PIColloquium v4

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Information about PIColloquium v4

Published on November 15, 2007

Author: Nevada

Source: authorstream.com

Probing the Properties of the Quark-Gluon Plasma and Studying Strong-Field QCD in Heavy Ion Collisions @ RHIC and the LHC:  Probing the Properties of the Quark-Gluon Plasma and Studying Strong-Field QCD in Heavy Ion Collisions @ RHIC and the LHC Prof. Brian A. Cole. Columbia University PHENIX and ATLAS The “Big Picture”:  The “Big Picture” Heavy Ion (Au+Au) collision as seen by the STAR time-projection chamber. Why??? Fundamental Interactions:  Fundamental Interactions Matter usually studied in the lab has properties determined by EM interactions. How would non-Abelian matter be different? The Big Picture:  The Big Picture We have a fundamental theory of strong interactions exhibits asymptotic freedom at large momentum transfer. What about other limits of QCD? High temperature High field strength QCD Thermodynamics (on Lattice):  QCD Thermodynamics (on Lattice) Rapid cross-over from “hadronic matter” to “Quark-Gluon Plasma” at T  170 MeV Energy density,  ~ 1 GeV/fm3. Only fundamental “phase transition” that can be studied in the laboratory. Is the QGP weakly interacting?? Energy Density / T4 Pressure / T4 Relativistic Heavy Ion Collider :  Relativistic Heavy Ion Collider Run 1 (2000): Au-Au SNN = 130 GeV Run 2 (2001): Au-Au, p-p SNN = 200 GeV Run 3 (2003): d-Au, p-p SNN = 200 GeV Run 4 (2004): Au-Au SNN = 200, 64 GeV, p-p SNN = 200 GeV Run 5 (2005): Cu-Cu SNN = 200, 64 GeV, p-p SNN = 200 GeV STAR Heavy Ion Collision Time History:  Heavy Ion Collision Time History RHIC collision space-time history in “parton cascade” model RHIC Initial Conditions:  RHIC Initial Conditions Au+Au @ 200 GeV per nucleon,  = E/m  100. Au diameter, d  14 fm, contracted d/  0.2 fm Crossing time < 0.2 fm/c. Add quantum mechanics: E  ħc / t Fluctuations with E > 1 GeV are “on shell” These are primarily gluons (~ 200/collision) RHIC is a gluon collider! (10 GeV/fm3) “Saturation” @ low x:  “Saturation” @ low x @ High energy nuclei are highly Lorentz contracted Except for soft gluons Which overlap longitudinally And recombine producing broadened kT distribution Generates a new scale: Qs Typical kT of gluons If Qs >> QCD, perturbative calculations possible. Large occupation #s for kT<Qs  classcial fields Saturation is a result of unitarity in QCD QCD: Evolution:  QCD: Evolution Quarks radiate copiously Evolution of proton (e.g.) parton distribution functions Growth of gluon distribution @ low x @ high gluon density recombination starts to limit growth. Qs - resolution scale where recombination starts to dominate Limiting density  Qs2/s ~ Classical field Saturation @ HERA?:  Saturation @ HERA? Measurements of DIS cross-section vs x, Q2 for x < 0.01. Plotted vs All x dependence in the saturation scale. “Geometric scaling” Precursor to saturation in PDF evolution Golec-Biernat and Wusthoff (GBW) Saturation Model (empirical) RHIC Particle Multiplicities:  RHIC Particle Multiplicities Multiplicity @ RHIC on low end of predicted range Slow growth with impact parameter (Npart) Inconsistent with factorized mini-jet production Best described by saturation model Multiplicity per colliding nucleon pair But, Have We Created “Matter” ?:  But, Have We Created “Matter” ? “Pressure” converts spatial anisotropy to momentum anisotropy. Requires early thermalization. Unique to heavy ion collisions Answer: yes dN/d “Elliptic Flow”:  “Elliptic Flow” Parameterize  variation by “v2” parameter Compare to “eccentricity”: Data consistent w/ hydrodynamic calculations (Ideal) Hydrodynamics in one slide:  (Ideal) Hydrodynamics in one slide Estimating the (Shear) Viscosity:  Estimating the (Shear) Viscosity Relevant parameter for determining collective motion of quark-gluon plasma viscosity to entropy ratio: /s. Finite viscosity leads to dependence