Photon Analysis in EMCal: Pi0 Invariant Mass, Photon Identification, Direct Photons, and Gamma-Jet Correlation

1. EMCal PPR:Photons section EMCal PPR: Photons

2. Proposed table of content Blue: Close to be finished Green: Under progress. Some work previously done that could be used but new simulations are helpful Red: Not for the next 2 months, need new simulations and time. EMCal PPR: Photons

3. Task: Pi0 (eta) invariant mass analysis • In charge: • In a first moment Jocelyn (Sergei). Student, cannot dedicate full time. • This is the most important physics topic for the first runs. • Need to define a group of people to work on this now. • Acceptance, efficiency, corrections to be estimated • pT reach for different EMCal configurations and different running times • … • Analysis task code already available and working. • Min bias generation is produced now in the grid, suitable for this study, need PbPb • RAA extraction …? EMCal PPR: Photons

4. Task: Pi0 invariant mass analysis  in EMCal, e+-e- in TPC • In charge: Raphaëlle? • Code is ready • Photon converts in ITS and e+e- pair measured in TPC. • Analysis code for converted photon reconstruction developed Ana Kenneth et al and available. • Need to implement in next weeks the converted photon AOD output. • Matching between this code and cluster in calorimeter available in PartCorr frame. • Need to tune the code, see the feasibility of the method: pT reach, resolution etc  e+ e-  EMCal PPR: Photons

5. Task: Photon identification via conversion and signal in TRD/TOF PHOS, Single particle • New identification procedure suggested by Nicola • In charge: We proposed to a master Brazilian student but not available in the next months. • Idea: Photon convert in material in front of EMCal, in TRD and TOF. The shower will also produce signal in the detectors. • A photon is a bigger cluster, or several clusters in the calorimeter with a match in the TRD and TOF and no match in the TPC. • I did a similar study with PHOS 5 years ago but in this case the charged signal from the shower is given by the CPV • At least 60% of converted photon, combination of 2 “electrons”, were tagged as converted photons both in pp and PbPb environment. • Material and many things have changed. PHOS, Single particle + Hijing EMCal PPR: Photons

6. Direct photons and isolation cuts:Generators predictions • In charge: Amaya • Poster in QM, presentation in PWG4 • Main conclusions: • Comparison between Herwig and Pythia, no detector effects, ideal conditions, open geometry • Jets and fragmentation photons are less produced in Herwig, at a maximum of a factor 2 • Fragmentation function very similar. • Prompt photons are similarly produced, at maximum a 20% more with Herwig. • Sum of fragmentation+prompt photons give similar cross section to NLO calculation (JetPHOX) • Isolation Cuts: • Similar isolation trends for different particle species • In general a shift of about 10% in isolation, HERWIG underlying event is smaller, less isolated particles. EMCal PPR: Photons

7. Direct photons and isolation cuts:Reevaluation of isolation cuts • In Charge: Gustavo • Nothing new: • I could try to extrapolate the missing points, knowing the input background spectrum and the isolation and identification rejection factors. • Add a systematic error coming from the generator studies. • Problem, old simulations, PID better than now … • Need new data. pp @ √14 TeV PbPb @ √5.5 TeV, qhat = 50 EMCal PPR: Photons

8. Direct photons and isolation cuts:Isolation efficiency study in a model free measurement • In charge : Raphaëlle? • Method 1: Event by Event Pi0 identification with 2 photons in the calorimeter • Need to see up to which pT this is feasible, reasonable counting rate. More than 10 GeV difficult • Code available • Method 2: Pi0 identification via shower shape • Feasible between 10 and 40 GeV • Code available • Raphaelle is looking to it, see her presentation in PWG4 • Method 3: Event by Event pi0 identification, photon in EMCal, photon reconstructed in TPC • Need to study feasibility • Code that connects calorimeter and TPC photon reconstruction is available EMCal PPR: Photons

9. Direct photons and isolation cuts:RAA RHIC • Direct photons suppression due to: • Isospin • Nuclear Parton distribution functions • Fragmentation photons suppression due to jet-quenching • With isolated photons we should be sensitive to cold nuclear matter suppression effects (isospin nPDF) • Without isolation, it will involve more work considering the statistical extraction of the decay photon yield, etc. LHC Prediction suppression photons directs au LHC F. Arleo et al. arXiv:0707.2320v1 [hep-ph] EMCal PPR: Photons

10. Gamma-jet correlation • In charge: Guenole is gone so Gustavo, code not available, only my old code that should be updated with Guenole’s improvements. • Remaining questions: • Improve UE subtraction • Include systematic error due to jet-jet. PbPb/pp EMCal PPR: Photons

11. Gamma-Jet (Jet finder) correlation • Standard jet algorithms energy measurement can be calibrated with gamma-jet events ( not considering kT effect) • “Small” acceptance of EMCal, and “tiny” of PHOS makes it difficult. • Study feasibility in pp and PbPb and how to apply this corrections. • Code that connects isolated photon and jet found with JETAN (package with different algorithms) is available. • In charge: Gustavo EMCal PPR: Photons

12. preliminary Gamma-Hadron correlation • No need to reconstruct the jet to construct a meaningful fragmentation function • In charge: Yaxian? 8 < p T trigger< 16 GeV/c, pT asso > 3Gev/c EPJC (2008) 57: Y. Mao et al. zT=0.9 zT=0.3 Tomographie de la collision! XN Wang arXiv:0902.4000v1 [nucl-th] EMCal PPR: Photons

13. Backup EMCal PPR: Photons

14. Conversions in front of EMCalLHCC response High conversion in TOF and TRD EMCal PPR: Photons

15. Conversions in front of EMCalLHCC response Overlapped Pi0 misidentification via Shower shape Photon identification via Shower shape Overlapped photon pairs misidentified as photons does not change for converted photons 50-60% of converted photons not identified EMCal PPR: Photons

16. Conversions in front of EMCalLHCC response Normalized Pi0 invariant mass does not change much in case of conversions EMCal PPR: Photons

17. Cynthia Hadjidakis PID: Shower shape single cut with ellipse main axisStudy for CD2 identified : 02 < 0.25 identified 0: 02 > 0.25 For energies larger than 10 GeV, 0 produce most likely a single cluster, try to separate 0 and  via shower shape. p+p Pb+Pb p+p 14 TeV g identified as g Ndirect g / Ng from p0 PID efficiency g identified as p0 g identified as p0 p0 as p0 Ndirect g / Ng from p0 p0 as g central Pb+Pb 5.5 TeV factor 5 p0 suppression pT (GeV/c) Needto be revised since digitization and reconstruction parameters have changed New Task for Amaya? pT (GeV/c) EMCal PPR: Photons

18. Task: PID bayesian with shower shape analysis • In charge: Marie Germain • Shape of clustersλ02 (main axis of the cluster ellipsoide) + Bayesian analysis to determine probability for a cluster to be originating from (, π0, hadron). • Now in AliRoot, parametrization for pp events found with old AliRoot version with different digitization parameters. • PID determination: • Generation of 10000 single particles (, 0, kL0) • Merged single events with HIJING PbPb at 5.5 TeV • Only EMCal present in the simulation • Fit of λ02distributions:Gaussian + landau Distribution • Gaussian: NormG * TMath::Gaus(λ02 ,mG,σG ) : 3 parameters • Landau : NormL* TMath::Landau(λ02 ,mL,σL ): 3 parameters • Evolution of each parameter with Energy is fitted by: • Param (E(GeV)) = p0E-2 + p1E-1 + p2 + p3E + p4E2 EMCal PPR: Photons

19. Task list EMCal PPR: Photons