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Lecture IVa: jets

Lecture IVa: jets. Marco van Leeuwen, Utrecht University. Lectures for Helmholtz School Feb/March 2011. Jet quenching event generators. Analytical models BDMPS, ASW, GLV, AMY, HT: exact interference, but approximate treatment of kinematic limits (energy conservation).

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Lecture IVa: jets

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  1. Lecture IVa: jets Marco van Leeuwen, Utrecht University Lectures for Helmholtz School Feb/March 2011

  2. Jet quenching event generators Analytical models BDMPS, ASW, GLV, AMY, HT: exact interference, but approximate treatment of kinematic limits (energy conservation) • PyQuench/Hydjet (Lokhtin et al) • Mostly phenomenological • qPYTHIA (Armesto, Cunqueiro, Salgado) • BDMPS-based modified showering • JEWEL (Wiedemann and Zapp) • Start from elastic E-loss, trying to systematically implement LPM effecy • MARTINI (Schenke) • AMY-based, modular • YaJEM (Renk) • Medium-induced increase of virtuality Monte-Carlo excellent tool to include kinematic limits; interference effects difficult MC generators are also an important tool for experimentalists

  3. Jet RAA at RHIC M. Ploskon, STAR, QM09 Jet RAA >> 0.2 (hadron RAA) Jet finding recovers most of the energy loss  measure of initial parton energy Some dependence on jet-algorithm? Under study…

  4. Jet broadening in qPythia Armesto, Cunqueiro, Salgado, arXiv:0907.1014 Parton level Hadron level (dijet) E=10 GeV E=10 GeV R=0.4 R=0.4 Large effect of medium on transverse jet shape

  5. Jet-hadron correlations Recoil peak width Experiment indicates: strong pT-dependence of broadening Soft radiation at larger angle Large difference between broadening of number density vs energy density NB: no correction for trigger bias (jet energy), jet energy resolution (background fluctuations)

  6. Comparison to qPythia qPythia: medium modified fragmentation These calculations: realistic path length, density distribution ALICE EMCal PPR, arXiv:1008.0413 qPythia: if p0 RAA~0.2, expect jet RAA ~0.2-0.3 (R=0.4) Hadron RAA small, strong interactions  out-of-cone radiation Not seen in data

  7. STAR vs PHENIX jet RAA STAR Preliminary M. Ploskon, STAR, QM09 PHENIX, Y-S Lai, HP2010 PHENIX Au+Au: jet RAA ~ 0.6 STAR Au+Au: jet RAA ~ 1 Gaussian filter, s=0.3 +’fake rejection’ kT, anti-kT, R=0.4 Not clear whether STAR and PHENIX results are in agreement

  8. Jet broadening in qPythia ALICE EMCal PPR, arXiv:1008.0413 R(0.2)/R(0.4) measured by STAR smaller than qPythia expectations

  9. Di-jet spectra Jet IAA Away-side jet yield suppressed  partons absorbed E. Bruna, STAR, QM09 STAR Preliminary ... due to large path length (trigger bias) STAR Preliminary 9

  10. Jets at LHC LHC: jet energies up to ~200 GeV in Pb+Pb from 1 ‘short’ run Large energy asymmetry observed for central events

  11. Jets at LHC Centrality ATLAS, arXiv:1011.6182 (PRL) Large asymmetry seen for central events Jet-energy asymmetry Energy losses: tens of GeV, ~ expected from BDMPS, GLV etc beyond kinematic reach at RHIC N.B. only measures reconstructed di-jets Does not show ‘lost’ jets Large effect on recoil: qualitatively consistent with RHIC jet IAA

