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Probing the Quark-Gluon Plasma at RHIC: Jet Dynamics and Power Corrections

This presentation, delivered by Justin Frantz at the FRIF Workshop on QCD Power Corrections, explores the behaviors of jets in the Quark-Gluon Plasma (QGP) produced at the Relativistic Heavy Ion Collider (RHIC). Key topics include the impact of temperature, density, and pressure on particle interactions, the role of collective behavior in high-energy collisions, and the modifications of jet observables in the QGP context. The discussion also covers elliptic flow, jet suppression, and di-jet correlations, presenting evidence from centrality-dependent measurements and hydrodynamic models.

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Probing the Quark-Gluon Plasma at RHIC: Jet Dynamics and Power Corrections

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  1. Jet Probes at RHIC Justin Frantz Stony Brook University FRIF Workshop on QCD Power Corrections January 13, 2006 Frif Power Corr. Wkshop – Justin Frantz

  2. The Heavy Ion/QGP Mission • …in the context of this workshop… • Seeq’s/g’s outside of pQCD • (Often delicate) NP effects in pQCD jet event shape… • Lattice QCD predicts deconfinement phase change → a Quark Gluon Plasma • Specifically, observe collective behavior of many q/g‘s in this plasma? • “Larger Scale” observables • Temperature, Pressure, Density… • Also how does it modify particle physics? • Chiral symmetry restoration? • Color screening melts J/Psi? • aS modified @ finite Temp. Lattice Calculation Energy Density / T4 pion gas T/TC TC estimates ~ 170 MeV Frif Power Corr. Wkshop – Justin Frantz

  3. RHIC • The Relativistic Heavy Ion Collider: QGP Search STAR NYC RHIC • Collides AuAu, pp, dAu, CuCu, … at energies √s = , 20, 62, 130, 200, 400, 500 GeV • Polarized proton beams, Spin program → probe gluon spin structure Frif Power Corr. Wkshop – Justin Frantz

  4. Jargon: (%) Peripheral Central Npart participating nucleons Highlights of Basic Results • Runs 1/yr 2001-2006… interesting yield of results: • Requisite Densities • Thermalization: success of statistical models w/ T in the critical range • Hydrodynamic Flow: Too large for ideal QGP but evidence against hadron gas • Baryon/Meson flow vs pT follows (common!) quark number scaling instead of mass scaling • Hydro-models with only hadrons fail to reproduce • Hadron cross sections (esp. strange) too small to build it up • Large Baryon Excess at soft-hard transition energies (p/p≈ 1) • Recombination of quarks promising way to explain • “Strongly interacting QGP” (sQGP)– perfect liquid Frif Power Corr. Wkshop – Justin Frantz

  5. Hard Scattering Probes Au+Au → gdirect + X Au+Au → p0 + X p+p → p0 + X • Hard scattering in Au+Au → pQCD (works well in p+p) • Insert into HI medium, observe differences • E.g. high pT hadron and direct photon production • High pT spectral shapes clearly power law as expected for all centralities • And same shape— & ~ same as p+p Frif Power Corr. Wkshop – Justin Frantz

  6. RAA • = Ratio of A+A/ scaled p+p • Scaling factor: number of equiv N+N crossings (Ncoll) • FLAT • Prediction: jet energy loss leads to suppression effect for fragmentation products • But not for EM direct photons • Energy loss models depend on dN/dygluons • Many models: LPM effect, Modified D(z) • → Density! • DE ~ E was surprise (just E shift - like NP?) Frif Power Corr. Wkshop – Justin Frantz

  7. Elliptic Flow (v2) • In semi-central events initial state spacial f anisotropy → momentum space • v2 – second Fourier harmonic w/ w.r.t the (measured) global reaction plane • 2 Kinds: • At low pT (soft), hydrodynamic (of quarks we believe) • At high pT, energy loss of jet partons traversing the matter PHENIX dN/d Incl. Hadrons pT 3-4 GeV/c Frif Power Corr. Wkshop – Justin Frantz

  8. P(A,B) P(A)P(B) Di-Jet Di-Hadron Correlations • Huge Soft background (dN/dh ~ 1000) • Jet Finding difficult (Impossible?) in HI environment • Rely on 2-particle opening angle (azimuthal) correlations • 2 categories in pT: “Trigger” (high pT) & “Assoc” = 6 5 4 3 2 1 Nearside Awayside STAR 200 GeV pTtrig 5-10, pTassoc 1-2 GeV/c h-h Au+Au p+p PHENIX Frif Power Corr. Wkshop – Justin Frantz

  9. Experimental Method: Flow Subtraction • Assume 2-source correlation Flow + Jet • Main source of systematic error • b0 determined by “Zero Yield At Minimum” (ZYAM), other methods PHENIX p0–h pTtrig 5-10 GeV/c pTassoc 3-5 GeV/c Note scale Frif Power Corr. Wkshop – Justin Frantz

  10. First Results (High x Low pT) • Jet suppression of awayside shape • Nearside per trigger yield same • Absolute NS yield suppressed • At low pT, “recovered” 4-6 x 2-4 GeV/c 0.2 0.1 0.0 0 p w/ pT,assoc 0.2 GeV/c 0 p Frif Power Corr. Wkshop – Justin Frantz

  11. High x High “Re-emergence” • Low/No Background (Flow Sub. Unimportant) • Clear emergence of jet structure at the away-side • Away side width consistent with constant • Away side yield suppressed STAR Preliminary 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV/c Frif Power Corr. Wkshop – Justin Frantz

