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A Precise Measurement of the EMC Effect in Light Nuclei

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. The EMC Effect. Measurements of

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A Precise Measurement of the EMC Effect in Light Nuclei

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  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 • x<0.1: shadowing • 0.1<x<0.3: small enhancement (nuclear pions?) • x>0.3: suppression -> “EMC Effect” • Fourth region at x>0.7 -> 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 x>0.2 • Measured sA/sD for A=4 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

  5. 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 x=0.6

  6. Measurement of EMC effect for very light nuclei (A=3 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 EMC Effect in Light Nuclei 3He 4He

  7. JLab Experiment E03-103 • Ran in Hall C at JLab summer and fall 2004 • Concurrent with E02-019 (measured inclusive cross sections at x>1) • 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 (W>2 GeV) up to x=0.6 • Large Q2 at x>0.6 suggests we may be able to extract meaningful EMC ratios up to x ~ 0.85

  8. 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)

  11. 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 x>0.6, E03-103 data at W<4 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 W2>2 GeV2 (for Q2 > 3 GeV2) E89008 – 4 GeV

  13. EMC Measurements at W<2 GeV • EMC ratio extracted using resonance region data from E89-008 • 1.2<W2<3.0 GeV2 at Q2≈4 GeV2 • Where there is overlap, JLab resonance data agrees well with SLAC (DIS) results • E03-103 has data at W2>2 GeV2 at Q2=6 GeV2 (x=0.82) • Data at smaller angles will allow us to put quantitative limits on deviation from scaling in the cross sections AND ratios

  14. 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 x>0.4 • Observation of cross section scaling in deuterium for W2>2 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 x~0.85 • Stay tuned – final results soon

  15. 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 M.E. Christy, C.E. Keppel, S. Malace, E. Segbefia, L. Tang, V. Tvaskis, L. Yuan Hampton University, Hampton, VA G. Niculescu, I. Niculescu James Madison University, Harrisonburg, VA P. Bosted, A. Bruell, V. Dharmawardane, R. Ent, H. Fenker, D. Gaskell (spokesperson), M.K. Jones, A.F. Lung, D.G. Meekins, J. Roche, G. Smith, W.F. Vulcan, S.A. Wood Jefferson Laboratory, Newport News, VA 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 University of Maryland, College Park, MD D. Day, N. Fomin, C. Hill, R. Lindgren, P. McKee, O. Rondon, K. Slifer, S. Tajima, F. Wesselmann, J. Wright University of Virginia, Charlottesville, VA R. Asaturyan, H. Mkrtchyan, T. Navasardyan, V. Tadevosyan Yerevan Physics Institute, Armenia S. Connell, M. Dalton, C. Gray University of the Witwatersrand, Johannesburg, South Africa E03-103 Collaboration

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