Search for a Light Pseudoscalar Particle in the Decay ${K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}X$

Search for a Light Pseudoscalar Particle in the Decay $K_{L}^{0} \to π^{0} π^{0} X$

Y. C. Tung et al. (E391a Collaboration)

Phys. Rev. Lett. 102, 051802 – Published 5 February 2009

Abstract

We performed a search for a light pseudoscalar particle $X$ in the decay $K_{L}^{0} \to π^{0} π^{0} X$ , $X \to γ γ$ with the E391a detector at KEK. Such a particle with a mass of $214.3 MeV / c^{2}$ was suggested by the HyperCP experiment. We found no evidence for $X$ and set an upper limit on the product branching ratio for $K_{L}^{0} \to π^{0} π^{0} X$ , $X \to γ γ$ of $2.4 \times 10^{- 7}$ at the 90% confidence level. Upper limits on the branching ratios in the mass region of $X$ from 194.3 to $219.3 MeV / c^{2}$ are also presented.