We present measurements of pion transverse momentum (pt) spectra in central Si-nucleus collisions in the rapidity range 2.0 < y < 5.0 for pt down to and including pt = 0. The data exhibit an enhanced pion yield at low pt 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.
Bibliographical noteFunding Information:
We wish to thankt he BrookhavenT andema nd AGS staff for theire xcellents upporta rep articularly gratefufl or the experth elp of W. McGaherna ndD r. H. Brown. R. Hutter and J. Sonderickerp rovided importantt echnicals upport.W e thankD r. R. Mat- tie110fo r helpful discussionsF. inancials upportb y the US DOE, the NSF, the CanadianN SERC, and CNPq Brazil is acknowledged.
ASJC Scopus subject areas
- Nuclear and High Energy Physics