Post on 30-Dec-2015
31 Oct 2001 Mike Lisa - Kent State Seminar 1
STARHBT
Emergence of a Consistent Picture from First Results of STAR at RHIC?
Mike Lisa, Ohio State UniversitySTAR Collaboration
U.S. Labs: Argonne, Lawrence Berkeley National Lab, Brookhaven National Lab
U.S. Universities: Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton,Indiana,Kent State,Michigan State,CCNY, Ohio State,Penn State, Purdue, Rice,Texas A&M, UT Austin,Washington, Wayne State,Yale
Brazil: Universidade de Sao Paolo
China: IHEP - Beijing, IPP - Wuhan
England: University of Birmingham
France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes
Germany: Max Planck Institute – Munich, University of Frankfurt
Poland: Warsaw University, Warsaw University of Technology
Russia: MEPHI – Moscow, LPP/LHE JINR–Dubna, IHEP-Protvino
31 Oct 2001 Mike Lisa - Kent State Seminar 2
STARHBT
Overview• ~ 1 year from initial data-taking in new energy regime• overall picture / underlying driving physics unclear
Outline• Ultrarelativistic Heavy Ion Collisions and STAR at RHIC• First data
Transverse momentum spectra Momentum-space anisotropy (elliptic flow)• Initial quantitative success of hydrodynamics• Two-pion correlations (HBT) STAR HBT and the “HBT Puzzle”
• Characterization of freeze-out from the data itself K- correlations particle-identified elliptical flow azimuthally-sensitive HBT: theory and first data
• Summary
Skipped
Skipped
31 Oct 2001 Mike Lisa - Kent State Seminar 3
STARHBT
Why heavy ion collisions?
• Study bulk properties of strongly-interacting matter far from ground state
• 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 ~ s
• 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”): the only way to experimentally probe the deconfined state
The “little bang”
31 Oct 2001 Mike Lisa - Kent State Seminar 4
STARHBT
The “little bang”Stages of the collision
• pre-equilibrium (deposition of initial energy density)• rapid (~1 fm/c) thermalization (?)
QGP formation (?)
hadronic rescattering
hadronization transition (very poorly understood)
freeze-out: cessation of hard scatterings
• low-pT hadronic observables probe this stage
“end result” looks very similar whether a QGP was formed or not!!!
31 Oct 2001 Mike Lisa - Kent State Seminar 5
STARHBT
Already producing QGP at lower energy?
J. Stachel, Quark Matter ‘99
Thermal model fits to particle yields (& strangeness enhancement, J/ suppression) approach QGP at CERN?
• is the system really thermal?• dynamical signatures? (no)• what was pressure generated?• what is Equation of State of strongly-interacting matter?
warning: e+e- yields fall on similar line!!
Must go beyond chemistry: study dynamics of system well into deconfined phase (RHIC)
lattice QCD applies
31 Oct 2001 Mike Lisa - Kent State Seminar 6
STARHBT
uRQMD simulation of Au+Au @ s=200 GeV
pure hadronic & stringdescription (cascade)
generally OK at lower energies
applicability in very high density (RHIC) situations unclear
produces too little collective flow at RHIC
freeze-out given by lasthard scattering
31 Oct 2001 Mike Lisa - Kent State Seminar 7
STARHBT
First RHIC spectra - an explosive source
data: STAR, PHENIX, QM01model: P. Kolb, U. Heinz
• various experiments agree well
• different spectral shapes for particles of differing mass strong collective radial flow
mT1/m
T d
N/d
mT
light
heavyT
purely thermalsource
explosivesource
T,mT1/
mT d
N/d
mT
light
heavy• very good agreement with hydrodynamic
prediction
31 Oct 2001 Mike Lisa - Kent State Seminar 8
STARHBT
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 pressure, temperature, chemical potential, volume– direct access to underlying physics
• Works qualitatively at lower energybut always overpredicts collectiveeffects - infinite scattering limitnot valid there
lattice QCD input
31 Oct 2001 Mike Lisa - Kent State Seminar 9
STARHBT
Hydro time evolution of
non-central collisions
Equal energy density linesP. Kolb, J. Sollfrank,and U. Heinz
• correlating observations with respect to event-wise reaction plane allows much more detailed study of reaction dynamics
• entrance-channel aniostropy in x-space pressure gradients (system response) p-space anisotropy (collective elliptic flow)
self-quenching effect - sensitive to early pressure
31 Oct 2001 Mike Lisa - Kent State Seminar 10
STARHBT
Azimuthal-angle distribution versus reaction plane
• v2 increases from central to peripheral collisions– natural space-momentum
connection
φ= 2cosv2
particle-reaction plane
( )φ+φ
2cosv21~d
dN2or
31 Oct 2001 Mike Lisa - Kent State Seminar 11
STARHBT
Measurements at AGS; E895 and E877 (Protons)
• At low beam energies negative v2 (“squeeze-out”)
• Balancing energy around 4 AGeV, sensitive to EOS
Elab (AGeV)
0.04
-0.08
-0.04
0
1 10
v 2E895, Phys. Rev. Lett. 83 (1999) 1295
P. Danielewicz, Phys. Rev. Lett. 81 (1998) 2438
31 Oct 2001 Mike Lisa - Kent State Seminar 12
STARHBT
Local thermal equilibrium versus Low Density Limit
SPS; Low-Density-Limit and Hydro miss pt dependence
RHIC; pt dependence quantitatively described by Hydro
pt dependence sensitive to early thermalization?
