Parton distribution functions(PDFs)are defining expressions of hadron structure.Exploiting the role of effective charges in quantum chromodynamics,an algebraic scheme is described which,given any hadron’s valence par...Parton distribution functions(PDFs)are defining expressions of hadron structure.Exploiting the role of effective charges in quantum chromodynamics,an algebraic scheme is described which,given any hadron’s valence parton PDFs at the hadron scale,delivers predictions for all its PDFs(unpolarized and polarized)at any higher scale.The scheme delivers results that are largely independent of both the value of the hadron scale and the pointwise form of the charge;and,inter alia,enables derivation of a model-independent identity that relates the strength of the proton’s gluon helicity PDF,ΔG_(p)ζ,to that of the analogous singlet polarized quark PDF and valence quark momentum fraction.Using available data fits and theory predictions,the identity yieldsΔG_(p)(ζC=√3 GeV)=1.48(10).It furthermore entails that the measurable quark helicity contribution to the proton spin is a_(op)^(ζC)=0.32(3),thereby reconciling contemporary experiment and theory.展开更多
Beginning with precise data on the ratio of structure functions in deep inelastic scattering(DIS)from ^3He and ^3H,collected on the domain 0.19≤xB≤0.83,where xBis the Bjorken scaling variable,we employ a robust meth...Beginning with precise data on the ratio of structure functions in deep inelastic scattering(DIS)from ^3He and ^3H,collected on the domain 0.19≤xB≤0.83,where xBis the Bjorken scaling variable,we employ a robust method for extrapolating such data to arrive at a model-independent result for the xB=1 value of the ratio of neutron and proton structure functions.Combining this with information obtained in analyses of DIS from nuclei,corrected for target-structure dependence,we arrive at a prediction for the proton valence-quark ratio:d_(v)/u_(v)|_(xB→1)=0.230(57).Requiring consistency with this result presents a challenge to many descriptions of proton structure.展开更多
Using a procedure based on interpolation via continued fractions supplemented by statistical sampling,we analyze proton magnetic form factor data obtained via electron+proton scattering on Q^(2)∈[0.027,0.55]GeV^(2)wi...Using a procedure based on interpolation via continued fractions supplemented by statistical sampling,we analyze proton magnetic form factor data obtained via electron+proton scattering on Q^(2)∈[0.027,0.55]GeV^(2)with the goal of determining the proton magnetic radius.The approach avoids assumptions about the function form used for data interpolation and ensuing extrapolation onto Q^(2)■0 for extraction of the form factor slope.In this way,we find r_(M)=0.817(27)fm.Regarding the difference between proton electric and magnetic radii calculated in this way,extant data are seen to be compatible with the possibility that the slopes of the proton Dirac and Pauli form factors,F1,2(Q^(2)),are not truly independent observables;to wit,the difference F_(1)’(0)-F_(2)’(0)/κp=[1+Kp]/[4 m_(p)^(2)],viz.,the proton Foldy term.展开更多
A novel method for constructing a kernel for the meson bound-state problem is described.It produces a closed form that is symmetry-consistent(discrete and continuous)with the gap equation defined by any admissible glu...A novel method for constructing a kernel for the meson bound-state problem is described.It produces a closed form that is symmetry-consistent(discrete and continuous)with the gap equation defined by any admissible gluon-quark vertex,Γ.Applicable even when the diagrammatic content ofΓis unknown,the scheme can foster new synergies between continuum and lattice approaches to strong interactions.The framework is illustrated by showing that the presence of a dressed-quark anomalous magnetic moment inΓ,an emergent feature of strong interactions,can remedy many defects of widely used meson bound-state kernels,including the mass splittings between vector and axial-vector mesons and the level ordering of pseudoscalar and vector meson radial excitations.展开更多
Understanding why the scale of emergent hadron mass is obvious in the proton but hidden in the pion may rest on mapping the distribution functions(DFs)of all partons within the pion and comparing them with those in th...Understanding why the scale of emergent hadron mass is obvious in the proton but hidden in the pion may rest on mapping the distribution functions(DFs)of all partons within the pion and comparing them with those in the proton;and since glue provides binding in quantum chromodynamics,the glue DF could play a special role.Producing reliable predictions for the proton’s DFs is difficult because the proton is a three-valence-body bound-state problem.As sketched herein,the situation for the pion,a two-valence-body problem,is much better,with continuum and lattice predictions for the valence-quark and glue DFs in agreement.This beginning of theory alignment is timely because experimental facilities now either in operation or planning promise to realize the longstanding goal of providing pion targets,thereby enabling precision experimental tests of rigorous theory predictions concerning Nature’s most fundamental Nambu-Goldstone bosons.展开更多
