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Hadron Correlations and Parton Recombination

Hadron Correlations and Parton Recombination. Rainer Fries University of Minnesota. Hard Probes 2006 Asilomar June 11, 2006. q. q. Hard Probes. Hard processes as well controlled probes to measure properties of the QGP.

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Hadron Correlations and Parton Recombination

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  1. Hadron Correlations and Parton Recombination Rainer Fries University of Minnesota Hard Probes 2006 Asilomar June 11, 2006

  2. q q Hard Probes • Hard processes as well controlled probes to measure properties of the QGP. • Hard probes  high momentum transfer, high quark mass, high temperature • Careful: which value of our scale is sufficiently high depends strongly on the question we ask. Recombination and Hadron Correlations

  3. Hard Probes • Careful: which value of our scale is sufficiently high depends strongly on which question we ask. • Single inclusive pion spectrum in p+p: pQCD works from PT 1 GeV • But: single inclusive spectra in A+A: don’t work up to 5 GeV, • Maybe not even at 10 GeV ?? Recombination and Hadron Correlations

  4. Why Recombination: B/M • Enhanced baryon yield • p/ ~ 1 in Au+Au (for PT ~ 2 …4 GeV/c) • p/ ~ 0.3 in p+p, • p/ ~ 0.1….0.2 in e++e- PHENIX Recombination and Hadron Correlations

  5. Why Recombination: RAA • No jet quenching for baryons? (RAA ~ RCP ~ 1) • In the range PT ~ 1.5 … 5 GeV/c. • Jet quenching not on the parton level? PHENIX Recombination and Hadron Correlations

  6. Why Recombination: v2 scaling • Different v2 saturation for mesons and baryons Recombination and Hadron Correlations

  7. Baryon/Meson Anomaly • General baryon/meson pattern: p, , ,  versus K, , , K* In the region PT  1.5 … 6 GeV/c Recombination and Hadron Correlations

  8. Baryon/Meson Anomaly • General baryon/meson pattern: p, , ,  versus K, , , K* In the region PT  1.5 … 6 GeV/c • No mass effect:  behaves like a pion (m  mp , m >> m) STAR Preliminary Recombination and Hadron Correlations

  9. Baryon/Meson Anomaly • General baryon/meson pattern: p, , ,  versus K, , , K* • No mass effect:  behaves like a pion (m  mp , m >> m) • v2 of  < v2 of proton; behaves like meson Recombination and Hadron Correlations

  10. Baryon/Meson Anomaly • General baryon/meson pattern: p, , ,  versus K, , , K* • No mass effect:  behaves like a pion (m  mp , m >> m) • Hadron properties do not matter in this kinematic region. • Only the number of valence quarks! • We catch a glimpse of hadronization Recombination and Hadron Correlations

  11. Hadron Correlations • Away-side jets vanishes • Ridge on the near side Away side gone/diffuse Wiedemann et al. STAR A+A p+p  Broadening+pedestal on near side  Recombination and Hadron Correlations

  12. STAR preliminary Signatures in Correlations • Deviations from jet shapes below PT = 5 GeV/c • E.g.  broadening of the near-side jet cone Width of the peak in  STAR preliminary Recombination and Hadron Correlations

  13. Fragmentation? • Hard processes + vacuum fragmentation are ruled out below 4 … 6 GeV/c because of RHIC results on • hadron chemistry • elliptic flow v2 • Recombination idea: hadrons at intermediate PT from recombination of soft partons Recombination and Hadron Correlations

  14. Recombination! • Fragmentation = limit of hadronization for very dilute systems (parton density  0) • Recombination = hadronization in the opposite limit: thermalized phase of partons just above Tc Recombination and Hadron Correlations

  15. Recombination revisited • Basic assumptions • Recombine valence quarks • Instantaneous projection of quark states on hadron states • For simplicity: factorize 2-parton distribution in 1-parton distributions • No correlations assumed! Recombination and Hadron Correlations

  16. Recombination revisited • Conspiracy of thermal distributions and large P • i. e. P >> M, kT (collinear situation); Boltzmann w • No dependence on shape of ! • Baryon ~ meson • Reco  Frag competition fragmenting parton: ph = z p, z<1 recombining partons: p1+p2=ph Recombination and Hadron Correlations

