Strong and Electroweak Matter, June 16, 2004
Manuel Calderón de la Barca Sánchez
RHIC Collisions
The road so far.
RHIC Collisions
The road so far.
2
A little background Main goal of RHIC Heavy Ion program:
To search for QGP formation in the laboratory, and To study the properties of this state of matter
Today’s talk: On the progress made in the last 3 years of RHIC Present some of the striking measurements obtained at
RHIC so far Many open questions!!
“RHIC Whitepapers”:Critical evaluation of the data and its (possible)
interpretationPresent questions to the (theory) community
for open discussionHope: Reach a better assessment of the
implications of these measurements and of the next steps
3
The Relativistic Heavy Ion Collider
STAR
PHENIX
PHOBOS BRAHMS
RHIC
Design Performance Au + Au p + p
Max snn 200 GeV 500 GeV
L [cm-2 s -1 ] 2 x 1026 1.4 x 1031
Interaction rates 1.4 x 103 s -1 6 x 105 s -1
TwoSuperconducting Rings
Ions: A = 1 ~ 200, pp, pA, AA, AB
4
Suppression at high transverse momenta
Suppression of particle yield is a final state effect! Consistent with expectations from parton energy loss in a
dense medium Not consistent with predictions for initial state gluon
saturation (Color Glass Condensate) at mid-rapidity.
Compare yields in Au+Au to yields in pp by taking the ratio R
Yield is suppressed in Au+Au
It is not suppressed in d+Au
5
Dissappearance of the back-to-back correlation
In central Au+Au, the away side jet is strongly suppressed
d+Au data do not show this!
Back to back supression is a final state effect
Consistent with expectations of parton energy loss in a dense medium
6
Away-side suppression is larger out-of-plane compared to in-planeThe back to back correlation depends on the average distance traveled through the medium!
Geometry of dense medium imprints itself on correlations
STAR Preliminary
Geometry of away-side suppression
7
High-pt: summary of the d+Au run
In Au+Au, suppression of high-pt hadrons and of away side jet, not seen in d+Au. Final state effect…consistent with the production of dense matter!!
From cover ofPRL 91 (2003)
072302 Phobos072303 Phenix072304 Star072305 Brahms
8
Where does the jet go? Away side <pT>
away side associated
particle <pT> decreaseswith centrality, approaching
medium hadron <pT> in central collisions
equilibration between the two sources of particles
9
Suppression phenomena
The observed strong suppression can be described efficiently by parton energy loss in matter Implication: large energy density, large gluon density
Does the magnitude of the energy loss inferred from the measurements demand an explanation in terms of traversal through deconfined matter? Does factorization still apply in medium? Do
fragmentation functions get modified? Does the treatment of energy loss in the expanding
system amplify the uncertainties inherent in the above assumption?
Can one prove that the densities require the formation of a deconfined system?
10
Particle ratios and statistical models
Chemical freeze-out ~ 170 MeV, close to expected Tc Particle ratios similar in pp for most abundant species Deviations of the resonance yields compared to thermal model
predictions indicative of hadronic phase after chemical freeze-out
STARPHENIX
Strangeness Enhancement Resonance Suppression
12
Identified particle spectra
Mass dependence of particle spectra described reasonably well by ideal hydrodynamics
Hydro (P. Kolb & U. Heinz)
With initial flow kick
Central AuAu √s = 200 GeV
13
Anisotropy parameter v2
)(tan,2cos 1222
22
x
y
p
pv
xy
xy
y
x
py
px
coordinate-space-anisotropy momentum-space-anisotropy
Initial/final conditions, dof, EOS
14
“Elliptic flow” data
Hydrodynamic limit
STAR
PHOBOS
Hydrodynamic limit
STAR
PHOBOS
Compilation and Figure from M. Kaneta
First time in Heavy-Ion Collisions a system created which at low pt is in quantitative agreement with ideal hydrodynamic model predictions for v2 up to mid-central collisions
2 cos 2( )rv
PHOBOS: Phys. Rev. Lett. 89, 222301 (2002) STAR: Phys. Rev. Lett. 86, 402 (2001)
PHENIX: Phys. Rev. Lett. 89, 212301 (2002)
RQMD
15
v2(m,pt)
Hydro calculation constrained by particle spectra Clear mass dependence; signature of collective flow (not
only in hydro) Dependence on particle mass: Hydrodynamics gives a
natural description at low transverse momenta Still some deviations of 20-30%
Hydro calculations: Kolb, Heinz and Huovinen
16
Thermalization
Is the system in approximate local thermal equilibrium?
Evidence: Hydrodynamics successfully accounts for v2 and soft
particle spectra (for the first time in HI collisions). Indirectly points to a rapid thermalization Comparison with data favors a soft equation of state.
