Update on the Hadron Structure Explored at Current and Future Facilities

Transcription

1 3D Nucleon Tomography Workshop Modeling and Extracting Methodology Update on the Hadron Structure Explored at Current and Future Facilities Jianwei Qiu September 25-29, 2017 Salamanca, Spin

2 Atomic Structure QED q Rutherford s experiment (over 100 years ago): Atom: Experiment Theory J.J. Thomson s plum-pudding model Rutherford s planetary model Quantum orbitals Discovery: ² Tiny nucleus - less than 1 trillionth in volume of an atom ² Quantum probability - the Quantum World!

3 Atomic Structure QED q Rutherford s experiment (over 100 years ago): Atom: Experiment Theory J.J. Thomson s plum-pudding model Rutherford s planetary model Quantum orbitals Discovery: ² Tiny nucleus - less than 1 trillionth in volume of an atom ² Quantum probability - the Quantum World! q Localized mass and charge centers vast open space: Molecule: Crystal: Nanomaterial: Water Rare-Earth metal Infinite opportunities to create & improve! Carbon-based

4 Hadronic Structure QCD q Modern Rutherford experiment SLAC (about 50 years ago): Quark-Model QCD DIS SIDIS EDIS Nucleon: Strongly interacting, relativistic bound state of quarks & gluons

5 Hadronic Structure QCD q Modern Rutherford experiment SLAC (about 50 years ago): Quark-Model QCD DIS SIDIS EDIS Nucleon: Strongly interacting, relativistic bound state of quarks & gluons q NO localized mass and charge centers Strong fluctuation : Nuclei Molecule XYZ Nuclei Short-range correlation Light-flavor Heavy-flavor New frontier of hadron physics! Femto-technology

6 Outline of my talk q How to quantify the hadron structure in QCD? q How to see hadron structure? q What have we learned from existing facilities? q What do we hope to learn from future facilities? ² From Electron-Ion Collider Next talk by C. Keppel ² From Lattice QCD Complementary to experiments q Summary

7 How to quantify hadron structure in QCD? q What do we need to know for the structure? ² In theory: hp, S O(,,A µ ) P, Si Hadronic matrix elements of all possible operators: O(,,A µ ) Correlations between any number of fields in QCD ² BUT: None of these matrix elements is a direct physical observable color confinement!

8 How to quantify hadron structure in QCD? q What do we need to know for the structure? ² In theory: hp, S O(,,A µ ) P, Si Hadronic matrix elements of all possible operators: O(,,A µ ) Correlations between any number of fields in QCD ² BUT: None of these matrix elements is a direct physical observable color confinement! ² In practice: Accessible hadron structure = hadron matrix elements of quarks and gluons, satisfying 1) can be related to physical cross sections of hadrons and leptons with controllable approximation; and/or 2) can be calculated/extracted from lattice QCD ² Resolution: Wave vs. particle nature of quarks and gluons? Need two-scale probes/observables! Large scale particle nature, small scale the structure

9 How to quantify hadron structure in QCD? q No elastic color current form factor! QED: QCD: Form factors Gluon carries color! Electric charge distribution Proton radius EM charge Parton density distributions Proton radius quark & gluon density distributions

10 How to quantify hadron structure in QCD? q No elastic color current form factor! QED: Form factors Electric charge distribution Proton radius EM charge QCD: q Single-parton structure seen by a short-distance probe: ² 5D structure encoded into the following density distribusions: xp k T b T Z d 2 b T 1) f(x, k T,µ) TMDs: 2D confined motion! Z 2) d 2 k T F (x, b T,µ) 3) Z d 2 k T d 2 b T Gluon carries color! Parton density distributions Proton radius quark & gluon density distributions GPDs: 2D spatial imaging! f(x, µ) PDFs: Number density!

11 How to quantify hadron structure in QCD? q No elastic color current form factor! QED: Form factors Electric charge distribution Proton radius EM charge QCD: Gluon carries color! q Multi-parton, quark-gluon corretions: Single-spin asymmetry: / [ (Q, ~s) (Q, ~s)] Parton density distributions Proton radius quark & gluon density distributions 2 p, ~s k (Q, ~s) / t 1/Q Expansion Quantum interference 3-parton matrix element not a probability!

