Transcript Slide 1

Fluctuation Studies at STAR
Supriya Das* (for STAR Collaboration)
Variable Energy Cyclotron Center,
Kolkata, India
* Present address : Gesellschaft für Schwerionenforschung mbH (GSI)
Darmstadt, Germany
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
1
Solenoidal Tracker At RHIC
Tracking Detectors:
TPC, FTPC, SVT
Calorimeters:
BEMC, EEMC, ZDC
Trigger Detectors:
CTB, BBC, MWPC
Photon Detector:
Others: TOF, FPD
PMD
Goal : to track the hadrons (and photons) in each collision
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
2
Features of STAR data
(shown in this talk)
+ Au @ sNN1/2 = 20, 62, 130, 200 GeV
 TPC data with || < 1.0, -p < f <p
 PID from TPC dE/dx
 Collision centrality measured by charged particle multiplicity in ||<0.5
 Centrality slices 0-5%, 5-10%, 10-20 %, …
 Use Glauber MC model to estimate number of participants.
 Au
Supriya Das
M. Anderson et al. for STAR Collaboration, NIMA499 (2003)
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
3
Fluctuation Analyses from STAR so far
Published papers :
 Net Charge / Multiplicity fluctuation : PRC 68 (2003) 044905
PLB 634 (2006) 347
 Mean pt fluctuation / correlation : PRC 71 (2005) 064906
PRC 72 (2005) 044902
J. Phys G 32 (2006) L37
 Balance function : PRL 90 (2003) 172301
Submitted to arXive :
 Mean pt fluctuation / correlation: nucl-ex/0408012
nucl-ex/0605022
Many interesting presentations by others on these topics
Recent ongoing analyses within the working group:




Supriya Das
Charge fluctuation (energy dependence, higher moments)
Balance function (mass dependence)
Long range correlation
Event by event K/p ratio
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
4
Mean pt fluctuation
CI
CD
G distribution
Results for hadrons for pt < 2GeV/c
PRC 71 (2005) 064906
Supriya Das
• Deviations from statistical reference
• Excess in charge independent fluctuation
- varies smoothly and monotonically
with centrality
• RHIC events are not fully equilibrated –
even for low pt and most central events
• No evidence of critical fluctuation
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
5
pt correlation
(energy dependence)
PRC 72 (2005) 044902





Non-zero pt correlations in Au+Au collisions from 20 to 200 A Gev
<Dpt,i Dpt,j> decreases with increasing centrality
dN/d <Dpt,i Dpt,j>  Dspt:n shows similar behavior as earlier
HIJING shows little or no centrality dependence
Saturation attributed to onset of thermalization or jet suppression
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
6
pt correlation
(energy dependence)
PRC 72 (2005) 044902
 Scaled value of correlation show a little or no dependence on incident
energy.
 HIJING calculations under predict the data.
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
7
pt angular correlation
(scale dependence)
 pt variance difference increases with increasing collision energy.
 Same side peak and away-side ridge in autocorrelation attributed to minijets
nucl-ex/0605022
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
8
pt angular correlation
(scale dependence)
Rapid rise within d < 0.2
SSC
Slow linear rise after that
LSC
--- Scale dependence
Supriya Das
  2 Nbin / Npart
 pt variance difference is centrality dependent
 saturation in energy dependence for peripheral
collisions
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
9
pt angular correlation
(scale dependence)
pt variance difference increases with increasing collision energy
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
10
pt correlation on , f
Autocorrelations after subtracting
monopole, dipole and quadrupole
components
variance difference
auto-correlation
Scale dependence of variance difference
and corresponding autocorrelations
Supriya Das
Structures attributed to minijets
J. Phys G 32 (2006) L37
Au + Au @ 200 GeV
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
11
Net Charge fluctuation
(motivation)
confined:
few d.o.f.
• Prediction: A drastic decrease in the EbyE
fluctuations of net charge in local phase space
regions in the deconfined QGP phase compared to
that of the confined case hadronic gas.
QGP:4 and pion gas: 1-2
Jeon, Koch: PRL (2000) 2076
Asakawa, Heinz & Muller: PRL (2000) 2072
deconfined:
many d.o.f.
Charged multiplicity: nch = n+ + n–
Net charge:
Q = n + - n–
Charge ratio:
R = n + / n(1) v(Q)  Var(Q)/<nch>
(for stochastic emission, v(Q) = 1)
(2) v(R)  Var(R) * <nch>
(for stochastic emission, v(R) = 4)
(3) F(Q)
• Evolution of fluctuation
Shuryak & Stephanov: PR C63 (2001) 064903
Heiselberg & Jackson: PR C63 (2001) 064904
Mohanty, Alam & Nayak: PR C67 (2003) 024904
Supriya Das
(4) dynamic
 ,dyn      ,stat
(5) Moments of Net charge
distributions
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
12
Net Charge fluctuation
Charge conservation limit

