International Conference of the Structure of Baryons Baryons

International Conference of the Structure of Baryons (Baryons 2013) Nucleon Spin Structure: Experimental View Zein-Eddine Meziani Temple University Philadelphia Disclaimer: no comprehensive overview 9/8/2021 Baryons 2013, University of Glasgow, Scotland Courtesy of CERN Courier

Nucleon Spin; Why should we / you care? Has been a laboratory for QCD in the last 30 years – Example: Test of the Bjorken Sum Rule The nucleon is a strongly interacting many body confined system Turns out to be an important window into QCD dynamics 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Historical Perspective Spin an “intrinsic property” emerges during the development of quantum mechanics; Ø Stern-Gerlach experiment 1922 Spin (magnetic moment) hinted that the nucleon is not point like Ø Otto Stern (1933) measured the magnetic moment of the proton to be Quantum Statistics: According to Pauli (1940) “particles of half integer spin obey Fermi-Dirac statistics and those of integer spin obey Bose-Einstein statistics. Nature: http: //www. nature. com/milestones/milespin/index. html 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Low Q 2 Nu Fast moving proton cle on Qu ark A portrait in a chocolate store in downtown Seattle 9/8/2021 Baryons 2013, University of Glasgow, Scotland s High Q 2

Unified View of Nucleon Structure 6 D Dist. Wpu(x, k. T, r ) Wigner distributions d 2 k. T drz d 3 r TMD f 1 u(x, k. T), . . h 1 u(x, k. T) GPDs/IPDs 3 D imaging d 2 k T PDFs f 1 u(x), . . h 1 u(x) 9/8/2021 dx & Fourier Transformation d 2 r T 1 D Form Factors GE(Q 2), GM(Q 2) Baryons 2013, University of Glasgow, Scotland

Experimental Tools Electromagnetic Probes – Deep inelastic scattering (DIS) – Semi-inclusive DIS – Deep Virtual Compton Scattering (DVCS)/Meson Production – e+e- collisions Hadronic Probes – Inclusive hadron production – Inclusive Jet production – Drell-Yan Use of Protons and Nuclei targets – Targets are polarized p, D, NH 3, ND 3, 3 He 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Impressive experimental progress in QCD spin physics in the last 25 years Inclusive spin-dependent DIS ➥ CERN: EMC, SMC, COMPASS ➥ SLAC: E 80, E 142, E 143, E 154, E 155 ➥ DESY: HERMES ➥ JLab: Hall A, B and C Semi-inclusive DIS ➥ EMC, SMC, COMPASS ➥ HERMES, JLab Polarized pp collisions ➥ BNL: PHENIX & STAR Polarized e+e- collisions ➥ KEK: Belle, SLAC: Babar 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Spin of the Proton: Two views http: //www. int. washington. edu/PROGRAMS/12 -49 w/ INT Workshop INT-12 -49 W, Orbital Angular Momentum in QCD, February 6 - 17, 2012 Ji 1997 9/8/2021 Jaffe. Manohar 1990 Baryons 2013, University of Glasgow, Scotland

Ji’s proton spin decomposition Ji 1997 Kinetic Pros: • Gauge-invariant decomposition • Accessible in DIS and DVCS Cons: • Does not satisfy canonical relations • Incomplete decomposition News: 9/8/2021 • Complete decomposition [Wakamatsu (2009, 2010)] Baryons 2013, University of Glasgow, Scotland Courtesy of C. Lorce

Jaffe-Manohar proton spin decomposition Jaffe-Manohar 1990 Canonical News: Pros: • Satisfies Canonical relations • Complete decomposition • Gauge-invariant extension Cons: • Gauge variant decomposition • Missing observables for OAM • OAM accessible via Wigner distributions 9/8/2021 Baryons 2013, University of Glasgow, Scotland [Chen et al. (2008)] Lorce, Pasquini (2011) Lorce, Pasquini, Xiong, Yuan(2011) Hatta (2011), Leader (2012)

Quark Helicity Distributions from SIDIS Results from inclusive and semi- inclusive experiments from different experiments (COMPASS, HERMES, JLab) are consistent 9/8/2021 Baryons 2013, University of Glasgow, Scotland Courtesy of F. Kunne

