1 / 62

Craig Roberts Physics Division

Revealing and mapping parton dressing and correlations through diverse hadron structure measurements. Craig Roberts Physics Division. Students Postdocs Asst. Profs. Collaborators: 2011-Present. Adnan BASHIR ( U Michoácan ); Stan BRODSKY (SLAC); Gastão KREIN (São Paulo)

evelyn
Download Presentation

Craig Roberts Physics Division

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Revealing and mapping parton dressing and correlations through diverse hadron structure measurements Craig Roberts Physics Division

  2. Students Postdocs Asst. Profs. Collaborators: 2011-Present • Adnan BASHIR (U Michoácan); • Stan BRODSKY (SLAC); • Gastão KREIN (São Paulo) • Roy HOLT (ANL); • Mikhail IVANOV (Dubna); • Yu-xin LIU (PKU); • Michael RAMSEY-MUSOLF (UW-Mad) • Alfredo RAYA (U Michoácan); • Sebastian SCHMIDT (IAS-FZJ & JARA); • Robert SHROCK (Stony Brook); • Peter TANDY (KSU); • Tony THOMAS (U.Adelaide) • Shaolong WAN (USTC) Craig Roberts: Mapping Parton Structure and Correlations (62p) Rocio BERMUDEZ (U Michoácan); Chen CHEN (ANL, IIT, USTC); Xiomara GUTIERREZ-GUERRERO (U Michoácan); Trang NGUYEN (KSU); Khépani Raya (U Michoácan); Hannes ROBERTS (ANL, FZJ, UBerkeley); Chien-Yeah SENG (UW-Mad) Kun-lun WANG (PKU); Lei CHANG (FZJ); J. JavierCOBOS-MARTINEZ (U.Sonora); Ian CLOËT (ANL); Bruno EL-BENNICH (São Paulo); Mario PITSCHMANN (ANL & UW-Mad); Si-xue QIN(U. Frankfurt am Main); Jorge SEGOVIA (ANL); David WILSON (ODU);

  3. Table of Contents Craig Roberts: Mapping Parton Structure and Correlations (62p) Introduction Pion valence-quark distribution Pion valence-quark parton distribution amplitude Charged pion elastic form factor Nucleon form factors Nucleon structure functions at large-x Epilogue

  4. Science Challenges for the coming decade: 2013-2022 Craig Roberts: Mapping Parton Structure and Correlations (62p) • Exploit opportunities provided by new data on hadron elastic and transition form factors • Chart infrared evolution of QCD’s coupling and dressed-masses • Reveal correlations that are key to nucleon structure • Expose the facts or fallacies in modern descriptions of hadron structure

  5. Science Challenges for the coming decade: 2013-2022 Craig Roberts: Mapping Parton Structure and Correlations (62p) • Precision experimental study of valence region, and theoretical computation of distribution functions and distribution amplitudes • Computation is critical • Without it, no amount of data will reveal anything about the theory underlying the phenomena of strong interaction physics

  6. Overarching Science Challenges for the coming decade: 2013-2022 Discover meaning of confinement, and its relationship to DCSB – the origin of visible mass Craig Roberts: Mapping Parton Structure and Correlations (62p)

  7. What is QCD? Craig Roberts: Mapping Parton Structure and Correlations (62p)

  8. QCD is a Theory (not an effective theory) Craig Roberts: Mapping Parton Structure and Correlations (62p) • Very likely a self-contained, nonperturbativelyrenormalisable and hence well defined Quantum Field Theory This is not true of QED – cannot be defined nonperturbatively • No confirmed breakdown over an enormous energy domain: 0 GeV < E < 8000 GeV • Increasingly likely that any extension of the Standard Model will be based on the paradigm established by QCD • Extended Technicolour: electroweak symmetry breaks via a fermion bilinear operator in a strongly-interacting non-Abelian theory. (Andersen et al. “Discovering Technicolor” Eur.Phys.J.Plus 126 (2011) 81) Higgs sector of the SM becomes an effective description of a more fundamental fermionic theory, similar to the Ginzburg-Landau theory of superconductivity

  9. Strong-interaction: QCD • Nature’sonly (now known) example of a truly nonperturbative, fundamental theory • A-priori, no idea as to what such a theory • can produce Craig Roberts: Mapping Parton Structure and Correlations (62p) • Asymptotically free • Perturbation theory is valid and accurate tool at large-Q2 • Hence chiral limit is defined • Essentiallynonperturbative for Q2 < 2 GeV2

