Systematic investigation of two-pion correlations at the AGS Original Research Article

We summarize recent HBT results from the Henry Higgins and Forward Spectrometers of BNL E866. These measurements are for pions of both signs in the mid- and forward-rapidity regions, 1.2 < Y < 2.3, for a range of mean pair momenta, 0.1 < kT < 0.5, spanning the full range of system-size and centrality from peripheral Si+Al to central Au+Au. All particles are identified as pions by time-of-flight to better than 3σ. Source radii are fit using Bertsch-Pratt and Yano-Koonin parameterizations. The transverse momentum dependences imply transverse expansion in all systems. The radii scaling with centrality is consistent with both geometric and freeze-out interpretations. Comparisons to geometric overlap of the projectile-target system also give evidence for expansion. Emission durations are in the range, 2–4 fm/c, and for the first time show a linear correlation with geometric size.