The reactions pp -» iV* ++ (1238)rc and pn-*N*~~(1238)p at 2.8 GeV/c incident laboratory momentum are analyzed with the Brookhaven National Laboratory 20-in. bubble chamber. Isobar and anti-isobar production differential cross sections and decay angular distributions are compared with the predictions of an absorptive single-pion-exchange model. The absolute values, shapes, and ratios of the cross sections are in good agreement with the theory when the absorptive parameters 71 and 72 are 0.033 and 0.016 for the pn reaction, and 0.057 and 0.019, respectively, for the pp reaction.T HE observed peripherally of reactions producing quasi-two-body final states in particle collisions at high energies indicates the importance of singleparticle-exchange mechanisms. Experimental results for a variety of reactions are in general agreement with the predictions of a single-pion-exchange model in which effects of absorption due to competing interaction channels in the initial and final states are included. 1 A comparison of isobar and anti-isobar production in pp and pn collisions provides a further test of this model in that it includes the added absorptive effects of the annihilation channels in the pn reaction. For, while the absorption reduces cross sections of both pp and pn reactions leading to quasi-two-body final states, the model predicts a stronger absorption of low partial waves for the pn than for the pp interactions; in consequence, anti-isobar production shows a more collimated forward differential cross section and an additional reduction of total cross section over that for isobar production. Since the isospins of the two reactions reported here differ only in the sign of the third component, the two channels can be compared directly.In this paper we present an analysis of 1302 events of the type pp->pw + n and 944 events of the type pn^-^p^pip),where (p) represents the spectator proton of the deuteron. An account of the pp reaction at 2.8 GeV/c has been published 2 ; the data are presented here in a form suitable for comparison with the predictions of the absorptive one-pion-exchange model. The pn sample was obtained from approximately 15 000 three-and four-prong events observed in the deuteriumfilled 20-in. bubble chamber exposed to 2.8-GeV/c antiprotons at the Brookhaven alternating gradient synchrotron. We shall discuss only those events with at [Phys. Rev. 139, B428 (1965)] in which experimental results on several different quasi-two-body reactions are compared with the predictions of an absorptive single-particle-exchange model. 2 W. J. Fickinger, E. Pickup, D. K. Robinson, and E, O. Salant, Phys. Rev. 125, 2082 (1962). 162 least one proton of momentum less than 200 MeV/c, a range in which the impulse approximation appears valid by comparison of the proton momentum distribution with that predicted by the Hulthen wave function. 3 For the purpose of analysis the proton with lower momentum was chosen as the "spectator." Total cross sections have been computed using all events. In Figs. 1 (a) and 1 (b) are sho...
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The properties of the K* (895 MeV) and N* (1238 MeV) resonances produced in the reaction K + p -> K°ir + p at 2.26 BeV/c are studied. The production of one or the other of these resonances is found to occur in this channel 80% of the time. The decay correlations of the K* and N* indicate that the dominant mechanism involved in their production may be single-vector-meson exchange. In particular, the decay angular distributions of the N* are in good agreement with the predictions of the Stodolsky-Sakurai model. The experimental differential cross sections for production of each of these resonances are also compared with theoretical predictions based on a single-meson-exchange model which includes the effects of absorption due to competing channels. The agreement of the data with the theory is found to be only moderate here.
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