Electron Ion Collider: A New Science Frontier Rik Yoshida - PowerPoint PPT Presentation

Electron Ion Collider: A New Science Frontier Rik Yoshida Jefferson Lab US QCD All-Hands Mee<ng Newport News, Apr. 28, 2017 1

A short history: QCD and nucleons Quark Model: hadrons are made of quarks. Quantum Chromodynamics: theory of quark and gluon interac<on. QCD is a strongly interac<ng theory except at short distances.. perturba<ve QCD: ok at short distances But nucleon size is long-distance in this scale: perturba<ve theory cannot tell us about how nucleons come about from quarks and gluons. (LaUce QCD. Nuclear Structure Theory) 2

Factorization i ( x , Q 2 ) = f a ⊗ ⌢ Q 2 → large, x fixed F σ lim QCD-Factoriza<on Same Parton Distribu<ons Different process Parton distribu<ons are process independent! 3

Using pQCD to understand protons: so far • Protons at high momentum can be treated as a beam of partons— now iden<fied as free quarks and gluons: (Asympto<c freedom!) • QCD nature of quark and gluons make their densi<es “evolve” with Q 2 • This evolu<on itself is conceptually simple and the partons behave incoherently. • You can measure DIS (and other) cross-sec<ons -> extract pdfs -> predict cross-sec<ons for another process. (Factoriza<on!) Jet cross-sec<ons at the LHC predicted and measured This is great if you are interested in studying the hard interac<on (LHC physics) 4

What about the proton? • Proton structure is embedded in the quark and gluon distribu<ons. • Gluons dominate below x of 0.1 • We imagine a proton looks something like the cartoon below.. • But we so far only have longitudinal informa<on… Transverse structure unmeasured When does the finite size of the proton begin to maeer X (longitudinal) structure measured (satura<on! confinement!) 5

Limits of Longitudinal Information infinite What we know momentum frame Parton frozen transversely. Framework does not What is the quark and gluon structure of the proton? incorporate any transverse informa<on. -orbital mo<on? -color charge distribu<on? But this was the only way to -spin? -how does the mass come about? define quark-gluon structure -origin of nucleon-nucleon interac<on? of proton in pQCD. 6

Progress in pQCD Theory (~1980 -Now ) Factoriza<on of TMD, GPD (Q 2 ) Parton Distribu<on Func<ons: 3D (Transverse) Structure Longitudinal only— TMD’s, GPD’s— Pert. quarks and gluons can only Now we know what to measure to be thought of longitudinally making up p. understand the 3D structure of nucleons HERMES, Transverse Momentum Dependent Distribu<ons (TMD): k t COMPASS, Generalized Parton Distribu<ons (GPD): b t JLAB 12

3D Imaging of Quarks and Gluons W(x,b T ,k T ) Momentum Coordinate ∫ d 2 k T ∫ d 2 b T space space k T xp f(x,k T ) f(x,b T ) b T Quarks Gluons 4 20 e + p → e + p + J/ ψ 3 25 6.2 < Q 2 < 15.5 GeV 2 Distribution of gluons 15 2 4 2 50 20 unpolarized sea-quarks unpolarized gluons 1 10 10 10 10 10 10 10 10 10 3 6 1 1 1 150 x ≈ 0.1 40 15 15 15 1 15 5 5 1.5 0 u quark 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2 5 5 10 10 10 10 10 30 30 30 30 0 0.5 1 4 1 100 20 20 20 20 5 − 1 x ≈ 0.01 10 3 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 k y (GeV) 0.5 10 x 2 b x (fm) 50 − 2 10 1 0 0 x ≈ 0.001 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -0.5 − 3 10 → 0 0.2 0.4 0.6 0.8 1 S Transverse distance from center, b T (fm) -1 Transverse momentum, k T (GeV) -0.5 ⊙ proton -1.5 Spin-dependent 2D (transverse Spin-dependent 3D momentum space -0.5 0 0.5 -1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 spatial) + 1D (longitudinal images from semi-inclusive scattering b y (fm) b y (fm) k x (GeV) momentum) coordinate space images from exclusive scattering Position r X Momentum p à Orbital Motion of Partons 8

Understanding the Nucleon at the Next Level Nucleon: A many-body system with challenging characteris<cs Rela<vis<c (M proton >> M quark ) Strongly Coupled (QCD) Quantum Mechanical (Superposi<on of configura<ons) Measure in the Mul<-Body regime: - Region of quantum fluctua<on + non-perturba<ve effects à dynamical origin of mass, spin. For the first <me, get (almost?) all relevant informa<on about quark-gluon structure of the nucleon Designing EIC à Designing the right probe • Resolu<on appropriate for quarks and gluons • Ability to project out relevant Q.M. configura<ons 9