Quark Helicity distributions (continued) LSS parametrization Recent data analyses ➥De Florian, Sassot, Stratmann, Vogelsang, 2008/2009 ➥Blumlein, Bottcher, 2010 ➥Leader, Sidorov, Stamenov, 2010 ➥Ball, Forte, Guffanti, Nocera, Ridolfi, Rojo, 2013 ➥RHIC results on Wproduction are providing further information(PHENIX, 2010 / STAR, 2010). Need to be included in global analyses, impact on the sea 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Sea polarization through W production • Provides an important check of SIDIS method • No fragmentation function • Q 2=MW 2 (no high twist effects) New fit points towards rather sizable 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Recent results - Gluon polarization program STAR: Mid-rapidity Inclusive Jet ALL measurement (Run 9) Preliminary Run 6 D. de. Florian et al. , Prog. Nucl. Part. Phys. 67, 251 (2012) 9/8/2021 Courtesy of Bernd Surrow Baryons 2013, University of Glasgow, Scotland Bernd Surrow

Transversity and the Tensor Charge Quark transverse polarization in a transversely polarized nucleon: h 1 T = Nucleon Spin Quark Spin – Can be probed in Semi-Inclusive DIS, Drell-Yan processes. – Does not mix with gluons, has valence like behavior. – Nucleon tensor charge can be extracted from the lowest moment of h 1 and compared to LQCD calculations Tensor Charge Intrinsic property Like axial or vector charge Bjorken Sum rule GDH sum rule 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Transversity and Tensor charge (cont. ) M. Anselmino, M. Boglione, U. D'Alesio, S. Melis , F. Murgia, A. Prokudin, Phys. Rev. D 87 (2013) 094019 COMPASS: PLB 692 (2010) 240, PLB 717 (2012) 376] HERMES: [PLB 693 (2010) 11] Belle Collaboration, Phys. Rev. D 86 032011(E) (2012 Jefferson Lab [PRL 107 (2011) 072003] 9/8/2021 combined SIDIS and e+e- data from Belle More data to come in the future including s-p interference of 2 hadrons fragmentation Baryons 2013, University of Glasgow, Scotland

Gluon Helicity Phys. Lett. B 718 (2013) 922 -930 Phys. Rev. D 87, 052018 (2013) 9/8/2021 Baryons 2013, University of Glasgow, Scotland

LARGE Orbital Angular Momentum is the quark helicity distribution and has been determined from inclusive and semi-inclusive experiments (COMPASS, HERMES, JLab) measured by COMPASS, HERMES, RHIC Connection of made and with observables not yet clear but progress is The conclusion from the data is that orbital momentum is important 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Jaffe. Manohar The Other View: Beyond 1 -D description (Change in OAM as quark leaves nucleon) M. Burkardt ar. Xiv: 1205. 2916 Ji DVCS, DVMP 9/8/2021 Baryons 2013, University of Glasgow, Scotland Talk: T. Horn

Example: DVCS Measurements at JLab 6 Ge. V Unprecedented set of Deeply Virtual Compton Scattering data accumulated in Halls A and B and more to come See talks: H. Moutarde, A. Biselli, F. Hermann. M. Murray 9/8/2021 Baryons 2013, University of Glasgow, Scotland

DVCS on longitudinal target @ JLab 12 Ge. V L = 2 x 1035 cm-2 s-1 T = 1000 hrs of beam on target in CLAS 12 Coutesy of H. Avakian 9/8/2021 Baryons 2013, University of Glasgow, Scotland

Model Dependent Extraction of Ju and Jd • Major program for JLab 12 Ge. V, COMPASS-II, EIC 9/8/2021 Baryons 2013, University of Glasgow, Scotland Courtesy of Bacchetta and Radici

From GPDs to Angular Momentum 9/8/2021 Baryons 2013, University of Glasgow, Scotland Peter Kroll

Spin Summary and Future Prospects 3 -dimensional mapping of the nucleon structure has just begun allowing for the determination of the orbital angular momentum of partons See talk of A. Bacchetta Near-term studies: COMPASS, JLab 12 Ge. V upgrade. Emphasis will be on quarks’ orbital angular momentum F. Gautheron et al. COMPASS II proposal SPSC-P-340 J. Dudek, et al. , `Physics Opportunities with the 12 Ge. V Upgrade at JLab, '' Eur. Phys. J. A 48, 187 (2012) Long-term studies: Future High Energy Facilities Emphasis will be on the glue and the sea Electron Ion Collider, the Next QCD Frontier http: //arxiv. org/abs/1212. 1701 9/8/2021 Baryons 2013, University of Glasgow, Scotland See talk of T. Horn