Nuclear Physics at an ElectronIon Collider

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Nuclear Physics at an Electron-Ion Collider
Nucleon GDR 18-19 novembre 2008 LPSC, Grenoble

• Charles Earl Hyde
• Université Blaise Pascal
• Old Dominion University

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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.

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ELIC Conceptual Design
prebooster
30-225 GeV protons 15-100 GeV/n ions
12 GeV CEBAF Upgrade
Green-field design of ion complex directly aimed
at full exploitation of science program.
3-9 GeV electrons 3-9 GeV positrons
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ELIC Ring-Ring Design Features

• Unprecedented high luminosity
• Enabled by short ion bunches, low ß, high rep.
  rate
• Large synchrotron tune
• Require crab crossing
• Electron cooling is an essential part of ELIC
• Four IPs (detectors) for high science
  productivity
• Figure-8 ion and lepton storage rings
• Ensure spin preservation and ease of spin
  manipulation
• No spin sensitivity to energy for all species.

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ELIC (e/A) Design Parameters
Luminosity is given per nuclean per IP
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ERL-based eRHIC Design

• 10 GeV electron design energy.
• Possible upgrade to 20 GeV by
• doubling main linac length.
• 5 recirculation passes ( 4 of them in the RHIC
  tunnel)
• Multiple electron-hadron interaction points (IPs)
  and detectors
• Full polarization transparency at all energies
  for the electron beam
• Ability to take full advantage of transverse
  cooling of the hadron beams
• Possible options to include polarized positrons
  compact storage ring compton backscattered
  undulator-based. Though at lower luminosity.

e-ion detector
Possible locations for additional e-ion detectors
eRHIC
PHENIX
Main ERL (1.9 GeV)
STAR
Beam dump
Low energy recirculation pass
Four recirculation passes
Electron source
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Recirculation passes

• Separate recirculation loops
• Small aperture magnets
• Low current, low power consumption
• Minimized cost

eRHIC
10 GeV (20 GeV)
8.1 GeV (16.1 GeV)
Common vacuum chamber
6.2 GeV (12.2 GeV)
4.3 GeV (8.3 GeV)
Approved LDRD for the compact magnet development
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ERL-based eRHIC Parameters e-p mode
If effective high energy transverse cooling
becomes possible the proton emittance and
electron beam current can be reduced
simultaneously, keeping the same luminosity.
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Nuclear Physics with an EIC

• Bound Nucleon Structure Functions
• Glue in Nuclei
• Higher Twist Matrix Elements
• Quark Correlations in Nuclei
• Polarized EMC effect
• SIDIS/Hadronization

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Bound Nucleon Structure Functions

• Spectator Tagging D(e,epS)X
• Fixed Target examples
• CLAS 12 Polarized, pSgt200 MeV/c
• BoNuS pSgt 70 MeV/c
• Collider can tag down to pS0,
• Resolution limited by intrinsic pT in beam
• Quasi-free neutron for pS0
• EMC effect of proton in Deuteron
• D(e,enS)X
• ZeroDegreeCalorimeter
• Energy Resolution 30/sqrt(E/GeV)
• Neutral/charged, n/? separations
• Angular resolution 1 cm/ 20 m 0.5 mr ? ?pT
  25 MeV/c at pD100 GeV/c ? Measure structure
  functions vs pT.
• EMC effect of quasi-free p,n in 3He
• 3He(e,eD)X, 3He(e,epp)X

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Kinematic reconstruction with tagged protons
E 4.223 GeV
W2 (pn q)2 pnm p nm 2(MD-Esn pn . q)
Q2 M2 2Mn(2- as ) - Q2
Spectator protons four momentum pnµ -(Es
MD, ps)? Light-cone momentum fraction as (Es
psz)/M
W2 M2 2Mn - Q2
Method Works! - Neutron Elastic and D peaks are
very prominent and nicely separated
June 3 2008
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JLab-CLAS-BoNuS
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Measuring Gluons in Nuclei I. PDFs

• QCD evolution dF2(x,Q2)/dln(Q2)
• Light NZ nuclei, 2H, 4He, 12C, 16O, 20Ne
• Two PDFs (ud)/2, g(x)
• FL (x) ?L Q2/(????) x ?S?x dz g(z)()
• Multiple beam energies at fixed (x,Q2)
• Open charm, High PT jets
• Compare (kinematics, luminosity)
• eRHIC/ELIC (typical) 10 ? 100A, L 1032 -
  41034 Hz/cm2
• Equivalent to 2 TeV on fixed target.
• SLAC 25 GeV on Nuclei. 40 GeV electrons on
  polarized H,D.
• EMC, SMC, COMPASS 200 GeV L1031 Hz/cm2.
• FNAL E665 470 GeV/c muons, L 41030 Hz/cm2.
• BCDMS 280 GeV/c muons.
• H1,ZEUS only proton data.