  10. What is Confinement? Craig Roberts: Mapping Parton Structure and Correlations (62p)

  11. Light quarks & Confinement • Folklore “The color field lines between a quark and an anti-quark form flux tubes. Craig Roberts: Mapping Parton Structure and Correlations (62p) A unit area placed midway between the quarks and perpendicular to the line connecting them intercepts a constant number of field lines, independent of the distance between the quarks. This leads to a constant force between the quarks – and a large force at that, equal to about 16 metric tons.” Hall-DConceptual-DR(5)

  12. Light quarks & Confinement Craig Roberts: Mapping Parton Structure and Correlations (62p) • Problem: 16 tonnes of force makes a lot of pions.

  13. Light quarks & Confinement Craig Roberts: Mapping Parton Structure and Correlations (62p) Problem: 16 tonnes of force makes a lot of pions.

  14. G. Bali et al., PoS LAT2005 (2006) 308 Light quarks & Confinement Craig Roberts: Mapping Parton Structure and Correlations (62p) In the presence of light quarks, pair creation seems to occur non-localized and instantaneously No flux tube in a theory with light-quarks. Flux-tube is not the correct paradigm for confinement in hadron physics

  15. Confinement Confined particle Normal particle complex-P2 complex-P2 timelike axis: P2<0 s ≈ 1/Im(m) ≈ 1/2ΛQCD≈ ½fm • Real-axis mass-pole splits, moving into pair(s) of complex conjugate singularities • State described by rapidly damped wave & hence state cannot exist in observable spectrum Craig Roberts: Mapping Parton Structure and Correlations (62p) • QFT Paradigm: • Confinement is expressed through a dramatic change in the analytic structure of propagators for coloured states • It can almost be read from a plot of the dressed-propagator for a coloured state

  16. Light quarks & Confinement Craig Roberts: Mapping Parton Structure and Correlations (62p) • In the study of hadrons, attention should turn from potential models toward the continuum bound-state problem in quantum field theory • Such approaches offer the possibility of posing simultaneously the questions • What is confinement? • What is dynamical chiral symmetry breaking? • How are they related? Is it possible that two phenomena, so critical in the Standard Model and tied to the dynamical generation of a mass-scale in QCD, can have different origins and fates?

  17. Dynamical ChiralSymmetry Breaking Craig Roberts: Mapping Parton Structure and Correlations (62p)

  18. Dynamical ChiralSymmetry Breaking Craig Roberts: Mapping Parton Structure and Correlations (62p) • DCSB is a fact in QCD • Dynamical, not spontaneous • Add nothing to QCD , no Higgs field, nothing! • Effect achieved purely through the dynamics of gluons and quarks. • It’s the most important mass generating mechanism for visible matter in the Universe. • Responsible for approximately 98% of the proton’s mass. • Higgs mechanism is (almost) irrelevant to light-quarks.

  19. DCSB C.D. Roberts, Prog. Part. Nucl. Phys. 61 (2008) 50 M. Bhagwat & P.C. Tandy, AIP Conf.Proc. 842 (2006) 225-227 • In QCD, all “constants” of quantum mechanics are actually strongly momentum dependent: couplings, number density, mass, etc. • So, a quark’s mass depends on its momentum. • Mass function can be calculated and is depicted here. • Continuum- and Lattice-QCD Mass from nothing! • are in agreement: the vast bulk of the light-quark mass comes from a cloud of gluons, dragged along by the quark as it propagates. Craig Roberts: Mapping Parton Structure and Correlations (62p)

  20. In QCD, Gluons, too, become massive Craig Roberts: Mapping Parton Structure and Correlations (62p) Not just quarks … Gluons also have a gap equation … 1/k2behaviour signals essential singularity in the running coupling: Impossible to reach in perturbation theory

  21. Valence quarks Parton structure of hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p)

  22. Parton Structure of Hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p) • Valence-quark structure of hadrons • Definitive of a hadron – it’s how we tell a proton from a neutron • Expresses charge; flavour; baryon number; and other Poincaré-invariant macroscopic quantum numbers • Via evolution, determines background at LHC • Sea-quark distributions • Flavour content, asymmetry, intrinsic: yes or no? • Any nontrivial answers are essentially nonperturbative features of QCD

