1. Quarks and Gluons in the Nuclear Medium – Opportunities at JLab@12 GeV and an EIC Rolf Ent, ECT-Trento, June 06, 2008 Nuclear Medium Effects on the Quark and Gluon Structure of Hadrons Main Workshop Topics Nuclear effects in polarized and unpolarized deep inelastic scattering Nuclear generalized parton distributions Hard exclusive and semi-inclusive processes Nuclear hadronization Color transparency Future facilities and experiments

2. The Quark Structure of Nuclei

3. The QCD Lagrangian and Nuclear “Medium Modifications” Leinweber, Signal et al. The QCD vacuum Long-distance gluonic fluctuations Lattice calculation demonstrates reduction of chiral condensate of QCD vacuum in presence of hadronic matter Does the quark structure of a nucleon get modified by the suppressed QCD vacuum fluctuations in a nucleus?

4. Quarks in a Nucleus Effect well measured,over large range of x and A, but remains poorly understood 1) ln(A) or  dependent? Observation that structure functions are altered in nuclei stunned much of the HEP community ~25 years ago 2) valence quark effect only? A=3 EMC Effect at 12 GeV

5. E772 Is the EMC effect a valence quark phenomenon or are sea quarks involved? Anti-Quarks in a Nucleus Solution: Detect a final state hadron in addition to scattered electron Deep inelastic electron scattering probes only the sum of quarks and anti- quarks  requires assumptions on the role of sea quarks 0.5 1.0 gluons sea valence 0.1 1.0 S. Kumano, “Nuclear Modification of Structure Functions in Lepton Scattering,” hep-ph/0307105 x R Ca  Can ‘tag’ the flavor of the struck quark by measuring the hadrons produced: ‘flavor tagging’ Tremendous opportunity for experimental improvements!

6. g 1 (A) – “Polarized EMC Effect” New calculations indicate larger effect for polarized structure function than for unpolarized: scalar field modifies lower components of Dirac wave function Spin-dependent parton distribution functions for nuclei nearly unknown Can take advantage of modern technology for polarized solid targets to perform systematic studies – Dynamic Nuclear Polarization

7. Valence only Valence + Sea Miller, Smith  Valence only calculations consistent with Cloet, Bentz, Thomas calculations  Same model shows small effects due to sea quarks for the unpolarized case (consistent with data) Large enhancement for x>0.3 due to sea quarks Sea is not much modified Chiral Quark-Soliton model (quarks in nucleons (soliton) exchange infinite pairs of pions, vector mesons with nuclear medium)

8. New calculations indicate larger effect for polarized structure function than for unpolarized: scalar field modifies lower components of Dirac wave function Spin-dependent parton distribution functions for nuclei nearly unknown Can take advantage of modern technology for polarized solid targets to perform systematic studies – Dynamic Nuclear Polarization (polarized EMC effect) Curve follows calculation by W. Bentz, I. Cloet, A. W. Thomas. g 1 (A) – “Polarized EMC Effect”

9. Extend measurements on nuclei to x > 1: Superfast quarks Correlated nucleon pair Six-quark bag (4.5% of wave function) Fe(e,e’) 5 PAC days Mean field

10. Does the quark structure of a nucleon get modified by the suppressed QCD vacuum fluctuations in a nucleus? 1)Measure the EMC effect on the mirror nuclei 3 H and 3 He 2)Is the EMC effect a valence quark only effect? 3)Is the spin-dependent EMC effect larger? 4)Can we reconstruct the EMC effect on 3 He and 4 He from all measured reaction channels? 5)Is there any signature for 6-quark clusters? 6)Can we map the effect vs. transverse momentum/size? Reminder: EMC effect is effect that quark momenta in nuclei are altered Now: use the nuclear arena to look for QCD

11. Use the Nuclear Arena to Study QCD

12. Total Hadron-Nucleus Cross Sections Hadron– Nucleus total cross section Fit to  K  p p _ Hadron momentum 60, 200, 250 GeV/c  < 1 interpreted as due to the strongly interacting nature of the probe A. S. Carroll et al. Phys. Lett 80B 319 (1979)  = 0.72 – 0.78, for p, , k

13. Traditional nuclear physics expectation: transparency nearly energy independent. T 1.0 Energy (GeV) Ingredients  h-N cross-section Glauber multiple scattering approximation (or better transport calculation!) Correlations & Final-State Interaction effects hN Physics of Nuclei: Color Transparency From fundamental considerations (quantum mechanics, relativity, nature of the strong interaction) it is predicted (Brodsky, Mueller) that fast protons scattered from the nucleus will have decreased final state interactions Quantum ChromoDynamics: A(e,e’h), h = hadron

