The Electron-Ion Collider (EIC)

The Electron-Ion Collider (EIC) A. Accardi, R. Ent, V. Guzey, T. Horn, C. Hyde, P. Nadel-Turonski, A. Prokudin, C. Weiss,... + CASA / accelerator team + lots of JLab of users! JLab Users' Town Hall Meeting, March 16, 2012 2007 Long-Range Plan EIC: half recommendation 2010 JLab User Workshops INT10-3 program >500 page report

Outline 1. Introduction 2. Short project overview 3. Some physics highlights

The physics program of an EIC (sea quarks and gluons) Map the spin and spatial structure of quarks and gluons in nucleons Sea quark and gluon polarization Transverse spatial distributions Orbital motion of quarks / gluons Parton correlations: beyond one-body densities Discover the collective effects of gluons in nuclei Color transparency: small-size configurations Nuclear gluons: EMC effect, shadowing Strong color fields: unitarity limit, saturation Fluctuations: diffraction Understand the emergence of hadronic matter from color charge Materialization of color: fragmentation, hadron breakup, color correlations Parton propagation in matter: radiation, energy loss Opportunities for fundamental symmetry measurements?

EIC why a collider? s = Ecm2 (GeV2) Q2 ~ ysx y Medium-energy EIC s = 4 Ee Ep = 4 x 11 x 100 = 4400 GeV2 Fixed-target experiments s = 2 Ee Mp = 2 x 11 x 0.938 = 20 GeV2 C. Weiss s = 2 Ee Mp = 2 x 75 x 0.938 = 140 GeV2 s = 2 Ee Mp = 2 x 2345 x 0.938 = 4400 GeV2 Range in the inelasticity y determines the coverage at each energy setting LHeC? EIC Stage II EIC Stage I JLab 12 GeV

EIC consensus on many global requirements The EIC project is pursued jointly by BNL and JLab, and both labs work towards implementing a common set of goals Polarized electron, nucleon, and light ion beams Electron and nucleon polarization > 70% Transverse polarization at least for nucleons Ions from hydrogen to A > 200 Luminosity reaching 1034 cm-2s-1 Stage I energy: s = 20 70 GeV (variable) Stage II energy: s up to about 150 GeV Sometimes there is a slight difference in emphasis JLab always emphasizes stage I Covers the main science interests of the JLab user community This is what we are actually going to ask for funding to build BNL often emphasizes stage II Driven by an interest in saturation From base EIC requirements in the INT report

EIC similar energies at both BNL and JLab erhic @ BNL MEIC / ELIC @ JLab Stage I Stage II s = 25 71 GeV Ee = 3 5 GeV s = up to ~170 GeV Ee = up to ~30 GeV Ep = 50 250 GeV Ep = up to 250 300 GeV EPb = up to 100 GeV/A EPb = up to 100 120 GeV/A s = 15 66 GeV Ee = 3 11 GeV s = up to ~140 GeV Ee = up to ~20 GeV Ep = 20 100 GeV Ep = up to 250 300 GeV EPb = up to 40 GeV/A EPb = up to 100 120 GeV/A (MEIC) (ELIC)

EIC different luminosity profiles Luminosity (x 1032 cm-2s-1) high-luminosity detector Ee = 5 GeV full-acceptance detector erhic, max total luminosity Ee = 10 GeV Proton Energy (GeV) The MEIC is optimized for a high luminosity at mid-range (4-8 GeV) electron energies over a wide range of proton energies. Luminosities are listed per detector. erhic offers a high luminosity at high proton energy. The luminosity is the limit for the sum of all detectors

JLab a ring-ring collider Accumulating leptons from CEBAF in a storage ring allows: Simultaneous use of multiple detectors Linac-ring designs can only use one detector at a time. Additional detectors have to wait for their turn. Electon and positron beams High currents of polarized leptons Running fixed-target experiments in parallel with collider Greatly reduced critical R&D risks No coherent electron cooling No gatling gun electron source No multi-pass energy-recovery linac (ERL)

JLab novel figure-8 ion ring When accelerated to higher energies, ions lose polarization Figure-8 shape helps ions to avoid crossing depolarizing resonances Improves polarization for all light ions (p, d, t, 3He, etc) Only way to have polarized deuterium beams!

