Thesis: Pion, Kaon, Proton and Antiproton Spectra in d+Au and p+p Collisions at $\sqrt{s_{NN}}$= 200GeV at the Relativistic Heavy Ion Collider

TL;DR

This study reports on the spectra of pions, kaons, protons, and antiprotons in p+p and d+Au collisions at 200 GeV, revealing differences in particle production and nuclear modification factors, and discusses the underlying mechanisms of the Cronin effect.

Contribution

First detailed measurement of identified particle spectra in d+Au collisions at RHIC, analyzing the particle species dependence of the Cronin effect and the role of initial and final state effects.

Findings

Spectra are harder in d+Au than p+p collisions.

Protons' nuclear modification factor rises faster than pions and kaons.

The baryon-to-hadron ratio in d+Au is lower than in Au+Au, indicating final state effects.

Abstract

Identified mid-rapidity particle spectra of $\pi^{\pm}$, $K^{\pm}$, and $p(\bar{p})$ from 200 GeV p+p and d+Au collisions are reported. This data were taken in 2003 run from the Solenoidal Tracker at RHIC (STAR) experiment. A time-of-flight detector based on multi-gap resistive plate chamber (MRPC) technology is used for particle identification. The intrinsic timing resolution 85 ps was achieved after the calibration. We observe that the spectra of $\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$ are considerably harder in d+Au than those in p+p collisions. In $\sqrt{s_{_{NN}}} = 200$ GeV d+Au collisions, the nuclear modification factor $R_{dAu}$ of protons rise faster than those of pions and kaons. Besides, the particle-species dependence of the Cronin effect is observed to be significantly smaller than that at lower energies. The ratio of the nuclear modification factor ($R_{dAu}$) between $(p+\bar{p})$ and charged hadrons ($h$) in the transverse momentum range $1.2<p_{T}<3.0$ GeV/c is measured to be $1.19\pm0.05$(stat)$\pm0.03$(syst) in minimum-bias collisions and shows little centrality dependence. The yield ratio of $(p+\bar{p})/h$ in minimum-bias d+Au collisions is found to be a factor of 2 lower than that in Au+Au collisions, indicating that the relative baryon enhancement observed in heavy ion collisions at RHIC is due to the final state effects in Au+Au collisions. The mechanism for Cronin effect is also discussed in this thesis by comparison with the recombination model and with the initial multiple parton scattering model. From the comparisons, we conclude that the Cronin effect in 200 GeV d+Au collisions is not initial state effect only, and that final state effect plays an important role.