Transparency ratio in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mi>γ</mml:mi><mml:mi>A</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mrow><mml:mi>η</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>A</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:math> and the in-medium <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:msup><mml:mrow><mml:mi>η</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:math> width

The photoproduction of -mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500-2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations describing the propagation of -mesons in nuclei. The comparison indicates a width of the -meson of the order of = 15-25 MeV at = 0 for an average momentum p = 1050 MeV/c, at which the -meson is produced in the nuclear rest frame. The inelastic N cross section is estimated to be 3-10 mb. Parameterizing the photoproduction cross section of -mesons by (A) = 0 A , a value of = 0.84 0.03 has been deduced.