Kinematically complete measurement of the reactionπ−p→π+<

Abstract

The first kinematically complete, good-statistics data for the {n.ln) reaction on the proton are presented. They involve double-and triple-differential cross sections as well as K^7t~ angular correlations. At energies around the A resonance, they exhibit a marked difference from phase space. The data are qualitatively described within the framework of an extension of Weinberg's effective chiral Lagrangian.PACS numbers: 13.75.Gx, lI.40.Fy, 13.75.LbThe nN interaction at medium energies is beyond the scope of perturbative QCD, since it is dominated by confinement. However, on a less fundamental level, the symmetries of QCD guide the formulation of effective Lagrangians. Among other symmetries, the importance of chiral symmetry has been increasingly realized in recent years.' The resulting chiral Lagrangians involve highly nonlinear contributions in the pion field, as already realized in the nonlinear <T model ^ and extended later on by Weinberg to low-energy ;rA^ scattering. ^ A natural testing ground of the nonlinear nN dynamics, and thus of the underlying chiral symmetry, should be the excitation of multipion states. The most elementary process is the pion-induced {IK) production on the nucleon. Attempts to extract information on chiral symmetry from these reactions reach back to Olsson and Turner."* Recently, with the formulation of different theoretical approaches to the (n,2n) reaction, both on the nucleon^ and on nuclei,^ the need for exclusive data has been emphasized repeatedly.The reaction K~p-^ K^K~n has been measured in previous experiments in the low-energy region, but no kinematically complete data, with good statistics, covering a reasonable part of the phase space have yet been published. Bubble-chamber experiments^ delivered less than 100 kinematically complete events below ^c.m. = 1400 MeV. Other experiments^'^ achieved good statistics, but no kinematical completeness, and therefore only provide total cross sections as well as single-and double-differential cross sections. The OMICRON experiment'^ provides exclusive data, but suffers from medium statistics.In this Letter, we present the first experiment, which provides full-kinematics, high-statistics data for the reaction n~p-^ n^K~n, slightly above the (3,3) resonance, spread over a reasonable part of the phase space (preliminary data were already presented in Ref. 11).The experiment was performed at the KM 1 channel of

Summary of π-π scattering experiments

“…Several experiments presently under way at TRIUMF and LAMPF are expected to yield new results shortly, on both exclusive and inclusive cross sections in the (+−n), (++n), (+0p) and (−0p) channels. We also note the high-statistics angular correlation measurements in the (+−n) channel performed by the Erlangen group, who did not report total cross sections [25].…”