Production of strange particles at intermediate pT at RHIC

Abstract

The recombination model is applied to the production of $K, ϕ, Λ$ and $Ω$ at all $p_T$ in central Au+Au collisions. The thermal-shower component of the recombination is found to be important for $K$ and $Λ$, but only in a minor way for $ϕ$ and $Ω$ in the intermediate to high $p_T$ region. The normalization and inverse slope of the thermal partons in the strange sector are determined by fitting the low-$p_T$ data. At higher $p_T$ the data of $K, ϕ, Λ$ and $Ω$ in the log scale are all well reproduced in our study that extends the thermal contribution and includes the shower contribution. The calculated result on the $Λ/K$ ratio rises to a maximum of around 2 at $p_T\approx 4$ GeV/c, arching over the data in linear scale. The production of $ϕ$ and $Ω$ are shown to arise mainly from the recombination of thermal partons, thus exhibiting exponential $p_T$ dependences in agreement with the data. Their ratio, $R_{Ω/ϕ}$, rises linearly to $p_T\approx 4$ GeV/c and develops a maximum at $p_T\approx 5.5$ GeV/c. It is argued that the $p_T$ spectra of $ϕ$ and $Ω$ reveal directly the partonic nature of the thermal source that characterizes quark-gluon plasma. Comments are made on the $Ω$ puzzle due to the simultaneous observation of both the exponential behavior of the $Ω$ spectrum in $p_T$ and the existence of low-$p_T$ particles associated with $Ω$ as trigger.