Violation of both s- and t-channel helicity conservation from and LPS analysis of diffraction dissociation in πp → πππp

Abstract

Conservation of helicity in the s- and t-channels has been investigated for the dissociation processes π ± → ( π ± π − π +) and p → (p π ± π −) in π −p → π − π − π +p at 16 GeV/ c and π +p → π + π + π −p at 8 and 16 GeV/ c. The method used consists of studying the modifications in the event distribution in longitudinal phase space (LPS), under rotation of all events around the z-axis in the helicity ( s-channel) and Gottfried-Jackson ( t-channel) frames. Strong violation of s-channel helicity conservation is confirmed. A small, but systematic, violation of t-channel helicity conservation is found for low (3 π) masses, but it does not seem present in the (p π + π −) dissociation. It is found experimentally that the violation is such that if the angular distribution of the decay particles were studied, this violation could be detected only when the “beam-unlike” pion is used as the analyser, the other analysers averaging out the effect.