Experimental Search for a Low-Mass Scalar Boson

Two experiments are reported in which a search was made for the scalar boson predicted to be produced in the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(6.05 MeV) to ground state and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(20.2 MeV) to ground state $0^{+}$ to $0^{+}$ transitions with subsequent in-flight decay into electron-positron pairs. Taken together, our results show that the light scalar boson proposed by Sundaresan and Watson to account for certain muonic x-ray energy discrepancies cannot have a mass in the range $1.030<~m<~18.2$ MeV.