Parameters of the Probe Q 2 x Ability to change x projects out different configura<ons where different dynamics dominate Ability to change Q 2 changes the resolu<on scale Q 2 = 400 GeV 2 => 1/Q = .01 fm 10

Where EIC Needs to be in x (nucleon) Collec<ve Few-body Satura<on Many-body Regime Regime Regime: Regime Needs to be Accessed via Ions (see later) 10 -4 10 -3 10 -2 10 -1 1 X (for proton) QCD Radia<on Dominated Hadron Structure Dominated (Studied at HERA) Main interest for EIC Nucleon/Nuclear Program Spin,TMD, GPD… 11

Where EIC needs to be in Q 2 (Q 1 2 ) X > 10 -3 ,10 -2 to 1 Non-perturba<ve Perturba<ve Regime Regime Transi<on Region HERMES, COMPASS, JLAB 6 and 12 EIC HERA high-x Q 2 [GeV 2 ] 10 3 10 10 2 10 -1 1 • Include non-perturba<ve, perturba<ve and transi<on regimes • Provide long evolu<on length and up to Q 2 of ~1000 GeV 2 (~.005 fm) • Overlap with exis<ng measurements Disentangle Pert./Non-pert., Leading Twist/Higher Twist 12

Bjorken x and length scale quark-an<quark dipole Correla<on Length in proton rest frame 10 1 100 fm Corresponds to Bjorken x X 0.1 0.001 0.01 In the proton rest frame, dipole life<me (x < 0.1) extends far beyond the proton charge radius 13

Parameters of the Probe (Nuclei) [Cosyn, Armesto, Fazio] x Q 2 X > 0.1 Nuclear modifica<on of nucleon. (“EMC effect”) X ≈ 0.05 Nucleon-Nucleon Interac<on Probing the nucleon interac<on 1/Q in the nuclei (note this is X ≈< 0.005 different from Mul<-nucleon interac<on correla<on (“shadowing” eventually satura<on) measurements) Note: the x range for nuclear explora<on is similar to the nucleon explora<on 14

QCD at Extremes: Parton Saturation HERA discovered a drama<c rise in the number of gluons carrying a small frac<onal longitudinal momentum of the proton (i.e. small-x). This cannot go on forever as x becomes smaller and smaller: parton recombina<on must balance parton spliUng. i.e. Satura<on—unobserved at HERA for a proton. (expected at extreme low x) In nuclei, the interac<on probability enhanced by A ⅓ Will nuclei saturate faster as color leaks out of nucleons?

Luminosity/Polarization Needed HERA Central mission of EIC (nuclear and nucleon structure) requires high luminosity and polariza<on (>70%). 16

The Electron Ion Collider For e-N collisions at the EIC: 1212.1701.v3 A. Accardi et al ü Polarized beams: e, p, d/ 3 He ü e beam 3-10(20) GeV ü Luminosity L ep ~ 10 33-34 cm -2 sec -1 100-1000 times HERA ü 20-~100 (~140) GeV Variable CoM For e-A collisions at the EIC: ü Wide range in nuclei ü Luminosity per nucleon same as e-p ü Variable center of mass energy World’s first Polarized electron-proton/light ion and electron-Nucleus collider Two proposals for realization of the science case - both designs use DOE’s significant investments in infrastructure 17

Past, Existing and proposed DIS Facilities EIC will be a unique facility. No other machine, exis<ng or planned can address the Studies underway physics of interest sa<sfactorily. EIC Physics range 1991-2007 18

US-Based EIC Proposals Brookhaven Lab Long Island, NY JLEIC Jefferson Lab Newport News, VA 19

JLEIC Realiza@on • Use exis<ng CEBAF for polarized electron injector • Figure 8 Layout: Op<mized for high ion beam polariza<on – polarized deuterons • Energy Range: √s : 20 to 65 - 140 GeV (magnet technology choice) • Fully integrated detector/IR • JLEIC achieves ini<al high luminosity, with technology choice determining ini<al and upgraded energy reach 20

eRHIC Realization • Use existing RHIC – Up to 275 GeV protons – Existing: tunnel, detector halls & hadron injector complex • Add 18 GeV electron accelerator in the same tunnel – Use either high intensity Electron Storage Ring or Energy Recovery Linac • Achieve high luminosity, high energy e-p/A collisions with full acceptance detector • Luminosity and/or energy staging possible 21

Nuclear Science Long-Range Planning • Every 5-7 years the US Nuclear Science community produces a Long- Range Planning (LRP) Document • The final document includes a small set of recommendations for the field of Nuclear Science for the next decade October 2015 -> Report Finalized (Including cost review of EIC) USDOE (NP) is ac<ng based on this planning Na<onal Academy Science Review being commissioned (Larger science case must be endorsed) 22