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Probe the QGP via dihadron correlations: Jet quenching and Medium-response

Probe the QGP via dihadron correlations: Jet quenching and Medium-response. Df. Jiangyong Jia Stony Brook University. Medium. Jet. ?. Particle production mechanisms. R AA =A+A/p+p. 1. Flow+Recombination. factor of 5. 0.2. Jet. 3. 5. pT. Production mechanisms

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Probe the QGP via dihadron correlations: Jet quenching and Medium-response

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  1. Probe the QGP via dihadron correlations: Jet quenching and Medium-response Df Jiangyong Jia Stony Brook University Medium Jet ?

  2. Particle production mechanisms RAA=A+A/p+p 1 Flow+Recombination factor of 5 0.2 Jet 3 5 pT Production mechanisms Jet fragmentation (>5 GeV/c) and Flow+Recombination High pT: surface emission

  3. Particle production mechanisms RAA=A+A/p+p 1 Flow+Recombination factor of 5 0.2 Jet 3 5 pT Production mechanisms Jet fragmentation (>5 GeV/c) and Flow+Recombination High pT: surface emission Low pT: bulk emission Locally thermalized QGP -> flow -> recombination TTthermal+m<v>2

  4. Jet contribution via dihadron correlation RAA=A+A/p+p 1 Flow+Recombination 0.2 Jet 3 5 pT • High pT: Jet quenching and Jet tomography. • Low pT: Dissipation of lost energy to medium How the energy of the 80% jet redistributed to low pT? • pT scan: Evolution of jet fragmentation and medium response

  5. Azimuth correlation at high pT 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV Au+Au 0-5% d+Au • Observed jet are those “do not” suffer energy loss. • Near-side: surface emission • Away-side: tangential emission (factor of 5 suppression) Per-trigger yield

  6. Azimuth correlation at high pT STAR, Phys. Rev. Lett. 97 (2006) 162301 IAA 0.2 IAA  0.2  RAA, Why?? 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV Au+Au 0-5% d+Au • Observed jet are those “do not” suffer energy loss. • Near-side: surface emission • Away-side: tangential emission (factor of 5 suppression) Per-trigger yield • Direct proof that high pT hadrons are from vacuum fragmentation. • But they do not directly constrains the energy loss processes. • Calculations model dependent: qhat 1~10 GeV2/fm

  7. Average energy loss vs. absorption? Case II Absorption Downward shift Case I Shift to left Yield p+p A+A pT RAA alone can’t distinguish the two cases. But, Case I: Suppression factor depends on the spectra shape, Flatter spectra -> larger shift. Case II: Suppression factor almost independent of the spectra shape

  8. Consider only absorption term Yield PRC.71:034909,2005 pT Due to longer pathlength for away-side jet, it always leads to IAA<RAA. Need shift term!

  9. Consider only Energy shift n=4.8 in dn/dpt for 5-10 GeV/c trigger Single spectra n= 8.1 in dn/ptdpt Per-trigger spectra Away spectra flatter than single spectra

  10. Consider only Energy shift n=4.8 in dn/dpt for 5-10 GeV/c trigger Single spectra n= 8.1 in dn/ptdpt Per-trigger spectra Away spectra flatter than single spectra nucl-ex/0410003 50% bigger • Flatter spectra and longer pathlength) compensated by bigger • fractional energy loss --> IAA ~ RAA • For g-jet, pure absorption: IAA=RAA pure energy shift: IAA>RAA. • By combing IAA and RAA, one gain some sensitivity on energy loss

  11. Low pT: medium response to jet • Near-side: elongated structure in Dh, enhancement in yield. • Jet + medium-induced component (ridge) • Away-side: strongly modified shape and yield • Suppressed jet (head region) + medium-induced component (Shoulder region) PHENIX STAR

  12. Away-side particle composition 0-20% 2.5-4x1.6-2 GeV/c • Similar shape for asso Baryon and asso Meson • Jet frag.<Bayron/meson< bulk medium. W.Holtzmann Recombine into correlated pairs?

  13. Away-side energy dependence Same pT cut, similar Dh window Head200 GeV  Head17.2 GeV Shoulder200 GeV 2.5x Shoulder17.2 GeV At SPS Smaller jet quenching -> Less suppressed Head Smaller medium component -> Smaller Shoulder p+p |h|<0.35 0.1<h-hCM<0.7

  14. pT Scan: Competition between Jet and medium arXiv:0705.3238 [nucl-ex] Dip grows Jet emerges • Suppression in HR, enhancement in SR. • Jet shape become similar between pp and AuAu at high pT.

  15. Away-side modification pattern vs pT pTB • Many possible routes! • A single number summarizing the shape: RHS • Dip: RHS<1; Peak: RHS>1; flat: RHS=1 pTA Head region: Upper limit of jet fragmentation Shoulder Region: Response of the medium jet medium

  16. pT Scan: Competition between Jet and medium Peak Flat Cone • 1<pTA,B < 4 -> RHS<1 -> Shoulder region dominant! • pTAor B >5 -> RHS>1 -> Head region dominant! • pTA or B < 1 -> RHS~1 pt,1 pt,2>5 1<pt,1 pt,2<4 Competition between “Head” and “shoulder”. Suppression and enhancement arXiv:0705.3238 [nucl-ex]

  17. Jet spectra slope at low pT • Near-side: flat with Npart (>100), increase with pTA. • Dominated by jet fragmentation arXiv:0705.3238 [nucl-ex] Mean-pT at intermediate pT (1<pTB< 5) 4<pTA<5 3<pTA<4 2<pTA<3 • Shoulder region: flat with Npart (>100), independent of pTA ! • Dominated by medium. • Universal slope ~0.44 GeV/c, reflects property of the medium?

