Physical Review C 75,6 (2007) 064901;
We present strange particle spectra and yields measured at midrapidity in root s = 200 GeV proton-proton (p + p) collisions at the BNL Relativistic Heavy Ion Collider (RHIC). We find that the previously observed universal transverse mass (m(T) = root PT2 + m(2)) scaling of hadron production in p + p collisions seems to break down at higher m(T) and that there is a difference in the shape of the m(T) spectrum between baryons and mesons. We observe midrapidity antibaryon to baryon ratios near unity for Lambda and Xi baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum < p(T)> on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared with previous measurements made at the CERN Super Proton Synchrotron and Intersecting Storage Rings and in Fermilab experiments and with leading-order and next-to-leading-order string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from p + p collisions at RHIC energies have large contributions from gluon jets rather than from quark jets.
Date of this Version