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Physics with ELIC at JLab

Physics with ELIC at JLab. Introduction ELIC Concept Physics with ELIC Rolf Ent 05/23/2003. ELIC@JLab - Science. Science addressed by ELIC: How do quarks and gluons provide the binding and spin of the nucleons? How do quarks and gluons evolve into hadrons?

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Physics with ELIC at JLab

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  1. Physics with ELIC at JLab Introduction ELIC Concept Physics with ELIC Rolf Ent 05/23/2003

  2. ELIC@JLab - Science Science addressed by ELIC: • How do quarks and gluons provide the binding and spin of the nucleons? • How do quarks and gluons evolve into hadrons? • How does nuclear binding originate from quarks and gluons? (x 0.01) Glue ÷100 ELIC 12 GeV

  3. ELIC@JLab - Science • Clear scientific case by 12-GeV JLab Upgrade, addressing outstanding issues in Hadron Physics: • Unprecedented measurements to region in x (> 0.1) where basic three-quark structure of nucleons dominates. • Measurements of correlations between quarks, mainly through Deep-Virtual Compton Scattering (DVCS) and constraints by nucleon form factors, in pursuit of the Generalized Parton Distributions. • Finishing the job on the transition from hadronic to quark-gluon degrees of freedom. • At present, uncertain what range of Q2 really required to determine complete structure of the nucleon. Most likely Q2 ~ 10 GeV2? • Upcoming years wealth of data from RHIC-Spin, COMPASS, HERMES, JHF, JLab, etc. • DVCS (JLab-12!) and single-spin asymmetries possible at lower Q2 • Range of Q2 directly linked to required luminosity • What energy and luminosity, fixed-target facility or collider (or both)? • 25 GeV Fixed-Target Facility? • Electron-Light Ion Collider, center-of-mass energy of 20-65 GeV?

  4. Basis of the ELIC Proposal (Lia Merminga, Slava Derbenev, et al.) • A Linac-Ring Collider Design (with additional Circulator Ring) • Linac • CEBAF is used for the (one-pass) acceleration of electrons • Energy recovery is used for rf power savings and beam dump requirements • Ring • “Figure-8” storage ring is used for the ions for flexible spin manipulations of all light-ion species of interest • Circulator ring for the electrons may be used to ease high current polarized photoinjector requirements Luminosity of up to 1035 cm-2 sec-1 But .... still needs integration of detector with interaction region ....

  5. Ion Source RFQ DTL Snake CCL IR IR Snake Solenoid 5 GeVelectrons 50-100 GeV light ions Injector CEBAF with Energy Recovery Beam Dump ELIC Layout One accelerating & one decelerating pass through CEBAF

  6. The same electron accelerator can also provide 25 GeV electrons for fixed target experiments for physics • Implement 5-pass recirculator, at 5 GeV/pass, as in present CEBAF (straightforward upgrade, no accelerator R&D needed) • Exploring whether collider and fixed target modes can run simultaneously (can in alternating mode)

  7. Luminosity Potential with ELIC x10,000 More info: Talk on ELIC Project by Lia Merminga

  8. ELIC@JLab - Kinematics ELIC kinematics at Ecm = 45 GeV, and beyond the resonance region. • Luminosity of up to 1035 cm-2 sec-1 • One day  5,000 events/pb • Supports precision experiments • DIS Limit for Q2 > 1 GeV2 implies (Bjorken) x down to 5 times 10-4 • Significant results for 200 events/pbfor inclusive scattering • IfQ2 > 10 GeV2 required for Deep Exclusive Processes, can reach x down to 5 times 10-3 • Typical cross sections factor 100-1,000 smaller than inclusive scattering  still easily accessible

  9. The Structure of the Proton – F2 F2 Structure Function measured over impressive range of x and Q2. Q2 evolution also constrains glue! Still large uncertainty in glue, especially at Q2 < 20 GeV2

  10. The Structure of the Proton – FL Great Opportunity to (finally) determine FL with good precision (JLab-6 example here in the nucleon resonance region only) Complementarity of 25-GeV fixed-target and ELIC for this example!  Glue at low Q2 De > 0.3 > > 20 known

  11. The Spin Structure of the Proton ½ = ½ DS + DG + Lq + Lg • From NLO-QCD analysis of DIS measurements … (SMC analysis) DS = 0.38 (in AB scheme) DG = 1.0+1.9 ,, • quark polarization Dq(x) first 5-flavor separation from HERMES (see later) • transversity dq(x) a new window on quark spin azimuthal asymmetries from HERMES and JLab-6 • gluon polarization DG(x) RHIC-spin and COMPASS will provide some answers! • orbital angular momentum L how to determine?  GPD’s -0.6 CEBAF II/ELIC Upgrade can solve this puzzle due to large range in x and Q2 and precision due to high luminosity

  12. Orbital Angular Momentum Analysis of hard exclusive processes leads to a new class of generalized parton distributions Four new distributions: helicity conserving  H(x,x,t), E(x,x,t) helicity-flip  H(x,x,t), E(x,x,t) • “skewedness parameter” x • mismatch between quark momenta sensitive to partonic correlations ~ ~ • New Roads: • Deeply Virtual Meson • Production @ Q2 > 10 GeV2 •  disentangles flavor and • spin! • r and f Production give access to gluon GPD’s at small x (<0.2) 3-dimensional GPDs give spatial distribution of partons and spin • Angular Momentum Jq = ½ DS + Lq ! Can we achieve same level of understanding as with F2?

