Measurements of Strange Particle Production in $p+p$ Collisions at $\sqrt{s}$= 200 GeV
STAR Collaboration, B. Abelev
TL;DR
This paper studies strange-hadron production in $\sqrt{s}=200$ GeV $p+p$ collisions at RHIC to test soft vs. hard production mechanisms. It measures identified strange-hadron spectra from $K^{\pm}$ to $\Omega^{-}+\overline{\Omega}^{+}$ at mid-rapidity and analyzes $m_T$-scaling, $dN/dy$ yields, and $\langle p_T \rangle$ as functions of particle mass and event multiplicity. By comparing with LO and NLO string fragmentation predictions and prior CERN-SPS/ISR/FNAL data, the work finds breakdown of universal $m_T$-scaling at higher $m_T$ and a difference in the spectral shapes of baryons versus mesons, with anti-baryon to baryon ratios near unity for $\Lambda$ and $\Xi$ and no $p_T$-dependence, suggesting data are not yet in a quark-jet dominated regime. The results indicate substantial gluon-jet contributions to spectral shapes and yields at RHIC energies, constraining fragmentation-based models of $p+p$ collisions and informing hadronization mechanisms. These measurements provide a benchmark for understanding strangeness production and jet flavor composition in high-energy hadronic collisions.
Abstract
We present strange particle spectra and yields measured at mid-rapidity in $\sqrt{\text{s}}=200$ GeV proton-proton ($p+p$) collisions at RHIC. We find that the previously observed universal transverse mass ($\mathrm{m_{T}}\equiv\sqrt{\mathrm{p_{T}}^{2}+\mathrm{m}^{2}}$) scaling of hadron production in $p+p$ collisions seems to break down at higher \mt and that there is a difference in the shape of the \mt spectrum between baryons and mesons. We observe mid-rapidity anti-baryon to baryon ratios near unity for $Λ$ and $Ξ$ 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 (\mpt) 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 to previous measurements from CERN-SPS, ISR and FNAL experiments and to Leading Order (LO) and Next to Leading order (NLO) 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 quark jets.