2. E.C. Aschenauer arXiv: 1212.1701 & 1108.1713

3. This is us !!! protons, neutrons electrons increase beam energy beam energy Quarks and Gluons 10 -17 m Proton 10 -15 m Binding-energy: ~10 9 eV Proton: Quark-Masses: ~1% M p Proton mass completely generated by QCD dynamics HOW ? Need a high resolution microscope to resolve quark and gluon structure  eRHIC Gluon density dominates at x<0.1 HERA’s discovery:

4. 3  gluons distribution cannot rise forever  non-linear pQCD effects provide a  non-linear pQCD effects provide a natural way to tame this growth natural way to tame this growth  characterized by the saturation  characterized by the saturation scale Q 2 s (x) scale Q 2 s (x) QCD: Dynamical balance between splitting and recombination and recombination A new regime of QCD matter  Color Glass Condensate (CGC) Hints from HERA, RHIC and LHC discover it unambiguously at eRHIC Enhancement of Q S with A Enhancement of Q S with A ⇒ saturation regime reached at ⇒ saturation regime reached at significantly lower √s in nuclei significantly lower √s in nuclei Au: ~200 times smaller effective x ! E.C. Aschenauer  Which correlations constitute the dynamics of the multi body system at low x of the multi body system at low x  How does quark and gluon dynamics generate the proton spin? It is more than the number 1/2 ℏ ! It is more than the number 1/2 ℏ !  crucial interplay between the intrinsic  crucial interplay between the intrinsic properties and interactions of quarks and properties and interactions of quarks and gluons gluons  How do hadrons emerge from a created quark or gluon? or gluon? Neutralization of color - hadronization Neutralization of color - hadronization  2+1D Structure of nucleons and nuclei How does the glue bind quarks and itself into How does the glue bind quarks and itself into nucleons and nuclei? nucleons and nuclei? Q 2 GeV 2 Probingmomentum 200 MeV (1 fm) 2 GeV (1/10) fm) Color Confinement Asymptotic freedom

5. Proton spins are used to image the structure and function of the human body using the technique of magnetic resonance imaging. 4e’ (Q 2 ) e L*L*L*L* x+ξ x-ξ H, H, E, E (x,ξ,t) ~ J  p/A p’/A’ t Measure exclusive cross sections for different final states ( , J/Ψ, …) as fct. of t, x and Q 2  spatial parton distributions (GPDs)  access to orbital angular momentum E.C. Aschenauer

6. 5  Hard diffraction at small x Why is diffraction so important  Sensitive to spatial gluon distribution (t  b T )  Hot topic:  Lumpiness?  Just Wood-Saxon+nucleon g(b T )  coherent part probes “shape of black disc”  incoherent part (large t) sensitive to “lumpiness” of the source sensitive to “lumpiness” of the source (fluctuations, hot spots,...) (fluctuations, hot spots,...) t = Δ 2 /(1-x) ≈ Δ 2 (for small x) possible Source distribution with b T g = 2 GeV -2 Analogy: plane monochromatic wave incident on a circular screen of radius R Impact:  discover unambiguously a new state of QCD matter  understand the initial conditions for AA collisions  influence on Sphaleron transition probabilities  one of the possibilities to generate CP-violation in the early universe needed to explain the in the early universe needed to explain the baryon-antibaryon ratio baryon-antibaryon ratio

7. 6 Current knowledge about Gluons in p /A Why eRHIC now? “all stars align”:  theory developments will allow to obtain the answers to the critical questions the answers to the critical questions discussed discussed  accelerator technologies allow for a high energy, high luminosity polarized ep/eA energy, high luminosity polarized ep/eA collider collider  detector technologies allow for a collider detector with high resolution, wide detector with high resolution, wide acceptance and particle ID in the acceptance and particle ID in the entire  range entire  range with eRHIC eRHIC science program will profoundly impact our understanding of QCD, uniquely tied to a future high energy, high luminosity, polarized ep / eA collider never been measured before & never without E.C. Aschenauer

8. 7 BACKUP

9. 8  Utilize the theoretical concepts of transverse momentum distributions (TMDs) and un-integrated PDFs, which encode correlations and un-integrated PDFs, which encode correlations  spin-orbit correlations on parton level  hydrogen atom  teach us how colors charges in QCD interact  Observable: azimuthal modulations of 6-fold differential cross section in semi-inclusive DIS cross section in semi-inclusive DIS can be viewed as parton flow inside nucleus analogy: currents in oceans

10. 9 Measure of resolution power Measure of inelasticity Measure of momentum fraction of struck quark Kinematics: Quark splits into gluon splits into quarks … Gluon splits into quarks higher √s increases resolution 10 -19 m 10 -16 m E.C. Aschenauer

11. 10 Does this saturation produce matter of universal properties in the nucleon and all nuclei viewed at nearly the speed of light? Where does the saturation of gluon densities set in? Is there a simple boundary that separates the region from the more dilute quark gluon matter? If so how do the distributions of quarks and gluons change as one crosses the boundary? How are sea quarks and gluons and their spin distributed in space and momentum inside the nucleon? How are these quark and gluon distributions correlated with the over all nucleon properties, such as spin direction? What is the role of the motion of sea quarks and gluons in building the nucleon spin? How does the nuclear environment affect the distribution of quarks and gluons and their interaction in nuclei? How does matter respond to fast moving color charge passing through it? Is this response different for light and heavy quarks? How does the transverse spatial distribution of gluons compare to that in the nucleon? q h **** e’e’e’e’ e only at EIC EIC only in eA/ep E.C. Aschenauer

