lanny rayohio state seminar - july 29, 20031 large scale correlations and the dissipative medium...
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Lanny Ray Ohio State Seminar - July 29, 2003 1
Large Scale Correlations and the DissipativeMedium Produced in Au+Au
Collisions at RHIC
Lanny RayUniversity of Texas at Austin
Ohio State University, July 29, 2003
Lanny Ray Ohio State Seminar - July 29, 2003 2
Acknowledgements:STAR Collaboration
Event Structure Working Group
With special thanks to my collaboratorswhose work will be shown:
Aya Ishihara - thesis work included (U. Texas Ph.D. student)Jeff Reid - thesis work included (U. Washington, Post Doc)
Qingjun Liu - (U. Washington, Post Doc)Zubayer Ahammed - (Purdue U. Post Doc)
Tom Trainor - (U. Washington)
Lanny Ray Ohio State Seminar - July 29, 2003 3
RHIC at BNLSTAR
Lanny Ray Ohio State Seminar - July 29, 2003 4
E-M Calorimeter
Time of Flight
Projection Chamber
The STAR detector
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PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
hadronizationinitial state pre-equilibrium
STAR Event viewedalong beam axis
decoupling
?
Graphics from Steffen Bass and John Harris
x
z
y
I. The general view of RHIC collisions
typicalminimumbias event
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+-
Color string fragmentation,charge ordering,
local momentum conservation,bulk production at midrapidity
from hot, dense medium
Also hard and semi-hardpQCD processes
which punch into medium
How does the hot, dense medium respond?
What’s happening just after the nuclei collide?
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STAR’s large acceptance
Short-range dynamics;non-statistical fluctuations
Large momentum scale correlations
Initial state scattering (soft & pQCD),color string fragmentation along beam
axis and transverse toward detector
Processes modified bydeveloping, dissipative
medium
Medium fluctuates as a result of semi-hard punches
We’ll measure the response of medium to learn about its properties
What’s our game plan?
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II. Mean Transverse Momentum Fluctuation Analysis - Au+Au @ 130 GeV
Event cuts: event vertex |z| < 75cm,
|x|,|y| < 1cm
Track cuts: 0.1 < pt < 2 GeV
|<1.0, full 2
Principal Authors: Ahammed, LR, Reid (thesis), Trainor
183k central trigger events (15%)205k minimum bias events
x
z
y
magnitude is where,1
1ti
N
itit pp
Np
tp
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tdp
dN
tptp̂
tp̂
Inclusive pt distribution,(all particles in all events) Randomly sample this
distribution n times to make “events” with multiplicity n. Compute the event-wise <pt> for these “events.”
tptp̂
ntt pp /ˆ
Reduced width given by:
Central Limit Theorem results
Statistical reference with which to compare real events
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183K top 15% central eventsusing 70% of all primary particles
Both (+) and (-) charges|| < 1, full
0.1 < pt < 2.0 GeV/c
Nonstatistical fluctuationsincrease the rms width
by 13.7+1.3(syst)%
n/
p̂ p
Tp̂
tt
Centered at 0In units of
expected rmsfrom CLT
Gamma dist. with increased rms
Statistical ref. from inclusivepT spectrum*
STAR Preliminary(*) N sampled inclusive spectrum approx. equals Gamma dist.
Event-wise <pt> distribution:
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(See: www.rhip.utexas.edu/projects/Star/ebye/meanpt)
Quantitative Mean pt Fluctuation Analysis
tt
tt
tt
pp
prealp
ptjtj
jp
N
ppN
nN
ˆ
2ˆ
2,
2ˆ
2
1
2
2
ˆ1
t
t
t
t pp
pp
ˆ
2
2
(removes multiplicity fluctuation bias)
(Direct application of CLT)
(Analogous to dx2 =2xdx)
This last step defines a fluctuation measure
linear in the mean pt distribution width
Relation to pt of Gazdzicki and Mrowczynski,Z. Phys. C 54, 127 (1992).