14. Search for Color Transparency in Quasi-free A(e,e’p) Scattering Constant value line fits give good description:  2 /df = 1 Conventional Nuclear Physics Calculation by Pandharipande et al. (dashed) also gives good description Fit to  =   A a  = constant = 0.75 Close to proton-nucleus total cross section data  No sign of CT yet 

15. Physics of Nuclei: Color Transparency AGS A(p,2p) Glauber calculation P p (GeV/c) 5.17.39.62.9 Results inconsistent with CT only. But can be explained by including additional mechanisms such as nuclear filtering or charm resonance states. The A(e,e’p) measurements will extend up to ~10 GeV/c proton momentum, beyond the peak of the rise in transparency found in the BNL A(p,2p) experiments.

16. 678910 Physics of Nuclei: Color Transparency Total pion-nucleus cross section slowly disappears, or … pion escape probability increases  Color Transparency  Unique possibility to map out at 12 GeV (up to Q 2 = 10) Total pion-nucleus cross section slowly disappears, or … pion escape probability increases  Color Transparency? A(e,e’  + )

17. Physics of Nuclei: Color Transparency A(e,e’  + ) at 12 GeV (at fixed coherence length) 12 GeV

18. Using the nuclear arena How long can an energetic quark remain deconfined? How long does it take a confined quark to form a hadron? Formation time t f h Production time t p Quark is deconfined Hadron is formed Hadron attenuation CLAS Time required to produce colorless “pre- hadron”, signaled by medium-stimulated energy loss via gluon emission Time required to produce fully- developed hadron, signaled by CT and/or usual hadronic interactions

19. Using the nuclear arena L e e’ ** ++ pTpT  p T 2 = p T 2 (A) – p T 2 ( 2 H) “p T Broadening” dE/dx ~ L  E ~ L (QED) ~ L 2 (QCD)? How long can an energetic quark remain deconfined? How long does it take a confined quark to form a hadron? Or How do energetic quarks transform into hadrons? How quickly does it happen? What are the mechanisms?

20. How long can an energetic quark remain deconfined? How long does it take a confined quark to form a hadron? Or How do energetic quarks transform into hadrons? How quickly does it happen? What are the mechanisms? Deep Inelastic Scattering Relativistic Heavy-Ion Collisions Initial quark energy is known Properties of medium are known  e e’  Using the nuclear arena Relevance to RHIC and LHC

21.  p T 2 vs. for Carbon, Iron, and Lead C Pb Fe  p T 2 (GeV 2 ) (GeV) (GeV) ~ 100 MeV/fm (perturbative formula) ~dE/dx Preliminary CLAS Hall B

22. Production length from JLab/CLAS 5 GeV data (Kopeliovich, Nemchik, Schmidt, hep-ph/0608044) What we have learned Quark energy loss can be estimated Data appear to support the novel  E ~L 2 ‘LPM’ behavior ~100 MeV/fm for Pb at few GeV, perturbative formula Deconfined quark lifetime can be estimated, ~ 5 fm @ few GeV Outstanding questions Higher energy data to confirm “plateau” for heavy (large-A) nuclei Much more theoretical work needed to provide a quantitative basis for jet quenching at RHIC/LHC?

23. Using the nuclear arena  p T 2 reaches a “plateau” for sufficiently large quark energy, for each nucleus (L is fixed). pT2pT2 Projected Data

24. DOE Project Critical Decisions CD-0 Approve Mission Need CD-1 Approve Alternative Selection and Cost Range Permission to develop a Conceptual Design Report Defines a range of cost, scope, and schedule options CD-2 Approve Performance Baseline Fixes “baseline” for scope, cost, and schedule Now develop design to 100% Begin monthly Earned Value progress reporting to DOE Permission for DOE-NP to request construction funds CD-3 Approve Start of Construction DOE CD3 (IPR/Lehman) review scheduled for July 22-24 DOE Office of Science CD-3 Approval meeting in late Sept 2008 CD-4 Approve Start of Operations or Project Close-out

25. DOE CRITICAL DECISION SCHEDULE CD-0 Mission NeedMAR-2004 (A) CD-1 Preliminary Baseline RangeFEB-2006 (A) CD-2 Performance BaselineNOV-2007 (A) CD-3 Start of ConstructionSEP-2008 CD-4A Accelerator Project Completion and Start of Operations DEC-2014 CD-4B Experimental Equipment Project Completion and Start of Operations JUN-2015 (A) = Actual Approval Date Note → 6 to 18 months schedule float included Now split in two to ease transition into operations phase