Conceptually,radii are amongst the simplest Poincaré-invariant properties that can be associated with hadrons and light nuclei.Accurate values of these quantities are necessary so that one may judge the character...Conceptually,radii are amongst the simplest Poincaré-invariant properties that can be associated with hadrons and light nuclei.Accurate values of these quantities are necessary so that one may judge the character of putative solutions to the strong interaction problem within the Standard Model.However,limiting their ability to serve in this role,recent measurements and new analyses of older data have revealed uncertainties and imprecisions in the radii of the proton,pion,kaon,and deuteron.In the context of radius measurement using electron+hadron elastic scattering,the past decade has shown that reliable extraction requires minimisation of bias associated with practitioner-dependent choices of data fitting functions.Different answers to that challenge have been offered;and this perspective describes the statistical Schlessinger point method(SPM),in unifying applications to proton,pion,kaon,and deuteron radii.Grounded in analytic function theory,independent of assumptions about underlying dynamics,free from practitioner-induced bias,and applicable in the same form to diverse systems and observables,the SPM returns an objective expression of the information contained in any data under consideration.Its robust nature and versatility make it suitable for use in many branches of experiment and theory.展开更多
We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spe...We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small-to large-Q2; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12135007)Nanjing University of Posts and Telecommunications Science Foundation(Grant No.NY221100)+2 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20220122)Spanish Ministry of Science and Innovation(MICINN Grant No.PID2019-107844GBC22)Junta de Andalucía(Grant No.P18-FR-5057)。
文摘Parton distribution functions(PDFs)are defining expressions of hadron structure.Exploiting the role of effective charges in quantum chromodynamics,an algebraic scheme is described which,given any hadron’s valence parton PDFs at the hadron scale,delivers predictions for all its PDFs(unpolarized and polarized)at any higher scale.The scheme delivers results that are largely independent of both the value of the hadron scale and the pointwise form of the charge;and,inter alia,enables derivation of a model-independent identity that relates the strength of the proton’s gluon helicity PDF,ΔG_(p)ζ,to that of the analogous singlet polarized quark PDF and valence quark momentum fraction.Using available data fits and theory predictions,the identity yieldsΔG_(p)(ζC=√3 GeV)=1.48(10).It furthermore entails that the measurable quark helicity contribution to the proton spin is a_(op)^(ζC)=0.32(3),thereby reconciling contemporary experiment and theory.
基金supported by the National Natural Science Foundation of China(Grant Nos.12135007 and 11805097)the Alexander von Humboldt Foundation+1 种基金and STRONG-2020“The strong interaction at the frontier of knowledge:fundamental research and applications”which received funding from the European Union’s Horizon 2020 research and innovation programme(Grant No.824093)。
文摘Beginning with precise data on the ratio of structure functions in deep inelastic scattering(DIS)from ^3He and ^3H,collected on the domain 0.19≤xB≤0.83,where xBis the Bjorken scaling variable,we employ a robust method for extrapolating such data to arrive at a model-independent result for the xB=1 value of the ratio of neutron and proton structure functions.Combining this with information obtained in analyses of DIS from nuclei,corrected for target-structure dependence,we arrive at a prediction for the proton valence-quark ratio:d_(v)/u_(v)|_(xB→1)=0.230(57).Requiring consistency with this result presents a challenge to many descriptions of proton structure.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12135007 and 11805097)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20180323)STRONG-2020,“the strong interaction at the frontier of knowledge:fundamental research and applications”which received funding from the European Union’s Horizon 2020 Research and Innovation Programme(Grant No.824093)。
文摘Using a procedure based on interpolation via continued fractions supplemented by statistical sampling,we analyze proton magnetic form factor data obtained via electron+proton scattering on Q^(2)∈[0.027,0.55]GeV^(2)with the goal of determining the proton magnetic radius.The approach avoids assumptions about the function form used for data interpolation and ensuing extrapolation onto Q^(2)■0 for extraction of the form factor slope.In this way,we find r_(M)=0.817(27)fm.Regarding the difference between proton electric and magnetic radii calculated in this way,extant data are seen to be compatible with the possibility that the slopes of the proton Dirac and Pauli form factors,F1,2(Q^(2)),are not truly independent observables;to wit,the difference F_(1)’(0)-F_(2)’(0)/κp=[1+Kp]/[4 m_(p)^(2)],viz.,the proton Foldy term.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11805024 and 11947406).
