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Back-to-Back Jets in PHENIX at RHIC by Jiangyong Jia

Explore intermediate and high pT jet correlations and shapes, reaction plane dependence, and QGP probes. Discover jet quenching, suppression near medium, and di-jet correlations in Au+Au collisions.

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Back-to-Back Jets in PHENIX at RHIC by Jiangyong Jia

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  1. Back-to-back jets in PHENIX at RHIC Jiangyong Jia Columbia University, Nevis Labs Introduction The method Intermediate pT jet correlation Jet shape Reaction plane dependence high pT jet correlation

  2. Jet Probes the sQGP (A+A) Leading hadron Induced gluon Radiation • ~collinear but broadened • “Softened” fragmentation Q2 nucl-th/0302077 decreases Jiangyong Jia

  3. Jet “quenched” by the medium pT>3,4 GeV/c p0 • Energy loss depends • on path length x4-5 suppression near • Medium-induced energy loss away Medium Jiangyong Jia

  4. Di-jet correlation are also strongly modified pT(assoc) > 2 GeV/c Pedestal&flow subtracted How opaque is the medium? What is the fate of very high pT jets? How the energy is distributed to the medium? Detailed study of intermediate and low pT correlation Correlation of high pT jets Higher pT→ Away-side suppression Lower pT→ Away-side enhancement pT(assoc) > 0.15 GeV/c Jiangyong Jia

  5. Jet properties via two particle correlation 1 dN Ntrig d p+p • Jet shape • Jet Yield • Underlying event Jiangyong Jia

  6. Underlying event in AuAu 1 dN Ntrig d elliptic flow causes another correlation in them: l(1+2v2(pTtrig)v2(pTassoc)cos(2)) combinatorial background is large in Au+Au! And is not constant! flow+jet flow jet CF = J(Df) + l(1+2v2tv2a cos2Df) Jiangyong Jia

  7. Intermediate pT Jet shape Jiangyong Jia

  8. The Correlation function 2.5-4 x 3-5 GeV/c 0-5% C(Df) 2.5-4 x 1-2.5 GeV/c PHENIX Preliminary Flat or slight dip at the away side! Small jet signal! (1/50) Shape can’t be pure di-jet broadening Jiangyong Jia

  9. Now subtract the v2 • 2v2tv2a ~ few %, thus the change in B only slightly affect subtracted away side jet shape. • Sensitive to the v2 systematic. CF = J(Df) + l(1+2v2tv2a cos2Df) • v2 background is scaled to match the correlation function (ZYAM). l Jiangyong Jia

  10. Centrality dependence of the jet shape PHENIX preliminary Jiangyong Jia

  11. Centrality dependence of the jet shape PHENIX preliminary Jiangyong Jia

  12. Centrality dependence of the jet shape D D PHENIX preliminary Away side: splitting Near side : broadening Jiangyong Jia

  13. Near side width Trigger pT = p0-hadron 2.5-4 x 2-3 GeV/c hadron-hadron Broadening is seen for pairs at intermediate pT Energy loss effect? Or baryon/meson difference? Jiangyong Jia

  14. D parameter D D Splitting Parameter D increasing with centrality Turn on in rather peripheral bins Similar trend for all systems and energies Jiangyong Jia

  15. Mach Cone? the dip? f nucl-th/0406018 Stoecker hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaney • Sound excitation at angle of cos(q)=cs/c independent of pT • Cone narrows as pT increases • Number of particles in the cone not calculated yet. • The dipness of the dip? • Sensitive to flow subtraction • Fill up can happens at both 1 and p. • Part of the jet is in ‘Underlying event’, has been subtracted out. • Jet broadening from large angle gluon emission (I. Vitev) • Deflection of jets by the flowing medium Armesto,Salgado,Wiedemann. • Cherenkov gluon radiation in medium Koch, Majumder, X.-N. Wang Jiangyong Jia

  16. Di-jet w.r.p to reaction plane Jiangyong Jia

  17. RP dependence The mixed events gives C(Df) = = x(1+b/a cos2Df) x accounts for the difference in normalization factor, in dependent of trigger direction and is close to 1. The only free parameter • Study (di)jet correlations vs angle of trigger h relative to reaction plane • J. Bielcikova et al, Phys. Rev. C69:021901, 2004 a is proportional to the N triggers in the bite Jiangyong Jia

  18. The six trigger windows used • 6 bins from 0 to /2 Jiangyong Jia

  19. Check • Constrain v2 of trigger hadron and • associated hadron simultaneously • The extracted v2 is consistent with • the RP v2 • Verification of the method! Jiangyong Jia

  20. 0-5% PHENIX preliminary PHENIX preliminary • is fixed !! v4 not included. Jiangyong Jia

  21. V2 subtracted jet yield in each trigger direction • Can study dependence of modification on overlap geometry • Can constrain the v2 Clearly the systematics dependence on trigger direction Jiangyong Jia

  22. PHENIX Preliminary 30-40% PHENIX Preliminary Jiangyong Jia

  23. RP dependence of the yield • Flow change dramatically vs trigger bin • However, the subtracted distribution agrees in errors • Shoulder and dip seen in all bins • Split caused by small v4 and small remaining v2 Jiangyong Jia

