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This paper presents experimental results on fluctuations and correlations as signatures of QCD phase transitions in heavy-ion collisions. Various variables such as K/π fluctuations, balance function, net charge fluctuations, and multiplicity fluctuations are studied at different incident energies. The results provide insights into the QCD critical point and the energy dependence of the system.
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Experimental Results for Fluctuations And Correlations as a Signature of QCD Phase Transitions in Heavy Ion Collisions Gary Westfall Michigan State University, USA Gary Westfall, Quark Matter 2008
Correlations and Fluctuations • Depend on previous talk for theoretical justification • Look for discontinuities or changes in experimental results for correlations and fluctuations as a function of incident energy • K/π Fluctuations • Balance Function • Net Charge Fluctuations • Multiplicity Fluctuations - several approaches • pt Correlations • RHIC Energy Scan • SPS Program 2 Gary Westfall, Quark Matter 2008
See talk by M. Rybczynski, Session X K/π Fluctuations NA49 Preliminary See talk by Z. Ahammed in Session X Gary Westfall, Quark Matter 2008
K/π Fluctuations Torrieri QM06 See talk by Z. Ahammed in Session X Gary Westfall, Quark Matter 2008
K/π FluctuationsScaling with dN/dη Au+Au statistical errors Cu+Cu statistical+systematic errors See talk by Z. Ahammed in Session X Gary Westfall, Quark Matter 2008
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) Gary Westfall, Quark Matter 2008
Balance Function NA49 Phys. Rev. C 76, 024914 2007 Balance functions for Pb+Pb at sNN½ = 6.3 to 17.3 GeV Data Shuffled STAR, QM 02, QM 04 Balance functions for Au+Au at sNN½ = 20 to 200 GeV Au+Au 200 GeV Gary Westfall, Quark Matter 2008
Balance Function NA49 Phys. Rev. C 76, 024914 2007 NA49 Large W means narrow balance function Gary Westfall, Quark Matter 2008
Net Charge Fluctuations at RHIC See poster by M. Sharma Gary Westfall, Quark Matter 2008
Net Charge Fluctuations at RHIC The slope in p+p, Cu+Cu and Au+Au 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 10 Gary Westfall, Quark Matter 2008
Net Charge Fluctuations at the SPS NA49 PRC 70, 064903 (2004) Gary Westfall, Quark Matter 2008
Multiplicity Fluctuations at the SPS NA49, 0712.321 [nucl-ex] 2007 1% most central Scaled to 4π Gary Westfall, Quark Matter 2008
Multiplicity Fluctuations at RHIC PHENIX, PRC 76, 034903 (2007) 13 Gary Westfall, Quark Matter 2008
Multiplicity Fluctuations at RHIC PHENIX, PRC 76, 034903 (2007) See talk by K. Homma in Session X 14 Gary Westfall, Quark Matter 2008
Forward/Backward Multiplicity Correlations See talk by B. Srivistava Session XIX See poster 220 by T. Tarnowsky Gary Westfall, Quark Matter 2008
Energy Dependence of F/B Multiplicity Fluctuations Central Au+Au 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 220 by T. Tarnowsky Gary Westfall, Quark Matter 2008
pt Fluctuations Adamova et al., CERES Miskowiec for NA49, CPOD 2007 Gary Westfall, Quark Matter 2008
pt Fluctuations Calculate <Δpt,i,Δpt,j> for pairs within a given range of Δϕ and multiply by dN/dη The region of 30° < Δϕ < 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 Gary Westfall, Quark Matter 2008
RHIC Energy Scan Energies as low as sNN1/2 = 4.5 GeV (10 AGeV fixed target) T. Satogota, RHIC 19 Gary Westfall, Quark Matter 2008
NA 49/61 Future Program M. Gazdzicki Gary Westfall, Quark Matter 2008
Proposed Energy and Mass Scans Gary Westfall, Quark Matter 2008
Addition of TOF to STAR • STAR will add TOF for Run 10 • The TOF will provide excellent particle identification for π, K, and p for a large fraction of the measured particles event-by-event • Improved K/π fluctuation measurements • Improved balance functions with identified π, K, and p • See talk by G. Odyniec, session XXIV P. Sorensen Charged pions and kaons 0.2 < pt < 0.6 GeV/c Gary Westfall, Quark Matter 2008
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 Gary Westfall, Quark Matter 2008
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 Gary Westfall, Quark Matter 2008
Extra Slides Gary Westfall, Quark Matter 2008
Balance Function with Identified Pions • The excellent particle identification for π, 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 < pt < 0.6 GeV/c Gary Westfall, Quark Matter 2008
Relation between Net Charge Fluctuations and the Balance Function Jeon and Pratt PRC 65, 044902 (2002) Gary Westfall, Quark Matter 2008
HBT Gary Westfall, Quark Matter 2008
HBT Gary Westfall, Quark Matter 2008
