Measurement of Coulomb Interference in 113-Mevπ+−pScattering

Pion-proton scatterings with a small angle cutoff of 12.5° in the center-of-mass system were detected using the area-scanning, nuclear-emulsion technique. Ilford G5 plates 600 microns thick were exposed to a flux of 4.4×${10}^5$ mesons/${\mathrm{cm}}^2$ in the 122-Mev ${\pi }^{+}$ beam of the Chicago cyclotron. Various checks indicated a scanning efficiency greater than 90 percent for scatterings on the hydrogen content of the emulsion between 12.5° and 160°. Out of a total 420 hydrogen events only two scatterings were less than 20°. The data when analyzed according to the two possible sets of signs of the phase shifts give a strong preference for destructive interference, i.e., attractive $p_{\frac{3}{2}}$ interaction. In this case the maximum likelihood solution is ${\alpha }_3=-(10.9\mathrm{}\pm 2)°$, ${\alpha }_{33}=(27.0\mathrm{}\pm 1.5)°$, and ${\alpha }_{31}=-(3.2\mathrm{}\pm 1)°$ for the $s$- and $p$-wave phase shifts with no definite indication of a $d$-wave component. The total nuclear cross section is (79±5) millibarns. The mean energy of pions in the emulsion is (113.0±1.6) Mev as determined from 33 events where the proton stops in the emulsion.