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Initial Insights and Plans for ALICE Collaboration at LHC in Heavy Ion Physics

This presentation outlines the status and future plans of the ALICE experiment at the LHC, focusing on the study of quark-gluon plasma (QGP) through photon production in heavy ion collisions. Key topics include the expected timeline for LHC operations, photon physics in early years of ALICE, insights on neutral mesons, and predictions for direct and thermal photon measurements. The innovative design of the Photon Spectrometer (PHOS) and its capabilities for high-resolution measurements are also discussed, along with parallels to other experiments like PHENIX.

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Initial Insights and Plans for ALICE Collaboration at LHC in Heavy Ion Physics

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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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