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.

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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

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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

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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

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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

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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

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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

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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

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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?

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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

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Identified particle spectra

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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

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Anisotropy parameter v2

)(tan,2cos 1222

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x

y

p

pv

xy

xy

y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Initial/final conditions, dof, EOS

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“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

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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

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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)

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Space-Time information: HBT correlations

HBT “radii” show an azimuthal dependence; qualitative centrality dependence fits into picture obtained from v2 and spectra

Rside2

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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

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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

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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

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Fragmentation + Recombination

qq

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]

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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)

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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

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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%

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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?

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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

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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

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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!

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…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