p
Charged particles
31 Oct 2001 Mike Lisa - Kent State Seminar 13
STARHBT
• Momentum-space characteristics of freeze-out appear well understood
• Coordinate-space ?• Probe with two-particle intensity interferometry (“HBT”)
The other half of the story…
31 Oct 2001 Mike Lisa - Kent State Seminar 14
STARHBT
“HBT 101” - probing source geometry
12 ppqrrr −=
2
21
2121 )q(~1
)p(P)p(P)p,p(P
)p,p(C ρ+== C (Qinv)
Qinv (GeV/c)
1
2
0.05 0.10
Width ~ 1/R
Measurable! F.T. of pion source
( ))xx(iq2
*21
*1T
*T
21e1UUUU −⋅+⋅⋅=ψψ
Creation probability ρ(x,p) = U*U
222111 p)xr(i22
p)xr(i11T e)p,x(Ue)p,x(U
rrrrrr rrrr ⋅−⋅−=
5 fm
1 m sourceρ(x)
r1
r2
x1
x2
{2
1
}e)p,x(Ue)p,x(U 212121 p)xr(i21
p)xr(i12
rrrrrr rrrr ⋅−⋅−+
p1
p2
31 Oct 2001 Mike Lisa - Kent State Seminar 15
STARHBT
“HBT 101” - probing the timescale of emission
K
( ) ( ) ( )( ) ( )( ) ( ) ( )Kt~x~KR
Kx~KR
Kt~x~KR
2llong
2l
2side
2s
2out
2o
rr
rr
rr
β−=
=
β−= ⊥
xxx~ −≡
∫∫
⋅⋅⋅
≡)K,x(Sxd
)x(f)K,x(Sxdf
4
4
RoutRside ( ) ( )y,xx,x sideout ≠
Decompose q into components:qLong : in beam directionqOut : in direction of transverse momentumqSide : qLong & qOut
(beam is into board)( )22
s2o RR τ⋅β+=
beware this “helpful” mnemonic!
( )2l2l
2s
2s
2o
2o RqRqRq
lso e1)q,q,q(C ++−⋅λ+=
31 Oct 2001 Mike Lisa - Kent State Seminar 16
STARHBT
Large lifetime - a favorite signal of “new” physics at RHIC
• hadronization time (burning log) will increase emission timescale (“lifetime”)
• magnitude of predicted effect depends strongly on nature of transition
• measurements at lower energies (SPS, AGS) observe <~3 fm/c
“”
withtransition
c
Rischke & GyulassyNPA 608, 479 (1996)
3D 1-fluid Hydrodynamics
~
…but lifetime determination is complicated by other factors…
31 Oct 2001 Mike Lisa - Kent State Seminar 17
STARHBT
First HBT data at RHIC
STAR Collab., PRL 87 082301 (2001)
( )2l2l
2s
2s
2o
2o RqRqRq
lso e1)q,q,q(C ++−⋅λ+=
Data well-fit by Gaussian parametrization
Coulomb-corrected(5 fm full Coulomb-wave)
“raw” correlation function projection
1D projections of 3D correlation functionintegrated over 35 MeV/cin unplotted components
31 Oct 2001 Mike Lisa - Kent State Seminar 18
STARHBT
HBT excitation function
STAR Collab., PRL 87 082301 (2001)
•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!?
