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Large-x S tructure of Nucleons and Nuclei

Large-x S tructure of Nucleons and Nuclei. John Arrington Argonne National Lab. Nuclear Physics Symposium: Exploring the Heart of Matter Sep. 27, 2014. Roy Holt – many things to many people…. Mr. Deuteron At Jefferson Lab Early days( g ,d ): Mr. Radiation More recently: Mr. Triton

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Large-x S tructure of Nucleons and Nuclei

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  1. Large-x Structure of Nucleons and Nuclei John Arrington Argonne National Lab Nuclear Physics Symposium: Exploring the Heart of Matter Sep. 27, 2014

  2. Roy Holt – many things to many people… • Mr. Deuteron • At Jefferson Lab • Early days(g,d): Mr. Radiation • More recently: Mr. Triton • Currently: Mr. “Superheated laughing gas and liter of mercury” And while he’s busy mucking about with SeaQuest now…… Mr. “Oh no, he’s back again” • To me: Mr. Bubba Ho-Tep

  3. Large-x physics in the “Mr. Triton” Era • Low x (x<0.8) • EMC effect in light nuclei • EMC effect in deuteron, free neutron structure function • MARATHON • Moderate x (x=1 (x=2)) • T20 at Novosibirsk/VEPP-3 • Two-photon exchange at Novosibirsk/VEPP-3 • Intermediate x (1 < x < 3) • n(p) for proton/neutron in A=3 • SRCs in 3H, 3He • Large x (x=3) • 3H, 3He charge radii Ideas initiated/driven by Roy Measurements that wouldn’t have been possible without ‘parastic’ use of novel ideas Roy led/developed Internal gas target, 3H target,…

  4. Quark distributions in nuclei: EMC effect Deeply-inelastic scattering (DIS) measures structure function F2(x) • x = quark longitudinal momentum fraction • F2(x) related to parton momentum distributions (pdfs) Nuclear binding << energy scales of probe, proton/neutron excitations Expected F2A(x) ≈ Z F2p(x) + N F2n(x) i.e. insensitive to details of nuclear structure beyond Fermi motion F2(x)~ Sei2qi(x) i=up, down, strange R = F2A(x) / F2D(x)

  5. Models of the EMC effect Nucleon structure is modified in the nuclear medium or Nuclear structure is modified due to hadronic effects • Nucleon ‘swelling’ • Dynamical rescaling • Multiquark clusters (6q, 9q ‘bags’) • More detailed binding calculations - Fermi motion + binding - N-N correlations • Nuclear pions Many models, no complete and accepted picture that is consistent with other data (e.g. Drell-Yan)

  6. EMC effect: x dependence A dependence SLAC E139 • Most precise large-x data • Nuclei from A=4 to 197 Conclusions • Universal x-dependence • Limited data at large x • A-dependence unclear • Scales with ln(A), A1/3 • Scales with density • Something else?? J. Gomez, et al., PRD 94, 4348 (1994)

  7. Importance of few-body nuclei 4Hemuch lighter than 12C, but has similar average density 9Be much lower density than 12C, but similar mass 3He has low A and low density Light nuclei help test scaling with mass vs. density Constrain 2H – free nucleon difference

  8. JLab E03-103: Light nuclei 12C 9Be 3He Consistent shape for all nuclei (curves show shape from SLAC fit) 4He If shape (x-dependence) is same for all nuclei, the slope (0.35<x<0.7) can be used to study dependence on A J. Seely, et al., PRL103, 202301 (2009) 8

  9. A-dependence of EMC effect in light nuclei Density determined from ab initio calculation S.C. Pieper and R.B. Wiringa, Ann. Rev. Nucl. Part. Sci. 51, 53 (2001) Data show smooth behavior as density increases… except for 9Be 9Be has low average density, but large component of structure is 2a+n Most nucleons in tight, a-like configurations K. Arai, et al., PRC54, 132 (1996) Credit: P. Mueller

  10. A-dependence of EMC effect in light nuclei Density determined from ab initio calculation S.C. Pieper and R.B. Wiringa, Ann. Rev. Nucl. Part. Sci. 51, 53 (2001) Data show smooth behavior as density increases… 9Be too heavy for Roy, so let’s ignore it – focus on H, He EMC effect very small for 3He Suggests small nuclear corrections in 2H, impact on extraction of free neutron as extracted from 2H

  11. E140 E139 Neutron Structure Function • Attempts to extract F2n(x) from deuteron and proton data yield large range of results, depending on the model of the deuteron • “Scaled EMC effect”: Use F2A/F2D data as measure of nuclear effects; scale to determine effects in the deuteron • Yields larger n/p • Neglects Fermi motion, difference in F2p and F2n, Q2 dependence of smearing

  12. F2n/ F2n, d/u Ratios and A1 Limits for x→1 Extensive recent review on the valence/high-x structureof the nucleon: R. J. Holt and C. D. Roberts, Rev. Mod. Phys. 82, 2991 (2010).

