Spin-averaged Nucleon Structure at “Large” x John Arrington Physics Division Argonne National Laboratory HiX2014: The 4th International Workshop on Nucleon Structure at Large Bjorken x Laboratori Nazionali di Frascati, Nov 17, 2014 Odd talk to be giving, given that this is my “low-x” program: x>1 (SRCs), x=1,3 (FFs, TPE), x~1 (CT), x<1 (EMC).

High-x experiments are providing benchmark data for hadron structure Why high-x? Valence structure of the hadron Key aspect of structure in Constituent Quark Models QCD and QCD-inspired predictions of x1 behavior Combination of proton and neutron provides unique sensitivity to models/symmetries of nucleon distributions Study quark – hadron transition, quark-hadron duality Resonance structure of the hadron Combination of proton and neutron provide sensitivity to isospin structure High-x experiments are providing benchmark data for hadron structure

Why high-x now? Jefferson Lab is the “valence” machine Dramatic progress in 6 GeV Era; remarkable coverage of resonance, duality physics 12 GeV provides huge opportunities in the duality/QCD region Other experiments (Drell-Yan, n-A scattering) providing complementary new information Future EIC provides some additional opportunities to explore high-x region Physics plan still being fully developed High-x structure at low Q2 provides key input (via evolution) to very high Q2

Large x is essential for particle physics Large Hadron Collider Parton distributions at large x are important input into simulations of hadronic background at colliders, e.g. the LHC. High x at low Q2 evolves into low x at high Q2 Small uncertainties at high x are amplified HERA anomaly: (1996): excess of neutral and charged current events at Q2 > 10,000 GeV2 Leptoquarks???? ~0.5% added to u(x) at x > 0.75 S. Kuhlmann et al, PLB 409 (1997) [Owens, Accardi, other PDF talks?] Lake of Geneva CMS LHCb Airport ALICE ATLAS

Outline Proton Neutron F2n/F2p, d(x)/u(x) Nuclei and nuclear effects Duality pdfs as x1, hadron structure Neutron Resonance structure, Duality Recent extractions, new experimental techniques F2n/F2p, d(x)/u(x) Recent deuteron/proton, model-dependent extractions Model-independent and model-less-dependent measurements Flavor dependence: Drell-Yan, n-A scattering, form factors Nuclei and nuclear effects New information/ideas on A dependence, isospin dependence

Impact of proton structure function data Data at very high x sensitive to: Target mass corrections High twist effects Soft gluon resummation [Corcella] Quark-hadron duality [Keppel] Constrain u(x) with minimal sensitivity to nuclear effects [Owens, Accardi] Test hadronic models F2 ~ (1-x)a as x1 Much better with n/p ratio Data taken in DIS at JLab, Drell-Yan at FNAL, with more on the way FNAL E906/SeaQuest [Reimer] JLab 12 [Malace] CTEQ6X, A. Accardi et al, PRD 81, 034016 (2010)

Quark-Hadron Duality Proton structure function in resonance region follows, on average, the DIS curve

Duality: there and back again 1970: Bloom-Gilman Duality [532 citations] 1996: “parasitic” measurements of duality in unpolarized e-p scattering I.Niculescu, et al., PRL 85 (2000) 1186; ibid, 85 (2000) 1182 Deuteron (neutron) duality Nuclear duality (scaling) Separated structure functions Semi-inclusive duality Parity-violating duality Spin duality Neutron structure EMC effect 12 GeV SIDIS Flavor dependence, nuclear effects in light nuclei Both duality and duality-enabled physics having large impact EMC/SRC correlation

Large-x parton distributions in Drell-Yan xtarget xbeam

Large-x parton distributions Proton beam, proton target: 4u(x)+d(x) with no nuclear corrections Sensitive to u(x) Some sensitivity to d(x), combined with DIS and proton-deuteron Drell-Yan Fermilab E906 will add much more precise high-x data. JLab inclusive scattering from H, 2H at large x, Q2 Extend duality studies, increase reach/precision for DIS at large x Planned for first running period in Hall C JLab E12-10-002: S. Malace, M. Christy, C. Keppel, M. Niculescu

