Date post: | 21-Jan-2016 |
Category: |
Documents |
Upload: | garey-cook |
View: | 214 times |
Download: | 0 times |
Zooming in on the QGP?Heavy-Ion Collisions: an Overview
Thomas UllrichHard Probes 2005
June 10, 2006
2
“The physical picture emerging from the four (RHIC) experiments is consistent and surprising. The quarks and gluons indeed break out of confinement and behave collectively, if only fleetingly. But this hot mélange acts like a liquid, not the ideal gas theorists had anticipated.”
M. Riordan, W. Zajc, Sci. Am., May 2006, 34-41.
3
Azimuthal Anisotropy: Elliptic Flow
D. Morrison, SQM’06
dN/d ~ 1+2 v2(pT)cos(2) + …. = atan(py/px) v2 = cos2
v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane
EoS & geometry-driven momentum anisotropy
Density & geometry-driven absorption anisotropy
R
Elliptic flow observable sensitive to early evolution of system
Large v2 is an indication of early thermalization
4
v2: RHIC Measurements
Rich set of data on v2 at RHIC: h±, ±,0, K±,0, p,p, ,, , Ω, ϕExperiments: dN/dy|y=0 → dN/dpT → v2
v2: Magnitude, pT, centrality and mass dependence, dependence (h± only)
v2 stronger than at SPS, AGS v2() > v2(K) > v2 (p) ~ v2()
200 GeV Au+AuSTAR preliminary
min. bias (0-80%)
pT (GeV/c)
5
The Method Matters: v2EP, v22 versus v24
In more central Au+Au collisions the difference between v22 and v24 increases from 10% at low-pt to about 40-50% at intermediate-pt
Difference smaller for > 2 Huge for Cu+Cu (reason unknown)
W. Gang QM’05
Phys. Rev. C 72 (2005) 014904
v2EP: Assume all correlations between particles due to flowv22: Non flow correlation contribute order 1/Nv24: Non flow correlation contribute order 1/N3
6
Ideal hydro overpredicts flow init. conditions, viscosity?
Afterburner (Teaney, Hirono, Bass ...) Adds dissipative hadron phase “Late” viscosity in hadron phase Break up thermalization: viscosity
effectNeed to fix initial conditions
CGC conditions → need “early” viscosity
BGK/Glauber OK?
Hydrodynamics: Modeling High-Density Scenarios
Full 2(3)-d Hydrodynamics
• EoS :1st order phase transition QGP + excluded volume model
Cooper-Fryeformula
RQMD, UrQMD, JAM, …
t fm/c
final stateinteractionsMonte Carlo
Hadronization
TC TSW
The “era” of the afterburner
7
Elliptic & Radial Flow: Non-Viscous Hydro Works
200 GeV Au+AuSTAR preliminary
pT (GeV/c)
v 2 (
pT)
0.20
0.15
0.10
0.05
0
0
P. Huovinen
P. Huovinen
all: full hydro, all compare to v2EP Au+Au central , √s = 200 GeV
Hydro pQCD
RHIC: Tfo~ 100 MeV, T ~ 0.55 c
D. d'Enterria, D. Peressounko , EPJ .C46:451-464
8
Hydro Limits: Like a Perfect Liquid?
Hydro- dynamics without any viscosity describes heavy ion reactions at RHIC (QGP+H EoS) Thermalization time = 0.6 fm/cEnergy Density: =20 GeV/fm3
=spatial eccentricity = y2-x2/y2+x2S=overlap area
Hydro: Kolb, Sollfrank, Heinz PRC62:054909
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)
9
Another Word of Caution … v4/(v24)2
Incomplete thermalization? Need theory input how this would look
in microscopic model
Ratio v4/v22 is sensitive to degree of thermalization
Borghini, Ollitrault nucl-th/0506045:
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
STAR Preliminary
10
Constraints on Viscosity - What Do We Know?
s = 4/3sT (sound attenuation length)
pQCD: s/ = 0.18/(T) ~ 0.18(for s = 0.5 ?)
AdS/CFT: s/ = 1/(3T) ~ 0.11
What we urgently need is viscoushydro but experts tell us this is really hard 3 years away (always?)