midrapidity, low pT -
from central AuAu/PbPb
31 Oct 2001 Mike Lisa - Kent State Seminar 19
STARHBT
First STAR HBT data - systematics
STAR Collab., PRL 87 082301 (2001)
• +, - HBT parameters similar• Grossly similar to AGS/SPS
• all radii increase with multiplicity• Ro, Rs - geometric effect
• Rl - increase not seen at AGS/SPS
• With increasing mT
• increases fewer resonances
• radii decrease x-p correlations
• stronger effect in Ro than at AGS/SPS
systematic errors
31 Oct 2001 Mike Lisa - Kent State Seminar 20
STARHBT
mT dependence at ycm for 2 AGeV central collisions
• collective flow dynamical correlation between position and momentum R(mT)
• R’s are “lengths of homegeity”
• - from decays (mT)
x (fm)
y (f
m)
31 Oct 2001 Mike Lisa - Kent State Seminar 21
STARHBT
Hydro attempts to reproduce data
out
side
long
KT dependence approximately reproduced correct amount of collective flow
Rs too small, Ro & Rl too big source is geometrically too small and lives too long in model
Right dynamic effect / wrong space-time evolution? the “RHIC HBT Puzzle”
generichydro
31 Oct 2001 Mike Lisa - Kent State Seminar 22
STARHBT
“Realistic” afterburner makes things worse
pure hydro
hydro + uRQMD
STAR data
1.0
0.8
Currently, no physical modelreproduces explosive space-timescenario indicated by observation
RO/R
S
31 Oct 2001 Mike Lisa - Kent State Seminar 23
STARHBT
Now what?
• No dynamical model adequately describes freeze-out distribution• Seriously threatens hope of understanding pre-freeze-out dynamics• Raises several doubts
– is the data consistent with itself ? (can any scenario describe it?)– analysis tools understood?
• Attempt to use data itself to parameterize freeze-out distribution• Identify dominant characteristics• Examine interplay between observables• Isolate features generating discrepancy with “real” physics models
31 Oct 2001 Mike Lisa - Kent State Seminar 24
STARHBT
Characterizing the freezeout: An analogous
situation
31 Oct 2001 Mike Lisa - Kent State Seminar 25
STARHBT
Probing f(x,p) from different angles
∫ ∫ ∫
⋅⋅⋅φφ=2
0
2
0
R
0Tps2
T
)p,x(fmdrrdddm
dN
Transverse spectra: number distribution in mT
∫ ∫ ∫∫ ∫ ∫
⋅⋅φφ
⋅φ⋅⋅φφ=φ≡
20
20
R0sp
20
20
R0 psp
pT2)p,x(fdrrdd
)p,x(f)2cos(drrdd)2cos()m,p(v
Elliptic flow: anisotropy as function of mT
HBT: homogeneity lengths vs mT, p
( )
( ) ν
ν
ν
−⋅⋅φ
⋅⋅⋅φ=φ
⋅⋅φ
⋅⋅⋅φ=φ
∫ ∫∫ ∫
∫ ∫∫ ∫
xx)p,x(fdrrd
)p,x(fxxdrrd,px~x~
)p,x(fdrrd
)p,x(fxdrrd,px
20
R0s
20
R0s
pT
20
R0s
20
R0s
pT
31 Oct 2001 Mike Lisa - Kent State Seminar 26
STARHBT
mT distribution from Hydrodynamics-inspired model
)r(tanh 1=ρ −
E.Schnedermann et al, PRC48 (1993) 2462
R
s
( ) ( )rRcosT
sinhpexp
T
coshmK)p,x(f pb
TT1 −Θ⋅⎥⎦
⎤⎢⎣⎡ φ−φ⋅
ρ⋅⎟⎠⎞
⎜⎝⎛ ρ
=
Infinitely longsolid cylinder
b = direction of flow boost (= s here)
2-parameter (T,) fit to mT distribution
)r(g)r( s ⋅=
31 Oct 2001 Mike Lisa - Kent State Seminar 27
STARHBT
• 2 contour maps for 95.5%CL
T th [
GeV
]
s [c]
- K-p
T th [
GeV
]
s [c]
T th [
GeV
]
s [c]
Tth =120+40-30MeV
<r >=0.52 ±0.06[c]
tanh-1(<r >) = 0.6
<r >= 0.8s
Fits to STAR spectra; r=s(r/R)0.5
-
K-
p
1/m
T d
N/d
mT
(a
.u.)
mT - m [GeV/c2]thanks to M. Kaneta
preliminary
STAR preliminary
31 Oct 2001 Mike Lisa - Kent State Seminar 28
STARHBT
Excitation function of spectral parameters
• Kinetic “temperature” saturates ~ 140 MeV already at AGS
• Explosive radial flow significantly stronger than at lower energy
• System responds more “stiffly”?
