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Physics with Spin

Physics with Spin. Krishna Kumar University of Massachusetts thanks to A. Deshpande, R. Ent, E. Hughes, X. Ji, N. Makins, Z-E. Meziani, and all parallel session speakers The Second Electron-Ion Collider Workshop, Jefferson Laboratory March 17, 2004. Outline. Introduction

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Physics with Spin

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  1. Physics with Spin Krishna Kumar University of Massachusetts thanks to A. Deshpande, R. Ent, E. Hughes, X. Ji, N. Makins, Z-E. Meziani, and all parallel session speakers The Second Electron-Ion Collider Workshop, Jefferson Laboratory March 17, 2004 Physics with Spin

  2. Outline • Introduction • Parallel Session Program • Inclusive Scattering • Semi-inclusive scattering • Exclusive scattering • Summary Physics with Spin

  3. Historical Context It is now common wisdom that lepton scattering experiments are greatly enhanced by the availability of spin degrees of freedom Jefferson Laboratory was conceived (I was in undergraduate school), proposed and approved without polarized beam! Fundamental spin physics experiments over the past 30 years have helped bring about a major change in attitude - Beam and target spin greatly increase the scope of anticipated and unexpected results - Experimental technology is pushed in ways that benefit other subfields of science Physics with Spin

  4. Spin and the EIC Giant strides in the production of intense, highly polarized electron and ion beams • High electron longitudinal beam polarization • High light ion beam polarization (longitudinal and transverse) • High luminosity • High Center of Mass Energy • Positron Beam (high luminosity for GPDs?!) Physics with Spin

  5. Parallel Session Overview • Spin (I) • Inclusive measurements and Gluon spin • Transversity • Polarized Semi-Inclusive measurements • Spin (II) • Using Spin for Flavor Separation • Angular Momentum • Quark Spatial Distributions and GPDs Physics with Spin

  6. Parallel Sessions (I) Monday, March 15, 2004 - VARC 53/55 Spin (I) - Chair: Oscar Rondon (UVa) 14:00 - 14:15 The g1 Structure Function at Low x - Introduction Werner Vogelsang 14:15 - 14:45 Measurement of g1 at the Future Collider and G from pQCD Evolution of the Structure Function Ernst Sichtermann 14:45 - 15:15 Open Charm Production at Colliders Antje Bruell 15:15 - 15:45 The Photon Content of Unpolarized and Polarized Nucleons Asmita Mukherjee 15:45 - 16:00 Electroweak and SM Physics at EIC Rolf Ent 16:00 - 16:20 Coffee Break   Transversity - Chair: Zein-Eddine Meziani (Temple) 16:20 - 16:45 Azimuthal Spin Asymmetries for the Large pt Hadron Production at eRHIC Yuji Koike 16:45 - 17:10 Transversity Measurements at Colliders Naomi Makins 17:10 - 17:35 SIDIS and Current Fragmentation Stefan Kretzer Physics with Spin

  7. Parallel Session (II) Tuesday, March 16, 2004 - VARC 53/55 Spin (II) - Chair: Werner Vogelsang (BNL/RBRC) 14:00 - 14:25 Polarized Semi-Inclusive Physics Measurements at HERMES and Future Prospects at the Colliders Ed Kinney 14:25 - 14:50 Polarized Photoproduction at ep Colliders Marco Stratmann 14:50 - 15:15 Lambda and Hyperon Physics Naomi Makins 15:15 - 15:40 Spatial Distributions of Quarks/Gluons in the Nucleon at Large Nc Christian Weiss Angular Momentum - Chair: Latifa Elouadrhiri (JLab) 15:40 - 16:05 Quantum Phase-Space Tomography of Quarks in the Proton Xiangdong Ji 16:05 - 16:20 Coffee Break   16:20 - 16:45 Measurement of GPDs at JLab and Future Colliders Harut Avakian 16:45 - 17:10 Generalized Parton Distributions at Large x Feng Yuan 17:10 - 17:35 Detector Issues N. Smirnov 17:35 - 18:00 GPDs and Color Transparency Phenomena Simonetta Liuti Physics with Spin

  8. Inclusive DIS Sichtermann, Vogelsang Spin structure functions g1 and g2 describe the spin-dependent cross-sections Precision measurements on 1H, 2H and 3He targets at CERN, DESY and SLAC Physics with Spin

  9. Gluon Spin in the Nucleon Gluon contribution is likely to be substantial: Profound implications for our basic understanding of the nucleon which must be directly measured by experiment RHIC Spin and COMPASS experiments will provide the first precise measurements towards this goal The gold standard: measure G from a variety of experiments, where the dominant theoretical input is NLO QCD and residual model dependence is negligible and non-controversial Physics with Spin

  10. HERA The dream is to produce a similar plot for xg(x) vs x G from Q2 Evolution of g1 Sichtermann EIC expected improvement in statistical uncertainty on G with analyzed data with 100 pb-1: ~3 5 on 250 GeV ~4 10 on 250 GeV ~7 20 on 250 GeV with respect to the present uncertainty of ~0.5 Physics with Spin

  11. Gluon Spin from Open Charm Bruell charm charm several stiff kaons in the central regions and a forward electron • Critical, complementary method to obtain G • Simulation work on open charm is just beginning • EIC should provide a clean, high statistics data sample Physics with Spin

  12. High Energy Convergence of the GDH sum rule Polarized Photoproduction Mukherjee, Stratmann Estimate for a 1 fb-1 data sample Asymmetry sufficient resolution to tag photoproduction and measure jet 4-momentum Direct Photon Resolved Photon Physics with Spin

