Zooming in on the QGP? Heavy-Ion Collisions: an Overview

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Zooming in on the QGP?Heavy-Ion Collisions an
Overview

• Thomas Ullrich
• Hard Probes 2005
• June 10, 2006

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(No Transcript)
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Azimuthal Anisotropy Elliptic Flow
dN/df 12 v2(pT)cos(2f) . f
atan(py/px) v2 ?cos2f? v2 2nd
harmonic Fourier coefficient in dN/d? with
respect to the reaction plane
Density geometry-driven absorption anisotropy
EoS geometry-driven momentum anisotropy

• Elliptic flow observable sensitive to early
  evolution of system
• Large v2 is an indication of early thermalization

YR
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v2 RHIC Measurements

• Rich set of data on v2 at RHIC
• h, p,0, K,0, p,?p, L,?L, X, ?, ?
• Experiments dN/dyy0 ? dN/dpT ? v2
• v2 Magnitude, pT, centrality and mass
  dependence, h dependence (h only)
• v2 stronger than at SPS, AGS
• v2(p) gt v2(K) gt v2 (p) v2(L)

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The Method Matters v2EP, v22 versus v24
v2EP Assume all correlations between
particles due to flow v22 Non flow correlation
contribute order 1/N v24 Non flow correlation
contribute order 1/N3
Phys. Rev. C 72 (2005) 014904

• In more central AuAu collisions the difference
  between v22 and v24 increases from 10 at
  low-pt to about 40-50 at intermediate-pt
• Difference smaller for h gt 2
• Huge for CuCu (reason unknown)

W. Gang QM05
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Hydrodynamics Modeling High-Density Scenarios
The era of the afterburner

• Full 2(3)-d Hydrodynamics
• EoS 1st order phase transition
• QGP excluded volume model

RQMD, UrQMD, JAM,
Cooper-Frye formula
Hadronization
final state interactions
Monte Carlo
TC
TSW
t fm/c

• Ideal hydro overpredicts flow
• init. conditions, viscosity?
• Afterburner (Teaney, Hirono, Bass ...)
• Adds dissipative hadron phase
• Late viscosity in hadron phase
• Break up thermalization viscosity effect
• Need to fix initial conditions
• CGC conditions ? need early viscosity
• BGK/Glauber OK?

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Elliptic Radial Flow Non-Viscous Hydro Works
all full hydro, all compare to v2EP
AuAu central , vs 200 GeV
Hydro pQCD
P. Huovinen
RHIC Tfo 100 MeV, ? bT ? 0.55 c
D. d'Enterria, D. Peressounko , EPJ .C46451-464
P. Huovinen
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Hydro Limits Like a Perfect Liquid?
Hydro Kolb, Sollfrank, Heinz PRC62054909
espatial eccentricity ?y2-x2?/?y2x2? Soverlap
area
Hydro- dynamics without any viscosity describes
heavy ion reactions at RHIC (QGPH EoS)
Thermalization time t0 0.6 fm/c Energy
Density e20 GeV/fm3

• Issues
• No consistent set of hydro calculation that
  describes all observables
• Lattice inspired EoS in ideal hydro does as
  poorly as a hadron gas EoS
• Before we can make a connection to the EoS using
  v2(pT,m) much more work needed in theory (test
  different EoS, viscosity, hadronic phase)

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Another Word of Caution v4/(v24)2
Ratio v4/v22 is sensitive to degree of
thermalization Borghini, Ollitrault
nucl-th/0506045
STAR Preliminary
v4/v22 0.5 for ideal hydro (more accurate for
increasing values of pT) Observed integrated
ratio larger than unity For more peripheral
collisions increasing fast as function of
transverse momentum

• Incomplete thermalization?
• Need theory input how this would look in
  microscopic model

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Constraints on Viscosity - What Do We Know?
One attempt D. Teaney 1st correction to thermal
distribution function of an expanding gas ?
estimate viscous corrections to spectra and
elliptic flow using boost invariant blast wave
model
Gs 4h/3sT (sound attenuation length) pQCD
Gs/t 0.18/(tT) 0.18 (for as 0.5
?) AdS/CFT Gs/t 1/(3ptT) 0.11
What we urgently need is viscous hydro but
experts tell us this is really hard ? 3 years
away (always?)
Lack of Proof ? Proof of Lack
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Maybe a Perfect Fluid - But Not Ideal
Parton Transport Model MPC Ideal Hydro

• Same initial conditions for MPC hydro
• Very opaque system but still dissipative even for
  sgg 50 mb, l 0.1 fm
• Still 30 smaller than ideal hydro (diff.
  established early 1 fm/c)
• Note s 3 mb in pQCD (2 ? 2)
• Note h 1/s

s 47 mb as good as it gets ? troublesome ?

