LHC HeavyIon Program a CMS Perspective

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LHC Heavy-Ion Program a CMS Perspective

• Edwin Norbeck
• University of Iowafor the CMS Collaboration

20th Winter Workshop on Nuclear Dynamics
CMS HI groups Athens, Auckland, Demokritos,
Dubna, Lyon, MIT, Moscow, Rice, Tbilisi, U
Ioannina, U Iowa, U Kansas, UC Davis, UI
Chicago, UC Riverside,
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The experiments
ALICE dedicated HI experiment
CMS pp experiment with HI program

• ATLAS pp experiment, HI proposal in progress

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The Physics Landscape PbPb Collisions
SPS-gtRHIC-gtLHC
Extrapolation of RHIC results favors low values
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Heavy Ion Physics at the LHC

• Medium modification at high pT
• Copious production of high pT particles
• Different melting for members of ? family
• Large cross section for J/? and ? family
  production
• Correlations, scattering in medium
• Large jet cross section, jets directly
  identifiable

?
J/?
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CMS as a Detector for Heavy Ion Physics

• Fine Grained High Resolution Calorimeter
• Hermetic coverage up to hlt5
• (hlt7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
• Tracking m from Z0, J/?, ?
• Wide rapidity range hlt2.4
• sm 50 MeV at ?
• Silicon Tracker
• Good efficiency and low fake rate for pTgt1 GeV
• Excellent momentum resolution Dp/p1 for pTlt25
  GeV and higher

• DAQ and Trigger
• High rate capability for AA, pA, pp
• High Level Trigger capable of full reconstruction
  of most HI events in real time

m chambers
HF
Fully functional at highest expected
multiplicities Detailed studies at 3000-5000 and
cross-checks at 7000-8000
Solenoid with Si Tracker, ECAL and most of HCAL
inside
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CMS under construction
Magnet Muon Absorber
Hadron Calorimeter
Si tracker Pixels
Electromagnetic Calorimeter
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CMS Detector in the Heavy Ion Environment
High Multiplicity of Low pT Hadrons Occupancies
still Reasonable Large Event Size but Lower Event
Rate
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CMS as a Heavy Ion Experiment

• Excellent detector for high pT probes
• High rates and large cross sections
• quarkonia (J/? ,?) and heavy quarks (bb)
• high pT jets
• high energy photons
• Z0
• Correlations
• jet-g
• jet-Z0
• multijets
• Global event characterization
• Energy flow to very forward region
• Charged particle multiplicity
• Centrality
• Azimuthal asymmetry
• CMS can use highest luminosities available at LHC
  both in AA and pA modes

-
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Global Measurements dNch/d? (single event) a la
Phobos

• Use high granularity pixel detectors
• Use pulse height measurement of pixel clusters to
  reduce background
• Very low pT reach, pTgt26 MeV ! (inner pixel layer
  at R45 mm)

Ecluster
Preliminary
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Azimuthal asymmetry, calorimeters

• Use highly segmented calorimeters to determine
  event plane
• Simulations of PbPb with b6 fm

s0.1 rad
Event plane determination
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Quarkonia in CMS
? family
J/?
Yield/month (k events, 50 eff) Nominal
luminosity for each ion species
 
PbPb, 1 month at L1027
 
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High Mass Dimuon, Z0 Production

• Z0-gtmm can be reconstructed with high efficiency
• A probe to study nuclear shadowing
• Z0 also proposed as reference for ? production.
• Dimuon continuum dominated by b decays
• Heavy quark energy loss
• High statistics (1 month)

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sz190 mm
Vertex Reconstruction
Outside-In
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Jet Reconstruction in CMS using Calorimeters
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Charged Particle Jet Studies in CMS

• Detailed study of phenomena which are already
  apparent at RHIC
• Study the centrality dependence of
• Charged particle spectra starting at pT1 GeV
• Possibly lower pT cutoff with reduced B field
• Back-to-back correlations a la STAR
• Azimuthal asymmetry vs. pT

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Performance of the Track Reconstruction
Inside-Out

• Match Reconstructed tracks to MC input on a hit
  by hit basis
• (Event sample dN/dy 3000 one 100 GeV
  Jet/Event)

DpT/pT lt 1
h lt 0.7
Efficiency
Fakes
Tracking efficiency

• The increased local track density in a jet-cone
  leads to a decrease in reconstruction efficiency
  of 5-10
• Can be corrected for since jets will be
  reconstructed by the calorimetry

Fake tracks
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Jet fragmentation
Longitudinal momentum fraction z along the thrust
axis of a jet
pT relative to thrust axis

• Fragmentation function for 100 GeV Jets embedded
  in dN/dy 5000 events.

High precision tracking out to high momenta will
allow for detailed jet shape analysis to study
the energy loss mechanism
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Heavy Ion Trigger

• Main types of trigger as required by physics
• multiplicity/centrality min-bias,
  central-only
• high pT probes muons, jets, photons, quarkonia
  etc.
• High occupancy but low luminosity !
• many low level trigger objects may be present,
  but less isolated than in pp, Level 1 might be
  difficult for high pT particles
• but we can read most of the events up to High
  Level Trigger and do partial reconstruction
• HLT for HI needs significant software/simulation
  effort.

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CMS Forward Calorimeter 3 lt ? lt 5
36 x 2 72 Wedges with a total of 500,000 fibers
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CMS Very Forward Region CASTOR, TOTEM and ZDC
CASTOR
CASTOR Coverage

• Multiplicity and hermetic coverage to ?lt7
• Zero Degree Energy
• Physics
• Centrality
• Limiting Fragmentation
• Peripheral and ultra-peripheral collisions
• Low-x, Color-Glass Condensate
• DCC, Centauros, Strangelets

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CMS Very Forward Region CASTOR, TOTEM and ZDC
ZDC
TOTEM Roman Pots
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PPAC Test at ANL
PPAC under beam line to beam dump
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Energy Resolution Data of PPAC Test at ANL
Ratio Efront to Eback is constant to within 2
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Conclusions

• LHC will extend energy range and in particular
  high pT reach of heavy ion physics
• CMS is preparing to take advantage of its
  capabilities
• Excellent coverage and resolution
• Quarkonia
• Jets
• Centrality, Multiplicity, Energy Flow reaching
  very low pT
• Essentially no modification to the existing
  detector hardware
• New High Level Trigger algorithms
• Zero Degree Calorimeter, CASTOR and TOTEM as
  important additions extending forward coverage
• Heavy Ion program is well integrated into overall
  CMS Physics Program
• The knowledge gained at RHIC will be extended to
  the new energy domain