EIC Overview

1
EIC Overview
(mainly EIC_at_JLab accelerator and detector
parameters)
Lots of credit to Yuhong Zhang, Alex Bogacz,
Slava Derbenev, Geoff Krafft, Tanja Horn, Charles
Hyde, Pawel Nadel-Turonski for multiple
accelerator and detector/interaction region ideas
Rolf Ent Nuclear Chromo-Dynamic Studies with a
Future EIC Workshop at Argonne National
Laboratory April 07-09, 2010
2
EIC Project - Status
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.
3
Current Ideas for a Collider
Design Goals for Colliders Under Consideration
World-wide
Energies s luminosity
MEIC_at_JLab Up to 11 x 60 240-2650 Close to 1034
Future ELIC_at_JLab Up to 11(22?) x 250 11000 (22000?) Close to 1035
Staged MeRHIC_at_BNL Up to 4 x 250 800-4000 Close to 1033
eRHIC_at_BNL Up to 20 x 325 26000 Few x 1033
ENC_at_GSI Up to 3 x 15 180 Few x 1032
LHeC_at_CERN Up to 70 x 7000 1960000 1033
Present focus of interest (in the US) are the
(M)EIC and Staged MeRHIC versions, with s up to
2650 and 4000, resp.
4
4 GeV e x 250 GeV p 100 GeV/u Au MeRHIC
2 x 60 m SRF linac 3 passes, 1.3 GeV/pass
s 800 - 4000
Polarized e-gun
Beam dump
MeRHIC detector
3 pass 4 GeV ERL
PHENIX
MeRHIC Medium Energy eRHIC _at_ IP2 of
RHIC (IP12?) Up to 4 GeV e- x 250 GeV p L
1032-1033 cm-2 sec -1
STAR
V.N. Litvinenko, RHIC ST Review, July 23, 2009
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A High-Luminosity EIC at JLab - Concept
Note sHERMES 51 unpol. L
1032 sCOMPASS 340 unpol. L
1032 sCOMPASS 340 L 1032
Legend MEIC EIC_at_JLab 1 low-energy IR (s
200) 2 medium-energy IRs (s lt 2600)
ELIC high-energy EIC_at_JLab (s 11000)
(Ep 250 limited by JLab site)
Use CEBAF as-is after 12-GeV Upgrade
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EIC_at_JLab assumptions
(x,Q2) phase space directly correlated with s
(4EeEp) _at_ Q2 1 lowest x scales like
s-1 _at_ Q2 10 lowest x scales as 10s-1
x Q2/ys
General science assumptions (Medium-Energy)
EIC_at_JLab option driven by access to sea quarks
(x gt 0.01 or so) deep exclusive scattering at
Q2 gt 10 (?) any QCD machine needs range in
Q2 ? s few 100 - 1000 seems right ballpark ?
s few 1000 allows access to gluons,
shadowing Requirements for deep exclusive and
high-Q2 semi-inclusive reactions also drives
request for (lower ) more symmetric beam
energies. Requirements for very-forward angle
detection folded in IR design
7
MEIC/ELIC Design Goal

• Energy
• Wide CM energy range between 10 GeV and 100 GeV
• Low energy 3 to 11 GeV e on 3
  to 12 GeV p (and ion)
• Medium energy up to 11 GeV e on
  60 GeV p or 24 GeV/n ion
• and for future upgrade
• High energy up to 11 (22?) GeV e on
  250 GeV p or 100 GeV/n ion
• Luminosity
• 1033 up to 1035 cm-2s-1 per collision point
• Multiple interaction points
• Ion Species
• Polarized H, D, 3He, possibly Li
• Up to heavy ion A 208, all stripped
• Polarization
• Longitudinal at the IP for both beams,
  transverse for ions
• Spin-flip of both beams

8
MEIC Design Choices

• Achieving high luminosity
• Very high bunch repetition frequency (1.5 GHz)
• Very small ß to reach very small spot sizes at
  collision points
• Short bunch length (sz ß) to avoid luminosity
  loss due to hour-glass effect (unless other
  mitigation schemes used)
• Relatively small bunch charge for making short
  bunch possible
• High bunch repetition restores high average
  current and luminosity

This luminosity concept has been tested at two
B-factories very successfully, reaching
luminosity above 1034 cm-2/s-1
MeRHIC Low repetition rate Very high bunch
charge Long bunch length Large ß
MEIC High repetition rate Small bunch charge
Short bunch length Small ß
VS.
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MEIC Design Choices (cont.)