  18. Jet spectra slope at head region • Low trigger pT, decrease with Npart • Onset of jet quenching, soft contribution dominates (feed in from shoulder) • High trigger pT, flat with Npart • Soft contribution dies out, Jet dominate. Jet and medium dominates different pT |Df-p|<0.4 Fuqiang STAR Preliminary dn/dh

  19. Parton-medium interaction Collective mode Deflected jet Propagation mode Punch-through jet Large angle radiation/Cerenkov 1) Radiative energy loss -> High pT suppression 2) Radiated energy converted into flow -> Low pT enhancement 3) Radiated energy propagate -> Gluon feedback at low pT 4) Or propagating partons get deflected

  20. Radiation contribution • Polosa, C. Salgado, hep-ph/0607295, • sudokov splitting Can explain multiplicity Can be large angle => But for hard jets, radiation almost collinear I. Vitev, gluon feedback C. Salgado, U. Wiedemann, hep-ph/0310079

  21. Near-side yield modification: IAA Dilution effects due to soft triggers Jet Ridge • Modifications decrease with increasing trigger pT (flattening) • Modification limited to pTA,B 4 GeV/c, similar to the away-side Shoulder. • STAR: This is due to the Ridge. J. Putschke

  22. Low pT : dilution effect per-jet yield IAA at low pT is complicated since the trigger jet is modified.  per-trig yield • We define pair suppression JAA • IAA reflects modification on Pairs √ and Triggers x

  23. Are low pT particles from jets? • Near-side jet pairs with one particle in 5-10 GeV/c. • Most of these pairs comes from jet fragmentation. When normalized by 5-10 GeV/c trigger, Iaa ~1. But when normalized by low pT triggers, Iaa <1. • Origins: 1) low pT triggers from soft processes such as Thermal-T recombination. 2) low pT triggers are jet-induced but don’t have high pT partners: fragmentation of radiated partons

  24. Near side JAA Jet pair suppression Leading hadron suppression = • At high pT, both hadrons comes from same jet! • JAA represent the suppression on the jet (>pt1+pt2). Since Jet suppression is constant at high pT, JAA should approach the constant RAA level at high pT! • Low pT Jaa is factor of 4-5 of the high pT limit? (almost no suppression) • These pairs are remnants of quenched jets (not from surface!)

  25. Near jet p 0 Ridge Cone Away jet • Sources of pairs • Fragmentation contribution from survived jets • Medium-induced contribution from quenched jets • Both important at pT<4, softer than jet, similar PID chemistry (see Jana, Anne’s talk). • Mechanisms for Ridge and cone should play a role on both sides. • They do not suffer surface bias. high pT pairs are rare Df Df Connection between Ridge and Cone

  26. Summary • Jet correlation @ high pT provide constraints on the jet quenching and geometrical bias • Jet correlation @ low pT shows complex evolution due to competition between Jet quenching and medium response on both near- and away-side. • Models should describe the full pT dependence (shape and yield).

  27. Backup

  28. Recombination is important u u d d u u u d d u u d u u d • Medium are boosted by shock wave, which then recombine into hadrons? => jet frag<Bayron/meson Cooper-Fryer

  29. Outline • Single particle production mechanisms • High pT: jet fragmentation and surface bias. • Low pT: medium response • Away-side properties. • Away-side Jet and medium competition • Near-side properties. • Near-side Pair suppression • Connection between near- and away-side medium response • Summary

  30. Should I worry about non-flow in correlation? DΦ Away jet Near jet Dη PHENIX: event plane measured at 3<|h|<4, tracks in |h|<0.35 • Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets • HIJING event is weighed with measured v2(pt,h,b) • PYTHIA has 10 GeV dijet • Dijet->Biased Event plane->Fake v2 for trigger of the embedded jets. • Use away-side pp jet to approximate the ridge Y Ridge Hijing+flow

  31. Should I worry about non-flow in correlation? 0.4<h<2.8 DΦ Away jet Near jet 3.0<h<4.0 Dη PHENIX: event plane measured at 3<|h|<4, tracks in |h|<0.35 • Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets • HIJING event is weighed with measured v2(pt,h,b) • PYTHIA has 10 GeV dijet • Dijet->Biased Event plane->Fake v2 for trigger of the embedded jets. • Use away-side pp jet to approximate the ridge Y Ridge Hijing+flow Fake v2 nucl-ex/0609009

  32. What v2 to use in correlation? C(Df) = x(1+2<v2tv2a>cos2Df) + J(Df) • Non-flow due to jet is small with BBC Event plane • Other Non-flow and v2 fluctuations contribute to C(Df), so should be included in the two source model. • If minijets are important, then it should be much longer range in h, or many minijets emitted in a correlated way?

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