Probing the Medium at RHIC via J Production

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Probing the Medium at RHIC via J/? Production

• Abigail Bickley
• University of Colorado
• November 10, 2005

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Phase Diagrams of Matter
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Cosmology
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Quantum Chromodynamics
Confinement
Asymptotic Freedom
q
q
q
q
q
q
q
q

• QCD potential between color carriers increases
  with distance
• Energy required to separate quark pair greater
  than the rest mass of the pair

• QCD potential weak at small distances
• Quarks behave as if they are unbound

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Relativistic Heavy Ion Collider
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Relativistic Heavy Ion Collider
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Relativistic Heavy Ion Collider
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The Ring

• 5x1026 cm-2s-1 store averaged luminosity
• 109 ions per bunch
• 45 bunches per fill
• 15 kHz collision rate
• 2 kHz PHENIX daq rate

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The Data
Run Species s1/2 GeV NTot
Data Size 01 AuAu 130 10M
3 TB 02 AuAu 200
170M 10 TB pp
200 3.7G 20 TB 03 dAu
200 5.5G 46 TB
pp 200 6.6G 35 TB
04 AuAu 200 1.5G 270 TB
AuAu 62 58M
10 TB 05 CuCu 200 8.6G
173 TB CuCu 62
0.4G 48 TB CuCu
22.5 9M 1 TB pp
200 85B 262 TB
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Collision Evolution
1 fm/c 3x10-24 seconds
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Collision Evolution
1 fm/c 3x10-24 seconds
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Collision Evolution
Quarks and gluons combine to form particles, but
inelastic collisions continue.
1 fm/c 3x10-24 seconds
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Collision Evolution
Inelastic collisions cease Final particle
yields fixed.
1 fm/c 3x10-24 seconds
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Collision Evolution
Elastic collisions cease Particles travel to
detector.
1 fm/c 3x10-24 seconds
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Global Properties of the Collision System
PHOBOS

• Multiplicity
• How many particles are generated?
• Pseudorapidity
• ? -ln tan(?/2)

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Collision Centrality

• Physically characterized by impact parameter
• BUT
• Not experimentally observable

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Collision Centrality
participant
spectator

• Npart the number of participating nucleons
  (2-392, Au)
• OR
• Ncoll the number of binary collisions (1-1200,
  Au)

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J/?s in the Medium

• Quarkonia Production -
• hard scattering processes result in the
• production of heavy quark pairs that interact
• with the collision medium during hadronization
• In medium interactions convey information about
  the fundamental properties of the medium itself
• Competing effects are predicted to govern J/?
  production
• J/? color screening
• Suppression of J/? yield with increasing
  collision centrality
• J/? recombination
• Increased J/? yield with increasing collision
  centrality
• Narrowed J/? rapidity and pT distributions with
  increasing centrality
• Shadowing, Heavy quark energy loss, Normal
  nuclear absorption, etc

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Early Predictions Matsui Satz

• J/? Suppression by Quark-Gluon Plasma Formation,
  PLB 178, 461 (1986).
• It is concluded that J/ ? suppression in nuclear
  collisions should provide an unambiguous
  signature of quark-gluon plasma formation.
• Color screening
• Color charge of one quark masked by the
  surrounding quarks
• Prevents cc-bar binding in the interaction region
• Characterized by Debye screening radius (rD)
• If the screening radius is smaller than the J/ ?
  radius then the quarks are effectively masked
  from one another

rD
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Early Predictions Matsui Satz

• Both the screening and J/? radii are temperature
  dependent
• J/? radius (rJ/?)
• T0
• Radius dominated by confining potential
• 0.2 rJ/? 0.5 fm
• TTc
• Include color screened coulombic potential
• 0.5 rJ/? 1.3 fm
• Screening radius (rD)
• Calculated from lattice QCD
• Tc fixed at 200 MeV
• rD 0.2 fm

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Recombination

• J/? Suppression Models
• assume heavy quarkonia are formed only during the
  initial hard nucleon-nucleon collisions
• Subsequent interactions only result in additional
  loss of yield
• Recombination Models
• In central heavy ion collisions more than one
  c-cbar pair is formed
• Regeneration of J/? pairs possible from
  independently produced c and cbars
• Leads to an enhancement of J/? yield (or less
  dramatic suppression)

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• Charm Anticharm Quark Production

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• Charm Anticharm Quark Production
• J/? Formation Models

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• J/? Decay Channels

J/? ? hadrons 87.7
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• J/? Decay Channels

J/? ? hadrons 87.7
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The PHENIX Experiment
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PHENIX Detector Muon Arms

• J/? ? ? ?-
• Reconstruct dimuon candidates at forward
  rapidities
• Coverage p gt 2GeV/c, 1.2 lt y lt 2.2, ???????

