Photoproduction of Mesons off Light Nuclei

Abstract

During the last few years, a series of experiments has been done at the ELSA accelerator in Bonn with the Crystal Barrel/TAPS setup and at the MAMI accelerator in Mainz with the Crystal Ball/TAPS setup. Photoproduction of light mesons off the deuteron and 3He‐nuclei has been studied in detail. We will report some of the most interesting results.A completely unexpected finding, is the pronounced structure in the excitation function of the γn → nη reaction around 1 GeV, which has no counterpart for the proton. Recent measurements at GRAAL, Sendai, ELSA [1] and MAMI estimate it’s width below 50 MeV, which would be extremely narrow for a nucleon resonance at this excitation energy. In the experiment with the 3He target, special attention was given to the threshold behavior of the γHe3 reactions in view of possible indications for the formation of (quasi‐)bound η‐nucleus states, so‐called η‐mesic nuclei. A very strong threshold enhancement of coherent η‐photoproduction off 3He was found. In a new experiment, this reaction was measured with much better statistical accuracy compared to an earlier experiment at MAMI‐B using the TAPS detector [2].