JLab integrated full-acceptance detector low-q2 electron detection small angle hadron detection central detector with endcaps large aperture electron quads dipole ion quads dipole IP dipole ultra forward hadron detection small diameter electron quads 50 mrad beam (crab) crossing angle Solenoid yoke + Muon Detector EM Calorimeter Hadron Calorimeter Muon Detector Tracking RICH Cherenkov HTCC EM Calorimeter Solenoid yoke + Hadronic Calorimeter 5 m solenoid A second high-luminosity detector can have a more compact interaction region

JLab small-angle detection in GEANT4 Neutron detection in a 25 mrad cone down to zero degrees Excellent acceptance for all ion fragments Recoil baryon acceptance up to 99.5% of beam energy for all angles down to 2-3 mrad for all momenta Momentum resolution only limited by intrinsic beam momentum spread (2-3 x 10-4) Lower maximum ion energy allows using largeaperture magnets with achievable field strengths e p n n 2 Tm dipole solenoid 20 Tm dipole p e

Spectator tagging kinematically corrected W spectrum on n in D smeared W spectrum on D BoNuS data with tagged spectators In fixed target experiments, scattering on bound neutrons is complicated Fermi motion, non-nucleonic degrees of freedom, and binding effects like the EMC effect and shadowing Low-momentum spectators A collider allows straightforward tagging of spectators, and in general, nuclear fragments MEIC CLAS + BoNuS CLAS

Spectator tagging nuclear DIS Quasi-free neutron target spect. (Quasi)-free proton target spect. p n X D p D n 3 p X 3 p H D p D H n He D 3 X D He X p He n D D 3 4 n X p 4 3 He He 3 A. Accardi He 4 He 3 H X p 4 He 3 H

Spectator tagging polarized deuterium Sivers asymmetry EIC kinematics If one could tag neutron, it typically leads to larger asymmetries Z. Kang Z. Kang MEIC will provide longitudinal and transverse polarization for d, 3 He, and other light ions Polarized neutrons are important for probing d-quarks through SIDIS Measurements of exlusive reactions like DVCS also greatly benefit from polarized neutron targets c.f. Hall A and B programs at JLab C. Hyde

DVCS with a transversely polarized target x = 10-3 Model: Ei(x, ξ, t) = κi(t) Hi(x, ξ, t) Error bars shown only for κsea = +1.5 F. Sabatie DVCS asymmetries with a transversely polarized target are sensitive to the GPD E GPD H can be measured through the beam spin asymmetry and cross section Colliders provide an exceptional Figure-Of-Merit (FOM) Unpolarized FOM = Rate = Cross section x Luminosity x Acceptance Polarized FOM = Rate x (Polarization)2 x (Target dilution)2

Transverse spatial imaging of sea quarks and gluons (DVCS) (J/Ψ, φ) Weiss et al, INT 10-3 Are the radii of quarks and gluons, or strange and light sea quarks, different at a given x? Full image of the proton can be obtained by mapping t-distributions for different processes. ep e'k+λ ep e'π n + Horn et al. 08+, INT10-3

Transverse spatial imaging recoil baryons 40 mrad @ t = -1 GeV2 5x30 GeV DVCS on the proton ep e'π+n 8 mrad @ t = -1 5x250 GeV ~ t/ep J.H. Lee T. Horn Colliders allow straightforward detection of recoil baryons, making it possible to map the t-distribution down to very low values of -t At very high proton energies, recoil baryons are all scattered at small angles Moderate proton energies give the best resolution High luminosity at intermediate proton energies and excellent small-angle detection make the MEIC a perfect tool for imaging of the proton

Transverse Momentum Distributions (TMDs) TMDs encode the 3D partonic picture in momentum space Target polarization essential for a comprehensive study of TMDs A collider gives a wide kinematic coverage Sea quarks Sivers function @ EIC Range in Q2 PT dependence Transition from TMD to colinear factorization at high kt Prokudin, Qian, Huang Dark band: 1σ statistical uncertainties for EIC Simulations show very good statistical uncertainties Multi-dimensional binning

TMDs and Orbital Angular Momentum x = 0.1 (Ji sum rule) A. Prokudin Do valence u and d quarks have opposite signs of their OAM? TMD data and Lattice calculations suggestive (despite different sum rules) LHPC Collaboration What about sea quarks?

