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What is the EIC ?

What is the EIC ?. Electron Ion Collider as the ultimate QCD machine Variable center of mass energy between 20 and 100 GeV High luminosity Polarized electron and proton (deuteron, 3He) beams Ion beams up to A=208. Explore the new QCD frontier: strong color fields in nuclei

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What is the EIC ?

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  1. What is the EIC ? • Electron Ion Collider as the ultimate QCD machine • Variable center of mass energy between 20 and 100 GeV • High luminosity • Polarized electron and proton (deuteron, 3He) beams • Ion beams up to A=208 Explore the new QCD frontier: strong color fields in nuclei Precisely image the sea-quarks and gluons in the nucleon

  2. e-cooling (RHIC II) 5 – 10 GeV e-ring 5 -10GeV full energy injector RHIC PHENIX Main ERL (3.9 GeV per pass) STAR e+ storage ring 5 GeV - 1/4 RHIC circumference e-cooling (RHIC II) Four e-beam passes 2 different eRHIC Design options ERL-based eRHIC Design • Electron energy range from 3 to 20 GeV • Peak luminosity of 2.6  1033 cm-2s- • high electron beam polarization (~80%) • full polarization transparency at all energies • multiple electron-hadron interaction points •  5 meter “element-free” straight section(s) • ability to take full advantage of electron cooling of the hadron beams; • easy variation of the electron bunch frequency to match the ion bunch frequency at different ion energies. • Based on existing technology • Collisions at 12 o’clock interaction region • 10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference (similar to PEP II HER) • Inject at full energy 5 – 10 GeV • Polarized electrons and positrons

  3. ELIC design at Jefferson Lab 30-225 GeV protons 30-100 GeV/n ions 3-9 GeV electrons 3-9 GeV positrons • Polarized H, D, 3He, • Ions up to A = 208 • Average Luminosity from 1033to 1035 cm-2 sec-1 per Interaction Point Green-field design of ion complex directly aimed at full exploitation of science program.

  4. World Data on F2p Structure Function Next-to-Leading-Order (NLO) perturbative QCD (DGLAP) fits

  5. World Data on F2p World Data on g1p 4 orders of magnitude in x and Q2 < 2 orders of magnitude, precision much worse !

  6. Region of existing g1p data World Data on F2p EIC Data on g1p An EIC makes it possible!

  7. G from scaling violations of g1

  8. G from scaling violations of g1 • EIC will allow precision determination of g1(x,Q2) over very large kinematic range • and thus will: • precisely determine the integral of G • allow to distinguish between different functional forms of g(x) • Measurement of G is likely to be limited by systematic uncertainty in polarization measurement • ---- needs careful investigation (similar for existing global fits)

  9. c D mesons c D mesons Polarized gluon distribution via charm production very clean process ! LO QCD: asymmetry in D production directly proportional to G/G

  10. Polarized gluon distribution via charm production problems:luminosity, charm cross section, background !

  11. Polarized gluon distribution via charm production • starting assumptions for EIC: • vertex separation of better than 100m • full angular coverage (3<<177 degrees) • perfect particle identification for pions and kaons • (over full momentum range) • detection of low momenta particles (p>0.5 GeV) • measurement of scattered electron • (even at very small scattering angles) • 100% efficiency very demanding detector requirements !

  12. incl PID invariant mass of K  system Polarized gluon distribution via charm production Background suppression: Separation of primary and secondary vertex absolutely essential ! Pion/kaon separation very helpful !

  13. Polarized gluon distribution via charm production Momenta of decay kaon and pion: 1.5 < p < 10 (15) GeV Angles of decay kaon and pion: 1600 <  < 1770 

  14. Polarized gluon distribution via charm production Precise determination of  G/G for 0.003 < xg < 0.4 at common Q2 of 10 GeV2 however RHIC SPIN

  15. Precise determination of  G/G for 0.003 < xg < 0.4 at common Q2 of 10 GeV2 Polarized gluon distribution via charm production • If: • We can measure the scattered electron even at angles close to 00 (determination of photon kinematics) • We can separate the primary and secondary vertex to better than 100 m () • We understand the fragmentation of charm quarks () • We can control the contributions of resolved photons • We can calculate higher order QCD corrections ()

  16. charm production: influence of fragmentation xgrec = x(shat/Q2+1) shat = 4 Minv2 correction presently by simple parametrisation of xg-xrec vs xg

  17. Future: x g(x,Q2) from RHIC and EIC EIC 0.003 < x < 0.5 Statistical uncertainty in xg typically < 0.01 !!! EIC

  18. Polarized gluon distribution vs Q2

  19. Other processes • G from dijet production • promising channel for determination of G • needs more detailed study !

  20. Next Steps • determine sensitivity of g1 to different “realistic” models for G (including different functional forms !) • generate pseudo EIC data and include in full QCD fit procedure (including estimates of systematic uncertainties !) • study fragmentation in charm production • include other charm decay channels (including D* tagging) • understand the possibility to determine the charm mass from charm cross section measurements

  21. Summary • EIC is the ideal machine to finally determine the contribution of the gluons to the nucleon spin! • measurements of g1 will allow • a precise determination of G from its scaling violation • systematics due to uncertainty in proton beam polarization ? • measurements of charm cross section asymmetries will provide a precise determination of G/G for 0.003<x<0.5 at a fixed value of Q2 of ~10 GeV2 • ……. provided we can • measure the scattered electron at extremely small angles • separate the primary and secondary vertex with sufficient precision • control the contribution of resolved photons • understand NLO corrections and the mass of the charm quark

  22. g1 and the Bjorken Sum Rule

  23. Bjorken Sum Rule: Γ1p - Γ1n = 1/6 gA [1 + Ο(αs)] Needs: O(1%) Ion Polarimetry!!! determination of as(Q2) • Sub-1% statistical precision at ELIC • (averaged over all Q2) • 7% (?) in unmeasured region, in future • constrained by data and lattice QCD • 3-4% precision at various values of Q2

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