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New Measurements of the EMC Effect in Few-Body Nuclei - APS GHP06 Nashville Meeting

Explore the latest measurements and analysis of the EMC effect in few-body nuclei, highlighting nuclear structure functions, related experiments, and implications. Delve into the conventional versus exotic explanations, importance of binding calculations, and insights from JLab E03-103 data. Understand the scaling behavior at lower Q2 and W2, with comparisons to SLAC E139 results. Gain valuable insights into the EMC effect's significance in understanding nuclear structure.

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New Measurements of the EMC Effect in Few-Body Nuclei - APS GHP06 Nashville Meeting

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  1. New measurements of the EMC effect in few-body nuclei John Arrington, Physics Division, ArgonneSecond meeting of the APS Topical Group on Hadron Physics GHP06, Nashville, TN 23 Oct 2006

  2. Overview • Nuclear structure functions and EMC effects • Review of measurements • Limitations in the data • JLab E03-103 • Status of the analysis • Preliminary results and future plans

  3. Nuclear structure functions and the EMC effect • Structure functions related to nuclear quark distributions • Non-trivial nuclear dependence (“EMC effect”) observed by EMC, BCDMS, SLAC experiments • Much larger than effect expected from Fermi motion • Significant (20+%) deviations between heavy nuclei and deuterium • Universal dependence on xBj • Shadowing : x<0.1 • Anti-shadowing: 0.1<x<0.3 • EMC effect x>0.3 • Size of the effect varies with A E139 (Fe)EMC (Cu)BCDMS (Fe)

  4. EMC effect: Large x region • SLAC E139 • Most precise data for large x region • Nuclei from A=4 to 197 • Conclusions • Independent of Q2 • Universal x-dependence (shape) for all A • Magnitude varies with A • Scales with ave. density • Scales with A • Limitations • Poor precision at large x • Limited data for low A

  5. EMC effect: Easy to explain (too easy?) • Many “exotic” explanations • Fermi motion insufficient • Dynamical rescaling, nuclear pions, multi-quark clusters, medium modification to nucleon structure, etc… • More careful treatment of “conventional” effects • Reexamination of binding effects • Effects of nucleon correlations • Unique explanation? • Most models could provide an EMC-like effect • Some could explain only part of the observed effect • Many appeared inconsistent with other measurements such as Drell-Yan or limits on medium modification • Others fully explained the data without any contribution from binding.

  6. EMC effect: Conventional vs. exotic • More systematic understanding necessary • Fermi motion and binding are clearly important, and must be included in any evaluation of “exotic” effects Benhar, Pandharipande, and Sick, Phys. Lett. B469, 19 (1999) • A reliable binding calculation will tell us if we’re need a new explanation for THIS or THIS • Binding calculations must be evaluated against high-x data, which is dominated by Fermi motion and binding • Current data is limited at large x, where one can evaluate binding models, and low-A, where uncertainties due to nuclear structure are smallest

  7. EMC effect: Importance of few-body nuclei • Calculations predict different x-dependence for 3He and 4He • Different models predict different x-dependence • Some models predict different shapes for 3He and 4He • Smaller nuclear structure uncertainties • Sensitive to A-dependence • Scaling EMC effect with <r> very different from A • Data lower quality • Lower precision for 4He • No data at large x for 3He

  8. EMC effect: JLab E03-103 • JLab E03-103: JA and D. Gaskell, spokespersons, Jason Seely and Aji Daniel – thesis students • Measured structure function for 1H, 2H, 3He, 4He, Be, C, Al, Cu, and Au • High density 3,4He cryotargets allow improved statistics and systematics compared to SLAC E139 • Lower Q2 allows access to large-x region, but only for W2<4 GeV2 SLAC fit to heavy nuclei (scaled to 3He) 3He and 4He calculations by Pandharipande and Benhar HERMES dataE03103 projected uncertainty

  9. Q2¼ 4 GeV2 1.3 < W2 < 2.8 GeV2 EMC effect: Scaling at lower Q2, W2 • Measurement is not entirely in usual DIS region (W2>4 GeV2) • DIS-scaling behavior has been observed to extend to lower Q2, W2 in nuclei • Yields resonance region EMC ratios identical to DIS results • Can be understood as consequence of quark-hadron duality • E03-103 data at higher Q2, with precise measurement of Q2 dependence B.W.Filippone, et al., PRC45:1582 (1992) JA, et al., PRC64:014602 (2001) W.Melnitchouk, R. Ent, and C. Keppel, Phys. Rept. 406:127 (2005) JA, et al., PRC73:035205 (2006)

  10. E03-103: Experimental details Main improvement over SLAC due to improved He targets: JLab E03-103 0.5-0.7% 0.4% 1.0% SLAC E139 1.0-1.2% 1.4% 2.1% Source of uncertainty Statistics *Density fluctuations Absolute density *- sizeof correction is 8% at 4 uA vs. 4% at 80 uA Main drawback is lower beam energy Requires larger scattering angle to reach same Q2 • Larger p- contamination • Large charge-symmetric background • Larger Coulomb distortion corrections Ratio of e+ to e- production

  11. E03-103: Analysis status • Ran in Hall C at Jefferson Lab, summer/fall of 2004 (EMC and x>1) • Cross section extraction • Calibrations, efficiency corrections, background subtraction completed • Finalizing model-dependence in radiative corrections, bin centering, etc… • Investigating Coulomb distortion corrections (heavy nuclei) • EMC Ratios • Isoscalar EMC correction (requires sn/sp)

  12. E03-103: Carbon EMC ratio Preliminary results, 12C/2H ratio compared to SLAC and EMC

  13. E03-103: Carbon EMC ratio • Data taken for 12C and 2H at ten Q2 setting • Measure Q2 dependence of the nuclear structure functions • Verify Q2 independence of the EMC ratios • Extracted EMC ratio for Carbon for the five highest Q2 settings 21435 Data show no indication of Q2 dependence, even at the lowest values of Q2, W2 shown