  13. Updated F2n Extraction • Similar to previous extractions – emphasis on improved treatment of the data, evaluation of systematics • Interpolate Rdp= F2d/F2p data to fixed Q02 = 12 GeV2 • Fit Q2 dependence using full Q2 range (3-230 GeV2) • Average Rdp from 6<Q2<30 GeV2, W2>3.5 GeV2 • Average Q2 for each bin always within factor of two of Q02 • Interpolation to fixed Q2 typically 0.5% • Use fit to F2p(from M.E.Christy) • Deuteron evaluated in a light cone impulse approximation, without “DIS” approximations (e.g. doesn’t assume scaling, doesn’t neglect k┴)

  14. Neutron Structure Function Newer CTEQ6x analysis (model similar to Melnitchouk and Thomas) yields consistent results (A. Accardi, et al., PRD 81 (2010) 034016) JA, F.Coester, R.J.Holt, T.S.-H.Lee, J.Phys.G36, 025005 (2009) • Ave. Q2 values for the D/p ratios have a strong dependence on x • We interpolate data to fixed Q2 • Previous extractions treated data as if it were at fixed Q2 • Significant Q2 dependence in Sp at large x, F2n ~ Rdp - Sp • Much of the “model-dependence” due to evaluating Sp, Sn at fixed Q2

  15. Detailed investigations of model-dependence N3L0 Av18CDBonn WJC2 WJC1 • Extract F2n/F2p with a variety of microscopic deuteron calculations • Vary N-N potential – top plot • Vary deuteron model – bottom REF: Arrington, MST offshell Melnitchouk&Thomas WBA [CTEQ6X] Kulagin&Petti Arrington, et al Rinat, et al Solid: On-shell Dashed: Off-shell [MST or KP]

  16. Detailed investigations of model-dependence Extracted n/p ratio including estimates of experimentaland model-dependent uncertainties

  17. Conclusions • Significantly reduced sensitivity to deuteron model • F2n/F2p relatively well known, barring significant extra nuclear effects (e.g. large “EMC effect” in 2H) • Calculations for 3He, 4He allow comparison to EMC ratios [T.-S. H. Lee] • Model-independent extractions of F2n/F2p at large x still critical: 3H/3He • Significant cancellation between nuclear effects in 3H and 3He • Improved precision, reduced model dependence, in extraction of F2n • Combined with extraction from d/p ratio, sensitive to nuclear effects beyond convolution, standard off-shell prescriptions, in the deuteron

  18. MARATHON: DIS from A=3 • Mirror symmetry of A=3 nuclei • Extract F2n/F2p from ratio of measured 3He/3H structure functions R= Ratio of ”EMC ratios” for 3He and 3H Relies only on difference in nuclear effects Calculated to within 1% Most systematic, theory uncertainties cancel

  19. Triton (3He & 3H) Measurements E12-10-103: Marathon u/d ratios from 3He(e,e’)/3H(e,e’) DIS measurements [A]* E12-14-001: elastic: 3H – 3He charge radius difference [3H “neutron skin”] [A] E12-11-112: x>1 measurements of correlations [A-]* E12-14-012: (e,e’p) momentum distribution measurements [B+] Relatively small amount of tritium (~1kC) in a cell machined from single block of Al.

  20. Triton (3He & 3H) Measurements E12-10-103: Marathon u/d ratios from 3He(e,e’)/3H(e,e’) DIS measurements [A]* E12-14-001: elastic: 3H – 3He charge radius difference [3H “neutron skin”] [A] E12-11-112: x>1 measurements of correlations [A-]* E12-14-012: (e,e’p) momentum distribution measurements [B+] Relatively small amount of tritium (~1kC) in a cell machined from single block of Al.

