An earlier measurement of the ${\rho }^0$ mass in the nuclear medium, reported by the TAGX Collaboration, indicated a substantial mass reduction of $\delta m_{{\rho }^0}=160\mathrm{}\mathrm{MeV}{/c}^2$ in the ${}^3\mathrm{He}(\gamma ,{\pi }^{+}{\pi }^{-})$ reaction. In this Letter, we report the reanalysis of previously published data for the same reaction at lower photon energies, $E_{\gamma }=380\mathrm{}–700\mathrm{MeV}$, which lie below the ${\rho }^0\to {\pi }^{+}{\pi }^{-}$ detection threshold unless the ${\rho }^0$ mass is significantly modified by the nuclear medium. We find the resulting mass shift in this region to be even larger, $\delta m_{{\rho }^0}=280\mathrm{}\pm 40\mathrm{MeV}{/c}^2$, consistent with ${\rho }^0$ decay in the field of the nucleon as the dominant effect.

• Received 8 December 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.5285