Measurement of Form Factors for the Decay {eta}{sup '} {yields} {eta}{pi}{sup -}{pi}{sup +}

Form factors measured for the decay {eta}{sup '} {yields} {eta}{pi}{sup -}{pi}{sup +} in {pi}{sup -}A {yields} {eta}{sup '}{pi}{sup -}A{sup *} reactions at a beam momentum of p{sub {pi}} = 28 GeV are presented. The distribution in Dalitz variables for 7000 decay events is described well within a linear and a nonlinear parametrization of the relevant matrix element. The slope parameter in the variable y differs from zero significantly. It is Re{alpha} = -0.072 {+-} 0.012(stat.) {+-} 0.006(syst.) in the linear and a = -0.120 {+-} 0.027(stat.) {+-} 0.015(syst.) in the nonlinear parametrization. In this decay, the C-violation parameter is compatible with zero, c = 0.021 {+-} 0.024.