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eRHIC: Science and Perspective

eRHIC: Science and Perspective. Introduction Science of eRHIC Realization Summary. Study of the Fundamental Structure of Matter with an Electron-Ion Collider Deshpande, R. Milner, R. Venugopalan, W. Vogelsang hep-ph/0506148, to appear in Ann. Revs. Nucl. Part. Sci.

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eRHIC: Science and Perspective

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  1. eRHIC: Science and Perspective Introduction Science of eRHIC Realization Summary • Study of the Fundamental Structure of Matter with an Electron-Ion Collider • Deshpande, R. Milner, R. Venugopalan, W. Vogelsang • hep-ph/0506148, to appear in Ann. Revs. Nucl. Part. Sci. RHIC Planning Meeting October 29-20, 2005

  2. The study of the fundamental structure of matter • QCD tells us that the nucleon and atomic nuclei are made of pointlike constituents bound by powerful gluon fields • The valence quark region is well explored experimentally and reasonably well understood theoretically • Frontier research in QCD demands a concerted experimental effort directed at the role of the gluons and sea quarks • A new accelerator which directly probes the quarks and gluons is required Lepton probe High center of mass energy High luminosity  precision Polarized lepton, nucleon Optimized detectors • This accelerator is urgently needed to make progress in this field of research and has substantial discovery potential RHIC Planning Meeting October 29-20, 2005

  3. Deep inelastic scattering – the experimental cornerstone of QCD RHIC Planning Meeting October 29-20, 2005

  4. Running of the strong coupling αs RHIC Planning Meeting October 29-20, 2005

  5. Quark and gluon momentum in proton RHIC Planning Meeting October 29-20, 2005

  6. Lattice QCD making significant progress quenched approximation full QCD HPQCD hep-lat/0304004 agreement with experiment at level of few percent RHIC Planning Meeting October 29-20, 2005

  7. Nucleon axial charge in full lattice QCD LHPC Collaboration hep-lat/0510062 RHIC Planning Meeting October 29-20, 2005

  8. Why a Collider ? • High Ecm (20 to 100 GeV)  large range of x, Q2 x range (10-4 to 1): valence, sea quarks, glue Q2 range ( 1 to 1000 GeV2): utilize evolution equations of QCD • High luminosity ~ 1033 cm-2 s-1 • High polarization ( ~ 70%) of lepton, nucleon achievable • Complete mass range of nuclear targets • Collider geometry allows complete reconstruction of final state Qmax2 = ECM2 · x RHIC Planning Meeting October 29-20, 2005

  9. Why eRHIC? • RHIC is the world’s first and only polarized proton collider • In addition, RHIC accelerates heavy ion beams to 100 GeV/nucleon • eRHIC would capitalize on ~ $ 1 billion investment in RHIC • RHIC scientific program strongly motivates eRHIC • Leadership from BNL in evolution of lepton-ion collider since 1999 • eRHIC is viewed at BNL as a necessary and natural upgrade of RHIC after 2010 as the heavy ion and spin programs mature RHIC Planning Meeting October 29-20, 2005

  10. The Electron-Ion Collider (EIC) • A high luminosity (~1033cm-2s-1) polarized lepton-ion collider is the QCD machine hadronic physicists worldwide require for future research • Workshops Seeheim, Germany 1997 MIT 2000 IUCF 1999 BNL 2002 BNL 1999 JLab 2003 Yale 2000 • Electron Ion collider (EIC) received very favorable review of science case in US 2001 Nuclear Physics Long Range Plan, with strong endorsement for R&D • NSAC in March 2003, declared EIC science `absolutely central’ to Nuclear Physics • DOE Office of Science 20 Year Strategic Plan in 2004: eRHIC identified as a long term (realized ~ 2015) priority RHIC Planning Meeting October 29-20, 2005

  11. EIC Steering Committee • A. Caldwell (MPI Munich) • A. Deshpande (StonyBrook) • R. Ent (JLab) • G. Garvey (LANL) • R. Holt (ANL) • E. Hughes (Caltech) • K.-C. Imai (Kyoto Univ.) • R. Milner (MIT) • P. Paul (BNL) • J.-C. Peng (Illinois) • S. Vigdor (Indiana Univ.) RHIC Planning Meeting October 29-20, 2005

  12. eRHIC will be a unique accelerator RHIC Planning Meeting October 29-20, 2005

  13. Scientific Highlights • nucleon structure sea quarks and gluespin and flavor structure new parton distributions • Meson structure , K are Goldstone Bosons of QCD essential to nuclear binding • hadronization evolution of parton into hadron process in nuclei of fundamental interest • nuclei role of partons initial conditions for relativistic heavy ion collisions • matter under extreme conditionssaturation of parton distributions new phenomena, e.g. colored glass condensate RHIC Planning Meeting October 29-20, 2005

