Two-particle correlations and Heavy Ion
Collision Dynamics at RHIC/STAR
Mike Lisa, Ohio State University
STAR Collaboration
• Motivation / STAR
• Central collision dynamics – spectra & HBT(pT)
• Non-central collision dynamics – elliptic flow & HBT()
• Further info from correlations of non-identical particles
• Consistent picture of RHIC dynamics
• Conclusions
STAR
HBT
4 oct 2002
malisa - seminar IUCF
1
Why heavy ion collisions?
The “little bang”
• Study bulk properties of nuclear matter
• Extreme conditions
(high density/temperature) expect a transition
to new phase of matter…
• Quark-Gluon Plasma (QGP)
• partons are relevant degrees of freedom over
large length scales (deconfined state)
• believed to define universe until ~ ms
• Study of QGP crucial to understanding QCD
• low-q (nonperturbative) behaviour
• confinement (defining property of QCD)
• nature of phase transition
• Heavy ion collisions ( “little bang”)
STAR
HBT
• the only way to experimentally probe
deconfined state
4 oct 2002
malisa - seminar IUCF
2
Relativistic Heavy Ion Collider (RHIC)
12:00 o’clock
PHOBOS
10:00 o’clock
BRAHMS
2:00 o’clock
PHOBOS
PHENIX
8:00 o’clock
RHIC
RHIC
STAR
6:00 o’clock
STAR
PHENIX
U-line
BAF (NASA)
LINAC
m g-2
BRAHMS
4:00 o’clock
9 GeV/u
Q = +79
BOOSTER
AGS
AGS
HEP/NP
1 MeV/u
Q = +32
TANDEMS
• 2 concentric rings of 1740 superconducting magnets
TANDEMS
RHIC
Runs
• 3.8 km circumference
Run I: Au+Au at
= from
130 GeV
• STAR
counter-rotating
beams of s
ions
p to Au
Run
II: Au+Au and energy:
pp at sAuAu
= 200200
GeVGeV, pp 500 GeV
• max
HBT center-of-mass
4 oct 2002
malisa - seminar IUCF
3
The STAR Collaboration
451 Collaborators
45 Institutions
9 Countries:
Brazil, China,
STAR
HBT
Russia,
US
4 oct 2002
(294 authors)
England, France, Germany, India, Poland,
malisa - seminar IUCF
4
Geometry of
STAR
Magnet
Time
Projection
Chamber
Coils
Silicon
Vertex
Tracker
TPC Endcap
& MWPC
FTPCs
ZCal
ZCal
Vertex
Position
Detectors
Endcap
Calorimeter
Central Trigger
Barrel or TOF
Barrel EM
Calorimeter
RICH
STAR
HBT
4 oct 2002
malisa - seminar IUCF
5
Au on Au Event at CM Energy ~ 130 AGeV
Event Taken June 25, 2000.
STAR
HBT
4 oct 2002
malisa - seminar IUCF
6
Particle ID in STAR
RICH
STAR
dE/dx
dE/dx PID range:
[s (dE/dx) = .08]
RICH PID range:
p  ~ 0.7 GeV/c for K/
1 - 3 GeV/c for K/
 ~ 1.0 GeV/c for p/p
Topology
1.5 - 5 GeV/c for p/p
Decay vertices
Ks   + +  -
L  p +-
L  p +  +
X +
L +  +
Combinatorics
Ks   + +  -
  K++K-
X- L + -
L  p + -
L  p +  +
W  L + K-
[ r   + +  -]
[D  p +  -]
dn/dm
 from K+ K- pairs
background
subtracted
Vo
m inv
dn/dm
same event dist.
mixed event dist.
“kinks”:
K m + 
STAR
HBT
4 oct 2002
K+ K- pairs
malisa - seminar IUCF
7
m inv
Kaon Spectra at Mid-rapidity vs
Centrality
K-
K+
Centrality
cuts
Centrality
cuts
STAR preliminary
Exponential fits to mT spectra:
STAR
HBT
4 oct 2002
(K++K-)/2
Ks
STAR preliminary
1 dN
 m 
 A exp   T 