(varianceincrease)
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Numerical measures of mean-pt fluctuations
CI
CD x 3
205K minbias events70% of primaries
Extrapolated to 100%+0.5 MeV/c stat. errors
+20% syst. ErrorsDCA cut < 3 cm
Strong nonstatistical fluctuationsCentrality dependenceCI larger than at SPS (more later)CD smaller at RHICPHENIX null result is not inconsistent with STAR’s measurement (more later)
STAR Preliminary
Charge-independent:CI = [(++)+(--)]+[(+-)+(-+)]
Charge-dependent:CD = [(++)+(--)]-[(+-)+(-+)]
centrality
Extrapolation to 100%
70% ofprimaries
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3/1)2/(/2 partpartBC NNN
estimates averagepath length <l>
• Glauber-model : mean path length < l >
• Stochastic multiple scattering scales as (path length)
Saturation -dissipation
for most centralevents?
STAR Preliminary
Binary collisions, Path length and
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Status of <pt> comparisons with SPS, PHENIX and Hijing
CERES experiment at CERN-SPS (Adamova et al., nucl-ex/0305002)measured pt = 3.3 +/- 2 MeV/c for Pb+Au at lab energy of 158 AGeV (fixed target), [17 GeV/NN (cm)] for N = 162 and 0.25.
PHENIX at RHIC [Adcox et al., PR C66, 024901 (2002)] measuredpt = 6+/-6 MeV/c for Au+Auat 130 GeV/c for 0.35 and|| = 58.5 deg. for top 5% central events.
STAR (almost submitted to PRL) measured pt=14+/-2 MeV/cfor N = 180 and ||<0.25
which is 4-5 times larger.
STAR also measured pt=9+/-1 MeV/c
at the PHENIX acceptance.
NA49 [Appelshausser et al., Phys. Lett. B459, 679 (1999)] measured pt=0.6+/-1 MeV/c for Pb+Pb at 158 AGeV for N = 270 and ycm=[1.1,2.6].
II. ptpt Charge Average (CI) Correlations
Au+Au @ 130 GeV
PAs: Ishihara (thesis), Trainor, LR
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Two-Particle Correlations and Kinematics
]1),()[()(
)()(),(),(
21)2(2)1(1)1(
2)1(1)1(21)2(212
pprpp
ppppppC
Useful kinematics:
mfor E
ditypseudorapi is , ]/2)-log[tan(
rapidity is , log2
1
),,(
y
pE
pEy
ypp
z
z
t
)()( , , 2121
2211
dyddydpp ttProjection onto
2D subspaces:
z, beam
x
y tp
p
]1),()[,(1
212122112
ttttmixttttp pprppdppdppNt
Relation ofvariance tocorrelations Differential study of nonstatistical fluctuations
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Projected, Two-Point Correlations
Count # pairs in () 2D binfrom same events (“siblings”)
Count # pairs in () 2D binfrom different events (“mixed”)
The 2D bin counts are easily obtained as the
product of(# in bin- x (# in bin-
Number Density
pt pt
Event 1 2 3 4 5
ttdpp
dN
pt1 pt1
pt2 pt2
Numerator Denominator
We can do this for any measure, e.g. pt, <pt>, E, net Q, ...
bins
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Construct the Correlation
2,1
2,12,1 pp
ppppr
mixed
sibling
Sum numerator anddenominator over allevents in ensemble,
divide, and normalizeusing total number of sibling and mixed eventpairs.
Differences from 1.0indicate correlations.
(Ratios formed usingsimilar events, then r’ssummed over all events.)
Correlations
exampleonly, not
actual data
1.01
1.00
0.99
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pt x pt two-point number density ratiosfor Au+Au at 130 GeV
Central 21% by multiplicity~100k events
0.15 < pt<2 GeV/c||<1.3, full
mass se transver,
]1,0[ ]GeV 4.0/)(exp[1)(
22
mpm
mmpX
tt
tt
(produces flat dist. on X)(1) HBT+Coul. at low pt.
(2) Stochastic semi-hard scattering and fragmentation at larger pt
(3) Overall “saddle” shape due to fluctuations in bulk medium; measured by curvature [Sum-diag (main) up - Diff-diag (off) down].