of flow strength on pT. Correction  (/s) pT2 From data shown to right, obtain estimate: /s ~ 0.1 Very small! s is “sound attenuation length”  mean free path Comparison to “Typical” Vicosities:  Comparison to “Typical” Vicosities /s ~ 0.1 Thus the statement: QGP is most perfect fluid every created Lattice QCD Estimate of /s:  Lattice QCD Estimate of /s “Casual” Viscous Hydrodynamics:  “Casual” Viscous Hydrodynamics Causal fix introduces a new scale, , relaxation time. Uncertainty in  weakens /s constraint Concludes /s < 0.5, but elliptic flow? P. Romatschke nucl-th/0701032 Comparison of viscous hydro results to meson spectra from PHENIX Thermalization via Plasma Instabilities?:  Thermalization via Plasma Instabilities? pT vs pz anisotropy Generates strong local chromo-magnetic fields Lorentz forces produce rapid isotropization. Pressure from macro-scopic color fields?! Energy density Penetrating Probes of Created Matter:  Use self-generated quarks/gluons/photons as probes of the medium (classic physics technique!) Penetrating Probes of Created Matter z t Collisions between partons How to directly probe medium ?:  How to directly probe medium ? Use quarks & gluons from high-Q2 scattering “Created” at very early times (~ 0.1 fm). Propagate through earliest, highest  matter. (QCD) Energy loss of (color) charged particle ~ Entirely due to radiation Virtual gluon(s) of quark multiply scatter. e.g. GLV (Gyulassy, Levai, Vitev) formalism Perturbative quantum chromo-dynamics:  Perturbative quantum chromo-dynamics Factorization: separation of  into Short-distance physics: – calculable using perturbation theory** Long-distance physics: ’s – universal, measured separately. Valid @ large momentum transfer – high pT particles From Collins, Soper, Sterman Phys. Lett. B438:184-192, 1998 pQCD – Single Hadron Production:  pQCD – Single Hadron Production Add fragmentation to hadrons D(z) – fractional momentum distribution of particles in “jet” KKP Kretzer data vs pQCD Phys. Rev. Lett. 91, 241803 (2003) PHENIX Au-Au 0 Spectra:  PHENIX Au-Au 0 Spectra Calculations with no energy loss Calculations with energy loss Observe 20% of expected yield @ high pT Deduce energy density  ~15 Gev/fm3 Compare crit ~ 1 GeV/fm3 100 x normal nucleus energy density! pT spectrum Expected PHENIX: Au-Au High-pT 0 Suppression:  PHENIX: Au-Au High-pT 0 Suppression 0 Suppression: dE/dx Comparisons:  0 Suppression: dE/dx Comparisons Quark & gluon dE/dx analysis: Turbide et al (McGill) Essentially an ab initio calculation Compared to precision (relatively) data Prompt Photon Production:  Prompt Photon Production Prompt photons provide an independent control measurement for jet quenching. Produced in hard scattering processes But, no final-state effects (???) Au-Au Prompt Photon Production:  Au-Au Prompt Photon Production Photon control measurement shows no quenching pQCD calculations OK, quenching a final-state effect High-pT Single Particle Summary:  High-pT Single Particle Summary 5 violation of factorization up to 20 GeV/c In hadron production (jets), but not prompt  Hard scatterings occur at expected rates Suppression from final-state energy loss To explain data: Unscreened color charge dn/dy~1000 Energy density ~15 GeV/fm3 > 10 “critical” energy density Analysis of Single Hadron Data: BDMS-Z-SW:  Analysis of Single Hadron Data: BDMS-Z-SW “Thick medium” energy loss calculation Central 200 GeV Au+Au Transport coefficient: for radiated gluon Baier [Nucl. Phys. A715, 209 (2003)]: C = 2 expected for ideal QGP 14 GeV/fm2  c = 8-10!! Strong coupling [Eskola et al, Nucl. Phys. A747, 511 (2005)] STAR Experiment: “Jet” Observations :  STAR Experiment: “Jet” Observations proton-proton jet event In Au-Au collisions we see only one “jet” at a time ! How can this happen ? Jet quenching! Analyze by measuring (azimuthal) angle between pairs of particles Di-jet Distortion vs “Impact Parameter”:  Di-jet Distortion vs “Impact