mT dmT
 T 
Centrality
cuts
STAR preliminary
Good agreement between
different PID methods
malisa - seminar IUCF
8
Hadrochemistry: particle yields vs statistical models
STAR
HBT
4 oct 2002
malisa - seminar IUCF
9
STAR
HBT
lattice QCD applies
4 oct 2002
malisa - seminar IUCF
10
Already producing QGP at lower energy?
Thermal model fits to particle yields
(including strangeness, J/)
 approach QGP at CERN?
• is the system really thermal?
• warning: e+e- falls on similar line!!
• dynamical signatures? (no)
• what was pressure generated?
• what is Equation of State of
strongly-interacting matter?
Must go beyond chemistry:
 study dynamics of system well into
deconfined phase (RHIC)
STAR
HBT
lattice QCD applies
4 oct 2002
malisa - seminar IUCF
11
Collision dynamics - several timescales
low-pT hadronic observables
QGP and
hydrodynamic expansion
initial state
hadronization
hadronic phase
and freeze-out
pre-equilibrium
CYM & LGT
dN/dt
PCM
& clust. hadronization
“temperature”
NFD
NFD & hadronic TM
1 fm/c ?
string & hadronic TM
10 fm/c ?
50 fm/c ?
time
PCM & hadronic TM
Chemical freeze out
“endSTAR
result” looks very similar
Kinetic freeze out
whether
HBTa QGP was formed or not!!!
4 oct 2002
5 fm/c ?
malisa - seminar IUCF
12
First RHIC spectra - an explosive source
• various experiments agree well
T
explosive
source
T,b
STAR
HBT
1/mT dN/dmT
purely thermal
source
1/mT dN/dmT
• different spectral shapes for
particles of differing mass
 strong collective radial flow
4 oct 2002
light
heavy
mT
light
heavy
mT
• very good agreement with hydrodynamic
prediction
malisa - seminar IUCF
data: STAR, PHENIX, QM01
model: P. Kolb, U. Heinz 13
Hydrodynamics: modeling high-density
scenarios
• Assumes local thermal equilibrium (zero mean-free-path limit) and solves
equations of motion for fluid elements (not particles)
• Equations given by continuity, conservation laws, and Equation of State (EOS)
• EOS relates quantities like pressure, temperature, chemical potential, volume
– direct access to underlying physics
• Works qualitatively at lower energy
but always overpredicts collective
effects - infinite scattering limit
not valid there
– RHIC is first time hydro works!
STAR
HBT
4 oct 2002
malisa - seminar IUCF
lattice QCD input
14
“Blast wave” Thermal motion superimposed
on radial flow (+ geometry)
Hydro-inspired “blast-wave”
thermal freeze-out fits to , K, p, L
bs
R
preliminary
s
u (t , r , z  0)  (cosh r , er sinh r , 0)
r  tanh 1 br
STAR
HBT
b r  b s f (r )
Tth = 107 MeV
b = 0.55
M. Kaneta
E.Schnedermann et al, PRC48 (1993) 2462
4 oct 2002
malisa - seminar IUCF
15
The other half of the story…
• Momentum-space characteristics of freeze-out appear well understood
• Coordinate-space ?
• Probe with two-particle intensity interferometry (“HBT”)
STAR
HBT
4 oct 2002
malisa - seminar IUCF
16
“HBT 101” - probing source geometry
p1
 source
r(x)
1m
x2
p2
5 fm
r2
T 
  