  24. Difference of di-jet yield in/out plane Bin1 - Bin6 • Differences can almost be described by the harmonics • Mainly due to residual v2 and v4 • Path length dependence of the modification should • cause the asymmetry between 0 and p. • We see hint of this for 30-40% bin. PHENIX preliminary Jiangyong Jia

  25. Let’s look at the dip again Look in bin #4 • For PHENIX reaction plane resolution & chosen bin sizes, trigger bin 4 has smallest effect from v2. • Even without subtracting flow contribution, a dip is seen for central collisions. PHENIX Preliminary Jiangyong Jia

  26. Jet correlation at High pT Jiangyong Jia

  27. Evolution of away-side jet shape Jiangyong Jia

  28. Evolution of away-side jet shape Jiangyong Jia

  29. Evolution of away-side jet shape • Jet like peak clearly visible • Near side jet yield is constant with centrality. • Suppression of awayside peak increases with centrality Look at much better data from STAR! Jiangyong Jia

  30. STAR: Di-jets at higher pT 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV/c STAR Preliminary Clear emergence of jet structure at the away-side No background subtraction! Jiangyong Jia

  31. Di-jets and the interaction mechanism Measuring Low z is necessary 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV/c • Away side jet shape not modified! • Away side jet fragmentation function is not modified but overall yield is suppressed! Jiangyong Jia

  32. Jet reappears, but still should still have significant distortion at low pTassoc. Jiangyong Jia

  33. Put things together pT(assoc) > 2 GeV/c Interaction of the jet with the flowing medium Pedestal&flow subtracted Surface emissions (again?) Higher pT→ Away-side suppression Lower pT→ Away-side enhancement pT(assoc) > 0.15 GeV/c Jiangyong Jia

  34. Summary • We studied the jet shape at intermediated pT • Near side jet is broadened • Away side jet developed shoulder and dip structure (not likely due to jet broadening.) • Requires novel mechanism? • Reaction plane dependence at intermediate pT • Supporting the away side jet shape. • Slight modification of the jet function from in plane to out of plane • High pT correlation • Jet shape and fragmentation function not modified (need soft region) • But the jet yield is reduced by factor of 5 in central AuAu collisions. • A puzzle for the community Jiangyong Jia

  35. To determine B • ZYAM will find different B in two cases. • But the true background should be same • Assuming jet width is same in same sign and opposite sign then we can determine B absolutely +- -+ ++ -- • Opposite/same sign correlation • Identical away side strength • Different near side strength • v2 contribution is identical Jiangyong Jia

  36. STAR and PHENIX “converges” • STAR’s measurement imposing PHENIX acceptance. • Agrees within systematics. The main difference comes from the assumed v2 values. 0-5% Jiangyong Jia

  37. d-Au/p-p,  - h,  Correlations d-Au p-p PHENIX preliminary 1-2 GeV/c 0.4-1 GeV/c pT,trig > 5 GeV/c 2-3 GeV/c 3-5 GeV/c Underlying event yield drops quickly, negligible >2 GeV/c Jiangyong Jia

  38. 200 GeV 63 GeV bg shape • The away side jet yield associated with the leading hadron has a much flat pT distribution than single inclusive Trigger pion 5-10 GeV/c Jiangyong Jia

  39. Where the cross happens PHENIX Preliminary • Cross happens at the right locations p/4, p±p/4 • The vertical values are different at the near and far side!! • 1.02 vs 1.03 Jiangyong Jia

  40. Jiangyong Jia

  41. Jet yield in different regions • Study jet structure in three regions: • Near |Df|<p/3. • Away dip |Df-p|<p/6, • Away peaks p/2 <Df-p<5p/6, 7p/6 <Df-p<3p/2 Jiangyong Jia

  42. Jet yield Jiangyong Jia

  43. Ratio to the near side peaks Jiangyong Jia

  44. Jet yield ratio to the peripheral bins Jiangyong Jia

  45. Underlying event study from CDF Leading Jet From Rick Field, ISMD2004 Jiangyong Jia

  46. Initial/ final state radiation from Pythia • Initial radiation: • Near side: enhanced yield at large pT,assoc • Far side: small change Due to initial kT + trigger bias effect? ztrig decrease, and zassoc increase Fixed trigger! (>5 ) Near Far • Final radiation : • Near side: small change. Energy available: (1-zTrig)EJet • Far side: enhanced yield at low pT,assoc. Full jet energy available: EJet Jiangyong Jia

  47. RP dependence • Study (di)jet correlations vs angle of trigger h relative to event plane • J. Bielcikova et al, Phys. Rev. C69:021901, 2004 a is proportional to the n trig in the bite x accounts for the difference in normalization factor, and is close to 1. The mixed events gives C(Df) = = x(1+b/a cos2Df) dNpairs/dDf Jiangyong Jia

  48. Difference of jet per trigger yieldBetween “max in plane” and “max out of plane” Jiangyong Jia

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