• Ring-ring vs. Linac(ERL)-ring
• Linac-ring option requires very high average
  current polarized electron sources (few decades
  times state-of-the-art)
• Linac-ring option does not help ELIC which
  already employs high repetition electron and ion
  beams
• ? ring-ring collider
• Ensuring high polarization for both electron beam
  and light ion beams
• ? Figure-8 shape rings
• Simple solution to preserve full ion polarization
  by avoiding spin resonances during acceleration
• Energy independence of spin tune
• g-2 is small for deuterons a figure-8 ring is
  the only practical way to arrange for
  longitudinal spin polarization at the IP

10
MEIC Luminosity Energy Dependence

• MEIC luminosity is limited by
• Electron beam current ? synchrotron
  radiation Ne?4/?
• (radiation power, emittance
  degradation)
• Proton/ion beam current ? space charge effect
  Ni/?2
• (emittance growth,
  tune-shift/instabilities)
• (Vertical) beam-beam tune-shift (bad
  collisions) 1/?
• Main design limits (based on experience)
• Electron beam SR power density 20 kW/m
• Ion beam space charge tune-shift 0.1
• (Vertical) beam-beam tune-shift 0.015
  (proton), 0.1 (electron)
• Given an energy range, MEIC collider ring
  optimized with
• Synchrotron radiation ? prefers a large ring
  (for more arc bends)
• Space charge effect of i-beam ? prefers a small
  ring circumference
• Multi IPs and other components require long
  straight sections

11
MEIC Luminosity with a Compact Ring

• 660 m ring circumference was determined to be the
  minimum arc length required to accommodate 60 GeV
  protons in a Figure-8 ring
• Illustration is based on back-of-envelope
  estimations, using three main design limits,
  omitting more complicated beam dynamics issues
• Given the ring size, the synchrotron limit
  determines the optimal luminosity/electron
  energy. Beyond this electron energy a fast drop.

Just an illustration
12
MEIC Luminosity with a Compact Ring

• Luminosity of 60 GeV protons in a 1 km ring,
  based on a back-of-the-envelope calculation, is
  lower than in 0.6 km ring, since space charge
  effects are more severe in a larger ring
• Luminosity of 100 GeV protons is on the other
  hand much better in a 1 km ring, since space
  charge effects are reduced with higher energy
• Consider what the minimum luminosity is at both
  lower and higher ion energies!

