Determination of the eta'-proton scattering length in free space
  Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton-beam of the Cooler Synchrotron COSY we determine the excitation function for the pp --> pp eta' reaction close-to-threshold. Combining these data with previous results we extract the scattering length for the eta'-proton potential in free space to be Re(a_{p eta'}) = 0+-0.43 fm and Im(a_{p eta'}) = 0.37(+0.40)(-0.16) fm. 
E. Czerwinski, P. Moskal, M. Silarski, S. D. Bass, D. Grzonka, B.   Kamys, A. Khoukaz, J. Klaja, W. Krzemien, W. Oelert, J. ...
nucl-ex