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Physics in Initial Years at ALICE

Physics in Initial Years at ALICE. Kenta Shigaki, Hiroshima University (ALICE Collaboration) 30, October 2007 Workshop on Phenomenology of QGP in Heavy Ion Collisions: from SPS and RHIC to LHC at RCNP, Osaka University. - Presentation Outline -. LHC/ALICE/PHOS status and plans

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Physics in Initial Years at ALICE

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  1. Physics in Initial Yearsat ALICE Kenta Shigaki, Hiroshima University (ALICE Collaboration) 30, October 2007 Workshop on Phenomenology of QGP in Heavy Ion Collisions: from SPS and RHIC to LHC at RCNP, Osaka University

  2. - Presentation Outline - • LHC/ALICE/PHOS status and plans • physics via photons in initial few years at ALICE • neutral mesons • pQCD photons • thermal photons • ALICE/PHOS news • physics at PHENIX in parallel to ALICE • summary and concluding remarks Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  3. - Plans at LHC/ALICE - • LHC start up plan • 2008/04 accelerator/experiments closed • 2008/05 beam commissioning • 2008/07 p+p, s = 14 TeV, first collision • 2008/end p+p, s = 14 TeV, 1032 cm-2s-1 • soon after ? Pb+Pb, sNN = 5.5 TeV, 5×1025 cm-2s-1 • expectation in initial few years • p+p s = 14 TeV, < 1031 cm-2s-1 at ALICE • Pb+Pb s = 5.5 TeV, 1027 cm-2s-1, 2 – 3 years • “p”+Pb s = 8.8 TeV, 1029 cm-2s-1, 1 year • Ar+Ar s = 6.3 TeV, 1029 cm-2s-1, 1 year last cryo-dipole installated in August 2007 Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  4. 1000thALICE member - ALICE: A Large Ion Collider Experiment - • the heavy ion experiment at LHC • 30 countries, 90 institutions, ~1,015 members Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  5. (charged particles) µ arm -  ALICE ≈ STAR + PHENIX  - • central barrel: -0.9 < h < 0.9 • tracking and particle identification in full azimuth • partial coverage of HMPID, PHOS, EMCal • forward m arm: - 4 < h < -2.4 • multiplicity: - 3 < h < 5.4 Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  6. - ALICE Photon Spectrometer: PHOS - • photons, neutral mesons, jet tagging • + level 0 and level 1 trigger capability • high resolution, high granularity • s/E ~ 3 %/E up to 100 GeV • PbWO4 of 22 (1.0 RMoliere)×22×180 (20 X0) mm3 • APD + charge sensitive preamplifier readout • temperature controlled at -250.1 ˚C • |h| < 0.12, Df = 100 degrees • 56×64×5 modules • 17,920 crystals, 12.5 t Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  7. - PHOS #1 (Out of 5) - waiting for installation in 2 weeks Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  8. - ALICE/PHOS Start Up Timeline - • 2007/11/12 – 14 PHOS #1 installation • 2007/12/02 PHOS #2 ready (?) • 2007/12/10 – 21 magnet test • 2007/12/10 – 21 cosmic test run • 2008/01/08 – TPC commissioning • 2008/02 cosmic run • 2008/02/08 PHOS #3 ready (?) • 2008/04 LHC/ALICE closed • 2008/07 – physics run • by 2009 ? PHOS #4, #5 installed Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  9. - Physics via Photons at LHC - • vital probe of initial hot dense phase • thermal photons… temperature • thermal photon HBT… space-time evolution • direct photons… pQCD processes + jet tagging • neutral mesons… quark energy loss • experimental virtues • photons and neutral mesons in same detector • particle identification to very high pt • even more powerful at LHC than ever • large rates up to ~ 100 GeV hadron decays pQCD processes ~ pT-n compton scattering annihilation fragmentation thermal ~ e-E/T jet-medium interaction jet-photon conversion bremsstrahlung Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  10. - Physics Topic #1: Neutral Mesons - • first piece of physics • enough acceptance with 2 – 3 PHOS modules • stronger quenching and higher pt reach • clearer measurement of quark energy loss • leading to less background for direct photons Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  11. - Physics Topic #2: pQCD Photons - K.J.Eskola et al., NPB535 (1998) 351 F.Arleo, hep-ph/0601075 (2006) Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop • direct photons at RHIC consistent with pQCD • consistent with simple accumulation of p+p • consistent with structure function modification • consistent with/without quenched fragmentation