26.  2004-2005 Conceptual Design (CDR) - finished  2004-2008 Research and Development (R&D) - ongoing  2006 Advanced Conceptual Design (ACD) - finished  2006-2009 Project Engineering & Design (PED) - ongoing  2009-2014 Construction – starts in ~1/2 year!  Parasitic machine shutdown May 2011 through Oct. 2011  Accelerator shutdown start mid-May 2012  Accelerator commissioning start mid-May 2013  2013-2015 Pre-Ops (beam commissioning)  Hall A commissioning start October 2013  Hall D commissioning start April 2014  Halls B and C commissioning start October 2014 12 GeV Upgrade: Phases and Schedule (based on funding guidance provided by DOE-NP in June-2007)

27. The Gluon Structure of Nuclei

28. Gluons dominate QCD QCD is the fundamental theory that describes structure and interactions in nuclear matter. Without gluons there are no protons, no neutrons, and no atomic nuclei Facts: –The essential features of QCD (e.g. asymptotic freedom, chiral symmetry breaking, and color confinement) are all driven by the gluons! –Unique aspect of QCD is the self interaction of the gluons –98% of mass of the visible universe arises from glue –Half of the nucleon momentum is carried by gluons However, gluons are dark: they do not interact directly with light  high-energy collider!

29. 29 The Low Energy View of Nuclear Matter nucleus = protons + neutrons nucleon  quark model quark model  QCD The High Energy View of Nuclear Matter The visible Universe is generated by quarks, but dominated by the dark glue! Remove factor 20 Exposing the high-energy (dark) side of the nuclei

30. EIC science has evolved from new insights and technical accomplishments over the last decade ~1996 development of GPDs ~1999 high-power energy recovery linac technology ~2000 universal properties of strongly interacting glue ~2000 emergence of transverse-spin phenomenon ~2001 world’s first high energy polarized proton collider ~2003 RHIC sees tantalizing hints of saturation ~2006 electron cooling for high-energy beams

31. NSAC 2007 Long Range Plan “An Electron-Ion Collider (EIC) with polarized beams has been embraced by the U.S. nuclear science community as embodying the vision for reaching the next QCD frontier. EIC would provide unique capabilities for the study of QCD well beyond those available at existing facilities worldwide and complementary to those planned for the next generation of accelerators in Europe and Asia. In support of this new direction: We recommend the allocation of resources to develop accelerator and detector technology necessary to lay the foundation for a polarized Electron Ion Collider. The EIC would explore the new QCD frontier of strong color fields in nuclei and precisely image the gluons in the proton.”

32. Explore the new QCD frontier: strong color fields in nuclei - How do the gluons contribute to the structure of the nucleus? - What are the properties of high density gluon matter? - How do fast quarks or gluons interact as they traverse nuclear matter? Precisely image the sea-quarks and gluons in the nucleon - How do the gluons and sea-quarks contribute to the spin structure of the nucleon? - What is the spatial distribution of the gluons and sea quarks in the nucleon? - How do hadronic final-states form in QCD? How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD?

33. Explore the structure of the nucleon Parton distribution functions Longitudinal and transverse spin distribution functions Generalized parton distributions Transverse momentum distributions

34. RHIC-Spin region Precisely image the sea quarks Spin-Flavor Decomposition of the Light Quark Sea | p = + + + … > u u d u u u u d u u d d d Many models predict  u > 0,  d < 0 No competition foreseen!

35. GPDs and Transverse Gluon Imaging Deep exclusive measurements in ep/eA with an EIC: diffractive:transverse gluon imagingJ/ ,  o,  (DVCS) non-diffractive:quark spin/flavor structure , K,  +, … [ or J/ , ,  0 , K,  +, … ] Describe correlation of longitudinal momentum and transverse position of quarks/gluons  Transverse quark/gluon imaging of nucleon (“tomography”) Are gluons uniformly distributed in nuclear matter or are there small clumps of glue?