  21. Short-Range Correlations N-N interaction Hard interaction at short range Nucleon momentum distribution in 12C n(k) [fm-3] Mean field part k [GeV/c]

  22. SRC evidence at JLab Experimental observations: • Clear evidence for 2N-SRC at x>1.5 • Suggestion of 3N-SRC plateau • Isospin dependence ? K. Egiyan et al, PRL96, 082501 (2006) Simple SRC Model: • 1N, 2N, 3N contributions dominate at x≤1,2,3 • 2N, 3N configurations “at rest” (total ppair = 0) • Isospin independent N. Fomin, et al, arXiv:1107.358 (2011) CLAS - <Q2>1.5 GeV2 E02-019 - Q2=2.7 GeV2 N. Fomin, et al., PRL 108 (2012) 092052 22 22

  23. Density dependence? J.Seely, et al., PRL103, 202301 (2009) N. Fomin, et al., PRL108 (2012) 092052 Credit: P. Mueller

  24. Correlation between SRCs and EMC effectImportance of two-body effects? J. Seely, et al., PRL103, 202301 (2009) N. Fomin, et al., PRL 108, 092052 (2012) JA, A. Daniel, D. Day, N. Fomin, D. Gaskell, P. Solvignon, PRC 86 (2012) 065204 L. Weinstein, et al., PRL 106, 052301 (2011) O. Hen, et al, PRC 85, 047301 (2012)

  25. R. Subedi et al, Science 320, 1476(2008) Tensor force dominance Simple SRC Model: • 1N, 2N, 3N contributions dominate at x≤1,2,3 • 2N, 3N configurations “at rest” (total ppair = 0) • Isospin independent R. Schiavilla, R. Wiringa, S. Pieper and J. Carlson, PRL98, 132501 (2007) pp np Scaled deuteron momentum distribution From A(p,p’pn) and 12C(e,e’pN): 90% of observed pN pairs are pn; tensor force  isosinglet dominance R(pp/pn) = 0.0560.018 R(T=1/T=0) = 208% 25

  26. Isospin structure of 2N-SRCs Simple estimates for 2N-SRC • 3He/3H is simple/straightforward case: Isospin independent Full n-p dominance (no T=1) • 40% difference between full isosinglet dominance and isospin independent • Few body calculations [M. Sargisan, Wiringa/Peiper (GFMC)] predict n-p dominance, but with sizeable contribution from T=1 pairs • Goal is to measure 3He/3H ratio in 2N-SRC region with 1.5% precision  Extract R(T=1/T=0) with uncertainty of 3.8% Extract R(T=1/T=0) with factor of two improvement over previous triple-coincidence, smaller FSI 26

  27. Momentum-isospin correlations “Linear configuration” p3 = p1 + p2 extremely large momentum “Star configuration” p1 = p2 = p3 (a) yields R(3He/3H) ≈ 3.0 if nucleon #3 is always the doubly-occurring nucleon (a) yields R(3He/3H) ≈ 0.3 if nucleon #3 is always the singly-occurring nucleon (a) yields R(3He/3H) ≈ 1.4 if configuration is isospin-independent, as does (b) R≠1.4 implies isospin dependence AND non-symmetric momentum sharing 27 27

  28. 3He(e,e’p)/3H(e,e’p) E12-14-011: Proton and Neutron Momentum Distributions in A = 3 Asymmetric Nuclei 3He/3H ratio for proton knockout yields n/p ratio in 3H np-dominance at high-Pmimplies n/p ratio  1 n/p at low Pm enhanced arXiv:1409.1717

  29. Charge radii: 3He and 3H(e,e’p) One-time opportunity for 3H at JLab Precise theoretical calculations of <r2rms>3H, <r2rms>3He Experimental results: large uncertainties, discrepancies DRRMS= 0.20(10) DRRMS= 0.29(04) With new tritium target and JLab Luminosity, we aim to improve precision on DRRMS by factor 3-5 over SACLAY results

  30. Large-x physics in the “Mr. Triton” Era • Very-low x (x<0.8) • EMC effect in light nuclei • EMC effect in deuteron, free neutron structure function • MARATHON • Low x (x=1 (x=2)) • T20 at Novosibirsk/VEPP-3 • Two-photon exchange at Novosibirsk/VEPP-3 • Intermediate x (1 < x < 3) • n(p) for proton/neutron in A=3 • SRCs in 3H, 3He • Large x (x=3) • 3H, 3He charge radii Ideas initiated/driven by Roy Measurements that wouldn’t have been possible without ‘parastic’ use of novel ideas Roy led/developed Internal gas target, 3H target,…

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