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The Frontiers of Nuclear Science: from 12 GeV to EIC

The Frontiers of Nuclear Science: from 12 GeV to EIC. Rolf Ent INT10-03 Program, Institute for Nuclear Theory, Seattle, WA Workshop on “The Science Case for an EIC”, November 16-19, 2010. A personal perspective on the 12-GeV and EIC science The 12-GeV Upgrade

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The Frontiers of Nuclear Science: from 12 GeV to EIC

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  1. The Frontiers of Nuclear Science: from 12 GeV to EIC Rolf Ent INT10-03 Program, Institute for Nuclear Theory, Seattle, WA Workshop on “The Science Case for an EIC”, November 16-19, 2010 • A personal perspective on the 12-GeV and EIC science • The 12-GeV Upgrade • The 12 GeV science (relevant to an EIC) Highlights & Shortcomings • The 12 GeV Roadmap • The Electron-Ion Collider • - The EIC science • - The EIC Roadmap • Conclusions

  2. NSAC 2007 Long Range Plan Recommendation I “We recommend completion of the 12 GeV Upgrade at Jefferson Lab. The Upgrade will enable new insights into the structure of the nucleon, the transition between the hadronic and quark/gluon descriptions of nuclei, and the nature of confinement.” A fundamental challenge for modern nuclear physics is to understand the structure and interactions of nucleons and nuclei in terms of QCD. Doubling the energy of the JLAB accelerator will enable three-dimensional imaging of the nucleon, revealing hidden aspects of the internal dynamics.

  3. Highlights of the 12 GeV Science Program • Unlocking the secrets of QCD: quark confinement • New and revolutionary access to the structure of the proton and neutron • Discovering the quark structure of nuclei • High precision tests of the Standard Model Items in blue related to

  4. Measuring High-x Structure Functions Also with 3H/3He and EW d/u REQUIRES: • High beam polarization • High electron current • High target polarization • Large solid angle spectrometers 12 GeV will access the regime (x > 0.3), where valence quarks dominate

  5. X. Ji, D. Mueller, A. Radyushkin (1994-1997) Proton form factors, transversecharge & current densities Structure functions, quark longitudinal momentum & helicity distributions Beyond form factors and quark distributions – Generalized Parton Distributions (GPDs) Correlated quark momentum and helicity distributions in transverse space - GPDs Extend longitudinal quark momentum & helicity distributions to transverse momentum distributions - TMDs 2000’s

  6. Ds 2s e p epg s+ - s- s+ + s- A = = x = xB/(2-xB) The path towards the extraction of GPDs Use polarization! Subset of projected results DsLU~ sinfIm{F1H+ ...}df Kinematically suppressed H(x,t)

  7. Projected precision in extraction of GPD H at x = x Spatial Image Projected results Rich program in DVCS in valence quark region

  8. Deep Exclusive Meson Production @ 12 GeV B (GeV-2) Fit with ds/dt = e-Bt • Measurements at DESY of diffractive channels (J/y, f, r, g) confirm the applicability of QCD factorization: • t-slopes universal at high Q2 • flavor relations f:r Pseudoscalar (and vector) meson production at 12 GeV: typically up to Q2 = 10 GeV2 Experimental QCD factorization tests of (e,e’p+) and (e,e’K+) essential

  9. Valence Quark Structure and Parton Distributions Access to valence quark region through DIS at large x will be augmented with a SIDIS program Boer-Mulders asymmetry for pions as function of Q2 and pT

  10. Onset of the Parton Model in SIDIS @ JLab 1H,2H(e,e’p+/-)X GRV & CTEQ, @ LO or NLO Good description for p and d targets for 0.4 < z < 0.65 (Note: z = 0.65 ~ Mx2 = 2.5 GeV2) Seq2q(x) Dqp(z) factorization Closed (open) symbols reflect data after (before) events from coherent r production are subtracted 6 GeV: z > 0.4