Parameter” (di)Jet Angular Correlations (PHENIX):  (di)Jet Angular Correlations (PHENIX) PHENIX (nucl-ex/0507004): moderate pT Origin of di-jet Distortion?:  Origin of di-jet Distortion? Mach cone? Jets may travel faster than the speed of sound in the medium. While depositing energy via gluon radiation. QCD “sonic boom” Mach Cone (2):  Mach Cone (2) Ideal QGP, cs2 = 1/3 Cos M = cs M = 55º Detailed calculation taking into account evolving speed of (gluon) sound from hydrodynamics. But, other possible mechanisms proposed. What I Didn’t Show You:  What I Didn’t Show You Charm quarks also are quenched And show rapid thermalization! Large charm quark elliptic flow signal Can only be established at the quark level. Large baryon excess for 2 < pT < 5 GeV/c Hadron formation by quark recombination We see final state particle flavor distributions consistent with “freeze-out” from chemically equilibrated system. We are rapidly approaching stage where QGP is ONLY viable interpretation of data RHIC Physics:  RHIC Physics Since start of RHIC, substantial progress on development of a rigorous foundation for understanding stages of a heavy ion collision: Particle production from strong gluon fields Thermalization (ideas but not yet understood) Hydrodynamic evolution Hadronization With jets as calibrated probe But jet quenching is still not completely understood We are probing the properties of the QGP – with surprising results Strong coupling – why? Speed of sound? Comparison to “Typical” Vicosities:  Comparison to “Typical” Vicosities But what is this “viscosity bound”? Calculation of viscosity using string theory Huh???? /s ~ 0.1 AdS/CFT Correspondence:  AdS/CFT Correspondence Main idea Duality between string theory in anti-DeSitter space and conformal field theories. Weakly coupled string theory  strongly coupled CFT Example conformal theory: N=4 supersymmetric Yang-Mills Which is not QCD (e.g. no running of s) But similar enough?? AdS/CFT now being applied to many apsects of RHIC physics Viscosity, /s. Jet quenching “Sound” waves Why Heavy Ions @ LHC?:  Why Heavy Ions @ LHC? Low x – Gluon production from saturated initial state Energy density – ~ 50 GeV/fm3 (?) Rate – “copious” jet production above 100 GeV Jets – Full jet reconstruction Detector – necessary detector “for free”! Heavy Ion Initial Conditions: Modern:  Heavy Ion Initial Conditions: Modern At LHC we (think we) will be able to study “classical” gluon fields in nuclei And their quantum evolution A+A Multiplicity vs Energy:  A+A Multiplicity vs Energy LHC measurements will provide an essential test of whether we understand the mechanism responsible for bulk particle production. e.g. does saturation correctly extrapolate? RHIC 200 GeV Saturation? Something else? Saturation: Geometric Scaling to A-A?:  Saturation: Geometric Scaling to A-A? Extension of GBW analysis to NMC nuclear targets Using kT factorization calculate mult. (parton-hadron duality) Compare to PHOBOS data Armesto, Salgado, Wiedemann Phys. Rev. Lett. 94 :022002,2005 Why should it work here? Elliptic Flow @ LHC:  Elliptic Flow @ LHC LHC data will provide an essential test of our understanding of elliptic flow data @ RHIC And test whether QGP is still strongly coupled Extremely high priority given the possible relevance of AdS/CFT. Large ATLAS acceptance a big advantage ?? Can change horizontal scale by x2 @ LHC Why Jets @ LHC? Rate @ High pT:  Why Jets @ LHC? Rate @ High pT Can access jet energies in excess of 100 GeV Complete jet measurements  greater precision in use of jet tomography as a probe 80 GeV Jet in Pb+Pb Jets as Color Antennas:  Jets as Color Antennas Studies of modified jets in heavy ion collisions may shed light on a “fundamental” problem in (particle) physcs A high-energy quark/gluon acts like a “color antenna” In vacuum, radiation strongly affected by quantum interference. But, in medium thermal gluons “regulate” radiation. LHC Physics