  23. Parton Structure of Hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p) • Light front provides a link with quantum mechanics • If a probability interpretation is ever valid, it’s in the infinite-momentum frame • Enormous amount of intuitively expressive information about hadrons & processes involving them is encoded in • Parton distribution functions • Generalisedparton distribution functions • Transverse-momentum-dependent parton distribution functions • Information will be revealed by the measurement of these functions – so long as they can be calculated Success of programme demands very close collaboration between experiment and theory

  24. Parton Structure of Hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p) • Need for calculation is emphasised by Saga of pion’s valence-quark distribution: • 1989: uvπ ~ (1-x)1 – inferred from LO-Drell-Yan & disagrees with QCD; • 2001: DSE- QCD predicts uvπ ~ (1-x)2 argues that distribution inferred from data can’t be correct;

  25. Parton Structure of Hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p) • Need for calculation is emphasised by Saga of pion’s valence-quark distribution: • 1989: uvπ ~ (1-x)1 – inferred from LO-Drell-Yan & disagrees with QCD; • 2001: DSE- QCD predicts uvπ ~ (1-x)2 argues that distribution inferred from data can’t be correct; • 2010: NLO reanalysis including soft-gluon resummation, inferred distribution agrees with DSE and QCD

  26. Pion’s valence-quark Distribution Amplitude Pion’s Bethe-Salpeter wave function Whenever a nonrelativistic limit is realistic, this would correspond to the Schroedinger wave function. Craig Roberts: Mapping Parton Structure and Correlations (62p) Exact expression in QCD for the pion’s valence-quark parton distribution amplitude Expression is Poincaré invariant but a probability interpretation is only valid in the light-front frame because only therein does one have particle-number conservation. Probability that a valence-quark or antiquark carries a fraction x=k+ / P+ of the pion’s light-front momentum { n2=0, n.P = -mπ}

  27. Pion’s valence-quark Distribution Amplitude Pion’s Bethe-Salpeter wave function Craig Roberts: Mapping Parton Structure and Correlations (62p) Moments method is ideal for φπ(x): entails Contact interaction (1/k2)ν , ν=0 Straightforward exercise to show ∫01 dxxmφπ(x) = fπ1/(1+m) , hence φπ(x)= fπ Θ(x)Θ(1-x)

  28. Pion’s valence-quark Distribution Amplitude Craig Roberts: Mapping Parton Structure and Correlations (62p) The distribution amplitude φπ(x) is actually dependent on the momentum-scale at which a particular interaction takes place; viz., φπ(x)= φπ(x,Q) One may show in general that φπ(x) has an expansion in terms of Gegenbauer–α=3/2 polynomials: Only even terms contribute because the neutral pion is an eigenstate of charge conjugation, so φπ(x)=φπ(1-x) Evolution, analogous to that of the parton distribution functions, is encoded in the coefficients an(Q)

  29. Imaging dynamical chiral symmetry breaking: pion wave function on the light front, Lei Chang, et al., arXiv:1301.0324 [nucl-th], Phys. Rev. Lett. 110 (2013) 132001 (2013) [5 pages]. Pion’s valence-quark Distribution Amplitude Craig Roberts: Mapping Parton Structure and Correlations (62p) • However, practically, in reconstructing φπ(x) from its moments, it is better to use Gegenbauer–α polynomials and then rebuild the Gegenbauer–α=3/2 expansion from that. • Better means – far more rapid convergence because Gegenbauer–α=3/2 is only accurate near ΛQCD/Q=0. • One nontrivial Gegenbauer–α polynomial provides converged reconstruction cf. more than SEVEN Gegenbauer–α=3/2 polynomials • Results have been obtained with rainbow-ladder DSE kernel, simplest symmetry preserving form; and the best DCSB-improved kernel that is currently available. • xα (1-x)α, with α=0.3

  30. Imaging dynamical chiral symmetry breaking: pion wave function on the light front, Lei Chang, et al., arXiv:1301.0324 [nucl-th], Phys. Rev. Lett. 110 (2013) 132001 (2013) [5 pages]. Pion’s valence-quark Distribution Amplitude • This may be claimed because PDA is computed at a low renormalisation scale in the chiral limit, whereat the quark mass function owes entirely to DCSB. • Difference between RL and DB results is readily understood: B(p2) is more slowly varying with DB kernel and hence a more balanced result Asymptotic DB RL Craig Roberts: Mapping Parton Structure and Correlations (62p) Both kernels agree: marked broadening of φπ(x), which owes to DCSB

