1. 1 2014 Joint Halls A/C Summer Meeting Jefferson Lab – June 5-6, 2014 Semi-Inclusive Physics at the Electron-Ion Collider Rolf Ent (JLab) EIC white paper arXiv:1212.17010 (v2) 2007 Long-Range Plan EIC: “half” recommendation 2010 JLab User Workshops INT10-3 program >500 page report

2. 2 Semi-Inclusive Physics at the Electron-Ion Collider (EIC*) The Worldwide Quest for Electron-Ion Colliders Into the “Sea”: the EIC* Science Semi-Inclusive Physics – Nucleon Structure The Utilization of Nuclear Beams * EIC is the generic name for the Nuclear Science-driven Electron-Ion Collider, presently considered in the US EIC = QCD Mass Explorer of the atomic nucleus

3. 3 Possible FuturePast High-Energy PhysicsHadron Physics Electron Ion Colliders HERA@DESYLHeC@CERNeRHIC@BNLMEIC@JLabHIAF@CASENC@GSI E CM (GeV)320800-130070-15012-70  14012  6514 proton x min 1 x 10 -5 5 x 10 -7 4 x 10 -5 5 x 10 -5 7 x10 -3  3x10 -4 5 x 10 -3 ionpp to Pbp to Up to Pbp to Up to ~ 40 Ca polarization--p, 3 Hep, d, 3 He ( 6 Li)p, d, 3 Hep,d L [cm -2 s -1 ]2 x 10 31 10 33-34 10 33  10 34 10 34-35 10 32-33  10 35 10 32 IP212+ 11 Year1992-20072025 Post-12 GeV2019  2030 upgrade to FAIR Figure-8 Dormant Followed by FCC-he? EIC CEIC Note: x min ~ x @ Q 2 = 1 GeV 2 Europe ChinaUS

4. 4 The CM Energy vs Luminosity Landscape CEIC1 = Chinese version of Electron-Ion Collider (“A dilution-free mini-COMPASS”) MEIC1 = EIC@Jlab eRHIC = EIC@BNL LHeC = ep/eA collider @ CERN CEIC2 MEIC2 HL-eRHIC FCC-he } future extensions

5. 5 EIC vs LHeC LHeC: L = 10 33-34 cm -2 s -1 E cm ~ 1 TeV EIC: L = about 10 34 cm -2 s -1 E cm = 20- ~100 GeV Add ~60 GeV electrons to LHC Use IP2 interaction region High luminosity takes benefit of large  ’s (= E/m) of beams Variable energy range Polarized and heavy ion beams High luminosity in energy region of interest for nuclear science/QCD world’s first polarized e-p collider and world’s first e-A collider high-energy e-p collider to follow on DESY, plus plans for e-A collider x min ~ 1 x 10 -4 x min ~ 5 x 10 -7 Small x High Q 2

6. 6  Nuclear Science: to discover, explore, and understand all forms of nuclear matter and its benefits to our society  QCD: A fundamental theory for the dynamics of quarks and gluons It describes the formation of all forms of nuclear matter  the nucleus  the nucleons  the quarks and gluons  Nuclear matter:  QCD and the Origin of Mass – 99% of the proton’s mass is due to the self-generating gluon field – Higgs mechanism has almost no role here – M(up) + M(up) + M(down) ~ 10 MeV << M(proton) Understanding QCD and the Origin of Mass

7. 7 The Structure of the Proton Naïve Quark Model:proton = uud (valence quarks) QCD:proton = uud + uu + dd + ss + … The proton sea has a non-trivial structure: u ≠ d  The proton is far more than just its up + up + down (valence) quark structure & gluons are abundant  Gluon photon: Radiates and recombines: gluon dynamicsNon-trivial sea structure

8. 8 US-based Electron-Ion Collider EIC design and range driven by: access to sea quarks and gluons  s = E CM 2 = few 100 - 1000 GeV 2 seems right ballpark  s = few 1000 allows access to gluons, shadowing Polarization + good acceptance to detect spectators & fragments Into the “sea”: the EIC An EIC aims to study the sea quarks and gluon-dominated matter. EIC

9. 9 EIC: Physics – see EPJA 48 (2012) 92; arXiv:1212.17010 (v2) (Jlab theory paper on MEIC science; EIC White Paper) Explore and image the spin and 3D structure of the nucleon (show the nucleon structure picture of the day…) Discover the role of gluons in structure and dynamics Discover the role of gluons in structure and dynamics (without gluons there are no protons, no neutrons, no atomic nuclei) Understand the emergence of hadrons from color charge (how does M = E/c 2 work to create pions and nucleons?) Search for physics beyond the Standard Model Needs high (polarized) luminosity and range of energies: s ~ 500-5000+ Needs range of ions up to A ~ 200 and energies: s ~ 1000-10000 Needs access to ion fragments and energy: s ~ few 100-few 1000 Needs energy & ultra-high polarized luminosity

