Photon Multiplicity RHIC CuCu 200 GeV

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Photon Multiplicity _at_ RHIC CuCu 200 GeV

• Monika Sharma
• Sunil Dogra
• Surjeet Singh
• Neeraj Gupta

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Outline of the presentation

• STAR experiment
• Photon Multiplicity Detector
• Recent results from charge particles
• Comparison of STAR-PMD results from AuAu 62.4 GeV
  CuCu 200 GeV
• Outlook summary

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The STAR experiment

• The STAR (Solenoidal
• tracker At RHIC)
• experiment at
• Relativistic Heavy
• Ion Collider (RHIC) is
• designed to search
• for different signals of QGP formation.

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The Photon Multiplicity Detector

• Preshower detector with fine granularity
• Two planes Veto Pre
• - shower.
• ? coverage -2.3 - 3.9
• Total no. of cells 82,944
• Distance from vertex 540 cm
• Cell cross section 1.0cm2, depth 0.8cm
• Readout GASSIPLEX C-RAMS

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• Area of the detector 4.2m2
• Weight of the detector 900 kg
• F coverage 2p
• Detector design criteria
• Confine charged particle hits to
• single cell.
• Reduce cross-talk stop d-rays
• with in a cell.
• Uses a gas mixture of 70Ar30CO2.

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Detector
Principle of Preshower

• Photons passing through the
• converter initiate an
• electromagnetic shower
• produce large signals on
• several cells of the
• sensitive volume of the
• detector. Hadrons normally
• affect only one cell
• produce a signal
• representing minimum ionizing particles.

? CLUSTER
ISOLATED CH PARTICLE HIT
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Techniques of PMD data analysis

• ADC distribution of isolated cells is studied to
  calculate the gain of each cell.
• Gain is normalized to ensure uniformity over the
  entire detector.
• Photon counting efficiency purity in photon
  samples are calculated from simulation
  (HIJINGGEANT).
• Photon discriminating threshold 3MIP NCellgt 1 is
  now applied to identify photons.
• Geometrical acceptance correction factors are
  applied to the data to correct for any dead
  region of the detector.

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Results for STAR-PMD dataRun V CuCu 200 GeV
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Centrality Selection is STAR
275K events were used in the presnt analysis
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Pseudorapidity Distribution of photons (CuCu 200
GeV)
STAR preliminary
Upper limit on systematic Error 24
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Comparison of results from PHOBOS (Charge
Particles)
Charge particle production at forward rapidities
are independent of system size
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Previous STAR-PMD results

• Reference PRL 95, 062301 (2005)
• First results of photon multiplicity measurement
  were shown.
• Photons are observed to follow a centrality
  independent limiting
• fragmentation scenario.
• Photons and pions
• follow an energy
• independent limiting
• fragmentation behaviour.

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Pseudorapidity distribution per participant pair

STAR preliminary
STAR preliminary
Pseudorapidity distribution per participant pair
is independent of centrality. Results agree with
previous STAR-PMD Photon 62.4 GeV results!!!
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Limiting Fragmentation

• Number of particles produced per participant
  pairs as a function of
• ?-ybeam is independent of beam energy.
• Why limiting fragmentation?
• At higher energies target fragments seen in lab
  frame reach a limit in momentum space.

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Particle production at forward rapidities is
independent of centrality as well as system size
STAR preliminary
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Photons and pions follow an energy independent
limiting fragmentation behaviour
STAR preliminary
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Summary Outlook

• Results of photon multiplicity measurements at
  RHIC in the pseudorapidity region 2.3 lt ? lt 3.7
  are shown.
• Photon production per participant pair is found
  to be approximately independent of centrality in
  this eta region.
• The comparison of AuAu and CuCu most central
  collisions indicate that the pseudorapidity
  density per participant pair does not depend on
  the size of the two colliding nuclei.