1. Update on JLEIC Interaction Region Design
V.S. Morozov
on behalf of the JLEIC detector study group
JLEIC Collaboration Meeting, JLab
October 5-7, 2016
F. Lin

2. Detector Region Design Ingredients
Detector requirements (Interaction Region session)
Acceptance
Large detector space
Forward tagging
Emittance (Beam Cooling session)
Background
Dynamic requirements (Beam Dynamics session)
Magnet strengths
Optical integration
Magnet multipoles
Non-linear dynamics
Chromaticity compensation
Dynamic aperture
(Simulation Studies session)
Geometric integration (Machine Design sessions)
Crossing angle
Matched beam-line footprints
IR magnet dimensions (Superconducting Magnets session)
Ring geometry decoupled from IR design

3. IR & Detector Concept
Ion beamline
Electron beamline
Possible to get ~100% acceptance for the whole event
Central Detector/Solenoid
Dipole
Forward (Ion) Detector
Scattered Electron
Particles Associated
with Initial Ion
Particles Associated with struck parton
Courtesy of R. Yoshida

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
P. Nadel-Turonski, R. Ent, C.E. Hyde

5. Optimized Ion IR *x,y = 10 / 2 cm, D* = D* = 0
Three spectrometer dipoles (SD)
Large-aperture final focusing quadrupoles (FFQ)
Secondary focus with large D and small D
Dispersion suppressor geometric match
geom. match/
disp. suppression IP
SD1
SD2
SD3
FFQ
~14.4 m
4 m
D = 0, D’ = 0
D’ ~ 0
forward detection
x , y < ~0.6 m
middle of straight
limit x and y

6. Optimized Detector Region Geometry
Overall geometry fixed: the beam position and angle at the end point are the same as in the earlier version
e beam
i beam
2nd spectrometer dipole
56 mrad ( GeV)
“3rd” spectrometer dipole
-56 mrad ( GeV)
length of this straight
controls overall length
controls overall height
Three dispersion-suppression/
geometry-control dipoles
|56 mrad| ( GeV)
cannot be much smaller
geometrically fixed point

7. Baseline Electron IR Optics
IR region (baseline, has been slightly optimized since)
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

8. Forward e- Detection & Pol. Measurement
Dipole chicane for high-resolution detection of low-Q2 electrons
Compton polarimetry has been integrated to the interaction region design
same polarization at laser as at IP due to zero net bend
non-invasive monitoring of electron polarization 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

9. Detector Region Layout
GEANT4 detector model developed, simulations in progress IP e-
Compton polarimetry
forward ion detection
ions
forward e- detection
dispersion suppressor/
geometric match
spectrometers
Forward hadron spectrometer
low-Q2 electron detection
and Compton polarimeter p
(top view in GEANT4) e
ZDC

10. JLEIC 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

11. 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) 11

12. Far-Forward Ion Acceptance
Transmission of particles with initial angular and p/p spread
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)
More accurate simulations are in progress
6 T max
 electron beam 12

13. Far-Forward Ion Acceptance for Neutrals
Transmission of neutrals with initial x and y angular spread
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
 electron beam 13

14. 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 14

15. 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 15

16. Parameter Choice
Impact of * and  on luminosity and detector acceptance
Luminosity
Smaller * and   higher luminosity
nx,y = 1 / 0.5 m  0.5 / 0.1 m  a factor of 3 increase in L
*x,y = 10 / 2 cm  6 / 1.2 cm  another factor of 1.7 increase in L
Fundamental limit on detector angular acceptance
nx,y = 1 / 0.5 m, *x,y = 10 / 2 cm  min > 3-5 mrad at 100 GeV/c
nx,y = 1 / 0.5 m  0.5 / 0.1 m  a factor of reduction in min
*x,y = 10 / 2 cm  6 / 1.2 cm  a factor of 1.3 increase in min

17. Parameter Choice
Fundamental limit on momentum acceptance at the secondary focus
Roman pot at the secondary focus has finite length l , therefore where sx is the  function at the secondary focus
Smaller x  smaller (p/p)min
Optimum is when sx = l / 2 (similar to the hour-glass effect)
Currently, sx ~ 0.6 m, it changes proportionally to *x
In our case, the beam size is dominated by Dx , changes in *x and sx have very little effect
Assume l = 2 m, nx = 1 m, sx = 0.6 m, Dx = 1 m,  = 5 10-4  (p/p)min > 510-3

18. Ion Beam Envelope & 99%p Trajectory
Assuming beam momentum of 100 GeV/c, ultimate normalized x/y emittances xN/yN of 0.35/0.07 m, and ultimate momentum spread p/p of 310-4
The horizontal size includes both betatron and dispersive components
2nd focus IP

19. 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)
Detailed simulations are in progress

20. Addition of 2nd Detector Region
Design of the 2nd IR can be tailored to experimental needs
Adding 2nd IR in the 2nd straight
Electron beam line geometry does not change
Beam crossing produced by shaping the ends of ion arcs e-
ions IP

21. Summary & Outlook
Detector region design is fairly complete from the accelerator integration point of view
Most detector optimization does not affect the beam dynamics significantly
Ongoing work
Quantification of detector performance
Background simulations
Need to better define
Solenoid compensation elements
Orbit diagnostics and correction elements in the detector region
Engineering parameters of detector region magnets