1 A guide through pT landscale of di-hadron correlation Jiangyong Jia Stony Brook University EIC, 2007 and what can we learn about the partonic medium?

2 Should I worry about non-flow in correlation? PHENIX: event plane measured at 3<|  <4, tracks in |  |<0.35 Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets HIJING event is weighed with measured v2(pt, ,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 Near jet Away jet ΦΦ ηη Ridge  Hijing+flow

3 Should I worry about non-flow in correlation? PHENIX: event plane measured at 3<|  <4, tracks in |  |<0.35 Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets HIJING event is weighed with measured v2(pt, ,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 3.0   2.8 Fake v2 nucl-ex/ Near jet Away jet ΦΦ ηη Ridge  Hijing+flow

4 What v2 to use in correlation? C(  ) =  (1+2 cos2  ) + J(  ) Non-flow due to jet is small with BBC Event plane Other Non-flow and v2 fluctuations contribute to C(  ), so should be included in the two source model. If minijets are important, then it should be much longer range in , or many minijets emitted in a correlated way?

5 5 3 R AA pT 1 Jet Flow+coalescense How the energy of the 80% jet redistributed to low pT? How to separate the Hard and Soft contribution down to low pT? Production mechanisms: Jet (>5 GeV/c) and Flow+coalescense 0.2 Sources of single particles

6 5 3 R AA pT 1 Jet Flow+coalescense How the energy of the 80% jet redistributed to low pT? How to separate the Hard and Soft contribution down to low pT? Jet correlation: Energy dissipation to low pT partonic stage: Jet energy couple with hydro-flow hadronization stage: Correlation affected by the coalescence process Jet correlation provide constraints on the Geometrical bias Production mechanisms: Jet (>5 GeV/c) and Flow+coalescense 0.2 Sources of single particles

7 Sources of “jet” pairs Jet fragmentation contribution: Near jet and away jet Medium-induced contributions: Near-side Ridge, away-side Cone. Energy at low pT How they evolve/compete in pT1 vs pT2 landscape? Ridge Cone Near jet Away jet 0 

8 High pT : Geometrical bias I AA  R AA, Why?? STAR, Phys. Rev. Lett. 97 (2006) I AA Transmission, Absorptionshift T. Renk notation 0.2

9 PRC.71:034909,2005 Absorption picture always predicts I AA <R AA. Need shift term! High pT : Geometrical bias I AA  R AA, Why?? STAR, Phys. Rev. Lett. 97 (2006) I AA pT R AA Transmission, Absorptionshift T. Renk notation 0.2 Shift term is needed For fixed R AA, a larger eloss required for a flatter spectra

10 Energy shift  0 spectra n= 8.1 in dn/ptdpt n=4.8 in dn/dpt for 5-10 GeV/c trigger Per-trigger spectra Away spectra flatter than single spectra

11 Energy shift  0 spectra n= 8.1 in dn/ptdpt n=4.8 in dn/dpt for 5-10 GeV/c trigger Per-trigger spectra Bigger fractional eloss + flatter spectra --> Iaa ~ Raa For  -jet, I AA >R AA ! constrains the geometry bias by combing Iaa and Raa nucl-ex/ % bigger Away spectra flatter than single spectra

12 Correlation landscape in pTA, pTB Suppression in HR, enhancement in SR Peak location D independent of pT, jet reappearance not due to merging of side peaks? Dip grows Jet emerges arXiv: [nucl-ex]

13 Correlation landscape in pTA, pTB Head region: Suppression of jet Shoulder Region: Response of the medium pTApTA pTBpTB Many possible routes! A single number summarizing the shape: R HS Dip: R HS 1; flat: R HS =1 Jet shape symmetry : R HS (p T A, p T B ) = R HS (p T B, p T A )

14 Awayside modification pattern vs pT 1 R HS Shoulder region dominant! p T A,B >5 -> R HS >1 -> Head region dominant! p T A,B R HS ~1 -> SR feed in + radiated gluons? arXiv: [nucl-ex] Cone Flat Peak p t,1 p t,2 >  5 1  <p t,1 p t,2 <  4 Competition between “Head” and “shoulder”. Suppression and enhancement

15 Near side Jet spectra shape: Near and Shoulder region Near-side: flat with Npart (>100), increase with p T A. Jet fragmentation S region: flat with Npart (>100), independent of p T A ! Universal slope, reflects property of the medium? Mean-pT at intermediate pT (1<pTB< 5) vs. Npart arXiv: [nucl-ex] 2<p T A <3 3<p T A <4 4<p T A <5

16 Near side Away shoulder Jet spectra shape: Near and Shoulder region Near-side: flat with Npart (>100), increase with p T A. Jet fragmentation S region: flat with Npart (>100), independent of p T A ! Universal slope, reflects property of the medium? Mean-pT at intermediate pT (1<pTB< 5) vs. Npart arXiv: [nucl-ex] 2<p T A <3 3<p T A <4 4<p T A <5

