Electron Ion Collider A. Accardi, R. Ent, V. Guzey, Tanja Horn, C. Hyde, A. Prokudin, P. Nadel-Turonski, C. Weiss, … + CASA/accelerator team LRP 2007 JLab User Workshops 2010 INT10-3 programEIC White Paper EIC half recommendation >500 pages Under construction

EIC: Probing the Sea Quarks and Gluons Tanja Horn, Electron Ion Collider, JLab Strategic Planning Why care about sea quarks and gluons Structure of proton ̶ Naïve quark model: proton==uud (valence quarks) ̶ QCD: proton == uud … ̶ Proton sea has a non-trivial structure and Proton is far more than just its up + up+down (valence) quark structure QCD and Origin of Mass ̶ 99% of the proton mass/energy is due to the self- generating gluon field o Higgs mechanism has almost no role there ̶ Similarity of mass between proton/neutron arises from fact that gluon dynamics are the same o Quarks contribute almost nothing

valence quarks/gluons sea quarks/gluons radiative gluons/sea Hadrons in QCD are relativistic many-body systems –Fluctuating number of elementary quark and gluon constituents –Rich structure of the wave function Internal Landscape of the Nucleon Key physical interests –Transverse spatial distribution –Correlations: transverse, longitudinal, and nuclear modifications –Tests of reaction mechanism Components probed in ep scattering: –JLab 12 GeV: valence region –EIC: probes sea quark and gluon components 3 Q 2 ~ xys Accessible range of energies and resolution, Q 2, for probing components of the hadron wave function

Why an Electron-Ion Collider? Tanja Horn, Electron Ion Collider, JLab Strategic Planning Easier to reach high Center of Mass energies ( ) – for colliders (e.g., 4 x 10 x 100=4000 GeV 2 ) – for fixed target experiments (e.g., 2 x 11 x 0.938=20 GeV 2 ) Spin physics with high Figure Of Merit (FOM) – Unpolarized FOM = Rate = Luminosity x Cross Section x Acceptance – Polarized FOM = Rate x (Target Polarization) 2 x (Target Dilution) 2 – No dilution and high ion polarization (also transverse) – No current (luminosity) limitations, no holding fields (acceptance) – No backgrounds from target (Moller electrons) Easier detection of reaction products – Can optimize kinematics by adjusting beam energies – More symmetric kinematics improve acceptance, resolution, particle ID, etc. – Access to neutron structure with deuteron beams ( ) Targetf dilution, fixed_target P fixed_target f 2 P 2 fixed_target f 2 P 2 EIC p d

Science of an EIC: Explore and Understand QCD 5 Map the spin and spatial quark-gluon structure of nucleons ̶ Image the 3D spatial distributions of gluons and sea quarks through exclusive J/ Ψ, γ (DVCS) and meson production ̶ Measure Δ G, 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 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 quarks and gluons −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 [INT ] Needs high luminosity and range of energies

3D partonic picture of the nucleon Information about 3D partonic picture is encoded in Generalized Parton Distributions and Transverse Momentum Dependent Distributions Transverse Momentum Dependent distributions Generalized Parton Distributions Wigner distribution SIDIS DES

J/ Ψ, φ Transverse Spatial Imaging through GPDs Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011 Mesons select definite charge, spin, flavor component of GPD EIC enables a comprehensive program of transverse imaging of gluons and sea quarks pointlike? π, ρ, K, K* Λ, Σ γ √ s~140 GeV √ s~30 GeV ep → e'π + n ~100 days, ε= 1.0, L =10 34 s -1 cm -2 ep → e'K + Λ [Geraud, Moutarde, Sabatie 10+, INT10-3 report] [Horn et al. 08+, INT10-3 report] EIC: singlet quark size from deeply virtual compton scattering EIC: Imaging of strange sea quarks! EIC: Gluon size from J/  and  electroproduction (Q 2 > 10 GeV 2 ) 40<W 2 <60 GeV 2 [Weiss INT10-3 report] 80<W 2 <100 GeV 2 -t (GeV 2 ) Cross section 3<Q 2 <6 GeV 2 1.6E-3 < x B < 2.5E-3 √ s~140 GeV ~30 days, L =10 34 s -1 cm -2 √ s~30 GeV ~100 days, ε= 1.0, L =10 34 s -1 cm -2 -t (GeV 2 )

Only a small subset of the (x,Q 2 ) landscape has been mapped here: terra incognita Gray band: present “knowledge” of TMDs with current experimental data Dark gray band: EIC (1  ) Exact k T distribution presently poorly known! Mapping of k T distribution is crucial to our understanding of interplay of collinear and 3D partonic pictures [Prokudin, Qian, Huang] An EIC with good luminosity & high transverse polarization is the optimal tool to study this! Image the Transverse Momentum of the Quarks [Prokudin, Qian, Huang] 3D partonic picture is encoded in TMDs

Nucleon Structure: Orbital Motion Goal: explore quark/gluon orbital motion and its polarization dependence through both deep exclusive and semi-inclusive multi-dimensional processes Can we learn about orbital motion from a comprehensive approach based on TMDs, GPDs, etc., even if model- dependent? Potential new insight from jets or p’ T of target fragmentation? EIC: wide kinematic range low to high p T

Gluons in Nuclei NOTHING!!! What do we know about gluons in a nucleus? Ratio of gluons in lead to deuterium EIC: access gluons through F L (needs variable energy) and dF 2 /dln(Q 2 ) Knowledge of gluon PDF essential for quantitative studies of onset of saturation

