In-medium modification of the Delta(1232) resonance at SIS energies

Abstract

From the pion production rates n_{pi} / A_{part} and the pion charge ratios R_{pi} = n_{pi^-} / n_{pi^+} and S_{pi} = n_{pi^0} / (n_{pi^-} + n_{pi^+}), measured in p + A and A + A reactions, it is concluded that the mass of the Delta(1232) resonance is reduced in dense nuclear matter. This conclusion is supported by the Delta(1232) mass distribution extracted from correlated (p,pi^{+-}) pairs and the pi^{+-} transverse momentum distributions.