New approach to finding invisible states in $e^+e^-$ annihilation and application to BESIII data

Abstract

We compare precision $e^+e^-$ to $\mu^+\mu^-$ cross section measurements by BESIII in the E_cm =3.8-4.6 GeV range, to predictions based on measured R_had data. The consistency is poor (p-value <0.012). Allowing for resonance contributions not seen in R_had gives an excellent fit, with the state at 4421 MeV ( 4.6 sigma) giving insight into the psi(4415) and the 3.1 sigma structure at 4211 MeV, if confirmed, being a new, very narrow resonance. This analysis shows the power of precision $e^+e^-$ to $\mu^+\mu^-$ measurements to uncover or probe otherwise difficult to access states.