Craig Roberts Physics Division. 1.Rocio BERMUDEZ (U Michoácan); 2.Xiomara GUTIERREZ-GUERRERO (U...
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Transcript of Craig Roberts Physics Division. 1.Rocio BERMUDEZ (U Michoácan); 2.Xiomara GUTIERREZ-GUERRERO (U...
Images of theOrigin of Mass
Craig Roberts
Physics Division
Craig Roberts: Images of the Origin of Mass (44p)
2
Collaborators: 2011-Present1. Rocio BERMUDEZ (U Michoácan);2. Xiomara GUTIERREZ-GUERRERO (U Michoácan);3. S. HERNÁNDEZ (U Michoácan);4. Trang NGUYEN (KSU);5. Khépani RAYA (U Michoácan);6. Hannes ROBERTS (ANL, FZJ, UBerkeley);7. Chien-Yeah SENG (UW-Mad)8. Kun-lun WANG (PKU);9. Chen CHEN (USTC);10. J. Javier COBOS-MARTINEZ (U.Sonora);11. Mario PITSCHMANN (ANL & UW-Mad);12. Si-xue QIN (U. Frankfurt am Main);13. Jorge SEGOVIA (ANL);14. David WILSON (ODU);15. Lei CHANG (U.Adelaide); 16. Ian CLOËT (ANL);17. Bruno EL-BENNICH (São Paulo);
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18. Adnan BASHIR (U Michoácan);19. Stan BRODSKY (SLAC);20. Gastão KREIN (São Paulo)21. Roy HOLT (ANL);22. Mikhail IVANOV (Dubna);23. Yu-xin LIU (PKU);24. Michael RAMSEY-MUSOLF (UW-Mad)25. Alfredo RAYA (U Michoácan);26. Sebastian SCHMIDT (IAS-FZJ & JARA);27. Robert SHROCK (Stony Brook);28. Peter TANDY (KSU);29. Tony THOMAS (U.Adelaide)30. Shaolong WAN (USTC)
StudentsPostdocsAsst. Profs.
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Overarching Science Challenges for the coming
decade: 2013-2022 Discover the meaning of confinement Determine its connection with DCSB
(dynamical chiral symmetry breaking) Elucidate their signals in observables
… so experiment and theory together can map the nonperturbative behaviour of the strong interaction
In my view, it is unlikely that two phenomena, so critical in the Standard Model and tied to the dynamical generation of a single mass-scale, can have different origins and fates.
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Craig Roberts: Images of the Origin of Mass (44p)
Craig Roberts: Images of the Origin of Mass (44p)
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Immediate Science Challenges for the coming decade: 2013-
2022 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 baryon structure– Expose facts & fallacies in modern descriptions of hadron structure
Precision experimental study of (far) 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
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What is QCD?MENU 2013: 30/09-04/10
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Very likely a self-contained, nonperturbatively renormalisable and hence well defined Quantum Field TheoryThis is not true of QED – cannot be defined nonperturbatively
No confirmed breakdown over an enormous energy domain: 0 GeV < E < 8 TeV
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
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(not an effective theory)QCD is a Theory
Craig Roberts: Images of the Origin of Mass (44p)
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What is Confinement?
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Light quarks & Confinement
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.”
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Craig Roberts: Images of the Origin of Mass (44p)
Folklore … Hall-D Conceptual Design Report(5) “The color field lines between a quark and an anti-quark form flux tubes.
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Light quarks & Confinement
Problem: 16 tonnes of force makes a lot of pions.
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Light quarks & Confinement
Problem: 16 tonnes of force makes a lot of pions.
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Light quarks & Confinement 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
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G. Bali et al., PoS LAT2005 (2006) 308
Craig Roberts: Images of the Origin of Mass (44p)
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Confinement 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
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complex-P2 complex-P2
o Real-axis mass-pole splits, moving into pair(s) of complex conjugate singularities, (or other qualitatively analogous structures chracterised by a dynamically generated mass-scale)o State described by rapidly damped wave & hence state cannot exist in observable spectrum
Normal particle Confined particle
timelike axis: P2<0
s ≈ 1/Im(m) ≈ 1/2ΛQCD ≈ ½fm
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Dynamical Chiral Symmetry Breaking
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Dynamical Chiral Symmetry BreakingDCSB is a fact in QCD
– Dynamical, not spontaneous• Add nothing to QCD , no Higgs field, nothing! • Effect achieved purely through the quark+gluon dynamics.
