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Bolek Wyslouch Massachusetts Institute of Technology for the CMS Collaboration

c. a. b. d. CMS Experiment at LHC: Detector Status and Physics Capabilities in Heavy Ion Collisions. Bolek Wyslouch Massachusetts Institute of Technology for the CMS Collaboration. Winter Workshop Big Sky, MT February 2009.

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Bolek Wyslouch Massachusetts Institute of Technology for the CMS Collaboration

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  1. c a b d CMS Experiment at LHC: Detector Status and Physics Capabilities in Heavy Ion Collisions Bolek Wyslouch Massachusetts Institute of Technology for the CMS Collaboration Winter Workshop Big Sky, MT February 2009 CMS HI groups: Athens, Auckland, Budapest, CERN, Colorado, Cukurova, Ioannina, Iowa, Kansas, Korea, Lisbon, Los Alamos, Lyon, Maryland, Minnesota, MIT, Moscow, Mumbai, Paris, Seoul, Vanderbilt, UC Davis, UI Chicago, Zagreb

  2. Heavy Ion Physics at the LHC Pb+Pb Collisions at sNN ~ 5.5TeV Large Cross section for Hard Probes High luminosity 1027/cm2s • Copious production of high pT particles • Nuclear modification factors RAA out to very high pT • Large cross section for J/ψ and family production • sccLHC ~ 10x sccRHIC • sbbLHC ~ 100x sbbRHIC • Different “melting” for members of  family with temperature • Large jet cross section • Jets directly identifiable • Study in medium modifications

  3. Z0  J/y Saturation Coverage Rate/Trigger Kinematics at the LHC Access to widest range of Q2 and x

  4. CMS detector at the LHC SUPERCONDUCTING HCAL ECAL COIL Plastic scintillator/brass sandwich Scintillating PbWO4 crystals IRON YOKE human TRACKER Silicon Microstrips Si Pixels MUON ENDCAPS Length: 21.6 m Diameter: 15 m Weight: ~12500 tons Magnetic Field: 4 Tesla MUON BARREL Cathode Strip Chambers (CSC )‏ Resistive Plate Drift Tube Chambers ( DT ) Resistive Plate Chambers (RPC‏ Chambers ( RPC )

  5. CMS detector will extend deep into LHC • CMS (+TOTEM): Largest phase-space coverage ever in a collider. Dh~14 TOTEM RPs -420m TOTEM T2 (FP420)‏ ZDC TOTEM T2 TOTEM RPs CASTOR ZDC funded by US DOE NP & NSF CASTOR ZDC 420m (FP420)‏

  6. Particle detection layers in CMS

  7. LHC proton beam on September 10th CMS recorded several splash events when the proton beam was steered onto the collimators; halo muons were observed once beam started passing through CMS Detectors flooded by few hundred thousand muons resulting from 109 protons (one bunch) simultaneous hitting a collimator Correlation between the energies collected in the HCAL and ECAL calorimeters from several “beam-collimator collisions”

  8. Cosmic Muons in CMS A cosmic muon that traversed the barrel muon systems, the barrel calorimeters, and the silicon strip and pixel trackers Improved track quality in the strip trackeras the nominal design geometry is replaced by versions aligned with cosmic muons

  9. Tracker Performance • On track Strip clusters S/N ratio, corrected for the track angle • TOB thick sensors: S/N = 32 • TIB/TID thin sensors: S/N = 27/25 • TEC (mixed thickness): S/N = 30 Entries • Track hit finding efficiency • TIB and TOB layers S/N Layer • Muon momentum distribution • high quality tracks (8 hits, one in TIB layers 1-2, one in TOB layers 5-6) • Partial CRAFT statistics (expected >70K tracks at PT>100 GeV for full CRAFT)

  10. Physics cases for HI@CMS Case no. We will look into… in order to learn about… 0 MB L1 trigger, centrality Global event characterization 1 dNch/dη Color Glass Condensate, xGA(x,Q2) 2 Low pT π/K/p spectra Hydrodynamics, Equation of State 3 Elliptic Flow Hydrodynamics, Medium viscosity 4 Hard-probes (triggering) Thermodynamics & transport properties 5 Quarkonia suppression εcrit, Tcrit ^ Parton density, <q> transport coefficient 6 Jet “quenching”

  11. 3<||<5 HF pp Minimum Bias using Forward HCAL Min-bias trigger: Number of HF trigger towers over threshold > N: any side (OR), or on both sides (AND) of I.P. Unfolding the effect of HF min-bias triggering on physical measurements preliminary preliminary Re-weighted charged-particle multiplicity per evt. AND OR all evts Inverse weighting  

  12. d2N/dydpT  Simulation “Data” K p k p k  p dE/dx (MeV/cm)  CMS Si-Strip CMS Si-Pixel 0 1 2 pT (GeV) 0.1 1 10 pT (GeV) 0.1 1 10 pT (GeV) Charged-Hadron Spectra pp • One of the first measurements to be done: charged-hadron spectrum • Important tool for calibration, alignment & understanding of detector response • Min-bias and/or Zero-bias trigger • Statistics: ~ 2 million events

