Thermal Photon Measurement using the HBD in PHENIX :Status and Update Sky RolnickUC RiversideAPS April Meeting 2011

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. Sky RolnickUC RiversideAPS April Meeting 2011

 Hydrodynamic models explain pT spectrum of thermal photons and imply high initial T and rapid τ 0.  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. Some Theoretical Predictions Sky RolnickUC RiversideAPS April Meeting 2011 D.d’Enterria, Eur.Phys.J.C 46 (2006) Chatterjee, Srivastava & Heinz PhysRevC79, T ini = 300 to 600 MeV t 0 = 0.15 to 0.5 fm/c

The PHENIX Detector at RHIC  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. Sky RolnickUC RiversideAPS April Meeting 2011 π 0      e + e - π 0   e + e - comb. backg. pair e+e+ e+e+ e-e- e-e-

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) % (CF4) % (backplane) Sky RolnickUC RiversideAPS April Meeting 2011

HBD Performance Estimate from Run-9 p+p: StepBckg. reduction factor 1matching to HBD7.1  double hit cut close hit cut 6.5 3single pad cluster cut2 Sky RolnickUC RiversideAPS April Meeting 2011 Pairs in Central Arms Pairs matched to HBD Pairs after HBD reject.

Inclusive Photon v2 using External Conversions from HBD  Utilizes external conversions … Sky RolnickUC RiversideAPS April Meeting 2011 v2

Direct Photons from Internal Conversions Internal conversion  should be produced with a mass distribution that follows a “Dalitz” form. Sky RolnickUC RiversideAPS April Meeting 2011 Data can be described through a two component fit. PRL 104, (2010)

r γ Direct  over Inclusive  p+p result with  * method agrees with NLO pQCD predictions. For Au+Au there is a significant low p T excess above p+p expectations Interpreted as thermal emission -> Initial T Error Bars expected with HBD Statistical Errors will be reduced significantly with HBD. Systematic errors, dominated by cocktail subtraction, will need to be reduced. Sky RolnickUC RiversideAPS April Meeting 2011

Direct Photon v2 using EmCal Sky RolnickUC RiversideAPS April Meeting 2011 Source1-3GeV/c V2 Inc. gamma hadron subtracted ~2-3% V2 from Hadron contamination ~6% Rgamma~35% Reaction Plane~6-7% Systematic Uncertainties on v2 v2 measurement using EmCal

Expected error bars on v2 using HBD Sky RolnickUC RiversideAPS April Meeting 2011 Expected errors using HBDv2 measurement using EmCal Using our results of r γ from before, and leaving everything else the same, we see significant improvement on direct photon v2 using the HBD over EmCal.

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. Sky RolnickUC RiversideAPS April Meeting 2011

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, Mihael Makek  UC Riverside: Rich Seto, Sky D. Rolnick

The End

Expected Stat. Errors from Run10/Run4  Au+Au collisions at 200 GeV:  5x data than in Run-4 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. Quick and dirty

Expected error bars on v2 using HBD Sky RolnickUC RiversideAPS April Meeting 2011 Source1-3GeV/c V2 Inc. gamma hadron subtracted ~2-3% V2 from Hadron contamination ~6% Rgamma~17% Reaction Plane~6-7% Systematic Uncertainties on v2 Use analysis note 518 Extract data for each chart 0-92% Propagate statistical error assuming same factor deduced earlier for each pT bin.