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

BESIII Collaboration, M. Ablikim, M. N. Achasov +644

A massless particle beyond the Standard Model is searched for in the two-body decay ${\Sigma }^{+}\to p+\mathrm{invisible}$ using $(1.0087\pm 0.0044)\times 10^{10}$ $J/\psi$ events collected…