Spin ΔG JLab 12 GeV RHIC spin EIC ~10x100 χ2 profile slims down significantly already for erhic stage-1 M. Stratman, INT-12-49W EIC stage I (MEIC or erhic) will greatly improve our understanding of ΔG Stage II can further reduce the uncertainty

Gluons in nuclei HERA measured the longitudinal gluon distributions in the nucleon FL and df2/dln(q2) Very little is known about gluons in nuclei New discoveries awaiting an EIC? Ratio of gluons in lead to deuterium Guzey et al., Phys.Rept. 512 (2012) 255-393

Hadronization parton propagation in matter large υ e g* smaller υ h q pt e e g* h q pt e tproduction>ra tproduction< RA Accardi, Dupre pt2 vs. Q2 pt broadening strongly constrains theory Large range in υ at a collider allows Isolation of pqcd energy loss (large υ) Study of (pre)hadronization (smaller υ) Heavy flavors: B, D mesons, J/Ψ... Jets above s = 1000 GeV2 real pqcd, IR safe

The physics program of an EIC Map the spin and spatial structure of quarks and gluons in nucleons Image the 3D spatial distributions of gluons and sea quarks through DVCS and exclusive meson production (J/Ψ, light mesons) Measure ΔG, and the polarization of the sea quarks through SIDIS, g1, and open charm production Establish the orbital motion of quarks and gluons through transverse momentum dependent observables in SIDIS and jet production Discover the collective effects of gluons in nuclei Explore the nuclear gluon density and coherence in shadowing through e + A e + X and e + A e + cc + X Discover novel signatures of dynamics of strong color fields in nuclei at high energies in e + A e + X(A) and e + A e + hadrons + X Measure gluon/quark radii of nuclei through coherent scattering γ* + A J/Ψ + A Understand the emergence of hadronic matter from color charge Explore the interaction of color charges with matter (energy loss, flavor dependence, color transparency) through hadronization in nuclei in e + A e' + hadrons + X Understand the conversion of quarks and gluons to hadrons through fragmentation of correlated quarks and gluons and breakup in e + p e' + hadron + hadron + X

EIC timeline Mont, INT-10-03 The EIC project will be a pursued jointly by BNL and JLab in the Long Range Plan

Summary EIC is the ultimate tool for studying sea quarks and gluons An EIC is required to fully understand nucleon structure and the role of gluons in nuclei Collider environment offers tremendous advantages Kinematic coverage (high center-of-mass energy) Polarization measurements with excellent figure of merit Straightforward detection of recoil baryons, spectators, and target fragments EIC is a maturing project Designs ongoing at JLab and BNL Funds for joint detector R&D projects and accelerator R&D have been allocated White paper (summary of INT report) in progress

Backup

Spin ΔG DSSV DIS RHIC & pp pp x W. Vogelsang, INT-10-3 The integral ΔG as function of the lower bound xmin (right) based on current DSSV fits of xδg (left).

F2d and F2n at high x F2d fitted extrap. d/u Nuclear uncertainties can be reduced through spectator tagging, measuring F2n directly CTEQ-JLab collaboration Q2 ~ ysx

Small-angle detection ion acceptance spectator protons (from d) recoil protons (e.g. DVCS) neutrons electron beam Red and Green: Green Detection between upstream 2 Tm dipole and ion quadrupoles Yellow: Yellow Detection between ion quadrupoles and downstream 20 Tm dipole Blue: Blue Detection after the 20 Tm downstream dipole Reasonable ion quad peak fields at maximum ion energy: 9 T, 9 T, and 7 T Aperture of downstream dipole (blue) can be adjusted shown shifted for illustration Angles shown are scattering angles at IP with respect to the ion beam direction

Small-angle detection low-q2 electron tagger Yellow: Yellow Detection between quadrupoles and downstream dipole Blue: Blue Detection after the downstream dipole Large aperture electron quads with peak fields of 6 T, 6 T, and 3 T at 11 GeV Long drift space between quads and dipole allow easy analysis of yellow electrons