Impact of neutron structure function data Data at very high x sensitive to: Resonance structure [Niculescu, Malace] Quark-hadron duality [Keppel] Neutron + proton data: Separate u(x) and d(x) [Owens, Accardi] Test hadronic models F2n/F2p or d(x)/u(x) as x1 Approaches to extracting F2n/F2p Model-dependent extraction from deuteron Model-less-dependent extractions 3H/3He ratios “Tagged” measurements on A=2 Model-independent extractions PVDIS on proton S. Malace, PRL 104 (2010) 102001 CJ11, A. Accardi et al, PRD 84, 014008 (2011)

Extracting neutron resonance structure First approach: extract neutron structure function from deuteron, proton data S. Malace, PRL 104 (2010) 102001 Left: proton, neutron, deuteron structure functions Right: Ratio of F2(neutron) to theory calculation over 1st, 2nd, 3rd resonances and full resonance region

Spectator Tagging: Deuteron as an effective neutron target “Tag” scattering from slow (nearly on-shell) nucleon in 2H Proton and neutron have equal and opposite momenta Use low-momentum spectator, coming opposite to virtual photon direction, to tag interaction with low-momentum nucleon (and correct for its momentum) BONUS: Neutron structure function in resonance region, DIS for lower x BONUS12: Extend DIS from tagged neutron to large x L.L. Frankfurt and M.I. Strikman, Phys. Rep. 76, 217 (1981) C. Ciofi degli Atti and S. Simula, Phys. Lett. B319, 23 (1993); Few-Body Systems 18, 55 (1995) S. Simula, Phys. Lett. B387, 245 (1996); Few-Body Systems Suppl. 9, 466 (1995) W. Melnitchouk, M. Sargsian and M.I. Strikman, Z. Phys. A359, 99 (1997)

Neutron structure function from tagged neutrons F2n from BONUS, two beam energies Curve from fit to previous extraction from deuteron Duality tests for F2n [Niculescu] S. Tkachenko, et al., PRC 89 (2014) 045206

Focus on F2n/F2p, ratio of d(x)/u(x) as x  1 Several predictions based on simple assumptions about symmetries in proton SU(6)-symmetric wave function of the proton in the quark model (spin up): u and d quarks identical N and D degenerate in mass d/u = 1/2, F2n/F2p = 2/3 SU(6) symmetry is broken: N-D Mass Splitting Mechanism produces mass splitting between S=1 and S=0 diquark spectator. symmetric states are raised, antisymmetric states are lowered (~300 MeV). S=1 suppressed => d/u = 0, F2n/F2p = 1/4, for x -> 1 pQCD: helicity conservation (qp) => d/u =2/(9+1) = 1/5, F2n/F2p = 3/7 for x -> 1 Dyson-Schwinger Eq.: Contains finite size S=0 and S=1 diquarks d/u = 0.28, F2n/F2p = 0.49

PDF predictions at large-x Nucleon Model F2n/F2p d/u Du/u Dd/d A1n A1p SU(6) 2/3 1/2 -1/3 5/9 Valence Quark 1/4 1 DSE contact interaction 0.41 0.18 0.88 0.38 0.83 DSE realistic interaction 0.49 0.28 0.65 -0.26 0.17 0.59 pQCD 3/7 1/5

Neutron structure function as x  1 Attempts to extract F2n(x) from deuteron and proton data yield large range of results, depending on the model of the deuteron [green and red points] Treat data as fixed Q2: neglects Q2 dependence of smearing function Result can vary strongly with assumed Q2 PDF analyses used to assume d/u0 “Scaled EMC effect”: Use F2A/F2D data as measure of nuclear effects; scale to density of the deuteron Neglects several effects: Q2 dependence of smearing A-dependence of Fermi motion Difference in F2p and F2n

Neutron Structure Function Two recent analysis addressed these issues Structure function analysis: interpolate data to fixed Q2 (J. Arrington, et al., JPG 36 (2009) 025005) PDF analysis (CJ6.X): calculate smearing, TMC, for each x, Q2 point (A. Accardi, et al., PRD 81 (2010) 034016) Both avoid high-Q2 approximations in convolution Assume identical p, n higher twist Results shown for initial F2n/F2p analysis Consistent with CTEQ6x analysis, which included off-shell effects similar to Melnitchouk and Thomas JA, F.Coester, R.J.Holt, T.S.-H.Lee, J.Phys.G36, 025005 (2009)

