Hunting of the axion

In a unified description of the strong and electroweak forces, we face the problem of parity and charge-parity violation in the strong-interaction part of the quantum chromodynamics (QCD) theory. This problem led R. Peccei and H. Quinn to postulate a global U(1) symmetry for the total Lagrangian. Wilczek and Weinberg pointed out that this assumption leads, by way of the Higgs mechanism, to the existence of a light pseudoscalar particle, the axion a0. In the standard model the axion interacts weakly, like an isovector (weak π0) and/or like an isoscalar (weak eta) particle. If its mass is 2m /sub e/ it decays chiefly into two gammas. Axion production proceeds in completion with the production of particles such as gammas, pions, etc. Axion searches have been performed by different groups. We briefly summarized the results