Production of resonant particles in pion-deuteron interactions at 4 GeV/c

Abstract

From a 400K picture sample of an exposure of 4 GeV/c π(^+) mesons in deuterium, the two channels π(^+)d → P(_s)Pπ(^+)π(^-) and π(^+)d → dπ(^+)π(^+)π(^-) are examined both by mass cut techniques and by a statistical cluster searching technique in the full 3n-5 dimensional kinematic space defined by the number of final state particles (n). The clustering technique is shown to reproduce the distributions found by mass cut methods with some sharpening of the angular distributions and an increase in the statistics of the resunance signular available for analysis. The method is tested by applying it to a Monte Carlo simulated experiment and the results are shown to give a high degree of seperation of the various sub-channels. The reaction π(^+)d → p(_s)pπ(^+)π(^-), with a cross-section of 2.10 ± 0.17 mb, is seen tobe dominated by the production of the pº and fº mesons. The regions of the pº and fº mesons are examined, and their spin structures determined by density matrix element analyses. These show that at low t values there are substantial S and S+P wave components under the pº and fº respectively. The pº meson data are shown to be compatible with >90% pure pion exchange at low values of t. For the coherent reaction π+d →dπ(^+)π(^-), which is dominated by pº production and the d* effect, the cross section is seen to be 0.316 ± 0.025 mb. The d* effect is shown to be compatible with the production of an intermediate Δ state, the subsecuent decay of which leaves an intact deuteron in the final state.