Intersecting Storage Rings

Abstract: We present strange particle spectra and yields measured at midrapidity in $\sqrt{s}=200$ GeV proton-proton ($p+p$) collisions at the BNL Relativistic Heavy Ion Collider (RHIC). We find that the previously observed universal transverse mass (${m}_{T}\ensuremath{\equiv}\sqrt{{{p}_{T}}^{2}+{m}^{2}}$) 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 \ensuremath{\Lambda} and \ensuremath{\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 $\ensuremath{\langle}{p}_{T}\ensuremath{\rangle}$ 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.