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WG.9: Working Group on International Cooperation in Nuclear Physics (ICNP). The Structure of the Nucleon. CPHT. Cédric Lorcé. August 29, Riken Tokyo Office, Tokyo, Japan. Outline. Fundamental questions Hadron imaging Impact on other fields Current pictures Conclusions.
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WG.9: Working Group on International Cooperation in Nuclear Physics (ICNP) The Structure of the Nucleon CPHT Cédric Lorcé August 29, Riken Tokyo Office, Tokyo, Japan
Outline • Fundamental questions • Hadron imaging • Impact onotherfields • Currentpictures • Conclusions
Fundamental questions about the nucleon Nucleons are key building blocks of all matteraround us, and yetwe do not know thatmuch about them ! Origin of mass and spin ? Mproton = Mquarks + Ekinetic + Einteraction ~ 2% ~ 98% Higgsboson Strong interaction Proton Quarks
Fundamental questions about the nucleon But also … Size ? Shape ? Structure ? 2010
Approaches to the problem Hadron spectroscopy Latticeprediction of light mesonspectrum [J. Dudeket al. (2011)] • Mesonspectrumbetterknownthan baryon spectrum • Missingresonances (other production channel ?) • Exotic states (glueballs, hybrids, tetraquarks, pentaquarks, …) • Nature (bound state, molecule, mixing, …)
Approaches to the problem Hadron imaging « Quantum billiard » Charge distribution [Carlson, Vanderhaeghen (2008)] Electron Proton • Large number of distributions (charge, spin, flavor, momentum, …) • Requires high luminositiesIntensityfrontier • Essential input for high-energyphysics (electroweak, BSM, darkmatter, …)
1D imaging Parton distribution functions (PDFs) Electrocardiogram [PDG (2016)] Perturbative QCD evolution Momentum fraction Deepinelasticscattering (DIS)
3D imaging Transverse momentumPDFs (TMDs) 3D model of heart Polarizedtarget Unpolarizedtarget Courtesy of A. Bacchetta Semi-inclusive DIS (SIDIS)
1+2D imaging GeneralizedPDFs (GPDs) 1+2D model of heartbeat Nucleon transverse extent [Dupré et al. (2017)] x-dissected charge distribution Sea quarks & gluons Pion cloud Valence quarks Deeplyvirtual Compton scattering (DVCS)
3+2D imaging TMDs PDFs GPDs Momentumtransfer
3+2D imaging TMDs PDFs FFs GPDs Charges Formfactors Elasticscattering
3+2D imaging GTMDs TMDs PDFs FFs GPDs Charges GeneralizedTMDs Phase-space (Wigner) distribution [Meissner, Metz, Schlegel (2009)] [C.L., Pasquini, Vanderhaeghen (2011)]
Rich spin structure TMDs GPDs Quark polarization Spin-orbit Nucleonpolarization Spin-spin [C.L., Pasquini (2016)]
Multipoledecomposition UU LU [C.L., Pasquini (2016)]
Multipoledecomposition UU LU Density mode Inflation mode Orbital mode Spiral mode [C.L., Pasquini (2016)]
Impact on high-energyphysics Main uncertainty on precision SM and BSM studiescomesfromPDFs [Forte, Watt (2013)] [LHeCStudy Group (2012)]
Impact on high-energyphysics GPDs and TMDsoffer new opportunities Gluon TMD contributions to Higgs production Multiple parton scattering [Boer et al. (2012)] [Diehl et al. (2012)] Gluon linearpolarization ratio Double PDF GPD2 GPD1
Connections withotherfields Quantum optics Twistedbeams of photons and electrons Solid-state physics Spin Hall effect Astrophysics Hydrodynamicalpicture General relativity Gravitational memory effect quark pressure gluon pressure Before After
Back to the fundamental questions Nucleonmomentumdecomposition Phenomenological extraction [Harland-Lang et al. (2015)] Pq 54,6(5) % Latticeestimate [Alexandrouet al. (2017)] 27,3(2,3) % PG Pq 74(10) %
Back to the fundamental questions Nucleonmassdecomposition Phenomenological extraction [Gao et al. (2015)] 11(1) % Em Eq 33(1) % Latticeestimate [Bali et al. (2016)] [Alexandrouet al. (2017)] 29,1(1,5) % Em Eq 33,7(7,5) % EG 20,5(1,7) %
Back to the fundamental questions Nucleonmassdecomposition Trace decomposition Ji’sdecomposition New decomposition [Shifmanet al. (1978)] [Ji (1995)] [C.L. (2017)] ~ 11% ~ 11% ~ 11% ~ 33% ~ 33% ~ 14% Em Em Em ~ 22% Ea Eq Eq Ea Ea EG EG ~ 42% ~ 89% ~ 34% Trace anomaly
Back to the fundamental questions Nucleonspindecomposition Phenomenological extraction [Nocera et al. (2014)] [DSSV (2014)] 25(10) % Sq SG 40(?) % Latticeestimate [Alexandrouet al. (2017)] Lq Sq 42,4(9,0) % 39,8(3,2) % JG 27,2(?) %
Back to the fundamental questions Reviews: [Leader, C.L. (2014)] [Wakamatsu (2014)] [Liu, C.L. (2016)] Nucleonspindecomposition Kineticdecomposition Canonical decomposition [Ji (1997)] [Wakamatsu (2010)] [Jaffe, Manohar (1990)] [Chen et al. (2008)] [Hatta (2012)] ~ 20% ~ 25% ~ 25% ~ 29% Lq Sq Sq Lq LG LG ~ 15% SG SG ~ 6% ~ 40% ~ 40% « Outside » the nucleon « Inside » the nucleon Struck quark Chromo Lorentz force [Burkardt (2013)] [Burkardt, C.L. (in preparation)]
Hot topics for the near future • Gluon distributions • Orbital angularmomentum • QCD trace anomaly • Transverse polarizationeffects • Saturation effects • Higher-twists effects • Quark flavordecomposition • Medium modifications • … Lattice QCD
Conclusions • Understandingnucleon structure is a fundamentalproblem • Nucleonimagingoffers key insight • Rich spin structure withnumerouseffects • Gluon contributions and OAM stillmissing • Electron-ion collider and Lattice QCD willplay an essential role • Connections withotherfieldsshouldbefurtherexplored !