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

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

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

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

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

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 (4.7 T @ 100 GeV) “3rd” spectrometer dipole -56 mrad (4.7 T @ 100 GeV) length of this straight controls overall length controls overall height Three dispersion-suppression/ geometry-control dipoles |56 mrad| (4.7 T @ 100 GeV) cannot be much smaller geometrically fixed point

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 0.44 T @ 10 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

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

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

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

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

Far-Forward Ion Acceptance Transmission of particles with initial angular and p/p spread Quad apertures = B max / (fixed field gradient @ 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

Far-Forward Ion Acceptance for Neutrals Transmission of neutrals with initial x and y angular spread Quad apertures = B max / (fixed field gradient @ 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

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| > 0.005 @ x,y = 0 14

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 mrad @ p/p = 0  electron beam  electron beam ±10 @ 60 GeV/c 15

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 0.5-0.7 reduction in min *x,y = 10 / 2 cm  6 / 1.2 cm  a factor of 1.3 increase in min

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

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

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 / 100000)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

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

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