Proton-proton elastic scattering at 400 GeV/c has been measured in the region $5.4<-t<\mathrm{}14.4\mathrm{}$ Ge${\mathrm{V}}^2$ with no sign of a second dip or "break." If the data are fitted by $\exp \mathrm{}\left(\mathrm{At}\right)\mathrm{}$, the slope $A$ decreases from 1.5±0.1 to 0.7±0.2 Ge${\mathrm{V}}^{-2\mathrm{}}$ over the range. At fixed $t$ the 400-GeV/c cross sections are about 0.6 times those at 200 GeV/c in this $t$ range. At fixed ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=15\mathrm{}°$, $\frac{d\sigma }{\mathrm{dt}}\propto s^{-n}$ where $n=9.7\mathrm{}\pm 0.3$.

• Received 3 August 1978

DOI:https://doi.org/10.1103/PhysRevLett.41.924