– It’s the most important mass generating mechanism for visible matter in the Universe. • Responsible for ≈98% of the proton’s mass.• Higgs mechanism is (almost) irrelevant to light-quarks.
– Just like gluons and quarks, and for the same reasons, condensates are confined within hadrons. • There are no vacuum condensates.
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Craig Roberts: Images of the Origin of Mass (44p)Confinement contains condensates, S.J. Brodsky, C.D. Roberts, R. Shrock and P.C. Tandy, arXiv:1202.2376 [nucl-th], Phys. Rev. C85 (2012) 065202
Craig Roberts: Images of the Origin of Mass (44p)
DCSB
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Mass from nothing!
C.D. Roberts, Prog. Part. Nucl. Phys. 61 (2008) 50M. 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 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.
16
Parton structure of
hadronsMENU 2013: 30/09-04/10
Craig Roberts: Images of the Origin of Mass (44p)
Valence quarks
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Parton Structure of Hadrons
Valence-quark structure of hadrons– Definitive of a hadron.
After all, it’s how we distinguish 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?
Answers are essentially nonperturbative features of QCD
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Parton Structure of Hadrons
Need for calculation is emphasised by Saga of pion’s valence-quark distribution:o 1989: uv
π ~ (1-x)1 – inferred from LO-Drell-Yan & disagrees with QCD;
o 2001: DSE- QCD predictsuv
π ~ (1-x)2 argues that distribution inferred from data can’t be correct;
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Valence quark distributions in the pion, M.B. Hecht, Craig D. Roberts, S.M. Schmidt, nucl-th/0008049, Phys.Rev. C63 (2001) 025213 .
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Parton Structure of Hadrons
Need for calculation is emphasised by Saga of pion’s valence-quark distribution:o 1989: uv
π ~ (1-x)1 – inferred from LO-Drell-Yan & disagrees with QCD;
o 2001: DSE- QCD predicts uv
π ~ (1-x)2 argues that distribution inferred from data can’t be correct;
o 2010: NLO reanalysis including soft-gluon resummation, inferred distribution agrees with DSE and QCD
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Soft-gluon resummation and the valence parton distribution function of the pion, M. Aicher, A. Schafer, W. Vogelsang, Phys.Rev.Lett. 105 (2010) 252003, arXiv:1009.2481 [hep-ph]
Valence quark distributions in the pion, M.B. Hecht, Craig D. Roberts, S.M. Schmidt, nucl-th/0008049, Phys.Rev. C63 (2001) 025213 .
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Pion’s valence-quark Distribution Amplitude
Same methods can be used to compute φπ(x) = projection of the pion’s Poincaré-covariant wave-function onto the light-front
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
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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].
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Pion’s valence-quark Distribution Amplitude
Both kernels agree: marked broadening of φπ(x), which owes to DCSB
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Asymptotic
RL
DB
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
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].
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Pion’s valence-quark Distribution Amplitude
Both kernels agree: marked broadening of φπ(x), which owes to DCSB
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Craig Roberts: Images of the Origin of Mass (44p)
Asymptotic
RL
DB
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
These computations are the first to directly expose DCSB – pointwise – on the light-front; i.e., in the infinite momentum frame.
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].
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Pion’s valence-quark Distribution Amplitude
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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
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
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].
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When is asymptotic PDA valid?
PDA is a wave function not directly observable
but PDF is. φπ
asy(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
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Q2=27 GeV2
This is not δ(x)!
Explanation and Prediction of Observables using Continuum Strong QCD, I.C. Cloët & C.D. Roberts
Craig Roberts: Images of the Origin of Mass (44p)
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When is asymptotic PDA valid? When is asymptopia reached?