  14. The Spin Structure of the Nucleon ½ = ½ DS + DG + Lq + Lg • Bjorken Sum Rule • From NLO-QCD analysis of DIS measurements … ΔG = 1.0±1.2 • quark polarization Δq(x) first 5-flavor separation from HERMES • transversity δq(x) a new window on quark spin azimuthal asymmetries from HERMES and JLab • gluon polarization ΔG(x) RHIC-spin and COMPASS will provide some answers! • orbital angular momentum L how to determine?  GPD’s ? ΔΣ ≈ 0.2 RHIC Planning Meeting October 29-20, 2005

  15. Inclusive spin-dependent DIS RHIC Planning Meeting October 29-20, 2005

  16. QCD Test: Bjorken Sum Rule • Γ1p - Γ1n = 1/6 gA [1 + Ο(αs)] • Sum rule verified to ±10% • eRHIC can approach ±1% • G. Igo • Precision QCD test RHIC Planning Meeting October 29-20, 2005

  17. Polarized parton densities of the proton SU(3) flavor symmetry assumed Blümlein and Böttcher RHIC Planning Meeting October 29-20, 2005

  18. HERMES Flavor Decomposition of Quark Spin Semi-inclusive DIS RHIC Planning Meeting October 29-20, 2005

  19. Gluon polarization data from COMPASS 2002+3 data analysis; as much again in 2004 on disk RHIC Planning Meeting October 29-20, 2005

  20. Gluon polarization from STAR New more precise data from PHENIX STAR preliminary 2003+4 results for double longitudinal spin asymmetry ALL versus jet pT in p + p → jet + X, compared with NLO pQCD RHIC Planning Meeting October 29-20, 2005

  21. Spin structure function gp1 at low x x = 10-3 0.7 Q2 = 0  103 GeV Fixed target experiments 1989 – 1999 Data x = 10-4 0.7 Q2 = 0  104 GeV eRHIC 250 x 10 GeV Lumi=85 inv. pb/day 10 days of eRHIC run Assume: 70% Machine Eff. 70% Detector Eff. RHIC Planning Meeting October 29-20, 2005

  22. eRHIC determination of polarized quarks and anti-quarks Kinney and Stösslein RHIC Planning Meeting October 29-20, 2005

  23. Gluon polarization from di-jets in LO for eRHIC Deshpande et al. RHIC Planning Meeting October 29-20, 2005

  24. Parity violating lepton scattering • requires a positron beam • determines new combinations of Δu, Δd, Δs etc. • analog sum rule to Bjorken A. Deshpande RHIC Planning Meeting October 29-20, 2005

  25. Saturation: the Color Glass Condensate RHIC Planning Meeting October 29-20, 2005

  26. Using Nuclei to Increase the Gluon Density • Parton density at low x rises as • Unitarity  saturation at some • In a nucleus, there is a large enhancement of the parton densities / unit area compared to a nucleon Example Q2=4 (GeV/c)2 < 0.3 A = 200 Xep=10-7 for XeA = 10-4 RHIC Planning Meeting October 29-20, 2005

  27. Gluon Momentum Distribution from DIS RHIC Planning Meeting October 29-20, 2005

  28. RHIC Data consistent with Gluon Saturation RHIC Planning Meeting October 29-20, 2005

  29. Longitudinal structure function FL • Extracted from scaling violations of • F2 • Experimentally can be determined • directly • Highly sensitive to effects of gluon • With precise enough F2 and FL one • can extract the coefficient λ of the • saturation scale • Logarithmic derivatives of F2 and FL • with Q will be sensitive to CGC RHIC Planning Meeting October 29-20, 2005

  30. Quarks in a Nucleus 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 n!) F2A/F2D “EMC Effect” 10-4 10-3 10-2 10-1 1 x Nuclear attenuation negligible for n > 50 GeV hadrons escape nuclear medium undisturbed Space-Time Structure of Photon RHIC Planning Meeting October 29-20, 2005

  31. eRHIC projections for nuclear quark distributions 1 pb-1 T. Sloan RHIC Planning Meeting October 29-20, 2005

  32. 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? Constraints on possible nuclear modifications of glue come from 1) Q2 evolution of nuclear ratio of F2 in Sn/C (NMC) 2) Direct measurement of J/Psi production in nuclear targets F2 G • Compatible with EMC effect? • Precise measurements possible of • Nuclear ratio of Sn/C (25 GeV) • J/Psi production (ELIC) Flavor tagging can also (in principle) disentangle sea-quark contributions RHIC Planning Meeting October 29-20, 2005

  33. 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. RHIC Planning Meeting October 29-20, 2005

  34. eRHIC - machine design aspects See talk by V. Ptitsyn • First detailed document (252 pages) reporting on the eRHIC accelerator and interaction region (IR) design studies • Collaborative effort between BNL, MIT-Bates, BINP and DESY • Goal: • Develop an initial design for eRHIC • Investigate accelerator physics issues most important to its design • Evaluate luminosities that could be achieved with minimal R&D effort including IR design • Identify specific R&D extensive accelerator aspects which could lead to significantly higher luminosities • Review planned in June 2005 http://www.bnl.gov/eic/ RHIC Planning Meeting October 29-20, 2005

