Transcript Long-Range Multiplicity Correlations in Relativistic Heavy

Correlations and Fluctuations from
the STAR Experiment
Terence J Tarnowsky
for the STAR Collaboration
January 6, 2010
Winter Workshop on Nuclear Dynamics
2010
Ocho Rios, Jamaica
Motivation Behind Correlations and
Fluctuations
• Many theoretical predictions that behavior of correlations
and fluctuations in a deconfined phase different than that in
hadron gas.
• Justification from experimental studies of the
thermodynamics of phase transitions.
• Even w/o such guidance, can search for discontinuities in
fluctuations and correlations as functions of incident
energy and centrality (not an inclusive list):
–
–
–
–
–
T. Tarnowsky
Particle ratio fluctuations (K/p, p/p, K/p).
Forward-Backward multiplicity correlations.
Balance Functions
Net Charge Fluctuations
Net-proton kurtosis, <pT> flucuations, Dh-Dj correlations, etc.
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STAR Detector
• STAR is a large acceptance
detector.
– Good h and j coverage for
measuring fluctuations.
• |h| < 1.0
• PID:
– p, K, p ID for pT < 1 GeV.
• ToF upgrade will enhance PID
capabilities.
STAR Preliminary
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F-B Multiplicity Correlations
• Predicted in context of Dual Parton Model [DPM] (and
Color Glass Condensate [CGC]).
• Test of multiple elementary [partonic] scattering.
• Linear expression relating Nb and Nf (forward and
backward multiplicity), found in hadron-hadron
experiments (ex. UA5),
N = # of hadrons
 N  ( N )  a  bN
b
f
f
• “b” is correlation strength.
– Function of √s and A.
– Coefficient can be
expressed as,
b
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 N f N b  -  N f  N b 
 N  -  Nf 
2
f
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
Dbf2
D 2ff
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Strings
Low Energy

 1 


h  - ln  tan  
2

Long Range
Long Range
Backward nb
High
- η2 - η 1
0
Pseudorapidity
Gap
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Pseudorapidity interval
Forward nf
Energy
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η1
η2
η
Probes longitudinal
characteristics of the
5
system.
F-B Correlations
•
Central 200 GeV
Au+Au collisions
show a strong longrange correlation.
•
Most peripheral
Au+Au have
negligible LRC, as
does pp.
•
HIJING and Parton
String Model (PSM)
do not agree w/
Au+Au data.
•
Multiparton
interaction in central
Au+Au collisions.
•
See talk by M.
Skoby.
T. Tarnowsky
Phys.Rev.Lett.103:172301,2009
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Characterize Fluctuations
• NA49 uses the variable dyn
2
2
2
2
 dyn  sign  data
-  mixed
-  mixed
  data
 is relative width of K / p distribution
• Measure deviation from Poisson behavior using dyn
 dyn,Kp 
N K N K - 1
NK
2

Np Np - 1
Np
2
N K Np
-2
N K Np
• It has been demonstrated (for K/p and p/p) that,
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dyn
dyn 
dyn
dyn
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Excitation Function for σdyn,K/π
STAR central Au+Au (0-5%) collisions with SPS central Pb+Pb
collisions (0-3.5%).
Phys.Rev.Lett.103:092301,2009
• Large decrease in
fluctuations as
function of energy
from NA49.
• Fluctuations
measured by STAR
approximately
constant as function of
energy from 19.6-200
GeV.
• p : 0.2 < pT < 0.6
GeV/c
•K: 0.2 < pT < 0.6
GeV/c
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Scaling w/ dN/dh in Au+Au
Phys.Rev.Lett.103:092301,2009
• Charge
dependent and
independent
dyn,K/p was
found to scale
linearly with
dN/dh (at small
dn/dh) in
Au+Au at 200
and 62.4 GeV
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Excitation Function for σdyn,pπ
• Solid points are
data from STAR
or NA49.
• Open black
points are HSD
prediction from
Konchakovski, et.
al.
arXiv:0906.3229.
• Open red points
are UrQMD run
locally with
STAR
acceptance.
dyn,p/p, STAR and NA49
• dyn,p/p displays
strong system
size dependence
for small dN/dh.
• Fit is to STAR
Cu+Cu 22.4
GeV data only.
• Interpretation
still under study.
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Excitation Function for σdyn,Kp
HSD points from arXiv:0906.3229
NA49 data from CPOD 2009 talk by T. Schuster
• dyn,K/p for central
Cu+Cu 22.4 GeV is
strongly negative.
-General agreement w/
NA49 at 17.3 GeV.
-Does not show large
increase seen in model
predictions.
• dyn,K/p for central
Au+Au 200 and 62.4
GeV are also negative.
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Balance Function
• Prediction that delayed hadronization will cause width of
longitudinal charge balance function to be narrower in
central vs. peripheral collisions.
• Definition:
1  D - - D  D - - D -- 
B 