  i( r2  x 2 )p 2
i ( r1  x1 )p1
1 {  
U(x1, p1)e
U(x 2 , p2 )e
2
  i( r1  x 2 )p1   i( r2  x 1 )p 2
 U(x 2 , p1)e
U(x1, p2 )e
}

*TT  U1*U1  U*2 U 2  1  eiq( x1  x 2 )
1-particle probability
r(x,p) = U*U
2-particle probability
P(p1, p 2 )
2
C(p1, p 2 ) 
 1 ~
r (q )
P(p1 )P(p 2 )
C (Qinv)
r1
x1

  
q  p 2  p1
Width ~ 1/R
2
1
Measurable!
STAR
HBT
F.T. of pion source
0.05
4 oct 2002
malisa - seminar IUCF
0.10
17
Qinv (GeV/c)
“HBT 101” - probing the timescale of emission
C(qo , qs , ql )  1    e 
 q o2 R o2  q s2 R s2  q l2 R l2
Decompose q into components:
qLong : in beam direction
qOut : in direction of transverse momentum
qSide :  qLong & qOut
 
 
  

~2
K  ~
x out  b t 

2 
2
~
R s K  x side K

~2
2
Rl K  ~
x long  bl t
R o2
K

 

K
 
  

K
~
xx x
Rout
Rside
(beam is into board)
STAR
HBT
d 4 x  S( x, K )  f ( x )

f 
4
 d x  S( x, K )
4 oct 2002
R o2
 R s2
 b  
2
x out , x side   x, y 
beware this “helpful” mnemonic!
malisa - seminar IUCF
18
Large lifetime - a favorite signal of “new”
physics at RHIC
• hadronization time
(burning log) will
increase emission
timescale (“lifetime”)
• measurements at lower
energies (SPS, AGS)
observe <~3 fm/c
with
transition
~
• magnitude of predicted
effect depends strongly
on nature of transition
3D 1-fluid Hydrodynamics
Rischke & Gyulassy
NPA 608, 479 (1996)
ec
“e”
…but lifetime determination is complicated by other factors…
STAR
HBT
4 oct 2002
malisa - seminar IUCF
19
First HBT data at RHIC
“raw” correlation function projection
Coulomb-corrected
(5 fm full Coulomb-wave)
Data well-fit by Gaussian parametrization
C(qo , qs , ql )  1    e 
 q o2 R o2  q s2 R s2  q l2 R l2