  11. 12-GeV: study x-z Factorization for kaons P.J. Mulders, hep-ph/0010199 (EPIC Workshop, MIT, 2000) At large z-values easier to separate current and target fragmentation region  for fast hadrons factorization (Berger Criterion) “works” at lower energies If same arguments as validated for p apply to K: At W = 2.5 GeV: z > 0.6 (but, z < 0.65 limit may not apply for kaons!) Access to sea/strange quarks not clear with 12 GeV

  12. p quark R = sL/sTin (e,e’p) SIDIS Knowledge on R = sL/sT in SIDIS is essentially non-existing! • If integrated over z (and pT, f, hadrons), RSIDIS = RDIS • RSIDIS may vary with z • At large z, there are known contributions from exclusive • and diffractive channels: e.g., pions from D and r p+p- • RSIDIS may vary with transverse momentum pT • Is RSIDISp+ = RSIDISp- ? Is RSIDISH = RSIDISD ? • Is RSIDISK+ = RSIDISp+ ? Is RSIDISK+ = RSIDISK- ? We measure kaons too! (with about 10% of pion statistics) • RSIDIS = RDIS test of dominance of quark fragmentation “A skeleton in our closet” Seq2q(x) Dqp(z)

  13. R = sL/sT in SIDIS (ep  e’pX) Cornell data of 70’s Cornell data conclusion: “data both consistent with R = 0 and R = RDIS” RDIS Some hint of large R at large z in Cornell data? JLab@12: scans vs. Q2/x, z (Q2 = 2& 4) & PT RDIS (Q2 = 2 GeV2)

  14. Transverse Momentum Dependence of Semi-Inclusive Pion Production • Not much is known about the orbital motion of partons • Significant net orbital angular momentum of valence quarks implies significant transverse momentum of quarks Final transverse momentum of the detected pion Pt arises from convolution of the struck quark transverse momentum kt with the transverse momentum generated during the fragmentation pt. Pt= pt +zkt+ O(kt2/Q2) z = Ep/n pT ~ L < 0.5 GeV optimal for studies as theoretical framework for Semi-Inclusive Deep Inelastic Scattering has been well developed at small transverse momentum [A. Bacchetta et al., JHEP 0702 (2007) 093].

  15. Unpolarized SIDIS – JLab @ 6 GeV Constrain kT dependence of up and down quarks separately 1) Probe p+ and p- final states 2) Use both proton and neutron (d) targets 3) Combination allows, in principle, separation of quark width from fragmentation widths (if sea quark contributions small) Example { 1st example: Hall C, PL B665 (2008) 20 Simple model, host of assumptions (factorization valid, fragmentation functions do not depend on quark flavor, transverse momentum widths of quark and fragmentation functions are gaussian and can be added in quadrature, sea quarks are negligible, assume Cahn effect, etc.)  x = 0.32 z = 0.55 Example <pt2> (favored) 12 GeV: start testing assumptions! <kt2> (up)

  16. Does the quark structure of a nucleon get modified by the suppressed QCD vacuum fluctuations in a nucleus? Reminder: EMC effect is effect that quark momenta in nuclei are altered • Measure the EMC effect on the mirror nuclei 3H and 3He • Is the EMC effect a valence quark only effect? • Is the spin-dependent EMC effect larger? • Can we reconstruct the EMC effect on 3He and 4He from all measured reaction channels? • Is there any signature for 6-quark clusters? • Can we map the effect vs. transverse momentum/size? 12 GeV is probably our best chance to understand the origin of the EMC effect in the valence quark region

  17. Using the nuclear arena How long can an energetic quark remain deconfined? How long does it take a confined quark to form a hadron? Formation time tfh Hadron is formed { Production time tp Hadron attenuation Quark is deconfined CLAS Time required to produce fully-developed hadron, signaled by CT and/or usual hadronic interactions Time required to produce colorless “pre-hadron”, signaled by medium-stimulated energy loss via gluon emission

  18. Transverse Momentum Broadening DpT2 reaches a “plateau” for sufficiently large quark energy, for each nucleus (L is fixed), related to production length (start seeing this effect in 6-GeV data). DpT2 Projected Data n

