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Hard Probes of the Quark Gluon Plasma Lecture II: heavy flavour, geometry

Hard Probes of the Quark Gluon Plasma Lecture II: heavy flavour, geometry. Marco van Leeuwen, Nikhef and Utrecht University. Lectures at: Quark Gluon Plasma and Heavy Ion Collisions Siena, 8-13 July 2013. So what are we trying to do. High-energy parton (from hard scattering). Hadrons.

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Hard Probes of the Quark Gluon Plasma Lecture II: heavy flavour, geometry

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  1. Hard Probes of the Quark Gluon PlasmaLecture II: heavy flavour, geometry Marco van Leeuwen, Nikhef and Utrecht University Lectures at: Quark Gluon Plasma and Heavy Ion Collisions Siena, 8-13 July 2013

  2. So what are we trying to do... High-energy parton (from hard scattering) Hadrons • First: understand (parton) energy process • Magnitude, dominant mechanism(s) • Probability distribution • Lost energy • Radiated gluons/fragments • Path length dependence* • Flavour/mass dependence* • Large angle radiation? • Goal: use this to learn about the medium * Topics of today’s lecture

  3. A simplified approach This is the simplest ansatz – most calculation to date use it (except some MCs) Parton spectrum Energy loss distribution Fragmentation (function) known pQCDxPDF extract `known’ from e+e- This is where the information about the medium is P(DE) combines geometry with the intrinsic process From yesterday’s lecture: Absolute calibration unknown  Always need to compare 2 or more measurements

  4. Heavy quarks Definition: heavy quarks, m >> LQCD ‘Perturbative’ hadronisation Charm: m ~ 1.5 GeV Bottom: m ~ 4.5 GeV Top: m ~ 170 GeV Complications exist: QCD, EW corrections; quark mass defined in different ways M. Cacciari, CTEQ-MCNet summer school 2008 Heavy quarks: m >> TQGP Heavy quarks are (mostly) produced in hard scattering, no (or small)contribution from hadronisation and thermal production in QGP

  5. Dead cone effect Radiated wave front cannot out-run source quark Heavy quark: b < 1 Result: minimum angle for radiation  Mass regulates collinear divergence

  6. Heavy quark suppression Calculated energy loss light Wicks, Horowitz et al, NPA 784, 426 Expect: heavy quarks lose less energy due to dead-cone effect Most pronounced for bottom Interference effect: Radiated wave front cannot out-run source quark M.DjordjevicPRL 94 Heavy quark: b < 1 Result: minimum angle for radiation  Mass regulates collinear divergence

  7. Heavy-to-Light ratio expectations at LHC Colour-charge and mass dep. of E loss Heavy-to-light ratios: mass effect For pT > 10 GeV charm is ‘light’ RD/h : colour-charge dependence of E loss RB/h : mass dependence of E loss Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

  8. Charm decay reconstruction D meson mass ~ 1.8 GeV/c2 Decay length ~ 100 mm Branching ratios ~ 4%

  9. Heavy vs light comparison Charm meson and light hadron RAA similar at LHC No dead cone effect? or Not sensitive? Jury still out... Experiment: measure Beauty Challenging, but not impossible,see Andrea Beraudo’s talk

  10. D meson RAA RAA < 1: charm also loses energy Agrees with (most) model calculations However: some models have no prediction for light quarks. Calibration?

  11. So how about beauty? Would like to measure beauty – Heavier, so larger dead cone effect Experimentally very challenging : Very few all-hadron decays; tiny branching ratios: BR: 0.48% BR: 0.1% • Current techniques: • Semi-leptonic decays; displaced electrons • Electron-hadron correlations ‘partial reconstruction’ of the decay • Secondary J/y • Beauty in jets (displaced electrons, muons)

  12. Heavy quark fragmentation Heavy quarks Light quarks Heavy quark fragmentation: leading heavy meson carries large momentum fraction (Dead cone in vacuum) Can we use this to get a handle on parton pT? To be studied...

  13. Part II: Path length dependence

  14. Geometry Density along parton path Density profile Profile at t ~ tform known Longitudinal expansion dilutes medium  Important effect Space-time evolution is taken into account in modelling

  15. RAA vs j and elastic eloss Out of Plane In Plane Elastic E-loss gives small v2 T. Renk, PRC76, 064905, J. Auvinen et al, PRC82, 051901 Data require L2 or stronger path length dependence However, also quite sensitive to medium density evolution

  16. Path length dependence: RAA vs j Out of Plane In Plane PHENIX, arXiv:1208.2254 Suppression depends on angle, path length Not so easy to model: calculations give different results

  17. RAA vs j: heavy flavour In- vs out-of-plane difference also seen for charm  Additional constraint for models?

  18. Di­hadron correlations Combinatorialbackground 8 < pTtrig < 15 GeV associated pTassoc > 3 GeV  trigger Near side Away side Use di-hadron correlations to probe the jet-structure in p+p, d+Au and Au+Au

