LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 1 Polarimeter Studies for TESLA O General Considerations O Compton Polarimetry O The TDR Baseline Compton Polarimeter O Downstream (Extraction Line) Studies Polarimeter Concept for NLC Beam-Beam Depolarization Effects

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 2 Spin Motion Spin vector must be vertical in the damping ring Spin Rotator in the transfer line to the linac: manipulate spin direction for any desired orientation at the experiment must compensate all technical spin rotation effects along the machine requires fast polarimeter at the high-energy end for efficient tune-up

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 3 Spin motion along the accelerator

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 4 Suitable Polarimeter Locations most favorable upstream location: z = m  can use beam line magnets as spectrometer elements  has excellent infrastructure for polarimetry

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 5 Alignment Tolerances Beam-Beam Effects  tight, but within machine tolerances  estimated depolarization:  0.25%  upstream polarimetry should be ok 

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 6 Compton Polarimetry Kinematics

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 7 Compton Polarimetry Cross Sections, Spin Asymmetries - 1 < P < < < + 1

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 8

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 9 The TDR Baseline Compton Polarimeter Layout of the configuration

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 10 luminosity for pulsed lasers ( with finite laser crossing angle)

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 11 Laser parameters laser schematic of TTF injector gun: operates at nominal pulse &  -bunch pattern of TESLA

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 12 Laser for TTF injector gun S. Schreiber et al. NIM A 445 (2000) 427  t = 8 ps

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 13 electron detector: gas Cerenkov calibration scheme (proposed)

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 14 The Ellerhoop Campus The TDR Baseline Compton Polarimeter

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 15 The TDR Baseline Compton Polarimeter Summary table For details: V. Gharibyan, N. Meyners, K.P. Schüler, LC-DET

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 16 Downstream (Extraction Line) Studies for TESLA single beam polarimetry:  feasible beam-beam polarimetry:  impossible for TESLA at zero crossing angle issues to address:  laser beam topology  detector location  degraded beam halo

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 17 Downstream (Extraction Line) Studies

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 18 Downstream ( Extraction Line ) Studies: Laser Beam Topology 9 90° 100 mrad Laser (100 mrad) Laser (90°)

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 19 Downstream (Extraction Line) Studies Detector at z = 65 m

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 20 Downstream (Extraction Line) Studies 250 GeV nominal disrupted beam: events from N. Walker, distributions at e+e- IP

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 21 Downstream (Extraction Line) Studies Extrapolated background For standard 20 mm x 20 mm collimator aperture

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 22 Downstream (Extraction Line) Studies green laser, head-on collision

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 23 Conclusions TDR Baseline Polarimeter (630 m upstream)  Precision of 0.5% should be straightforward, 0.25% may be possible with corrections  Works equally well for e- and e+  Excellent infrastructure, robust facility  Very fast Downstream (Extraction Line) Studies  Single beam polarimetry appears feasible  Disrupted beam polarimetry is impossible for TESLA beam extraction (with zero crossing angle geometry)

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 24

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 25 Beam-Beam Depolarization: Kathleen Thompson: SLAC-PUB-8761 (Jan. 2001) (see also Yokoy & Chen: SLAC-PUB-4692) NLC-500: outgoing e- depolarization: BMT ST TOTAL BMT ST TOTAL (analytic results) (simulation results) NLC-A 0.6% 0.4% 1.1% 0.4% 0.5% 0.9% NLC-B 0.8% 0.4% 1.1% 0.5% 0.4% 0.9% NLC-C 0.9% 0.3% 1.1% 0.5% 0.3% 0.9% NLC-500: luminosity-weighted e- beam depolarization: BMT ST TOTAL BMT ST TOTAL (analytic results) (simulation results) NLC-A 0.2% 0.1% 0.3% 0.1% 0.1% 0.2% NLC-B 0.2% 0.1% 0.3% 0.1% 0.1% 0.2% NLC-C 0.2% 0.1% 0.3% 0.1% 0.1% 0.2%  P (downstream)  4 x  P (lumi-weighted)  Upstream value is much closer to lumi-weighted polarization!

LCWS Paris – April 19-23, 2004 Polarimeter Issues K. Peter Schüler Polarimeter Issues 26 Summary on beam-beam effects Upstream polarimeter expected to measure  0.2% higher than lumi-weighted value Downstream polarimeter expected to measure  0.9% lower than upstream, and  0.7% lower than lumi-weighted value upstream vs downstream polarimetry Therefore, for the typical case with both beams interacting, an upstream polarimeter measurement will need less correction. However, only a downstream polarimeter can measure the actual degree of depolarization, by comparison btw interacting and non-interacting (single beam) bunch data.