1. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Physics with ELIC at JLab Introduction ELIC Concept Physics with ELIC Rolf Ent 05/23/2003

2. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 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? How does nuclear binding originate from quarks and gluons? 12 GeVELIC (x 0.01) Glue ÷100

3. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 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 Q 2 really required to determine complete structure of the nucleon. Most likely Q 2 ~ 10 GeV 2 ? Upcoming years wealth of data from RHIC-Spin, COMPASS, HERMES, JHF, JLab, etc. DVCS (JLab-12!) and single-spin asymmetries possible at lower Q 2 Range of Q 2 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. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Basis of the ELIC Proposal  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 10 35 cm -2 sec -1 But.... still needs integration of detector with interaction region.... (Lia Merminga, Slava Derbenev, et al.)

5. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 ELIC Layout One accelerating & one decelerating pass through CEBAF Ion Source RFQ DTL CCL IR Beam Dump Snake CEBAF with Energy Recovery 5 GeV electrons 50-100 GeV light ions Solenoid Injector

6. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 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  Exploring whether collider and fixed target modes can run simultaneously (can in alternating mode) (straightforward upgrade, no accelerator R&D needed)

7. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Luminosity Potential with ELIC ParameterUnitsDesign e-e- Ions EnergyGeV550/100 Electron Cooling --Yes Circulator Ring -Yes- Luminositycm -2 sec -1 6x10 34 / 1x10 35 I ave A2.5 fcfc MHz1500 x10,000 More info: Talk on ELIC Project by Lia Merminga

8. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 ELIC@JLab - Kinematics Luminosity of up to 10 35 cm -2 sec -1 One day  5,000 events/pb Supports precision experiments DIS Limit for Q 2 > 1 GeV 2 implies (Bjorken) x down to 5 times 10 -4 Significant results for 200 events/pb for inclusive scattering If Q 2 > 10 GeV 2 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 ELIC kinematics at E cm = 45 GeV, and beyond the resonance region.

9. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 The Structure of the Proton – F 2 F 2 Structure Function measured over impressive range of x and Q 2. Q 2 evolution also constrains glue! Still large uncertainty in glue, especially at Q 2 < 20 GeV 2

10. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 The Structure of the Proton – F L  Great Opportunity to (finally) determine F L 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 Q 2 known > > 20

11. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 The Spin Structure of the Proton From NLO-QCD analysis of DIS measurements … (SMC analysis)  = 0.38 (in AB scheme)  G = 1.0 +1.9,, quark polarization  q(x)  first 5-flavor separation from HERMES (see later) transversity  q(x)  a new window on quark spin  azimuthal asymmetries from HERMES and JLab-6 gluon polarization  G(x)  RHIC-spin and COMPASS will provide some answers! orbital angular momentum L  how to determine?  GPD’s ½ = ½  +  G + L q + L g -0.6 CEBAF II/ELIC Upgrade can solve this puzzle due to large range in x and Q 2 and precision due to high luminosity

12. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Orbital Angular Momentum Analysis of hard exclusive processes leads to a new class of generalized parton distributions Four new distributions: helicity conserving  H(x, ,t), E(x, ,t) helicity-flip  H(x, ,t), E(x, ,t) ~ ~ “skewedness parameter”   mismatch between quark momenta  sensitive to partonic correlations 3-dimensional GPDs give spatial distribution of partons and spin  Angular Momentum J q = ½  + L q ! New Roads:  Deeply Virtual Meson Production @ Q 2 > 10 GeV 2  disentangles flavor and spin!   and  Production give access to gluon GPD’s at small x (<0.2) Can we achieve same level of understanding as with F 2 ?

13. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Generalized Parton Distributions What could be the role of a 25 GeV Fixed Target facility?  Enhances phase space to Q 2 >10 GeV 2  Comfortable to do flavor separation of GPD’s  Also L/T separations to verify how hard process really is!  L dominant, and ~ Q -6 ? Deep Virtual Meson Production

14. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 New Spin Structure Function: Transversity 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? - (in transverse basis)  q(x) ~ Estimates for TESLA-N (E cm = 22 GeV)

15. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 How Do Quarks and Gluons form Hadrons? Study quark-gluon substructure of nucleon target  parton distribution functions q(x,Q 2 ) hadron formation (or hadronization)  fragmentation functions D(z,Q 2 ) In semi-inclusive DIS a hadron h is detected in coincidence with the scattered lepton Process both of interest in its own right and as a tool (see also next slides)

16. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Hadronization as a Tool  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 First 5-flavor fit to  q(x) (  s(x) =  s(x) assumed) _Quark Polarization from Semi-Inclusive DIS Chiral-Quark Soliton Model  Light sea quarks polarized but Data consistent with zero - -

17. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Hadronization What do we 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? What don’t we (exactly) know? (Or: The Long-Range Dynamics of Confinement) 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. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 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. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Quarks in a Nucleus “EMC Effect” Space-Time Structure of Photon F 2 A /F 2 D 10 -4 10 -3 10 -2 10 -1 1 x 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 !) Nuclear attenuation negligible for > 50 GeV  hadrons escape nuclear medium undisturbed

20. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 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? Flavor tagging can also (in principle) disentangle sea-quark contributions Constraints on possible nuclear modifications of glue come from 1) Q 2 evolution of nuclear ratio of F 2 in Sn/C (NMC) 2) Direct measurement of J/Psi production in nuclear targets Compatible with EMC effect? Precise measurements possible of  Nuclear ratio of Sn/C (25 GeV)  J/Psi production (ELIC) F2F2 G

21. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003  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 10 35 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 ELIC@JLab – Conclusions

22. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 ELIC Physics Specifications  Center-of-mass energy between 20 and 65 GeV (with energy asymmetry of ~10)  E e ~ 3 GeV on E i ~ 30 GeV up to E e ~ 5 GeV on E i ~ 100 GeV worked out in detail (gives E cm up to 45 GeV)  E e ~ 7 GeV on E i ~ 150 GeV seems o.k., but details to be worked out (extends E cm to 65 GeV)  CW Luminosity up to 10 35 cm -2 sec -1  Ion species of interest: protons, deuterons, 3 He, 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. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 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. Operated by the Southeastern Universities Research Association for the U. S. Department of Energy Thomas Jefferson National Accelerator Facility Rolf Ent CIPANP 05/23/2003 Luminosity Potential with ELIC ParameterUnitsFinal Design e-e- Ions EnergyGeV550/100 Electron Cooling --Yes Circulator Ring -Yes- Luminositycm -2 sec -1 6x10 34 / 1x10 35 I ave A2.5 fcfc MHz1500 x10,000 EIC x100