SPring-8 makes contribution to particle physics

Recently a team at SPring-8 [Phys. Rev. Lett. (2003). 91, 012002] produced photons with a maximum energy of 2.4 GeV by Compton backscattering of laser photons (351 nm Ar laser) and 8 GeV electrons in the SPring-8 storage ring. A carbon nucleus was irradiated with these photons. By analyzing the data carefully, the group has found that a K⁻ meson and a new particle are simultaneously generated when a neutron inside the nucleus absorbs a photon, and that the new particle subsequently decays into a neutron and K⁺ meson. The mass of the new particle, 1.54 GeV/c², which was calculated from the energy of the photon beam and the K⁻ meson, is very close to the five-quark θ⁺ particle predicted by a Russian theorist, Dmitri Diakonov, and his colleagues in 1997. We note with interest that major expansion in synchrotron radiation activities resulted from the parasitic use of accelerators built for the high-energy physics community in the early 1960s. Now, some 40 years later, the largest dedicated synchrotron radiation facility is being used to make a contribution to the discovery of new particles.