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Photon Physics at LHC-ALICE

Photon Physics at LHC-ALICE. JSPS Research Fellow / University of Tsukuba T. Horaguchi Oct. 15 2009 for HAWAII2009. Outline. Introduction Photon Physics Low p T Photon Virtual Photon Measurement LHC ALICE Experiment Electron Identification with TRD Invariant Mass Spectrum

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Photon Physics at LHC-ALICE

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  1. Photon Physics at LHC-ALICE JSPS Research Fellow / University of Tsukuba T. Horaguchi Oct. 15 2009 for HAWAII2009 HAWAII 2009

  2. Outline • Introduction • Photon Physics • Low pTPhoton • Virtual Photon Measurement • LHC ALICE Experiment • Electron Identification with TRD • Invariant Mass Spectrum • Evaluation of Statistics for LHC First Year • Summary & Future Plan HAWAII 2009

  3. Introduction • What dose mean the measurement of direct photons ? • Direct photons in p+p collisions • Test of pQCD calculation • Obtain the gluon distribution function • Reference data of the heavy ion collisions • Direct photons in heavy ion collisions • Jet quenching • Thermal photons • Direct photons are a clear probe to investigate the characteristics of evolution of the matter created by heavy ion collisions. • Penetrate the created matter without the strong interaction • Emitted from every stage of collisions • Hard photons (High pT) • Initial hard scattering, Pre-equilibrium • Thermal photons (Low pT) • Carry the thermodynamic information from QGP and hadron gas HAWAII 2009

  4. Direct Photon Measurement in ALICE • Hard photon • Strong suppression of high pT hadrons will help to improve the S/N ratio • High pT photons can be found • Thermal photon • Direct evidence of thermal equilibration • Created matter in LHC will have high temperature, high density and long life time matter comparison with RHIC, so we can expect large thermal photon component in ALICE • Primary contributor in low pTregion • Thermal photon measurement is very challenging because it is very hard due to a large background from hadron decays. HAWAII 2009

  5. Experimental determination is very important since applicability of pQCD is doubtable in low pTregion Low pT Photons • In ‘real’ photon measurement • Measured yield with a large systematic error • Difficulty on measuring low pT “real” direct photons • Finite energy resolution of the EMCal • Large hadron background • Advantages on measuring ‘virtual’ photons • High momentum resolution of the TPC • Reliable estimation of the hadron decay components using Kroll-Wada formula HAWAII 2009

  6. Virtual Photon Measurement e+ q e- • Any source of real g can emit g* with very low mass. • Convert direct g* fraction to real direct photon yield g* g q Kroll-Wada formula S : Process dependent factor • Possible to separate hadron decay components from virtual photon in the proper mass window. HAWAII 2009

  7. TPC (Time Projection Chamber) • Main tracking device • |h| < 0.9, full azimuth • Largest ever • 88 m3, 10m long, 5.6 m diameter, 570 k channels • 3 % X0, Ne (86)/CO2 (9.5)/ N2 (4.5), O2 ~ 1 ppm • max. 80 MB/event (after compression) • ITS(Inner Tracking System) • Tracking (|h|< 1) + multiplicity (|h|< 2) • Si pixel/drift/strip; 2 layers each rf resolution: 12, 38 • TRD(Transition Radiation Detector) • Tracking and particle identification • |h| < 0.9, full azimuth • 400 – 600 mm resolution in rf, 23 mm in z • e/p separation > 100 at pT > 3 GeV/c • Track finding efficiency ~ 90 % @ pT> 1GeV/c • Momentum resolution of electrons ~ 2% @ pT> 4GeV/c LHC ALICE Experiment CMS LHC-b • LHC can accelerate up to • 14TeVp+pcollisions • 5.5TeVPb+Pbcollisions • In first year , 7TeV pp collisionswill run from this November ! ALICE ATLAS HAWAII 2009

