A New State of Matter at the
Relativistic Heavy Ion Collider?
Jane M. Burward-Hoy
Lawrence Livermore National Laboratory
Au-Au event in PHENIX Central Arms
Outline of Topics
• The Quark Gluon Plasma and “soft physics”
• The PHENIX Central Arm Spectrometers
– The Drift Chamber Detectors, Momentum
Reconstruction and Track Model
– The RICH Detector
• Data from the Drift Chamber and TOF
• Interpretation of the Data
• Conclusion
• Outlook
U. Heinz, PANIC 2002
The “Little Bang”
(GeV/c)
Npart
Open symbols:
sNN = 130 GeV
Npart
• Mean pt increases with Npart and particle mass, indicative of radial expansion.
• Relative increase from peripheral to central greater for (anti)p than for , K.
• Systematic uncertainties: 10%, K 15%, and (anti-)p 14%
ln tan 2
Total Hadron Multiplicities
PHENIX Preliminary
130 GeV
Npart
~ 5 GeV/fm3 (well over the threshold for a QGP)
PHENIX: PRL 86 (2001) 3500 STAR: PRL 87 (2001) 112303 PHOBOS: PRL 85 (2000) 3100
Towards Conclusions
• Energy density obtained is well over threshold
for QGP formation (charged yields)
HBT: Space-time Extent of the Source
(HBT = Hanbury-Brown and Twiss Interferometry)
x1,p1
S(x,p) ~ probability C(q)
particle emitted at x
with p ~ 1/R
1
Summing sources over
x2, p2 0
space-time x q
2
S ( x, k )e d x
iq x
q p1 p2
4
C (k , q) ~ 1 2
S ( x, k )d x
4
k p1 p2
1
2
LCMS-Frame, where pair moves with source in the
longitudinal direction : k = (kT, kL) = (kT, 0)
C(k,q) and Experimental Data
For the two-particle qT qs
correlation function: py 1
q vector is written in terms of kT
– Two transverse coordinates qo
(“out” and “side”)
2
– One longitudinal coordinate
(“long”), parallel to beam axis. px
Plane transverse to beam axis
3D Gaussian approximation is
assumed for the source
C2 1 exp R q 2 2
side side R q R
2 2
out out
2 2
q
long long
kT Dependence of HBT Radii
Ro R
RSIDE 2 2
out s
RSIDE
Geometrical Source Size R
ROUT
RLONG Emission
Freeze-out time duration
Beam axis : R
LONG
Measure two-particle correlations in different windows.
Centrality is in top a
The observed kT dependence of fitted HBT radii indicate30%
radial expansion of the source
Towards Conclusions
• Energy density obtained is well over threshold
for QGP formation (charged yields)
• Radial Expansion of Source (mean Pt and kt
dependence of HBT radii)
Hydrodynamic Interpretation (QM02)
• The study uses the s 17GeV Eur. Phys. J. C 2 (1998) 661.
most recent PHENIX
data at 200 GeV.
• Measure the
characteristics of the
particle emitting
source from both
spectra and HBT radii
simultaneously.
• Inspired by the CERN Pb+Pb
NA49 measurement at
lower cm energies
Constraining the expansion parameters
from single and two-particle distributions.
A “Simple” Model for the Source
• Model by Wiedemann, Scotto, and Heinz , Phys. Rev. C 53, 918 (1996)
E. Schnedermann, J. Sollfrank, and U. Heinz, Phys. Rev. C 48, 2462 (1993)
• Fluid elements each in local thermal equilibrium move in space-time
with hydrodynamic expansion. r
No temperature gradients
z
• Boost invariance along collision axis z.
• Infinite extent along rapidity y = ½ ln(E + pz / E – pz).
• Cylindrical symmetry with radius r. t 0 t 2 z2
• Particle emission
Hyperbola of constant proper time 0
z
• Short emission duration
t = 2T/3
t() surface velocity T
Avoid contributions from hard processes
(mt-m0) 1.0 and Tfo 1.4 and Tfo > 100 MeV
• (R-contours not closed)
Using spectra information to constrain HBT fits…
From the spectra (systematic errors):
T = 0.7 ± 0.2 syst. Tfo = 110 23 syst. MeV
PHENIX Preliminary
Rs (fm) Ro (fm) RL (fm)
++
R = 9.6±0.2 fm Duration < 1 fm/c Freezout at 132 fm/c
• 10% central positive pion HBT radii (similar result for negative pion data).
• Systematic uncertainty in the data is 8.2% for Rs, 16.1% for Ro, 8.3% for RL.
Towards Conclusions
• Energy density obtained is well over threshold
for QGP formation (charged yields)
• Radial Expansion of Source (mean Pt and kt
dependence of HBT radii)
• Expansion stronger in Central Collisions
• HBT puzzle, NO consistent description of
spectra and radii
• Very short emission duration < 1fm/c
Conclusions
• Energy density obtained is well-over threshold for
QGP formation
• Explosive expansion due to large thermal pressure
• The hadron data at pT < 2 GeV are well described
by hydrodynamics and expansion can be
determined quantitatively
• Other soft physics measurements (elliptic flow)
suggest early thermalization time < 1 fm/c
• The suppressed yield of high pT hadrons suggest a
strong energy loss of high-pT partons traveling
through the core (jets from surface are emitted).
• The space-time picture of the source is not well
understood, see comparison to the radii.
Outlook
• The upcoming run will begin in January.
• “Cold” nuclear matter will be created by colliding
deuteron and Au beams.
• Hadrons produced in cold matter will be studied
and compared to the hadrons produced in hot,
dense matter from the Au-Au collisions.
• The muon spectrometer arms will be used to
measure charm and the muon decay channel of
J/psi.
• Stay tuned for the formal announcement that we
have created a Quark Gluon Plasma in the
laboratory!
Suppressed Yield of Charged Hadrons at High pT
schematic view of jet production
hadrons
leading
particle
h+ + h- q
q
hadrons
leading
particle
Predictions from Hydrodynamics