1. 9/15/06Ali Hanks1 Measuring bremsstrahlung photons in sqrt(s)=200 GeV pp collisions Ali Hanks Hard/Photon analysis fest September 15, 2006

2. 9/15/06Ali Hanks2 Motivation Zakharov hep-ph/0405101 no quenching with quenching pp collisions important for study of nuclear modifications Understanding jet quenching: – a probe of the QGP Just Bremsstrahlung photons Provides direct measurement of radiation spectrum Expect strong final state interaction effects on bremsstrahlung contribution significant enhancement for p T < 10GeV/c

3. 9/15/06Ali Hanks3 In pp - pQCD predictions NLO pQCD describes data well At NLO distinction between direct photons and bremsstrahlung (fragmentation) photons blurs –“isolation” cuts made to distinguish direct photons –difficult to match to theory fragmentation component > 20% for p T < 10 GeV/c direct measurement of fragmentation contribution good test of theory “direct” photons will be excluded Curves: INCNLO 1.4 INCNLO(v1.4): J. Ph. Guillet, M. Werlen et al fragmentation = bremsstrahlung

4. 9/15/06Ali Hanks4 Methodology Pick out bremsstrahlung photons by selecting photons associated with a jet – Trigger on high p T hadrons – Calculate correlations with associate photons in various p T bins – Look at yields for determining bremsstrahlung contribution Remove background sources – Tag photons coming from π 0 decays – Correct for tagging efficiency – Estimate contribution from other decay sources

5. 9/15/06Ali Hanks5 Inclusive h-  correlations

6. 9/15/06Ali Hanks6 Next step - removing π 0 background Tag photons from pairs that fall within π 0 mass peak 120-160 MeV/c 2 π 0 invariant mass Calculate combinatorial background Evaluate tagging efficiency “trigger” photon has p T > 1 GeV/c “sister” photon has p T >.5 GeV/c To do:

7. 9/15/06Ali Hanks7 Summary Have inclusive hadron-γ correlations Working on calculating hadron-γ tag correlations with: –combinatorial background correction –tagging efficiency estimate Next begin subtraction to obtain hadron-γ dir

8. 9/15/06Ali Hanks8 Backup Slides  0 tagging efficiency for p T > 3GeV/c ∆∆

9. 9/15/06Ali Hanks9 Initial QA – hot tower maps p T 1-2GeV/c sector 0sector 1 sector 2sector 3 sector 4sector 5 sector 6sector 7

10. 9/15/06Ali Hanks10 hot tower maps p T 2-3 GeV/c sector 0sector 1 sector 2sector 3 sector 4sector 5 sector 6sector 7

11. 9/15/06Ali Hanks11 hot tower maps p T 3-10 GeV/c sector 0sector 1 sector 2sector 3 sector 4sector 5 sector 6sector 7

12. 9/15/06Ali Hanks12 Evaluating the π 0 tagging efficiency Simulations of π 0 decays provide efficiency correction –π 0 s generated with p T dependent Gaussian distribution around “trigger” hadron –∆  distribution of decay photons calculated –Compare to photons from pairs where both photons accepted –Ratio gives tagging efficiency p T dependence of input π 0 distribution implies p T dependence in efficiency Input π 0 ∆  distribution ∆∆ π0π0 trigger  hadron-  ∆  distribution ∆∆ no cut pair acceptance ( p T > 3GeV/c )

13. 9/15/06Ali Hanks13 Evaluating the π 0 tagging efficiency Separate efficiency into several bins in p T of decay photon Tagging efficiency p T < 3.5 GeV/c ∆∆ Tagging efficiency 4 < p T < 4.5 GeV/c ∆∆ Tagging efficiency p T > 6 GeV/c ∆∆

14. 9/15/06Ali Hanks14 Other sources of background  decay also source of background –distribution of decay photons may differ from that of π 0 s Try simulation with  kinematics –Same input p T spectrum weighted by  /π 0 ratio Fit decay distributions to check similarity Similarity means  decays can be subtracted using π 0 distribution hadron-  ∆  distribution π 0 photons  photons ∆∆ hadron-  (  ) ∆  distribution  ~.102+/-.001 ∆ ∆ hadron-  (π 0 ) ∆  distribution ∆ ∆  ~.0995+/-.0005 3.5 < p T < 4.0GeV/c