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Overview of Heavy-Ion Physics Program in CMS

Overview of Heavy-Ion Physics Program in CMS. Heavy-Ion Meeting, APCTP, Pohang, Korea September 25-26, 2009. Byungsik Hong (Korea University) for the Collaboration. Historical Remark. 2009 : A centennial Anniversary of Ion-Ion Collisions. 1909 Rutherford gold foil experiment.

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Overview of Heavy-Ion Physics Program in CMS

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  1. Overview of Heavy-Ion Physics Program in CMS Heavy-Ion Meeting, APCTP, Pohang, Korea September25-26, 2009 Byungsik Hong(Korea University) for the Collaboration

  2. Historical Remark 2009 : A centennial Anniversary of Ion-Ion Collisions 1909 Rutherford gold foil experiment 2009 LHC experiments • Beam: 5 MeVa + fixed Au (√sNN~1 GeV) ⇒ 5.5 TeV (X5,000) • # of collaborators: 3 (+Geiger+Marsden) ⇒ ~3,500 (X1,000) • Constructioncost: (X∞) Heavy-Ion Meeting

  3. Outline • Motivation • Importance & challenges • CMS Detector • Acceptance • High-level trigger • Plan for the first Pb+Pb run • Heavy-Ion Physics Capability of CMS • Soft probes • Hard probes • Ultra-peripheral collisions • Summary Heavy-Ion Meeting

  4. Many Facets of QCD • Quantum Field Theory with rich dynamical content • asymptotic freedom, confinement, spontaneous broken chiral symmetry & its restoration at high density, non-trivial vacuum, etc. • Standard Model of the collective behavior becomes important • phase transition, thermalization, flow, etc. • Very diverse many-body phenomenology at various limits: Heavy-Ion Meeting

  5. Origin of Visible Mass • QCD (i.e. c-sym. breaking), not Higgs (i.e. EW-sym. breaking), is truly responsible for the “origin of the visible(baryonic) mass” • About 98% of the (light quark) mass generated dynamically (gluons) in the QCD confining potential B. Müller, arXiv:nucl_th/0404015 • Connection between QCD & HI • Role of CMS for the detailed investigation of QCD Heavy-Ion Meeting

  6. Motivation • Characterizing the early stage by hard probes • Color charge density, Transport coefficient, QCD εc & Tc , Tomography, … • High pT spectra, Jets, g(or g*, Z0)-jet correlations, Quarkonia, … • Characterizing the later stage by soft probes • Hydrodynamics, QCD EoS, Medium viscosity, ... • dNch/dη, Low pT spectra, Elliptic flow, Thermal photons, … Heavy-Ion Meeting

  7. Initial Evidence at RHIC Strongly coupled matter is hot & dense! Flow & NQ scaling: quark recombination & low h/s Jet quenching: strong interaction of high-pT hadrons with dense medium J/y suppression: SPS≈RHIC, larger at forward (CGC?) Jets are modified in medium. Heavy-Ion Meeting

  8. What is New at LHC? • LHC energies arefar exceeding previous heavy-ion accelerators • A hotter, denser, and longer lived partonicmatter ~ ~ Heavy-Ion Meeting

  9. LHC RHIC SPS Production Rate at LHC • Large rates of various hard probes over a larger kinematic range • Plenty of heavy quarks (b & c) • Weakly interacting probes are available (W± & Z0) d3s/dyd2pT [mb GeV-2] pT [GeV] Heavy-Ion Meeting

  10. CMS Stands for Content Management System Creative Marketing Solutions Centers for Medicare & Medicaid Services Convention on Migratory Species Cash Management Service Church Missionary Society CollegeMusic Society Cryptographic Message Syntax Canadian Mathematical Society Classic Motorcycle Supplies Common Management System Credit Management Solutions Conceptual Models for Services … CompactMuonSolenoid Heavy-Ion Meeting

  11. Heavy-Ion Meeting

  12. Forward Detectors CASTOR (5.2 <<6.6) TOTEM Total weight : 12,500 t Collar shielding (5.3 << 6.7) Overall diameter : 15 m Overall length : 21.6 m T2 Magnetic field : 4 Tesla ZDC (z = 140 m) EM HAD Beams CMS Detector SUPERCONDUCTING COILS ECAL PbWO4 Crystals HCAL Cu-Scintillator Sampling IRON YOKE TRACKER Si Pixels & Strips Δp/p ≈1-2% Occupancy < 2% for central Pb+Pb MUON BARREL Drift Tubes & RPCs sm≈50 MeV at 10 GeV/c2 MUON ENDCAPS Cathode Strip Chambers & Resistive Plate Chambers (RPCs) Heavy-Ion Meeting

  13. HCAL (Barrel+Endcap+Forward) CMS Acceptance Large Range of Hermetic Coverage • Extended kinematic reach • x~(1/40) of RHIC • <10-4 measurable Heavy-Ion Meeting

  14. Plan for the First Pb+Pb Coll. Note from the Chamonixmeeting: Early Pb Beam will have lower beam energy ⇒ 10 TeV in pp corresponds to 4 TeV in Pb+Pb. →2 • Low collision rate in Year-1 allows us to write all min. bias events to mass storage. • Fully functional high-level trigger (HLT) is needed at nominal luminosity. Heavy-Ion Meeting

  15. CMS High-Level Trigger Level 1 (MuonChambers+Calorimeters) Pb+Pbat 5.5 TeV Nominal luminosity ET reach x2 jets • High-Level Triggers (high ET-jet, γ, e, μ) • Large computing farm • (Start up with 7.2k CPU cores) • Run “offline algorithm” on every Pb+Pb events • Significantly enhanced statistics • for hard processes (see the right figure) ¡ Heavy-Ion Meeting

