PHOTON

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PHOTON
MULTIPLICITY
DETECTOR FOR THE
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EXPERIMENT
_at_ RHIC
COLLISIONS
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(WA98
COLLABORATION)
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EVENT-by-EVENT PHYSICS

• Motivation
• Critical fluctuation at the phase boundary
• Tricritical point of QCD phase transition
• Disoriented Chiral condensates (DCC)
• Understanding thermalization

• Analysis using
• Multiplicities of charged particles, photons
• Particle ratios
• Transverse energy, transverse momentum
• HBT correlations (Rinv, R.)
• .

• Control parameters
• Centrality
• Acceptance
• Different colliding systems at different
  energies

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• First results of localized charged-neutral
  fluctuations in heavy-ion experiments.
• Using a subset of detectors in the WA98
  experiment
• Photon Multiplicity Detector (PMD)
• Silicon Pad Multiplicity Detector (SPMD)
• Analysis tool
• Discrete Wavelet Transformation (DWT)
• Ng Nch Correlation

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CHARGED-NEUTRAL FLUCTUATIONS
DISORIENTED CHIRAL CONDENSATES
Formation of DCC gives rise to a pulse of low pT
pions with a probability P(f) 1/(2
sqrt( f )) where f is the neutral pion
fraction

• Domain of DCC
• occupies a part in phase space
• contains pions with above probability

Large fluctuations in number of photons and
charged particles
Bose-Einstein correlations, resonance decays and
.
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(No Transcript)
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WA98 _at_ SPS
PMD
SPMD
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Data, Mixed events and simulation
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SINGLE EVENT DISPLAY of photons and charged
particles

• To study localized fluctuations we use
• Discrete wavelet method (DWT)
• Correlation method

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MIXED EVENTS

• Remove various correlations in a controlled
  manner
• Preserving the characteristics of the
  measured distributions.
• N g-like and Nch correlations are
  maintained.
• Constructed from real events.
• Also constructed from simulated events to
  understand their behavior.

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A SIMPLE DCC MODEL

• 1. Start with VENUS event generator.
• 2. Assume a single domain DCC in a
  selected h-f zone. Within the zone the charge of
  the pions is interchanged pair-wise
• pp- p0p0
• as per DCC probability distribution.
• 3. The neutral pions decay to photons.
  Full GEANT simulation.

Analysis using DWT method where FFC (father
function coefficients) are extracted. These
distributions are gaussian-like. We study rms
deviations of the FFC (and Sz) distributions
nDCC events is a combination of VG events with
DCC events where the Fraction of DCC events
depends on DCC Probability.
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UNDERSTANDING MIXED EVENTS FROM nDCC events
For VG (no DCC) rms values are lower than
those of the mixed events.
Root-mean-square (rms) deviations increase
strongly by increasing the probability of DCC
events.
M1 independent of DCC probability
M2 increase with DCC probability
M3-g and M3-ch lie between M1 and M2
sets.
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CORRELATION ANALYSIS
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CORRELATION ANALYSISSZ Distributions

• Ng-like - Nch correlation for each f bin
• A polynomial of 2nd order fitted
• Minimum distance (DZ) between data points and the
  line (Z) obtained.
• SZ DZ / rms(DZ of VG)

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DISCRETE WAVELET TRANSFORMATION FFC DISTRIBUTIONS

• 1-d analysis using D4 basis
• binning in f
• Starting at highest resolution
• scale, jmax 5 (32 bins)
• Input sample function is the
• photon fraction
• f Ng-like/(Ng-like Nch)
• Output is a set of FFCs
• 1-D analysis using D4 basis
• FFCs carry information
• about fluctuation

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LOCALIZED FLUCTUATIONS
Comparison of data, M1 and simulation

• Presence of
• localized fluctuations.
• Possibilities in
• Ng
• Nch
• These two may be correlated

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CORRELATED FLUCTUATIONS
Comparison of data and M2

• Mix one PMD event with another
• SPMD event.
• Hit structures are unaltered
• Ng Nch correlation maintained

Absence of E-by-E Correlated Fluctuations
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INDIVIDUAL FLUCTUATIONS
Comparison of data and M3-ch and M3-g
M3-ch hits in PMD mixed and hits
in SPMD unaltered M3-g hits in SPMD mixed and
hits in PMD unaltered. Ng-Nch
correlations are maintained.

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