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 $N_{\rm coll}$ scaled p+p jet pair yields. The nuclear modification factor for jet pair yields, $J_{\rm dAu}$, seems to scale with $p_T^{\rm sum}$= $p_T^a+p_T^b$ (scaler sum), and shows a characteristic Cronin-like enhancement at $p_T^{\rm 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 $\rm N_{coll}-1$ minimum bias p+p events. The possible interpretation of these results and their implications for Au+Au measurements are discussed.