  12. - Quenched Fragmentation at LHC - ~ 60 % suppression at 10 GeV/c F.Arleo, hep-ph/0707.2320 (2007) • pQCD photons to be suppressed significantly • another view of quark energy loss • leading to less background for thermal photons Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  13. - Physics Topic #3: Thermal Photons - Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop • indirect measurement at PHENIX • suggesting thermal component of 300 – 500 MeV • high quality direct measurement at ALICE • longer life of thermalized high temperature phase • background photons suppressed due to quenching • superb PHOS detector

  14. - Direct Photon Yield Predictions - pt direct/decay direct/decay thermal/decay thermal/decay (GeV/c) w/o suppression 80% suppression w/o suppression 80% suppression 3 [1] 4 – 10 % 4 – 10 % 3 – 9 % 3 – 9 % [2] 5 – 9 % 5 – 9 % 5 – 9 % 5 – 9 % [3] 5 – 10 % 5 – 10 % 4 – 8 % 4 – 8 % 5 [1] 6 – 12 % 12 – 25 % 3 – 9 % 6 – 18 % [2] 6 – 10 % 12 – 20 % 3 – 5 % 6 – 10 % [3] 11 – 15 % 20 – 30 % 7 – 12 % 14 – 22 % 10 [1] ~ 10 % ~ 50 % ~ 5 % ~ 25 % [2] ~ 10 % ~ 50 % < 1 % < 5 % [4] 25 – 30 % 15 – 20 % [1] F.Arleo et al., hep-ph/0311131 [2] F.Arleo, D.d’Enterria, D.Peressounko, nucl-th/0707.2357 [3] S.Turbide, R.Rapp, C.Gale, hep-ph/0308085 [4] S.Turbide, C.Gale, S.Y.Jeon, G.D.Moore, hep-ph/0502248 Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  15. - Expectation at a Glance - predicted fraction of direct/decay photons Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  16. - Limiting Factors in Photon Measurement - Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop • major systematic error sources in PHENIX • conversion (uncertainty in amount of material) • off-vertex photon (uncertainty in amount of material) • acceptance (uncertainty in bad module map) • calibration and linearity • efficiency (uncertainty in reconstruction probability) • charged/neutral hadron contamination • peak extraction (uncertainty in background shape)

  17. - Extrapolated Systematic Errors - • extrapolated from PHENIX/EMC to ALICE/PHOS • based on expected PHOS performance Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  18. - Potential at a Glance - expected sensitivity versus theory prediction Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  19. - Thick Detectors in Front of PHOS: TRD+TOF - Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  20. - Transition Radiation Detector - • tracking and particle identification • 400 – 600 mm resolution in rf, 23 mm in z • e/p separation > 100 at pt > 3 GeV/c • |h| < 0.9, full azimuth Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  21. - Time of Flight Detector - • multi-gap resistive plate chamber (MRPC) • time resolution < 100 ps • |h| < 0.9, full azimuth; 3.7 m from beam axis Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  22. - Material Budget Comparison - • material budget in front of EM calorimeter • WA80 11 % • WA98 8.5 – 10 % • PHENIX 15 % • STAR 10 % • D0 15 % • material in front of PHOS • ITS+TPC w/o TRD+TOF 20 % • ITS+TPC and TRD+TOF in technical design report 40 % • ITS+TPC and TRD+TOF in current design 85 % Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  23. - Radiation Length Map - Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  24. - Problems Due to TRD/TOF Materials - Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop • loss of photon statistics • factor ~ 2 for single photons • significant especially in hard high pt region • leading to lower pt reach • extra systematic errors • factor ~ 3 on neutral meson yield • due to factor ~ 3 lower S/N ratio for photon pairs • leading to increased (major) systematic error • extra background photons • factor ~ 4 of off-vertex photons • leading to increased systematic error