  12. Jets at LHC CMS, arXiv:1102.1957 CMS sees similar asymmetries

  13. Lecture IVb: Intermediate pT Marco van Leeuwen, Utrecht University Lectures for Helmholtz School Feb/March 2011

  14. Intermezzo: particle detectors and particle identification Tracking Momentum measurement Charged particles in magnetic field Muon detection Charged particle tracking in magnetic field EM Calorimeter Energy measurement Showering of g, e (e -> eg, g-> ee) High-Z material e.g. Pb-Scintillator, Pb-glass,PbWO crystals, Pb-LAr, W-Si sandwich Hadron Calorimeter Energy measurement Showering of hadrons h → p0 →gg Need large total mass (e.g. big piece iron with scintillators) ‘Standard’ high-energy physics detector stackMain goal: measure all particles/energy flow (except n)

  15. PID in HEP detectors Identify hadrons/leptons/photons by signature in detectors EMCal HCal tracker muon system Charged hadron (p, K, p) Neutral hadron (n, K0L) electrons photons muons Note: large expense for muons (EW probe, < 1 % of primary tracks in QCD event)neutral hadrons (~5% in QCD event) HI experiments normally do without HCal and with limited muon capability

  16. From sketch to reality: CMS

  17. Detector examples ‘General purpose’detectors at LHC ALICE CMS ATLAS (not to scale: RATLAS>RCMS >RALICE )

  18. PID: weak decays in tracker ‘topological reconstruction’ With a tracker, reconstruct weak decays: Λ, |y|<1 0.4 <pt< 0.6 K0→pp (ct = 2.7 cm ) L0→ pp (ct = 7.9 cm) D0 → Kp (ct = 124 mm) D+ → Kpp (ct = 315 mm) And also: t -> hadrons t -> Wb ->…

  19. Charged hadron identification kaons protons deuterons pions electrons Other techniques identify p, K, p by measuring mass (velocity) Specific energy loss dE/dx Time-of-flight (TOF) STAR TPC STAR Depends on bg Mostly at low pT < 1 GeV Depends on b < 100 ps resolution, PID up to few GeV TPC-dE/dx and TOF are basic features of most Heavy-Ion detectors

  20. Ring Imaging Cherenkov (RICH) Ring reconstruction Cherenkov angle depends onindex of refraction  tunable Advantage: RICH can be optimised for large momentum Not so easy with high track densities

  21. STAR and PHENIX at RHIC STAR PHENIX PHENIX STAR Large acceptance at mid-rapidity: TPC tracking (coarse) EMCal Some forward Calorimeters PID: TPC-dE/dx, TOF Central tracking/calo arms (partial coverage, finely segmented calo) Forward muon arms PID: TOF, RICH General purpose detector Focus on rare probes (electrons/photons) (PHOBOS, BRAHMS even more specialised)

  22. ALICE Barrel: tracking + secondary vertices + PID • Charged particles |h| < 0.9 • Excellent momentum resolution up to 100 GeV/c (Dp/p < 6%) • Tracking down to 100 MeV/c • Particle ID: dE/dx, TOF, RICH • Heavy flavor tagging: ITS EMCal for jet reconstruction • Pb-scintillator, 13k towers • Df = 107, |h| < 0.7 • Energy resolution ~10%/√Eg • Trigger capabilities PHOS: small acceptance, High granularity EMCal • High resolution PbWO4 crystals • |h| < 0.12, 220 < f < 320 • Energy resolution: DEg/Eg = 3%/Eg Forward muon arm ‘STAR+PHENIX in one’ at LHC

  23. Baryon excess STAR Preliminary B. Mohanty (STAR), QM08 High pT: Au+Au similar to p+p  Fragmentation dominates Baryon/meson = 0.2-0.5 Intermediate pT, 2 – 6 GeV Large baryon/meson ration in Au+Au

  24. Hadronisation through coalescence Fries, Muller et al Hwa, Yang et al fragmenting parton: ph = z p, z<1 R. Belmont, QM09 recombining partons: p1+p2=ph Recombination enhancesbaryon/meson ratio Recombination of thermal (‘bulk’) partonsproduces baryons at larger pT Baryon pT=3pT,parton MesonpT=2pT,parton Note also: v2 scaling Hot matter

