Abstract
We present measurements of pion transverse momentum ( p t) spectra in central Si-nucleus collisions in the rapidity range 2.0 < y < 5.0 for p t down to and including p t = 0. The data exhibit an enhanced pion yield at low p t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Δ resonance abundance at freeze-out. The results are consistent with a direct measurement of the Δ resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.
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