K. Moffeit 6 Jan 2005 WORKSHOP Machine-Detector Interface at the International Linear Collider SLAC January 6-8, 2005 Polarimetry at the ILC Design issues and measurement strategy Ken Moffeit SLAC

K. Moffeit 6 Jan 2005 Layout of the ILC TESLAUS Option

K. Moffeit 6 Jan 2005 Spin Precession Change in spin direction for various bend angles and the projection of the longitudinal polarization. Electron beam energy is 250 GeV. Change in Bend AngleChange in Spin Direction Longitudinal Polarization Projection 1 mrad32.5 o 84.3% 275  rad 8.9 o 98.8% 100  rad 3.25 o 99.8%

K. Moffeit 6 Jan 2005 Extraction Line Beam Properties Angular divergences of the incoming and outgoing disrupted beams for ILC collision parameters. BMT depolarization due to the angular divergences. Parametere+e-e+e-  (  x ) in 35  rad  (  y ) in 10  rad  (  x ) out 275  rad  (  y ) out 55  rad (  P BMT ) IP 1.2 %

K. Moffeit 6 Jan 2005 Summary of Expected Depolarization Effects for the ILC Design Note: 1.In the NLC design, there was an additional 1% depolarization from the 180 o turn around at 8 GeV (not present in the current ILC design). 2.Need to revisit spin-flip calculation. RegionLuminosity-weighted Depolarization Injector<0.1% Damping Ring<0.1% Compressor and Pre-Linac Linac<0.1% Beam Delivery<0.1% Beam orbit jitter<0.1% IP incoming Beam divergence<0.1% IP disrupted beam divergence0.3% Spin-flips from collisions~0.1% TOTAL~0.4%

K. Moffeit 6 Jan 2005 Important Design Considerations Common for upstream and downstream polarimeters Beam size at Compton IP (<100  m) Direction of beam at Compton IP is the same as at the Detector IP (<50  rad) Dedicated Chicanes for both upstream and downstream polarimeters (~50 meters in length) Upstream Polarimeter Compton IP before energy slit (to avoid backgrounds in the Physics Detector from low energy Compton electrons) Downstream polarimeter Compatible with the energy spectrometer Design exist for 20 mrad crossing angle at e+e- IP Create design for 2 mrad crossing angle? Backgrounds from beam-beam collisions (0.75 to 1 mrad beam stay clear) Positron polarization or e-e- option Plan for polarimeters in both beam lines

K. Moffeit 6 Jan 2005 Crossing Angle Direction of beam at Compton IP is the same as at the Detector IP (<50  rad) Simultaneous running of 2 IRs and spin orientation selected for each IR Not possible to change spin orientation train to train with the spin rotation solenoids Use spin precession to find energies for  spin rotation with 11 mrad between beam direction at two IRs For  =11mrad spin direction changes by  every GeV Both IR 1 and IR 2 will have longitudinal polarization at energies: GeV and GeV At these energies you can switch beams train to train between the two IRs and have longitudinal polarization at both.

K. Moffeit 6 Jan 2005 Layout of the Beam Delivery System to two Interaction Regions with Crossing Angles IR-1 and IR-2 Requires locations for upstream Compton Polarimeters with beam direction within 50  rad of that at the IP. Upstream Polarimeter before energy slit Mark Woodley ref talk IR2 IR1 Energy SlitPolarimeter Chicane

K. Moffeit 6 Jan 2005 Upstream Polarimeter Design Issues Direction of beam at Compton IP is the same as at the Detector IP (<50  rad) Laser beam access to Compton IP Measure laser polarization near Compton IP Measure Compton Scattered electrons (Energy ~25 GeV) Momentum analyzed Detected with a segmented gas Cerenkov Counter Tesla design vs Chicane design?

K. Moffeit 6 Jan 2005 Tesla Design Minimal space and no special magnets required Need to change laser wavelength for z-pole running

K. Moffeit 6 Jan 2005 Dedicated Upstream Polarimeter Chicane Requires ~50 meters length Same B-field at Z-pole, 250 GeV and 500 GeV running Same magnet design as for upstream energy chicane Good acceptance of Compton Spectrum at all energies without changing laser wavelength

K. Moffeit 6 Jan 2005 Extraction Beam Line Optics Yuri Nosochkov: Extraction Line for 20mrad Crossing Angle IR Energy Chicane Compton IP

K. Moffeit 6 Jan 2005 Extraction Line Polarimeter Elements Energy Chicane and Polarimeter Chicane Separate

K. Moffeit 6 Jan 2005 Polarimeter Chicane Plan View

K. Moffeit 6 Jan 2005 Measurement of Polarization with Compton Gammas Requires: Quadrupole after Chicane off Single beam running 1 mrad beam stay clear ½ mrad beam stay clear

K. Moffeit 6 Jan 2005 Running at different beam energies Z-pole Running 250 GeV

K. Moffeit 6 Jan 2005 Detector Options Segmented Gas Cherenkov Detector Propane Gas or C 4 F 10 Gas (nonflammable) Threshold ~10 MeV (good for reducing backgrounds from synchrotron radiation and low energy electrons Other Detector Schemes Quartz detector Threshold ~200keV Greater flexibility for small channel width (may be useful for upstream polarimeter) Simple detector Other

K. Moffeit 6 Jan 2005 Laser System Options Collide every bunch (for possible upstream choice) (complex) Low Rate high power Laser similar to SLC (probably required downstream); 5Hz laser can have timing varied to scan thru all bunches in train (simple) Resonate cavity—HERA (very complex) e + /e - beamUpstream Laser beam Downstream Laser Beam Energy250 GeV2.3 eV Charge or energy/bunch  J 100 mJ Bunches/sec Bunch length  t 1.3 ps10 ps1 ns Average current (power) 45  A 0.5 W  x.  y (  m) upstream downstream

K. Moffeit 6 Jan 2005 Compton Polarimeter Parameters at 250 GeV (cont.) Upstream PolarimeterDownstream Polarimeter Beam crossing angle10 mrad11.5 mrad Luminosity cm -2 s cm -2 s -1 Event rate at 25 GeV endpoint 300,000/GeV/sec10,000/GeV/sec  P/P stat. error <1% / sec< 1% / min  P/P syst. error <0.5% Requirements on measurement times for 0.25% stat error? for sqrt(s)=500 GeV, 0.25% per week/month? for Z-pole, 0.25% per day/week? for systematic studies, 0.25%/hour useful?

K. Moffeit 6 Jan 2005 Fabry-Perot Cavity at HERA

K. Moffeit 6 Jan 2005 Backgrounds and Collimation Need to study Synchrotron radiation backgrounds from bends and quads Low energy disrupted electrons Beam gas Beam dump backsplash

K. Moffeit 6 Jan 2005 Summary Accelerator design issues –Location of polarimeters –Downstream polarimeter may be difficult for e+e- 2 deg crossing angle –No net bend angle in e- beam direction at Compton IP and e- direction at e+e- IP –Positron polarization or e- e- needs polarimeters in both beam lines Polarimeter design issues –Laser + optics (5 to 10 hz high power al la SLC, every bunch-TESLA design, resonate cavity--HERA) –Detectors: Gas Cherenkov, Quartz Cherenkov Beam test needs before TDR –Nothing stands out