36. GPDs and Transverse Gluon Imaging gives transverse size of quark (parton) with longitud. momentum fraction x EIC: 1) x < 0.1: gluons! x < 0.1x ~ 0.3x ~ 0.8 Fourier transform in momentum transfer x ~ 0.001 2)  ~ 0  the “take out” and “put back” gluons act coherently. 2)  ~ 0 x -  x +   d

37. GPDs and Transverse Gluon Imaging Goal: Transverse gluon imaging of nucleon over wide range of x: 0.001 < x < 0.1 Requires: - Q 2 ~ 10-20 GeV 2 to facilitate interpretation - Wide Q 2, W 2 (x) range - Sufficient luminosity to do differential measurements in Q 2, W 2, t Q 2 = 10 GeV 2 projected data Simultaneous data at other Q 2 -values EIC enables gluon imaging! Scaled from 2 to 16 wks. EIC (16 weeks)

38. 38 eA Landscape and a New Electron Ion Collider Well mapped in e+p Not so for ℓ+A ( A) Electron Ion Collider (EIC): L(EIC) > 100  L(HERA) eRHIC (e+Au): E e = 10 (20) GeV E A = 100 GeV  s eN = 63 (90) GeV L eAu (peak)/n ~ 2.9·10 33 cm -2 s -1 ELIC (e+Au): E e = 9 GeV E A = 90 GeV  s eN = 57 GeV L eAu (peak)/n ~ 1.6·10 35 cm -2 s -1 Terra incognita: small-x, Q  Q s high-x, large Q 2

39. F 2 : Sea (Anti)Quarks Generated by Glue at Low x F 2 will be one of the first measurements at EIC nDS, EKS, FGS: pQCD based models with different amounts of shadowing Syst. studies of F 2 (A,x,Q 2 ):  G(x,Q 2 ) with precision  distinguish between models

40. Longitudinal Structure Function F L Experimentally can be determined directly IF VARIABLE ENERGIES! Highly sensitive to effects of gluon F L at EIC: Measuring the Glue Directly

41. Explore gluon-dominated matter At high gluon density, gluon recombination should compete with gluon splitting  density saturation. What is the role of gluons and gluon self-interactions in nucleons and nuclei? NSAC-2007 Long-Range Plan Report. –The nucleus as a “gluon amplifier” Color glass condensate Oomph factor stands up under scrutiny. Nuclei greatly extend x reach: x EIC = x HERA /18 for 10+100 GeV, Au Longitudinal Structure Function F L

42. Diffractive Surprises ‘Standard DIS event’ Detector activity in proton direction 7 TeV equivalent electron bombarding the proton … but proton remains intact in 15% of cases … Diffractive event No activity in proton direction Predictions for eA for such hard diffractive evens range up to: ~30-40%... given saturation models Look inside the “Pomeron”  Diffractive structure functions  Diffractive vector meson production ~ [G(x,Q 2 )] 2

43. Explore the transition from partons to hadrons What governs the transition of quarks and gluons in pions and nucleons? NSAC-2007 –Fragmentation and parton energy loss –The nucleus as a “femto-meter stick” Nuclear SIDIS: Suppression of high-pT hadrons analogous but weaker than at RHIC Clean measurement in ‘cold’ nuclear matter Energy transfer in lab rest frame EIC: 10 < < 2000 GeV (HERMES: 2-25 GeV) EIC: can measure heavy flavor energy loss

44. Using the nuclear arena  p T 2 reaches a “plateau” for sufficiently large quark energy, for each nucleus (L is fixed). pT2pT2 In the pQCD region, the effect is predicted to disappear (arbitrarily put at =1000)

45. Quarks and Gluons in the Nuclear Medium – Opportunities at JLab@12 GeV and an EIC Rolf Ent, ECT-Trento, June 06, 2008 JLab 12 GeV Upgrade: The 12 GeV Upgrade, with its 10 38 + luminosity, is expected to allow for a complete spin and flavor dependence of the valence quark region, both in nucleons and in nuclei. Electron Ion Collider (eRHIC/ELIC) Provide a complete spin and flavor dependence of the nucleon and nuclear sea, study the explicit role that gluons play in the nucleon spin and in nuclei, open the new research territory of “gluon GPDs”, and study the onset of the physics of saturation. Personal View:

47. Longitudinal Structure Function F L Experimentally can be determined directly IF VARIABLE ENERGIES! Highly sensitive to effects of gluon + 12-GeV data + EIC alone F L at EIC: Measuring the Glue Directly

48. eRHIC Gluons in the Nucleus Note: not all models carefully checked against existing data + some models include saturation physics

49. GPDs and Transverse Gluon Imaging k k'k' ** q q'q'  pp'p' e A Major new direction in Nuclear Science aimed at the 3-D mapping of the quark structure of the nucleon. Simplest process: Deep-Virtual Compton Scattering Simultaneous measurements over large range in x, Q 2, t at EIC! At small x (large W):  ~ G(x,Q 2 ) 2