1D projections of 3D correlation function
integrated over 35 MeV/cin unplotted components
STAR Collab., PRL 87 082301 (2001)
STAR
HBT
4 oct 2002
malisa - seminar IUCF
20
HBT excitation
function
midrapidity, low pT from central AuAu/PbPb
• decreasing  parameter partially
due to resonances
• saturation in radii
• geometric or dynamic
(thermal/flow) saturation
• the “action” is ~ 10 GeV (!)
• no jump in effective lifetime
• NO predicted Ro/Rs increase
(theorists: data must be wrong)
• Lower energy running needed!?
STAR
HBT
Collab., PRL 87 082301 (2001)
4STAR
oct 2002
malisa - seminar IUCF
21
Central collision dynamics @ RHIC
• Hydrodynamics reproduces p-space aspects
of particle emission up to pT~2GeV/c
(99% of particles)
 hopes of exploring the early, dense stage
STAR
HBT
4 oct 2002
Heinz & Kolb, hep-th/0204061
malisa - seminar IUCF
22
Central collision dynamics @ RHIC
• Hydrodynamics reproduces p-space aspects
of particle emission up to pT~2GeV/c
(99% of particles)
 hopes of exploring the early, dense stage
• x-space is poorly reproduced
• model source is too small and lives too
long and disintegrates too slowly?
• Correct dynamics signatures with wrong
space-time dynamics?
• The RHIC HBT Puzzle
• Is there any consistent way to understand the
data?
• Try to understand in simplest way possible
STAR
HBT
4 oct 2002
Heinz & Kolb, hep-th/0204061
malisa - seminar IUCF
23
Blastwave parameterization:
Implications for HBT: radii vs pT
Assuming b, T obtained from spectra fits
 strong x-p correlations, affecting RO, RS differently
K
2
RO
pT=0.2
2
 RS
 b  
2
RO
K
RS
pT=0.4
STAR
HBT
4 oct 2002
“whole source” not viewed
malisa - seminar IUCF
24
Blastwave: radii vs pT
Using flow and temperature from spectra,
can account for observed drop in HBT
radii via x-p correlations, and Ro<Rs
…but emission duration must be small
Four parameters affect HBT radii
STAR data
K
R o2  R s2  b2 2
pT=0.2
blastwave: R=13.5 fm,
freezeout=1.5 fm/c
K
pT=0.4
STAR
HBT
4 oct 2002
malisa - seminar IUCF
25
From Rlong: tkinetic = 8-10 fm/c (fast!)
Simple Sinyukov formula
– RL2 = tkinetic2 T/mT
• tkinetic = 10 fm/c (T=110 MeV)
STAR
HBT
4 oct 2002
B. Tomasik (~3D blast wave)
– tkinetic = 8-9 fm/c
malisa - seminar IUCF
26
Noncentral collision dynamics
hydro evolution
v2  cos2
dN
~ 1  2v2 cos2
or
d
• Dynamical models:
• x-anisotropy in entrance channel
 p-space anisotropy at freezeout
• magnitude depends on system
response to pressure
STAR
HBT
4 oct 2002
malisa - seminar IUCF
27
Noncentral collision dynamics
hydro evolution
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
• Dynamical models:
• x-anisotropy in entrance channel
 p-space anisotropy at freezeout
• magnitude depends on system
response to pressure
STAR
HBT
4 oct 2002
Heinz & Kolb, hep-ph/0111075
28
malisa - seminar IUCF
Effect of dilute stage
hydro evolution
later hadronic stage?
• hydro reproduces v2(pT,m) (details!)
RHIC
@ RHIC for pT < ~1.0 GeV/c
• system response  EoS
• early thermalization indicated
• dilute hadronic stage (RQMD):
• little effect on v2 @ RHIC
STAR
HBT
SPS
4 oct 2002
malisa
- seminar
IUCF & Shuryak, nucl-th/0110037
Teaney,
Lauret,
29
Effect of dilute stage
hydro evolution
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
later hadronic stage?
hydro only
hydro+hadronic rescatt
• dilute hadronic stage (RQMD):
• little effect on v2 @ RHIC
• significant (bad) effect on HBT radii
STAR
HBT
4 oct 2002
STAR
PHENIX
calculation:
Soff, Bass, Dumitru, PRL 2001
malisa - seminar
IUCF
30
Effect of dilute stage
hydro evolution
later hadronic stage?
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
• dilute hadronic stage (RQMD):
• little effect on v2 @ RHIC
• significant (bad) effect on HBT radii
• related to timescale? - need more info
STAR
HBT
4 oct 2002
malisa - seminar
IUCF
31
Teaney,
Lauret, & Shuryak, nucl-th/0110037
Effect of dilute stage
hydro evolution
later hadronic stage?
in-planeextended
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
• dilute hadronic stage (RQMD):
• little effect on v2 @ RHIC
• significant (bad) effect on HBT radii
• related to timescale? - need more info
• qualitative change of freezeout shape!!
• important piece of the puzzle!
STAR
HBT
4 oct 2002
out-of-plane-extended
malisa - seminar
IUCF
32
Teaney,
Lauret, & Shuryak, nucl-th/0110037
Possible to “see” via HBT relative to reaction plane?
p=90°
• for out-of-plane-extended source, expect
• large Rside at 0
2nd-order
• small Rside at 90
oscillation
Rside (small)
Rside (large)
p=0°
2
Rs [no flow expectation]
p
STAR
HBT
4 oct 2002
malisa - seminar IUCF
33
“Traditional HBT” - cylindrical sources
(reminder)
Decompose q into components:
C(qo , qs , ql )  1    eq o R o  q s R s  q l R l 
qLong : in beam direction

~2 
2
~
R o K  x out  b t
K
qOut : in direction of transverse momentum
qSide :  qLong & qOut