  19. Di-hadrons at high-pT: recoil suppression d+Au Au+Au 20-40% Au+Au 0-5% pTassoc > 3 GeV pTassoc > 6 GeV High-pT hadron production in Au+Au dominated by (di-)jet fragmentation Suppression of away-side yield in Au+Au collisions: energy loss

  20. Di­hadron yield suppression trigger Near side associated Away side 8 < pT,trig < 15 GeV Near side Yield in balancing jet, after energy loss Yield of additional particles in the jet trigger STAR PRL 95, 152301 Away side associated Near side: No modification  Fragmentation outside medium? Away-side: Suppressed by factor 4-5  large energy loss

  21. Path length II: ‘surface bias’ Near side trigger, biases to small E-loss Away-side large L Away-side suppression IAA samples longer path-lengths than inclusives RAA

  22. Di-hadron modeling Model ‘calibrated’ on single hadron RAA T. Renk, PRC, arXiv:1106.1740 L (YaJEM): too little suppresion L2 (YaJEM-D) slightly above L2 (ASW) fits data L3 (AdS) slightly below Modified shower generates increase at low zT

  23. Di-hadrons and single hadrons at LHC Need simultaneous comparison to several measurements to constrain geometry and E-loss Here: RAA and IAA Three models: ASW: radiative energy loss YaJEM: medium-induced virtuality YaJEM-D: YaJEM with L-dependent virtuality cut-off (induces L2)

  24. Di-hadron with high-pT trigger pTtrig (GeV): 19.2 - 24.0 GeV 14.0 - 28.8 GeV 28.8-35.2 GeV 35.2-48.0 GeV pttrig > 20 GeV at LHC: strong signals even at low pTassoc 1-3 GeV CMS-PAS-HIN-12-010

  25. CMS di-hadrons: near side pTtrig (GeV): 19.2 - 24.0 GeV 14.0 - 28.8 GeV 28.8-35.2 GeV 35.2-48.0 GeV CMS-PAS-HIN-12-010 central 0-10% peripheral 50-60% Transition enhancement → suppression @ pT ~ 3 GeV also compatible with IAA=1 at pT > 3 GeV?

  26. CMS di-hadrons: away side pTtrig (GeV): 19.2 - 24.0 GeV 14.0 - 28.8 GeV 28.8-35.2 GeV 35.2-48.0 GeV central 0-10% CMS-PAS-HIN-12-010 peripheral 50-60% Transition enhancement → suppression @ pT ~ 2 GeV

  27. Part III: Low, intermediate pT

  28. Identified hadron RAA M. Ivanov, A. Ortiz@QM2012 M. Ivanov, A. Ortiz@QM2012 Low-intermediate pT (1-6 GeV): Large baryon/meson ratio Baryon, meson RAA similar at pT > 8 GeV As expected from parton energy loss • Probably due to: • radial flow • parton recombination

  29. Identified hadron RAA (strangeness) L: RAA~1 at pT~3 GeV/c Smaller suppression, L/K enhanced at low pT Kaon, pion RAA similar pT ~8 GeV/c: All hadrons similar partonic energy loss + pp-like fragmentation?

  30. Hadronisation by recombination ‘Shower-thermal’ recombination Fries, Muller et al Hwa, Yang et al Baryon pT=3pT,parton MesonpT=2pT,parton fragmenting parton: ph = z p, z<1 recombining partons: p1+p2=ph Hot matter Hard parton (Hwa, Yang) Expect large baryon/meson ratio associated with high-pT trigger Recombination of thermal (‘bulk’) partonsproduces baryons at larger pT Baryon pT=3pT,parton MesonpT=2pT,parton Hot matter

  31. Di-hadrons: p/p in jets associated  trigger 5 < pTtrig < 10 GeV Jet peak Background/Bulk region (v2, v3 peak here) Use TOF+dE/dx to identify particles

  32. p/p bulk vs jets p/p ratio in jet* agrees with Pythia *after background subtraction p/p ratio in Bulk regionagrees with inclusive M. Veldhoen, HP No effect of shower-thermal recombination and/or modified color flow observed

  33. Near-side ridge in AA – Flow  trigger d+Au, 200 GeV Au+Au 0-10% STAR preliminary 3 < pt,trigger < 4 GeV pt,assoc. > 2 GeV d+Au: ‘jet’-peak, symmetric in f, h Au+Au: extra correlation strengthat large Dh ‘Ridge’ First seen at RHIC – Unexplained for a while Most likely: flow, v3

  34. Di-hadron correlations and flow at low pT Low pT <~ 3 GeV: di-hadron correlations dominated by flow ALICE, PRL 107, 032301 Important contributions from v3, v4 Alver and Roland,PRC81, 054905 Also NB: v1 can mimick jet (near or away-side)