• Whats going on?
• hard EoS strongly dissipative evolution
• softer EoS negligible dissipative evolution
  (system stays in perfect local kinetic
  equilibrium how, why?)
• Whats about 2?3 processes?

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The gg ? ggg Puzzle

• Z. Xu and C. Greiner, PRC 71, 064901 (2005)
• 31 dimensional cascade calculation solving
  on-shell Boltzmann equations for partons
  including inelastic gg ? ggg pQCD processes

new development
(Z)MPC, VNI/BMS
Thermal (exp.) spectra after 1 fm/c
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Whats Going On ?

• Old idea about the transport cross-section is
  wrong (Xu, HQ 2006)
• This issue addresses the questions on
• Fast thermalization (t0 0.6 fm/c)
• s in parton cascade models to describe v2?
• Is it the solution or is something wrong ?
• Need to check more signatures (RAA ...)
• Issue needs to be solved!

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It Started 20 Years Ago

• Key Idea Melting in the plasma
• Color screening of static potential between heavy
  quarks in deconfined matter
• Suppression of states is determined by TC and
  their binding energy
• Color screening ? Deconfinement
• QCD thermometer ? Properties of QGP

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Quarkonia Lattice QCD

• Recent developments
• Heavy Quark potential?
• Singlet free energy F1 (entropy term?)
• Singlet energy V1
• When do states really melt?
• Neither F1 nor V1 are potentials, they are
  models!
• ? spectral functions (results consistent with V1)
• ? J/y melts at 1.5-2.5 TC
• Tdiss(y) ? Tdiss(cc)lt Tdiss(?(3S)) lt Tdiss(J/y)
  ? Tdiss(?(2S)) lt Tdiss(?(1S))

F. Karsch, RHIC-II Science Workshop
Is the sequential suppression pattern the smoking
gun?
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Just When You Think You Start to Understand

• Charmonia correlators potentials vs. lattice
  (Mócsy, Petereczky, hep-ph/0512156)
• Lattice ? reliable calculation of ?c and ?c
  correlators
• Taking F,V as plain (Cornell) potentials ?
  calculate correlators

• Temperature-dependence of ?c and ?c lattice
  correlators is not explained with screened
  Cornell potential.
• Screening likely not responsible for quarkonia
  suppression
• time scale of screening not small compared to
  time scale of heavy quark motion
• Suppression from collisions with thermal gluons
  only?
• dNJ/y/dt -Ng ?sdis?

Potential model with screening Á. Mócsy,
P.P, hep-ph/0512156
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SPS NA50 and NA60

• ? Normalized to
• Drell-Yan
• Using Glauber
• nuclear absorption ?
• (from pA studies)
• Suppression beyond nuclear absorption
• observed in
• PbPb and InIn
• at vs 17 GeV

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Origin of Suppression at SPS ?

• J/y absorption by produced hadrons (comovers)
• Capella and Ferreiro, Eur.Phys.J. C42 (2005) 419
• J/y suppression in the QGP and hadronic phases
• including thermal regeneration and in medium
  properties of open charm and charmonium states
• Grandchamp, Rapp, Brown, NPA715 545 PRL. 92
  212301 JPG 30 S1355
• Or is it much simpler?

F. Karsch, D. Kharzeev, H. Satz, hep-ph/0512239

• Assume
• NJ/y(observed) 0.6 NJ/y 0.4 Ncc
• (compatible w Hera-B data)
• J/y doesnt melt
• cc dissociation y dissociation
• Right or wrong, it shows how important
• the missing cc measurement is!

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Charmonium at RHIC Screening and Regeneration

• Most actual models have suppression various
  regeneration mechanisms
• Rapp - PRL 92, 212301 (2004)
• screening in-medium production
• Thews - PRC73 (2006) 014904c
• pQCD NLO charm recombination
• Andronic - PLB57, 136 (2003)
• statistical hadronization model with screening of
  primary J/?s statistical recombination of
  thermalized ?ccs
• Kostyuk PRC 68, 041902 (2003)
• statistical coalescence co-movers or QGP
  screening
• Bratkovskaya PRC 69, 054903 (2004)
• hadron-string dynamics transport
• Zhu - PLB607, 107 (2005)
• J/? transport in QGP co-movers, gluon breakup,
  hydro for QGP evolution no cold nuclear matter,
  no regeneration

sum
regeneration
M. Leitch, SQM06
screening

• General Observations
• Models with regeneration, i.e., single charm
  quarks combining in the later stages to form
  J/?s match the observed RHIC suppression
  better!

