STAR and RHIC; past, present and future.

1
STAR and RHIC past, present and future.

• Part of the ALICE program
• See Thomas talk for more details
• Starting at NIKHEF coming year with 2 staff
  members, 2 post-docs and 2 PhD students.

2
Overview

• What have we learned (first two years of
  running)?
• What are we up to this year?
• The next couple of years?

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Phase structure
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Highly dynamic system!
5
Main questions to answer

• Study QCD at extreme densities (Quark Gluon
  Plasma)
• What is the initial condition?
• Does the created system thermalize? What is the
  timescale?

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INT/RHIC Winter Workshop 2002 Dec. 13

• questions that are important and timely for
  understanding the underlying physics of heavy-ion
  collisions and resolving some of the puzzles at
  RHIC
• What is the real mechanism for the observed
  particle production which is lower than what was
  commonly expected?
• Does the hydrodynamic behavior of the elliptic
  flow imply early partonic thermalization?
• What quantitative conclusions can one draw from
  the observed jet quenching or suppression of
  large transverse momentum hadrons?

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Particle yields
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Particle spectra
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Elliptic flow
coordinate space

• Coordinate space configuration anisotropic
  (almond shape) however, initial momentum
  distribution isotropic (spherically symmetric)
• Only interactions among constituents (mean free
  path small) generate a pressure gradient which
  transforms the initial coordinate space
  anisotropy into the observed momentum space
  anisotropy (no analogy in pp)
• Multiple interactions lead to thermalization -gt
  limiting behavior ideal hydrodynamic flow

Momentum space
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Ideal Hydrodynamic Model Predictions
First time in Heavy-Ion Collisions a system
created which at low pt is in quantitative
agreement with hydrodynamic model predictions for
v2 up to mid-central collisions
STAR, PRL 86, (2001) 402
? lt 1.3 0.1 lt pt lt 2.0
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A Detailed look at Hydro predictions
STAR, PRL 87, 182301 (2001)
Fluid cells expand with collective velocity v,
different mass particles get different Dp
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Measurements at RHIC STAR, identified particles
The STAR Collaboration, Phys. Rev. Lett. 87,
182301 (2001)
solid
T (MeV) 100 ? 24
?0(c) 0.54 ? 0.03
?a (c) 0.04 ? 0.01
S2 0.04 ? 0.01
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What have we learned from elliptic flow at RHIC?

• L. McLerran one needs very strong interactions
  amongst the quark and gluons at very early times
  in the collision (hep-ph/0202025).
• U. Heinz resulting in a well-developed
  quark-gluon plasma with almost ideal
  fluid-dynamical collective behavior and a
  lifetime of several fm/c (hep-ph/0109006).
• E. Shuryak probably the most direct signature of
  QGP plasma formation, observed at RHIC
  (nucl-th/0112042).

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Two Particle Interferometry (RHIC puzzle)
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Fast Partons (Quarks Gluons) Traversing Matter

• Jets
• high-pt parton produced in a hard (high momentum
  transfer) scattering process
• leading particles particles in cone with highest
  momentum
• Calculable in QCD (at high-pt)
• created early in the collision

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High-pt probes

• New to heavy-ion collisions
• Energy loss mechanism sensitive to density of the
  surrounding environment

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Using the (initial) geometry high-pt event
anisotropy
R.S QM2001, Nucl. Phys. A 698 (2002) 193c. STAR,
nucl-ex/0206006
http//www.lbl.gov/nsd/annual/rbf/nsd1998/rnc/RNC.
htm R17. Event Anisotropy as a Probe of Jet
QuenchingR.S and X.-N. Wang R.S, A.M.
Poskanzer, S.A. Voloshin, STAR note,
nucl-ex/9904003
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Centrality dependence of v2(pt)
E.V. Shuryak nucl-th/0112042
200 GeV, preliminary
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Inclusive high-pt yields
Conformation of the 130 GeV discovery. However
this time normalized with measured pp spectra
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Azimuthal correlation at high-pt
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This years run

• The signatures (strong flow, jet quenching and
  mono-jets) are consistent with the production of
  a highly opaque locally thermalized quark gluon
  plasma.
• They are not inconsistent with the interpretation
  of a shadowed/saturated structure of initial
  nuclear/parton wavefunctions (Kharzeev, McLerran
  et al). In this interpretation final state
  interactions can be ignored.
• dA data will provide the reference for cold
  nuclear matter, for the high-pt suppression these
  two opposite interpretations yield opposite
  predictions.

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2004 -

• High statistics AuAu run
• Increase range in pt
• Rare probes D0, J/Psi, Omega etc.
• Detector upgrades
• Full calorimetry
• Time of flight
• Inner vertex detector
• Accelerator upgrades
• Increase luminosity
• Different source

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Time evolution in a ideal hydrodynamic model
calculation

• Elliptic Flow reduces spatial anisotropy -gt shuts
  itself off

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Boosted thermal model fit

• Source is assumed to be
• Local thermal equilibrated
• Boosted radically

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v2 scaled with initial spatial eccentricity
P. Jacobs and G. Cooper, nucl-ex/0008015
STAR, nucl-ex/0206001