  19. Sensitivity: C1 and C2 Plots after 12 GeV (Vector quark and axial-vector quark couplings) 6 GeV World’s data 12 GeV PVDIS Precision Data (w. Qweak, 6 GeV/PVDIS, 12 GeV/PVDIS) Gain factor of 80 or so in C2 combination with 12 GeV! Qweak 12 GeV PVDIS Cs Solid

  20. Møller Parity-Violating Experiment: New Physics Reach(example of large installation experiment with 11 GeV beam energy) N JLab Møller LHC ee ~ 25 TeV New Contact Interactions Not “just another measurement” of sin2(Qw) AFB(b) measures product of e- and b-Z couplings ALR(had) measures purely the e-Z couplings Proposed APV(b) measures purely the e-Z couplings at a different energy scale

  21. 12 GeV Upgrade: Phases and Schedule • 2004-2005 Conceptual Design (CDR) - finished • 2004-2008 Research and Development (R&D) - finished • 2006 Advanced Conceptual Design (ACD) - finished • 2006-2009 Project Engineering & Design (PED) - finished • 2009-2014 Construction – in second yearof construction • Parasitic machine shutdown May 2011 through Oct. 2011 • Accelerator shutdown start mid-May 2012 • Accelerator commissioning start mid-May 2013 • 2013-2015 Pre-Ops (beam commissioning) • Hall A commissioning start October 2013 • Hall D commissioning start April 2014 • Halls B and C commissioning start October 2014 Timescale (for 310M$ project): over 10 years – after numbered recommendation

  22. Highlights (& Shortcomings) of the 12 GeV Science Program • New and revolutionary access to the structure of the proton and neutron • Form factors to high Q2 (about 10 GeV2) • Large x PDFs, DVCS & TMD measurements for x > 0.1 • No strange/sea quarks, probing r/p/K production • Discovering the quark structure of nuclei • Disentangle the origin of the (valence) EMC effect • Establish Color Transparency for meson production • No target fragmentation, limited hadronization studies • High precision tests of the Standard Model - Probably as good as anyone can do in EW at E < Mz

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

  24. A High-Luminosity Electron Ion Collider 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.” • Base EIC Requirements: • 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

  25. Why an Electron-Ion Collider? • Longitudinal and Transverse Spin Physics! • 70+% polarization of beam and target without dilution • transverse polarization also 70%! • Detection of fragments far easier in collider environment! • fixed-target experiments boosted to forward hemisphere • no fixed-target material to stop target fragments • access to neutron structure w. deuteron beams (@ pm = 0!) • Easier road to do physics at high CM energies! • Ecm2 = s = 4E1E2 for colliders, vs. s = 2ME for fixed-target •  4 GeV electrons on 12 GeV protons ~ 100 GeV fixed-target • Easier to produce many J/Y’s, high-pT pairs, etc. • Easier to establish good beam quality in collider mode Longitudinal polarization FOM

  26. Why a New-Generation EIC? Why not HERA? • Obtain detailed differential transverse quark and gluon images • (derived directly from the t dependence with good t resolution!) • Gluon size from J/Y and f electroproduction • 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 the 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? • Explore the interaction of color charges • with matterand understand the • conversion of quarks and gluons to • hadrons through fragmentation and • breakup. longitudinal momentum orbital motion quark to hadron conversion Dynamical structure! Gluon saturation? transverse distribution

  27. 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 spatial structure of quarks and gluons in nucleons (show the nucleon structure picture of the day…) Discover the collective effects of gluons in atomic nuclei (without gluons there are no protons, no neutrons, no atomic nuclei) Understand the emergence of hadronic matter from quarks and gluons (how does E = Mc2 work to create pions and nucleons?) + Hunting for the unseen forces of the universe?

  28. The Science of an (M)EIC Or, Elevator-Talk EIC science goals: Map the spin and spatial structure of quarks and gluons in nucleons (show the nucleon structure picture of the day…) Discover the collective effects of gluons in atomic nuclei (without gluons there are no protons, no neutrons, no atomic nuclei) Understand the emergence of hadronic matter from quarks and gluons (how does E = Mc2 work to create pions and nucleons?) + Hunting for the unseen forces of the universe?