17 Chemistry of Shoulder Similar shape for asso Baryon and Meson 0-20% 2.5-4x1.6-2 GeV/c Jet frag.<Bayron/meson<  bulk medium. W. Holtzmann

18 Chemistry of the Shoulder? u d u u d uu d d u uu d d u Bulk medium are boosted by shock wave, which then coalesce into hadrons? => jet frag.<Bayron/meson<Bulk Coalescence plays a big role here. Cooper-Fryer

19 Parton-medium interaction 1) Radiative energy loss -> High pT suppression 2) Lost energy converted into flow -> Intermediate pT enhancement 3) Remaining propagate -> Gluon feedback at low pT Propagation mode Collective mode Coupling with medium: Mach flow / deflection. Deflected jet Punch-through jet Large angle radiation Deflection: Deflection angle decrease with increasing pT? No enhancement in multiplicity?

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

21 Near side: jet+ ridge Near side Components  jet peak  Elongated ridge 3 < p t,trigger < 4 GeV p t,assoc. > 2 GeV Au-Au 0-10% STAR preliminary

22 Near-side shape modification Trigger p T = x 2-3 GeV/c  width broadening limited to intermediate pT Broaden at intermediate pT unmodified at high pT

23 Modifications decrease with increasing trigger pT (flattening) Modification limited to p T A,B  4 GeV/c, similar to the away-side Shoulder. STAR: This is due to the Ridge. Near-side yield modification: I AA Jet Ridge Dilution effects due to soft triggers

24 Intermediate pT : dilution effect per-jet yield Quantification via I AA is complicated when the trigger jet is modified.  per-trig yield Dilutions effects Triggers have recombination contribution Boost from the radial flow? Trigger jet multiplicity is enhanced due to interaction with medium I AA reflects modification on Pairs √ and Triggers x

25 Near side Iaa We calculate the pair suppression factor, Jaa, from Iaa and Raa R AA

26 Near side Jaa At high pT, both hadrons comes from same jet! The J AA represent the suppression on the jet (>pt1+pt2). Since Jet suppression is constant at high pT, Jaa should approach the constant R AA level at high pT! Real enhancement is factor of 4-5 at low pT? (no suppression of jet pairs!) Imply intermediate pT single enhancement not due to jets?! Leading hadron suppression Jet pair suppression =

27 Role of hadronization in correlation? Bulk hadronization mechanisms can affect both the single (Thermal+Thermal Reco) and pairs (Thermal+Shower reco). Can it modify the correlation? If so, how to isolate the pure partonic medium effect? X.N. Wang et.al : in medium fragmentation Parton-medium interaction Hadronization via Coalescence

28 Jet contribution at low pT? Once we map out the jet properties in pT1, pT2, can we combine correlation results with single particle measurements and estimate the jet contribution or contribution initiated by jet, as function of pT. 5 3 R AA pT 1 Jet Flow+coalescense 0.2

29 We know the ratio of jet pair/combinatoric pair vs pT1, pT2. How to translate this into single yield from jet? Jet contribution at low pT?

30 Ridge and cone : different mechanism? Both have similar property in pT and PID composition and softer than jet. They are results of same matter, ridge and cone mechanism should play a role on both sides. Reduced/no surface bias for intermediate pT correlation. Ridge Cone Near jet Away jet 0  

31 Summary Jet high pT provide constraints on the and geometrical bias Jet intermediate pT shows complex evolution due to competition between Jet quenching and medium response on both near- and away-side. Constrain the particle production mechanism by combing single and correlation landscape in pT. Physics varying drastically with pT, good model should describe the full pT dependence.

32 Backup

33 Head region: jet punch-through Low pTB range, decrease with Npart Turn on of jet quenching, soft contribution dominates High pTB range, flat with Npart Punch through jet dominate and has same slope (soft contribution dies out) STAR Preliminary |  |<0.4 dn/d  Fuqiang

34 Details of the suppression and enhancement HR exhibits early onset of suppression, relative to p+p, approach Raa at high pT: jet quenching! H+S (entire away side) exhibits overall enhancement due to SR, up to p T A,B <4 GeV/c I AA depends on the integration window! arXiv: [nucl-ex]

35 Integration range and pT matters! One might reach misleading conclusion if only focus on limited pT. No Modification seen in HR for this pTA x pTB bin but: Would see enhancement for this pTA x pTB bin in the SR+HR, and At high pT, would see a suppression even in SR+HR, and At low pT, would see an enhancement even in HR. Thus it is important to map out the full pTA, pTB and  space! HR SR

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37 pT evolution of jet function

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