CMS Heavy Ion Physics

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CMS Heavy Ion Physics

• Edwin Norbeck
• University of Iowa

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Energy for Pb Pb at LHC

• Beam is 7 TeV/charge?s 5.5 TeV/nucleon pairor
  1140 TeV total.
• Total energy, ?mc2, in center of mass is 30 ?
  energy at RHIC.
• Energy density ?2 900 ? energy density at RHIC

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Large Hadron Collider at CERN
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What To Expect from LHC

• LHC (Large Heavy ion Collider) is expected to
  provide pA and AA collisions.
• Energy 7 TeV/charge
• 6 weeks/year
• First heavy ion run in March 2007

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The experiments

• CMS pp experiment with approved Heavy Ion
  program, lt50 HI physicists (out of 2000)

ALICE dedicated HI experiment, 900 collaborators
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Pile-up problems

• For CMS
• None for Pb Pb (125 ns between bunches)
• None for p p (25 ns between bunches)
• For Ca Ca should reduce luminosity by 10 (25 ns
  between bunches)
• For ALICE
• None for Pb Pb
• For p p reduce luminosity by factor of 104

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CMS High pt edge of HI physics
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Stretching CMS
Pb-Pb
??mm
Detector designed for pp. However due to flexible
design offers unique capabilities for AA
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Some CMS Assets

• CMS has excellent muon detection capabilities
• hlt1.3 for barrel and hlt2.4 with endcaps.
• Good mass resolution 46 MeV for the Upsilon.
• Efficient suppression of background from p/K
  decays
• Electromagnetic calorimeter at 1.3 m from beam
  axis.
• PT threshold at 3.5 GeV/c for a single muon to
  reach the m-chambers.
• Large calorimeter coverage with good jet
  reconstruction capabilities.

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Selected Physics Topicsfirst physics studies by
CMS

• Event Characterization
• Quarkonium Production Upsilon and J/Y in the
  barrel
• Z detection
• Jet Production
• Single/Double jet ratios, jet quenching
• Z and g tagged jets
• Ultra-Peripheral Collisions gg and g-Pomeron

Muon detector
Calorimetry
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Particle production in Heavy Ion collision, signs
of QGP

• mass and width of resonances (r, w)
• thermal photons or dileptons (ee- , mm-)
• strangeness enhancement (K, f, L, X, W)
• energy loss of initial partons (jet quenching)
• suppression of heavy-quark bound states (J/y ,
  s ? mm-)

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Tracking
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Detector Pitch mm

• Developed for dNch/dy8000 and dN0/dy4000.
• Track only particles with tracks in m detector.
• Use m-chambers tracks as seeds.
• Use only tracking detector providing 3D space
  points.

MSGC 200
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MSGC 240
Silicon 147
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Occupancy ()
30
20
10
0
60
70
80
90
100
110
120
Radius of tracking layer (cm)
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Quarkonia Cross Sections
Production Cross Sections for CMS studies

• A scaling law sAA A2a spp
• spp from CDF _at_ 1.8 TeV extrapolated to 5.5(7)
  TeV. (central 2300)
• a0.9(0.95) for J/Y (Upsilon).

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Most products at small angles
Simulations for pp show average per event of 760
GeV into 3 lt lt 5 (HF) 0.8 to 5.7 100 GeV
into -3 lt lt 3 (rest of CMS) In HF most of the
760 GeV is at small angles. For Pb Pb ?
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HF Longitudinal Segmentation
0.6 mm quartz fibers in iron
TC (30 cm)
HAD (143 cm)
EM (165 cm)
Half a million quartz fibersviewed with 2400
phototubes
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Shower and jets in HF (forward calorimeter)

• Radius (80) of e.m. shower 2.5 cm
• Radius (80) of hadron shower 5 cm
• For jet radius h 0.3 h(jet) radius in
  HF 3
  (5.7) 35 cm
  4 (2.1) 14 cm
  5 (0.77) 4.7cm h ? -ln
  tan(?/2) ? rapidity for p gtgt m tanh(h) cos (?)

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Higgs tagging jets

• Heavy Higgs 2mZ or 2mW lt mHlt 1 TeV
• qq ? (WW, ZZ ? H)jj
• For jets 2 lt lt 5
• But 3 lt lt 5 seen only in HF

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Response to Electrons and Pions

• HF responds linearly within 1 to electrons in
  the energy range tested (6 200 GeV). The pion
  (neg) response is highly nonlinear.

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Beam-beam interactions

• Hadronic nuclear interactions
• Electromagnetic dissociation
• Ion is excited by a - nucleon interaction
  (mostly by the giant dipole resonance) and
  subsequently decays.
• Electron capture to form H-like ion
• A two-photon process creates an electron-positron
  pair with the electron retained in an atomic
  orbit (mostly the K-shell).
• Magnetic-monopole production?

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Summary

• LHC will be a natural continuation of the series
  of Heavy Ion accelerators
• CMS will have unique capabilities at the high
  transverse momentum frontier
• ?, Z0, g, high pt jets
• CMS can provide a natural place to do these
  measurements in the late-RHIC and post-RHIC era
• Complementary to RHIC

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6th Workshop on Heavy Ion Physics with CMS
detector at the LHC
High pt heavy ion physics at the LHC
Massachusetts Institute of TechnologyFebruary
8-9, 2002Cambridge, MA
http//bolek.lns.mit.edu or wyslouch_at_mit.edu Offi
ce [phone] Cell (781 354-5023