Pentaquark
A schematic drawing of how a pentaquark particle is created in high
energy collisions at the SPring-8 accelerator in Japan and at the Jefferson
Lab in the US. First, an energetic gamma ray, or photon, strikes a nucleus.
Within the nucleus are nucleons, which are either protons (consisting
in turn of two "up" quarks and one "down" quark)
and neutrons (consisting of two down quarks and one up quark). In some
collisions, the debris particles will include a pentaquark (consisting
of 2 up quarks, 2 down quarks, and a strange antiquark), a negative
K meson (a strange quark and an up antiquark), and other particles.
Later, after a time not yet determined (but maybe as short as 10-20
seconds), the pentaquark decays into a positively charged K meson (up
quark plus strange antiquark) plus a neutron, which are sensed in detectors
farther along. Studying the properties of the end-product neutrons and
K+ mesons is what determines the existence of the pentaquark. (Courtesy
Malcolm Tarlton, AIP)
