MEIC Overview: Physics, Project & Timeline

1. MEIC Overview: Physics, Project & Timeline Rolf Ent MEIC Accelerator Design Review September 15-16, 2010

2. 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 morethan just its up + up + down (valence) quark structure

3. QCDand the Origin of Mass • 99% of the proton’s mass/energy is due to the self-generating gluon field • Higgs mechanism has almost no role here. • The similarity of mass between the proton and neutron arises from the fact that the gluon dynamics are the same • Quarks contribute almost nothing.

4. Gluons and QCD • QCD is the fundamental theory that describes structure and interactions in nuclear matter. • Without gluons there are no protons, no neutrons, and no atomic nuclei • Gluons dominate the structure of the QCD vacuum • Facts: • The essential features of QCD (e.g. asymptotic freedom, chiral symmetry breaking, and color confinement) are all driven by the gluons! • Unique aspect of QCD is the self interaction of the gluons • 99% of mass of the visible universe arises from glue • Half of the nucleon momentum is carried by gluons

5. Nuclear Physics – 12 GeV to EIC Study the Force Carriers of QCD The role of Gluons and Sea Quarks

6. EIC@JLab High-Level Science Overview • Hadrons in QCD are relativistic many-body systems, with a fluctuating number of elementary quark/gluon constituents and a very rich structure of the wave function. • With an (M)EIC we enter the region where the many-body nature of hadrons, coupling to vacuum excitations, etc., become manifest and the theoretical methods are those of quantum field theory. An EIC aims to study the sea quarks, gluons, and scale (Q2) dependence. • With 12 GeV we study mostly the valence quark component, which can be described with methods of nuclear physics (fixed number of particles). 12 GeV

7. The Science of an (M)EIC Nuclear Science Goal: How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD? Overarching EIC Goal: Explore and Understand QCD • Three Major Science Questions for an EIC (from NSAC LRP07): • What is the internal landscape of the nucleons? • What is the role of gluons and gluon self-interactions in nucleons and nuclei? • What governs the transition of quarks and gluons into pions and nucleons? Or, Elevator-Talk EIC science goals: Map the spin and 3D quark-gluon structure of protons (show the nucleon structure picture of the day…) Discover the role of gluons in atomic nuclei (without gluons there are no protons, no neutrons, no atomic nuclei) Understand the creation of the quark-gluon matter around us (how does E = Mc2 work to create pions and nucleons?) + Hunting for the unseen forces of the universe

8. Why a New-Generation EIC? • Obtain detailed differential transverse quark and gluon images • (derived directly from the t dependence with good t resolution!) • Gluon size from J/Y and felectroproduction • Singlet quark size from deeply virtual compton scattering (DVCS) • Strange and non-strange (sea) quark size frompand K production • Determine the spin-flavor decomposition of the light-quark sea • Constrain the orbital motions of quarks & anti-quarks of different flavor • - The difference between p+, p–, and K+ asymmetries reveals these orbits. • Map both the gluon momentum distributions of nuclei (F2 & FL measurements) • and the transverse spatial distributions of gluons on nuclei • (coherent DVCS & J/Y production). • At high gluon density, the recombination • of gluons should compete with gluon • splitting, rendering gluon saturation. • Can we reach such state of saturation? • Map the physical mechanism of • fragmentation of correlated quarks • and gluons, and understand how • we can calculate it quantitatively. longitudinal momentum orbital motion quark to hadron conversion Dynamical structure! Gluon saturation? transverse distribution

9. A High-Luminosity ELectron Ion Collider at JLab NSAC 2007 Long-Range Plan: “An Electron-Ion Collider (EIC)with polarized beams has been embraced by the U.S. nuclear science community as embodying the vision for reaching the next QCD frontier. EIC would provide unique capabilities for the study of QCD well beyond those available at existing facilities worldwide and complementary to those planned for the next generation of accelerators in Europe and Asia.” • Requirements in our view: • range in energies from s = few 100 to s = few 1000 & variable • fully-polarized (>70%), longitudinal and transverse • ion species up to A = 200 or so • high luminosity: about 1034 e-nucleons cm-2 s-1 • upgradable to higher energies

10. Current Ideas for a Collider Design Goals for Colliders Under Consideration World-wide Present focus of interest (in the US) are the (M)EIC and Staged MeRHIC versions, with s up to ~3000 and 5000, respectively

11. EIC Advisory Committee • Both laboratories (BNL & JLab) are working together to get advice on the best steps towards a US Electron-Ion Collider. • Sam Aronson and ChristophLeemann/Hugh Montgomery have named an international EIC Advisory Committee: • Joachim Bartels Allen Caldwell • Albert De Roeck Walter Henning (chair) • David Hertzog XiangdongJi • Robert Klanner Alfred Mueller • KatsunobuOideNaohitoSaito • UliWienands*likely add few more accelerator experts • 1stmeeting Feb. 16, 2009 at SURA headquarters, D.C. • 2ndmeeting Nov. 2&3, 2009 at Jefferson Lab • 3rdmeeting anticipated Fall 2010 (at BNL?) • Concrete design for EIC@Jlab requested by this meeting • Internal reviewed cost estimate requested by this meeting

