Experimental study of pp eta dynamics in the pp ---> pp eta reaction
Jul, 2003Citations per year
Abstract:
A high statistics measurement of the pp --> ppeta reaction at an excess energy of Q = 15.5 MeV has been performed at the internal beam facility COSY-11. The stochastically cooled proton beam and the used detection system allowed to determine the momenta of the outgoing protons with a precision of 4 MeV/c (sigma) in the center-of-mass frame. The determination of the four-momentum vectors of both outgoing protons allowed to derive the complete kinematical information of the ppeta-system. An unexpectedly large enhancement of the occupation density in the kinematical regions of low proton-eta relative momenta is observed. A description taking the proton-proton and the eta-proton interaction into account and assuming an on-shell incoherent pairwise interaction among the produced particles fails to explain this strong effect. Its understanding will require a rigorous three-body approach to the ppeta system and the precise determination of contributions from higher partial waves. We also present an invariant mass spectrum of the proton-proton system determined at Q = 4.5 MeV. Interestingly, the enhancement at large relative momenta between protons is visible also at such a small excess energy. In contrast to all other determined angular distributions, the orientation of the emission plane with respect to the beam direction is extracted to be anisotropic.Note:
- Dedicated to Adam Strzalkowski on the occasion of his 80th birthday •
- 18 pages, 27 figures, submitted to Phys. Rev. C Journal-ref: Phys. Rev. C 69 (2004) 025203
- p p: inelastic scattering
- eta: hadroproduction
- channel cross section: momentum transfer
- Dalitz plot
- three-body problem
- p: momentum spectrum
- partial wave analysis
- mass spectrum: (2p)
- angular distribution
- mass spectrum: missing-mass
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