10. 10 World Data on F 2 p World Data on g 1 p momentum spin World Data on h 1 p transverse spin ~ angular momentum An EIC makes it possible! HERMES COMPASS EIC coverage

11. 11 5 x 250 starts here 5 x 100 starts here Q 2 = 10 GeV 2 g 1 (Q 2 ) and x  g at an EIC DIS

12. 12 current data w/ EIC data GG  Helicity (collinear) PDFs at an EIC k t -integrated pdfs

13. 13 Sea Quark Polarization 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 Needs intermediate √s ~ 30 (and good luminosity) }

14. 14 Illustration of the possible correlation between the internal motion of an up quark and the direction in which a positively- charged pion (ud) flies off. - A surprise of transverse-spin experiments 3D Parton Distributions: TMDs transversitypretzelosity U L T ULT f1f1 g 1L g 1T h1h1 T h 1L T f 1T T h1h1 h 1T T, nucleon polarization quark polarization Boer-Mulders worm-gear Sivers helicity worm-gear  Access orbital motion of quarks  contribution to the proton’s spin  Observables: Azimuthal asymmetries due to correlations of spin q/n and transverse momentum of quarks

15. 15 Separate Sivers and Collins effects Sivers angle, effect in distribution function: (  h -  s ) Collins angle, effect in fragmentation function: (  h +  s ) Or other combinations: Pretzelosity: (3  h -  s ) TMDs Accessible through Semi-Inclusive Physics Scattering Plane target angle hadron angle Naturally, two scales: High Q: localized probe to “see” quarks and gluons Low P T : sensitive to confining scale to “see” their confined motion + Theory input: TMD QCD factorization TMD QCD evolution

16. 16 TMD Landscape at an EIC: Sivers as example √s ~ 15 GeV √s ~ 45 GeV √s ~ 140 GeV ( ) upgraded EIC

17. 17 TMD at an EIC: Experimental Intermezzo DIS TMD X Can determine scattering kinematics (x, Q 2 ) from: Electron kinematics methody (=E’/E) > 0.01 Hadron X kinematics methody (=E’/E) < 0.01 (as resolution  x blows up at small y with electron method) x = Q 2 /ys Accessible (x,Q 2 ) phase space directly correlated with y Need to determine (  h -  s ), (  h +  s ), (3  h -  s ) On the other hand, to determine the scattering kinematics: Work it out, one needs high y!  one can not use hadron X kinematics method to do TMD measurements  Use versatility of EIC to get range in √s (=15, 45, 100) hh

18. 18 Imaging the Transverse Momentum of Quarks into the Sea Only a small subset of the (x,Q 2 ) landscape has been mapped here: terra incognita Gray band: present “knowledge” Purple band: EIC (2  ) u u An EIC with good luminosity & high transverse polarization is the optimal tool to to study this! Sivers (Distortion of quark distribution due to nucleon polarization)

19. 19 Sivers effect: sea contributions Negative Kaons most sensitive to sea contributions. Biggest uncertainty in experimental measurements (K - suppressed at large x). GRV98, DSS FF S. ArnoldS. Arnold et al arXiv:0805.2137 M. AnselminoM. Anselmino et al arXiv:0805.2677 GRV98, Kretzer FF (Harut Avakian)

20. 20 Vanish like 1/p T (Yuan) Correlation between Transverse Spin and Momentum of Quarks in Unpolarized Target All Projected Data Perturbatively Calculable at Large p T - Assumed 100 days of 10 35 luminosity Transition from low p T (TMD factorization) to high p T (collinear factorization)

21. 21 Access to the Gluon TMDs Access to gluon TMDs may be possible by: Di-jet/di-hadron production Heavy quark production Quarkonium production Integrated luminosity of 100 fb -1 Example: where both D and D are in the current fragmentation region, with momentum k 1 and k 2, respectively, and N is a transversely polarized nucleon. Gluon Sivers will introduce an azimuthal asymmetry correlating k’ = k 1 + k 2 of the DD pair with the transvers polarization S

22. 22 Hadronization – semi-inclusive physics in a nucleus un-integrated parton distributions current fragmentation target fragmentation Fragmentation from QCD vacuum +  -  EIC: Understand the conversion of quarks and gluons to hadrons through fragmentation and breakup EIC: Explore the interaction of color charges with matter