Just an illustration
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Near-Term MEIC Design Parameters
Electron Proton
Collision energy GeV 3 11 20 - 60 Ion booster 312 GeV, ring accepts 12 GeV injection
Max dipole field T 6 Not too aggressive after LHC
Max SR power kW/m 20 Factor two beyond best achieved?
Max current A 2 1 max B-factory current, HOM in component HERA 0.15 A (?) RHIC 0.3 A
RF frequency GHz 1.5 1.5 Use combination of gap (crossing angle) and RF shift to accommodate lower ion energies
Bunch length mm 5 5 6 mm demonstrated in B-factory, 10 cm in RHIC (?)
IP to front face of 1st quad (l) m /- 3 to 4 /- 7
Vertical ß cm 2 2 Keep ßmax below 2 km, with bmax l2/b
Crossing angle mrad 100 100 50 to 150 desired for detector advantages
Luminosity expected to reach up to 1 x 1034
e-nucleons/s/cm2 around 60x5 GeV2
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Detector/IR in simple formulas
bmax 2 km l2/b (l distance IP to 1st quad)
Example l 7 m, b 20 mm ? bmax 2.5 km
IP divergence angle 1/sqrt(b)
Example l 7 m, b 20 mm ? angle 0.3
mr Example 12 s beam-stay-clear area ? 12
x 0.3 mr 3.6 mr 0.2o
Making b too small complicates small-angle
(0.5o?) detection before ion Final Focusing
Quads, AND would require too much focusing
strength of these quads, preventing large
apertures (up to 0.5o?)
Luminosity 1/b
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Figure-8 Ion Ring Optics
Uncompensated dispersion from arcs
Arc length C 120 m 20 m (for spin
manipulation) 120 m (increased due to
assumption of 60 GeV 6T max dipole
fields) Straight length L 194 m Total Ring
Circumference would then be 2 (L C) 908 m
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Interaction Region Optics (ions)
IP
f
l 7m
FF triplet Q3 Q2 Q1
Natural Chromaticity ?x -44 ?y
-137
Q1 GkG/cm -9.7 Q2 GkG/cm 6.7 Q3
GkG/cm -6.3
Q3 aperture 10 cm (_at_12 m) ? 7T peak field ?
Particles lt 0.5 degrees through FF quads
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Figure-8 Collider Rings
(Reminder MEIC/ELIC scheme uses 100 mr crab
crossing)
Present thinking ion beam has 100 mr horizontal
crossing angle Advantages for dispersion, crab
crossing, very-forward particles
total ring circumference 908 m 64
degrees arc/straight crossing angle
200 mr bend would need 40 Tm dipole _at_ 20 m from
IP
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Ion Ring Beam envelopes
FF Quads _at_ about 10 m, sx,y 2-3 mm
Very forward tagging?
Beam-stay-clear area near IP 10-12 s ? 5
cm _at_ 10 m 5 mr Beam-stay-clear area away
from IP 8-10 s ? 2 mm _at_ 20 m 0.1 mr
19
Overview of central detector layout
(not to scale)
Solenoid yoke integrated with a hadronic
calorimeter and a muon detector
Time-of-flight detectors shown in green
Hadronic calorimeter
EM calorimeter
Muon Detector?
EM calorimeter
EM calorimeter
RICH
HTCC
RICH (DIRC?)
ions
Tracking
electrons
DIRC would have thin bars arranged in a cylinder
with readout after the EM calorimeter on the left

• IP is shown at the center, but can be shifted
  left
• Determined by desired bore angle and forward
  tracking resolution
• Flexibility of shifting IP also helps accelerator
  design at lower energies (gap/path length
  difference induced by change in crossing angle)

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Detector/IR - Kinematics

• Vertical lines at 30 (possibly up to 40)
  indicate transition from central barrel to
  endcaps
• Horizontal line indicates maximum meson momentum
  for p/K separation with a DIRC

Q2 gt 10 GeV2

• With 12 GeV CEBAF, MEIC_at_JLab has the option of
  using higher electron energies
• DIRC no longer sufficient for p/K separation

• RICH based on ALICE design might push the limit
  from 4 to 7 GeV
• Requires a more detailed study

• RICH would extend the minimum diameter of
  solenoid from approximately 3 to 4 m
• Main constraint since bore angle is not an issue
  in JLab kinematics

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Detector/IR Particle Momenta
SIDIS p
1H(e,ep)n
4 on 60
11 on 60


Need Particle ID for p gt 4 GeV in central
region ? DIRC wont work, need more space for
RICH Need Particle ID for well above 4 GeV in
forward region (lt 30o?) ? determines bore of
solenoid In general region of interest up to 10
GeV/c mesons (not including very-forward angle
detection, see later)
22
Detector/IR Magnetic Fields
Pion momentum 5 GeV/c, 4T ideal solenoid field

