Study of diffraction dissociation in 19- and 28-GeV/cpdinteractions

Abstract

The reaction $pd\ensuremath{\rightarrow}{p}_{\mathrm{spec}}p{\ensuremath{\pi}}^{\ensuremath{-}}p$ is studied at 19 and 28 GeV/c with data from the Brookhaven National Laboratory 80-in. deuterium-filled bubble chamber. In addition, a separate study is made of the low-momentum pion spectra in selected low-multiplicity events presumed to be associated with either of two isospin-conjugate modes of deuteron fragmentation by a 28-GeV/c beam proton. Our results from these complementary studies are that low-multiplicity channels are dominantly of a diffractive nature; however, significant differences seen in the mass spectra and angular correlations in the slow $p\ensuremath{\pi}$ between the 19- and 28-GeV/c data indicate that asymptotic behavior has not been reached, as least at 19 GeV/c. Neither $s$- nor $t$-channel helicity conservation is seen in the excitation of the target neutron into a low-mass $p{\ensuremath{\pi}}^{\ensuremath{-}}$ system. The ${N}^{*}(1.4)$ of missing-mass experiments is shown to be a superposition of nucleon-pion and nucleon-two-pion states.