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Jet Probes at RHIC

Jet Probes at RHIC. Justin Frantz Stony Brook University FRIF Workshop on QCD Power Corrections January 13, 2006. The Heavy Ion/QGP Mission. …in the context of this workshop… See q ’s/ g ’s outside of pQCD (Often delicate) NP effects in pQCD jet event shape…

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Jet Probes at RHIC

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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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