Eur. Phys. J. A (2010) 44: 7-22
https://doi.org/10.1140/epja/i2010-10924-0

Regular Article - Experimental Physics

Systematic study of the pp pp reaction

¹ Institut für Kern- und Teilchenphysik, Technische Universität Dresden, D-01062, Dresden, Germany
² Physikalisches Institut, Universität Erlangen-Nürnberg, D-91058, Erlangen, Germany
³ Institut für Kernphysik, Forschungszentrum Jülich, D-52425, Jülich, Germany
⁴ Physikalisches Institut, Universität Tübingen, D-72076, Tübingen, Germany
⁵ Institut für Kern- und Hadronenphysik, Forschungszentrum Dresden-Rossendorf, D-01314, Dresden, Germany
⁶ Soltan Institute for Nuclear Studies, 05-400, Swierk/Otwock, Poland
⁷ INFN Torino, 10125, Torino, Italy
⁸ Institut für Experimentalphysik, Ruhr-Universität Bochum, D-44780, Bochum, Germany

^* e-mail: w.ullrich@physik.tu-dresden.de

Received: 15 September 2009
Revised: 1 December 2009
Accepted: 16 January 2010
Published online: 2 March 2010

Abstract

A systematic study of the production of -mesons in proton-proton collisions was carried out in a kinematically complete experiment at three excess energies ( = 92, 128, 173 MeV). Both protons were detected using the large-acceptance COSY-TOF spectrometer at an external beam line at the Cooler Synchrotron COSY at Forschungszentrum Jülich. The total cross-section, angular distributions of both -mesons and protons were measured and presented in various reference frames such as the overall CMS, helicity and Jackson frame. In addition, the orientation of the -spin and invariant-mass spectra were determined. We observe -production to take place dominantly in Ss and Sp final states at = 92, 128 MeV and, additionally, in Sd at = 173 MeV. No obvious indication of resonant -production via N^*-resonances was found, as proton angular distributions are almost isotropic and invariant-mass spectra are compatible with phase space distributions. A dominant role of ³ P ₁ and ¹ S ₀ initial partial waves for -production was concluded from the orientation of the decay plane of the -meson. Although the Jackson angle distributions in the p-Jackson frame are anisotropic we argue that this is not an indication of a resonance but rather a kinematical effect reflecting the anisotropy of the angular distribution. The helicity angle distribution in the p-helicity frame shows an anisotropy which probably reflects effects of the angular momenta in the final state; this observable may be, in addition to the orientation of the decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.