Statistical approach to particle ratios: excellent agreement with data
Tch = 170 MeV ~ Tc : lower limit Assumes thermal equilibrium for its applicability, does
not prove it.
How do we know that the observed elliptic flow can not result alternatively from a harder EOS coupled with incomplete thermalization? D. Teaney, J. Lauret, E.V. Shuryak; Phys. Rev. Lett 86,
4783 (2001)
17
Space-Time information: HBT correlations
HBT “radii” show an azimuthal dependence; qualitative centrality dependence fits into picture obtained from v2 and spectra
Rside2
18
Space-time Information: the oddball
Dynamical models which succeed with spectra and elliptic flow give a rather poor description of the HBT “radii”
Observables like elliptic flow are an integral over the time evolution this seems to be not very well under control
19
HBT, spectra and v2; the soft sector
The argument for the success of hydro: Resting on key soft-physics observables
The magnitude and centrality dependence of v2 Hadron mass-dependence of v2 to the EOS
How does the level of this EOS sensitivity compare quantitatively to that of uncertainties in the calculations? Range of adjustable parameters: what is the
uncertainty, and predictive power? Failure to describe the spectra, elliptic flow and HBT
at the same time
20
Identified particles at intermediate to high-pt
Two groups, baryons and mesons Are the valence quarks the relevant scaling? Coalescence/recombination provides an elegant description between
1.5-6 GeV/c
21
Fragmentation + Recombination
q
Baryon1
Meson
Fragmentation
q q
q q q
Baryon1
Meson
Recombination
M Q B Q2 3p p p p Bass et al. nucl-th/0306027
Lopez, Parikh, Siemens, PRL 53 (1984) 1216:Net charge and baryon number fluctuations [Asakawa, Heinz, BM, PRL 85 (2000) 2072; Jeon, Koch, PRL 85 (2000) 2076]
Balance functions [Bass, Danielewicz, Pratt, PRL 85 (2000) 2689]
Recombination / coalescence [Fries, BM, Nonaka, Bass, nucl-th/0301087; Greco, Ko, Levai, nucl-th/0301093; Molnar, Voloshin, nucl-th/0302014]
22
Does it fit the measured spectra?
Teff = 350 MeV blue-shifted temperature
pQCD spectrum shifted by 2.2 GeV
R.J. Fries, B. Müller, C. Nonaka, S.A. Bass; PRL 90 202303 (2003)
23
D. Molnar, S.A. Voloshin Phys. Rev. Lett. 91, 092301 (2003)V. Greco, C.M. Ko, P. Levai Phys. Rev. C68, 034904 (2003) R.J. Fries, B. Muller, C. Nonaka, S.A. Bass Phys. Rev. C68, 044902 (2003)
Coalescence
Coalescence, recombination work at intermediate p
Au+Au sNN=200 GeV
24
Quark coalescence:
Au+Au sNN=200 GeV
STAR Preliminary
MinBias 0-80%
• Works for: • K0
s (sd) (sdu) (ssd)
Partonic flow v2
s ~ v2u,d ~ 7%
25
Identified particles at intermediate to high-pt
Baryon-meson scaling: importance of constituent quark d.o.fSuggestive of collective flow at constituent
quark level Scaling is naturally accomodated in a
coalescence/recombination picture Would like to see predictions for future
measurements:Centrality dependence?Correlations between mesons-baryons?Does it work if one incorporates a more
complete space-time evolution?
26
First D Measurement at RHIC
D0, D, D* spectra from d+Au
Cover range 0.2 < pT < 11 GeV/c
Necessary baseline for Au+Au
27
Heavy Flavor D,B e + X
(e+ + e-)/2 spectrum, background subtracted
e-PID by TOF, dE/dx and EMC, measurements consistent
Consistent with measured D meson yield
PYTHIA: c e, dominates at pT ~ 2-4 GeV/c
b e, dominates at pT > 4-5 GeV/c
28
Summary, and the road ahead
High pt consistent with jet quenching scenario
Bulk properties: rapid thermalization, soft EOS
Hydrodynamics works well for spectra and v2, but not for HBT.
v2, RAB quark coalescence seems to work, 2-4 GeV/c partonic collectivity ?
Significant progress in our understanding of the matter produced in the collisions!
29
…and the road ahead
Study various particles: centrality dependence of spectra and v2 ofd, 0, , , ,…,
Heavy flavor production analysis is just getting started
J/, ’, maybe … better probes of deconfinement?
So far, no evidence whatsoever of chiral symmetry restoration
Does it occur? And can we measure it? What is the best way?
RUN 4 :
An order of magnitude more data…
with more complete detectors!
sNN = 200 GeV, 62.4 GeV
Top Related