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Understanding the jet quenching & medium response in Au+Au collisions

Understanding the jet quenching & medium response in Au+Au collisions. Jiangyong Jia Stony Brook University & BNL. Study the QGP. hadronic phase and freeze-out. QGP and hydrodynamic expansion. initial state. pre-equilibrium. hadronization. Form a matter in the overlap region.

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Understanding the jet quenching & medium response in Au+Au collisions

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  1. Understanding the jet quenching & medium response in Au+Au collisions Jiangyong Jia Stony Brook University & BNL

  2. Study the QGP hadronic phase and freeze-out QGP and hydrodynamic expansion initial state pre-equilibrium hadronization Form a matter in the overlap region. Matter expands under pressure. Matter interact with probes. Matter hadronize and freeze out.

  3. Properties to be studied z y x • Collective behavior • Expansion velocity • Elliptic flow • Viscosity • Thermal properties • Energy density • Temperature • Chemical potential Size R • Dynamical properties • Opacity, transport coefficient • Debye screening of bound state

  4. Using single jets and dijets as probe p 0 q q leading particle hadrons hadrons • Single hadron yield : vary pT • Correlated hadron pairs shape and yield: vary Df, Dh, pT1, pT2. Jet1  Jet2    

  5. Jets in Au+Au collisions @ 200 GeV Low pT correlated pairs Suppressed Jet + hump Jet + ridge d+Au Au+Au 0-5% Df 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV Df ridge Mach cone jet Medium response to lost energy Bulk emission Fragmentation of jets with minimal eloss Surface emission High pT correlated pairs

  6. Four components pTb Hard region (jet) pt,a pt,b>5 1<pt,a pt,a<4 Soft region (medium) pTa • Near-side : jet + medium (ridge) • Away-side : suppressed jet + medium (the shoulder) • Jets dominates high pT • Medium response dominates intermediate pT (<4 GeV/c)

  7. arxiv. 0801.4545 pT scan Near: dilution Away: shoulder develops Near: enhancement Near: little modification Away: jet reemerges Increase partner pT Increase trigger pT The evolution is consistent with four component picture

  8. Jet quenching vs. medium response • One can’t fully understand jet quenching without knowing the medium response. • Lack of constraints from jet quenching calculations due to DE bias. • Too many knobs to turns…… • Collision geometry, as, Radiative vs collisional eloss. • Medium response provide more constraints. • But theoretical progress is still quite qualitative. • Ultimately full jet reconstruction address both.

  9. Understanding medium response p 0 near    away   • Near/away sides are discussed separately in theoretical models • Away side: mach cone, jet deflection…… • Near-side: longitudinal flow, momentum kick…… • Ridge and shoulder have similar properties. • Similar pT range (<4 GeV/c), slope and particle composition. Typically assume triggers from jets, many 2-p 3-p are done in this region in this way

  10. What constitutes the triggers? P+P Produced pions • Jet fragmentation is important at rather low pT • pQCD calculation describe hadrons spectra done to 2 GeV • Large fraction of soft pairs show jet-like correlation. 2-3 x 0.4-1 GeV/c

  11. What constitutes the triggers? Au+Au • Intermediate pT particles are not jet-like. • Less suppression and large v2. • Strong dependence on flavor

  12. How to quantify the medium response • Per-trigger yield is useful if triggers comes fragmentation, • But origins of triggers are complicated at pT < 4 GeV/c. • Uncorrelated hadrons? feedback of quenched jets? either case, per-trigger yield can’t be compared with p+p directly. • Trigger has no surface bias

  13. Dilution for soft triggers High pT trigger Low pT trigger Near side IAA

  14. RP dependence. • We use to plot per-trigger yield as a function of angle between trigger and RP at trigger pT<4 GeV/c. • Per-trigger yield suffer from similar complication, since triggers may not come from jet fragmentation • they have their own large v2, which has nothing to do with jet quenching. • Maybe the pair v2 is more appropriate. 3<pTtrig<4GeV/c & 1.0<pTasso<1.5GeV/c 20-60% STAR

  15. Pair suppression factor : JAA q q leading particle hadrons hadrons • Pair yield in Au+Au normalized by ncoll scaled p+p pair yield.

  16. Pair yield modification: JAA • Energy scale is controlled by pTsum=pTa+pTb • Low pT pair yield is not suppressed! • Pair yield scale faster than Ncoll at lowpTa+pTb • These pairs are remnants of quenched jets. • Medium response important up to pTsum~7 GeV/c

  17. Dihadron correlation vs. single spectra 1 Flow+Recombination RAA 0.2 Jet fragmentation 3 5 pT • % of singles related to jets? • Jet fragmentation contribution • Fraction determined by the surface volume. • Or feedback of quenched jets (medium response) • Can estimate if the jet/feedback multiplicity is known. • Flow+recombination picture consistent with Mach cone or ridge?