If uvπ(x) ≈ δ(x), then
<x> = ∫01 dx x uv
π(x) = 0;
i.e., the light-front momentum fraction carried by valence-quarks is ZERO Asymptopia is reached when <x> is “small”
As usual, the computed valence-quark distribution produces (π = u+dbar)
2<x>2GeV = 44% When is <x> small?
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Explanation and Prediction of Observables using Continuum Strong QCD, I.C. Cloët & C.D. Roberts
NLO evolution of PDF, computation of <x>. Even at LHC energies, light-front fraction of
the π momentum:<x>dressed valence-quarks = 25%
<x>glue = 54%, <x>sea-quarks = 21%
LHC: 16TeV
Evolution in QCD is LOGARITHMIC
JLab 2GeV
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When is asymptotic PDA valid? When is asymptopia reached?
If uvπ(x) ≈ δ(x), then
<x> = ∫01 dx x uv
π(x) = 0;
i.e., the light-front momentum fraction carried by valence-quarks is ZERO Asymptopia is reached when <x> is “small”
As usual, the computed valence-quark distribution produces (π = u+dbar)
2<x>2GeV = 44% When is <x> small?
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Explanation and Prediction of Observables using Continuum Strong QCD, I.C. Cloët & C.D. Roberts
NLO evolution of PDF, computation of <x>. Even at LHC energies, light-front fraction of
the π momentum:<x>dressed valence-quarks = 25%
<x>glue = 54%, <x>sea-quarks = 21%
LHC: 16TeV
Evolution in QCD is LOGARITHMIC
JLab 2GeV
Even at LHC energy scales, nonperturbative effects, such as DCSB, are playing a crucial role in setting the scales in PDAs and PDFs.
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Charged pion elastic form factor
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Single interaction kernel, determined by just 1 parameter and preserving the one-loop RG-behaviour of QCD, had unified Fπ(Q2) and φπ(x) (and many other quantities)
New Algorithm
Pion electromagnetic form factor at spacelike momenta, Lei Chang et al. arXiv:1307.0026 [nucl-th], Phys. Rev. Lett. in press
DSE 2013
pQCD obtained with φπasy(x)
pQCD obtained with φπ(x;2GeV), i.e., the PDA appropriate to the scale of the experiment
15%DSE 2000
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Charged pion elastic form factor
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Single interaction kernel, determined by just 1 parameter and preserving the one-loop RG-behaviour of QCD, has unified Fπ(Q2) and φπ(x) (and many other quantities)
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
Pion electromagnetic form factor at spacelike momenta, Lei Chang et al. arXiv:1307.0026 [nucl-th], Phys. Rev. Lett. in press
DSE 2013
pQCD obtained with φπasy(x)
pQCD obtained with φπ(x;2GeV), i.e., the PDA appropriate to the scale of the experiment
15%
Near agreement between the pertinent perturbative QCD prediction and DSE-2013 prediction is striking.
Dominance of hard contributions to the pion form factor for Q2>8GeV2. Normalisation is fixed by a pion wave-function whose dilation with respect to φπ
asy(x) is a definitive signature of DCSB
Craig Roberts: Images of the Origin of Mass (44p)
Baryon Structure 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
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R.T. Cahill et al.,Austral. J. Phys. 42 (1989) 129-145
6333 SUc(3):
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Baryon Structure
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 massless pion 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
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SU(2) isospin symmetry of hadrons might emerge from mixing half-integer spin particles with their antiparticles.
Faddeev Equation
31
Structure of Hadrons 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 nonpointlike diquark
correlations– scale at which p-QCD effects become evident– strangeness content– meson-cloud effects– etc.
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Flavor separation of proton form factors
Very different behavior for u & d quarks Means apparent scaling in proton F2/F1 is purely accidental
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Cates, de Jager, Riordan, Wojtsekhowski, PRL 106 (2011) 252003
Q4F2q/k
Q4 F1q
Craig Roberts: Images of the Origin of Mass (44p)
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Diquark correlations!
