Mass of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$

The ground state Q value of the reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^7$Li, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$${)}^{57}$Cu has been measured [Q=-29.564(50) MeV]. The cross section for this reaction was found to be 130(30) nb/sr at 5.0 deg in the laboratory. This is the first report of the use of the ${(}^7$Li${,}^8$He) reaction and the first measurement of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ mass excess. The deduced ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ atomic mass excess is -47.35(5) MeV. The implications of this result with respect to Coulomb displacement energy anomalies and nucleosynthesis of elements with A>56 by the rp process are discussed.