  29. F2p & F2d @ high x still needed from EIC • Similar improvement in F2p at large x • F2n tagging measurements relatively straightforward in EIC designs • EIC will have excellent kinematics to further measure/constrain n/p at large x! F2 Similar reduction with neural networks (Rojo + Accardi) Q2 (GeV2) • s = 1000 • One year of running (26 weeks) at 50% efficiency, or 35 fb-1 Sensible reduction in PDF error, likely larger reduction if also energy scan

  30. Projected g1p Landscape of the EIC Access to Dg/g is possible from the g1p measurements through the QCD evolution, or from open charm (D0) production (see below), or from di-jet measurements. RHIC-Spin Similar for g2p(and g2n)!

  31. Sea Quark Polarization • Spin-Flavor Decomposition of the Light Quark Sea } 100 days, L =1033, s = 1000 Access requires s ~ 1000 (and good luminosity) u u u Many models predict Du > 0, Dd < 0 > u d | p = + + + … u u u u d d d d

  32. Transverse Quark & Gluon Imaging Deep exclusive measurements in ep/eA with an EIC: diffractive: transverse gluon imaging J/y, f, ro, g (DVCS) non-diffractive: quark spin/flavor structure p, K, r+, … Are gluons uniformly distributed in nuclear matter or are there small clumps of glue? Are gluons & various quark flavors similarly distributed? (some hints to the contrary) Describe correlation of longitudinal momentum and transverse position of quarks/gluons  Transverse quark/gluon imaging of nucleon (“tomography”)

  33. Detailed differential images from nucleon’s partonic structure EIC: Gluon size from J/Y and felectroproduction (Q2 > 10 GeV2) Hints from HERA: Area (q + q) > Area (g) Dynamical models predict difference: pion cloud, constituent quark picture - [Transverse distribution derived directly from tdependence] t t EIC: singlet quark size from deeply virtual compton scattering EIC: strange and non-strange (sea) quark size from p and K production • Q2 > 10 GeV2 • for factorization • Statistics hungry • at high Q2!

  34. Image the Transverse Momentum of the Quarks Swing to the left, swing to the right: A surprise of transverse-spin experiments The difference between the p+, p–, and K+ asymmetries reveals that quarks and anti-quarks of different flavor are orbiting in different ways within the proton. An EIC with high transverse polarization is the optimal tool to to study this! Only a small subset of the (x,Q2) landscape has been mapped here: terra incognita

  35. Correlation between Transverse Spin and Momentum of Quarks in Unpolarized Target (Harut Avakian, Antje Bruell) All Projected Data Perturbatively Calculable at Large pT - Assumed 100 days of 1035 luminosity Vanish like 1/pT (Yuan)

  36. The Science of an (M)EIC Or, Elevator-Talk EIC science goals: Map the spin and spatial structure of quarks and gluons in nucleons (show the nucleon structure picture of the day…) Discover the collective effects of gluons in atomic nuclei (without gluons there are no protons, no neutrons, no atomic nuclei) Understand the emergence of hadronic matter from quarks and gluons (how does E = Mc2 work to create pions and nucleons?) + Hunting for the unseen forces of the universe?

  37. Gluons in Nuclei Ratio of gluons in lead to deuterium • What do we know about • gluons in a nucleus? • NOTHING!!! • Large uncertainty in gluon distributions • need range of Q2 in shadowing region,  x ~ 10-2-10-3 sEIC = 1000+ + Transverse distribution of gluons on nuclei from coherent Deep-Virtual Compton Scattering and coherent J/Y production [Measurements at DESY of diffractive channels (J/y, f, r, g) confirmed the applicability of QCD factorization: t-slopes universal at high Q2&flavor relations f:rhold] Gluon radius of a nucleus?

