Analysis Run 4 Au+Au Centrality 20-60% Divide data into twelve 15 o slices

1. Is the ridge formed by aligned jet propagation and medium flow direction? Joshua Konzer(Purdue University) (For STAR Collaboration) • Motivation • Dihadron correlation relative to reaction plane (RP) is sensitive to medium effects due to variable path length • Previous studies show medium effects on both near- and away-side correlations. • Near-side ridge decreases as trigger particle ranges from in- to out-of-plane. • Motivated by above results, Hwa et.al. conjectured that alignment of jet propagation and medium flow–Correlated Emission Model (CEM)–may be the source of the ridge. • CEM predicts an asymmetry in azimuthal correlation dependent on φs • This work is to test • the CEM prediction. • Analysis • Run 4 Au+Au • Centrality 20-60% • Divide data into • twelve 15o slices • dependent on φs(φtrig - φEP) • ranging from -90o to 90o • Trigger particles: 3-4GeV • Associate particles: 1-1.5GeV Jet-Ridge Separation Ridge: correlation at ∆η>0.7. Jet: (∆η<0.7) – Acceptance*(∆η>0.7) |∆η|<0.7 (black) |∆η|>0.7 (color) Ridge φs = 15 to 30 φs = -15 to -30 STAR Preliminary Npairs/Ntrigger Npairs/Ntrigger Jet STAR Preliminary ∆φ (radians) • v2 Background Subtraction • v2{4}: Excludes most non-flow (anything involving fewer than 4 particles Further reduced by flow fluctuations Our minimum for all pT regions • v2{2}: Includes most non-flow (near-side jet, etc.) Commonly used as a maximum correction • v2{RP}: Similar to v2{2} Our maximum for trigger pT regions • Presented improvement • v2{2D away-side} • Use away side to calculate v2{2} • Removes near-side correlation effect • v2 modulation symmetric about p/2 in 2-particle correlation • Our maximum for associate pT regions v2 Background • J.Konzer and F.Wang, arXiv:0810.3282 ∆φ (radians) |∆η|>0.7 Away-Side 2 Gauss Fit (same σ) s 1/Ntrigger dN/d(∆φ) STAR Preliminary ∆φ (radians) φs 0 to 15 φs 15 to 30 φs 30 to 45 φs 45 to 60 φs 60 to 75 φs 75 to 90 STAR Preliminary Trigger Ridge 1/Ntrigger dN/d(∆φ) Jet STAR Preliminary ∆φ (radians) Conclusions Asymmetry • Dihadron correlations with RP are analyzed, separately for each side of RP. • Ridge and jet are separated by Dh cut. • Away-side is asymmetric. • Ridge is asymmetric! • Asymmetry consistent with CEM. • Asymmetry may indicate ridge is from jet and medium flow alignment. Hwa prediction Raw Signal φs0 to 15; 0 to -15 φs30 to 45;-30 to -45 φs60 to 75;-60 to -75 A Npairs/Ntrigger STAR Preliminary Ridge Jet φs 15 to 30;-15 to -30 φs45 to 60;-45 to -60 φs75 to 90;-75 to -90 STAR Preliminary