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PHENIX Detector Central Arm

• J/? ? e e-
• Reconstruct dielectron candidates at mid-rapidity
• Coverage p gt 0.2GeV/c, ? lt 0.35, ??????

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Lots of J/?s!
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Invariant Mass Plots
PHENIX
PHENIX
Raw J/? signal visible above the combinatorial
and physical background of like sign dimuon and
dielectron pairs
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Invariant Mass Plots
PHENIX
PHENIX
Raw J/? signal visible above the combinatorial
and physical background of like sign dimuon and
dielectron pairs
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Invariant Mass Plots
PHENIX
PHENIX
Like sign subtraction method used to isolate J/?
signal Integrate over mass range of 2.6-3.6
GeV/c2
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Acceptance Efficiency
PHENIX

• Detector geometrical coverage
• Detector hardware performance
• Trigger efficiency
• Reconstruction efficiency

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J/? Invariant Yield
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Comparing Systems and Energies

• PHENIX data
• AuAu 200GeV
• CuCu 200GeV
• CuCu 62GeV
• pp 200GeV
• dAu 200GeV
• Nuclear Modification Factor (RAA)
• Scale measured invariant yield by invariant yield
  found in pp collisions at the same energy
• Account for differing number of nucleons by
  scaling by the number of binary collisions

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CuCu AuAu Data
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Nuclear Modification Factor
System size comparison at forward rapidity
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Nuclear Modification Factor
System size comparison at mid rapidity
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Nuclear Modification Factor
Rapidity comparison in AuAu 200 GeV
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Nuclear Modification Factor
Rapidity comparison in CuCu 200 GeV
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Nuclear Modification Factor
Energy comparison in CuCu 200 62 GeV
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CuCu Theory
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What do the theorists predict??
Theory Curves R. Vogt nucl-th/0507027
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What do the theorists predict??
Theory Curves R. Vogt nucl-th/0507027, A.
Capella hep-ph/0505032
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What do the theorists predict??
Theory Curves R. Vogt nucl-th/0507027, A.
Capella hep-ph/0505032
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AuAu Theory
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What do the theorists predict??
Cold nuclear matter models
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What do the theorists predict??
Suppression models w/o regeneration
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What do the theorists predict??
Suppression models with regeneration
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Rapidity Dependence

• Shape of rapidity dependence of J/? yield
  consistent as a function of centrality
• No difference observed between CuCu and pp
  distributions at 200GeV

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Rapidity Dependence

• Shape of rapidity dependence of J/? yield
  consistent as a function of centrality
• No difference observed between CuCu and pp
  distributions at 200GeV
• Rapidity narrowing predicted by recombination
  models clearly not present

AuAu
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What have we learned?

• Cold nuclear matter models - do not exhibit J/?
  suppression observed in the data
• Suppression models
• Comovers
• Instantaneous melting in QGP
• Parton collisions in QGP
• Regeneration models
• Reproduction via D Dbar (HSD)
• Charm quark coalescence
• Statistical hadronization
• While the theoretical models help with the
  interpretation of the data, none provide an
  unambiguous message

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What have we learned?

• Suppression factor of x3 in central AuAu
• Suppression factor of x2 in central CuCu
• Nuclear modification factor
• Little difference observed between the different
  system sizes
• Little difference observed between the different
  system energies
• Little difference observed as a function of
  rapidity
• The real surprise is the similarities in all of
  the distributions gt none of the models account
  for this observation

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Transverse Momentum Dependence
fit to extract ltpt2gt
CuCu 200GeV
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Transverse Momentum Dependence
R.L. Thews, PHENIX Muon Workshop, June 13, 2005.

• Data ltpT2gt is consistent with flat as a function
  of centrality
• Theory Red shows NLO calculation without
  recombination
• Blue shows effect of including J/? produced via
  recombination

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Npart Scaling

• J/? yield scaled by the number of participants is
  consistent with flat when plotted versus
  centrality

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Collision Probes

• Direct Photons - high energy photons created in
  the collision pass unimpeded through the medium
• Jets - high energy sprays of back to back
  particles
• Flow - system expansion
• HBT - source size and lifetime
• Quarkonia Production - hard scattering processes
  result in the production of heavy quark pairs
  that interact with the collision medium during
  hadronization