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Feasibility Study of Direct Photon Measurement via Internal Conversion in ALICE

Feasibility Study of Direct Photon Measurement via Internal Conversion in ALICE. T. Horaguchi Hiroshima University takuma @hepl.hiroshima-u.ac.jp Feb. 4 for the 4 th International Workshop High- pT Physics at LHC09 @ Prague. Contents. Introduction Direct Photon Measurement in ALICE

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Feasibility Study of Direct Photon Measurement via Internal Conversion in ALICE

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  1. Feasibility Study of Direct Photon Measurement via Internal Conversion in ALICE T. Horaguchi Hiroshima University takuma@hepl.hiroshima-u.ac.jp Feb. 4 for the 4th International Workshop High-pT Physics at LHC09 @ Prague High-pT Physics at LHC09 @ Prague

  2. Contents • Introduction • Direct Photon Measurement in ALICE • Low pT Photon • Virtual Photon Measurement • Background Study • Background Sources • Combinatorial Background • Hadron Decay • Combinatorial + Hadron • PT Sliced Mass Spectra • Evaluation the Statistics of First Year • Summary & Future Plan High-pT Physics at LHC09 @ Prague

  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 High-pT Physics at LHC09 @ Prague

  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. High-pT Physics at LHC09 @ Prague

  5. Low pT Photons Experimental determination is very important since applicability of pQCD is doubtable in low pT region • 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 High-pT Physics at LHC09 @ Prague

  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 • Case of Hadrons • Obviously S = 0 at Mee > Mhadron • Case of g* • If pT2>>Mee2 • Possible to separate hadron decay components from virtual photon in the proper mass window. High-pT Physics at LHC09 @ Prague

  7. 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- High-pT Physics at LHC09 @ Prague

  8. 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- High-pT Physics at LHC09 @ Prague

  9. PYTHIA Simulation h distribution (p+p-) • PYTHIA • MSEL=1 • 14TeV pp • 10M event • 4 pcoverage • No Detector Simulation • No virtual photon event e++e- from hadron decay Pi+- PT distribution Red : p+ Blue : p- High-pT Physics at LHC09 @ Prague

  10. Hadron Decay Hadron Decay Mode • The hadron decay background affects mainly in low mass region. High-pT Physics at LHC09 @ Prague

  11. 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-’ High-pT Physics at LHC09 @ Prague

  12. Combinatorial + Hadron Decay • The combinatorial + hadron decay background is very good agreement with mass spectrum ! • The mass spectrum in Low mass region is mainly produced by hadron decay. • The mass spectrum in High mass region is mainly produced by combinatorial background. • The contribution of jet correlated pair seems to be negligible in this mass region. Black: Total unlike sign pair Red : Combinatorial + Hadron Decay Good Agreement ! High-pT Physics at LHC09 @ Prague

  13. pT Sliced Mass Spectra 0<pT<0.5GeV/c 0.5<pT<1.0GeV/c 1.0<pT<2.0GeV/c • The combinatorial + hadron decay background is very good agreement with mass spectra for each pT bin ! 2.0<pT<3.5GeV/c 3.5<pT<5.5GeV/c Total High-pT Physics at LHC09 @ Prague

  14. 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 : 14TeV pp • μ : 0.5pT,1.0pT,2.0pT • Evaluation of the number of the virtual photon • Assumed DAQ rate :100KHz • 1 Day：~2M • 1 Month：~60M • 3 Month: ~ 180M • Acceptance Correction • Considered TRD acceptance • | h|< 0.9 • f coverage: 8/18 x 2p 30 Days 90 Days Enough Statics ! High-pT Physics at LHC09 @ Prague

  15. Summary & Future Plan • The e+e-pair mass spectrum is calculated in p+p 14TeV collisions with PYTHIA simulation. • The mass spectrum is very good agreement with the combinatorial background + hadron decay background ! • More precise background study will be needed with the detector simulation. • The statistics of virtual photon is evaluated for first year. The signal will be seen if we have more one month beam time. This result strongly encourages us to measure the direct photon via internal conversion ! High-pT Physics at LHC09 @ Prague

  16. Backup High-pT Physics at LHC09 @ Prague

  17. Direct Photon Production • There are two processes: • “Direct process” • “Fragmentation process” • The direct photon production dominates two leading –order subprocesses • Quark-gluon Compton scattering (qg→gq) • Quark-anti-quark annhilation (qq-bar→ gg) Quark-gluon Compton scattering (qg→gq) at LO Quark-anti-quark annihilation (qq-bar→ gg) at LO Fragmentation Process High-pT Physics at LHC09 @ Prague

  18. Review of other experiments • The measurement of direct photon cross sections in proton-proton collisions • Midrapidity • varying from 19.4GeV to 63GeV was performed by • E706 at Tevatron. • E704 at FNAL. • UA6, WA70 and NA24 at SPS. • R110, R806 and R807 at ISR of CERN • The measurement of direct photon cross sections proton-anti-proton collisions • Midrapidity • varying from 24.3GeV to 1800GeV was performed by • UA6 at SPS. • UA1 and UA2 at • CDF and D0 at Tevatron. High-pT Physics at LHC09 @ Prague

  19. Review of the Direct Photon Measurement High-pT Physics at LHC09 @ Prague

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