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

Using a data sample containing 1.06 x 10(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 4 x 10(-7) to 2.1 x 10(-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 mu(+)mu-mass of 213.3 MeV/c(2) and the product-branching-fraction upper limit 5 x 10(-7).