  31. Imaging dynamical chiral symmetry breaking: pion wave function on the light front, Lei Chang, et al., arXiv:1301.0324 [nucl-th], Phys. Rev. Lett. 110 (2013) 132001 (2013) [5 pages]. Pion’s valence-quark Distribution Amplitude These computations are the first to directly expose DCSB – pointwise – on the light-front; i.e., in the infinite momentum frame. • This may be claimed because PDA is computed at a low renormalisation scale in the chiral limit, whereat the quark mass function owes entirely to DCSB. • Difference between RL and DB results is readily understood: B(p2) is more slowly varying with DB kernel and hence a more balanced result Asymptotic DB RL Craig Roberts: Mapping Parton Structure and Correlations (62p) Both kernels agree: marked broadening of φπ(x), which owes to DCSB

  32. Imaging dynamical chiral symmetry breaking: pion wave function on the light front, Lei Chang, et al., arXiv:1301.0324 [nucl-th], Phys. Rev. Lett. 110 (2013) 132001 (2013) [5 pages]. Pion’s valence-quark Distribution Amplitude C.D. Roberts, Prog. Part. Nucl. Phys. 61 (2008) 50 Dilation of pion’s wave function is measurable in pion’s electromagnetic form factor at JLab12 A-rated:E12-06-10 • Established a one-to-one connection between DCSB and the pointwise form of the pion’s wave function. • Dilation measures the rate at which dressed-quark approaches the asymptotic bare-parton limit • Experiments at JLab12 can empirically verify the behaviour of M(p), and hence chart the IR limit of QCD Craig Roberts: Mapping Parton Structure and Correlations (62p)

  33. Pion distribution amplitude from lattice-QCD, I.C. Cloëtet al. arXiv:1306.2645 [nucl-th] Lattice comparisonPion’s valence-quark PDA V. Braun et al., PRD 74 (2006) 074501 • Lattice-QCD • => one nontrivial moment: • <(2x-1)2> = 0.27 ± 0.04 • Legend • Solid = DB (Best) DSE • Dashed = RL DSE • Dotted (black) = 6 x (1-x) • Dot-dashed = midpoint lattice; and the yellow shading exhibits band allowed by lattice errors • DBα=0.31 but 10% a2<0 • RL α=0.29 and 0% a2 φπ~ xα (1-x)α α=0.35 +0.32 = 0.67 - 0.24 = 0.11 Craig Roberts: Mapping Parton Structure and Correlations (62p) Employ the generalised-Gegenbauer method described previously (and in Phys. Rev. Lett. 110 (2013) 132001 (2013) [5 pages]).

  34. Pion distribution amplitude from lattice-QCD, I.C. Cloëtet al. arXiv:1306.2645 [nucl-th] Lattice comparisonPion’s valence-quark PDA Craig Roberts: Mapping Parton Structure and Correlations (62p) • Establishes that contemporary DSE- and lattice-QCD computations, at the same scale, agree on the pointwise form of the pion's PDA, φπ(x). • This unification of DSE- and lattice-QCD results expresses a deeper equivalence between them, expressed, in particular, via the common behaviour they predict for the dressed-quark mass-function, which is both • a definitive signature of dynamical chiral symmetry breaking • and the origin of the distribution amplitude's dilation.

  35. Pion distribution amplitude from lattice-QCD, I.C. Cloëtet al. arXiv:1306.2645 [nucl-th] When is asymptotic PDA valid? asymptotic 4 GeV2 100 GeV2 • Consequently, the asymptotic distribution, • φπasy(x), is a poor approximation to the pion's PDA • at all such scales that are either currently accessible or • foreseeable in experiments on pion elastic and transition form factors. • Thus, related expectations based on φπasy(x) should be revised. Craig Roberts: Mapping Parton Structure and Correlations (62p) Under leading-order evolution, the PDA remains broad to Q2>100 GeV2 Feature signals persistence of the influence of dynamical chiral symmetry breaking.

