Search for a light pseudoscalar particle in the decay K_{L};{0}-->pi;{0}pi;{0}X

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Physics

Background:

• The HyperCP experiment suggested the existence of a light pseudoscalar particle (X).
• This particle was hypothesized to be produced in the decay of neutral kaons (K_{L}).

Purpose of the Study:

• To search for evidence of the light pseudoscalar particle X.
• To set upper limits on the branching ratio of the decay K_{L} --> pi^{0}pi^{0}X, with X decaying into gamma rays.

Main Methods:

• Utilized the E391a detector at the KEK facility for data collection.
• Analyzed K_{L} decays searching for the specific decay chain K_{L} --> pi^{0}pi^{0}X, X --> gamma gamma.

Main Results:

• No significant evidence for the existence of particle X was observed.
• An upper limit on the product branching ratio for K_{L} --> pi^{0}pi^{0}X, X --> gamma gamma was established at 2.4 x 10^{-7} (90% confidence level).
• Upper limits were also determined for particle X in the mass range of 194.3 to 219.3 MeV/c^{2}.

Conclusions:

• The experimental search did not confirm the existence of the light pseudoscalar particle X as suggested by HyperCP.
• The results provide stringent constraints on the properties and existence of such a particle within the studied mass range.