1. MEIC Interaction Region & Tagging
V.S. Morozov1, P. Brindza1, A. Camsonne1, Ya.S. Derbenev1, R. Ent1, D. Gaskell1, F. Lin1, P. Nadel-Turonski1, M. Ungaro1, Y. Zhang1, Z.W. Zhao1,2, C.E. Hyde2, K. Park2, M. Sullivan3
1JLab, 2ODU, 3SLAC
High Energy Nuclear Physics with Spectator Tagging
Old Dominion University, March 10, 2014
F. Lin

2. Outline Detector concept Detector integration Forward ion tagging
Forward electron tagging
Backgrounds
Summary

3. MEIC Layout & Detector Location
Cold Ion Collider Ring
(8 to 100 GeV)
Two IP locations:
One has a new detector, fully instrumented
Second is a straight-through, minor additional magnets needed to turn into IP
Ion Source
Booster
Linac
Warm Electron
Collider Ring
(3 to 10 GeV)
Considerations:
Minimize synchrotron radiation
IP far from arc where electrons exit
Electron beam bending minimized in the straight before the IP
Minimize hadronic background
IP close to arc where protons/ions exit

4. Full-Acceptance Detector
50 mrad crossing angle
Improved detection, no parasitic collisions, fast beam separation
Forward hadron detection in three stages
Endcap
Small dipole covering angles up to a few degrees
Far forward, up to one degree, for particles passing through accelerator quads
Low-Q2 tagger
Small-angle electron detection
R. Ent, C.E. Hyde, P. Nadel-Turonski

5. Detector Modeling & Machine Integration
Fully-integrated detector and interaction region satisfying
Detector requirements: full acceptance and high resolution
Beam dynamics requirements: consistent with non-linear dynamics requirements
Geometric constraints: matched collider ring footprints
far forward
hadron detection
low-Q2
electron detection
large-aperture
electron quads
small-diameter
central detector
with endcaps
ion quads
50 mrad beam
(crab) crossing angle
n, g e p
small angle
~60 mrad bend
(from GEANT4)
2 Tm dipole
Endcap
Ion quadrupoles
Electron quadrupoles
1 m IP FP
Roman pots
Thin exit windows
Fixed trackers
Trackers and “donut” calorimeter
RICH +
TORCH?
dual-solenoid in common cryostat
4 m coil
barrel DIRC + TOF
EM calorimeter
Tracking
e/π threshold
Cherenkov 5

6. Compton polarimetry region
Electron IR Optics
IP region
Final focusing quads with maximum field gradient ~63 T/m
Four 3m-long dipoles (chicane) with GeV for low-Q2 tagging with small momentum resolution, suppression of dispersion and Compton polarimeter IP e-
forward e-
detection region
FFQs
Compton polarimetry region

7. Ion IR Optics IR design features Modular design
Based on triplet Final Focusing Blocks (FFB)
Asymmetric design to satisfy detector requirements and reduce chromaticity
Spectrometer dipoles before and after downstream FFB, second focus downstream of IP
No dispersion at IP, achromatic optics downstream of IP
detector
elements
match/
beam compression IP
match/
beam expansion
geom. match/
disp. suppression
FFB
FFB
ions

8. Integrated Interaction Region & Detector
(top view)
Accelerator view of IR Layout
crab cavities
ions
FFQs
FFQs IP e-
crab cavities
Design emphasis on polarization (figure-8) and on integrated detector/interaction region
Nuclear Physics view of IR Layout
(top view)
central detector
with endcaps
small angle
hadron detection
ultra forward
hadron detection
low-Q2 electron detection
and Compton polarimeter
n,
large aperture
electron quads
ion quads
60 mrad bend p e
small diameter
electron quads e p
Thin exit windows
Fixed trackers
Roman pots
50 mrad beam
(crab) crossing angle

9. EIC Central Detector MEIC-IP1 detector ePHENIX
Focus on exclusive processes and semi-inclusive DIS
With forward dipole/detector constitutes “full-acceptance detector” with ion FFQ at 7 m
Could be based on dual solenoid or CLEO magnet
5 m
3 m
dual-solenoid in common cryostat
4 m inner coil
outer+inner EM cal
π/K Cherenkov
e/π HBD
TOF
(top view)
RICH
aerogel
+ CF4
Coil wall
EM calorimeter
barrel DIRC + TOF
Si-pixel vertex + Si disks
GEM/micromegas central and forward
Forward
dipole
ePHENIX
More focus on jet-physics
Ion FFQ at 4.5 meter consistent with MEIC-IP2 “high-luminosity detector” assumption
Based on BABAR magnet
(approximately to scale)
ePHENIX detector
(side view of top half)