  35. 2 – 10 GeV e-ring 2 -10GeV Injector RHIC e-cooling LINAC BOOSTER AGS TANDEMS eRHIC: ring-ring design • 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 2 – 10 GeV • Existing RHIC interaction region allows for typical asymmetric detector (similar to HERA or PEP II detectors) • Required modifications • of RHIC: • Electron cooling • Increase of total current • 120 → 360 bunches • Additional spin rotators RHIC Planning Meeting October 29-20, 2005

  36. eRHIC e-/e+ Ring Parameters 10 GeV electrons – 250 GeV protons Type your question here and then click Search. • Luminosity limited by beam-beam tune shifts: • ξi = 0.0065 ξe = 0.08 • Luminosity assumes collisions • at two other IPs • Dedicated operations yields • Luminosity ~ 1033 cm-2 s-1 RHIC Planning Meeting October 29-20, 2005

  37. eRHIC: linac-ring design • Two possible designs are presented in the ZDR • Electron beam is transported to collision point(s) directly from superconducting energy recovery linac (ERL) • Features: • Higher luminosity (~ X 5) possible • Rapid reversal of electron polarization • Machine elements free region approx. 5m • Simpler IR region design: Round beams possible • Multiple interaction regions • No positrons RHIC Planning Meeting October 29-20, 2005

  38. eRHIC: interaction region design - ZDR assumes IR region with zero crossing angle • Crab-crossing scheme considered (rotate ion bunch into direction of electron beam): However, required deflecting RF voltage: V=14.4MV  factor 10 larger then for KEKB crab cavities so excluded for now. • Initial design: dipole winding in the superconducting electron low- quadrupoles • Limitation: 1m machine element free region RHIC Planning Meeting October 29-20, 2005

  39. Review of eRHIC ZDR • Detailed technical review of both ring-ring and linac-ring designs by Machine Advisory Committee in June 2005 • Excellent technical criticism • Status of the present design studies is not yet advanced enough to make a decision • Ring-ring: challenging project, can be extrapolated from to-day’s experience and technology. Suggests pursuing ring-ring design as first priority with goal to develop a CDR • Linac-ring: much more attractive regarding luminosity. Requires successful extrapolations on a number of fronts that are beyond what can be achieved to-day. Requires intensive R&D. • Concentrate first on R&D which is useful to ring-ring and ring-linac options, e.g. ERL prototype, cooling of ion beams, and beam dynamics. RHIC Planning Meeting October 29-20, 2005

  40. eRHIC lepton ring vs. PEP-II rings • Ring type: all are collider lepton rings • Energy range: 5~10 GeV vs. 3-9 GeV • Beam currents: 0.5 ~1A vs. 1.5 ~ 3 A similar bunch current, PEP-II has more bunches • Beam dimensions: comparable emit.: ~50 nm rad, beta_ave: ~15 m (arc, rf) • Collective effects: similar In general, technical approaches are very similar. RHIC Planning Meeting October 29-20, 2005

  41. Preliminary conclusions D. Wang/Bates • RF : 90% from PEP-II with minimum modifications • Magnet/power supply: ~ 50 % from PEP-II • Feedback: 100% • Beam diagnostics / control: ~ 50% • Vacuum: now we count it as 20% ~ 30% • Injector: design not clear at this point. • A large amount of PEP-II components could be used for the eRHIC lepton ring. • A preliminary estimate shows that we may save 20% to 30% of cost by using PEP-II components. More detailed studies underway. RHIC Planning Meeting October 29-20, 2005

  42. A e e A eRHIC - Detector design • General purpose unpolarized/polarized ELECTRon-A - compact central detector with specialized forward/rear tagging detectors - required free region ± 3m • Forward detector unpolarized eA • specialized detector system to detect • complete final state in eA collisions • - Require dfree region ± 5 m • Common detector subsystems • R&D coherent with heavy ion • detector upgrades See talk by B. Surrow RHIC Planning Meeting October 29-20, 2005

  43. eRHIC realization • Science case must be strengthened and sharpened • Accelerator case must be developed so that the science can be made to happen in a timely fashion • eRHIC must be presented coherently in the context of future RHIC plans • It is essential to energize and organize the hadronic community worldwide in support of eRHIC • We expect a new Long Range planning exercise within the next several years • We have to be ready to argue for eRHIC in the context of other communities arguing strongly for other priorities RHIC Planning Meeting October 29-20, 2005

  44. Summary • A high luminosity lepton-ion collider offers a very exciting future for the study of the fundamental structure of matter • eRHIC appears to be a very attractive means to realize it in a cost-effective and timely way • It is essential to develop the most powerful eRHIC case with a sense of urgency RHIC Planning Meeting October 29-20, 2005

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