Bochum 2009 – wissenschaftliches Programm
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HK: Fachverband Hadronen und Kerne
HK 57: Hadron Structure and Spectroscopy II
HK 57.5: Vortrag
Mittwoch, 18. März 2009, 17:30–17:45, H-ZO 30
Search for η Mesic Nuclei — •Hartmut Machner — for the GEM Collaboration, Institut für Kernphysik, FZ Jülich, Jülich, Germany
There is a long standing interest whether η mesons can be bound to nuclei. We have performed two completely different experiments to search for such exotic states. First have studied the two nucleon transfer reaction p+27Al→ 3He+π−+p+X. The experimental conditions were chosen that the 3He emitted under zero degree carries all the beam momentum, and thus the remaining system π−+p+X is at rest in the laboratory. The most probable intermediate system is η+25Al with a second step η+n→ N*(1535)→ π−+p. A peak corresponding to a binding energy of 13 MeV and a FWHM of 10 MeV was found. The cross section for the peak is 150 pb. When the back-to-back condition for the π−+p system is released a smooth spectrum is obtained.
There are indications that already 4He is heavy enough to bind the η. We studied the d + d → η + α reaction at Q=16.6 MeV using a tensor polarised beam, by measuring angular distributions of cross section and analysing power. Other groups assumed that the s-wave strength is just the total cross section divided by 4π. This assumption is not appropriate at higher energies. The analysis of the present result shows that a possible p-wave is negligibly small and that there are two d-wave contributions. The s-wave amplitude can be factorised in a production amplitude and a final state enhancement factor depending on the scattering length. We show by comparing the present results with those for 3He that the system is quasi-bound.
Supported in part by FZ Jülich, INB of BMBF and EU (FP6).