Nuclear Physics at a Low Energy Electron-Ion Collider Charles Earl Hyde

Nuclear Physics at a Low Energy Electron-Ion Collider

• Charles Earl Hyde

• Université Blaise Pascal

• Old Dominion University

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.

• We recommend the allocation of resources to develop accelerator and detector technology necessary to lay the foundation for a polarized Electron Ion Collider. The EIC would explore the new QCD frontier of strong color fields in nuclei and precisely image the gluons in the proton.”

Conceptual Design of A Medium Energy Electron-Ion Collider Based on CEBAF

• A Staged Approach for ELIC

• S. Bogacz, Ya. Derbenev, R. Ent, G. Krafft, T. Horn, C.Hyde, A. Hutton, F. Klein, P. Nadel-Turonski, A.Thomas, C. Weiss, Y. Zhang

The Partonic Landscape of the Proton

Adding the Spatial Dimensions Spin breaks xy azimuthal symmetry

Jefferson Lab at 12 GeV and Beyond

• Partonic physics in the «Valence» regime x>0.1

• Polarized DIS, SIDIS, Form Factors, DVCS, GPDs …

• Many important topics are dominated by «large-x» physics

• g1(x), g, transversity Tq(x).
• Nuclear Binding (EMC effect)
• Momentum Sum Rules, Angular Momentum Sum Rules

• Important questions will remain after 12 GeV & COMPASS

• Spatial Distribution of Glue (also LG)
• Gluons in Nuclei
• Full evolution and twist analysis of SIDIS
• Full Evolution and twist analysis of Deep Virtual Meson Production

A «Low Energy» Electron-Ion Collider A new laboratory for large-x physics

• Polarized Electron - Proton collisions

• s=(k+P)2 ≈ 2k(E+P)
• (5 GeV/c e)  (5 GeV/c p)
• Luminosity 0.41033 Hz/cm2.
• (5 GeV/c e)  (30 GeV/c p)
• Luminosity 41033 Hz/cm2.

• Electron - Ion Collisions

• Momentum per Nucleon in ion beams ZPp/A
• Luminosity per nucleus 1/Z2.
• Polarized p, d, 3He, 6,7Li

• Compact 400 m circumference rings

• Superconducting ion ring to achieve 30 GeV/c

Why won’t this physics be done by a high energy collider and/or fixed target?

• A high energy collider ke  Pp is intrinsically optimized for x ≤ ke/Pp < 0.1

• Resolution, laboratory phase space of final state particles
• Transverse momentum spread of high luminosity ion beams is greater than 1/RA ==> Coherent nuclear processes impossible.

• Fixed target experiments, e.g. 200 GeV/c muons at COMPASS

• Statistics and detector acceptance dominated by low-x
• Unpolarized luminosity ≤ 1032 Hz/cm2.
• Polarized luminosity 1031 Hz/cm2.
• Polarized target DVCS almost impossible

• Collider with 5  5 --> 5  30 GeV/c2. (1033 Hz/cm2 )

• A unique machine for a unique physics program.

Glue in the Valence Region

• Glue ≈ down quarks (proton) for x>0.1

• TeV scale physics at the LHC requires knowledge of large-x parton structure of proton: x ≥ M/(2PLHC).

• Glue accounts for ≈50% of the momentum sum rule of the proton

• ≈ 50% of gluon sum rule lies at x>0.1

• Effect of nuclear binding on glue?

• No direct measurements of gluons in nuclei

• Experimental access to glue in (e,e’)

• QCD evolution dF/d(lnQ2)
• Open Charm
• High PT di-jets
• Coherent J/Psi production

J/ Photo-Production

Exclusive J/ Photo-Production

Spin Physics: Where’s the Beef? I. G

• g(x) from photo-production of high pT di-jets

• RHIC-spin

• Expectation for g(x)/g(x) peaks for x>0.1

Spin Physics II. g1(x)

• SLAC, HERMES s ≤ 80 GeV2.

• G from QCD evolution between SLAC & Jlab (s≤24 GeV2).

JLab G (CLAS12 A.Deur Habilitation 2008, Leader, Sidorov and Stamenov, Phys. Rev. D75 (2007))

Spin Physics III. Polarized SIDIS (E. Kinney, J. Seele EIC workshop May 2008)

• The Flavor Asymmetric Sea : Nucleon helicity-dependent PDFs

• Large-x requires lower energy

Transversity: e.g. COMPASS

Transversity, SIDIS in a new collider

• Polarized luminosity 40-400x COMPASS, HERMES

• Large range in s for full study of factorization:

• Q2 dependence
• Fully differential in xB, pT, z=Eh/

• Lower energy collider options have greatest sensitivity in xB ≥ 0.05 region.

