Experimental Results for Fluctuations And Correlations as a Signature of QCD Phase Transitions in Heavy Ion Collisions

1
Experimental Results for Fluctuations And
Correlations as a Signature of QCD Phase
Transitions in Heavy Ion Collisions

• Gary Westfall
• Michigan State University, USA

2
Correlations and Fluctuations

• Depend on previous talk for theoretical
  justification
• Search for discontinuities or changes in
  experimental results for correlations and
  fluctuations as a function of incident energy
• K/p Fluctuations
• Balance Function
• Net Charge Fluctuations
• Multiplicity Fluctuations
• pt Correlations
• RHIC Energy Scan
• SPS Program

2
Gary Westfall, Quark Matter 2008
3
Plan

• Present a sample of current experimental results
• Not a complete survey
• Will refer you to other talks at QM2008
• Make suggestions for measurements that could be
  done as a function of incident energy
• Outline current plans for SPS and RHIC to study
  the incident energies of interest to the QCD
  critical point

4
K/p Fluctuations
See talk by M. Rybczynski, Session X
NA49 Preliminary
See talk by Z. Ahammed in Session X
5
K/p Fluctuations
Torrieri QM06
See talk by Z. Ahammed in Session X
6
K/p FluctuationsScaling with dN/d?
AuAu statistical errors CuCu statisticalsystema
tic errors
See talk by Z. Ahammed in Session X
7
Balance Function

• Charge fluctuations can be studied with several
  different variables that can be expressed in
  terms of each other
• We choose to illustrate charge fluctuations using
  the balance function

Bass, Danielewicz, Pratt PRL 85 2689 (2000)
8
Balance Function
NA49 Phys. Rev. C 76, 024914 2007
Balance functions for PbPb at sNN½ 6.3 to 17.3
GeV
Data
Shuffled
STAR, QM 02, QM 04
Balance functions for AuAu at sNN½ 20 to 200
GeV
AuAu 200 GeV
9
Balance Function
NA49 Phys. Rev. C 76, 024914 2007
NA49
Large W means narrow balance function
10
Net Charge Fluctuations at RHIC
See poster by M. Sharma
11
Net Charge Fluctuations at RHIC
The slope in pp, CuCu and AuAu depends on the
correlation length the shorter the correlation,
the larger the slope The distributions indicate
that the correlation length is shorter for
central collisions and for larger systems, in
agreement with the observed reduction of the
width of the balance function
See poster by M. Sharma
11
Gary Westfall, Quark Matter 2008
12
Net Charge Fluctuations at the SPS
NA49 PRC 70, 064903 (2004)
13
Multiplicity Fluctuations
NA49, 0712.321 nucl-ex 2007
1 most central Scaled to 4p
14
pt Fluctuations
Adamova et al., CERES Miskowiec for NA49, CPOD
2007
15
pt Fluctuations
Calculate lt?pt,i,?pt,jgt for pairs within a given
range of ?? and multiply by dN/d?
The region of 30 lt ?? lt 60 is free from effect
such as HBT and jets and may be a fruitful region
to search for discontinuities as a function of
incident energy
Adamova et al., CERES
16
Forward/Backward Multiplicity Correlations
See talk by B. Srivistava Session XIX See poster
176 by T. Tarnowsky
17
Energy Dependence of F/B Multiplicity Fluctuations
Central AuAu 0 10
Long range correlations are an indicator of
multiple elementary elastic collisions
200 GeV
62.4 GeV
Long range correlations decreases as the incident
energy is decreased
STAR preliminary
See talk by B. Srivistava Session XIX See poster
176 by T. Tarnowsky
18
NA 49/61 Future Program
M. Gazdzicki
19
Proposed Energy and Mass Scans
20
Addition of TOF to STAR

• STAR will add TOF for Run 10
• The TOF will provide excellent particle
  identification for p, K, and p for a large
  fraction of the measured particles event-by-event
• Improved K/p fluctuation measurements
• Improved balance functions with identified p, K,
  and p
• See talk by G. Odyniec, session XXIV

P. Sorensen
Charged pions and kaons 0.2 lt pt lt 0.6 GeV/c
21
Balance Function with Identified Pions

• The excellent particle identification for p, K,
  and p for a large fraction of the measured
  particles event-by-event will allow new kinds of
  event-by-event measurements such as the balance
  function with identified particles

Charged pion pairs 0.2 lt pt lt 0.6 GeV/c
22
Conclusions 1

• We have experimental results for correlations and
  fluctuations covering incident energies where one
  might expect effects from the QCD critical point
  and we have some hints in the
• However, the results are not conclusive
• In particular, we have several different
  variables, acceptances, and interpretations that
  need to be unified
• We need to measure correlation fluctuation
  variables over the broadest range in incident
  energy and system size

23
Conclusions 2

• The SPS and RHIC scans will provide an excellent
  opportunity to study the QCD critical point
• SPS system/energy scan will add a large number of
  points in T/µB space in the search for the
  critical point
• We also look forward to correlations and
  fluctuations related to the QCD phase transition
  at GSI/FAIR

24
Extra Slides
25
Relation between Net Charge Fluctuations and the
Balance Function
Jeon and Pratt PRC 65, 044902 (2002)
26
HBT
27
HBT