Study of the K0(L) --> pi0 pi0 nu nu-bar decay
E391a Collaboration: R. Ogata, S. Suzuki, J. K. Ahn, Y. Akune, V., Baranov, K. F. Chen, J. Comfort, M. Doroshenko, Y. Fujioka, Y. B. Hsiung, T., Inagaki, S. Ishibashi, N. Ishihara, H. Ishii, E. Iwai, T. Iwata, I. Kato, S., Kobayashi, S. Komatsu, T. K. Komatsubara, A. S. Kurilin
TL;DR
This study searched for the rare decay K0(L) --> pi0 pi0 nu nu-bar using the E391a detector, setting upper limits on its branching fraction and on related invisible decay processes, thereby constraining new physics scenarios.
Contribution
First experimental search for the K0(L) --> pi0 pi0 nu nu-bar decay, establishing upper limits on its branching fraction and on decays involving invisible particles.
Findings
Upper limit of 8.1 x 10^{-7} on the decay's branching fraction.
Set limits on K0(L) --> pi0 pi0 X decays with X invisible, depending on X mass.
Constrained possible new physics involving invisible particles.
Abstract
The rare decay K0(L) --> pi0 pi0 nu nu-bar was studied with the E391a detector at the KEK 12-GeV proton synchrotron. Based on 9.4 x 10^9 K0L decays, an upper limit of 8.1 x 10^{-7} was obtained for the branching fraction at 90% confidence level. We also set a limit on the K0(L) --> pi0 pi0 X (X --> invisible particles) process; the limit on the branching fraction varied from 7.0 x 10^{-7} to 4.0 x 10^{-5} for the mass of X ranging from 50 MeV/c^2 to 200 MeV/c^2.
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