  36. Pion distribution amplitude from lattice-QCD, I.C. Cloëtet al. arXiv:1306.2645 [nucl-th] When is asymptotic PDA valid? Q2=27 GeV2 This is not δ(x)! Craig Roberts: Mapping Parton Structure and Correlations (62p) φπasy(x) can only be a good approximation to the pion's PDA when it is accurate to write uvπ (x) ≈ δ(x) for the pion's valence-quark distribution function. This is far from valid at currently accessible scales

  37. Pion electromagnetic form factor at spacelikemomenta, Lei Changet al. (in progress) Charged pionelastic form factor • P. Maris & P.C. Tandy,Phys.Rev. C62 (2000) 055204: numerical procedure is practically useless for Q2>4GeV2, so prediction ends! • Algorithm developed for pion PDA overcomes this obstacle • Solves the practical problem of continuing from Euclidean metric formulation to Minkowski space Craig Roberts: Mapping Parton Structure and Correlations (62p)

  38. Pion electromagnetic form factor at spacelikemomenta, Lei Changet al. (in progress) Charged pionelastic form factor • Improved DSE interaction kernel, based on DSE and lattice-QCD studies of gluon sector • S.-x. Qin, L. Chang et al. Phys.Rev. C84 (2011) 042202(R) • New prediction in better agreement with available data than old DSE result • Prediction extends from Q2=0 to arbitrarily large Q2, without interruption, unifying both domains DSE 2000 … Breakdown here Craig Roberts: Mapping Parton Structure and Correlations (62p)

  39. Pion electromagnetic form factor at spacelikemomenta, Lei Changet al. (in progress) Charged pionelastic form factor • Unlimited domain of validity emphasised in this figure • Depict prediction on domain 0<Q2<20GeV2 but have computed the result to Q2=100GeV2. • If it were necessary, reliable results could readily be obtained at even higher values. DSE 2013 Craig Roberts: Mapping Parton Structure and Correlations (62p)

  40. Pion electromagnetic form factor at spacelikemomenta, Lei Changet al. (in progress) Charged pionelastic form factor ρ-meson pole VMD • Predict a maximum at • 6-GeV2, • which lies within domain that is accessible to JLab12 • Difficult, however, to distinguish DSE prediction from Amendolia-1986 monopole • What about comparison with perturbative QCD? Amendoliaet al. DSE 2013 maximum A-rated:E12-06-10 Craig Roberts: Mapping Parton Structure and Correlations (62p)

  41. Pion electromagnetic form factor at spacelikemomenta, Lei Changet al. (in progress) Charged pionelastic form factor • Prediction of pQCD obtained when the pion valence-quark PDA has the form appropriate to the scale accessible in modern experiments is markedly different from the result obtained using the asymptotic PDA • Near agreement between the pertinent perturbative QCD prediction and DSE-2013 prediction is striking. DSE 2013 15% pQCD obtained with φπ(x;2GeV), i.e., the PDA appropriate to the scale of the experiment pQCD obtained withφπasy(x) • Single DSE interaction kernel, determined fully by just one parameter and preserving the one-loop renormalisation group behaviour of QCD, has unified the Fπ(Q2) and φπ(x) (and numerous other quantities) Craig Roberts: Mapping Parton Structure and Correlations (62p)

  42. Pion electromagnetic form factor at spacelikemomenta, Lei Changet al. (in progress) Charged pionelastic form factor • Leading-order, leading-twist QCD prediction, obtained with φπ(x) evaluated at a scale appropriate to the experiment underestimates DSE-2013 prediction by merely an approximately uniform 15%. • Small mismatch is explained by a combination of higher-order, higher-twist corrections & and shortcomings in the rainbow-ladder truncation. DSE 2013 15% pQCD obtained φπ(x;2GeV), i.e., the PDA appropriate to the scale of the experiment pQCD obtained withφπasy(x) • Hence, one should expect dominance of hard • contributions to the pion form factor for Q2>8GeV2. • Nevertheless, the normalisation of the form factor is fixed by a pion wave-function whose dilation with respect to φπasy(x) is a definitive signature of DCSB Craig Roberts: Mapping Parton Structure and Correlations (62p)

  43. R.T. Cahill et al., Austral. J. Phys. 42 (1989) 129-145 Structure of Hadrons SUc(3): Craig Roberts: Mapping Parton Structure and Correlations (62p) • Dynamical chiral symmetry breaking (DCSB) – has enormous impact on meson properties. • Must be included in description and prediction of baryon properties. • DCSB is essentially a quantum field theoretical effect. In quantum field theory • Meson appears as pole in four-point quark-antiquark Green function → Bethe-Salpeter Equation • Nucleon appears as a pole in a six-point quark Green function → Faddeev Equation. • Poincaré covariant Faddeev equation sums all possible exchanges and interactions that can take place between three dressed-quarks • Tractable equation is based on the observation that an interaction which describes colour-singlet mesons also generates nonpointlike quark-quark (diquark) correlations in the colour-antitriplet channel