• Resolution dp/p (for pions) better than 1 for p
  lt 10 GeV/c
• obtain effective 1Tm field by having 100 mr
  crossing angle
• 200 mr 12o gives effective 2Tm field
• ? need to add 1-2Tm dipole field for small-angle
  pions (1o-6o) only

Add 2Tm transverse field component to get dp/p
roughly constant vs. angle
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Detector/IR cartoon
Make use of a 100 mr crossing angle for ions!
(approximately to scale)
detectors
solenoid
ion FFQs
ion dipole w/ detectors
ions
IP
0 mrad
electrons
electron FFQs
100 mrad
23 m
2 m
2 m
0.2 - 2.5
4 on 30 GeV Q2 gt 10 GeV2

• Downstream dipole on ion beam line has several
  advantages
• No synchrotron radiation
• Electron quads can be placed close to IP
• Dipole field not determined by electron energy
• Positive particles are bent away from the
  electron beam
• Long recoil baryon flight path gives access to
  low -t
• Dipole does not interfere with RICH and forward
  calorimeters
• Excellent acceptance (hermeticity)

recoil baryons
exclusive mesons
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Detector/IR Forward Angles
t Ep2Q2 ? Angle recoil baryons t½/Ep
Example map t between tmin and 1 (2?) GeV ?
0.2 to 4.9 (9.8) degrees _at_ 12 GeV ? 0.2 to 3.0
(5.9) degrees _at_ 20 GeV ? 0.2 to 2.0 (3.9)
degrees _at_ 30 GeV

• Cover between about 0.5 and 6 degrees?

Example I separation between 0.5o and 0.2o
(BSC) 2.5 cm at 5 meter distance May be
enough for 30 GeV protons and neutrons from
an O(1A) beam (also need good angle (t)
resolution!) Example II 6 degrees 0.5 meter
radius cone at 5 meter
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Detector/IR Forward Angles
t Ep2Q2 ? Angle recoil baryons t½/Ep
Ep 12 GeV
Ep 30 GeV
Ep 60 GeV
DQ 1.3
DQ 5

• Must cover between 1 and 5 degrees
• Should cover between 0.5 and 5 degrees
• Like to cover between 0.2 and 7 degrees

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Detector/IR Very Forward

• Ion Final Focusing Quads (FFQs) at 7 meter,
  allowing ion detection down to 0.5o before the
  FFQs
• Use large-aperture (10 cm radius) FFQs to detect
  particles between 0.3 and 0.5o (or so) in few
  meters after ion FFQ triplet
• sx-y _at_ 12 meters from IP 2 mm
• 12 s beam-stay-clear ? 2.5 cm
• 0.3o (0.5o) after 12 meter is 6 (10) cm
• ? enough space for Roman Pots
• Zero-Degree Calorimeters
• Large dipole bend _at_ 20 meter from IP (to correct
  the 100 mr ion horizontal crossing angle) allows
  for very-small angle detection (lt 0.3o)
• sx-y _at_ 20 meters from IP 0.2 mm
• 10 s beam-stay-clear ? 2 mm
• 2 mm at 20 meter is only 0.1 mr
• D(bend) of 29.9 and 30 GeV spectators is 1.3 mr
  5 mm _at_ 4 m
• Situation for zero-angle n detection very
  similar as at RHIC!

27
Forward Neutron Detection Thoughts A Zero
Degree Calorimeter
The RHIC Zero Degree Colorimeters arXivnucl-ex/0
008005v1
Context The RHIC ZDCs are hadron calorimeters
aimed to measure evaporation neutrons which
diverge by less than 2 mr from the beam axis.
lt2 mr at 18 meters from IP ? neutron cone 4
cm ZDC 10 cm (horizontal) x 13 cm
(vertical) ( 40 cm thick)
Have good efficiency and only 1 cm dead-edge
(albeit not very good DE resolution).
Implication do not make earlier ion bend
dipole strong lt 2 TM!
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EIC Overview - Summary

• Near-term design concentrates on parameters that
  are within state-of-the-art (exception small
  bunch length small vertical b for proton/ioan
  beams)
• Detector/IR design has concentrated on
  maximizing acceptance for deep exclusive
  processes and processes associated with
  very-forward going particles
• Exact energy/luminosity profile still a work in
  progress
• Summer 2010 MEIC design review followed by
  internal cost review (and finalizing input from
  user workshops)
• Many parameters related to the detector/IR
  design seem to be well matched now (crossing
  angles, magnet apertures/gradients/peak fields,
  field requirements), such we may end up with not
  too many blind spots.