STAR Preliminary
Like sign Unlike sign
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pt x pt two-point number density ratiosfor Au+Au at 130 GeV
most-central
peripheral
r[X(pt1),X(pt2)]-1 for all charges
STAR Preliminary
HBT,Coul.removed
using trackpair cuts
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Fitting the pt x pt two-point number density ratiosfor Au+Au at 130 GeV
- remove HBT, Coul.- exclude higher pt peak from fit- use analytical 2D “saddle” shape derived from fluctuating
two-point temperature model
model residualProject residuals onto sum direction,
X=X(pt1)+X(pt2),and integrate peak
STAR Preliminary
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pt x pt two-point number density ratiosfor Au+Au at 130 GeV - Summary
Plot curvature vs path length (concave up along X - concave down along X)x(N)Plot integral (xN) of high pt residual vs
We observe semi-hard scattering production which increases with initial state path length.We also observe increasing fluctuations in the bulk medium.A possible interpretation is that with increasing centrality dissipation of pt from initial state semi-hard scattering processes into the soft pt bulk medium is increased.
STAR Preliminary
III. CD Correlations Au+Au @130 GeV
PAs: Ishihara (thesis), Trainor, LR
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Forming the CD Joint Autocorrelation
• CD = LS US• CI = LS + US
• CI - initial-state scattering• CD - final-state hadronization
LS US
individual two-point spaces joint autocorrelations
STAR PreliminarySTA
R P
relim
inary
charge ordering
elliptic flow, plus...
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x CD Data
1D autocorrelation projections with fits
2D joint autocorrelations
these are two-pointnumber densities
STAR Preliminary
STAR Preliminary
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x CD Summary• Short-range correlations
(SRC) well-studied in elementary collisions, this work extends such studies to A-A collisions
• Possible interpretation is that these data are consistent with correlated pairs escaping from an opaque medium - reduced mean free path - escape probability falls exponentially with opening angle
• Alternative hypothesis: e.g. distortion of opening-angle distribution by large radial flow
• Study changing geometry of hadronization - from 1D string fragmentation 2+D surface emission in A-A, which is an open issue in QCD phenomenology
IV. - Scaling of Fluctuations
PAs: Liu, Trainor
tp
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1
)(
1
2ˆ
2 2 ˆ1
),;,(j
xM
kptjktjkp tt
ppn
0 0 Ref
222 ,ˆ)1(),( ddA
ApN tpt
2121 ,
What is a scaled correlation analysis?
The idea is to measure fluctuations on one kinematic variable
(e.g. pt) while binning on orthogonal directions (e.g. ):
acceptance bin sizeor scale
avg.over
events
sumoccupied.
bins
functionof scale
compute variance among pairs in all ( bins
in the acceptance
The scale dependence reveals correlations:
Invert Volterra eq. in its discrete form, obtain autocorrelation
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Transverse momentum scaling analysis for Au+Au at 200 GeV
pt(CI)as function
of scale
pt auto-correlation
on axial space
peri
pher
alm
idce
ntra
lm
ost-
cent
ral
-Same side correlation-Away side p conserv.-Elliptical flow, plus ?-Away side suppression with centrality-Dissipation of away side pt into bulk
STA
R
Pre
lim
inary
Lanny Ray Ohio State Seminar - July 29, 2003 30
Conclusions• Large, non-statistical <pt>
CI fluctuations; centrality
dependence at RHIC.
• Structure in ptpt CI and CD distributions seen; data fit with simple, analytic functions.
• CD correlations possibly suggest growth of an opaque medium
• ptpt CI correlations possibly suggest a dissipative system, with space-correlated temperature fluctuations, and a non-dissipated hard component increasing with centrality.
• Close connection between correlations and variance scale differences.
This evidence suggests that semi-hard ISS processes excite a dissipative and opaque medium, generating the observed CI, CD correlation structure.
tp
Lanny Ray Ohio State Seminar - July 29, 2003 31
Russia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - Protvino
U.S. Laboratories:ArgonneBerkeleyBrookhaven
U.S. Universities: UC BerkeleyUC DavisUC Los AngelesCarnegie Mellon Creighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinU. of Washington Wayne State UniversityYale University
Brazil: Universidade de Sao Paulo
China: IHEP – BeijingIMP - LanzouIPP – WuhanUSTCSINR – ShanghaiTsinghua University
Great Britain: University of Birmingham
France:IReS StrasbourgSUBATECH - Nantes
Germany: MPI – MunichUniversity of Frankfurt
India:IOP - BhubaneswarVECC - CalcuttaPanjab UniversityUniversity of RajasthanJammu UniversityIIT - BombayVECC – Kolcata
Poland:Warsaw University of Tech.
The STAR Collaboration
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