Study of the reactionsπ−p→π+π−n<

Abstract

We have studied the reactions r p -.rrfr-n and r -p + K ' K n at 1.98 and 2.41 GeV/c over a dimeson mass range from 0.75 to 1.23 GeV/c 2. Final-state neutrons were detected near O" corresponding to It -t,,,j < 0.003 ( G~V / C )~ near a dimeson mass of 1.0 GeV/c 2 . Charged particles were detected in the Argonne Effective Mass Spectrometer and/or scintillation detectors surrounding the hydrogen target. The mass of the dimeson was calculated from the beam and neutron four-vectors, the latter being determined by the measured flight time of the neutrons, with a mass resolution of u = 4 MeV/c 2 . One of the prominent features of the . r r f r -mass spectrum is a sharp break near 0.95 GeV/c 2 . This feature and the rapid rise of the K +K -spectrum near threshold are analyzed in terms of the parameters of the S * resonance. In the kinematic region covered by our data the contribution of the p meson is small. The 62000 r f r -events(1 1000 three-constraint and 5 1000 one-constraint) and the 470 K ' K -events (all four-constraint) were analyzed with both a Breit-Wigner and a K-matrix formulation with various parameterizations of the background. Consistent values of the S * pole parameters were obtained in all of the various types of analyses for both beam momenta. An average of the parameters from these fits gives the position of the S * pole to be (969 * 5) -i (15 % 4) MeV/c 2, compared to the present world average of (993.2 % 4.4) -i(20.0 + 3.7)MeV/c 2 .