  13. Spin Structure Summary The final design parameters of the EIC must guarantee multiple, precision measurements of G Should a high precision test of the Bjorken Sum Rule be pursued? : requires a careful evaluation of systematics of polarimetry New information on the polarized photon’s partonic content What can be gained by precision studies of g2? Physics with Spin

  14. Polarized Semi-Inclusive DIS Makins, Kinney, Kretzer, Koike Flavor separation of parton distribution functions and fragmentation functions via azimuthal single and double-spin asymmetries with tagged pions and kaons Physics with Spin

  15. Transversity Makins • transverse polarization introduces a new structure fn. h1 • Cannot be accessed by inclusive scattering • Information on transverse quark distribution in the nucleon • The first moment of h1 yields the nucleon’s tensor charge The most favorable spin configuration is an unpolarized beam on a transversely polarized target While first measurements are being carried out at HERMES and new measurements will be carried out Jefferson Lab and spin RHIC, EIC will be a laboratory where transversity will be extracted with reduced theoretical uncertainty Physics with Spin

  16. Ultimate strategy: • Data on various hard exclusive processes • Deconvolution and global fits to obtain GPDs • Further constraints from Lattice QCD • Obtain tomographic 3-D pictures of the nucleon • Understand origins of mass and spin structure Tomography of the Nucleon Ji • A framework to extract 3-D spatial information of quarks in a nucleon at rest • Generate Wigner (quantum phase-space) distributions • Obtain proton images at fixed x • Direct connection to GPDs through Fourier Transforms Physics with Spin

  17. Proton Images at Fixed x Ji Up-quark densities x=0.01 z y x x=0.4 x=0.7 Physics with Spin

  18. GPDs Avakian, Luiti, Weiss, Yuan CLAS 5.7 GeV: DVCS SSA EIC Issues (Deconvolution!) • Resolution (especially t) • Acceptance • Luminosity • Kinematic coverage • Can we set a gold standard? • Can moments of GPDs make contact with Lattice QCD? Physics with Spin

  19. Detector Issues N. Smirnov Example HCAL EMCal (Not to scale) Solenoid AEROGEL TOF A HERA like Detector with dedicated PID: >>Time of flight >>Aerogel Ckov Beam elements P/A e Inner trackers AND Forward detectors including Roman Pots etc… 5m Outer trackers Physics with Spin

  20. Parity Violation (I) Ent Beyond the Standard Model E6 Z’ Based Extensions RPV SUSY Extensions Leptoquarks Due to finite Y 1035 /cm2/s Sub 0.5% polarimetry Physics with Spin

  21. Why even bother after HERA measurements? Any new physics signature can be characterized as a contact interaction at “low” energy The goal of “low” energy experiments is to characterize all chiral combinations with all initial and final state fermions The goal is NOT to find the first signature of new physics and go to Stockholm The goal is to help our LHC colleagues, who are likely to be staring at a tantalizing, low statistics signal Parity Violation (II) Tofirst order, there is no difference between fixed- target DIS and collider DIS for such a measurement • y dependence, perhaps gain in systematics • More selective x range: better theory control Physics with Spin

  22. Parity Violation (III) The g5 structure function • Experimental signature is a huge • asymmetry in detector (neutrino) • Unique measurement • Unpolarized xF3 measurements • at HERA in progress • Will access heavy quark • distribution in polarized DIS Worth doing even if no positron beam Physics with Spin

  23. Parity Violation (wild) The partonic structure of the Z boson? Suppose you had enough luminosity to see the PV Asymmetry at low Q2 Would one learn something new about the partonic content of the photon? What is the correct description to think about this process? Physics with Spin

  24. Polarized Sources • Polarized electron sources (polarization and intensity) are not a technical hurdle • Likely the same thing for proton sources • Some work on 2H at BNL • Precision inclusive physics requires polarized 3He. This is a new technical challenge Physics with Spin

  25. Polarimetry • Electron polarimetry at 0.5% likely doable in 10 years • If sub-0.5% is required, this is a major, independent effort • Beyond the Standard Model? • Proton polarimetry will reach ~5% at the RHIC spin program • Bjorken sum rule test needs sub-5%? • 2Hand 3He polarimetry? We need to start thinking about this. Physics with Spin

  26. Back to Physics….. • Inclusive DIS • EIC is the ultimate gluon spin machine • Close the book on longitudinal spin structure • Semi-Inclusive DIS • New window into spin structure • Transversity, flavor separation, fragmentation….. • Exclusive DIS • Deconvolve experimental data to extract GPDs? • GPDs provide full description of the nucleon? • Conceptual understanding of nucleon structure? • The focus should be to make as much contact with Lattice QCD as possible Physics with Spin

  27. A Look Forward • RHIC spin and Jlab physics will push a significant component of the required experimental technology • We will also learn a whole lot about how to analyze EIC data while grappling with analysis issues at these facilities • Key question: What is the optimum center of mass energy range and luminosity range? • You could make a strong case for 2 machines! • How many detectors should we plan for? Physics with Spin

  28. Closing Thoughts • Phew! That was hard! • I learnt a lot! (Did you?) • We in this room know that there is an extraordinary opportunity to further our understanding of the nucleon with an EIC • To make headway on funding outside this room, we need to focus our combined efforts on bringing a coherent case to the rest of the science community • Spin physics will play a critical role, both in strengthening the physics case and in communicating our field to the public Physics with Spin

  29. Tomography of the Nucleon Ji • Wigner operator • Wigner distribution: “density” for quarks having position r and 4-momentum k(off-shell) 7-dimensional distribution No known experiment can measure this! Physics with Spin

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