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Overview of Heavy-Ion Physics Program in CMS Byungsik Hong (Korea University) for the Collaboration Heavy-Ion Meeting, APCTP, Pohang, Korea September 25-26,

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Presentation on theme: "Overview of Heavy-Ion Physics Program in CMS Byungsik Hong (Korea University) for the Collaboration Heavy-Ion Meeting, APCTP, Pohang, Korea September 25-26,"— Presentation transcript:

1 Overview of Heavy-Ion Physics Program in CMS Byungsik Hong (Korea University) for the Collaboration Heavy-Ion Meeting, APCTP, Pohang, Korea September 25-26, 2009

2 Historical Remark September 25-26, 2009Heavy-Ion Meeting : A centennial Anniversary of Ion-Ion Collisions 1909 Rutherford gold foil experiment Beam: 5 MeV  + fixed Au (√s NN ~1 GeV) ⇒ 5.5 TeV(X5,000) # of collaborators: 3 (+Geiger+Marsden) ⇒ ~3,500(X1,000) Construction cost:(X ∞ ) 2009 LHC experiments

3 Outline 1.Motivation -Importance & challenges 2.CMS Detector -Acceptance -High-level trigger -Plan for the first Pb+Pb run 3.Heavy-Ion Physics Capability of CMS -Soft probes -Hard probes -Ultra-peripheral collisions 4.Summary September 25-26, 20093Heavy-Ion Meeting

4 Many Facets of QCD September 25-26, 2009Heavy-Ion Meeting4  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:

5 Origin of Visible Mass September 25-26, 2009Heavy-Ion Meeting5  QCD (i.e.  -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 -Connection between QCD & HI -Role of CMS for the detailed investigation of QCD B. Müller, arXiv:nucl_th/

6 Motivation September 25-26, 2009Heavy-Ion Meeting6 Characterizing the early stage by hard probes Color charge density, Transport coefficient, QCD ε c & T c, Tomography, … High p T spectra, Jets,  (or  *, Z 0 )-jet correlations, Quarkonia, … Characterizing the later stage by soft probes Hydrodynamics, QCD EoS, Medium viscosity,... dN ch /dη, Low p T spectra, Elliptic flow, Thermal photons, …

7 Initial Evidence at RHIC September 25-26, 2009Heavy-Ion Meeting7 Strongly coupled matter is hot & dense! Jet quenching: strong interaction of high-p T hadrons with dense medium Flow & NQ scaling: quark recombination & low  /s J/  suppression: SPS ≈ RHIC, larger at forward (CGC?) Jets are modified in medium.

8 What is New at LHC? September 25-26, 2009 LHC energies are far exceeding previous heavy-ion accelerators -A hotter, denser, and longer lived partonic matter 8Heavy-Ion Meeting ~ ~

9 Production Rate at LHC September 25-26, 20099Heavy-Ion Meeting -Large rates of various hard probes over a larger kinematic range -Plenty of heavy quarks (b & c) -Weakly interacting probes are available (W ± & Z 0 ) LHC RHIC SPS d 3  /dyd 2 p T [mb GeV -2 ] p T [GeV]

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 College Music Society Cryptographic Message Syntax Canadian Mathematical Society Classic Motorcycle Supplies Common Management System Credit Management Solutions Conceptual Models for Services … September 25-26, 2009Heavy-Ion Meeting10 Compact Muon Solenoid

11 September 25-26, Heavy-Ion Meeting

12 September 25-26, 2009 CASTOR T2 Collarshielding Forward Detectors (5.2 <  < 6.6) TOTEM ZDC (5.3 <  < 6.7) (z =  140 m) Beams EM HAD MUON BARREL Drift Tubes & RPCs  m ≈50 MeV at 10 GeV/c 2 SUPERCONDUCTING COILS IRON YOKE TRACKER Si Pixels & Strips Δp/p ≈1-2% Occupancy < 2% for central Pb+Pb Total weight : 12,500 t Overall diameter : 15 m Overall length : 21.6 m Magnetic field : 4 Tesla HCAL Cu-Scintillator Sampling ECAL PbWO 4 Crystals MUON ENDCAPS Cathode Strip Chambers & Resistive Plate Chambers (RPCs) CMS Detector 12Heavy-Ion Meeting

13 CMS Acceptance September 25-26, 2009 HCAL (Barrel+Endcap+Forward) Large Range of Hermetic Coverage -Extended kinematic reach x ~(1/40) of RHIC <10 -4 measurable 13Heavy-Ion Meeting

14 Plan for the First Pb+Pb Coll. September 25-26, 2009Heavy-Ion Meeting14 →2→2 Note from the Chamonix meeting: Early Pb Beam will have lower beam energy ⇒ 10 TeV in pp corresponds to 4 TeV in Pb+Pb. -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.

15 CMS High-Level Trigger September 25-26, 2009 Level 1 (Muon Chambers+Calorimeters) High-Level Triggers (high E T -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) High-Level Trigger Pb+Pbp+p Input Rate3 kHz (8 kHz peak)100 kHz Output Bandwidth225 MByte/sec Output Rate10 – 100 Hz150 Hz Rejection %99.85% Level 1 Pb+Pbp+p Collision Rate3 kHz (8 kHz peak)1 GHz Event Rate3 kHz (8 kHz peak)40 MHz L1 Accept Rate3 kHz (8 kHz peak)100 kHz Output Bandwidth100 GByte/sec E T reach x2 jets Pb+Pb at 5.5 TeV Nominal luminosity  15Heavy-Ion Meeting

