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The total cross section for the reaction pp-*ppn Q was measured at nine center-of-mass energies from 1.5 to 23 MeV above threshold. The experiment was carried out with the Indiana Cooler, a recently constructed storage ring. The experimental advantages of an electron-cooled proton beam were utilized. The data cover an energy range where only the lowest possible angular momentum state contributes in the exit channel. The measured energy dependence of the total cross section is not compatible with that predicted by models of s-wave pion production and rescattering. PACS numbers: 25.10,+s, 13.75.Cs, 21.30.+y, 29.25.Fb Meson-exchange models of the nucleon-nucleon (AW) interaction above the pion threshold rely on detailed information about the strongly coupled inelastic channels which must be treated coherently with the elastic interaction. Information on pion production in the NN system is also required in models of pion production or absorption in nuclei. Customarily, the partial waves in the exit channel of NN-* NNK reactions are labeled by Ll, where L is the angular momentum of the nucleon pair and / is the angular momentum of the pion with respect to the nucleon pair. l Within 100 MeV of threshold, because of the short range of the interaction, only Ss, Sp, Ps, and Pp final states contribute significantly; within 25 MeV the Ss configuration should dominate. In addition, the Sp final state is forbidden in the pp-* ppn° reaction.In the pp-^ppK° reaction, the normally dominant pion production via an intermediate A7V system is suppressed, since the N and the A cannot be in a relative S state. The rescattering contribution is also small because the dominant isovector part of low-energy nN scattering cannot contribute. Thus, near threshold, the pp-*ppn° reaction is dominated by the direct-production Born term. 2 The energy dependence of the cross section is customarily expressed in terms of n, the largest possible center-of-mass pion momentum (with nucleons at rest relative to each other) divided by the pion mass. Based on phase-space arguments, the assumption of r/ o)-This should greatly simplify the theoretical interpretation of the data. The experiment described here is the first to cover this energy range. Previous experiments were hampered by the fact that the cross section (due to the suppressed resonant production) is small and competes with background caused by nuclei other than hydrogen in the path of the beam. Because of the properties of the novel experimental environment described below, it becomes feasible to measure the four-momenta of both outgoing protons, making it possible to comple...

Measurements of 20 vector and tensor spin observables in d-p elastic scattering at a deuteron bombarding energy of 1.6 GeV (800 MeV equivalent proton beam energy) are reported. Of these 10 are two-spin observables and the remaining ten are three-spin observables. The twospin observables, six of which have been measured for the first time, were measured in the four-momentum-transfer range 0.12 to 0.85 (Gev/c) . The three-spin observables, of which eight were measured for the first time, were measured in the momentum-transfer range 0.2 to 0.85 (GeV jc) . The magnitude of the average vector polarization of the deuteron beam was 0.3, and of the average tensor alignment was 0.85. A frozen spin-polarized proton target was utilized for these measurements. These results are compared with previous measurements when possible, and show a general agreement. They are also compared with the predictions of the relativistic-impulse approximation, and its modified version, which takes into account a nontrivial oR'-mass-shell behavior of nucleon-nucleon scattering amplitudes. I. MOTIVATIONAmong all possible proton-nucleus elastic-scattering reactions, the p-d reaction at intermediate energies [i.e., I GeV equivalent proton beam energy (EPBE)j is a particularly rich source of information. Data from this reaction may be used to study aspects of the structure of the deuteron and to probe features of the nucleon-nucleon (N X) interaction -that do not play a role in elastic N scattering. The p-d reaction is especially interesting for the following reasons:Because of the comparatively simple structure of the deuteron, a relatively complete theoretical treatment of the scattering process is feasible.Due to the spin &-1 structure of the p-d system and availability of both polarized proton and polarized deuteron beams and targets, a large number of spin observables may be measured in scattering experiments.In the past few years, a number of p-d elastic scattering spin observables have been measured at intermediate energies, particularly at 800 MeV EPBE. A prime objective of those measurements and the present measurement is to obtain a sufFiciently large number of independent p-d spin observables, measured with sufFicient statistical accuracy, to allow, in a modelindependent manner, the reconstruction of the p-d elasticscattering amplitude. At this time, we are still a long way from reaching this objective. Therefore, comparison between the experiment and the theoretical models has to be made on the level of observables rather than the scattering amplitude.In p-d scattering, in the energy range of interest, the number of partial waves involved becomes so large that solving the three-body scattering problem explicitly becomes impractical. Therefore, realistic theoretical calculations of the p-d scattering amplitude have to rely on the multiple-scattering theory, which expresses the p-d scattering amplitude in terms of N-N interactions.It has been realized, in the last few years, that in such multiple-scattering models relativistic effects pl...

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