One attempt: D. Teaney1st correction to thermal distribution function of an expanding gas estimate viscous corrections to spectra and elliptic flow using boost invariant blast wave model
Lack of Proof ≠ Proof of Lack
11
Parton Transport Model – MPC & Ideal Hydro
Maybe a “Perfect” Fluid - But Not Ideal
What’s going on?a) hard EoS + strongly dissipative evolutionb) softer EoS + negligible dissipative evolution (system stays in perfect local
kinetic equilibrium – how, why?) What’s about 2↔3 processes?
D. Molnar, P. Huovinen PRL94 (’05)
Same initial conditions for MPC & hydro
Very opaque system but still dissipative even for gg 50 mb, ~ 0.1 fm
Still 30% smaller than ideal hydro (diff. established early ~ 1 fm/c)
Note: ~ 3 mb in pQCD (2 ↔ 2) Note: ~ 1/
~ 47 mb as good as it gets troublesome ?
12
The gg ↔ ggg PuzzleZ. Xu and C. Greiner, PRC 71, 064901 (2005)
3+1 dimensional cascade calculation solving on-shell Boltzmann equations for partons including inelastic gg ↔ ggg pQCD processes
),(),(),( pxIpxIpxfp ggggggggg
new development(Z)MPC, VNI/BMS
0.2 fm/c
0.5 fm/c1 fm/c2 fm/c3 fm/c4 fm/c
Thermal (exp.) spectra after ~1 fm/c
13
What’s Going On ?
Old idea about the transport cross-section is wrong (Xu, HQ 2006) This issue addresses the questions on
Fast thermalization (0 ~ 0.6 fm/c) 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!
54~ionequilibrattoofoncontributi
ionequilibrattoofoncontributi
gggg
ggggg
14
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
Coincides with Helmut’s Birthday !
15
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/ melts at 1.5-2.5 TC
Tdiss(y’) Tdiss(cc)< Tdiss((3S)) < Tdiss(J/y) Tdiss((2S)) < Tdiss((1S))
F. K
arsch, RH
IC-II S
cience
Workshop
Is the sequential suppression pattern the smoking gun?
16
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//dt = Ng dis
Lattice: Datta, et al.,PRD 69 (2004) 094507
Potential model with screening : Á. Mócsy, P.P, hep-ph/0512156
17
SPS: NA50 and NA60
Normalized to
Drell-Yan
Using Glauber &
nuclear absorption (from pA studies)
Suppression beyond nuclear absorption
observed in
Pb+Pb and In+In
at √s ~ 17 GeV
18
Origin of Suppression at SPS ? J/absorption by produced hadrons (comovers)
Capella and Ferreiro, Eur.Phys.J. C42 (2005) 419
J/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:1. NJ/(observed) = 0.6 NJ/ + 0.4 Nc
(compatible w Hera-B data)1. J/ doesn’t melt2. c dissociation = ’ dissociation
Right or wrong, it shows how importantthe missing c measurement is!
19
Charmonium at RHIC: Screening and Regeneration
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!
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 cc’s
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
screening
M.
Lei
tch
, S
QM
’06
20
regeneratio
n
dire
ct
Rec
ombi
ned
only
Regeneration Narrowing of pT and y?
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 p+p to the most central Au+Au : no significant change seen in the shape of the rapidity distribution.
No Recombination
Thews et al.