12. 11 time CGCJIMWLK/BK Hydro (EoS) Hard Processes (pQCD) FF/coal. HadronTransport I Our understanding of some fundamental properties of the Glasma, sQGP and Hadron Gas depend strongly on our knowledge of the initial state! 3 conundrums of the initial state: 1.What is the spatial transverse distributions of nucleons and gluons? 2. How much does the spatial distribution fluctuate? Lumpiness, hot-spots etc. fluctuate? Lumpiness, hot-spots etc. 3. How saturated is the initial state of the nucleus? nucleus?  unambiguously see saturation  unambiguously see saturation Advantage over p(d)A:  eA experimentally much cleaner no “spectator” background to subtract no “spectator” background to subtract  Access to the parton kinematics through scattered lepton (x, Q 2 )  initial and final state effects can be disentangled cleanly  Saturation: no alternative explanations, i.e. no hydro in eA no alternative explanations, i.e. no hydro in eA The Initial Conditions E.C. Aschenauer

13. 12 Hadron-Hadron: Electron-Hadron:  probe has structure as complex as the “target” the “target”  More direct information/access on the response of a nuclear medium to gluon response of a nuclear medium to gluon probe probe  Soft color interactions before the collision can alter the nuclear wave fct. collision can alter the nuclear wave fct. and destroy universality of parton and destroy universality of parton properties (break factorization) properties (break factorization)  no direct access to parton kinematics  Point-like probe  High precision & access to partonic kinematics kinematics  Dominated by single photon exchange  no direct color interaction  no direct color interaction  preserve the properties of partons  preserve the properties of partons in the nuclear wave function in the nuclear wave function  Nuclei always “cold” nuclear matter

14. 13  Idea: momentum transfer t conjugate to transverse position (b T ) o coherent part probes “shape of black disc” o incoherent part (dominant at large t) sensitive to “lumpiness” of the source (fluctuations, hot spots,...) Spatial source distribution: t = Δ 2 /(1-x) ≈ Δ 2 (for small x) ϕ, nosat Golden eA measurement for eRHIC E.C. Aschenauer

15. 14 Other than in p: G(x,Q 2 ) for nuclei is little known Key: F L (x,Q 2 ) ~ xG(x,Q 2 ) 99% of all h ± have p t < 2 GeV/c “Bulk Matter”  x < 0.01 E.C. Aschenauer

16. lowest x so far 4.6 x10 -3 COMPASS RHIC pp data constraining Δg(x) in approx. 0.05 < x <0.2 data plotted at x T =2p T /√S 15 eRHIC extends x coverage by up to 2 decades (at Q 2 =1 GeV 2 ) likewise for Q 2 E.C. Aschenauer

17. 16 5 x 250 starts here 5 x 100 starts here hep-ph:1206.6014 cross section: pQCD scaling violations world data E.C. Aschenauer

18. DIS scaling violations mainly determine Δg at small x in addition, SIDIS data provide detailed flavor separation of quark sea includes only “stage-1 data” includes only “stage-1 data” can be pushed to x=10 -4 with can be pushed to x=10 -4 with 20 x 250 GeV data 20 x 250 GeV data “issues”: (SI)DIS @ eRHIC limited by (SI)DIS @ eRHIC limited by systematic uncertainties systematic uncertainties need to control rel. lumi, need to control rel. lumi, polarimetry, detector performance, polarimetry, detector performance, … very well … very well 17 yet, small x behavior completely unconstrained  determines x-integral, which enters proton spin sum dramatic reduction of uncertainties: E.C. Aschenauer

19. can expect approx. 5-10% can expect approx. 5-10% uncertainties on ΔΣ and Δg uncertainties on ΔΣ and Δg but need to control systematics but need to control systematics current data w/ eRHIC data 18 total quark spin  spin  gluon spin  g ✔ what about the orbital angular momentum? E.C. Aschenauer

20. experimental program to address these questions: azimuthal asymmetries in DIS adds their transverse momentum dependence exclusive processes adds their transverse position inclusive and semi-inclusive DIS longitudinal motion of spinning quarks and gluons machine & detector requirements prerequisites all need √s ep > 50 GeV to access x < 10 -3 where sea quarks and gluons dominate multi-dimensional binning multi-dimensional binning to reach k T > 1 GeV to reach k T > 1 GeV to reach |t| > 1 GeV 2 to reach |t| > 1 GeV 2 19 E.C. Aschenauer

21. 20 Upstream low Q 2 taggerandluminositydetector PID: -1<  <1: DIRC or proximity focusing Aerogel-RICH + TPC: dE/dx 1<|  |<3: RICH Lepton-ID: -3 <  < 3: e/p 1<|  |<3: in addition Hcal response &  suppression via tracking 1<|  |<3: in addition Hcal response &  suppression via tracking |  |>3: ECal+Hcal response &  suppression via tracking -5<  <5: Tracking (TPC+GEM+MAPS)   To Roman Pots hadron beam lepton beam Mainly based on detector technologies as proposed in EIC-Detector R&D: https://wiki.bnl.gov/conferences/index.php/EIC_R%25D E.C. Aschenauer