  18. Source of pairs at intermediate pT jet-jet medium-medium jet-medium Nucl-ex/0806.1225 • Previous models only include jet-jet and jet-medium contribution. • We consider consequence of medium-medium contribution. • Large emission volume but fall fast with pT, not important at high pT

  19. Simulation set up rPart rNcoll nucl-th/0310044 • Jet absorption picture: loose all energy in a single interaction • Glauber modeling of Au+Au (Woods-Saxon), generated dijets according to rNcoll (x,y) with random direction, then swim the dijet through a medium with density rNpart (x,y) • Chose k=0.7 to reproduce <f> =RAA = 0.22 in 0-5% Au+Au collisions.

  20. Reproduce the centrality dependence IAA nucl-th/0310044 • Can reproduce the centrality dependence of RAA and IAA

  21. Simulation setup • The quenched jets are converted into jet-induced medium particles. Surviving jet Medium response to quenched jet (mach-cone, ridge) • We consider 1<pT<4 as a single bin and choose • <Nj> =1 according to Pythia for 6 GeV/c jet. • <Nm>=2 account for enhancement in Au+Au

  22. Centrality dependence • Jet-Jet decreases with Npart • Medium-medium increases with Npart • Jet-medium first increase then decrease with Npart. jet-jet < jet-med < med-med

  23. Fix jet kinematics • Jet fragmentation width 0.3 rad, jet kT smearing width 0.4 rad. accept 30% away-side jet pairs in Dh. • Medium response hadrons appear at D = 1.1, with a width of 0.3 rad.

  24. Jet-Jet and Jet-Medium term • Concentrated at 0, p, pD. • Jet-medium location is same for deflected jet or cone jet This step is trivial, what does it imply for med-med? Mach cone “Deflected” Jet

  25. Medium-Medium term 0 p 2D D 2D p • Cone jet: pairs from same jet split roughly equally at 0 and 2D, since 2Dp – D, it appears at same location as the jet-medium pairs. • Deflected jet: All hadrons bend in same direction a large near side peak • Both jets are converted into hadrons emitted at angle D from original jet direction. Pairs peaks at: 0, p, 2D, p 2D.

  26. Ridge and Mach cone • If only consider jet-medium pairs, near- and away-side are different. • But medium-medium pairs are symmetric between the two sides. No surface bias. • Ridge is simply the Mach cone coupled with longitudinal flow medium-medium jet-medium Mach cone ridge

  27. How about 3-p correlation? Au+Au Central 0-12% Triggered jet-med-med+jet-jet-med appears in off-diagonal and along-diagonal But med-med-med triplet do not show a clear off-diagonal component, because the kinematics is different from jet-med-med. The interpretation is complicated when triggering on the medium response

  28. V2 of survived jets Cylindrical Hard-sphere Woods-saxon • Positive but underestimate the data by factor of 2 (woods-saxon) V2quen = - v2surv Jetall= Jetsurv+Jetquen 0=v2all= v2surv+v2quen nucl-th/0310044

  29. Pair V2 • Quenched jets should have negative v2. • But large emission angle w.r.t the jet direction smears and changes the sign of v2.

  30. Conclusion • Correlation patterns are consistent with competition between jet fragmentation and medium response. • Understanding the medium response requires knowledge of the origins of the particles involved in the pair. • Both the spectra and correlation results suggest we are triggering on medium response at intermediate pT. • The correlation among medium response particles could dominate the pair yield at intermediate pT. • It can mimic the dihadron correlation pattern in Df and Dh, but not for the three-particle correlation. • The v2 of the correlated pairs depends on the emission pattern. Pair v2 should be small if Mach cone is correct mechanism.

  31. Dihadron correlation vs. single spectra 1 Flow+Recombination RAA 0.2 Jet fragmentation 3 5 pT • % of singles coming from jet fragmentation or feedback? • Need to know the jet/feedback multiplicity. • Flow+recombination picture consistent with Mach cone or ridge? Suppressed Jet + hump Jet + ridge d+Au Au+Au 0-5% 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV

  32. Peak Volume STAR Preliminary 200 GeV 62 GeV 8x increase

  33. V2 of survived jets • Finite near-side width reduce the pair v2.

  34. Put all together     p 0  • Assuming pairs are dragged by longitudinal flow, one can get ridge on both sides. However, at the away-side it is not distinguishable from the jet swing.

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