  17. Recombination & Fragmentation • “Dual” model of hadron production: • Recombination + pQCD/fragmentation to describe hadron production at RHIC for PT> 1…2 GeV/c • With B. Muller, C. Nonaka, S. A. Bass • For RHIC: • T = 175 MeV • Radial flow  = 0.55 • Constituent quark masses • Fit to pion data  predictive power for all other hadron species Recombination and Hadron Correlations

  18. Spectra & Ratios • Good description of spectra, ratios, RAA for all measured hadron species RJF, Muller, Nonaka, Bass Recombination and Hadron Correlations

  19. Elliptic Flow Scaling • Assume universal elliptic flow v2p of the partons before the phase transition • Recombination prediction: • Scaling works for all hadrons • Deviations for pions arise mostly from resonance decays (Greco et al.) Recombination and Hadron Correlations

  20. How robust is v2 scaling? • Scaling law uses the most primitive approximations • Momentum shared equally between constituents • Expect correction for realistic wave function with finite width. • Numerically: effects are small Momentum shared: fractions x and 1-x Recombination and Hadron Correlations

  21. Fate of the Gluons? • Are there gluons or sea quarks? • No effect on particle yields for thermal spectra! • Resulting elliptic flow for hadrons does not obey scaling • For equally shared momenta: Recombination and Hadron Correlations

  22. Zooming in on v2 Scaling • We proposed a new variable: baryon/meson v2 asymmetry (B-M)/(B+M) for scaled v2. • First results: • Size and sign of the effect predicted correctly. • Gluons could be accommodated. P. Sorensen, QM 05 Recombination and Hadron Correlations

  23. Hadron Correlations • How can hadrons at intermediate PT show jet-like structure? Recombination and Hadron Correlations

  24. Hadron Correlations • How can hadrons at intermediate PT show jet-like structure? • Naturally through soft-hard recombination • Soft-hard hadrons and jet hadrons correlated • Rudy Hwa’s talk • Naturally if the recombining partons are correlated Recombination and Hadron Correlations

  25. 2-Particle Correlations • Recombination of mesons A, B from partons 1,2,3,4 • New: permit 2-particle correlations • Possible ansatz Recombination and Hadron Correlations

  26. Hot Spots • Strong energy loss (dE/dx up to 14 GeV/fm) • a lot of quenched/partially thermalized jets • Localized deposition of energy and momentum • Hot Spots? • Hot spot can be correlated with remaining jet • Partons in the hot spot can be correlated with themselves • Add collective effects: Mach cone? Recombination and Hadron Correlations

  27. Associated Yield • List of assumptions • Only near side; integrate rapidity • Small correlations, keep only terms linear in c0 and v2 • Narrow wave functions • Correlations constant over volume Vc • Associated yield • Here Recombination and Hadron Correlations

  28. Amplification of Correlations • Q: Amplification factor • Count 2-parton pairs between the 2 hadrons; for effects linear in c0, only 1 correlation allowed. • Uncorrelated background (for meson-meson) 2 pairings without correlating the mesons 4 pairings that lead to meson correlations Recombination and Hadron Correlations

  29. Numerical Example • Using Duke parametrization • consistent with spectra and ratios! Consistency with PHENIX data can be reached. Baryon trigger Meson trigger Large correlations from Frag-Frag. F-F and SS-SS with C0=0.08x100/Npart (Vc~const.) Lower associated yield when adding SS-SS without correlations (C0=0), especially for baryon triggers. RJF, Muller, Bass: Phys. Rev. Lett. 94, 122301 (2005) Recombination and Hadron Correlations

  30. Identified Particles Recombination and Hadron Correlations

  31. Hadrochemistry in “Jet Cones” • The baryon/meson ratio can be an indicator for the amount of “thermalization” in a jet • Far side produces more baryons than near side Recombination and Hadron Correlations

  32. Where is Fragmentation? • Below PT = 4 … 6 GeV/c: no go for (hadronic) hard probes • Problems for pQCD + fragmentation even above PT = 6 GeV/c ?? • Baryon/meson ratio still too large above 5 GeV/c ?? Recombination and Hadron Correlations

  33. Where is Fragmentation? • Below PT = 4 … 6 GeV/c: no go for (hadronic) hard probes • Problems for pQCD + fragmentation even above PT = 6 GeV/c ?? • Baryon/meson ratio still too large above 5 GeV/c ?? • v2 from jet quenching ?? Recombination and Hadron Correlations