文摘A novel method for constructing a kernel for the meson bound-state problem is described.It produces a closed form that is symmetry-consistent(discrete and continuous)with the gap equation defined by any admissible gluon-quark vertex,Γ.Applicable even when the diagrammatic content ofΓis unknown,the scheme can foster new synergies between continuum and lattice approaches to strong interactions.The framework is illustrated by showing that the presence of a dressed-quark anomalous magnetic moment inΓ,an emergent feature of strong interactions,can remedy many defects of widely used meson bound-state kernels,including the mass splittings between vector and axial-vector mesons and the level ordering of pseudoscalar and vector meson radial excitations.
文摘Understanding why the scale of emergent hadron mass is obvious in the proton but hidden in the pion may rest on mapping the distribution functions(DFs)of all partons within the pion and comparing them with those in the proton;and since glue provides binding in quantum chromodynamics,the glue DF could play a special role.Producing reliable predictions for the proton’s DFs is difficult because the proton is a three-valence-body bound-state problem.As sketched herein,the situation for the pion,a two-valence-body problem,is much better,with continuum and lattice predictions for the valence-quark and glue DFs in agreement.This beginning of theory alignment is timely because experimental facilities now either in operation or planning promise to realize the longstanding goal of providing pion targets,thereby enabling precision experimental tests of rigorous theory predictions concerning Nature’s most fundamental Nambu-Goldstone bosons.
基金Supported by the National Natural Science Foundation of China(12135007)Natural Science Foundation of Jiangsu Province(BK20220122)STRONG-2020"The strong interaction at the frontier of knowledge:fundamental research and applications"which received funding from the European Union's Horizon 2020 research and innovation programme(824093)。
文摘Conceptually,radii are amongst the simplest Poincaré-invariant properties that can be associated with hadrons and light nuclei.Accurate values of these quantities are necessary so that one may judge the character of putative solutions to the strong interaction problem within the Standard Model.However,limiting their ability to serve in this role,recent measurements and new analyses of older data have revealed uncertainties and imprecisions in the radii of the proton,pion,kaon,and deuteron.In the context of radius measurement using electron+hadron elastic scattering,the past decade has shown that reliable extraction requires minimisation of bias associated with practitioner-dependent choices of data fitting functions.Different answers to that challenge have been offered;and this perspective describes the statistical Schlessinger point method(SPM),in unifying applications to proton,pion,kaon,and deuteron radii.Grounded in analytic function theory,independent of assumptions about underlying dynamics,free from practitioner-induced bias,and applicable in the same form to diverse systems and observables,the SPM returns an objective expression of the information contained in any data under consideration.Its robust nature and versatility make it suitable for use in many branches of experiment and theory.
基金Supported by the Project of Knowledge Innovation Program of the Chinese Academy of Sciences under Grant No. KJCX2.YW.W10Sistema Nacional de Investigadores+8 种基金CONACyT grant 46614-Fthe University of Adelaide and the Australian Research Council through Grant No. FL0992247Coordinación de la Investigación Científica (UMSNH) under Grant 4.10the U. S. Department of Energy, Office of Nuclear Physics, Grant No. DE-AC02-06CH11357Fundao de Amparo Pesquisa do Estado de So Paulo, Grant Nos. 2009/51296-1 and 2010/05772-3the National Natural Science Foundation of China under Grant Nos. 10425521, 10675002, 10705002, 10935001 and 11075052the Major State Basic Research Development Program, under Grant No. G2007CB815000Forschungszentrum Jülich GmbHthe U. S.National Science Foundation under Grant No. PHY-0903991, in conjunction with a CONACyT Mexico-USA Collaboration Grant
文摘We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small-to large-Q2; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.