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Regeneration ? Narrowing of pT and y?
Thews et al.
Recombined only
No Recombination

• pT broadening lies in between Thews direct
  in-medium formation suggesting some regeneration.
• Recombination predicts a narrower rapidity
  distribution with an increasing Npart.
• Strange Going from pp to the most central AuAu
  no significant change seen in the shape of the
  rapidity distribution.

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The Promise of Jet Tomography
medium
pp

• Simplest way to establish the properties of a
  system
• Calibrated probe
• Calibrated interaction
• Suppression pattern tells about density profile
• Heavy ion collisions
• Hard processes serve as calibrated probe
• Suppression provides density measure

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Calibrated Probe Hard Interactions

• Hard interactions ? pQCD
• Factorization holds
• PDF (initial) x NLO x FF (final)
• Example of probes well reproduced
• p0 in the forward direction, STAR PRL 92 (2004)
  171801
• proton production in pp, STAR nucl-ex/0601033
• Direct g production, PHENIX Phys. Rev. D 71
  (2005) 071102
• There are however issues
• (Strange) baryons, e.g. L, X
• Charm (at RHIC via D ? e X)
• Significant uncertainties in the calculations, so
  for precision the baseline needs to be measured
• N.B. RHIC contributes substantially in improving
  FF (e.g. AKK)

pp/FONLL
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Application to Heavy Ion Collisions Initial
Results
PHENIX Phys. Rev. Lett. 91 (2003) 072301 STAR
Phys. Rev. Lett. 91 (2003) 072304 PHOBOS Phys.
Rev. Lett. 91 (2003) 072302 BRAHMS Phys. Rev.
Lett. 91 (2003) 072303

• Strong suppression in AuAu collisions, no
  suppression in dAu
• Effect is due to interactions between the probe
  and the medium
• Established use as a probe of the density of the
  medium

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Interpretation

• Gluon radiation Multiple final-state gluon
  radiation off the produced hard parton induced by
  the traversed dense colored medium

• Formalisms BDMPS (thick plasma), GLV (thin
  plasma)
• Mean parton energy loss ? medium properties
• DEloss ?gluon (gluon density)
• DEloss DL2 (medium length) ? DL with
  expansion
• Characterization of medium
• transport coefficient
• gluon density dNg/dy
• Deduced initial gluon density at t0 0.2 fm/c
• dNglue/dy 800-1200
• e 15 GeV/fm3 (in static medium)

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Towards the Quantitative Limitations of RAA
K.J. Eskola, H. Honkanken, C.A. Salgado, U.A.
Wiedemann, Nucl. Phys. A747 (2005) 511
Central RAA Data
Increasing density
Distributions of parton production points in the
transverse plane
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J.
C38(2005) 461

• Surface bias effectively leads to saturation of
  RAA with density
• Challenge Increase sensitivity to the density of
  the medium

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One Way Increased Precision and Reach
H. Buesching, HQ06

• Successful RHIC runs in 2004 (AuAu) and 2005
  (CuCu)
• Probe systematic with beam energy, system size
• Increased reach from larger datasets
• e.g. p0 to 20 GeV/c with high precision ? still
  flat

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Black and White
S.S. Adler et al, Phys. Rev. Lett. 94, 232301
(2005)

• Medium extremely black to hadrons, limiting
  sensitivity to density
• Medium transparent to photons (white) no
  sensitivity
• Is there something grey?

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Grey Probes

• Not all models are completely black at the parton
  level
• Significant differences between predicted RAA,
  depending on the probe
• Experimental possibility increase sensitivity to
  the properties of the medium by varying the probe

Wicks et al, nucl-th/0512076
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Distinguishing Power Between Gluon and Quark?
Ruan WW06, I. Vitev, nucl-ex/0603010.
AKK, private communication
pT GeV/c

• In the NLO calculation that best describes pp
  data, significant difference in the gluon
  contribution between proton and pion spectra
• Yet, no significant difference in suppression no
  difference between gluon and quark energy loss?

