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Thermal Photon Measurement using the HBD in PHENIX :Status and Update

Thermal Photon Measurement using the HBD in PHENIX :Status and Update. Sky Rolnick UC Riverside APS April Meeting 2011. Thermal Photon Motivation.

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Thermal Photon Measurement using the HBD in PHENIX :Status and Update

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  1. Thermal Photon Measurement using the HBD in PHENIX :Status and Update Sky Rolnick UC Riverside APS April Meeting 2011

  2. Thermal Photon Motivation Photons are an ideal probe, carry information about the earliest, hottest, densest stages of the expanding medium as well as freeze out and other stages. The observation of thermal photons will allow the determination of the initial temperature of the medium, the thermalization time and help theorists understand the EoS.

  3. Some Theoretical Predictions • Hydrodynamic models explain pT spectrum of thermal photons and imply high initial T and rapid τ0. • Hydrodynamic models also predict a non-zero elliptic flow for thermal photons. • A measurement of thermal photon v2 will allow us to estimate η/S by matching data to models of viscous hydro. Tini = 300 to 600 MeV t0 = 0.15 to 0.5 fm/c Chatterjee, Srivastava & Heinz PhysRevC79, 021901 D.d’Enterria, Eur.Phys.J.C 46 (2006)

  4. The PHENIX Detector at RHIC π0e+e- π0e+e- comb. backg. pair • Drift and Pad Chambers to measure charged particle momentum. • RICH for electron identification. • Electromagnetic calorimeters for measuring photon energy and ID. • Provides 3 Techniques for Photon Measurement • Directly measured in EmCal. • Internal Conversions using dielectrons. • External Conversions using converter method. e+ e- e+ e-

  5. HBD Detector Concept • The HBD is a Windowless Cherenkov detector with CF4 as radiator gas. • Utilizes small opening angle of Dalitz decays and conversions to remove background. • Total radiation length: ~2.4% = 0.82% (vessel) + 0.56% (CF4) + 1.03% (backplane)

  6. HBD Performance Pairs in Central Arms Pairsmatched to HBD Estimatefrom Run-9 p+p: Pairsafter HBD reject.

  7. Inclusive Photon v2 using External Conversions from HBD v2 v2 v2 • Utilizes external conversions …

  8. Direct Photons from Internal Conversions Internal conversion shouldbe produced with a mass distribution that follows a “Dalitz” form. Data can be described through a two component fit. PRL 104, 132301 (2010)

  9. rγDirect over Inclusive  Error Bars expected with HBD • p+p result with * method agrees with NLO pQCD predictions. • For Au+Au there is a significant low pT excess above p+p expectations • Interpreted as thermal emission -> Initial T Statistical Errors will be reduced significantly with HBD. Systematic errors, dominated by cocktail subtraction, will need to be reduced.

  10. Direct Photon v2 using EmCal v2 measurement using EmCal Systematic Uncertainties on v2

  11. Expected error bars on v2 using HBD v2 measurement using EmCal Expected errors using HBD Using our results of rγ from before, and leaving everything else the same, we see significant improvement on direct photon v2 using the HBD over EmCal.

  12. Summary • Photons are a great way to understand the medium. • The Signal to Background is significantly reduced using the HBD. • The HBD will provide improved measurement of thermal photons and allow for better measurement of v2.

  13. Collaboration • Brookhaven National Lab: B. Azmoun, A.Milov, R. Pisani, T. Sakaguchi, A. Sickles, C. Woody • Columbia University: C.-Y. Chi • Stony Brook University: W. Anderson, Z. Citron, J. M. Durham, T.Hemmick, J. Kamin, V. Pantuyev • Weizmann Institute of Science: A. Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D. Sharma, I. Tserruya, MihaelMakek • UC Riverside: • Rich Seto, Sky D. Rolnick

  14. The End

  15. Expected Stat. Errors from Run10/Run4 • Au+Au collisions at 200 GeV: • 5x data than in Run-4 Quick and dirty Use S/B from Run4 and then assume 5x more signal and 5/20 more background since HBD will reduce B by 20 but stats will increase B by 5. S/B factor for Run10/Run4 The factor of 5 comes from 5x more statistics, and the value of x used was X=1/20 for the background reduction.

  16. Expected error bars on v2 using HBD Use analysis note 518 Extract data for each chart 0-92% Propagate statistical error assuming same factor deduced earlier for each pT bin. Systematic Uncertainties on v2

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