Abstract
We report the first search for the $K_L \to \pi^0 \gamma$ decay, which is forbidden by Lorentz invariance, using the data from 2016 to 2018 at the J-PARC KOTO experiment. With a single event sensitivity of $(7.1\pm 0.3_{\rm stat.} \pm 1.6_{\rm syst.})\times 10^{-8}$, no candidate event was observed in the signal region. The upper limit on the branching fraction was set to be $1.7\times 10^{-7}$ at the 90\% confidence level.
Highlights
We report the first search for the KL → π0γ decay, which is forbidden by Lorentz invariance, using the data from 2016 to 2018 at the J-PARC KOTO experiment
The E949 experiment at BNL searched for the Kþ → πþγ decay and set an upper limit on the branching fraction to be 2.3 × 10−9 [6] at the 90% confidence level (C.L.); no measurements have been made for neutral kaons
Photons in the beam were removed by a 35-mm-thick lead plate placed in the upstream, and charged particles were removed by a sweeping magnet
Summary
We report the first search for the KL → π0γ decay, which is forbidden by Lorentz invariance, using the data from 2016 to 2018 at the J-PARC KOTO experiment. KL → π0γ threatens Lorentz invariance and gauge invariance [1]. Such restrictions on KL → π0γ provide the opportunity to search for new physics beyond the standard model (SM). The E949 experiment at BNL searched for the Kþ → πþγ decay and set an upper limit on the branching fraction to be 2.3 × 10−9 [6] at the 90% confidence level (C.L.); no measurements have been made for neutral kaons
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