Proton/Pion ratios in \Delta\phi with respect to a jet in sqrt{s_{NN}} =200 GeV Au+Au collisions at STAR

TL;DR

This study investigates proton to pion ratios in jet-related correlations in high-energy gold-gold collisions, revealing medium effects and production mechanisms like coalescence, using jet reconstruction and particle identification techniques.

Contribution

It introduces a method to analyze particle ratios in jet and recoil regions in heavy-ion collisions, providing insights into medium modifications and particle production mechanisms.

Findings

Proton/pion ratios are enhanced at intermediate P_T in central collisions.

Jet-related particle ratios differ from inclusive ratios, indicating medium effects.

Reconstructed jets show similar P_T distributions as p+p jets, supporting surface bias.

Abstract

Inclusive Proton/pion ratios show an enhancement at intermediate transverse momentum (P_{T} ~ 1.5 - 4.0 GeV/c) in central sqrt{s_{NN}} = 200 GeV Au+Au collisions compared to peripheral Au+Au and p+p collisions. This effect suggests a production mechanism, different from fragmentation, which is consistent with coalescence and recombination models. A high E_{T} trigger particle selects a surface-biased jet, which is measured to have a similar p_{T} distribution as a p+p jet. This jet is used to enhance the quenching effects of the recoiling, medium traversing one. We reconstruct the trigger jet using the FASTJET algorithm, with a E_{T} (p_{T}) cut of 3.0 GeV(/c) on the towers(tracks) in order to reduce the heavy-ion collision background. The particle identification of tracks with p_{T} up to ~ 2.8 GeV/c is obtained by taking advantage of STAR TOF and TPC detectors with full azimuth coverage. Correlations in \Delta\phi between jets and identified hadrons are presented, and the particle ratios in different regions of azimuth are measured. Particle ratios associated with the trigger jet vs. the recoil jet, and comparisons to inclusive particle ratios can help to distinguish between jet-related (vacuum and medium-modified) and bulk-related contributions to the ratios enhancement.