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A massless particle beyond the Standard Model is searched for in the two-bodydecay $\Sigma^+\rightarrow p+{\rm invisible}$ using$(1.0087\pm0.0044)\times10^{10}$ $J/\psi$ events collected with the BESIIIdetector at the BEPCII collider. No significant signal is observed, and theupper limit on the branching fraction $B(\Sigma^+\rightarrow p+{\rminvisible})$ is determined to be $3.2\times10^{-5}$ at the 90% confidencelevel. This is the first search for a flavor-changing neutral current processwith missing energy in hyperon decays which plays an important role inconstraining new physics models.

Search for a massless particle beyond the Standard Model in the $\Sigma^+\rightarrow p+{\rm invisible}$ decay