  12. Really Weird! Low x Low • Large modication on the awayside! • Cone/ Volcano shape • Medium response to the jets? • Explained by: • Mach cone sound wave • Color cerenkov cone • Bending jets • If Mach Cone, size →vsound → direct measure of matter property 2.5-4 GeV/c trig STAR 1-2.5 GeV/c assoc PHENIX p 0 Df Frif Power Corr. Wkshop – Justin Frantz

  13. How Robust is The Volcano? • Still questions about robustness (oversubtraction in v2?) • Look @ trigger w.r.t. RP • Over subtraction→ opposite effect In plane Frif Power Corr. Wkshop – Justin Frantz

  14. IAA etc. • Looking for best way to analyze extracted jet (f-integrated) yields • Good parameter – pT, zT,xE ? • IAA : ratio of integrated per-trigger yield in A+A/p+p • How does it fit together with RAA? Better quantity? Still open An Eloss model: Wang et. al. Phys. Lett. B579 (2004) 299–308. STAR Awayside IAA (≈ RAA !) Frif Power Corr. Wkshop – Justin Frantz

  15. Measured Direct g Signal/Bkg (Decay g bkg) S/B Central Au+Au 200 GeV __ pQCD w/ had. suppression Direct g-Jet • In central Au+Au high suppression effect → higher purity of direct g • Complement of jet-jet Eloss • Probes interior of collision volume • Eg proxy for Ejet • Extraction of gdirect-jet from ginclusive correlations underway ≈p+p 200 GeV gdir-jet jet-jet Frif Power Corr. Wkshop – Justin Frantz

  16. Jet Event Shapes @ RHIC What am I doing @ this workshop? • Good things @ RHIC • Not just A+A: p+p, p+A, polarized p+p (& lots!) • Dectectors optimized for soft physics (Good E,p resolution/ PID above 50 MeV…) in addition to hard • Bad things • As h+h, central rapidity restriction • Ambiguity of Q/√s12 • In Au+Au…well… e.g. no jet finding (jets modified!)…etc… • From your standpoint • For p+p, best source of low Q? (mid-hx ranges like Tevatron/LHC, but lower s) • Au+Au Interesting modification to hadronization – could Power Correction frameworks say anything sensible? How about in d+Au ? • From HI experimentalist standpoint • Want to use jets to probe medium: event shapes are a natural goal Frif Power Corr. Wkshop – Justin Frantz

  17. Energy Energy Correlations • Instead of muliplicity correlations, energy flow, correlations (“combining” info in all pT bins) • No jet finding neccesary • auto-convolution of JCEF →other shape observable as correlations? • Sensitive to aS , NP effects (plasma?) (p – c) Frif Power Corr. Wkshop – Justin Frantz

  18. EEC in h+h? • EEC never measured in h+h? • Structure Fn complication x1x2 distribution of Q • But theory work says it should be possible • Basham, Et al: Use Tranverse EEC(f) • Gale et. al. QGP multiple scatt. → large effects to TEEC (hep-ph/9406208) • Measured and used in DIS @ HERA (1 S.F.) Frif Power Corr. Wkshop – Justin Frantz

  19. EEC in A+A • 2 EEC’s in A+A? sQGP has its own? (beyond flow?…) • Large flow harmonic contribution • Extract Jet EEC • Large underlying ET (shape distorting) • Combinatoric pair subtraction • PHENIX ½ f solid ang. → missed ET even p+p Lokhtin et al., hep-ph/0402108 Frif Power Corr. Wkshop – Justin Frantz

  20. Effect of Inaccurate ET • Pythia study of EEC (200 GeV p+p) In PHENIX ET (GeV) Q (GeV) Q (GeV) Ratio to Blue (Arbitrary Norm) EEC w/ Phenix ET Denom EEC(f) A.U. EEC w/ real Phx Acc Q = 10-15 GeV/c EEC w/ true Q in Denom EEC w/ ET in Denom Df Df Frif Power Corr. Wkshop – Justin Frantz

  21. Idea: EEC Direct-Gamma Events • Similar to the DIS t-channel • Does it probe the same properties? (g/q jet) • Ever done before? • Two varieties • only charged particles-Eg only • Including neutral (w/ direct g) • Is one better? 2EgTRIG(GeV) PYTHIA direct g events Q (GeV) PYTHIA direct g events Eg 10-15 GeV EEC(f) A.U. f Frif Power Corr. Wkshop – Justin Frantz

  22. Conclusions • Interesting time at RHIC • Jet/Hard observables continue to provide key information • We see jet modification! • Can we use “traditional” event shape? • …& same perturbative inspired frameworks? • Need help from theorists • What can be calculated? • What can be learned? Frif Power Corr. Wkshop – Justin Frantz

  23. Flat RAA? (Energy Loss) • Example of using hard scattering probes Frif Power Corr. Wkshop – Justin Frantz

  24. Understanding RAA(Npart, ) • Can we find a consistent description of centrality and  dependence of RAA? • Define with • Perform survival-weighted average over all production points, emission directions. • Survival weighting: Frif Power Corr. Wkshop – Justin Frantz

  25. Frif Power Corr. Wkshop – Justin Frantz

  26. Energy Loss Calculations Frif Power Corr. Wkshop – Justin Frantz

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