2
K
2
2
2
2
2
  
  
R s2 K   ~
x side2 K 

~2 
2
~
R l K   x long  bl t  K 
x out , x side   x, y 
~
xx x
Rout
Rside
d 4 x  S( x, K )  f ( x )

f 
4
d
 x  S( x, K )
(beam is into board)
STAR
HBT
4 oct 2002
malisa - seminar IUCF
34
Anisotropic sources Six HBT radii vs 
side
•Source in b-fixed system: (x,y,z)
•Space/time entangled in
pair system (xO,xS,xL)
R s2
~2
~2
y
K
p
x
 x sin   y cos   ~
x~y sin 2
2
out
2
b
~
~
~
R o2  ~
x 2 cos2   ~y 2 sin 2   b2 t 2  2b ~
x t cos  2b ~y t sin   ~
x~y sin 2
~
~
R l2  ~z 2  2bL ~z t  b2L t 2
~
~
2
R os
 ~
x~y cos 2  12 ( ~y 2  ~
x 2 ) sin 2  b ~
x t sin   b ~y t cos
~
~
~
~
2
R ol
( ~
x~z  bL ~
x t ) cos  ( ~y~z  bL ~y t ) sin   b ~z t  bLb t 2
~
~
R sl2  ( ~y~z  bL ~y t ) cos  ( ~
x~z  bL ~
x t ) sin 
• explicit
and implicit (xmx()) dependence on 
STAR
HBT
4 oct 2002
Wiedemann,
PRC57 266 (1998).
!
malisa - seminar IUCF
~
xx x
d 4 x  f ( x, K )  q( x )

q 
4
d
 x  f ( x, K)35
Symmetries of the emission function
I. Mirror reflection symmetry w.r.t. reactionplane
(for spherical nuclei):
S( x, y, z, t ;Y , KT , )  S( x, y, z, t ;Y , KT ,)

~
xm ~
x (Y , KT , )  1  ~
xm ~
x (Y , KT ,)
1  (1)
with
m 2   2
II. Point reflection symmetry w.r.t. collision center
(equal nuclei):
S( x, y, z, t ;Y , KT , )  S( x, y, z , t ;Y , KT ,   )
 ~
xm ~
x (Y , KT , )  2  ~
xm ~
x (Y , KT ,   )
with
STAR
HBT
2  (1)
4 oct 2002
m 0    0
Heinz, Hummel,
MAL,
Wiedemann, nucl-th/0207003
malisa - seminar
IUCF
36
Fourier expansion of HBT radii @ Y=0
Insert symmetry constraints of spatial correlation tensor into Wiedemann relations
and combine with explicit -dependence:
Rs2 ()
 Rs2,0 
2   n  2, 4,6,... Rs2, n  cos(n)
Ro2 ()
 Ro2,0 
2   n  2, 4,6,... Ro2, n  cos(n)
2
2   n  2, 4,6,... Ros
, n  sin( n)
2
Ros
() 
Rl2 ()

Rl2,0 
2   n  2, 4,6,... Rl2,n  cos(n)
Rol2 () 
2   n 1,3,5,... Rol2 , n  cos(n)
Rsl2 ()
2   n 1,3,5,... Rsl2 , n  sin( n)