Poincaré covariant Faddeev equation – Predicts scalar and axial-vector
diquarks Proton's singly-represented d-quark
more likely to be struck in association with 1+ diquark than with 0+
– form factor contributions involving 1+ diquark are softer
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Cloët, Eichmann, El-Bennich, Klähn, Roberts, Few Body Syst. 46 (2009) pp.1-36Wilson, Cloët, Chang, Roberts, PRC 85 (2012) 045205
Doubly-represented u-quark is predominantly linked with harder 0+ diquark contributions
Interference produces zero in Dirac form factor of d-quark in proton– Location of the zero depends on the relative probability of finding
1+ & 0+ diquarks in proton– Correlated, e.g., with valence d/u ratio at x=1
d
u
=Q2/M2
Craig Roberts: Images of the Origin of Mass (44p)
Visible Impacts of DCSB
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Apparently small changes in M(p) within the domain 1<p(GeV)<3have striking effect on the proton’s electric form factor
The possible existence and location of the zero is determined by behaviour of Q2F2
p(Q2) Like the pion’s PDA, Q2F2
p(Q2) measures the rate at which dressed-quarks become parton-like: F2
p=0 for bare quark-partons Therefore, GE
p can’t be zero on the bare-parton domain
I.C. Cloët, C.D. Roberts, A.W. Thomas: Revealing dressed-quarks via the proton's charge distribution, arXiv:1304.0855 [nucl-th], Phys. Rev. Lett. 111 (2013) 101803
Craig Roberts: Images of the Origin of Mass (44p)
Visible Impacts of DCSB
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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.
Leads to Prediction neutron:protonGEn(Q2) > GEp(Q2) at Q2 > 4GeV2
I.C. Cloët, C.D. Roberts, A.W. Thomas: Revealing dressed-quarks via the proton's charge distribution, arXiv:1304.0855 [nucl-th], Phys. Rev. Lett. 111 (2013) 101803
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Far valence domain x≃1
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Far valence domain x≃1
Endpoint of the far valence domain: x 1, is especially significant≃– All familiar PDFs vanish at x=1; but ratios of any two need not– Under DGLAP evolution, the value of such a ratio is invariant.
Thus, e.g., – limx→1 dv(x)/uv(x)
is unambiguous, scale invariant, nonperturbative feature of QCD. keen discriminator between frameworks that claim to explain nucleon structure.
Furthermore, Bjorken-x=1 corresponds strictly to the situation in which the invariant mass of the hadronic final state is precisely that of the target; viz., elastic scattering. Structure functions inferred experimentally on x 1 ≃
are determined theoretically by target's elastic form factors.
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Nucleon spin structure at very high-xCraig D. Roberts, Roy J. Holt and Sebastian M. SchmidtarXiv:1308.1236 [nucl-th], Phys. Lett. B in press
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Neutron Structure Function at high-x
Valence-quark distributions at x=1– Fixed point under DGLAP evolution– Strong discriminator between theories
Algebraic formula
– P1p,s = contribution to the proton's charge arising from diagrams
with a scalar diquark component in both the initial and final state
– P1p,a = kindred axial-vector diquark contribution
– P1p,m = contribution to the proton's charge arising from diagrams
with a different diquark component in the initial and final state.
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I.C. Cloët, C.D. Roberts, et al.arXiv:0812.0416 [nucl-th], Few Body Syst. 46 (2009) 1-36D. J. Wilson, I. C. Cloët, L. Chang and C. D. RobertsarXiv:1112.2212 [nucl-th], Phys. Rev. C85 (2012) 025205 [21 pages]
Measures relative strength of axial-vector/scalar diquarks in proton
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Neutron StructureFunction at high-x
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d/u=1/2
SU(6) symmetry
pQCD, uncorrelated Ψ
0+ qq only, d/u=0
Deep inelastic scattering – the Nobel-prize winning quark-discovery experiments
Reviews: S. Brodsky et al.
