Letters, upsets this tidy understanding. Acting on a suggestion from another physicist, Takashi Nakano of the Research Center for Nuclear Physics at Osaka University in Japan, and colleagues found the pentaquark signal in data from an experiment in which they fired high-energy particles of light at carbon atoms. Data from similar experiments conducted elsewhere contained the same pentaquark signature. Though the findings aren't conclusive, and could indicate a temporary association of quarks, the pentaquark signal was convincingly stable and long-lived. If proven, the discovery will change our understanding of how matter behaves.