12 How to see the hadron structure? q Need high energy probes to see the boosted structure: Boost = time dilation P Hard probe (t ~ 1/Q < fm): ² Longitudinal momentum fraction x : ² Transverse momentum confined motion: Catches the quantum fluctuation! xp Q 1/R QCD Q

13 How to see the hadron structure? q Need high energy probes to see the boosted structure: Boost = time dilation P Hard probe (t ~ 1/Q < fm): ² Longitudinal momentum fraction x : ² Transverse momentum confined motion: Catches the quantum fluctuation! xp Q 1/R QCD Q q Challenge: No modern detector can see quarks and gluons in isolation! q Question: How to quantify the hadron structure if we cannot see quarks and gluons? q Answer: QCD factorization! Not exact, but, controllable approximation!

14 Factorization: connecting hadrons to partons q One hadron: e p DIS σ tot : 1 + O QR Hard-part Probe Parton-distribution Structure Power corrections Approximation

15 Factorization: connecting hadrons to partons q One hadron: e p DIS σ tot : 1 + O QR q Two hadrons: Hard-part Probe Parton-distribution Structure Power corrections Approximation DY σ tot : s 1 + O QR q Predictive power: Universal Parton Distributions

16 Density, helicity, transversity distributions q General expansion of quark distribution (x): (x) = 1 2 q(x) P + sk q(x) 5 P + q(x) P 5 S? q 3-leading power quark parton distribution:

17 PDFs of a spin-averaged proton q Modern sets of with uncertainties: Consistently fit almost all data with Q > 2GeV

18 New data and kinematic coverage Experiments and x, Q 2 coverage Selection of data doe NNPDF3.1

19 Role of LHC data q Inclusive jet production at 7 TeV: ² Cross sections span 12 orders of magnitude ² Almost negligible statistical error

20 q Impact of the LHC data: Role of LHC data ² Changes are mainly for large-x region ² PDFs are well-determined for intermediate-x region

21 Partonic luminosities q - qbar g - g Uncertainties are mainly in large- and small-x regimes

22 Future large-x experiments JLab12 q NSAC milestone HP14 (2018): CLAS12 Plus many more JLab experiments: E (Hall C on 3 He), E (CLAS on NH 3, ND 3 ), and Fermilab E906, E (Hall A on 3 He), EIC help fix small-x PDFs! Can lattice QCD help large-x?

23 Hadron spin q How does QCD make up the nucleon s spin? ( Proton s helicity structure: S z ) Proton Spin 1 2 = G +(L q + L g ) Quark helicity Best known 30% Spin puzzle Gluon helicity Start to know 20%(with RHIC data) Orbital Angular Momentum of quarks and gluons Little known If we do not understand proton spin, we do not understand QCD

24 Polarized deep inelastic scattering q Spin asymmetries measured experimentally: ² Longitudinal polarization =0 Known function ² So far only fixed target experiments: CERN: EMC, SMC, COMPASS SLAC: E80, E130, E142, E143, E154 DESY: HERMES JLab: Hall A,B,C, many experiments with various polarized targets: p, d, 3 He,...

25 Sea quark polarization RHIC W program q Single longitudinal spin asymmetries: Parity violating weak interaction q From 2013 RHIC data: x u Q 2 = 10 GeV 2 15 χ 2 10 DSSV++ incl. proj. W data χ 2 =2% in DSSV anal DSSV DSSV+ DSSV++ with proj. W data 5 0 Q 2 = 10 GeV 2 DSSV x u(x,q 2 ) dx sign x d Q 2 = 10 GeV 2 15 χ 2 10 Q 2 = 10 GeV 2 DSSV++ incl. proj. W data χ 2 =2% in DSSV analysis x DSSV d(x,q 2 ) dx 0.05

26 Impact of RHIC measurements on Δg positive(δg in(rhic(x1region 0.2 x g Q 2 = 10 GeV RHIC 200 GeV 0 DSSV COMPASS measurement is consistent DSSV++ x x

27 Strange quark combining fits for PDFs & FFs q Strange quark polarization puzzle: Global fits for polarized PDFs using inclusive DIS data: s + s 0.1 s(x)+ s(x) < 0 for all x Global fits for polarized PDFs with SIDIS data: s(x)+ s(x) > 0 for measured x range

28 Strange quark combining fits for PDFs & FFs q Strange quark polarization puzzle: Global fits for polarized PDFs using inclusive DIS data: s + s 0.1 s(x)+ s(x) < 0 for all x Global fits for polarized PDFs with SIDIS data: s(x)+ s(x) > 0 for measured x range q First simultaneous analysis of spin-pdfs and FFs: Both polarized DIS and SIDIS + Single inclusive e+e-, including 6 GeV CLAS data Without SU(3) assumption Resolution of the puzzle s + s = 0.03 ± 0.10 Consistent with lattice result: [ s + s] Lattice = 0.02(1) Additional quark contribution to Proton Spin: 0.36 ± 0.09 at 1 GeV 25% larger J.J. Ethier et al

