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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Deep inelastic scattering – the experimental cornerstone of QCD

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Running of the strong coupling α s

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Quark and gluon momentum in proton

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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Nucleon axial charge in full lattice QCD LHPC Collaboration hep-lat/

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Why a Collider ? High E cm (20 to 100 GeV)  large range of x, Q 2 x range (10 -4 to 1): valence, sea quarks, glue Q 2 range ( 1 to 1000 GeV 2 ): utilize evolution equations of QCD High luminosity ~ 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 Q max 2 = E CM 2 · x

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 The Electron-Ion Collider (EIC) A high luminosity (~10 33 cm -2 s -1 ) polarized lepton-ion collider is the QCD machine hadronic physicists worldwide require for future research Workshops Seeheim, Germany1997 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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.)

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 eRHIC will be a unique accelerator

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Scientific Highlights nucleon structure sea quarks and glue spin 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 conditions saturation of parton distributions new phenomena, e.g. colored glass condensate

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 The Spin Structure of the Nucleon 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 ? ½ = ½  +  G + L q + L g ΔΣ ≈ 0.2

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Inclusive spin-dependent DIS

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 QCD Test: Bjorken Sum Rule Γ 1 p - Γ 1 n = 1/6 g A [1 + Ο(α s )] Sum rule verified to ±10% eRHIC can approach ±1% G. Igo Precision QCD test

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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 HERMES Flavor Decomposition of Quark Spin Semi-inclusive DIS

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Gluon polarization data from COMPASS data analysis; as much again in 2004 on disk

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Gluon polarization from STAR STAR preliminary results for double longitudinal spin asymmetry A LL versus jet p T in p + p → jet + X, compared with NLO pQCD New more precise data from PHENIX

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Spin structure function g p 1 at low x x =  0.7 Q 2 = 0  10 4 GeV eRHIC 250 x 10 GeV Lumi=85 inv. pb/day x =  0.7 Q 2 = 0  10 3 GeV Fixed target experiments 1989 – 1999 Data 10 days of eRHIC run Assume: 70% Machine Eff. 70% Detector Eff.

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 eRHIC determination of polarized quarks and anti-quarks Kinney and Stösslein

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

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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Saturation: the Color Glass Condensate

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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 Q 2 =4 (GeV/c) 2  < 0.3 A = 200 X ep =10 -7 for X eA = 10 -4

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Gluon Momentum Distribution from DIS

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 RHIC Data consistent with Gluon Saturation

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Longitudinal structure function F L Extracted from scaling violations of F 2 Experimentally can be determined directly Highly sensitive to effects of gluon With precise enough F 2 and F L one can extract the coefficient λ of the saturation scale Logarithmic derivatives of F 2 and F L with Q will be sensitive to CGC

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 Quarks in a Nucleus “EMC Effect” Space-Time Structure of Photon F 2 A /F 2 D x 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 !) Nuclear attenuation negligible for > 50 GeV  hadrons escape nuclear medium undisturbed

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 eRHIC projections for nuclear quark distributions T. Sloan 1 pb -1

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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? Flavor tagging can also (in principle) disentangle sea-quark contributions Constraints on possible nuclear modifications of glue come from 1) Q 2 evolution of nuclear ratio of F 2 in Sn/C (NMC) 2) Direct measurement of J/Psi production in nuclear targets Compatible with EMC effect? Precise measurements possible of  Nuclear ratio of Sn/C (25 GeV)  J/Psi production (ELIC) F2F2 G

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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.

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 eRHIC - machine design aspects –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 See talk by V. Ptitsyn

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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) AGS BOOSTER TANDEMS RHIC 2 – 10 GeV e-ring e-cooling 2 -10GeV Injector LINAC Required modifications of RHIC: Electron cooling Increase of total current 120 → 360 bunches Additional spin rotators

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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: ξ i = ξ e = 0.08 Luminosity assumes collisions at two other IPs Dedicated operations yields Luminosity ~ cm -2 s -1

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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.

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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.

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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. D. Wang/Bates Preliminary conclusions

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 eRHIC - Detector design General purpose unpolarized/polarized ELECTRon-A - compact central detector with specialized forward/rear tagging detectors - required free region ± 3m A e e A 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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

Richard G. MilnerRHIC Planning Meeting October 29-20, 2005 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