Note: These most general forms of the Fourier expansions for the HBT radii
are preserved when averaging the correlation function over a finite,
symmetric window around Y=0.
Relations between the Fourier coefficients reveal interplay between flow and
STAR geometry, and can help disentangle space and time
HBT
4 oct 2002
malisa - seminar
IUCF
Heinz, Hummel,
MAL,
Wiedemann, nucl-th/0207003
37
Anisotropic HBT results @ AGS (s~2 AGeV)
xside
xout
K
R2 (fm2)
Au+Au 2 AGeV; E895, PLB 496 1 (2000)
40
side
long
ol
os
sl
20
10
0
p = 0°
out
-10
0
180
0
180
0
180
p (°)
• strong oscillations observed
• lines: predictions for static (tilted) out-of-plane extended source
 consistent with initial overlap geometry
STAR
HBT
4 oct 2002
malisa - seminar IUCF
38
Meaning of Ro2() and Rs2() are clear
What about Ros2() ?
xxside
side
xxoutout
K
K
R2 (fm2)
Au+Au 2 AGeV; E895, PLB 496 1 (2000)
40
side
long
ol
os
sl
20
10
0
p =
~45°
0°
out
-10
No access to 1st-order
oscillations in STAR Y1
0
180
0
180
0
180
p (°)
• Ros2() quantifies correlation between xout and xside
• No correlation (tilt) b/t between xout and xside at p=0° (or 90°)
STAR
HBT
• Strong (positive) correlation when p=45°
• Phase of Ros2() oscillation reveals orientation of extended source
4 oct 2002
malisa - seminar IUCF
39
Indirect indications of x-space anisotropy @ RHIC
• v2(pT,m) globally well-fit by
hydro-inspired “blast-wave”
(Houvinen et al)
T (MeV)
dashed
solid
135  20
100  24
b0(c)
0.52  0.02 0.54  0.03
ba (c)
0.09  0.02 0.04  0.01
S2
STAR
HBT
0.0
4 oct 2002
0.04  0.01
temperature, radial flow
consistent with fits to spectra 
anisotropy of flow boost
spatial anisotropy (out-of-plane extended)
malisa - seminar IUCF
STAR, PRL 87 182301 (2001)
40
STAR data
Au+Au 130 GeV minbias
• significant oscillations observed
• blastwave with ~ same parameters as
used to describe spectra & v2(pT,m)
• additional parameters:
• R = 11 fm
full blastwave
preliminary
2
RO
R S2
•  = 2 fm/c !!
consistent with R(pT), K-
R 2L
STAR
HBT
2
R OS
4 oct 2002
malisa - seminar IUCF
41
STAR data
Au+Au 130 GeV minbias
full blastwave
no spatial
anisotropy
• significant oscillations observed
• blastwave with ~ same parameters as
used to describe spectra & v2(pT,m)
• additional parameters:
• R = 11 fm
preliminary
2
RO
no flow
anisotropy
R S2
•  = 2 fm/c !!
consistent with R(pT), K-
• both flow anisotropy and source shape
contribute to oscillations, but…
• geometry dominates dynamics
• freezeout source out-of-plane extended
 fast freeze-out timescale ! (7-9 fm/c)
STAR
HBT
4 oct 2002
R 2L
2
R OS
malisa - seminar IUCF
42
Azimuthal HBT: hydro predictions
RHIC (T0=340 MeV @ 0=0.6 fm)
• Out-of-plane-extended source (but flips
with hadronic afterburner)
• flow & geometry work together to
produce HBT oscillations
• oscillations stable with KT
(note: RO/RS puzzle persists)
STAR
HBT
4 oct 2002
Heinz & Kolb, hep-th/0204061
malisa - seminar IUCF
43
Azimuthal HBT: hydro predictions
RHIC (T0=340 MeV @ 0=0.6 fm)
• Out-of-plane-extended source (but flips
with hadronic afterburner)
• flow & geometry work together to
produce HBT oscillations
• oscillations stable with KT
“LHC” (T0=2.0 GeV @ 0=0.1 fm)
• In-plane-extended source (!)
• HBT oscillations reflect competition
between geometry, flow
• low KT: geometry
• high KT: flow
STAR
HBT
4 oct 2002
sign flip
Heinz & Kolb, hep-th/0204061
malisa - seminar IUCF
44
HBT(φ) Results – 200 GeV
• Oscillations similar to those
measured @ 130GeV
• 20x more statistics 
explore systematics in centrality, kT
• much more to come…
STAR
HBT
4 oct 2002
malisa - seminar IUCF
45
Kaon – pion correlations:
dominated by Coulomb interaction
Smaller source  stronger
(anti)correlation
K-p correlation well-described by:
• Blast wave with same parameters
as spectra, HBT
But with non-identical particles, we
can access more information…
STAR preliminary
Adam Kiesel, Fabrice Retiere
STAR
HBT
4 oct 2002
malisa - seminar IUCF
46
Initial idea: probing emission-time ordering
purple K emitted first
green  is faster
• Catching up: cosY  0
•
•
purple K emitted first