  34. Where is Fragmentation? • Below PT = 4 … 6 GeV/c: no go for (hadronic) hard probes • Problems for pQCD + fragmentation even above PT = 6 GeV/c ?? • Baryon/meson ratio still too large above 5 GeV/c ?? • v2 from jet quenching ?? • No difference between quark and gluon jets ?? • It may be “soft-hard” recombination. • Pick-up of soft quarks by jets Recombination and Hadron Correlations

  35. Soft (T) partons Shower (S) pT Soft/Hard Recombination • Attempt to treat reco + fragmentation consistently • Hwa and Yang: jets as cones of parton showers at late times; fitted to fragmentation functions • Majumdar, Wang and Wang: 2- and 3- quark constituent quark fragmentation + recombination ( Q2 evolution) • Recombine all partons: • Partons = soft/thermal + showers from jets • Two parton distribution function: Partons from 1 jets soft-soft Partons from 2 jets soft-shower Recombination and Hadron Correlations

  36. Soft/Hard Recombination • Soft/Hard Reco could be important. • Signatures in the p/, /K ratio at largePT. • Produces hadron correlations. Hwa and Yang Recombination and Hadron Correlations

  37. 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Intermediate PT • Naively expected behavior of observables • What is found at RHIC: • Some soft physics extends up to 4-6 GeV/c • But above 2 GeV/c not described by ideal hydrodynamics • Soft-hard region of phase space = new phenomena Soft/Hydro pQCD Hydro ReCo/soft-hard pQCD Recombination and Hadron Correlations

  38. Jets & Medium • Recombination alone is not sufficient to understand the soft-hard region. • Uses parameterizations of effects on the parton phase • Need understanding of the mechanisms behind jet-medium interaction • Still much to learn • LHC: will the soft/hard region be larger? Jets Medium Recombination and Hadron Correlations

  39. Summary • Soft-hard regime at intermediate PT; extends up to 6 GeV/c, maybe more. • Recombination describes hadronization in this regime. • Recombination translates parton correlations into hadron correlations: possible origin of jet correlations • Hot spots from jet-medium interactions create such correlations. • Soft-Hard correlations are an additional mechanism Recombination and Hadron Correlations

  40. Backup Recombination and Hadron Correlations

  41. Recombination & Fragmentation • Competition of hadronization mechanisms • Fragmentation dominates for power law spectra in the limit PT  • Recombination dominates for exponential spectra • Note: thermal recombination ~ statistical model for PT  Power law: for mesons Exponential: Recombination and Hadron Correlations

  42. Jets vs Medium • Apparent question: what is a jet, what is the medium? • Possible (not unique) definition: • Jets dominate when the hadron chemistry matches expectation for jets in the vacuum • No pure jet scenario when partons from the “medium” contribute to hadron production • We compare vacuum fragmentation with recombination • Medium influence on jets effectively taken into account via energy loss • Everthing that does not belong to a vacuum jet, e.g. additional gluon radiation, is assumed to be part of the medium (thermalized or not) Recombination and Hadron Correlations

  43. Correlations from Fragmentation • Simple model for correlations from fragmentation: • Dihadron fragmentation (Majumder & Wang) here factorized in single hadron fragmentation • Gaussian azimuthal dependence • Note: • Contributions from soft-hard are small in our parametrization • Correlations from soft-hard negligible because of the small yields • Different from other groups. u thermal - d Fragmentation u  + d + u minijet Recombination and Hadron Correlations

  44. PHENIX Preliminary Au+Au 200 GeV Identified Particles! • Again: no prediction about the input (correlations) on the parton side. • If predictive power, then for comparison of different hadron species. Recombination and Hadron Correlations

  45. Higher Fock States • Tower of Fock states, th state with n partons: • Probability for ejection of a very fast cluster with n partons from a thermal source at fixed P is independent of n! • Elliptic flow: • scaling violated even for very narrow wave functions (xi 1/n) Recombination and Hadron Correlations

  46. Conical Flow? • Preliminary data suggest double peak away side correlation • Mach cone? • More conservative scenario: flowing hot spots? • Defocussing through radial flow • Supported by PT,trig dependence? • Has to be ruled out before any more daring conclusion Recombination and Hadron Correlations

  47. Summary • “Jets” deviate in shape and hadrochemistry from vacuum for values below 6 GeV/c • Exact definition needed. • To study jets and energy loss PT,trigger > 6 GeV/c mandatory, maybe more Recombination and Hadron Correlations

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