  13. Occupancy in Pb+Pb dN/dy = 3500 1-2% in Pixel Layers < 10% in outer Strip Layers Efficiency ~75% above 1 GeV/c CMS Tracking Performance PbPb • Efficiency • Fake Rate Pb+Pb, dN/dy = 3500 Pb+Pb, dN/dy = 3500 Pb+Pb, dN/dy = 3500 Transverse Longitudinal Pb+Pb, dN/dy = 3500 CDF World’s best momentum resolution Excellent impact parameter resolution

  14. CMS Trigger and DAQ in Pb+Pb vs p+p Level 1 trigger - Uses custom hardware - Muon tracks + calorimeter information - Decision after ~ 3μsec High level Trigger - ~1500 Linux servers (~10k CPU cores) - Full event information available - Runs “offline” algorithms to be partially funded by US DOE NP

  15. Hard Probes: HLT vs Min Bias J/Y and Jet reconstruction available at HLT Example trigger table: HLT improves hard probe statistics by more than a factor of 10! Rates to tape with HLT Min bias with HLT Min bias

  16. ● produced in 0.5 nb-1 ■ rec. if dN/d ~ 2500 ○ rec. if dN/d ~ 5000  Statistical reach curves fromNucl. Phys.B492(1997) 301–337 Quarkonia: → • Expected rec. quarkonia yields: • J/ : ~ 180 000 •  : ~ 26 000 • Detailed studies of Upsilon family feasible with HLT • Statistical accuracy (with HLT) of expected’ /  ratio versus pT -> model killer...

  17. Heavy Ion Jet Finder Performance • A modified iterative cone algorithm running on calorimeter data gives good performance in Pb Pb collisions • Offline jet finder will run in the HLT • Other jet algorithms are being studied Good Resolution High Efficiency Pb+Pb dN/dy = 5000 p+p Jet studies from CMS Note 2003/004

  18. High pT Suppression Clear separation of different energy loss scenarios Efficient jet trigger is essential to extend the pT range

  19. Jet ET reach • Jet spectra up to ET ~ 500 GeV (Pb-Pb, 0.5 nb-1, HLT-triggered) • Detailed studies of medium-modified (quenched) jet fragmentation functions

  20. Jet axis Hadrons q,g q,g q,g Photon Photon-tagged jet fragmentation functions DOE Review Driven.. Jet axis provides parton direction Multiplicity and flow measurements characterize density, path length Charged hadron tracks used to calculate z = pT/ET Measure jet fragmentation function: dN/dξ with ξ=-log z Photon energy tags parton energy ET Ingredients: Main advantage • Event/Centrality selection • Reaction plane determination • Vertex finding • Track reconstruction • Jet finding • Photon identification • Photon unaffected by the medium • Avoids measurement of absolute jet energy All results based on full GEANT-4 simulations using full reconstruction algorithms on expected one run-year statistics

  21. Photon-tagged fragmentation functions generator- level 172o 172o σ~13% generator-level • Use isolated photons + “back-to-back” cut on azimuthal opening angle between the photon and the jet to suppress NLO and background events • Determines FF with <10% deviation LO NLO

  22. Signal and background statistics • Study for one nominal LHC Pb+Pb run “year” • 106 sec, 0.5nb-1, 3.9 x 109 events • Use 0-10% most central Pb+Pb • dN/dη|η=0~2400 • Simulate signal and background QCD (p+p) events • Mix into simulated Pb+Pb events (~1000 events)‏ generator-level Total 122158 Total 37490

  23. Reconstruction • Tracking • Low pT cutoff at 1GeV/c • Efficiency (algorithmic + geometric) ~ 50-60% • Fake rate ~ few % • Jet finding • Iterative cone algorithm with underlying event subtraction (R=0.5)‏ • Performance studies on away-side jet finding • Photon ID • Reconstruction of high-ET isolated photons Tracking: NIM A566 (2006) 123 Jet finding: Eur. Phys. J. 50 (2007) 117

  24. Photon identification performance Quenched Pb+Pb S/B=4.5 S/B=0.3 Before cuts: After cuts: WP=60% Seff Photon isolation and shape cuts improve S/B by factor ~15 ET >70GeV

  25. Fragmentation function ratio Reco quenched Pb+Pb / MC unquenched p+p • Medium modification of fragmentation functions can be measured • High significance for 0.2 < ξ < 5 for both, ET >70GeV and ET >100GeV ET >70GeV ET >100GeV

  26. Few words about schedule • Just announced by DG in a short e-mail, result of discussions at the annual “Chamonix” planning meeting • LHC will get physics data at the end of 2009 • There is a strong recommendation to run during winter • Collect 200 pb-1 pp at 5 TeV/beam and finish it with the short HI run (10 TeV Ecm pp ~ 4 TeV/nucleon PbPb) • More details will be available in the next few weeks.

  27. Summary • The CMS detector has excellent capabilities to study the dense QCD matter produced in very high energy heavy-ion collisions, through the use of hard probes such as high-ET (fully reconstructed) jets and heavy quarkonia • With a high granularity inner tracker (full silicon, analog readout), a state-of-the-art crystal ECAL, large acceptance muon stations, and a powerful DAQ & HLT system, CMS has the means to measure charged hadrons, jets, photons, electron pairs, dimuons, quarkonia, Z0, etc ! • The CMS Heavy Ion group is busily preparing for the upcoming physics runs in pp and PbPb

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