  16. Soft Probes of QCD Matter in CMS Heavy-Ion Meeting

  17. Charged Particle Multiplicity Total 66M Si Pixels Occupancy<2% at dNch/dη≈ 3500 Cluster shape or tracklet methods Needs only a few thousand events dNch/dh dNch/dh h Estimation of the Gluon Density Gluon Saturation Color Glass Condensate (CGC) h Heavy-Ion Meeting

  18. Hadron Spectra at Low pT Tracking: Pixel-Triplet Algorithm Efficiency pT [GeV/c] Relative resolution of pTrec Fake Rate |h|<1 pTsim [GeV/c] pT [GeV/c] Heavy-Ion Meeting

  19. Hadron Spectra at Low pT PID using the Gaussian unfolding method for dE/dx Pixels+Strips dN/dpT [c/GeV] dE/dx [MeV/cm] p [GeV/c] pT [GeV/c] pT [GeV/c] Hadron Chemistry Expansion Dynamics Equation-of-State Strangeness Production log(dE/dx [MeV/cm]) log(dE/dx [MeV/cm]) Heavy-Ion Meeting

  20. Elliptic Flow ReactionPlane Resolution dE/df [GeV] v2 (pT) dN/dDf Df f pT [GeV/c] • Open symbols: Simulated events • Close symbols: Reconstructed events Hydrodynamic Behavior QCD Equation-of-State Viscosity of Fluid Heavy-Ion Meeting

  21. Hard Probes of QCD Matter in CMS Heavy-Ion Meeting

  22. Percentage [%] Spectra at High pT Good Efficiency spT/pT [%] Low Fake Rate Importantfor the secondary vertex • dNch/d|h=0 3500 sz [cm] No trigger pT [GeV/c] pT [GeV/c] Heavy-Ion Meeting

  23. Spectra at High pT With high-ET HLT charged particle spectra can be measured up to pT ~300 GeV/c. MediumDensity 10% Central RAA pT [GeV/c] Transport Coefficient Heavy-Ion Meeting

  24. Jet Recon. in Calorimeters Iterative cone algorithm (R=0.5) with background subtraction • Spatial resolution • sf = 0.032, sh = 0.028 • which is smaller than • the calorimeter tower size 0.087ⅹ0.087 100 GeV jet ina Pb+Pb event,after the background subtraction • High efficiency • and purity • for ET>50 GeV • Good energy • resolution • for ET>100 GeV Heavy-Ion Meeting

  25. Jet Spectra Jet Energy Reconstruction • Pb+Pb (0.5 nb-1) Njet~6ⅹ106 Reconstructed ET (GeV) MC ET (GeV) • With high-ET jet HLT • jet spectra can be measured up to ET ~500 GeV for 1 year running @ nominal luminosity. HLT Min. Bias CMS can use true jets to study parton energy loss. Heavy-Ion Meeting

  26. Compton Bremsstrahlung Annihilation Fragmentation Photon-Tagged Jets Tagging parton energy g* (or Z0) →μ+μ- is being also studied g g (q) g (q) g (q) jet associated hadrons How is the energy loss distributed in the jet fragmentation cone? Background (NLO, Frag., Decay) Signal (LO) Heavy-Ion Meeting

  27. Photon-Tagged Jets ECAL cluster distributions in the most central 10% Pb+Pb After cuts: S/B=45 Before cuts: S/B=0.3 • Photons • - Cluster shape variable is used to differentiate isolated photons from mostly non-isolated hadrons (S/B was improved by factor ~15). • - ET(g) > 70 GeV Heavy-Ion Meeting

  28. Photon-Tagged Jets • Require the back-to-back g-jet correlation by Df(g,jet) > 3 rad. with ET(jet)>30 GeV PYQUEN p+p embedded in Pb+Pb event at 5.5 TeV Reco. FF = MC FF Depletion at high pT Enhancement at low pT Heavy-Ion Meeting

  29. Heavy Flavor (J/y) dNch/dη|η=0 =2500 • Pb+Pb (0.5 nb-1) BARREL+ Endcaps Events/0.4 GeV/c pT [GeV/c] The J/y spectra can be measured beyond 40 GeV/c using HLT. • σJ/Y=35 MeV/c2 for |h|<2.4 • S/B~5 for |h|<0.8 • NJ/y~1.8ⅹ105 for 0.5 nb-1 • Regeneration vs.Screening • J/ψ may survive up to 2TC (?) Heavy-Ion Meeting

  30. Heavy Flavor (¡) dNch/dη|η=0 =2500 • Pb+Pb (0.5 nb-1) Events/0.4 GeV/c pT [GeV/c] Suppression of ¡(1S) at LHC? • s¡ =54 MeV/c2 for |h|<0.8 • σ ¡=90 MeV/c2 for |h|<2.4 • S/B~1 for |h|<0.8 • N¡~2.6ⅹ104 for 0.5 nb-1 Heavy-Ion Meeting

  31. ¡ Production in UPC Strong E&M fields due to the coherent action of 82 protons (Egmax~80 GeV) Entries/60 MeV/c2 Entries/60 MeV/c2 Mee [GeV/c2] Mμμ [GeV/c2] ~500 ¡’s/0.5nb-1 Unexplored xG(x,Q2) region Heavy-Ion Meeting

  32. Summary • The CMS detector is versatile not only for pp, but also for heavy-ion collisions. • The CMS high-resolution trackers, calorimeters, and muon chambers cover almost 4p phasespace. • The CMS detector can measure various hard probes with the best resolution at the LHC. • The CMS detector can also measure soft hadrons for pT>200 MeV/c with good particle identification. Heavy-Ion Meeting

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