  35. Low pT di-hadron shapes at LHC 0-10% 60-70% pp 2 < pT,trig < 3 1 < pT,assoc < 2 Dh Dh Dh Dj Dj Dj pT 4 < pT,trig < 8 2 < pT,assoc < 3 Dh Dh Dh Dj Dj Dj

  36. Departure from Gaussian • The lowest pT bin shows a structure with a flat top in Dh • This feature is reproduced by AMPT • Qualitative and quantitative agreement of peak shapes with AMPT compatible with hypothesis of interplay of jets with the flowing bulk Data AMPT 0-10% 2 < pT,t < 3 GeV/c 1 < pT,a < 2 GeV/c Dj , Dh Dj , Dh

  37. Peak Deformation Calculation + STAR prel: 2 < pT,t < 3 1 < pT,a < 2 GeV/c 4 < pT,t < 8 2 < pT,a < 3 GeV/c h rms (calc.) sDj , sDh (fit) sDh sDj j rms (calc.) dNch/dh Centrality | 100 = pp Longitudinal flow deforms jet shape • Significant increase of sDhtowards central events • sDh > sDj (eccentricity ~ 0.2) Armesto, Salgado, Wiedemann PRL 93,242301 (2004)

  38. AMPT Comparison • AMPT (A MultiPhase Transport Code) describes collective effects (e.g. v2, v3, v4) in HI collisions at LHC • Here version with string melting (2.25) is shown • RMS of the near-side peak reasonably described by AMPT • Detailed mechanism not known; Interplay of jet and flow ? 2 < pT,t < 3 1 < pT,a < 2 GeV/c 3 < pT,t < 4 2 < pT,a < 3 GeV/c 4 < pT,t < 8 2 < pT,a < 3 GeV/c sDj (fit) (rad.) sDh (fit) (rad.) Lines: AMPT 2.25 and Pythia P-0 (for pp) Centrality | 100 = pp Centrality | 100 = pp

  39. Integrated vs differential • Inclusive hadron suppression RAA • Overall magnitude + pT dependence: limited dynamical information • Only useful when the energy loss mechanism is understood • Di-hadrons; IAA • Two ‘degrees of freedom’ • Adds constraints when compared to RAA; mostly geometry? • Low pT, shape info • More differential, but also more difficult to model

  40. Summary • Heavy flavour • Expect dead cone effect: reduced energy loss • No clear evidence of dead cone effect for charm in data • Path length dependence • RAA vs j • Di-hadron suppression Favours: L2 or stronger • Low, intermediate pT < 6-8 GeV/c • Large B/M ratio: flow or recombination? • B/M in jets ~0.2 • Jet-like correlations: • Large effect of bkg flow • Shapes change (broadening in Dh)

  41. Extra slides

  42. Comparing single- and di-hadron @ RHIC Armesto, Cacciari, Salgado et al. RAA and IAA fit with similar density Confirms ~L2 dependence Calculations with elastic loss give too little suppression

  43. D mesons QM2012, Zaida CdelV

  44. Jet Quenching High-energy parton (from hard scattering) Hadrons • How is does the medium modify parton fragmentation? • Energy-loss: reduced energy of leading hadron – enhancement of yield at low pT? • Broadening of shower? • Path-length dependence • Quark-gluon differences • Final stage of fragmentation outside medium? 2) What does this tell us about the medium ? • Density • Nature of scattering centers? (elastic vs radiative; mass of scatt. centers) • Time-evolution?

  45. Heavy Quark Fragmentation II Significant non-perturbative effects seen even in heavy quark fragmentation

  46. Di-hadron correlations associated  trigger After background subtraction ALICE, arXiv:1110.0121 Background Compare AA to pp • Di-hadron correlations: • Simple and clean way to access di-jetfragmentation • Background clearly identifiable • No direct access to undelying kinematics(jet energy) Near side: yield increases Away side: yield decreases Energy loss+fragmentation Quantify/summarise: IAA

  47. Comparing single- and di-hadron @ RHIC Armesto, Cacciari, Salgado et al. RAA and IAA fit with similar density Confirms ~L2 dependence Calculations with elastic loss give too little suppression

  48. Spectra at intermediate pT Schukraft et al, arXiv:1202.3233 • Probably due to: • radial flow • parton recombination Low-intermediate pT (1-6 GeV): Large baryon/meson ratio

  49. Parton energy loss – main questions High-energy parton (from hard scattering) Hadrons • Understand production rates • Understand parton energy loss process • Energy loss as a function of density • Path length dependence • Elastic, radiative, other? • Mass dependence • Interplay between vacuum and medium radiation • Broadening of shower: • Out-of-cone radiation • Leading hadron vs softening of FF • Use as a probe to determine medium density (and other properties)

  50. Di-hadron yields at LHC Near side Away side 8 < pTtrig < 15 GeV ALICE, PRL 108,092301 Near side: ~20% yield enhancement Away side: suppression by factor ~2 Fragmentation after energy loss Recoil parton energy loss

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