• Expect dominant space-momentum correlations from flow field
31 Oct 2001 Mike Lisa - Kent State Seminar 29
STARHBT
Implications for HBT: radii vs pT
Assuming , T obtained from spectra fits strong x-p correlations, affecting RO, RS differently
pT=0.2
pT=0.4
y (f
m)
y (f
m)
x (fm)
x (fm)
( )22S
2O RR τ⋅β+=
31 Oct 2001 Mike Lisa - Kent State Seminar 30
STARHBT
Implications for HBT: radii vs pT
STAR data
model: R=13.5 fm, =1.5 fm/c T=0.11 GeV, ρ0 = 0.6
Magnitude of 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
pT=0.2
pT=0.4
y (f
m)
y (f
m)
x (fm)
x (fm)
Four parameters affect HBT radii
31 Oct 2001 Mike Lisa - Kent State Seminar 31
STARHBT
Kaon – pion correlation:dominated by Coulomb interaction
• Static sphere :– R= 7 fm ± 2 fm (syst+stat)
• Blast wave – T = 110 MeV (fixed)
– <r> = 0.62 (fixed)
– R = 13 fm ± 4 fm (syst+stat)
• Consistent with other measurements
STAR preliminary
31 Oct 2001 Mike Lisa - Kent State Seminar 32
STARHBT
Initial idea: probing emission-time ordering
• Catching up: cos0• long interaction time• strong correlation
• Ratio of both scenarios allow quantitative study of the emission asymmetry
• Moving away: cos0• short interaction time• weak correlation
Crucial point: time-ordering meanskaon begins farther in “out” direction
purple emitted firstgreen is faster
purple emitted firstgreen is slower
31 Oct 2001 Mike Lisa - Kent State Seminar 33
STARHBT
Space-time asymmetry
• Evidence of a space – time asymmetry– -K ~ 4fm/c ± 2 fm/c, static
sphere
– Consistent with “default” blast wave calculation
pT = 0.12 GeV/c
STAR preliminary
KpT = 0.42 GeV/c
31 Oct 2001 Mike Lisa - Kent State Seminar 34
STARHBT
Non-central collisions: coordinate- and momentum-space anisotropies
Equal energy density lines
P. Kolb, J. Sollfrank, and U. Heinz
31 Oct 2001 Mike Lisa - Kent State Seminar 35
STARHBT
More detail: identified particle elliptic flow
soliddashed
0.04 0.010.09 0.02a (c)
0.04 0.01 0.0S2
0.54 0.030.52 0.020(c)
100 24135 20T (MeV)
STAR, in press PRL (2001)
( ) ( ) ( ) ( )( ) ( )∫
∫ ρρ
ρρ
φ
φφ=
20 T
coshm1T
sinhp0b
20 T
coshm1T
sinhp2bb
T2TT
TT
KId
KI2cosdpv
( )ba0 2cos φρ+ρ=ρFlow boost:
b = boost direction
Meaning of ρa is clear how to interpret s2?
hydro-inspiredblast-wave modelHouvinen et al (2001)
31 Oct 2001 Mike Lisa - Kent State Seminar 36
STARHBT
Ambiguity in nature of the spatial anisotroy
b = direction of the boost s2 > 0 means more source elements emitting in plane
( )( )
( ) ( )rR2cosR
rs21ecosh
T
mKp,xf s2
cossinhT
pT
1ps
T
−θ⎟⎠⎞
⎜⎝⎛ φ+⎟
⎠⎞
⎜⎝⎛ ρ=
φ−φρrr
case 1: circular source with modulating density
RMSx > RMSy
RMSx < RMSy
( )( ) ( )y222cossinh
T
pT
1 R/xy1ecoshT
mKp,xf
psT
η+−θ⎟⎠⎞
⎜⎝⎛ ρ=
φ−φρrr
case 2: elliptical source with uniform density
x
y
R
R≡η
1
1
2
1s
3
3
2 +η−η
≅
31 Oct 2001 Mike Lisa - Kent State Seminar 37
STARHBT
Azimuthal HBT: (transverse) spatial anisotropy
•Source in b-fixed system: (x,y,z)•Space/time entangled in
pair system (xO,xS,xL)
U. Wiedemann, PRC 57, 266 (1998)
( )( )( ) ( ) p
2221
ppT2os
pp22
p22
pT2s
22pp
22p
22pT
2o
2sinx~y~2cosy~x~,pR
2siny~x~cosy~sinx~,pR
t~2siny~x~siny~cosx~,pR
φ−+φ⋅=φ
φ⋅−φ+φ=φ
β+φ⋅+φ+φ=φ ⊥
large flow @ RHIC induces space-momentum
correlations
p-dependent homogeneity lengths
sensitive to more than “just” anisotropic geometry
( )pT ,px~x~ φνμ
out
b
K
x
yside
31 Oct 2001 Mike Lisa - Kent State Seminar 38
STARHBT