  25. Near-side ‘Ridge’  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’ Unexpected – what can it be?

  26. Mechanisms for ridge formation Long. flow Long. flow Long. flow Long. flow Three categories Jet broadening Medium response Trigger effect Gluons from fragmentation/energy loss couple to longitudinal flow Extra yield due to medium heating/drag or propagating parton Trigger selects existing structure in the medium (underlying event, color flux tubes) + ‘new’ suggestion: v3 Different scenarios suggest different behaviour, e.g. multiplicity, pT-dependence, Dh extent, baryon content

  27. Near-side Ridge  trigger 3 < pt,trig< 4 GeV/c Jet-like peak 4 < pt,trig < 6 GeV/c pt,assoc. > 2 GeV/c Au+Au 0-10% STAR preliminary Au+Au 0-10% STAR preliminary J. Putschke et al, QM06 `Ridge’: associated yield at large , small Df associated Weak dependence of ridge yield on pT,trig  Relative contribution reduces with pT,trig Ridge softer than jet – medium response?

  28. Ridge – Dh shape Projection provides more quantitative info Clearly 2 shapes: jet-like + ridge Ridge very broad in Dh, almost independent in acceptance Also note: ridge yield ~ independent of pt,trig

  29. Jet-peak shape Pt,trig > 4 GeV, jet-like peak symmetric in h,jand width similar to d+Au (no medium) Jet-like peak unmodified (like in high-pT correlations, lect II)

  30. Associated spectra jet, ridge Jet-like spectra similar in d+Au and Au+Au Ridge softer than jet – Different production mechanism?

  31. Associated yields from coalescence Recombination of thermal (‘bulk’) partons ‘Shower-thermal’ recombination Baryon pT=3pT,parton MesonpT=2pT,parton Baryon pT=3pT,parton MesonpT=2pT,parton Hot matter Hot matter Hard parton (Hwa, Yang) No jet structure/associated yield Expect large baryon/meson ratio associated with high-pT trigger Expect reduced associated yield with baryon triggers 3 < pT < 4 GeV

  32. Associated baryon/meson ratios pTtrig > 4.0 GeV/c 2.0 < pTAssoc< pTtrig p+p / p++p- C. Suarez et al, QM08 Associated yields Inclusive spectra Au+Au: Baryon enhancement Ridge (large Dh): Baryon enhancement p+p, d+Au: B/M  0.3 Jet (small Dh) B/M  0.3 Baryon/meson ratio in ridge close to Au+Au inclusive, in jet close to p+p Different production mechanisms for ridge and jet?

  33. Ridge summary • Most notable features: • Ridge much broader than jet in Dh • Jet-like peak similar to d+Au in shape and yield • Ridge yield ~ independent of pttrig • Ridge spectrum softer than jet • p/p ratio in ridge similar to bulk, lower in jet Strongly suggest different production mechanisms for ridge and jet However, the ridge is correlated with jets: causation, or trigger-bias (coincidence?)

  34. More medium effects: away-side 3.0 < pTtrig < 4.0 GeV/c 1.3 < pTassoc < 1.8 GeV/c Au+Au 0-10% d+Au STAR preliminary Away-side: Strong broadening in central Au+Au ‘Dip’ at  = 

  35. Away-side shapes Preliminary 3.0 < pTtrig < 4.0 GeV/c 4.0 < pTtrig < 6.0 GeV/c 6.0 < pTtrig < 10.0 GeV/c 1.3 < pTassoc < 1.8 GeV/c Au+Au 0-12% 0-12% M. Horner, M. van Leeuwen, et al Low pTtrig: broad shape, two peaks High pTtrig: broad shape, single peak Fragmentation becomes ‘cleaner’ as pTtrig goes up Suggests kinematic effect?