  38. gluons valence sea 0.1 1.0 Sea-Quarks in Nuclei Drell-Yan: Is the EMC effect a valence quark phenomenon or are sea quarks involved? Tremendous opportunity for experimental improvements! RCa E772 1.0 S. Kumano, “Nuclear Modification of Structure Functions in Lepton Scattering,” hep-ph/0307105 0.5 x  Use combination of FLA & F2A measurements, EW measurements,‘flavor tagging’, etc.

  39. Unresolved Questions in Nuclei • F2 structure functions, or quark distributions, are altered in nuclei • ~1000 papers on the topic; the best models explain the curve by change of nucleon structure - BUT we are still learning (e.g. local density effect) – and 12 GeV optimal to attack the valence region. F2A/F2D • EIC: • Is shadowing a leading- or higher-twist phenomenon? • What is the dynamical origin of anti-shadowing? x 12 GeV

  40. The Science of an (M)EIC Or, Elevator-Talk EIC science goals: Map the spin and spatial structure of quarks and gluons in nucleons (show the nucleon structure picture of the day…) Discover the collective of gluons in atomic nuclei (without gluons there are no protons, no neutrons, no atomic nuclei) Understand the emergence of hadronic matter from quarks and gluons (how does E = Mc2 work to create pions and nucleons?) + Hunting for the unseen forces of the universe?

  41. Hadronization EIC: Understand the conversion of quarks and gluons to hadrons through fragmentation and breakup • un-integrated parton distributions current fragmentation +h ~ 4 EIC Fragmentation from QCD vacuum target fragmentation -h ~ -4 EIC: Explore the interaction of color charges with matter

  42. Transverse Momentum Broadening DpT2 reaches a “plateau” for sufficiently large quark energy, for each nucleus (L is fixed). In the pQCD region, the effect is predicted to disappear (arbitrarily put at n =1000) DpT2 n

  43. Hadronization EIC: Explore the interaction of color charges with matter (1 month only) EIC: Understand the conversion of quarks and gluons to hadrons through fragmentation and breakup

  44. EIC Realization From Hugh Montgomery’s presentation at the INT10-03 Program in Seattle Assumes endorsement for an EIC at the next ~2012/13 NSAC Long Range Plan

  45. Summary • The last decade+ has seen tremendous progress in our understanding • of the partonic sub-structure of nucleons and nuclei, due to: • Findings at the US nuclear physics flagship facilities: RHIC and CEBAF • The surprises found at HERA (H1, ZEUS, HERMES), and now COMPASS/CERN. • The development of a theory framework allowing for a revolution in our • understanding of the inside of hadrons … GPDs, TMDs, Lattice QCD • … hand in hand with the stellar technological advances in polarized beam and • parity-quality electron beam delivery. • This has led to new frontiers of nuclear science: • - the possibility to truly explore and image the nucleon • - the possibility to understand and build upon QCDand study the role of gluons in structure and dynamics • - the unique possibility to study the interaction of color-charged objects in vacuum and matter, and their conversion to hadrons • - utilizing precision electroweak studies to complement direct • searches for physics beyond the Standard Model • We have unique opportunities to make a (future textbook) breakthrough in nucleon structure and QCD dynamics.

  46. EIC is intended to create and study gluons, which bind subatomic particles Einstein’s famous equation, E = mc2, predicts that small amounts of mass can be transformed into large amounts of energy. Although we have demonstrated this prediction and its practical applications, the truth is that we do not yet understand how the process works– the underlying mechanisms by which mass is transformed into energy and vice versa. EIC will allow scientists to tackle this very fundamental question in physics.

  47. Appendix

  48. 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

  49. Towards a “3D” spin-flavor landscape m m d3r d2kT p p x GPD B TMD GPDu(x,x,t) Hu, Eu, Hu, Eu TMDu(x,kT) f1,g1,f1T ,g1T h1, h1T , h1L , h1 ~ ~ Wu(x,k,r) (Wigner Function) Transverse-Momentum Dependent Parton Distributions Link to Orbital Momentum Link to Orbital Momentum Generalized Parton Distributions Want PT > L but not too large! dx x = 0, t = 0 d2kT u(x) Du, du F1u(t) F2u,GAu,GPu f1(x) g1, h1 Parton Distributions Form Factors

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