PARTICLE DENSITY FLUCTUATIONS

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PARTICLE DENSITY FLUCTUATIONS
Bedanga Mohanty Variable Energy Cyclotron Centre,
Calcutta (for the WA98 Collaboration)

• OUTLINE
• Motivation
• Ng and Nch multiplicity fluctuation
• Ng vs. Nch fluctuation
• Summary

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RELATIVISTIC HEAVY-ION COLLISIONS

• QCD transitions
• Deconfinement
• Chiral symmetry restoration

At Tricritical point Large e-by-e
fluctuations in observables
NPA 663 (2000)183 Peter Braun-Munzinger
PRL 81 (1998) 4816 Stephanov et al.
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EVENT-BY-EVENT FLUCTUATIONS
Thermodynamic properties of matter Total
heat capacity
PRL 75 (1995) 1044 L. Stodolsky
PLB 430 (1998) 9 S. Mrowczynski
Compressibility
Study of thermodynamical quantities (or
fluctuations in experimental observables) can
shed light on possible existence of phase
transition and its nature
At tricritical point singularities in
thermodynamical observables large e-by-e
fluctuations in Expt. Obs.
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CHIRAL SYMMETRY RESTORATION

• Through search for disoriented
• chiral condensates
• Study and detection of DCC
• Nature of chiral phase transition
• Vacuum structure of strong interaction

Look at Ng vs. Nch fluctuations
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FLUCTUATIONS IN HEAVY-ION COLLISIONS

• Large number of particles in single event
• Large acceptance detectors
• Near Gaussian distributions
• Fluctuation studied by width

SPS -gt RHIC -gt LHC
WA98
WA98
WA98
NA49
PRC 65 (2002) 054912 WA98 Collaboration
PLB 459 (1999) 679 NA49 Collaboration
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MEASURES OF FLUCTUATIONS
Measure Proposed by Reference
s2/mean Ratios Baym, Heiselberg Jeon, Koch PLB 469 (1999) 7 Phys. Rep. 351 (2001) 161 PRL 83 (1999) 5435
Correlator Stephanov, Rajagopal, Shuryak PRD 60 (1999) 114028
Fluctuation in conserved Quantities Jeon,Koch Asakawa,Heinz,Muller PRL 85 (2000) 2076 PRL 85 (2000) 2076
Balance Functions Bass, Danielewicz,Pratt PRL 85 (2000) 2689
fpT Gazdzicki, Mrowczynski Z. Phys. C54 (1992) 127
ndyn Pruneau, Gavin ,Voloshin nucl-ex/0204011
Space-time evolution of fluctuations are
important!
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FLUCTUATION STUDY IN
SPMD 2.35 lt h lt 3.75
PMD 2.9 lt h lt 4.2

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CERN SPS 158A GeV PbPb
Charged Particles
Ch. particles vs. Photons
Photons
Single event display
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MULTIPLICITY FLUCTUATIONS
Ng and Nch fluctuations are studied by looking at
the simple variable

• Centrality and pseudo-rapidity acceptance
  dependence

• Compare to participant model and VENUS

Participant model
N Particle Multiplicity Npart No. of
participants ni No of particles produced
by ith participant, accepted within
the acceptance of detector
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CENTRALITY SELECTION
Fluctuations in number of participants increases
with increasing cs but for 2 cs bins 1
Fluctuations should be calculated for narrow bins
in centrality ( 2 cs bins ) such that
fluctuations in number of participants are
Poisson-like
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CENTRALITY DEPENDENCE OF MULTIPLICITY FLUCTUATIONS
Data agree fairly well with model calculations
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PSEUDO-RAPIDITY ACCEPTANCE DEPENDENCE OF
MULTIPLICITY FLUCTUATIONS
Data agree fairly well with model calculations
based on binomial sampling
Int. J. Mod. Phys. A 17 (2002) 675
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Ng vs. Nch FLUCTUATIONS

• Top 5 central events ONLY
• Bins in f 1,2, 4, 8, 16
• Discrete Wavelet Analysis
• Correlation Analysis

Results from data compared to mixed events and
simulation
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MIXED EVENTS
Mixed events help in filtering out different
contributions to fluctuations
Type PMD - g SPMD - ch Behavior
M1 Mix hits Mix hits Does not preserve correlated or individual fluctuations.
M2 Unaltered hits Event mixing Unaltered hits Event mixing Does not preserve the correlated physics fluctuation.
M3-g Unaltered hits Mix hits Fluctuations due to photons are preserved.
M3-ch Mix hits Unaltered hits Fluctuations due to charged particles preserved.
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COMPARISON OF RMS WIDTH OF DATA, M1-MIXED EVENTS
AND SIMULATION
Mix hits in PMD and SPMD separately Maintain
global correlation
Data widths larger than M1-mixed

• Presence of
• localized fluctuations.
• Possibilities in
• Ng
• Nch
• Correlated fluctuation

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CORRELATED FLUCTUATIONS ? DATA AND M2-MIXED
EVENTS
Mix one event of PMD with Another event of
SPMD Hits unaltered in an event Ng Nch
correlation maintained
Data matches with M2-mixed
Absence of Correlated fluctuations.
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DO BOTH Ng and Nch CONTRIBUTE ? DATA AND
M3-MIXED EVENTS
Mix hits in one detector only Hits unaltered in
other detector This case is in between M1 and
M2 Maintain global correlation
M3-mixed between Data M1.

• Presence of individual
• Fluctuations in both
• Ng
• Nch

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CENTRALITY DEPENDENCE OF LOCALIZED CHARGE-NEUTRAL
FLUCTUATIONS
Total localized fluctuations in photon and
charged particle decreases with decrease in
centrality
Not detectable
Ref nucl-ex/0206017
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UPPER LIMIT ON DCC PRODUCTION AT SPS
Based on a simple model of DCC
Differences between data and M2 (event mixing)
assumed solely due to DCC
Ref nucl-ex/0206017
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SUMMARY

• Systematic study of centrality dependence of
  multiplicity fluctuations of photons and charged
  particles for the full acceptance of the
  detectors do not show any evidence of
  significant non-statistical contribution

Ref PRC 65 (2002) 054912

• A model independent analysis using mixed events
  indicates non-statistical localized fluctuations
  in data for limited regions of azimuthal angle

• No e-by-e correlated fluctuations (DCC-type)
  observed in photons and charged particles

• Upper limit on DCC production at SPS set at 90
  C.L.

Ref PRC 64 (2001) 011901 (R)
Ref nucl-ex/0206017