2
N
N
– Dij is number of charged particles pairs in a (pseudo)rapidity
range.
– Calculated by taking ith particle and incrementing a histogram of
Dh wrt all jth particles in that event.
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Balance Function
•
•
•
•
Width in 200 GeV Au+Au data narrows with increasing collision centrality.
Shuffled events and Hijing and URQMD show no centrality dependence.
Width from pp collisions agrees w/ most peripheral Au+Au bin.
Results consistent with narrowing of the balance function in most central Au+Au collisions.
STAR Preliminary
STAR Preliminary
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Net Charge Fluctuations
• Predictions that net charge fluctuations due to
QGP << Hadron Gas.
• Measured using,
  - ,dyn 
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N   N  - 1
N
2

N -  N - - 1
N-
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2
-2
N- N
N- N
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Net Charge Fluctuations
•
•
•
Large differences between pp, Cu+Cu, and Au+Au. Slope depends on correlation length
in h. Larger slope = shorter correlation length. Agrees w/ balance function results.
Larger slope indicate correlated pairs of -/+ particles emitted closer in rapidity than
those in peripheral Au+Au or pp collisions.
Could be related to narrowing of balance function, or radial flow.
Phys. Rev. C 79 (2009) 24906
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Search for the QCD Critical Point
•Proposal for future running at RHIC to
consist of an “energy scan” to search for
predicted QCD critical point.
•Fluctuations and correlations (particle ratios,
multiplicity, pT, etc.) and behavior of flow
(directed and elliptic) in vicinity of the
critical point are expected to be primary
signatures.
•STAR has the capability to measure
correlations and fluctuations at all energies.
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Search for the QCD Critical Point II
• In a phase transition near a
critical point, an increase in
non-statistical fluctuations is
expected.
• Finite system-size effects may
influence fluctuation
measurements.
• Finite-size scaling of
fluctuations may indicate
existence of critical point.
• E.g. Change in behavior of
quark susceptibilities.
Aoki, Endrodi, Fodor, Katz, and
Szabó Nature 443, 675-678 (2006)
• These may manifest in finalstate measurements.
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Critical Fluctuations
• An example of critical fluctuations:
• Mixture of cyclohexane (C6H12) and aniline
(C6H7N).
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2008 Test at √sNN =9.2 GeV
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STAR
• The STAR detector is in a prime configuration for
measuring fluctuations and correlations:
– Full ToF is installed. Will provide enhanced PID
capabilities.
– Low material budget between beam pipe and TPC.
– DAQ 1000 installed as of Run 9. Not rate limited by
DAQ at higher energies of BES.
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WWND 2010, Jamaica
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Summary
• The STAR experiment has results on fluctuations and correlations for
several colliding systems and energies that have provided new insights
into particle production.
– K/p fluctuations approximately constant at RHIC energies.
– First measurement of long-range forward-backward multiplicity correlations
provides information on multiparton interactions.
– Narrowing of balance function coincides with shorter correlation lengths as
measured from net charge fluctuations.
• The RHIC Beam Energy Scan (BES) program will probe new areas of
the QCD phase diagram while revisiting energies studied at fixed
target experiments using a mature collider and well understood
detector setup.
– Provide a comprehensive picture of the T-mB phase space at the same facility.
• The STAR experiment is fully prepared to capitalize on collisions at all
energies during the RHIC BES.
• STAR will continue to produce new results in the future from higher
statistics data sets w/ the Time-of-Flight upgrade.
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