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Away-side Modification and Near-side Ridge Relative to Reaction Plane

Away-side Modification and Near-side Ridge Relative to Reaction Plane at 200 GeV Au+Au Collisions. Aoqi Feng for the STAR Collaboration. Purdue University Institute of Particle Physics, Wuhan, China

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Away-side Modification and Near-side Ridge Relative to Reaction Plane

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  1. Away-side Modification and Near-side Ridge Relative to Reaction Plane at 200 GeV Au+Au Collisions Aoqi Feng for the STAR Collaboration Purdue University Institute of Particle Physics, Wuhan, China Lawrence Berkeley Lab, Berkeley QM2008, Jarpur, India Feb. 5th, 2008

  2. Outline • Motivation • Di-hadron correlation wrt reaction plane • Summary • Previous key measurements of di-hadron corr. • Path-length effect study via di-hadron corr. • Away-side discussion. • Near-side discussion.

  3. Motivation: the Away-side Modification • High pT di-hadron suppression • partonic energy loss. PRL 90 (2003) 082302 • Low pT di-hadron correlations • strong jet-medium interaction PRL 95 (2005) 152301 • High pT di-hadron correlations (w.r.t RP) path-length dependent jet quenching. Jet quenching: energy loss is path-length dependent. PRL 93 (2004) 252301

  4. 6 5 4 3 2 1 Motivation: the Near-side Ridge Au+Au 0-10% STAR preliminary Ridge (long range correlation in Dh)is observed on the near-side. The underlying physics is not understood yet! To gain more insights into the away-side modification and near-side ridge, we study RP dependence. Out-of-plane Non-central collision (20-60%): overlap region like almond. select trigger particle direction relative to reaction plane. In-plane

  5. Flow Background Subtraction Ref: Phys. Rev C 69, 021901, 2004 (1) VnR is the trigger flow in the angular slice R. , (2) The contribution from v4 terms is about 10%, can not be neglected!

  6. in-plane fS=0o out-of-plane fS=90o φS: the angle between trigger particle and reaction plane. Results: Correlations v.s. Reaction Plane 0.15 Histograms: v2 uncertainty. Red curves: dAu data 3<pTtrig<4GeV/c, 20-60% 0.5 1.0 Away-side: Evolves from single- to double-peak. Near-side: Amplitude drops. 1.5 STAR Preliminary 2.0 3.0 GeV

  7. in-plane fS=0 out-of-plane fS=90o Mid-Central v.s. Central Collisions Comparison 3<pTtrig<4GeV/c & 1.0<pTasso<1.5GeV/c STAR Preliminary 20-60% STAR Preliminary top 5% • In 20-60%, away-side evolves from single-peak (φS =0) to double-peak (φS =90o). • In top 5%, double peak show up at a smaller φS. • At large φS, little difference between two centrality bins.

  8. Slice 1: similar to dAu in 20-60% broader than dAu in 5%. Slice 6: no much difference in two centrality bins. Path-length effect Focus On Away-side: Broadness 3<pTtrig<4,1.0<pTasso<1.5GeV/c v2 sys. error RMS v2{RP} v2{4} STAR Preliminary 3<pTtrig<4GeV/c Slice 1: remains constant. not much broader than dAu. Slice 6: higher than slice1. increase with pTasso. Double peak: strongest when more out-of-plane and associate particle is harder.

  9. Focus On Away-side: Amplitude πregion 3<pTtrig<4,1.0<pTasso<1.5GeV/c double peak 20-60% top 5% STAR Preliminary πregion: drops with φs, similar between the two centrality bins. double peak region: constant over φs. top 5% > mid-central.

  10. in-plane fS=0 out-of-plane fS=90o jet ridge 3<pTtrig<4, 1.5<pTtrig<2.0 GeV/c Ridge STAR Preliminary Jet Focus On Near-side 3<pTtrig<4, 1.5<pTtrig<2.0 GeV/c Amplitude seems to change, whereas naively little modification is expected. Ridge part: ||>0.7, flow background subtracted. • Jet part: acceptance factor • Raw(| |<0.7) - C×Raw(| |>0.7) • Correlation in .

  11. Jet and Ridge Yield 3<pTtrig<4, 1.5<pTtrig<2.0 GeV/c jet part, near-side ridge part, near-side jet part, near-side ridge part, near-side 20-60% top 5% STAR Preliminary Ridge: seem to decrease with φs . More significant in 20-60% than top 5%. Jet: seem to slightly increase with φs . Strong near-side jet-medium interaction in reaction plane, generating sizable ridge? Minimal near-side jet-medium interaction perpendicular to reaction plane?

  12. STAR Preliminary Ridge In Two Centralities 3<pTtrig<4GeV/c 4<pTtrig<6GeV/c At φS=0o: Ridge yields are similar in two centralities. Collision geometry? Gluon density?

  13. Summary • Both near- and away-side are modified. The modification depends on the trigger particle direction relative to RP. • Away-side: ==>path-length dependence of jet quenching. • Near-side: ==> near-side strong jet-medium interaction in-plane. collision geometry? Gluon density effect? • In 20-60%, it evolves from single peak (φs =0o) to double peak(φs =90o). • In top 5%, double peak shows up at a small φs . • At large φs , little difference between the two centralities. • Ridge drops with φs , Jet slight increase. • At φs =90o, there appears small or no ridge in 20-60%. • At φs =0o, strong ridge generation.

  14. Thank you!

  15. backup

  16. Flow Background Estimation Flow background is suggested to be: (Phys. Rev C 69, 021901, 2004) (1) (2) (3)

  17. Something Relative to the Analysis • Determination of Event Plane: • modified reaction planereduce non-flow effect; • associate pT range excluded avoid auto-correlations. • Corrections to raw correlation function: • tracking efficiency is corrected for the associated particles; • 2-particle acceptance is corrected for by the event-mixing technique. • Systematic errors: • v2: average v2 as default results, v2_{4} and v2_{RP} as sys. estimation. • resolutions: random sub-event and charge sign sub-event. • B: from 3 different fitting methods.

  18. Systematics Errors • From v2 use v2_{EP}, average v2 and v2_{4} to estimate. • From event plane resolution it’s smaller than that from v2. • From B 2, 4 and 6 lowest data points are used to get 3 B values.

  19. Define: Y= Raw/F = (J+B*F)/F = B+ J/F Fitting Method J: jet signal F: [1+2v2trig,Rv2assocos(2Δφ)] Real Flow: B*F = B* [1+2v2trig,Rv2assocos(2Δφ)] Raw: raw signal = J+B*F Find 2(4/6) continuous lowest points as the fitting range.

  20. Raw signal/(1+2*v2*v2*cos(2*dphi)) 2 points 4 points 6 points

  21. 4<pTtrig<6 GeV/c, 20-60%

  22. 3<pTtrig<4GeV/c, top 5%

  23. 4<pTtrig<6GeV/c, top 5%

  24. Two Methods: Consistent

  25. Ridge Comparison 3<pTtrig<4, 1.5<pTasso<2.0GeV/c 4<pTtrig<6, 1.5<pTasso<2.0GeV/c

  26. dPhi x dEta and Projection

  27. Jet width

  28. Details Near-side amplitude: |Δφ|<0.52 (-30o,30o) πregion: 2.75<Δφ<3.53 (180o-22.5o,180o+22.5o) Double-peak region: 1.44<Δφ<2.49 and 3.80< Δφ<4.84 (82.5o,112.5o) and (217.5o,277.5o)

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