A Precise Measurement of the EMC Effect in Light Nuclei

1
A Precise Measurement of the EMC Effect in Light
Nuclei

• Dave Gaskell
• Jefferson Lab
• PANIC
• October 24, 2005

• Motivation and existing data
• JLab Experiment E03-103
• Preliminary Results

2
The EMC Effect

• Measurements of
• (EMC, SLAC, BCDMS) have demonstrated
  modification of quark distributions in nuclei
• Magnitude of effect depends on A, but not the
  shape

• Typically broken in 3 regions
• xlt0.1 shadowing
• 0.1ltxlt0.3 small enhancement (nuclear pions?)
• xgt0.3 suppression -gt EMC Effect
• Fourth region at xgt0.7 -gt ratio increases,
  crosses 1.0
• - Attributed to Fermi smearing

3
Explaining the EMC Effect

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

• Exotic Models
• Dynamical rescaling
• Multiquark clusters

K.E. Lassila and U.P. Sakhatme Phys. Lett. B209,
343 (1988)
Benhar, Pandharipande, and Sick Phys. Lett. B410,
79 (1997)
4
Existing EMC Data

• SLAC E139 probably the most extensive data set
  for xgt0.2
• 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

SLAC E139
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A-Dependence of the EMC Effect

• Existing 4He data cannot distinguish between
  log(A) and r dependence of EMC Effect
• Increased precision on 4He, addition of 3He will
  clearly put new constraints on parameterizations
  of A dependence

E139 x0.6
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EMC Effect in Light Nuclei
3He
4He

• Measurement of EMC effect for very light nuclei
  (A3 and 4) will allow comparison with exact
  nuclear calculations
• With the conventional nuclear physics under
  control, it will be easier to rule out or support
  more exotic explanations

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JLab Experiment E03-103

• Ran in Hall C at JLab summer and fall 2004
• Concurrent with E02-019 (measured inclusive cross
  sections at xgt1)
• Measured A(e,e) at 5.77 GeV from H, 2H, 3He,
  4He, Be, C, Al, Cu, and Au at 18, 22, 26, 32, 40,
  and 50 degrees

• Took additional data at 5 GeV on Carbon and
  Deuterium to investigate Q2 dependence
• In canonical DIS region (Wgt2 GeV) up to x0.6
• Large Q2 at xgt0.6 suggests we may be able to
  extract meaningful EMC ratios up to x 0.85

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E03-103 and E02-019 Analysis

• Analysis still ongoing
• Data processing pretty much final
• Track reconstruction
• Efficiencies
• Charge symmetric backgrounds
• 1st pass cross sections will be used to iterate
• Radiative corrections
• Bin-centering corrections
• To do Coulomb corrections

9
Carbon EMC Ratio

• Existing precision Carbon data serves as a nice
  cross-check
• Points include 1.5 point-to-point systematic
  uncertainty (radiative corrections, bin
  centering)
• 3 normalization uncertainty (target thickness,
  radiative and bin centering corrections)

10
4He EMC Ratio

• Projected final uncertainties will be 0.7
  point-to-point, 1.5 normalization (compare to
  1.6 and 2.2 respectively for E139)

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Projected Uncertainties for 3He

• Normalization uncertainty will be a little
  larger 1.9 mostly due to 3He thickness (large
  temperature and pressure derivatives)
• Extraction of 3He ratio made more difficult due
  to
• larger target boiling corrections
• zeroth-order model deficiencies (bin centering,
  radiative corrections)

12
Measuring the EMC Effect at Large x

• For xgt0.6, E03-103 data at Wlt4 GeV (resonance
  region)
• Recent data from JLab suggests that even in the
  resonance region inclusive cross sections scale
• Earlier Hall C data taken at 4 GeV, sees no
  apparent deviation (at the 10 level) from
  scaling for W2gt2 GeV2 (for Q2 gt 3 GeV2)

E89008 4 GeV
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EMC Measurements at Wlt2 GeV

• EMC ratio extracted using resonance region data
  from E89-008
• 1.2ltW2lt3.0 GeV2 at
• Q24 GeV2
• Where there is overlap, JLab resonance data
  agrees well with SLAC (DIS) results
• E03-103 has data at W2gt2 GeV2 at Q26 GeV2
  (x0.82)
• Data at smaller angles will allow us to put
  quantitative limits on deviation from scaling in
  the cross sections AND ratios

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Summary

• Study of the EMC effect in light nuclei will help
  us more cleanly separate conventional nuclear
  physics contributions to the cross section
  ratios from more exotic explanations
• JLab E03-103 will increase the precision of 4He
  ratios, and be the first precise measurement for
  3He at xgt0.4
• Observation of cross section scaling in deuterium
  for W2gt2 GeV2 and agreement of resonance region
  EMC ratio with DIS results gives us confidence
  that we will be able to extract precise ratios up
  to x0.85
• Stay tuned final results soon

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E03-103 Collaboration

• J. Arrington (spokesperson), L. El Fassi, K.
  Hafidi, R. Holt,
• D.H. Potterveld, P.E. Reimer, E. Schulte, X.
  Zheng
• Argonne National Laboratory, Argonne, IL
• B. Boillat, J. Jourdan, M. Kotulla, T. Mertens,
  D. Rohe, G. Testa,
• R. Trojer
• Basel University, Basel, Switzerland
• B. Filippone
• California Institute of Technology, Pasadena, CA
• C. Perdrisat
• College of William and Mary, Williamsburg, VA
• D. Dutta, H. Gao, X. Qian
• Duke University, Durham, NC
• W. Boeglin
• Florida International University, Miami, FL

• B. Clasie, J. Seely
• Massachusetts Institute of Technology, Cambridge,
  MA
• J. Dunne
• Mississippi State University, Jackson, MS
• V. Punjabi
• Norfolk State University, Norfolk, VA
• A.K. Opper
• Ohio University, Athens, OH
• H. Nomura
• Tohoku University, Sendai, Japan
• M. Bukhari, A. Daniel, N. Kalantarians, Y.
  Okayasu, V. Rodriguez
• University of Houston, Houston, TX
• F. Benmokhtar, T. Horn