Modification of the ρ meson detected by low-mass electron–positron pairs in central Pb Au collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mn>158</mml:mn><mml:mi>A</mml:mi><mml:mtext> </mml:mtext><mml:mtext>GeV</mml:mtext><mml:mo stretchy="false">/</mml:mo><mml:mi>c</mml:mi></mml:math>

We present a measurement of e+e− pair production in central PbAu collisions at 158AGeV/c. As reported earlier, a significant excess of the e+e− pair yield over the expectation from hadron decays is observed. The improved mass resolution of the present data set, recorded with the upgraded CERES experiment at the CERN-SPS, allows for a comparison of the data with different theoretical approaches. The data clearly favor a substantial in-medium broadening of the ρ spectral function over a density-dependent shift of the ρ pole mass. The in-medium broadening model implies that baryon induced interactions are the key mechanism to the observed modifications of the ρ meson at SPS energy.