16 September 25-26, 2009 Soft Probes of QCD Matter in CMS 16Heavy-Ion Meeting

17 Charged Particle Multiplicity September 25-26, 2009 Total 66M Si Pixels Occupancy<2% at dN ch /dη ≈ 3500 Cluster shape or tracklet methods Needs only a few thousand events Estimation of the Gluon Density Gluon Saturation Color Glass Condensate (CGC) 17Heavy-Ion Meeting  dN ch /d  

18 Hadron Spectra at Low p T September 25-26, 2009 Tracking: Pixel-Triplet Algorithm 18Heavy-Ion Meeting Relative resolution of p Trec p Tsim [GeV/c] Fake Rate |  |<1 p T [GeV/c] Efficiency p T [GeV/c]

19 Hadron Spectra at Low p T September 25-26, 2009 PID using the Gaussian unfolding method for dE/dx Hadron Chemistry Expansion Dynamics Equation-of-State Strangeness Production 19Heavy-Ion Meeting dE/dx [MeV/cm] Pixels+Strips p [GeV/c] log(dE/dx [MeV/cm]) p T [GeV/c] dN/dp T [c/GeV]

20 Elliptic Flow September 25-26, 2009 Hydrodynamic Behavior QCD Equation-of-State Viscosity of Fluid Reaction Plane Resolution 20Heavy-Ion Meeting - Open symbols: Simulated events - Close symbols: Reconstructed events dE/d  [GeV]   dN/d  p T [GeV/c] v 2 (p T )

21 September 25-26, 2009 Hard Probes of QCD Matter in CMS 21Heavy-Ion Meeting

22 Spectra at High p T September 25-26, Heavy-Ion Meeting Percentage [%] Good Efficiency Low Fake Rate No trigger p T [GeV/c]  p T /p T [%]  z [cm] Important for the secondary vertex p T [GeV/c] dN ch /d  |  =0  3500

23 Spectra at High p T September 25-26, 2009Heavy-Ion Meeting23 Medium Density Transport Coefficient With high-E T HLT charged particle spectra can be measured up to p T ~300 GeV/c. p T [GeV/c] R AA 10% Central

24 Jet Recon. in Calorimeters September 25-26, 2009 Iterative cone algorithm (R=0.5) with background subtraction High efficiency and purity for E T >50 GeV Good energy resolution for E T >100 GeV 100 GeV jet in a Pb+Pb event, after the background subtraction 24Heavy-Ion Meeting Spatial resolution  = 0.032,  = which is smaller than the calorimeter tower size ⅹ 0.087

25 Jet Spectra September 25-26, 2009Heavy-Ion Meeting25 CMS can use true jets to study parton energy loss. Pb+Pb (0.5 nb -1 ) Min. Bias HLT N jet ~6 ⅹ 10 6 With high-E T jet HLT jet spectra can be measured up to E T ~500 GeV for 1 year nominal luminosity. Reconstructed E T (GeV) MC E T (GeV) Jet Energy Reconstruction

26 Photon-Tagged Jets September 25-26, 2009  * (or Z 0 ) →μ + μ - is being also studied  associated hadrons jet g (q) How is the energy loss distributed in the jet fragmentation cone? 26Heavy-Ion Meeting Tagging parton energy Compton Annihilation Bremsstrahlung Fragmentation Signal (LO) Background (NLO, Frag., Decay)

27 Photon-Tagged Jets September 25-26, 2009   Photons - Cluster shape variable is used to differentiate isolated photons from mostly non-isolated hadrons (S/B was improved by factor ~15). - E T (  > 70 GeV 27Heavy-Ion Meeting ECAL cluster distributions in the most central 10% Pb+Pb After cuts: S/B=45 Before cuts: S/B=0.3

28 Photon-Tagged Jets September 25-26, 2009  Require the back-to-back  -jet correlation by  ( ,jet) > 3 rad. with E T (jet)>30 GeV Depletion at high p T Enhancement at low p T 28Heavy-Ion Meeting PYQUEN p+p embedded in Pb+Pb event at 5.5 TeV Reco. FF = MC FF

29 Heavy Flavor (J/  ) September 25-26, 2009 BARREL+ Endcaps dN ch /d η| η=0 = 2500 Regeneration vs. Screening J/ψ may survive up to 2T C (?) The J/  spectra can be measured beyond 40 GeV/c using HLT. 29Heavy-Ion Meeting  σ  J   =35 MeV/c 2 for |  |<2.4  S/B~5 for |  |<0.8  N J  ~1.8ⅹ10 5 for 0.5 nb -1 Pb+Pb (0.5 nb -1 ) p T [GeV/c] Events/0.4 GeV/c

30 Heavy Flavor (  ) September 25-26, 2009 dN ch /d η| η=0 = 2500     54 MeV/c 2 for |  |<0.8  σ   =90 MeV/c 2 for |  |<2.4  S/B~1 for |  |<0.8  N  ~2.6ⅹ10 4 for 0.5 nb -1 30Heavy-Ion Meeting Suppression of  (1S) at LHC? Pb+Pb (0.5 nb -1 ) p T [GeV/c] Events/0.4 GeV/c

31  Production in UPC September 25-26, 2009 Strong E&M fields due to the coherent action of 82 protons (   max ~80 GeV) ~500  ’s/0.5nb -1 Unexplored xG(x,Q 2 ) region 31Heavy-Ion Meeting M ee [GeV/c 2 ] Entries/60 MeV/c 2 M μμ [GeV/c 2 ] Entries/60 MeV/c 2

32 Summary 1.The CMS detector is versatile not only for pp, but also for heavy-ion collisions. 2.The CMS high-resolution trackers, calorimeters, and muon chambers cover almost 4  phase space. 3.The CMS detector can measure various hard probes with the best resolution at the LHC. 4.The CMS detector can also measure soft hadrons for p T > 200 MeV/c with good particle identification. September 25-26, Heavy-Ion Meeting


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