green  is slower
• Moving away: cosY  0
•
•
Crucial point:
kaon begins farther in “out” direction
(in this case due to time-ordering)
STAR
HBT
4 oct 2002
long interaction time
strong correlation
short interaction time
weak correlation
• Ratio of both scenarios
allow quantitative study of
the emission asymmetry
malisa - seminar IUCF
47
measured K- correlations - natural consequence
of space-momentum correlations
• clear space-time asymmetry observed
• C+/C- ratio described by:
– “standard” blastwave w/ no time shift
• Direct proof of radial flow-induced
space-momentum correlations
STAR preliminary
Pion
STAR
<pt> HBT
= 0.12 GeV/c
4 oct 2002
Kaon
<pt> = 0.42 GeV/c
malisa - seminar IUCF
48
Summary
RHIC 130 GeV Au+Au
K*
Tomasik (3D blastwave): 8-9 fm/c (fit to PHENIX even smaller)
Sinyukov formula: Rlong2=2T/mT = 10 fm/c for T=110 MeV
K-
Disclaimer: all numbers (especially time) are rough estimates
STAR
HBT
4 oct 2002
malisa - seminar IUCF
49
Summary
RHI – the only way to create/study deconfined colored matter
Hadrochemistry suggests creation of QGP @ RHIC (and SPS)
Quantitative understanding of bulk dynamics crucial to extracting real physics at RHIC
• p-space - measurements well-reproduced by models
• anisotropy [v2(pT,m)]  system response to compression (EoS)
• x-space - generally not well-reproduced
• anisotropy [HBT()] evolution, timescale information, geometry/flow interplay
• Azimuthally-sensitive HBT: correlating quantum correlation with bulk correlation
• reconstruction of full 3D source geometry
• relevant here: OOP freeze-out
Data do suggest consistent (though surprising) scenario
• strong collective effects
• rapid evolution, then emission in a “flash” (key input to models)
• where is the hadronic phase?
• K-, HBT(pT), HBT(), K*…
By combining several (novel) measurements, STAR severely challenges
our understanding of dynamics in the soft sector of RHIC
STAR
HBT
4 oct 2002
malisa - seminar IUCF
50
Backup slides follow
• Freezeout geometry out-of-plane extended
• early (and fast) particle emission !
• consistent with blast-wave parameterization of v2(pT,m), spectra, R(pT), K-
• With more detailed information, “RHIC HBT puzzle” deepens
• what about hadronic rescattering stage? - “must” occur, or…?
• does hydro reproduce t or not??
• ~right source shape via oscillations, but misses RL(mT)
• Models of bulk dynamics severely (over?)constrained
STAR
HBT
4 oct 2002
malisa - seminar IUCF
51
Summary
Freeze-out scenario f(x,t,p) crucial to understanding RHIC physics
• p-space - measurements well-reproduced by models
• anisotropy  system response to compression
• probe via v2(pT,m)
• x-space - generally not well-reproduced
• anisotropy  evolution, timescale information
• Azimuthally-sensitive HBT: a unique new tool to probe crucial information from
a new angle
elliptic flow data suggest x-space anisotropy
HBT R() confirm out-of-plane extended source
• for RHIC conditions, geometry dominates dynamical effects
• oscillations consistent with freeze-out directly from hydro stage (???)
• consistent description of v2(pT,m) and R() in blastwave parameterization
• challenge/feedback for “real” physical models of collision dynamics
STAR
HBT
4 oct 2002
malisa - seminar IUCF
52
RHIC  AGS
• Current experimental access only to second-order event-plane
• odd-order oscillations in p are invisible
• cannot (unambiguously) extract tilt (which is likely tiny anyhow)
• cross-terms Rsl2 and Rol2 vanish @ y=0
 concentrate on “purely transverse” radii Ro2, Rs2, Ros2
• Strong pion flow  cannot ignore space-momentum correlations
• (unknown) implicit -dependences in homogeneity lengths
 geometrical inferences will be more model-dependent
• the source you view depends on the viewing angle
STAR
HBT
4 oct 2002
malisa - seminar IUCF
53
Summary of anisotropic shape @ AGS
• RQMD reproduces data better in
“cascade” mode
• Exactly the opposite trend as
seen in flow (p-space anisotropy)
• Combined measurement much
more stringent test of flow
dynamics!!
STAR
HBT
4 oct 2002
malisa - seminar IUCF
54