Thermal Photon Measurement using the HBD in PHENIX :Status and Update
Sky Rolnick UC Riverside APS 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 Rolnick UC Riverside APS April Meeting 2011
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.
Some Theoretical Predictions
Sky Rolnick UC Riverside APS April Meeting 2011
D.d’Enterria, Eur.Phys.J.C 46 (2006)
Chatterjee, Srivastava & Heinz PhysRevC79, 021901
Tini = 300 to 600 MeV t0 = 0.15 to 0.5 fm/c
1
4
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 Rolnick UC Riverside APS April Meeting 2011
π0 e+ e-
π0 e+ e-comb. backg.pair
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) + 0.56% (CF4) + 1.03% (backplane)
Sky Rolnick UC Riverside APS April Meeting 2011
Z(cm)
(rad)
HBD Performance
Estimate from Run-9 p+p:
Step Bckg. reduction factor
1 matching to HBD 7.1 2.2
2double hit cutclose hit cut 6.5
3 single pad cluster cut
2Sky Rolnick UC Riverside APS 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 Rolnick UC Riverside APS April Meeting 2011
v2 v2 v2
Direct Photons from Internal Conversions
Internal conversion should be produced with a mass distribution that follows a “Dalitz” form.
eedirecteecocktaileedata MfrMfrMf 1
Sky Rolnick UC Riverside APS April Meeting 2011
Data can be described through a two component fit.
PRL 104, 132301 (2010)
r*dir(m 0.15)*inc(m 0.15)
*dir(m 0)*inc(m 0)
dirinc
rγ Direct over Inclusive
p+p result with * method agrees with NLO pQCD predictions.
For Au+Au there is a significant low pT excess above p+p expectationsInterpreted 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 Rolnick UC Riverside APS April Meeting 2011
Direct Photon v2 using EmCal
Sky Rolnick UC Riverside APS April Meeting 2011
Source 1-3GeV/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 EmCalR
NN
NN
incl
decay
d irect
decay 1
v2,dir
R(pT )v2,inc v2
,bg
R(pT ) 1
Expected error bars on v2 using HBD
Sky Rolnick UC Riverside APS April Meeting 2011
Expected errors using HBDv2 measurement using EmCal
Using our results of rγ from before, and leaving everything else the same, we seesignificant 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 Rolnick UC Riverside APS 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
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
A2 1B
S
5 x BS
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 Rolnick UC Riverside APS April Meeting 2011
Source 1-3GeV/c
V2 Inc. gamma hadron subtracted
~2-3%
V2 from Hadron contamination
~6%
Rgamma ~17%
Reaction Plane ~6-7%
Systematic Uncertainties on v2
RNN
NN
incl
decay
d irect
decay 1
v2,dir
R(pT )v2,inc v2
,bg
R(pT ) 1Use analysis note 518Extract data for each chart 0-92%
Propagate statistical error assuming same factor deduced earlier for each pT bin.
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