Understanding the Role of Jet and Underlying Event in p+p and d+Au Collisions from PHENIX at RHIC

Abstract

Dihadron azimuthal correlation measurements have revealed striking modifications of the jets by the dense medium created in heavy-ion collisions at RHIC. One important question is to what extent the modification can be attributed to cold nuclear matter effects. In this analysis, we carried out a detailed mapping of the correlation patterns using high-statistics RUN8 d+Au minimum bias data. A striking scaling behavior of the jet pair yields is observed at low and intermediate $p_T$. The jet pair yields are found to be enhanced relative to $N_{\mathrm{coll}}$ scaled p+p jet pair yields. The nuclear modification factor for jet pair yields, $J_{\mathrm{dAu}}$, seems to scale with $p_T^{\mathrm{sum}}$= $p_T^a+p_T^b$ (scaler sum), and shows a characteristic Cronin-like enhancement at $p_T^{\mathrm{sum}}<$5-7GeV/c. Interestingly, the level of yield modifications is similar between the near- and away-side pairs, and the jet shapes are not modified relative to p+p collisions. The pedestal yield under the jet peak is studied in p+p and d+Au collisions. The pedestal yield in p+p collisions is found to be larger than PYTHIA calculations. In d+Au collisions, it is found to exceed a simple sum of one p+p jet event and ${\mathrm{N}}_{\mathrm{coll}}-1$ minimum bias p+p events. The possible interpretation of these results and their implications for Au+Au measurements are discussed.

19 pages, 14 figures, Writeup for Posters Presented at 21st International Conference On Ultra-Relativistic Nucleus-Nucleus Collisions (QM2009) 30 Mar - 4 Apr 2009, Knoxville, Tennessee

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• Highlights from PHENIX-I: Initial State and Early Times
• High $p_T$ Parton Energy Loss from Jet Pair Correlation Observables in the PHENIX Experiment