12. EIC Project - Roadmap

13. EIC – JLab User Meetings Roadmap • March 12 + 13 @Rutgers: Electron-Nucleon Exclusive Reactions • March 14 + 15 @Duke: Partonic Transverse Momentum in Hadrons: • Quark Spin-Orbit Correlations and Quark-Gluon Interactions • April 07, 08, 09 @ANL: Nuclear Chromo-Dynamic Studies • May 17 +18 @W&M: Electroweak Studies • June 04 + 05 @JLab: MEIC Detector Workshop • June 07,08,09 2010 JLab Users Group Meeting • (with session dedicated to a summary of users workshops, • held in Spring 2010, that explored physics motivations of • an Electron-Ion Collider, entitled • “Beyond the 12 GeV Upgrade: an EIC at JLab?”) • In parallel: MEIC/ELIC design worked out following highest EICAC • (Nov. 2009 meeting) recommendation related to accelerator • Energy-Luminosity profile of EIC design will likely be optimized over time to adjust to novel accelerator science ideas & the nuclear science case • For now we assume a base luminosity, ~1034 e-nucleons/cm2/s • Study what luminosity is required at what energies to optimize the • science output, and fold in implications for the detector/acceptance

14. EIC Collaboration – Roadmap • EIC (eRHIC/ELIC) webpage: http://web.mit.edu/eicc/ • Weekly meetings at both BNL and JLab • Wiki pages at http://eic.jlab.org/ & https://wiki.bnl.gov/eic • EIC Collaboration has biannual meetings since 2006 • Last EIC meeting: July 29-31, 2010 @ Catholic University, DC • Long INT10-03 program @ Institute for Nuclear Theory, centered around • spin, QCD matter, imaging, electroweak Sept. 10 – Nov. 19, 2010 • Periodic EIC Advisory Committee meetings (convened by BNL & JLab) • After INT10-03 program (2011 – next Nuclear Science Long Range Plan) • need to produce single, community-wide White Paper • laying out full EIC science program in broad, compelling strokes • and need to adjust EIC designs to be conform accepted energy-luminosity • profile of highest nuclear science impact • followed by an apples-to-apples bottom-up cost estimate comparison • for competing designs, folding in risk factors • and folding in input from ongoing Accelerator R&D, EICAC and community

15. Summary • The last decade or so has seen tremendous progress in our understanding of the partonic sub-structure of nucleons and nuclei based upon: • The US nuclear physics flagship facilities: RHIC and CEBAF • The surprises found at HERA (H1, ZEUS, HERMES) • The development of a theory framework allowing for a • revolution in our understanding of the inside of hadrons … • Generalized Parton Distributions, Transverse Momentum Dependent Parton Distributions, Lattice QCD • This has led to new frontiers of nuclear science: • - the possibility to truly explore the nucleon • - a new QCD regime of strong color fields in nuclei • - mapping the mechanism of nucleon and pion creation • The EIC presents a unique opportunity to maintain US leadership in high energy nuclear physics and precision QCD physics

16. Backup

17. EIC@JLabassumptions (x,Q2) phase space directly correlated with s (=4EeEp) : @ Q2 = 1 lowest x scales like s-1 @ Q2 = 10 lowest x scales as 10s-1 x = Q2/ys General science assumptions: (“Medium-Energy”) EIC@JLab option driven by: access to sea quarks (x > 0.01 (0.001?)or so) deep exclusive scattering at Q2 > 10 (?) any QCD machine needs range in Q2  s = few 100 - 1000 seems right ballpark  s = few 1000 allows access to gluons, shadowing Requirements for deep exclusive and high-Q2 semi-inclusive reactions also drives request for (lower &) more symmetric beam energies. Requirements for very-forward angle detection folded in IR design

18. Why a Novel High-Luminosity EIC? • Several pluses of (M)EIC/ELIC conceptual design • - Four Interaction Regions available (only two can run simultaneously) • - novel design ideas promise high luminosity (& full acceptance) • - more symmetric beam energies (“central” angles facilitates detection) • - figure-8 design optimized for spin (allows for polarized deuteron beams) • High luminosity in our view a must • - Semi-inclusive and deep exclusive processes depend on many • kinematic variables beyond x, Q2, and y: • e.g. t and f for DES • z, pT and f for SIDIS • - More exclusive cross sections drop rapidly with Q2, t and/or pT • True progress only possible by multi-dimensional experiments • Multiple running conditions required: • Longitudinal and transversely polarized beam, • Various ion species: 1H, 2H, 3He, heavy A • Low Ecm and high Ecm runs • Full science program needs “n times 100 days of good luminosity”

19. Science versus Luminosity Matrix No scientific judgment applied: luminosity is taken from what EIC simulations assumed JLAB6&12 EW HERMES 1035 ENC@GSI COMPASS MEIC Legend: DIS deep inelastic scattering SIDIS semi-inclusive DIS DES deep exclusive (pseudoscalar and vector mesons) DIFF diffractive scattering JETS jet production EW electroweak processes 1034 ELIC DES  Luminosity [cm-2 s-1] 1033 JETS SIDIS Illustration only DIS 1032 DIFF  s [GeV2] 1000 10000 100000 10 100

20. Rough Ideas of Energies (don’t take these too strict)

21. MEIC Design Efforts - Status • Near-term design concentrates on parameters that are within state-of-the-art (exception: small bunch length & small vertical b* for proton/ion beams) • Detector/IR design has concentrated on maximizing acceptance for deep exclusive processes and processes associated with very-forward going particles •  detect remnants of both struck & spectator quarks • Optimalenergy/luminosity profile still a work in progress • Many parameters related to the MEIC detector/IR design seem well matched now (lattices, ion crossing angle, magnet apertures, gradients & peak fields, range of proton energies, detector requirements), such that we do not end up with large “blind spots”.

22. Reaching Saturation: EIC Options G ~ A1/3 x s0.3 (A = 208) Energies for heavy-ion beams At high gluon density, gluon recombination should compete with gluon splitting  density saturation. Color glass condensate