  14. E03-103: Helium-4 EMC ratio Preliminary results, 4He/2H ratio compared to SLAC Results consistent with SLAC fit to A=12 (using A-dependent fit) Consistent with density-dependent fit to A=4

  15. E03-103: Comparison of Carbon and Helium-4 Preliminary results, 4He/2H and12C/2H ratios 12C/4He ratio compared to previous 12C EMC ratios

  16. 4He 12C E03-103: Comparison of Carbon and Helium-4 12C much heavier than 4He, but has similar average density Preliminary results for 4He/2H and12C/2H ratios favor density-dependent EMC effect

  17. E03-103: Helium-3 EMC ratio Preliminary results, 3He EMC ratio compared to HERMES Blue is uncorrected 3He/2H ratio Green includes correction for proton excess in 3He (isoscalar EMC ratio) Larger EMC effect than most models Different x-dependence than calculations, heavier nuclei Might suggest larger EMC effect than expected for deuterium However, result isvery sensitive to isoscalar correction

  18. E03-103: Helium-3 EMC ratio • Bad news: • Large correction (5-20%) to extract isoscalar ratio • SLAC, NMC fits to sn/sp yield corrections that differ by 2-4% for x<0.6; difference changes sign at large x • Good news: • 197Au correction is roughly equal but has opposite sign; constrain combination of sn/sp and A-dependence of EMC[Working on Coulomb corrections, and checks on radiative corrections for heavy nuclei] • 3He/(2H+1H) ratio less sensitive to neutron cross section

  19. Summary, and more to come… • Preliminary results from E03-103 • EMC effect nearly identical for 4He and 12C • Indications of a large EMC effect in 3He • Ratios independent of Q2 down to quite low Q2 values • Results on the way • More reliable 3He isoscalar ratios, ratios to proton+deuteron • EMC ratios for Be, C, Al, Cu, Au – emphasis on large x region • Absolute cross sections for 1H, 2H, 3He, 4He • Test models of sn/sp + nuclear effects in few-body nuclei • E02-019: absolute cross sections for x>1 for 2H, 3He, 4He • More detailed, quantitative studies of the Q2 dependence • Structure functions • Ratios

  20. Scaling of the nuclear structure functions F2(x,Q2) consistent with QCD evolution in Q2 for low x values (x<0.5) Huge scaling violations at large x (especially for x>1) F2(x,Q2) consistent with QCD evolution in Q2 to much larger x values Scaling violations are mostly the “target-mass” corrections (plus a clear contribution from the QE peak)  Nearly independent of A

  21. Scaling of the nuclear structure functions • Low Q2 JLab data (from E89-008, 4 GeV) are consistent with extrapolated structure function from high Q2 SLAC data [ fixed dln(F2)/dln(Q2) ] • Above x=0.65, there is a large gap between JLab, SLAC data, but there are indications of scaling up to x=0.75 • Our data fill in the gap up to x¼0.75, show indications of scaling up to x¼0.9

  22. EMC ratios as a function ofxand x • EMC ratios vs x and x • Small differencefor x<.4 • SLAC E139 and JLab E03-103 have similar range in Q2, nearly identical difference between x, x JLab E03-103 SLAC E139

  23. Isoscalar corrections: 3He and 197Au • F2n/F2p from SLAC, CTEQ, NMC (bottom) • Correction to 3He (top right) and 197Au (bottom right)

  24. Nuclear Structure: High Momentum Nucleons • Short-range structure in nuclei [E02-019 (Arrington)] • Inclusive quasielastic scattering from nuclei at x>1 • Study distribution of extremely high momentum nucleons (>1 GeV/c) in 2H, 3He, 4He, and heavy nuclei • Goal is to understand high-momentum components and map out strength of Short Range Correlations (SRCs) in nuclei • Important part of nuclear structure, relevant to topics in nuclear and particle physics: neutron star structure, medium modification in sub-threshold hadron production, and n-A interactions in supernovae, in neutrino oscillation experiments, and in q13 measurements • Ran in 2004, data analysis in progress

  25. Projected 3He uncertainties HERMES Properties of Bound Nucleons: EMC effect • Medium modification: The EMC effect • Clear observation of nuclear (density) dependence in parton distributions • Still no consensus on the cause of the effect • Binding is important at all x values, but may also require modification to internal structure of the nucleon • EMC effect in 3He and 4He [E03-103 (Arrington)] • Allows reliable few-body calculations of binding • Test A dependence and x dependence for very light nuclei • First 3He data above x=0.4, factor of two improvement for 4He

  26. Properties of Bound Nucleons: EMC effect • Preliminary results: A- and x-dependence • SLAC E139: Can scale with ln(A) or <rA> • New data suggest it scales with density • Also indicates identical x-dependence for 4He and 12C x=0.6 4He 12C PRELIMINARY (statistical errors) x=0.6 4He PRELIMINARY (statistical errors) <rA>

  27. Properties of Bound Nucleons: JLab @ 12 GeV Three proposals for PAC30 • EMC effect • Map out A-dependence at large x (test binding calculations) • Precise measurements in anti-shadowing region • DIS from 3He and 3H • Ratio of 3H/3He provides measurements of sn/sp and d(x)/u(x), without uncertainty associated with nuclear effects • Combine with precise 3He/2H ratio to extract isoscalar EMC effect for A=3 • Inclusive scattering from nuclei at x>1 • At 6 GeV, dominated by QE scattering, map out distribution of high-p nucleons • At 12 GeV, begin to probe quark distributions at x>1

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