• Region of largest signals

Hard Exclusive Meson Production

• Need higher energy than Jlab12 to achieve Q2 ≥ 10 GeV2.

• Non-diffractive channels (, K, +) dominated by large x (flavor structure)

• Rosenbluth LT separations impossible with high energy collider (e.g.10x100).

• Need low energy to keep dynamic range in 

Nuclei in a Collider

• Gluons in Nuclei

• QCD evolution of EMC effect
• AZ(,J/) production and gluon GPDs

• Quarks in Nuclei

• Polarized EMC effect
• Polarized SIDIS on nuclei

• Spectator tagging

• Cleanest access to neutron structure
• Calibration measurement on bound protons

Bound Nucleon Structure Functions

• Spectator Tagging D(e,e’pS)X
• Fixed Target examples
• CLAS 12 Polarized, pS>200 MeV/c
• BoNuS pS> 70 MeV/c
• Collider can tag down to pS≈0,
• Resolution limited by intrinsic pT in beam
• Quasi-free neutron for pS≈0
• EMC effect of proton in Deuteron
• D(e,e’nS)X
• ZeroDegree tagging
• Neutral/charged, n/ separations
• Angular resolution ≈ 1 cm/ 5 m = 2 mr  pT = 30 MeV/c at pD= 30 GeV/c  Measure structure functions vs pT.
• EMC effect of quasi-free p,n in 3He

Polarized EMC Effect

Nuclear-SIDIS

• AZ(e,e’h)X

• d(Q2,xB, Eh/,pT2,A)
• A-dependent onset of factorization; or
• Nuclear filter of “Formation length”;
• Jet-propagation
• cold baryonic matter (DIS)
• boiling vacuum (RHIC, LHC).
• Collider opens new domain of target fragmentation
• p,, d, He, etc
• Evaporation residues A-1, A-2,,, measure temperature of residual system. (E665)

DVCS on proton and coherent DVCS on light nuclei

• Tag the coherent recoil nucleus at P’=()P

• Compare the matter and charge distributions of light N=Z nuclei
• Reconstruct 2 from either recoil or (e,e’) kinematics

• Recoil and/or spectator tagging

• Quasi Elastic D(e,e’N)N,…

• DVCS cross sections constant with s at fixed (Q2,xB), BH falls ~1/s.

• Differential sensitivity to Re[DVCS*BH].

• Luminosity is lower than CLAS12 but higher than COMPASS.

• Extend JLab12 to higher Q2 (maybe) and lower xB.

Gluons in Nuclei: I. EMC Effect

• SLAC E139

• s≤50 GeV2
• 2≤Q2≤10 GeV2.

Gluons in Nuclei: I. EMC Effect

• SLAC E139

• s≤50 GeV2
• 2≤Q2≤10 GeV2.

• BCDMS Q2 bin

• [46,106] GeV2 at x=0.22
• [70,200] GeV2 at x=0.55

• High Luminosity collider 100 ≤ s ≤ 600 GeV2

• Q2 evolution of EMC effect
• Glue in nuclei

Gluons in Nuclei: II. gGPDs

• A  A J/

• Transverse spatial image of gluons in nuclei
• Old question:
• What are the proton and neutron distributions in nuclei?
• New questions
• What are the spatial distributions of u, d, s, glue?
• Nuclear Charge Distributions measured in (e,e’).
• What is the Nuclear Mass distribution?
• N=Z nuclei, dominated by (u+d)/2, g
• Low momentum (5-30 Z GeV/c) needed to keep intrinsic Pperp of beam at IP << 1/RA.

Exclusive J/ Photo-Production on Nuclei

• Nuclear rates:

• Forward amplitude ~A
• ‹r2› ≈ B(A) ~A2/3.
• Rates on AZ < 16O ≈ 1/2 rate on proton

Conclusions

• An electron ion-collider in the s=100 to 600 GeV2 range would have an unprecedented combination of kinematic coverage, luminosity, polarization, and recoil tagging.

• Symmetric kinematics are important for coherent processes on nuclei and spectator tagging
• Low/medium energy stages enable rich physics program not covered by high-energy collider.

• Profound new insight into the source of mass and spin of the visible matter of the universe, including both nucleons and nuclei

• Join the simulation/design/R&D effort!

• http://www.jlab.org/meic/
• http://web.mit.edu/eicc/Organisation.html

Back-up Slides

Design Parameters

Spin Physics III. Polarized SIDIS (E. Kinney, J. Seele EIC workshop May 2008)

• 5 GeV e  50 GeV/c protons. (100 day)(1033Hz/cm2)