Detailed investigations of model-dependence Extracted n/p ratio including estimates of all uncertainties: Vary N-N potential, convolution, off-shell effects JA, W. Melnitchouk, J. Rubin, arXiv:1110.3362

Detailed investigations of model-dependence Extracted n/p ratio including estimates of all uncertainties: Vary N-N potential, convolution, off-shell effects NOT the best way to extract d/u Similar analysis done for CJ12 pdfs pdf style analysis can include more data (less sensitive to deuteron model), apply constraints (d(x)>0), go beyond LO,... *A. Accardi, et al., PRD84 (2011) 014008 Our analysis isolates model dependence, provides ‘baseline’ for comparison to model-independent n/p extractions JA, W. Melnitchouk, J. Rubin, arXiv:1110.3362

Detailed investigations of model-dependence Separation of pdfs from TMC, HT correction, impose constraint d(x)>0 Include additional data, look at strangeness, antiquarks, etc… Uncertainty dominated by data rather than model dependence: New high-x DIS data helps Compared to F2n analysis: Positivity constraint pushes results up Bands shown here are full range of (many) models; F2n analysis shows estimated 1-sigma range While this analysis appears to suggest larger d/u, results are in good agreement; main difference is the way they are presented GEn ? CJ12 J. Owens et al, PRD 87 (2013) 094012

GEn as constraint on d(x)/u(x) as x  1? Neutron transverse charge density Neutron IMF transverse charge density has negative core Distribution ‘squeezed’ to smaller impact parameter for high-x Negative core comes from d-quark charge dominance at large x, i.e. u/d < 0.5 for neutron  d/u < 0.5 for proton at some large x Question: can this limit be made tighter? Up Quark contribution Down Quark G. Miller and JA, PRC 78 (2008) 032201(R)

Conclusions 3 approaches for reducing model dependence experimentally F2n has “relatively” small uncertainty, including model dependence F2n/F2p fairly well known to x=0.6, barring significant “EMC effect” in 2H Additional high-x, high-Q2 data can further constrain F2n E12-10-002: Malace, Christy, Keppel, Niculescu Model-independent constraints on F2n/F2p at large x still vital Improved precision in extraction of F2n Sensitive to nuclear effects in the deuteron through comparison to extraction from inclusive deuteron data 3 approaches for reducing model dependence experimentally A=3 A=2 A=1

A=3 Solution: Add a nucleon Problem: Extraction from A=2 introduces model-dependence A=3 solution: 3H and 3He have larger nuclear corrections n/p can be extracted from 3H/3He ratio (many systematics cancel) n/p extraction sensitive only to difference between 3H, 3He corrections No DIS data on the triton! I. Afnan et al., Phys. Lett. B493, 36 (2000); Phys. Rev. C68, 035201 (2003) E. Pace, G Salme, S. Scopetta, A. Kievsky, Phys. Rev. C64, 055203 (2001) M. Sargsian, S. Simula, M. Strikman, Phys. Rev. C66, 024001 (2002)

A=3 Solution: Add a nucleon 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% up to x  0.8

A=3 Solution: Add a nucleon Thermo-mechanical design, B. Brajuskovic et al, NIM A, arXiv: 1306.6000 E12-06-118 MARATHON: G. Petratos, J. Gomez, R.J.Holt, R. Ransome Scheduled for 2016 at JLab Hall A BigBite Spectrometer

A=2 Solution: “remove” a nucleon “Tag” scattering from slow (nearly on-shell) nucleon in 2H Proton and neutron have equal and opposite momenta Use low-momentum spectator, coming opposite to virtual photon direction, to tag interaction with low-momentum nucleon (and correct for its momentum) BONUS12: DIS from tagged neutron at large x EIC: Forward spectator tagging will allow for broad set of measurements from tagged nearly on-shell (or far off-shell) nucleon

A=2 Solution: “remove” a nucleon Tag low momentum, backward angle spectator proton in deuteron: yields electron scattering from a free neutron target GEM-based radial TPC in JLab CLAS spectrometer Measure neutron structure function F2 to study quark structure of the nucleon at large x Slide credit: C. Keppel

