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Photon Multiplicity @ RHIC CuCu 200 GeV

Photon Multiplicity @ RHIC CuCu 200 GeV. Monika Sharma Sunil Dogra Surjeet Singh Neeraj Gupta. 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

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Photon Multiplicity @ RHIC CuCu 200 GeV

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  1. Photon Multiplicity @ RHIC CuCu 200 GeV Monika Sharma Sunil Dogra Surjeet Singh Neeraj Gupta

  2. 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 Monika Sharma, QGP workshop, 5-7 Jan 2006

  3. 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. Monika Sharma, QGP workshop, 5-7 Jan 2006

  4. The Photon Multiplicity Detector Preshower detector with fine granularity Two planes : Veto +Pre - shower. η 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 Monika Sharma, QGP workshop, 5-7 Jan 2006

  5. Area of the detector : 4.2m2 Weight of the detector : 900 kg Φ coverage : 2π Detector design criteria : Confine charged particle hits to single cell. Reduce cross-talk : stop δ-rays with in a cell. Uses a gas mixture of 70%Ar+30%CO2. Monika Sharma, QGP workshop, 5-7 Jan 2006

  6. 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. Detector γCLUSTER Monika Sharma, QGP workshop, 5-7 Jan 2006 ISOLATED CH PARTICLE HIT

  7. 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 (HIJING+GEANT). • Photon discriminating threshold 3MIP &NCell> 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. Monika Sharma, QGP workshop, 5-7 Jan 2006

  8. Results for STAR-PMD dataRun V CuCu 200 GeV Monika Sharma, QGP workshop, 5-7 Jan 2006

  9. Centrality Selection is STAR 275K events were used in the presnt analysis Monika Sharma, QGP workshop, 5-7 Jan 2006

  10. Pseudorapidity Distribution of photons (CuCu 200 GeV) STAR preliminary Upper limit on systematic Error ~ 24% Monika Sharma, QGP workshop, 5-7 Jan 2006

  11. Comparison of results from PHOBOS (Charge Particles) Charge particle production at forward rapidities are independent of system size Monika Sharma, QGP workshop, 5-7 Jan 2006

  12. 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. Previous STAR-PMD results : Monika Sharma, QGP workshop, 5-7 Jan 2006

  13. 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!!! Monika Sharma, QGP workshop, 5-7 Jan 2006

  14. Limiting Fragmentation • Number of particles produced per participant pairs as a function of ή-ybeam is independent of beam energy. • Why limiting fragmentation? • At higher energies target fragments seen in lab frame reach a limit in momentum space. Monika Sharma, QGP workshop, 5-7 Jan 2006

  15. Particle production at forward rapidities is independent of centrality as well as system size STAR preliminary Monika Sharma, QGP workshop, 5-7 Jan 2006

  16. Photons and pions follow an energy independent limiting fragmentation behaviour STAR preliminary Monika Sharma, QGP workshop, 5-7 Jan 2006

  17. Summary & Outlook • Results of photon multiplicity measurements at RHIC in the pseudorapidity region 2.3 <= ή <= 3.7 are shown. • Photon production per participant pair is found to be approximately independent of centrality in this eta region. • The comparison of Au+Au and Cu+Cu most central collisions indicate that the pseudorapidity density per participant pair does not depend on the size of the two colliding nuclei. Monika Sharma, QGP workshop, 5-7 Jan 2006

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