Search for a light exotic particle in J/psi radiative decays

TL;DR

This study searches for a hypothetical light exotic particle in J/psi radiative decays using BESIII data, finding no evidence but setting upper limits on possible production rates of such particles.

Contribution

First search for light exotic particles in J/psi radiative decays with BESIII data, establishing upper limits on their production in muon pairs.

Findings

No significant mu+ mu- mass peaks observed.

Upper limits on branching fractions range from 4x10^-7 to 2.1x10^-5.

One event observed below 255 MeV/c^2 with a 213.3 MeV/c^2 mass.

Abstract

Using a data sample containing 1.06x10^8 psi' events collected with the BESIII detector at the BEPCII electron-positron collider, we search for a light exotic particle X in the process psi' -> pi^+ pi^- J/psi, J/psi -> gamma X, X -> mu^+ mu^-. This light particle X could be a Higgs-like boson A^0, a spin-1 U boson, or a pseudoscalar sgoldstino particle. In this analysis, we find no evidence for any mu^+mu^- mass peak between the mass threshold and 3.0 GeV/c^2. We set 90%-confidence-level upper limits on the product-branching fractions for J/psi -> gamma A^0, A^0 -> mu^+ mu^- which range from 4x10^{-7} to 2.1x10^{-5}, depending on the mass of A^0, for M(A^0)<3.0 GeV/c^2. Only one event is seen in the mass region below 255 MeV/c^2 and this has a mu^+mu^- mass of 213.3 MeV/c^2 and the product branching fraction upper limit 5x10^{-7}.