  25. - Potential at another Glance - • reevaluated sensitivity versus theory prediction • ~ fatal for direct photon measurement • need to recover physics capability Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  26. - News: Good Sign for Resolution - Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop • proposal to reduce material in front of PHOS • backed up by (partly reviewed) physics arguments • contributions from Hiroshima based on PHENIX experiences • “holes” recommended and agreed • in 3 (out of 5) TRD+TOF modules in front of PHOS • on ALICE management board on 2007/10/04 • “hole” in reality yet to be defined

  27. - Summary and Concluding Remarks - • LHC/ALICE starting in summer, 2008 • uniquely suitable for hard (and/or heavy) probes • opening new ground for “soft” photonic probes • many physics via photons planned in initial years • suggestions/comments more than welcome • penetrating probes never easy to measure • material issue against PHOS being solved • Hiroshima in full commitment on ALICE/PHOS • based on old (PHENIX) and new (R&D) expertise • along with still exciting physics at RHIC/PHENIX Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  28. F. Arleo et al., “Yellow Report on Photon Physics in Heavy Ion Collisions at the LHC” hep-ph/0311131 P. Aurenche, “Photon and dilepton production at LHC”, Nucl.Phys.A783:395; hep-ph/0610218 No suppression in central AA collisions assumed! Decay photons: hydro + NLO pQCD (no quenching) DPMJET (LO pQCD + string formation) Direct photons: hydro + NLO pQCD Use this calculation of decay photon yield in later estimates. Note total hadron multiplicity for further comparisons: dNhadr/dy~4500 Decay photons: Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  29. F. Arleo et al., “Yellow Report on Photon Physics in Heavy Ion Collisions at the LHC” hep-ph/0311131 P. Aurenche, “Photon and dilepton production at LHC”, Nucl.Phys.A783:395; hep-ph/0610218 Ratio (total photon yield)/(decay photons): excess over 1 due to direct photons No suppression in central AA collisions assumed! Pt (GeV) Ngdir/Ngdec 3 (4-10) % 5 (6-12) % 10 ~10 % With suppression Pt (GeV) Ngdir/Ngdec 3 (4-10) % 5 (12-25) % 10 ~50 % Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  30. Francois Arleo, David d'Enterria, Dmitri Peressounko. “Direct photon spectra in Pb - Pb at s(NN)**(1/2) = 5.5-TeV: hydrodynamics + pQCD predictions“ Jul 2007Contributed to Workshop on Heavy Ion Collisions at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun 2007, arXiv:0707.2357 [nucl-th] Initial conditions of hydro corresponds to dNhadr/dy~2000 => scale properly decay photon yield from slide 1 Decay photons (dNhadr/dy~2000): Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  31. Hadronic Production of Thermal Photons Simon Turbide, Ralf Rapp, Charles Gale, arXiv:hep-ph/0308085 Decay photons from slide 1: Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  32. Energy Loss of Leading Hadrons and Direct Photon production in Evolving Quark-Gluon PlasmaAuthors: Simon Turbide (McGill University), Charles Gale (McGill University), Sangyong Jeon (McGill University, RIKEN-BNL Research Center), Guy D. Moore (McGill University) http://arxiv.org/abs/hep-ph/0502248 Decay photons: LO pQCD (tuned to PHENIX results) + jet-thermal processes Direct photons: LO pQCD (tuned to PHENIX results) + a la hydro parameterization for thermal Pt (GeV) Ngdir/Ngdec 10 (25-30) % Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

  33. - Systematic Errors Reevaluated - systematic errors on direct photon yield in ALICE Physics in Initial Years at ALICE / K.Shigaki / RCNP Workshop

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