Isospin 2 $\pi\pi$ phase shifts from an experiment $\pi^{+}$p$\rightarrow\pi^{+}\pi^{+}$n at at 12.5 GeV/c

Abstract

The I=2 s- and d-wave pi pi phase shifts delta /sub s//sup 2/ and delta /sub d//sup 2/ have been determined in the pi pi mass region from 500-1500 MeV, using a sample of 17500 events pi /sup +/p to pi /sup +/ pi /sup +/ from a spark chamber experiment. For this purpose the moments of the pi pi angular distribution in the s-channel helicity frame have been written as bilinear expressions of OPE amplitudes modified by absorption and have been fitted to the measured values of the moments in four mass bins of width 0.25 GeV/c/sup 2/. The value of delta /sub s//sup 2/ in the rho -mass region ( delta /sub s//sup 2/ approximately=-15.5 degrees ) corresponds to an elastic cross-section of approximately=7.5 mb. The values of delta /sub d//sup 2/ are about a factor of 10 smaller than the corresponding values of delta /sub s//sup 2/ for the whole mass region considered. (5 refs)