10. Forward Hadron Detection
Large crossing angle (50 mrad)
Moves spot of poor resolution along solenoid axis into the periphery
Minimizes shadow from electron FFQs
Dipole before quadrupoles
Further improves resolution in the few-degree range
Low-gradient quadrupoles
Allow large apertures for detection of all ion fragments
Crossing angle
89 T/m, 9.0 T, 1.2 m
51 T/m, 9.0 T, 2.4 m
36 T/m, 7.0 T, 1.2 m
Permanent magnets
34 T/m
46 T/m
38 T/m
2 x 15 T/m e
5 T, 4 m dipole
Ion quadrupoles: gradient, peak field, length
2 T dipole
Endcap detectors
Electron quadrupoles
Tracking
Calorimetry
1 m
7 m from IP to first ion quad 10

11. Far-Forward Hadron Detection
Good acceptance for ion fragments
Large downstream magnet apertures/ small downstream magnet gradients
Good acceptance for low-pT recoil baryons
Small beam size at second focus
Large dispersion
Good momentum and angular resolution
No contribution from D to angular spread at IP
Long instrumented magnet-free drift space
Sufficient separation between the beam lines
Asymmetric IR (minimizes chromaticity)
Ions x
βx* = cm
βFP < 1 m
DFP ~ 1 m
βy* = 2 cm
D* = D'* = 0 FP IP e p
(n, )
20 Tm dipole (in)
2 Tm dipole (out)
solenoid
Roman pots at focal point
Thin exit windows
Aperture-free drift space
ZDC
S-shaped dipole configuration optimizes acceptance for neutrals
50 mrad crossing angle 11

12. Far-Forward Acceptance for Charged Fragments
Δp/p = -0.5
Δp/p = 0.0
Δp/p = 0.5
(protons rich fragments)
(exclusive / diffractive recoil protons)
(tritons from N=Z nuclei)
(spectator protons from deuterium)
(neutron rich fragments) 12

13. Far-Forward Ion Acceptance
Transmission of particles with initial angular and p/p spread vs peak field
Quad apertures = B max / (fixed field 100 GeV/c)
Uniform particle distribution of 0.7 in p/p and 1 in horizontal angle originating at IP
Transmitted particles are indicated in blue (the box outlines acceptance of interest)
6 T max
9 T max
12 T max
 electron beam 13

14. Far-Forward Angular Ion Acceptance
Quad apertures = 9, 9, 7 T / (By 100 GeV/c), dipole aperture = -30/+50 40 cm
Uniform distribution of 1 in x and y angles around proton beam at IP for a set of p/p
The circle indicates neutrals’ cone
 electron beam
p/p = -0.5
p/p = 0
p/p = 0.5
neutrons 14

15. Far-Forward Ion Acceptance for Neutrals
Transmission of neutrals with initial x and y angular spread vs peak field
Quad apertures = B max / (fixed field 100 GeV/c)
Uniform neutral particle distribution of 1 in x and y angles around proton beam at IP
Transmitted particles are indicated in blue (the circle outlines 0.5 cone)
6 T max
9 T max
12 T max
 electron beam 15

16. Ion Momentum & Angular Resolution
Protons with p/p spread are launched at different angles to nominal trajectory
Resulting deflection is observed at the second focal point
Particles with large deflections can be detected closer to the dipole
 electron beam
±10 @ 60 GeV/c
|p/p| > x,y = 0 16

17. Ion Momentum & Angular Resolution
Protons with different p/p launched with x spread around nominal trajectory
Resulting deflection is observed 12 m downstream of the dipole
Particles with large deflections can be detected closer to the dipole
|x| > 3 p/p = 0
 electron beam
 electron beam
±10 @ 60 GeV/c 17

18. Example: DVCS Recoil Proton Acceptance
Kinematics: 5 GeV e- on 100 GeV p at a crossing angle of 50 mrad.
Cuts: Q2 > 1 GeV2, x < 0.1, E’e > 1 GeV, recoil proton 10σ outside of beam
DVCS generator: MILOU (from HERA, courtesy of BNL)
GEANT4 simulation: tracking through all magnets done using the JLab GEMC package
low-t acceptance
high-t acceptance
p beam at 50 mrad
High-t acceptance limited by magnet apertures
10σ beam size cut:
p < 99.5% of beam for all angles
θ > 2 mrad for all momenta
-t = 1.9 GeV2 ±14 mrad
Proton angle at IP
e- beam at 0 mrad
Recoil proton angle is independent of electron beam energy: θp ≈ pT/Ep ≈ √(-t)/Ep
A wider angular distribution at lower energies makes precise tracking easier
Z.W. Zhao