Charge conservation limit
Fluctuation for inclusive non-identified charge particles
exceed by factor of 2 compared to charge conservation
limit
 Results agree with expectation based on measurement
from p+p collisions at ISR
Resonance gas
 Two particle correlation may be modified in central
collisions relative to the peripheral collisions
 Fluctuation measure closer to the prediction with
resonance gas
Au+Au @ 130 GeV
PRC 68 (2003) 044905
Supriya Das
 Pions show little larger fluctuation compared to inclusive
measurement
 Kaons and protons show 2 to 4 times the value of
fluctuation compared to inclusive measurement
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
13
Net Charge fluctuation
(energy dependence)
 dyn
0
-0.001
-0.002
STAR: 5% Central Au+Au
PHENIX ||<0.35, Df=p/2
CERES 2.0<  <2.9
-0.003
0
50
100
150
200
SNN1/2
C. Pruneau - nucl-ex/0401016
(GeV)
C. Pruneau QM 05
Dynamical net charge fluctuation are invariant of beam energies
starting from top SPS onwards.
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
14
Moments of net charge distributions
(motivation)
Lattice calculations
Calculation of Non-linear susceptibilities (higher order
derivatives of pressure with respect to chemical potentials):
•Ejiri, Karsch and Redlich: hep-ph/0510126
•Gavai, Gupta: hep-lat/0510044
4th moment
2nd moment
(similar to kurtosis)
6th moment
•Net charge
•Isospin
•Strangeness
 Interesting structure close to T=TC
Is it possible to make precise measurement of
higher moments of net charge?
• bins in centrality
• bins in pT
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
15
Net charge (Q) distributions
Q distributions for AuAu 200GeV at 4
different centralities and 6 bins in pT
MEAN of Q distributions
<Q>
low pT
high pT
<Q>/Npart
Q (net charge)
T. Nayak – SQM ‘06
Supriya Das
<Q>/Npart is independent of centrality.
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
16
Variance and kurtosis of net charge distributions
(Q) with pT binned
AuAu 200GeV
Kurtosis
(4th moment)
Centrality & pT
T. Nayak – SQM ‘06
 (Q) is low at low pT and increases with
increase of pT. Could be an effect of more
resonance production at low pT.

Supriya Das
First analysis of the 4th moment of net
charge distribution is performed. Detailed
comparison in terms of lattice calculations
is expected soon.
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
17
Balance function
(motivation)
Z=0
• Bass-Danielewicz-Pratt, PRL 85, 2000
• D. Drijard et al, NP B(155), 1979
Opposite charged particles
are created at the same
location of space–time.
Charge–anticharge
particles created earlier
(early stage
hadronization) get further
separated in rapidity.
Particle pairs that were
created later (late stage
hadronization) are
correlated at small Δy.
The Balance Function
quantifies the degree of
this separation and relates
it with the time of
hadronization.
Supriya Das
Early Hadronization
 Large d
Late Hadronization
 Small d
1 N (Dy)  N (Dy) N (Dy)  N (Dy) 
B(Dy)   