  8. Electron ID with TRD (1) TRD 1 TRD 2 TRD 3 TRD 4 TRD 5 TRD 6 Blue : pion Gleen: material conversion Red : hadron decay pT(GeV/c) • Used the production of ALICE full detector simulation with PYTHIA . • The fraction of electron (material conversion or hadron decay) increase with increasing TRD layer. HAWAII 2009

  9. Electron ID with TRD (2) Magenta : purity Blue : efficiency Red : efficiency x purity • The “efficiency x purity” is the highest with more than 4 layers of TRD, so we decided to apply TRD 4 layers cut in current analysis. HAWAII 2009

  10. Invariant Mass Spectrum • Combinatorial background and Conversion electron pair dominates in the invariant mass spectrum. • Total mass yieldis almost described by the combinatorial and material conversion background within the statistical error. But it indicates to need more statistics and analysis is ongoing. HAWAII 2009

  11. Evaluation the Statistics in First Year • Evaluation from NLO pQCD calculation • Used INCNLO • http://wwwlapp.in2p3.fr/lapth/PHOX_FAMILY/readme_inc.htm • CTEQ6M, BFG • √s : 7TeV pp • μ : 0.5pT,1.0pT,2.0pT • Evaluation of the number of the virtual photon • Error propagation of background subtraction included. • Required Trigger : MB • Assumed DAQ rate :100Hz & Duty factor : ~25% • 100M event ~ 2 Month • 1G event ~ 20 Month • Measured pT will reach ~5GeV/c Red : 100M event Blue : 1G event HAWAII 2009

  12. Summary & Future Plan • ALICE at LHC starting in month ! • Photon Physics at LHC-ALICE is important • p+pcollisions : Test of pQCD calculation • Pb+Pbcollisions : Measurement of thermal photons • Preparation for low pTphotons measurement @ALICE • Using the direct photon measurement via internal conversion method • Working Group for this analysis was established. • Precise study in more statistics is ongoing at GRID! HAWAII 2009

  13. Backup Slides HAWAII 2009

  14. HAWAII 2009

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  17. Combinatorial Background • Combinatorial background is evaluated using mixed event method. • Normalization is done using the like sign pair. • The normalized combinatorial background is good agreement with the unlike sign pair in high mass region. Black : unlike sign pair Red : Like sign pair (++) Blue : Like sign pair (--) Black : unlike sign pair Red : Normalized combinatorial background Combinatorial pair e+ e+’ e- e-’ HAWAII 2009

  18. Photon Physics : Thermal Photons • RHIC outcome • radiation at 300 – 500 MeVimplied • indirect measurement via g* • cf. critical temperature ~ 170 MeV • models not strongly constrained • LHCprospect • direct measurement of thermal photons • higher temperature + longer life time • reduced background due to quenching • ALICE-PHOSdetector • understanding of thermal properties of partonic system HAWAII 2009

  19. Background Sources γ • Real signal • di-electron continuum • Background sources • Combinatorial background • Material conversion pairs • Additional correlated background • Cross pairs from decays with 4 electrons in the final state • Pairs in same jet or back-to-back jets • Hadron decays • p0, h, h’, w, f, r, J/y, y’ e- Jet cross pair e+ e+ π0 e+ e- π0 π0 γ e- γ e+ e- π0 γ Dalitz + conversion cross pair e+ e- HAWAII 2009

  20. Time Projection Chamber • Main tracking device • |h| < 0.9, full azimuth • Largest ever • 88 m3, 10m long, 5.6 m diameter, 570 k channels • 3 % X0, Ne (86)/CO2 (9.5)/ N2 (4.5), O2 ~ 1 ppm • max. 80 MB/event (after compression) HAWAII 2009

  21. Inner Tracking System • Tracking (|h|< 1) + multiplicity (|h|< 2) • Si pixel/drift/strip; 2 layers each • rf resolution: 12, 38, 20 mm HAWAII 2009

  22. Transition Radiation Detector • Tracking and particle identification • |h| < 0.9, full azimuth • 400 – 600 mm resolution in rf, 23 mm in z • e/p separation > 100 at pT> 3 GeV/c HAWAII 2009

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