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EMC Effect

• SLAC E139
• 2Q210 GeV2.
• BCDMS Q2 bin
• 46,106 GeV2 at x0.22
• 70,200 GeV2 at x0.55
• Explore Q2 evolution of EMC effect at higher
  precision
• Glue

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Polarized EMC Effect
Cloet,Bentz,Thomas Phys.Lett.B642
210-217,2006 Polarized 6,7Li beams, targets
exist. 11B?
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The Gluon Contribution to the Nucleon Spin

• Antje Bruell, Jlab
• EIC meeting, MIT, April 7 2007

• Introduction
• ?G from scaling violations of g1(x,Q2)
• The Bjorken Sum Rule
• ?G from charm production

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Gluons via high pT di-jets

• COMPASS
• DIS2008
• EIC Measure A-dependence of g(x).

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Nuclear-SIDIS

• AZ(e,eh)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)

HERMES DIS2007
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The Flavor Asymmetric Sea

• Nucleon helicity-dependent PDFs

• Extend measurements of unpolarized asymmetry to
  Nuclei
• 3He, 7Li, 15N,

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Low Energy Options

• Informal / Unofficial study groups at JLab for
  s100 GeV2 collider
• Pelican symmetric collider5 GeV/c electrons
  ? 5A GeV/c protons, ions
• iCollider 10GeV electrons on 2.4A GeV/c
  protons, ions.
• GSI/Mainz proposal MANUEL
• 3 GeV electrons on 15 GeV/c protons
• Luminosity 1032 - 1033 Hz/cm2.

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Physics at s100 GeV2 vs 104 GeV2

• Valence Physics (xgt0.1) emphasized over xlt0.01
• Lower beam momentum provides improved resolution
  in spectator tagging (5 MeV/c vs gt25 MeV/c)
• Spin effects dominant at larger x
• g1(x), ?g/g, Sivers effect,
• Higher Twist evident in precision measurements at
  modest Q2 (1-10 GeV2).
• JLab d2 sum rule of g2(x)- g2WW(x).
• Flavor asymmetric sea at xm?/M

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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 is the spatial distribution of u, d, s, glue
• Nuclear Charge Distributions known
• What is the Nuclear Mass distribution?

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Exclusive J/? Photo-Production
Quasi-real ?p?pJ/?
Statistical Errors on p (2 months)(1033Hz/cm2)
J/? momentum fraction

• Nuclear rates
• Rate on 20Ne 1/2 rate on proton

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Conclusions

• An electron ion-collider would have an
  unprecedented reach in kinematics, luminosity,
  polarization, and recoil tagging
• Profound new insight into the source of mass and
  spin of the visible matter of the universe,
  including both nucleons and nuclei

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Back-up Slides
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Where is the glue? Everywhere!!
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ELIC (e/p) Design Parameters
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ERL-based eRHIC Parameters e-Au mode
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Other design options

• Under consideration also
• ERL-based design for smaller energy.
• Electron energy up to 2-3 GeV. Acceleration
  done by a linac placed
• in the RHIC tunnel. It can serve as first
  stage for following higher
• electron energy machine.
• High energy (up to 20-30 GeV) ERL-based design
  with all accelerating
• linacs and recirculation passes placed in the
  RHIC tunnel.
• Can be elegant and cost saving design
  solution.
• Variation of this design option uses FFAG design
  of recirculating passses.
• Further details are in talks by V.N.Litvinenko
  and D.Trbojevic in Parallel
• Session.
• Ring-ring design option.
• Backup design solution. See eRHIC ZDR for
  more details.
• The peak luminosity is limited to 41032
  cm-2s-1

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F2D(x)
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J/? Photo-Production