NP B441 (1995) W. Melnitchouk & A.W.Thomas
PL B377 (1996) 11 N. Isgur, PRD 59 (1999) R.J. Holt & C.D. Roberts
RMP (2010)
d/u=0.28
DSE: “realistic”
Distribution of neutron’s momentum amongst quarks on the valence-quark domain
DSE: “contact”d/u=0.18
Melnitchouk, Accardi et al. Phys.Rev. D84 (2011) 117501
x>0.9
Melnitchouk, Arrington et al. Phys.Rev.Lett. 108 (2012) 252001
I.C. Cloët, C.D. Roberts, et al.arXiv:0812.0416 [nucl-th], Few Body Syst. 46 (2009) 1-36D. J. Wilson, I. C. Cloët, L. Chang and C. D. RobertsarXiv:1112.2212 [nucl-th], Phys. Rev. C85 (2012) 025205 [21 pages]
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Neutron StructureFunction at high-x
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d/u=1/2
SU(6) symmetry
pQCD, uncorrelated Ψ
0+ qq only, d/u=0
Deep inelastic scattering – the Nobel-prize winning quark-discovery experiments
Reviews: S. Brodsky et al.
NP B441 (1995) W. Melnitchouk & A.W.Thomas
PL B377 (1996) 11 N. Isgur, PRD 59 (1999) R.J. Holt & C.D. Roberts
RMP (2010)
d/u=0.28
DSE: “realistic”
Distribution of neutron’s momentum amongst quarks on the valence-quark domain
DSE: “contact”d/u=0.18
Melnitchouk, Accardi et al. Phys.Rev. D84 (2011) 117501
x>0.9
Melnitchouk, Arrington et al. Phys.Rev.Lett. 108 (2012) 252001
I.C. Cloët, C.D. Roberts, et al.arXiv:0812.0416 [nucl-th], Few Body Syst. 46 (2009) 1-36D. J. Wilson, I. C. Cloët, L. Chang and C. D. RobertsarXiv:1112.2212 [nucl-th], Phys. Rev. C85 (2012) 025205 [21 pages]
NB. d/u|x=1= 0 means there are
no valence d-quarks in the proton!
JLab12 can solve this enigma
Craig Roberts: Images of the Origin of Mass (44p)
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Neutron StructureFunction at high-x
“While it is quite hazardous to extrapolate from our limited xB range all the way to xB = 1, these results appear to disfavor models of the proton with d/u=0 at xB = 1”
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Short Range Correlations and the EMC Effect, L.B. Weinstein et al., Phys.Rev.Lett. 106 (2011) 052301, arXiv:1009.5666 [hep-ph]
Figure courtesy of D.W. Higinbotham
Observation: EMC effect measured in electron DIS at 0.35 < xB < 0.7, is linearly related to the Short Range Correlation (SRC) scale factor obtained from electron inclusive scattering at xB > 1.
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Nucleon spin structure at very high x
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Similar formulae for nucleon longitudinal structure functions.
Plainly, existing data cannot distinguish between modern pictures of nucleon structure
Empirical results for nucleon longitudinal spin asymmetries on x ≃ 1 promise to add greatly to our capacity for discriminating between contemporary pictures of nucleon structure.
NB. pQCD is actually model-dependent: assumes SU(6) spin-flavour wave function for the proton's valence-quarks and the corollary that a hard photon may interact only with a quark that possesses the same helicity as the target.
Nucleon spin structure at very high-xCraig D. Roberts, Roy J. Holt and Sebastian M. SchmidtarXiv:1308.1236 [nucl-th], Phys. Lett. B in press
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EpilogueMENU 2013: 30/09-04/10
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Epilogue The Physics of Hadrons is Unique:– Confronting a fundamental theory in which the
elementary degrees-of-freedom are intangible and only composites reach detectors
Confinement in real-world is NOT understood But DCSB is understood, and is crucial to any
understanding of hadron phenomena
They must have a common origin Experimental and theoretical study of the Bound-
state problem in continuum QCD promises to provide many more
predictions, insights and answers.MENU 2013: 30/09-04/10
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This is not the end
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Lattice comparisonPion’s valence-quark PDA
Employ the generalised-Gegenbauer method described previously (and in Phys. Rev. Lett. 110 (2013) 132001 (2013) [5 pages]).
