mTDependence of Boson Interferometry in Heavy Ion Collisions at the CERN SPS

Universal pion freeze-out phase-space density

“…If only the contamination by weak decay products were to explain the difference between λ −− (NA44) and λ ++ (NA44), as suggested by NA44 [9], then the contamination effect itself on λ ++ (NA44) should be quite strong, probably on the order of 10%. After shifting the NA44 results up by this ad hoc 10% correction, as shown in Fig.…”

“…Since there are more hyperons (Λ, Σ, Ξ) than antihyperons in the fireball which produce more negative than positive pions, the measurement of λ with positive pions is less affected and should be more reliable. Note that NA44 indeed reported [9] significantly different results: λ −− ≈ 0.52 ± 0.03 and λ ++ ≈ 0.66 ± 0.04, the difference being mostly reproduced in a detector simulation with the RQMD event generator, and thereby traced to the weak decay asymmetry.…”

“…We have calculated f (p T , y) for the S-S, S-Cu, S-Ag, S-Au, S-Pb and Pb-Pb data from the experiments NA35 [6], NA49 [7,8], and NA44 [9], and for the π-p data from the NA22 experiment [10] (all at the CERN SPS). The projectile energies were 200 GeV per nucleon in S-nucleus collisions, 158 GeV per nucleon in Pb-Pb collisions and 250 GeV in π-p collisions, which correspond to projectile rapidities 6, 5.8 and 8.2, respectively.…”

“…(ii) Corrections for Coulomb repulsion of like-sign pions play an important role in the Bose-Einstein correlation analysis, in particular in the measurement of λ. Certain sophisticated Coulomb correction methods have been applied [6,8,9,11,12], but not to all the data sets, as we shall discuss below.…”

“…Sophisticated Coulomb correction methods lead to higher λ measurements than the "old" Gamov correction. This effect seems to be around 5-15% for Pb-Pb data [8,9], and should be lower for S-nucleus data [12,11], probably 0-10%, depending on the way the normalization has been done [6,11,12]. Note that the Pb-Pb data have been Coulomb-corrected in the appropriate way, while the S-nucleus data were only Gamov corrected, which might be the reason for the discrepancy seen in Fig.…”