  13. Generalized Parton Distributions • What could be the role of a 25 GeV Fixed Target facility? • Enhances phase space to Q2>10 GeV2 • Comfortable to do flavor separation of GPD’s • Also L/T separations to verify how hard process really is! Deep Virtual Meson Production sL dominant, and ~ Q-6?

  14. New Spin Structure Function: Transversity (in transverse basis) - dq(x) ~ • Nucleon’s transverse spin content  “tensor charge” • No transversity of Gluons in Nucleon “all-valence object” • Chiral Odd  only measurable in semi-inclusive DIS • first glimpses exist in data (HERMES, JLab-6) • COMPASS, RHIC-spin plans • Future: Flavor decomposition? Estimates for TESLA-N (Ecm = 22 GeV)

  15. How Do Quarks and Gluons form Hadrons? In semi-inclusive DIS a hadron h is detected in coincidence with the scattered lepton Study quark-gluon substructure of • nucleon target  parton distribution functions q(x,Q2) • hadron formation (or hadronization)  fragmentation functions D(z,Q2) Process both of interest in its own right and as a tool (see also next slides)

  16. Hadronization as a Tool First 5-flavor fit to Dq(x) (Ds(x) = Ds(x) assumed) Quark Polarization from Semi-Inclusive DIS _ - - • Goal: Flavor Separation of quark and antiquark helicity distributions • Technique: Flavor Tagging The flavor content of the final state hadrons is related to the flavor of the struck quark through the agency of the fragmentation functions Chiral-Quark Soliton Model Light sea quarks polarized but Data consistent with zero

  17. Hadronization (Or: The Long-Range Dynamics of Confinement) What do we know? What don’t we (exactly) know? The Lund String Model Phenomenological description in terms of color-string breaking and parton clustering Evolution of the fragmentation functions • Spin Transfer: Is the spin of the struck quark communicated to the hadronic final state? • Single-Spin Asymmetries: How important is intrinsic transverse momentum? • Space-Time Structure: How long does it take to form a hadron? Present and future studies (HERMES, JLab-6, JLab-12) use the nuclear radius as a yardstick to measure the time scale of hadron formation

  18. Nuclear Binding • Natural Energy Scale of QCD: O(100 MeV) • Nuclear Binding Scale O(10 MeV) • Does it result from a complicated detail of near cancellation of strongly attractive and repulsive terms in N-N force, or is there another explanation? How can one understand nuclear binding in terms of quarks and gluons? Complete spin-flavor structure of modifications to quarks and gluons in nuclear system may be best clue.

  19. Quarks in a Nucleus Can pick apart the spin-flavor structure of EMC effect by technique of flavor tagging, in the region where effects of the space-time structure of hadrons do not interfere (large n!) F2A/F2D “EMC Effect” 10-4 10-3 10-2 10-1 1 x Nuclear attenuation negligible for n > 50 GeV hadrons escape nuclear medium undisturbed Space-Time Structure of Photon

  20. Sea-Quarks and Gluons in a Nucleus Drell-Yan  No Nuclear Modifications to Sea-Quarks found at x ~ 0.1 Where is the Nuclear Binding? Constraints on possible nuclear modifications of glue come from 1) Q2 evolution of nuclear ratio of F2 in Sn/C (NMC) 2) Direct measurement of J/Psi production in nuclear targets F2 G • Compatible with EMC effect? • Precise measurements possible of • Nuclear ratio of Sn/C (25 GeV) • J/Psi production (ELIC) Flavor tagging can also (in principle) disentangle sea-quark contributions

  21. ELIC@JLab – Conclusions • An excellent scientific case is developing for a high luminosity, polarized electron-light ion collider; will address fundamental issues in Hadron Physics: • The (spin-flavor) quark-gluon structure of the proton and neutron • How do quarks and gluons form hadrons? • The quark-gluon origin of nuclear binding • JLab design studies have led to an approach that promises luminosities as high as 1035 cm-2 sec-1, for electron-light ion collisions at a center-of-mass energy between 20 and 65 GeV • This design, using energy recovery on the JLab site, can be cost-effectively integrated with a 25 GeV fixed target program for physics

  22. ELIC Physics Specifications • Center-of-mass energy between 20 and 65 GeV (with energy asymmetry of ~10) • Ee ~ 3 GeV on Ei ~ 30 GeV up to Ee ~ 5 GeV on Ei ~ 100 GeV worked out in detail (gives Ecm up to 45 GeV) • Ee ~ 7 GeV on Ei ~ 150 GeV seems o.k., but details to be worked out (extends Ecm to 65 GeV) • CW Luminosity up to1035cm-2 sec-1 • Ion species of interest: protons, deuterons, 3He, light-medium ions • Proton and neutron • Light-medium ions not necessarily polarized • Longitudinal polarization of both beams in the interaction region(+Transverse polarization of ions +Spin-flip of both beams)

  23. R&D Topics • Several important R&D topics have been identified: • High charge per bunch and high average current polarized electron source • High energy electron cooling of protons/ions • High current and high energy demonstration of energy recovery • Integration of interaction region design with detector geometry

  24. Luminosity Potential with ELIC x100 x10,000 EIC

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