2 
N
N

Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
18
Balance function
Inclusive charged pairs
Identified pions
 Width of balance function is narrower
for more central collision.
 HIJING matches with data only for
peripheral collisions.
Au+Au @ 130 GeV
PRL 90 (2003) 172301
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
19
Balance function
(mass dependence)
s
2T
m
Heavier particles are characterized
by narrower bf distributions:
Dy
Dy
pions
 1.3-1.4
1.31
kaons
• The balance function width for pions
get narrower with increasing centrality,
remains constant for kaons.
• HIJING reproduces results for kaons,
but not for pions.
• The ratio of widths of pions to kaons is
consistent with delayed hadronization
picture.
Gary Westfall, J.Phys.G30, S345-S349 (2004)
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
20
Long-range multiplicity correlations
 Study of correlations among
particles produced in different rapidity
regions.
 The long-range correlations are
expected to be much stronger in p-A
and A-A, compared to p-p at the same
energy.
Correlation strength:
b
 N f N b    N f  N b 
 N    Nf 
2
f
2

Dbf2
D 2ff
•
STAR: forward region of 0.8<<1.0
& backward of -1.0<<-0.8.
•
Increase in correlation strength
observed for central collisions
compared to peripheral for Au+Au
collisions at 200GeV.
Supriya Das
Terence J Tarnowsky
Nuclear Dynamics, San Diego March 2006
nucl-ex/0606018
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
21
Long-range multiplicity correlations
nucl-ex/0606018
For central collision, long range correlation is less than PSM calculation
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
22
Strangeness fluctuation
(motivation)
S. Afanasiev for NA49 PRL 86 (2001)
 Dynamical fluctuation is positive
Supriya Das
C. Roland QM 2004
 Amount of fluctuation
decreases with increase in
collision energy.
 Data disagree with UrQMD model
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
23
Strangeness fluctuation : K/p distribution
[ Data not corrected for efficiency]
S. D. : SQM’06 Symposium
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
24
Strangeness fluctuation
(energy and centrality dependence)
srms/mean
sdyn = sqrt(sdata2 – smixed2)
 dyn,K p 
N K (N K  1)
NK
2

Np (Np  1)
Np
2
2
N K Np
NK
Np
S. D. : SQM’06 Symposium
Fluctuation in K/p decreases with increasing energy till the top SPS energy
and remains flat above it. The amount of fluctuation decreases with increasing
centrality and is similar for 62GeV as well as 200GeV AuAu collisions.
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
25
Summary
 STAR has the capability to study the event by event fluctuation for many
different observables.
 Mean pt fluctuation results show non-zero fluctuation which scales with centrality.
 Mean pt analysis in finer (,f) subspace shows interesting structures which could be
attributed to production of minijets.
 Net charge fluctuation is greater than predicted value from charge conservation
conjecture but closer to resonance gas picture.
 Dynamical net charge fluctuation is essentially flat for energies more that top SPS.
 Results from higher moments of net charge are promising, but needs more work.
 Balance function results support delayed hadronization picture.
 Long range multiplicity correlation reduces (compared to model calculation)
in central collisions.
 Event by event fluctuation in K/pratio is positive and centrality dependent but
show no dependence on collision energy at RHIC.
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
26
Outlook
STAR has a shining future in the proposed low energy scan at RHIC
With wider momentum range and K, p separation, it will play a key
role in strangeness fluctuation study
STAR will also give more insights in the energy dependence of
Balance function at lower energies
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
27
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
28
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
29
Dpt , iDpt , j 
1
Nevent
Nk Nk
Ck  
(p
t, i
Nevent

k 1
Ck
Nk ( Nk  1)
  pt )( pt , j   pt )
i 1 j 1,i  j
 Nevent
 pt    pt
 k 1

 Nk

pt k    pt , i 
 i 1



Supriya Das


k


Nevent
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
30
Supriya Das
Correlation and Fluctuation in Relativistic Nuclear Collisions - Florence, July 2006
31