Reminder: observations for Au(2 AGeV)Au
p (°) 0 180
0
0 180 0 180
10
-10
20
40
R2 (
fm2 ) out side long
ol os sl
E895 Collab., PLB 496 1 (2000)
p=0°
p=90°
out-of-planeextended source
interesting physics, but not currenly accessible in STARwith 2nd-order reaction plane
Lines are global fitOscillation magnitude eccentricityOscillation phases orientation
31 Oct 2001 Mike Lisa - Kent State Seminar 39
STARHBT
xout
xside
K
Meaning of Ro2() and Rs
2() are clearWhat about Ros
2()
p (°) 0 180
0
0 180 0 180
10
-10
20
40
R2 (
fm2 ) out side long
ol os sl
E895 Collab., PLB 496 1 (2000)
• Ros2() quantifies correlation between xout and xside
• No correlation (tilt) b/t between xout and xside at p=0° (or 90°)
K
x out x sid
e K x out x sid
e
K x out x side
K xout
x side
K xout
xside
K xout
xside
p = 0°p ~45°
• Strong (positive) correlation when p=45°
31 Oct 2001 Mike Lisa - Kent State Seminar 40
STARHBT
STAR HBT
“Out”
“Side”
“Long”
1.0
1.3
1.0
1.3
1.0
1.3
0 0.1 0.2
C(Q
)
Q (GeV/c)
Correlation function: p=45º
RO
2 (fm
2 )R
S2 (
fm2 )
RO
S2 (
fm2 )
- from semi-peripheral events
raw
corrected forreactionplane resolution
data fit
• only mix events with “same” RP
• retain relative sign between q-components• HBT radii oscillations similar to AGS• curves are not a global fit• RS almost flat
STAR preliminary
31 Oct 2001 Mike Lisa - Kent State Seminar 41
STARHBT
Out-of-plane elliptical shape indicated
case 1
using (approximate) values ofs2 and ρa from elliptical flow
case 2
opposite R() oscillations would lead to opposite conclusion STAR preliminary
31 Oct 2001 Mike Lisa - Kent State Seminar 42
STARHBT
s2 dependence dominates HBT signal
error contour fromelliptic flow data
color: 2 levelsfrom HBT data
STAR preliminary
s2=0.033, T=100 MeV, ρ0ρaR=10 fm, =2 fm/c
31 Oct 2001 Mike Lisa - Kent State Seminar 43
STARHBT
A consistent picture
parameter spectra elliptic flow HBT K-
Temperature T≈11MeV √ √ √ √
Radialflowvelocity
ρ≈. √ √ √ √
Oscillationinradialflow
ρa≈.4 √ √
Spatialanisotropy
s2≈.4 √ √
Radiusiny Ry≈1-1fm(dependsonb)
√ √
Natureofxanisotropy
* √
Emissionduration
≈2fm/c √ √
( )( ) ( ) 22ps
T
2/ty
222cossinhT
pT
1 eR/xy1ecoshT
mKp,xf τφ−φρ
⋅η+−θ⎟⎠⎞
⎜⎝⎛ ρ=
rr
31 Oct 2001 Mike Lisa - Kent State Seminar 44
STARHBT
SummarySpectra• Very strong radial flow field superimposed on thermal motion• T saturates rapidly ~ 140 MeV higher at RHIC
•space-momentum correlations important•“stiffer” system response?
• consistent with hydro expectation
Momentum-space anisotropy• sensitive to EoS and early pressure and thermalization• significantly stronger elliptical flow at RHIC, compared to lower
energy• indication of coordinate-space anisotropy as well as flow-field
anisotropy (v2 cannot distinguish its nature, however)• for the first time, consistent with hydro expectation
31 Oct 2001 Mike Lisa - Kent State Seminar 45
STARHBT
Summary (cont’)HBT• radii grow with collision centrality R(mult)• evidence of strong space-momentum correlations R(mT)• non-central collisions spatially extended out-of-plane R()• The spoiler - expected increase in radii not observed• presently no dynamical model reproduces data
Combined data-driven analysis of freeze-out distribution• Single parameterization simultaneously describes
•spectra•elliptic flow•HBT•K- correlations
• most likely cause of discrepancy is extremely rapid emission timescale suggested by data - more work needed!