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RCP at Lower Energies
Is the observed baryon/meson anomaly just due to
p, K suppression?
No, at vs17.3 GeV, baryons enhanced w/o pion
suppression
Baryon/meson splitting at SPS and RHIC (200 62
GeV ) is the same

• Recombination present in all systems?
• If the baryon enhancement is from a larger pT
  kick (or flow) for baryons, why doesnt B/M
  increase when the spectrum is steeper?

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Getting Heavy Heavy Flavor Energy Loss

• In 2001, Dokshitzer and Kharzeev proposed dead
  cone effect ? charm quark small energy loss
• Recent Heavy quark energy loss in medium, e.g.
  Armesto et al, PRD 71, 054027, 2005 M.
  Djordjevic et al., PRL 94, 112301, 2005.
• Heavy quarks will be important to understand the
  Energy Loss mechanisms and the competition
  between them

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RAA,v2 of Non-Photonic Electrons

• Charm energy loss via electrons from semileptonic
  D, B decays
• Experimental challenge subtraction of photonic
  electron background
• Evidence of large heavy quark energy loss!
• Substantial elliptic flow for pT lt 3 GeV/c

STAR, QM05
w.o. B meson (c flow)
w. B meson (c,b flow)
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The Return of the QCD Collisional Energy Loss

• 1982 - Initial idea
• Bjorken, Fermilab-Pub-82/59-THY
• early estimates lt 0.3 GeV/fm
• 2005 - Collisional loss in expanding QGP for
  heavy quarks
• Mustafa PRC72, 014905, Mazumder et al., PRD71,
  094061
• rebirth of collisional energy loss
• coll. loss rad. loss ? non-photonic electron
  (charm) RAA
• Wicks et al. nucl-th/0512076 finite size
  effects
• Yes - Peigne et al., hep-ph/0509185
• No Djordjevic, nucl-th/0603066

• Radiative Energy Loss

b
c
there must be something else ...
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The Question That Has Always Puzzled Me

• A. Peshier, hep-ph/0605294
• Take running coupling into account
• independent of jet energy
• for T gt 1.5 TC considerably larger than previous
  estimates

• In BJs collisional loss formula
• (adaption of rel. Bethe-Bloch)
• What is as in a QGP?
• A fixed parameter?
• Isnt it running ?

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Beyond Single Particle Spectra
T. Renk, nucl-ex/0602045

• Overlap zone has ellipticity
• path length dependence can be probed with
  dihadron correlations
• Dihadron correlations introduce geometric biases
  different from RAA
• Surface bias in trigger hadrons longer path
  lengths
• Photon-hadron and beauty-hadron correlations have
  yet different biases
• No surface bias in trigger photons full path
  length distribution?

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Dijets - Dihadrons High Trigger and High
Associated pT
8 lt pT(trig) lt 15 GeV/c
pT(assoc)gt6 GeV
STAR, nucl-ex/0604018
dAu
AuAu 20-40
AuAu 0-5
STAR Preliminary
1/Ntrig dN/d(Df)
dN/dzT
D(zT)

• Clear jet-like peaks seen on near and away side
  in central AuAu width not broadened
• Away-side yield strongly suppressed to level of
  RAA
• No modification of shape in the longitudinal (zT)
  or transverse (Df width) directions
• Strong set of additional constraints on E-loss
  models

STAR Preliminary
1
AuAu/dAu
0
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Where Does the Energy Go?

• Lower the associated pT to search for radiated
  energy
• Additional energy at low pT BUT no longer
  collimated into jets
• Active area additional handles on the properties
  of the medium?
• Mach Shocks, Cherenkov Cones
• e.g. Renk and Ruppert, Phys. Rev. C 73 (2006)
  011901

PHENIX, QM05 and nucl-ex/0507004
STAR, Phys. Rev. Lett. 95 (2005) 152301
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The good news The sQGP may not be as
difficult to understand as many have
feared. Berndt Müller I hope this is true Let
this conference be a success and let us a step
further in this direction Get well soon Miklos !

• Zooming in on the QGP
• your favorite plasma goes here s,w,bs,c,
• Soft and Medium Sector Data Driven
• RHIC, SPS plenty of data all you can eat
• except low energy scan at RHIC (hunt for critical
  point)
• need more theory (manpower)
• bounds on viscosity ?
• EoS ?
• short thermalization time ?
• Hard Sector Theory Driven ?
• need more measurements (running time upgrades)
• heavy flavor sector (Quarkonia, B, D)
• g-jet
• correlation studies (e.g. 3 particle)
• theory
• energy loss collisional vs. radiative, what
  else?
• LHC the clock is ticking
• will it simplify or complicate our picture ?