19. Far-Forward Ion Detection Summary
Neutrals detected in a 25 mrad (total) cone down to zero degrees
Space for large (> 1 m diameter) Hcal + Emcal
Excellent acceptance for all ion fragments
Recoil baryon acceptance:
up to 99.5% of beam energy for all angles
down to at least 2-3 mrad for all momenta
full acceptance for x > 0.005
Resolution limited only by beam
longitudinal p/p ~ 310-4
angular  ~ 0.2 mrad
n, γ
20 Tm dipole
2 Tm dipole p
solenoid e
15 MeV/c resolution for 50GeV/u tagged deuteron beam 19

20. Forward e- Detection & Pol. Measurement
Dipole chicane for high-resolution detection of low-Q2 electrons e-
ions IP
forward ion detection
forward e- detection
Compton polarimetry
local crab cavities
Compton polarimetry has been integrated to the interaction region design
same polarization at laser as at IP due to zero net bend c
Laser + Fabry Perot cavity
e- beam from IP
Low-Q2 tagger for low-energy electrons
Low-Q2 tagger for high-energy electrons
Compton electron
tracking detector
Compton photon
calorimeter
Compton- and low-Q2 electrons are kinematically separated!
Photons from IP
e- beam to spin rotator
Luminosity monitor
A. Camsonne, D. Gaskell

21. Downstream Electron Acceptance
5 GeV/c e-, uniform spreads: -0.5/0 in p/p and 25 mrad in horizontal/vertical angle
Apertures: Quads = 6, 6, 3 T / (By 11 GeV/c), Dipoles = 20 20 cm
ion beam  21

22. Downstream Angular Electron Acceptance
Uniform e- distribution horizontally & vertically within 25 mrad around 5 GeV/c beam
Apertures: Quads = 6, 6, 3 T / (By 11 GeV/c), Dipoles = 20 20 cm
ion beam 
ion beam 
p/p = -0.5
p/p = -0.1
p/p = 0
p/p = -0.25 22

23. Electron Momentum & Angular Resolution
Electrons with p/p spread launched at different angles to nominal 5 GeV/c trajectory
|p/p| > x,y = 0
ion beam 

24. Electron Momentum & Angular Resolution
e- with different p/p launched with x spread around nominal 5 GeV/c trajectory
|x| > p/p = 0
ion beam 

25. IR Quad: permanent magnet and superconducting
Requirements: 39 T/m
3 cm bore inner surface of quad
7 cm max radius of quad structure to clear i-beam tube
P. McIntyre et al., Texas A&M University

26. Synchrotron Radiation Background
Initial electron beam pipe design for evaluating SR
Conclusion: diameter at the vertex tracker could be reduced to mm
Surface: 1 2 3 4 5 6
Power 5 GeV
3.0
5.7
0.2
0.8 -
0.03
g >10 5GeV
5.6x105
3.4x105
1.4x104
5.8x104
167
3,538
Power 11 GeV
4.2
8.0
0.3
1.1
0.04
g >10 11 GeV
2.8x105
9.0x104
3.8x105
271
13,323
Photon numbers are per bunch
Modest synchrotron background
M. Sullivan, SLAC

27. Hadronic Backgrounds
HERA: Strong correlation between detector background rates and beam line vacuum.
 Random background assumed to be dominated by scattering of beam ions on residual gas (mainly H2) in the beam pipe between the ion exit arc and the detector
The conditions at the MEIC compare favorably with HERA
Typical values of s are 4,000 GeV2 at the MEIC and 100,000 GeV2 at HERA
Distance from arc to detector: 65 m / 120 m = 0.54
p-p cross section ratio σ(100 GeV) / σ(920 GeV) < 0.8
Average hadron multiplicity per collision (4000 / )1/4 = 0.45
Proton beam current ratio: 0.5 A / 0.1 A = 5
At the same vacuum the MEIC background is 0.54 * 0.8 * 0.45 * 5 = 0.97 of HERA
But MEIC vacuum should be closer to PEP-II (10-9 torr) than HERA (10-7 torr)

28. Summary & Outlook
Conceptual design of the interaction region completed
Interaction region integrated into collider rings
Forward detection requirements fully satisfied
Ongoing and future work
Detector modeling
Polarimetry development
Design optimization
Engineering design of interaction region magnets
Systematic investigation of non-linear dynamics
Development of beam diagnostics and orbit correction scheme