29 Paradigm shift: 5D imaging of hadrons Break the Proton

30 Paradigm shift: 5D imaging of hadrons q JLab12 + EIC 3D imaging of quarks and gluons: ² Break TMDs the Confined Proton motion in a nucleon (semi-inclusive DIS) ² GPDs Spatial imaging of quarks and gluons (exclusive DIS)

31 Paradigm shift: 5D imaging of hadrons q 5D boosted partonic structure: Momentum Space TMDs (3D) Confined motion d 2 b T f(x,k T ) xp k T b T Two-scales observables d 2 k T f(x,b T ) Coordinate Space GPDs (3D) Spatial distribution Break the Proton

32 Paradigm shift: 5D imaging of hadrons q 5D boosted partonic structure: Momentum Space TMDs (3D) Confined motion d 2 b T f(x,k T ) 3D momentum space images Semi-inclusive DIS Break the Proton Break the hadron! xp Q >> P T ~ k T k T b T Two-scales observables γ d 2 k T f(x,b T ) Coordinate Space GPDs (3D) Spatial distribution Why is diffraction so great? P 1 z Exclusive DIS 2+1D coordinate space images z t r (1 z) r x x p p Keep the hadron intact! Position r x Momentum p à Orbital Motion of Partons b V = J/ψ, φ, ρ Q >> t ~ 1/b T

33 Paradigm shift: 5D imaging of hadrons q 5D boosted partonic structure: Momentum Space TMDs (3D) Confined motion d 2 b T f(x,k T ) 3D momentum space images Semi-inclusive DIS Break the Proton Break the hadron! xp Q >> P T ~ k T k T b T Two-scales observables JLab12 valence quarks, EIC sea quarks and gluons γ d 2 k T f(x,b T ) Coordinate Space GPDs (3D) Spatial distribution Why is diffraction so great? P 1 z Exclusive DIS 2+1D coordinate space images z t r (1 z) r x x p p Keep the hadron intact! b V = J/ψ, φ, ρ Q >> t ~ 1/b T

34 TMDs: confined motion, its spin correlation q Power of spin many more correlations: s p k T Require two Physical scales Similar for gluons More than one TMD contribute to the same observable!

35 TMDs: confined motion, its spin correlation q Power of spin many more correlations: s p k T Require two Physical scales q A N single hadron production: Similar for gluons More than one TMD contribute to the same observable! Transversity Collins-type Sivers-type

36 SIDIS is the best for probing TMDs q Naturally, two scales & two planes: l l 1 N N AUT ( ϕh, ϕs ) = P N + N Collins Sivers = A sin( φ + φ ) + A sin( φ φ ) UT Pretzelosity + A sin(3 φ φ ) UT h h S S UT h S q Separation of TMDs: Collins A sin( φ + φ ) h H A A UT h S Sivers UT sin( φ φ ) h S UT 1 1 1T sin(3 φ φ ) h H Pretzelosity UT h S UT 1T 1 UT f D 1 Collins frag. Func. from e + e - collisions Hard, if not impossible, to separate TMDs in hadronic collisions Using a combination of different observables (not the same observable): jet, identified hadron, photon,

37 q Definition: Critical test of TMD factorization q Gauge links: SIDIS: DY: q Process dependence: Sivers function changes sign from SIDIS to Drell-Yan!

38 Hint of the sign change: A N of W production STAR Collab. Phys. Rev. Lett. 116, (2016) Data from STAR collaboration on A N for W-production are consistent with a sign change between SIDIS and DY COMPASS Drell-Yan data is consistent

39 Hint of the sign change from lattice QCD q Gauge link for lattice calculation: Engelhardt@TMD Collaboration meeting q Normalized moment of Sivers function at given b T :

40 Parton k T at the hard collision q Sources of parton k T at the hard collision: Gluon shower P h P Confined motion xp, k T ` P h z,k0 T `0 Emergence of a hadron hadronization q Large k T generated by the shower (caused by the collision): ² Q 2 -dependence linear evolution equation of TMDs in b-space ² The evolution kernels are perturbative at small b, but, not large b The nonperturbative inputs at large b could impact TMDs at all Q 2 q Challenge: to extract the true parton s confined motion: ² Separation of perturbative shower contribution from nonperturbative hadron structure QCD evolution - not as simple as PDFs ² Role of lattice QCD? Task of the DOE supported TMD collaboration