23. 23 e - A Physics Landscape at an EIC 12 GeV electrons and 40 GeV (= 100 GeV*Z/A) heavy ions  √s ~ 45 GeV

24. 24 Hadronization – energy loss Need the collider energy of EIC and its control on parton kinematics How do hadrons emerge from quarks or gluons? Neutralization of color – hadronization Different for light and heavy quarks? Wide range of and Q 2 possible (Controlled access to current quarks and correlation with fragments)

25. 25 Hadronization – parton propagation in matter EIC: Understand the conversion of color charge to hadrons through fragmentation and breakup L e e’ ** ++ pTpT  p T 2 = p T 2 (A) – p T 2 ( 2 H) “p T Broadening” pT2pT2 Comprehensive studies possible: wide range of energy v = 10-1000 GeV wide range of Q 2 : evolution Hadronization of charm, bottom High luminosity for 3D and correlations Accardi, Dupre

26. 26 Color neutralization – it’s a correlated 3D problem Can we learn more from correlating with the target fragmentation region? Final transverse momentum of the detected pion P t arises from convolution of the struck quark transverse momentum k t with the transverse momentum generated during the fragmentation p t. D u  + (z,p t )

27. 27 EIC Scientific Assessment “The EIC would be a unique and powerful microscope to provide a dynamical mapping of gluons in the nucleon and in nuclei. It is an ideal tool to investigate the mechanism of how quarks and gluons propagate in nuclear matter and join together to form hadrons. The EIC is our portal to an in-depth and fundamental understanding of gluonic matter and of QCD. As stated in the 2007 Long Range Plan, "An EIC with polarized beams has been embraced by the U.S. nuclear science community as embodying the vision for reaching the next QCD frontier." The Subcommittee ranks an EIC as Absolutely Central in its ability to contribute to world-leading science in the next decade.” From 2013 NSAC Subcommittee of Facilities, chaired by Bob Redwine (MIT): NSAC Long-Range Planning Effort in the US just started (April 24), hope to get a recommendation to build the EIC. EIC Workshop at Stony Brook University June 24-27, 2014 http://skipper.physics.sunysb.edu/~eicug/meetings/SBU.html http://skipper.physics.sunysb.edu/~eicug/meetings/SBU.html (US Nuclear Science Advisory Committee)

28. 28 Early Physics examples at EIC: √s ~ 45 GeV current data w/ EIC data Polarization! Benefit from polarization Nuclei!

29. 29 Semi-Inclusive Physics Outlook This is a defining period for the EIC with the LRP started EIC science requires polarization & luminosity & detection capability. EIC allows a unique opportunity to make a (textbook) breakthrough in nucleon structure and QCD dynamics explore and image the 3D (spin) structure of the nucleon discover the role of gluons in structure and dynamics understand the emergence of hadrons from color charge Specifically, for semi-inclusive physics: Next decade gets important input from COMPASS, JLab-12 GeV (Halls A, B and C), RHIC-spin, FNAL Polarized Drell-Yan? EIC will allow unprecedented measurements, making explicitly use of longitudinally and transversely polarized beams and correlating current and target fragmentation regions, e.g., of: Completion of quark flavor decomposition of proton spin Detailed mapping of valence and sea quark TMDs First-ever (?) measurement of gluon TMDs Detailed studies of energy loss and understanding of fragmentation in nuclei

30. 30

31. 31 EIC Design Specs Base EIC Requirements per Executive Summary INT Report : highly polarized (>70%) electron and nucleon beams ion beams from deuteron to the heaviest nuclei - uranium or lead center of mass energies from about 20 to about 150 GeV maximum collision luminosity ~10 34 e-nucleons cm -2 s -1 possibilities of having more than one interaction region non-zero crossing angle of colliding beams staged designs where the first stage would reach √s of ~70 GeV the possibility to have multiple interaction regions 31 Base EIC Requirements per Executive Summary EIC White Paper: highly polarized (~70%) electron and nucleon beams ion beams from deuteron to the heaviest nuclei (uranium or lead) variable center of mass energies from √s ~ 20 to √s ~ 100 GeV, upgradable to ~150 GeV high collision luminosity ~10 33-34 e-nucleons cm -2 s -1 possibilities of having more than one interaction region

32. 32 To cover the physics we need… arXiv:1212.17010 (v2) Most science plots in white paper for: √s ~ 45 GeV Some for √s ~ 140 x = Q 2 /ys (x,Q 2 ) phase space directly correlated with s (=4E e E p ) : @ Q 2 = 1 lowest x scales like s -1 @ Q 2 = 10 lowest x scales as 10s -1 Need for good polarized luminosity