Measurement of the EMC Effect in Light Nuclei and at Large x

1
Measurement of the EMC Effect in Light Nuclei and
at Large x

• Dave Gaskell
• Jefferson Lab
• NuINT07
• May 31 2007
• Motivation Why more studies of the EMC Effect?
• JLab Experiment E03-103
• Some preliminary results

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EMC Effect and Quark Distributions in Nuclei

• Measurements of (EMC, SLAC, BCDMS)
  have demonstrated modification of quark
  distributions in nuclei
• x-dependence is the same for all nuclei
• Shadowing x
• Anti-shadowing 0.1
• EMC effect x0.3
• Size of the effect depends
  on A (i.e., minimum at
  
  x0.7)

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Explaining the EMC Effect

• Models of the EMC Effect fall into two broad
  categories
• Conventional nuclear physics approaches these
  can include
• Fermi motion alone or with binding effects
• More realistic nuclear structure (spectral
  functions)
• Exchange mesons (nuclear pions)
• Exotic models some examples are
• Multiquark clusters
• Dynamical rescaling
• All models can (approximately) describe the EMC
  effect region
• Some inconsistent with other data (Drell-Yan)
• Others fail to describe all x
• Some describe the EMC effect ignoring
  binding/conventional nuclear effects

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Explaining the EMC Effect (II)
Benhar, Pandharipande, and Sick Phys. Lett. B410,
79 (1997)

• Exotic Models
• Dynamical rescaling
• Multiquark clusters

• Conventional Models
• Some combination of Fermi
• motion and binding
• Fermi motion binding
• nuclear pions

K.E. Lassila and U.P. Sakhatme Phys. Lett. B209,
343 (1988)
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Existing EMC Data
SLAC E139

• SLAC E139 most extensive and precise data set for
  x0.2
• Measured sA/sD for A4 to 197
• 4He, 9Be, C, 27Al, 40Ca, 56Fe, 108Ag, and 197Au
• Size at fixed x varies with A, but shape is
  nearly constant
• Data set could be improved with
• Higher precision data for 4He
• Addition of 3He data
• Precision data at large x

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JLab Experiment E03-103

• Measurement the EMC Effect in Light Nuclei (He3
  and He4) and at large x
• He3, He4 amenable to calculations using exact
  nucelar wave functions
• Large x dominated by binding, conventional
  nuclear effects
• Ran in Hall C at JLab
  summer and
  fall 2004
  (w/E02-109 see Donal
  
  Days talk)
• A(e,e) at 5.77 GeV
• Targets H, 2H, 3He,
  4He,
  Be, C, Al, Cu,
  and Au
• Six angles to measure
  Q2 dependence

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EMC Effect at Low W2

• At large x (0.6), E03-103 not in canonical DIS
  regime? W24 GeV2
• Nuclear structure functions show scaling at
  relatively low Q2 in the resonance region
  (duality)
• J.Arrington , et al., PRC64014602 (2001)
• EMC ratio extracted using resonance region data
  from JLab E89-008
• 1.2
• Where there is overlap, JLab resonance data
  agrees well with SLAC (DIS) results

J. Arrington, et al., PRC73035205 (2006)
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E03-103 (and E02-019) Analysis

• Analysis approaching final stages
• Data processing pretty much final
• Track reconstruction
• Efficiencies
• Charge symmetric backgrounds
• 1st pass cross sections have been used to
  iterate
• Radiative corrections
• Bin-centering corrections
• To do
• Radiative corrections for heavy (thick) targets
• Coulomb corrections

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Preliminary E03-103 Results Carbon

• E03-103 C/D ratios show good agreement with
  SLAC/EMC data
• Serves as good check of analysis procedure
  (charge symmetric background, radiative
  corrections)

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Preliminary E03-103 Results Carbon

• C/D ratio used to perform detailed check of Q2
  dependence
• Data taken at 10 Q2 settings
• No Q2 dependence seen for W21.5 GeV2 and Q22.5
  GeV2

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Preliminary E03-103 Results 4He

• 4He/D ratio consistent with SLAC result
• Consistent with SLAC param-eterization with A12

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Carbon to 4He Comparison
Preliminary 4He/D, C/D ratios
C/4He nuclear dependence of cross section
nearly identical
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Preliminary E03-103 Results 3He
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Coulomb Corrections

• Initial (scattered) electrons are accelerated
  (decelerated) in Coulomb field of nucleus with Z
  protons
• Not accounted for in typical radiative
  corrections
• Usually, not a large effect at high energy
  machines not true at JLab (6 GeV!)
• E03-103 uses modified
  Effective Momentum
  
  Approximation (EMA),
  
  Aste and Trautmann,
  
  Eur, Phys. J. A26, 167-178(2005)
• E ? ED, E?ED
• D -¾ V0, V0 3a(Z-1)/(2rc)

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Preliminary E03-103 Results Gold

• E03-103 data w/Coulomb Corrections (5-10)
• Corrections for SLAC data (not applied) would be
  1

• E03-103 results still pre-preliminary
• Radiative corrections are large ? target RL 6
• Some residual Q2 dependence not yet understood ?
  Coulomb corrections prescription?

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EMC Effect at Large x

• JLab resonance region data suggested that shape
  at large x changes with A
• Large x crossover moves to larger x for heavier
  nuclei
• Preliminary E03-103 results see no significant A
  dependence
• Large x behavior provides stringent test of EMC
  effect models shape dominated by binding and
  Fermi motion