21
The Promise of Jet Tomography
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
+
=
p+p medium
22
Calibrated Probe: Hard InteractionsHard interactions pQCD
Factorization holds PDF (initial) x NLO x FF (final)
Example of probes well reproduced in the forward direction, STAR PRL 92
(2004) 171801 proton production in p+p, STAR
nucl-ex/0601033 Direct production, PHENIX Phys. Rev. D
71 (2005) 071102
There are however “issues” (Strange) baryons, e.g. 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)
STAR preliminary
p+p→0+X
S.S. Adler et al, PRL 91 241803
p+
p/
FO
NL
L
23
Application to Heavy Ion Collisions: Initial Results
Strong suppression in Au+Au collisions, no suppression in d+Au: Effect is due to interactions between the probe and the medium Established use as a probe of the density of the medium
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
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
Binary collision scaling p+p reference
24
InterpretationGluon 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:
Eloss ~ gluon (gluon density) Eloss ~ L2 (medium length)
~ L with expansion Characterization of medium
transport coefficient
gluon density dNg/dy Deduced initial gluon density at =
0.2 fm/c: dNglue/dy ≈ 800-1200 ≈ 15 GeV/fm3 (in static medium)
Pion gas
Cold nuclear matter
RHIC data
sQGP
QGP
Baier’s plot
43
forcecolor of Range
2
scattering ofDensity
2
ˆ
ˆ4
ckq
LqC
E
T
SR
q
25
Central RAA Data
Increasing density
Towards the Quantitative: Limitations of RAA
Surface bias effectively leads to saturation of RAA with density
Challenge: Increase sensitivity to the density of the medium
K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461
Distributions of parton production points in the transverse plane
26
One Way: Increased Precision and Reach
Successful RHIC runs in 2004 (Au+Au) and 2005 (Cu+Cu) Probe systematic with beam energy, system size Increased reach from larger datasets:
e.g. 0 to 20 GeV/c with high precision still flat
H. Buesching, HQ06
27
Black and White
Medium extremely black to hadrons, limiting sensitivity to density Medium transparent to photons (white): no sensitivity Is there something grey?
S.S. Adler et al, Phys. Rev. Lett. 94, 232301 (2005)
28
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
29
Distinguishing Power Between Gluon and Quark?
In the NLO calculation that best describes p+p 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?
Ruan WW06, I. Vitev, nucl-ex/0603010.
pT [GeV/c]
AKK, private communication
30
STAR Preliminary
NA57: G. Bruno, A. Dainese: nucl-ex/0511020
RCP at Lower EnergiesIs the observed baryon/meson anomaly just due to , K suppression?
No, at √s=17.3 GeV, baryons enhanced w/o pion suppression
Recombination present in all systems? If the baryon enhancement is from a larger pT kick (or flow)
for baryons, why doesn’t B/M increase when the spectrum is steeper?
Baryon/meson splitting at SPS and RHIC (200 & 62 GeV ) is the same
31
light
(M.Djordjevic PRL 94 (2004))
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
32
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 < 3 GeV/c
STAR, QM05
Hendrik, Greco, Rappnucl-th/0508055
w.o. B meson (c flow)w. B meson (c,b flow)
33
1982 - Initial idea Bjorken, Fermilab-Pub-82/59-THY early estimates < 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/0509185No – Djordjevic, nucl-th/0603066
The Return of the QCD Collisional Energy Loss
Radiative Energy LossN. Armesto et al, nucl-ex/0511257
‘there must be something else ...’
b
c
34
A. Peshier, hep-ph/0605294
Take running coupling into account
independent of jet energy for T > 1.5 TC considerably
larger than previous estimates
In BJs collisional loss formula
(adaption of rel. Bethe-Bloch)
What is s in a QGP?
A fixed parameter?
Isn’t it running ?
The Question That Has Always Puzzled Me …
Ds
Bjgq
m
ETT
dx
dEln~ 22,
)(~ 2D
APcol mT
dx
dE
35
Beyond Single Particle Spectra
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?
T. Renk, nucl-ex/0602045
36
Dijets - Dihadrons High Trigger and High Associated pT
Clear jet-like peaks seen on near and away side in central Au+Au – width not broadened
Away-side yield strongly suppressed to level of RAA
No modification of shape in the longitudinal (zT) or transverse ( width) directions
Strong set of additional constraints on E-loss models
STAR, nucl-ex/0604018
STAR Preliminary
dN/d
z TA
u+A
u/d+
Au
STAR Preliminary
d+Au
1/N
trig
dN
/d() Au+Au 20-40% Au+Au 0-5%
8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV
D(zT)
1
0
37
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
Leadinghadrons
Medium
away
near
PHENIX, QM05 and nucl-ex/0507004STAR, Phys. Rev. Lett. 95 (2005) 152301
AA
/pp
away pT (GeV/c)
pT trigger ~ 4 GeV/cPHENIX preliminary
38
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)-jetcorrelation studies (e.g. 3 particle)
theoryenergy loss: collisional vs. radiative, what else?
LHC – the clock is ticking … will it simplify or complicate our picture ?
“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 !