Hadronization: Parton propagation in matter EIC: Explore the interaction of fast color charges with matter  p T 2 vs. Q 2 -Time scales for color neutralization t CN and hadron formation t F - eA/  A complementary to jets in AA: cold vs. hot matter EIC: Understand the conversion of color charge to hadrons through fragmentation and breakup [Accardi, Dupre INT10-03 Report] L e e’ ** ++ pTpT  p T 2 = p T 2 (A) – p T 2 ( 2 H) Comprehensive studies possible: wide range of energy v = GeV  move hadronization inside/outside nucleus, distinguish energy loss and attenuation wide range of Q 2 : QCD evolution of fragmentation functions and medium effects Hadronization of charm, bottom  Clean probes with definite QCD predictions High luminosity  Multi-dimensional binning and correlations √s > 30: jets and their substructure in eA

C. Weiss s For large or small y, uncertainties in the kinematic variables become large Range in y Q 2 ~ xys Range in s Range of kinematics Detecting only the electron y max / y min ~ 10 Also detecting all hadrons y max / y min ~ 100 – Requires hermetic detector (no holes) Accelerator considerations limit s min – Depends on s max (dynamic range) At fixed s, changing the ratio E e / E ion can for some reactions improve resolution, particle identification (PID), and acceptance C. Weiss valence quarks/gluons non-pert. sea quarks/gluons radiative gluons/sea [Weiss 09] s To cover the physics we need… 12 Vacuum fluct. pQCD radiation

EIC: Critical Capabilities But we get there in different ways: Input passed on to INT10-03 program: Base EIC Requirements per Executive Summary INT Report: range in energies from √s ~ 20 to √s ~ 70 & variable fully-polarized (>70%), longitudinal and transverse ion species up to A = 200 or so high luminosity: about e-nucleons cm -2 s -1 multiple interaction regions upgradable to higher energies (√s ~ 150 GeV) Proton Energy (GeV) Luminosity (x10 32 ) eRHIC-1, Ee=5 GeV Ee=5 GeV Ee=10 GeV

14 Exclusive Meson Production √ s=31.6 GeV √ s=44.7 GeV √ s=100GeV Momentum (GeV/c) Lab Scattering angle (rad) Q 2 > 10 GeV 2 → events of interest for imaging studies Exclusive measurements at very high CM energy require detection of high energy mesons over a very small angular range Best momentum resolution for symmetric or nearly symmetric collisions E p = 250 GeV E p = 30 GeV Δθ =1-2˚ Δθ <0.3˚ Better t-resolution with lower proton energy and more symmetric kinematics Nuclear Science: Map t between t min and 1 (2) GeV 2  Must cover between 1-5 deg  Should cover between deg  Like to cover between deg t ~ E p 2  2  Angle recoil baryons = t ½ /E p [Horn 08+, INT10-3 report] e - Beamp/A Beam

solenoid electron FFQs 50 mrad 0 mrad ion dipole w/ detectors ions electrons IP ion FFQs 2+3 m 2 m Detect particles with angles below 0.5 o. detectors Central detector EM Calorimeter Hadron Calorimeter Muon Detector EM Calorimeter Solenoid yoke + Muon Detector TOF HTCC RICH RICH or DIRC/LTCC Tracking 2m 3m 2m 4-5m Solenoid yoke + Hadronic Calorimeter Very-forward detector, Large dipole 20 meter from IP allows for very-small angle detection (<0.3 o ) Full MEIC: Full Acceptance Detector 7 meters Detect particles with angles down to 0.5 o. Need 1-2 Tm dipole. GEANT4 model

EIC: Design Parameters Base EIC Requirements per Executive Summary INT Report: highly polarized (>70%) electron and nucleon beams - longitudinally polarized electron and nucleon beams - transversely polarized nucleon beams ion species from deuterium to A = 200 or so center of mass energies from √s ~ 20 to √s ~ 70 GeV & variable -electron energies above 3 GeV to allow efficient electron trigger -proton energy adjustable to optimize particle identification upgradeable to center of mass energy of about √150 GeV high luminosity ~10 34 e-nucleons cm -2 s -1 -optimal luminosity in √s ~ region -luminosity ≥10 33 e-nucleons cm -2 s -1 in √s ~ region multiple interaction regions integrated detector/interaction region -non-zero crossing angle of colliding beams -crossing in ion beam to prevent synchrotron background - ion beam final focus quads at ~7 m to allow for detector space -bore of ion beam final focus quads sufficient to let particles pass through up to t ~ 2 GeV 2 (t ~ E p 2 Q 2 ) positron beam desirable 16

MEIC : Medium Energy EIC Use CEBAF “as-is” after the 12-GeV Upgrade polarimetry low-energy IP medium-energy IPs Three compact rings: 3 to 11 GeV electron Up to 12 GeV/c proton (warm) Up to 100 GeV/c proton (cold) Proton Energy (GeV) Luminosity (x10 32 ) eRHIC-1, Ee=5 GeV Ee=5 GeV Ee=10 GeV

EIC Realization Imagined Activity Name Gev Upgrade FRIB EIC Physics Case NSAC LRP EIC CD0 EIC Machine Design/R&D EIC CD1/Downsel EIC CD2/CD3 EIC Construction Note: 12 GeV LRP recommendation in 2002 – CD3 in 2008

19 Summary Collider environment provides tremendous advantages – polarization – Target fragmentation EIC is needed to completely understand nucleon structure and the role of gluons in nuclei EIC is a mature project – Designs ongoing at JLab and BNL – White paper for next LRP under construction – Accelerator R&D funds have been allocated – Joint detector R&D projects have started EIC is the ultimate tool to study sea quarks and gluons – Sea quarks and gluons play a prominent role in nucleon structure