Opportunity:  LHC Physics Opportunity Create & study quark-gluon plasma at T = 0.8~GeV Study particle production from strong gluon fields. New program with w/ new discoveries ~ guaranteed If RHIC is any guide … pT reach, rates, detector capabilities at LHC allow for qualitatively different (better!) measurements. Overlap w/ many other sub-fields of physics Particle physics Plasma physics Fluid/hydro dynamics Thermal field theory, lattice & non-lattice String theory (!?) – AdS-CFT correspondence General relativity (gluon production as Unruh radiation?) PHENIX: Cu-Cu 0 RAA:  PHENIX: Cu-Cu 0 RAA RAA PHENIX p-p Prompt  Production:  PHENIX p-p Prompt  Production Absolute comparison, no fudge factors. pQCD very well reproduces prompt  cross-section. Points: PHENIX Curve: PQCD “Centrality” Dependence of Suppression:  “Centrality” Dependence of Suppression Measure yield above 4.5 GeV/c. Find suppression relative to p-p. Plot vs nuclear overlap. Npart = number of “participating” nucleons Test against “best” energy loss model GLV = Gyulassy, Levai, Vitev Good agreement PHENIX: High-pT 0 v2 (Reaction Plane):  PHENIX: High-pT 0 v2 (Reaction Plane) Clear observation of decreasing v2 @ high pT From parallel session talk by D. Winter V2(pT): Energy Loss Calculations:  V2(pT): Energy Loss Calculations PHENIX: Reaction Plane Angle Dependence(2):  PHENIX: Reaction Plane Angle Dependence(2) For PHENIX reaction plane resolution & chosen bin sizes, trig bin 4 has smallest flow effects. Even without subtracting flow contribution, a dip is seen for central collisions. Look in bin #4 PHENIX Preliminary PHENIX: Reaction Plane Angle Dependence:  PHENIX: Reaction Plane Angle Dependence Study (di)jet correlations vs angle of trigger hadron relative to reaction plane J. Bielcikova et al, Phys. Rev. C69:021901, 2004 trig = trig -  6 bins from 0 to /2. Flow systematics change completely vs trig Can study dependence of distortion on geometry. Shoulder and dip seen in all trig bins. Jet Conversion Photons:  Jet Conversion Photons There is a new source of “hard” photons in QGP High pT quarks/gluons convert into photons in medium This extra contribution must be present @ large enough t, incident jet sees unscreened partons What about at low-t ? In principle, pole in the t channel produces “large” But medium screens @ low-t & regulates pole. Jet-conversion  rate sensitive to screening mass. And potentially also to quark/gluon thermal masses. Jet Quenching: Photon Bremstrahlung:  Jet Quenching: Photon Bremstrahlung For light quarks (and gluons??), in-medium energy loss dominated by radiation. Interference between vacuum & induced radiation. For large parton pT (> ~10 GeV/c) coherence crucial. Unfortunately, we can’t measure the gluons. But we could measure photon bremstrahlung! Direct measurement of medium properties. Put it all together …:  Put it all together … Extremely rich mixture of physics contributing to the photon spectrum in ~ 4-10 GeV/c range. How to unravel all of the different pieces? Shamelessly stolen from Simon’s talk. Measuring the Initial  ??:  PHENIX Measuring the Initial  ?? Bjorken Hydrodynamics: For 0 = 0.2 fm (kt ~ 1 GeV) eBj = 20 GeV/fm3 !!! dNg/dA ~ 6/fm2 But, estimate too model dependent. Need experimental probe of initial state … ~ 150 fm2 Formation time Quark-Gluon Thermodynamics:  Quark-Gluon Thermodynamics Lattice QCD Sudden change in # DOF in strongly interacting matter Critical temperature (Karsch et al) Tc = 150 – 170 MeV Energy density:  = 0.3 – 1.3 GeV / fm3 Large uncertainty due to T4 dependence. But accessible in heavy ion collisions Karsch, hep-lat/0106019 T/Tc  /T4 Quark-Gluon Plasma Hard high-Q2 processes are abundant at collider energy:  Hard high-Q2 processes are abundant at collider energy Production of hard partons is a standard candle, unaffected by medium Hard partons interact with medium during propagation

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