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Appendix
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Proton Tagging

• 100 mr horizontal crossing angle for ion beam
  would require large 40Tm magnet at 20 meter from
  the IP. If so, can need this for spectator proton
  tagging
• D(bend) 30 GeV vs. 29.9 GeV 1.3 mr
• If roman pots after 4 m ? 5 mm bend
• 1 (300 MeV/c) would become 15 mm

• Roman pots (photos at CDF (top) and LHC (bottom),
  ) 1 mm from beam achieve proton detection with
  lt 100m resolution
• Proton tagging concept looks doable, even if the
  horizontal crossing angle was reduced by a factor
  of two or three.

31
Neutron Tagging
The RHIC Zero Degree Colorimeters arXivnucl-ex/00
08005v1

• EIC_at_JLab case 40 Tm bend magnet at 20 meters
  from IP ?very comparable to above RHIC case!
• 40 Tm bends 60 GeV protons with 2 times 100 mr
• deflection _at_ a distance of about 4 meters 80
  cm (protons)
• no problem to insert Zero Degree Calorimeter in
  this design

• Zero Degree Calorimeter properties
• Example for 30 GeV neutrons get about 25
  energy resolution (large constant term due to
  unequal response to electrons and photons
  relative to hadrons)
• ? Should be studied more whether this is
  sufficient
• Timing resolution 200 ps
• Very radiation hard (as measured at reactor)

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(M)EIC_at_JLab Where we are
x Q2/ys
HERA experience Can map between y 0.8 and y
0.004
_at_ s 1200 x 0.8 12 (W2 4) lt Q2 lt 640 _at_
s 2640 Q2 1 down to x 4.7x10-4
Note for deuteron Z/A 0.5 for heavy ion Z/A
0.4

• Design provides excellent luminosity for s
  1000
• Good luminosity (1033 or more???) down to s
  240 and up to s 2640
• 
  (can access gluons down to x 0.001 or so)

33
CTEQ Example at Scale Q2 10 GeV2
Gluon splitting dominates
dip in u,d pdfs at x 0.01 (_at_ Q2 10 GeV2)
34
The Venerable (Nuclear) EMC Effect
EMC Effect
F2A/F2D
10-4 10-3 10-2 10-1
1

x
x lt (5 times 10-3) for saturation in shadowing to
start? Need about decade in Q2 to verify LT vs.
HT of effects ? want to push down to x 0.0005
(_at_ Q2 1) w. MEIC.
Space-Time Structure of Photon
Ecm 10 45 (s 100 2000) is in the right
ballpark for nucleon/nuclear structure studies
35
What Ecm and Luminosity are needed for Deep
Exclusive Processes?

• New Roads
• r and f Production give access
• to gluon GPDs at small x (lt0.2)
• Deeply Virtual Meson
• Production _at_ Q2 gt 10 GeV2

Well suited processes for the EIC ? transverse
spatial distribution of gluons in the
nucleon
Can we do such measurements at fixed x in the
valence quark region? Important to disentangle
flavor and spin
fixed x s s/Q2 (Mott) x 1/Q4 (hard gluon
exchange)2
s L Q2 reach DVCS Q2 reach (e,ep)
12-GeV 21 1035 7 7
EIC example 1000 3 x 1034 100 17
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Relaxed IR Optics (electrons)
Natural Chromaticity ?x -96 ?y
-444
37
MEIC Layout