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Craig Roberts: Images of the Origin of Mass (44p)
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
φπ~ xα (1-x)α
α=0.35+0.32 = 0.67- 0.24 = 0.11
DB α=0.31 but 10% a2<0RL α=0.29 and 0% a2
V. Braun et al., PRD 74 (2006) 074501
Pion distribution amplitude from lattice-QCD, I.C. Cloët et al. arXiv:1306.2645 [nucl-th]
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When is asymptotic PDA valid?
Under leading-order evolution, the PDA remains broad to Q2>100 GeV2
Feature signals persistence of the influence of dynamical chiral symmetry breaking.
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Craig Roberts: Images of the Origin of Mass (44p)
Consequently, the asymptotic distribution, φπ
asy(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.
asymptotic
4 GeV2
100 GeV2
Pion distribution amplitude from lattice-QCD, I.C. Cloët et al. arXiv:1306.2645 [nucl-th], Phys. Rev. Lett. 111 (2013) 092001 [5 pages]
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Flavor separation of proton form factors
Visible Impacts of DCSB
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Effect driven primarily by electric form factor of doubly-represented u-quark
u-quark is 4-times more likely than d-quark to be involved in hard interaction
So … GEpu ≈ GEp
Singly-represented d-quark is usually sequestered inside a soft diquark correlation
So, although it also becomes parton-like more quickly as α increases, that is hidden from view
d-quark
u-quark
I.C. Cloët & C.D. Roberts … continuing
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Confinement contains
condensatesMENU 2013: 30/09-04/10
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“Orthodox Vacuum”
Vacuum = “frothing sea” Hadrons = bubbles in that “sea”,
containing nothing but quarks & gluonsinteracting perturbatively, unless they’re near the bubble’s boundary, whereat they feel they’re trapped!
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u
u
ud
u ud
du
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New Paradigm
Vacuum = hadronic fluctuations but no condensates
Hadrons = complex, interacting systemswithin which perturbative behaviour is restricted to just 2% of the interior
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u
u
ud
u ud
du
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Regge Trajectories? Martinus Veltmann, “Facts and Mysteries in Elementary Particle Physics” (World Scientific,
Singapore, 2003): In time the Regge trajectories thus became the cradle of string theory. Nowadays the Regge trajectories have largely disappeared, not in the least because these higher spin bound states are hard to find experimentally. At the peak of the Regge fashion (around 1970) theoretical physics produced many papers containing families of Regge trajectories, with the various (hypothetically straight) lines based on one or two points only!
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Phys.Rev. D 62 (2000) 016006 [9 pages]
1993: "for elucidating the quantum structure of electroweak interactions in physics"
Systematics of radial and angular-momentum Regge trajectories of light non-strange qqbar-states“ P. Masjuan, E. Ruiz Arriola, W. Broniowski. arXiv:1305.3493 [hep-ph]
Craig Roberts: Images of the Origin of Mass (44p)
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Hybrid Hadrons & Lattice QCD – Robert Edwards, Baryons13
Heavy pions … so, naturally, constituent-quark like spectra To which potential does it correspond?
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arXiv:1104.5152, 1201.2349
Craig Roberts: Images of the Origin of Mass (44p)
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Hybrid meson models – Robert Edwards, Baryons13
With minimal quark content, , gluonic field can in a color singlet or octet
`constituent’ gluonin S-wave
`constituent’ gluonin P-wave
bag model
flux-tube model
arXiv:1104.5152, 1201.2349
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Hybrid baryon models – Robert Edwards, Baryons13
Minimal quark content, , gluonic field can be in color singlet, octet or decuplet
bag model
flux-tube model
Now must take into account permutation symmetry of quarks and gluonic field
arXiv:1104.5152, 1201.2349
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Table of ContentsI. IntroductionII. Pion valence-quark distributionIII. Pion valence-quark parton distribution amplitudeIV. When is the asymptotic PDA a good approximation?V. Charged pion elastic form factorVI. Nucleon form factorsVII. Nucleon structure functions at large-xVIII. Epilogue
A. DSE cf. Lattice PDA & PDA evolutionB. GE/GM flavour separationC. Confinement contains condensatesD. Regge Trajectories?
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