41 Global QCD analysis: extraction of TMDs q QCD TMD factorization: Connect cross sections, asymmetries to TMDs ² Factorization is known or expected to be valid for SIDIS, Drell-Yan (ϒ*, W/Z, H 0, ), 2-Jet imbalance in DIS, ² Same level of reliability as collinear factorization for PDFs, up to the sign change q QCD evolution of TMDs: TMDs evolve when probed at different momentum scales ² Evolution equations are for TMDs in b T -space (Fourier Conjugate of k T ) FACT: QCD evolution does NOT fully fix TMDs in momentum space, even with TMDs fixed at low Q large b T -input!!! ² Very different from DGLAP evolution of PDFs in momentum space FACT: QCD evolution uniquely fix PDFs at large Q, once the PDFs is determined at lower Q linear evolution in momentum space q Challenges: Predictive power, extraction of hadron structure,

42 Extraction of TMDs An Example q Combined fits for the Transversity & Collins FFs: First Fit using TMD evolution Fits without TMD evolution

43 Extraction of TMDs An Example q Impact of future SoLID at JLab12: Z. Ye et al. Phys Lett. B767, 91 (2017) ² Transversity distribution: After SoLID ² Tensor charge: Order of magnitude improvement in determining the tensor charge!

44 GPDs: spatial distribution, its spin correlation q Definition Quark form factor : P P 0 with H q (x,, t, Q), Ẽ q (x,, t, Q) Different quark spin projection q Total quark s orbital contribution to proton s spin: Ji, PRL78, 1997 q Connection to normal quark distribution: The limit when! 0

45 Exclusive DIS: Hunting for GPDs q Experimental access to GPDs: ² Diffractive exclusive processes high luminosity: DVCS: Deeply virtual Compton Scattering DVEM: Deeply virtual exclusive meson production Mueller et al., 94; Ji, 96; Radyushkin, 96 Require GPD Q 2 >>(-t), 2 QCD,M2 ² No factorization for hadronic diffractive processes EIC is ideal q Much more complicated (x, ξ, t) variables: Challenge to derive GPDs from data q Great experimental effort: HERA, HERMES, COMPASS, JLab JLab12, COMPASS-II, EIC

46 GPDs: just the beginning HERA HERMES CLAS Jlab-Hall-A

47 Unified view of nucleon structure q Wigner distribution 5D: Momentum Space TMDs d 2 b T xp k T b T d 2 k T Coordinate Space GPDs q Note: Confined motion f(x,k T ) Two-scales observables f(x,b T ) Spatial distribution ² Partons confined motion and their spatial distribution are unique the consequence of QCD ² But, the TMDs and GPDs that represent them are not unique! Depending on the definition of the Wigner distribution and QCD factorization to link them to physical observables q Can lattice QCD calculate hadron structure? Difficult, but, with tremendous potential very active now!

48 Hadron structure from lattice QCD calculation q Quasi quark distribution (spin-averaged): q(x, µ 2,P z ) q Proposed matching: Z d z 4 e ixp z z hp ( z ) z exp q(x, µ 2,P z )= Z 1 x ( ig Z z 0 d z A z ( z ) dy x y Z y, µ q(y, µ 2 2 )+O P z Pz 2, M 2 Pz 2 ) Ji, arxiv: (0) P i + UVCT(µ 2 ) t Power divergence renormalization? Mixing with lower dimension operators cannot be treated perturbatively, q Exploratory effort: 0 ξ z z Lin et al., arxiv:

49 Hadron structure from lattice QCD calculation q Our observations: ² PDFs are time-independent, so as the factorized cross sections! ² The operators, defining PDFs, located on the light-cone is a consequence of the approximation defining the twist-2 factorization More precisely, the collinear approximation q Our idea: ² NOT try to calculate PDFs directly from lattice QCD calculations ² Calculate a set of time-independent (fixed or integrated over time) and good single hadron matrix elements lattice cross sections with n( 2,!,P 2 )=hp T {O n ( )} P i O j1 j 2 ( ) d j 1 +d j2 2 Z 1 j 1 Z 1 j 2 j 1 ( ) j 2 (0) j S ( ) = 2 Z 1 S [ q q ]( ), j G ( ) = 3 Z 1 G [ 1 Lat E ( z, 1/a, P z ) Z! E ( z, µ 2,P z ) m Ma and Qiu, 2014, , ! = P 4 F µ F c µ ]( ) c Renormalization/continuum limit (lattice QCD expertise, ) M( z, µ 2 C,P z )! fi (x, µ 2 ), Factorization to PDFs (perturbative QCD, ) ² Derive PDFs from Global Analysis of data on lattice cross sections