  36. Shockwave/Mach Cone T. Renk, J. Ruppert Mach-cone/shockwave in the QGP? Gyulassy et al arXiv:0807.2235 Exciting possibility! Proves that QGP is really ‘bulk matter’ Measure speed of sound? B. Betz, QM09, PRC79, 034902 Are more mundane possibilities ruled out? – Not clear yet

  37. The fine-print: background High pT: background <~ signal Low pT: background >> signal 8 < pTtrig < 15 GeV 3.0 < pTtrig < 4.0 GeV/c pTassoc > 3 GeV 1.3 < pTassoc < 1.8 GeV/c Background normalisation: Zero Yield At Minimum v2 modulated background v2trig * v2assoc ~ few per cent N.B. no signal-free region at low pT

  38. v3, triangular flow Alver and Roland, PRC81, 054905 Participant fluctuations lead to triangular component of initial state anisotropy

  39. v3 in Hydro Schenke, Jeon, Gale, PRL 106, 042301 Evolution of initial state spatial anisotropy depends on viscosity

  40. v3 vs eps v3 from Hydrodynamics v3 from AMPT Schenke and Jeon Alver and Roland Initial triangular anysotropy gives rise to v3 in both parton cascade and hydrodynamics v3 can be the underlying mechanism for both ‘ridge’ and ‘Mach cone’

  41. Ridge: soft to hard Dh vs Dj Au+Au vs p+p Low pt: jet-like peak broadened in Dh High pt: jet-like peak similar to p+p reference + ridge

  42. Di-hadron correlation overview Low-low: soft jets? Fluid dynamics? PHENIX, arXiv:0801.4545 High-low: jets+medium response? High-high: jets + parton eloss

  43. Final note Hard probes of the QCD medium: Two important aspects: • Validate understanding of in-medium fragmentation • Determine medium properties • To test understanding, need fewer unknowns than measurements • Light quark energy loss • Heavy quark energy loss • Inclusive vs di-hadrons • Azimuthal modulation (RAA vs rplane, v2) • Jet-finding Need coherent picture (and understanding exceptions)before we can use energy loss as a tool

  44. Properties of medium at RHIC Transport coefficient 2.8 ± 0.3 GeV2/fm (model dependent) e 23 ± 4 GeV/fm3 pQCD: T  400 MeV (Baier) (Majumder, Muller, Wang)  ~5 - 15 GeV/fm3T ~ 250 - 350 MeV Viscosity Total ET t0 = 0.3-1fm/c (Bjorken) From v2 Lattice QCD: h/s < 0.1 (Meyer) Broad agreement between different observables, and with theory However, many pieces don’t fit comfortably; still work to do 

  45. Extra slides

  46. Naive picture for di-hadron measurements Fragment distribution (fragmentation fuction) Radiation softens fragmentation Fragments produce low-pT hadrons Ref: no Eloss PT,jet,1 PT,jet,2 Naive assumption for di-hadrons: pT,trig measures PT,jet So, zT=pT,assoc/pT,trig measures z

  47. Energy loss in action Near side yield Away side yield Away side yield ratio Near side yield ratio |Dj|<0.9 |Dj|>0.9 8 < pT < 15 GeV 8 < pTtrig < 15 GeV Au+Au / d+Au Au+Au / d+Au 8 < pT < 15 GeV Preliminary Preliminary M. Horner, QM06 zT=pTassoc/pTtrig zT=pTassoc/pTtrig zT=pTassoc/pTtrig zT=pTassoc/pTtrig Preliminary Lower pTtrig Lower pTtrig 1.0 M. Horner, M. van Leeuwen, et al 0.2 Near- and away-side show yield enhancement at low pT Away-side: gradual transition to suppression at higher pT Possible interpretation: di-jet → di-jet (lower Q2) + gluon fragments ‘primordial process’ Near side: ridge Away-side: broadening High-pT fragmentsas in vacuum

  48. Three-particle measurements ‘Cone’ case ‘kT’ case (deflected jets) Two classes of events: All events same distribution: Backgroundlevel 2-particle correlations measure event-average – Not sensitive to event-to-event changes in structure Next slides: simplistic simulation to illustrate 3-particle methods and background

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