F2n/F2p from BONUS at 6 GeV Pspectator< 100 MeV/c N.K. Baillie, et al, PRL 108, 199902 (2012) Pspectator< 100 MeV/c spectator < 90o Textbook physics :) Plot is in the new edition of Gauge Theories of the Strong, Weak, and Electromagnetic Interactions (Chris Quigg) xBj coverage in ~DIS region not quite enough to get to most interesting region for d(x)/u(x)

Tagged Neutron in the Deuteron – BONUS + CLAS12 JLab E12-06-113, S. Bueltmann, H. Fenker, M. Christy, C. Keppel, et al

Spectator tagging at an EIC [Nadel-Turonski] Ee=8 GeV, EN=30 GeV Luminosity=3.5E33 26 weeks at 50% efficiency Detect ~30 GeV proton – “super BoNuS” EIC in China or USA or … EIC has > 100 x luminosity of HERA, polarized e and light ions, nuclear beams Thanks to A. Accardi, R. Ent, C. Keppel 31

A=1 Solution: actually remove a nucleon Use proton ‘target’, but modify sensitivity to u(x) vs d(x) Drell-Yan with proton beam (high-x quarks), p/D target (low-x antiquarks) Neutrino-scattering: requires proton target, limited x resolution PVDIS: SOLID at JLab12 [Zheng] MINOS with 2 years data using high energy tune, LH2 target MINOS@FNAL nm m- d W+ m+ u W-

Slide credit: S. Riordan

Slide credit: S. Riordan

Nuclei and nuclear effects EMC effect: Modification of high-x pdfs in nuclei Light nuclei [Gaskell] – Unpolarized EMC effect Antiquark EMC effect [Reimer, Kovarik, Kumano] – Drell-Yan on nuclei Isospin dependence [Cloet] – Parity-violating electron scattering

EMC effect: A-dependence SLAC E139 Most precise large-x data Nuclei from A=4 to 197 Conclusions Universal x-dependence Magnitude varies Scales with A (~A-1/3) Scales with density J. Gomez, et al., PRD49, 4349 (1994)

Importance of light nuclei 1) Mass vs. density dependence 4He is low mass, higher density 9Be is higher mass, low density 3He is low mass, low density (no data) Calculations almost exclusively use nuclear matter, extrapolate to finite nuclei by scaling with density, A,… 2) Constrain 2H – free nucleon difference JLab E03-013: JA and D.Gaskell USING EXTRAPOLATION TO FREE NUCLEON HAS LIMITATIONS, BUT CLEARLY IMPROVED BY ADDING LIGHT NUCLEI

EMC effect in light nuclei J.Seely, et al., PRL103, 202301 (2009) Credit: P. Mueller N. Fomin, et al., PRL108 (2012) 092052 Short-range correlations in light nuclei NOTHING SURPRISING WITHOUT 9Be; BOTH EFFECTS HAD ALWAYS BEEN ASSUMED TO SCALE APPROX WITH DENSITY.

Recent question: Isospin dependence of EMC effect Typically assumed that EMC effect is identical for u(x) and d(x) Becoming hard to believe, at least for non-isoscalar nuclei EMC/SRC connection + SRC n-p dominance suggests enhanced EMC effect in minority nucleons [Gaskell] 48Ca, 208Pb expected to have significant neutron skin: neutrons preferentially sit near the surface, in low density regions Recent calculations show difference for u-, d-quark, as result of scalar and vector mean-field potentials in asymmetric nuclear matter [I. Cloet, et al, PRL 109, 182301 (2012); PRL 102, 252301 (2009)] [Cloet] In all 3 cases, neutron rich nuclei have enhanced EMC effect for up quarks, suppressed effect for down quarks --> cancellation in unpolarized EMC effect Measurements: EMC effect on 40Ca, 48Ca [Gaskell] parity-violating DIS from 48Ca (SoLID spectrometer at JLab) [Zheng]

Summary The large-x structure of hadrons is essential for a complete picture Valence region defines the hadron Test models of the nucleon Large-x studies on nuclei probe the impact of colored medium Large-x data important for understanding high-energy QCD studies New 21st century tools have positioned us well for the next decade JLab 6 GeV provided wealth of data for valence structure of hadrons FNAL E906/SeaQuest, MINERnA, and other stand-alone experiments JLab 12 GeV promises dramatic improvements and will address several key questions A future EIC can provide unique high-x capabilities