50 Summary q QCD has been extremely successful in interpreting and predicting high energy experimental data! < 1/10 fm q But, we still do not know much about hadron structure work just started! q Cross sections with large momentum transfer(s) and identified hadron(s) are the source of structure information q QCD factorization is necessary for any controllable probe for hadron s quark-gluon structure! q EIC is a ultimate QCD machine, will provide answers to many of our questions on hadron structure, in particular, the confined transverse motions (TMDs), spatial distributions (GPDs), and multi-parton correlations, NEXT talk! Thank you!

51 Backup slides

52 Two-momentum-scale observables q Cross sections with two-momentum scales observed: Q 1 Q 2 1/R QCD ² Hard scale: ² Soft scale: Q 1 Q 2 localizes the probe to see the quark or gluon d.o.f. could be more sensitive to hadron structure, e.g., confined motion q Two-scale observables with the hadron broken: + + Two-jet momentum imbalance in SIDIS, SIDIS: Q>>P T DY: Q>>P T ² Natural observables with TWO very different scales ² TMD factorization: partons confined motion is encoded into TMDs

53 Two-momentum-scale observables q Cross sections with two-momentum scales observed: Q 1 Q 2 1/R QCD ² Hard scale: ² Soft scale: Q 1 Q 2 localizes the probe to see the quark or gluon d.o.f. could be more sensitive to hadron structure, e.g., confined motion q Two-scale observables with the hadron unbroken: + + t=(p 1 -p 2 ) 2 GPD J/Ψ, Φ, + DVCS: Q 2 >> t DVEM: Q 2 >> t EHMP: Q 2 >> t ² Natural observables with TWO very different scales ² GPDs: Fourier Transform of t-dependence gives spatial b T -dependence

54 Orbital angular momentum OAM: Correlation between parton s position and its motion in an averaged (or probability) sense q Jaffe-Manohar s quark OAM density: L 3 q = q q Ji s quark OAM density: L 3 q = q h ~x ( i 3 q 3 h ~x ( i D)i ~ q q Difference between them: ² compensated by difference between gluon OAM density ² represented by Z different choice of gauge link for OAM Wagner distribution h i 3 L 3 q L 3 q = dx d 2 bd 2 k T ~b ~ kt Wq (x, ~ b, ~ n k T ) W q (x, ~ b, ~ o k T ) with W q {W q } (x, ~ b, ~ k T )= JM: staple gauge link Ji: straight gauge link Z d 2 Z T (2 ) 2 ei~ T ~b dy d 2 y T (2 ) 3 hp 0 q (0) between 0 and y=(y + =0,y -,y T ) + 2 Hatta, Lorce, Pasquini, e i(xp + y ~ kt ~y T ) JM{Ji} (0,y) (y) P i y + =0 Gauge link

55 Orbital angular momentum OAM: Correlation between parton s position and its motion in an averaged (or probability) sense q Jaffe-Manohar s quark OAM density: L 3 q = q q Ji s quark OAM density: L 3 q = q h ~x ( i 3 q 3 h ~x ( i D)i ~ q q Difference between them: ² generated by a torque of color Lorentz force Z dy d L 3 q L 3 2 y T q / (2 ) 3 hp 0 + Z 1 q (0) dz (0,z ) 2 y X 3ij yt i F +j (z ) (z,y) (y) P i y+ =0 i,j=1,2 Chromodynamic torque Hatta, Yoshida, Burkardt, Meissner, Metz, Schlegel, Similar color Lorentz force generates the single transverse-spin asymmetry (Qiu-Sterman function), and is also responsible for the twist-3 part of g 2

56 Proton s radius in color distribution? q The big question: How color is distributed inside a hadron? (clue for color confinement?) q Electric charge distribution: Elastic electric form factor Charge distributions q p p' q But, NO color elastic nucleon form factor! Hadron is colorless and gluon carries color Parton density s spatial distributions a function of x as well (more proton -like than neutron -like?) GPDs