  44. R.T. Cahill et al., Austral. J. Phys. 42 (1989) 129-145 Faddeev Equation quark exchange ensures Pauli statistics quark diquark composed of strongly-dressed quarks bound by dressed-gluons Craig Roberts: Mapping Parton Structure and Correlations (62p) • Linear, Homogeneous Matrix equation • Yields wave function (Poincaré Covariant FaddeevAmplitude) thatdescribes quark-diquark relative motion within the nucleon • Scalar and Axial-Vector Diquarks . . . • For nucleon, both have “correct” parity and “right” masses • In Nucleon’s Rest Frame Amplitude has s−, p− & d−wave correlations

  45. SU(2)isospin symmetry of hadrons might emerge from mixing half-integer spin particles with their antiparticles. Structure of Hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p) Remarks • Diquark correlations are not inserted by hand Such correlations are a dynamical consequence of strong-coupling in QCD • The same mechanism that produces an almost masslesspion from two dynamically-massive quarks; i.e., DCSB, forces a strong correlation between two quarks in colour-antitriplet channels within a baryon – an indirect consequence of Pauli-Gürsey symmetry • Diquark correlations are not pointlike • Typically, r0+ ~ rπ & r1+ ~ rρ(actually 10% larger) • They have soft form factors

  46. Structure of Hadrons Craig Roberts: Mapping Parton Structure and Correlations (62p) • Elastic form factors • Provide vital information about the structure and composition of the most basic elements of nuclear physics. • They are a measurable and physical manifestation of the nature of the hadrons' constituents and the dynamics that binds them together. • Accurate form factor data are driving paradigmatic shifts in our pictures of hadrons and their structure; e.g., • role of orbital angular momentum and nonpointlikediquark correlations • scale at which p-QCD effects become evident • strangeness content • meson-cloud effects • etc.

  47. L. Chang, Y. –X. Liu and C.D. RobertsarXiv:1009.3458 [nucl-th] Phys. Rev. Lett. 106 (2011) 072001 Photon-nucleon current Vertex must contain the dressed-quark anomalous magnetic moment • In a realistic calculation, the last three diagrams represent 8-dimensional integrals, which can be evaluated using Monte-Carlo techniques Oettel, Pichowsky, Smekal Eur.Phys.J. A8 (2000) 251-281 Craig Roberts: Mapping Parton Structure and Correlations (62p) Composite nucleon must interact with photon via nontrivial current constrained by Ward-Green-Takahashi identities DSE → BSE → Faddeev equation plus current → nucleon form factors

  48. I.C. Cloët, C.D. Roberts, et al. arXiv:0812.0416 [nucl-th] L. Chang, Y. –X. Liu and C.D. RobertsarXiv:1009.3458 [nucl-th] Phys. Rev. Lett. 106 (2011) 072001 • DSE result Dec 08 • DSE result • – including the • anomalous • magnetic • moment distribution • Highlights again the • critical importance of • DCSB in explanation of • real-world observables. Craig Roberts: Mapping Parton Structure and Correlations (62p)

  49. I.C. Cloët, C.D. Roberts, A.W. Thomas: Revealing dressed-quarks via the proton's charge distribution, arXiv: 1304.0855 [nucl-th] Visible Impacts of DCSB • Apparently small changes in M(p) within the domain 1<p(GeV)<3 • have striking effect on the proton’s electric form factor • The possible existence and location of the zero is determined by behaviour of Q2F2p(Q2) • Like the pion’s PDA, Q2F2p(Q2) measures the rate at which dress-ed-quarks become parton-like: • F2p=0 for bare quark-partons • Therefore, GEp can’t be zero on the bare-parton domain Craig Roberts: Mapping Parton Structure and Correlations (62p)

  50. I.C. Cloët, C.D. Roberts, A.W. Thomas: Revealing dressed-quarks via the proton's charge distribution, arXiv: 1304.0855 [nucl-th] Visible Impacts of DCSB • Follows that the • possible existence • and location • of a zero in the ratio of proton elastic form factors • [μpGEp(Q2)/GMp(Q2)] • are a direct measure of the nature of the quark-quark interaction in the Standard Model. Craig Roberts: Mapping Parton Structure and Correlations (62p)

More Related