31 Oct 2001 Mike Lisa - Kent State Seminar 47
STARHBT
Very large event anisotropies seen by STAR, PHENIX, PHOBOS
v2
centrality
• space-momentum connection clear in multiplicity dependence
• different experiments agree well
• finally, we reach regime of quantitative hydro validity evidence for early thermalization
• AGS: magnitude described by cascade models
• RHIC; Hydro description for central to mid-central collisions
– 26% more particles in-plane than out-of-plane (even more at high pT)!!
31 Oct 2001 Mike Lisa - Kent State Seminar 48
STARHBT
Experimental correlation functions
12 ppqrrr −=
B(q)
A(q)C(q)
)p(P)p(P
)p,p(P)p,p(C Practice In
21
2121 = →=
A(q
)
q (GeV/c)
# pairs fromsame event
B(q
)
q (GeV/c)
# pairs fromdifferent events
• most pairs at high q (need statistics!)
• shape of A(q), B(q) dominated by phasespace and single-particle acceptance (complicated in principle, especially in multiple dimensions)
q (GeV/c)0.1 0.2 0.3
C(q
)
00
2
1
• only correlated effects persist in ratio (including residual detector artifacts…)
• Correlation functions from different experiments (and from theory) can be compared
31 Oct 2001 Mike Lisa - Kent State Seminar 49
STARHBT
A consistent picture
parameter spectra elliptic flow HBTTemperature T ≈11MeV √ √ √
Radialflowvelocity
ρ≈. √ √ √
Oscillationinradialflow
ρa≈.4 √ √
Spatialanisotropy
s2≈.4 √ √
Radiusiny Ry≈1-1fm(dependsonb)
√
Natureofxanisotropy
* √
Emissionduration
≈2fm/c √main sourceof discrepancy?
( )( ) ( ) 22ps
T
2/ty
222cossinhT
pT
1 eR/xy1ecoshT
mKp,xf τφ−φρ
η+−θ⎟⎠⎞
⎜⎝⎛ ρ=
rr
31 Oct 2001 Mike Lisa - Kent State Seminar 50
STARHBT
Geometry of STAR
ZCal
Barrel EM Calorimeter
Endcap Calorimeter
Magnet
Coils
TPC Endcap & MWPC
ZCal
FTPCs
Vertex Position Detectors
Central Trigger Barrel or TOF
Time Projection Chamber
Silicon Vertex Tracker
RICH
31 Oct 2001 Mike Lisa - Kent State Seminar 51
STARHBT
Peripheral Au+Au Collision at 130 AGeV
Data Taken June 25, 2000.
Pictures from Level 3 online display.
31 Oct 2001 Mike Lisa - Kent State Seminar 52
STARHBT
Au on Au Event at CM Energy ~ 130 AGeV
Data Taken June 25, 2000.
31 Oct 2001 Mike Lisa - Kent State Seminar 53
STARHBT
Summary• Spectra, elliptic flow, and HBT measures consistent with a freeze-out
distribution including strong space-momentum correlations
• In non-central collisions, v2 measurements sensitive to existence of spatial anisotropy, while HBT measurement reveals its nature
• Systematics of HBT parameters:• flow gradients produce pT-dependence (consistent with spectra and v2(pT,m))
•anisotropic geometry (and anisotropic flow boost) produce -dependence
• (average) out-of-plane extension indicated• however, distribution almost “round,” --> more hydro-like evolution as
compared to AGS
While data tell consistent story within hydro-inspired parameterization, hydro itself tells a different story - likely point of conflict is timescale
31 Oct 2001 Mike Lisa - Kent State Seminar 54
STARHBT
STAR TPC • Active volume: Cylinder r=2 m, l=4 m
– 139,000 electronics channels sampling drift in 512 time buckets
– active volume divided into 70M3D pixels
On-board FEE Card:Amplifies, samples, digitizes 32 channels
31 Oct 2001 Mike Lisa - Kent State Seminar 55
STARHBT
Joint view of freezeout: HBT & spectra
• common model/parameterset describes different aspects of f(x,p) for central collisions
• Increasing T has similar effect on a spectrum as increasing
• But it has opposite effect on R(pT) opposite parameter correlations in
the two analyses tighter constraint on parameters
spectra ()
HBT
STAR preliminary