Polarized Positrons at a Linear Collider and FFTB (SLAC E-166)A.W.Weidemann, University of South Carolina, Columbia, SC 29208, USAFor the E-166 Collaboration*More Information: http://www.slac.stanford.edu/exp/e166 Work supported by the U.S. Department of Energy under contract DE-AC03-76SF00515(SLAC) and grant DE-FG02-95ER40910. achim@SLAC.Stanford.EDU Motivation Polarimetry E-166 uses the 50 GeV SLAC beam + 1 m-long, helical undulator to make polarized ~10MeV photons in the FFTB. These photons are converted in a ~0.5 rad.len. thick target into polarized positrons (and electrons). (~50% Pol. expected) The polarization of the positrons and photons will be measured. Installing now, run Oct. 2004, Jan. 2005At LC:At FFTB:Abstract Polarized positrons in addition to polarized electrons are a highly desirable feature of future linear e+e- colliders. The motivation for polarized positrons, and a demonstration experiment now under way - for the undulator-based production of polarized positrons are reviewed.Undulator Electroweak processes e+e- -> WW, Z, ZH ouple Only to e-Le+R or e-Re+L (NOT e-Le+L or e-e+R). Can double or suppress rate -Effective polarization enhanced, error decreased, in electroweak asymmetry measurements, (NL NR) / (NL + NR) = Peff ALR, Peff = (P- - P+) / (1 P-P+).-Improved accuracy in polarization measurement (Blondel scheme)Must have both e+ and e- polarization for Giga-Z project (sin2W )SUSY Slepton and squark produced dominantly via eR e+L (not eR eR or e LeL) Separation of the (LL, LR) selectron pair with longitudinally polarized beams to test association of chiral quantum numbers to scalar fermions in SUSY :With P(e-)= -80% and:P(e+)= 0% => no separation!P(e+)= -40% => 163fb vs 66 fb Cant do without positron polarization!Transverse polarization of both beams allows separation of new physics, e.g. extra dimensions.More examples in JLC, TESLA TDRs, Reviews, e.g. by G. Moortgat-Pick, (POWER [Polarizationat Work..) http://www.ippp.dur.ac.uk/~gudrid/power/)E-166Photon Transmission Polarimetry:Measure Asymmetry d (when changing Iron Magnetization; Pe=7% ); analysing Power A (from calculation, Geant3; energy / number weighted), P(gamma)= d / (Pe * A) Photon Number SpectrumPhoton Polarization SpectrumPositron polarization (blue), energy spectrum (red histogram Positron Polarimetry:Two-Step:-Convert e+ ->photon (brems/annihilation);-Polarization Transfer e+ to photon well-known-Measure photon polarization as above.Expect sys. Error del(P)/P of~ 5% dominated by eff Magnetization of Iron.Detectors:Si/W Calorimeter; Aerogel Cerenkov, CsI Calorimeter

Table 1: TESLA, NLC/USLCSG, E-166 Polarized Positron Parameters

Parameter

Units

TESLA*

NLC

E-166

Beam Energy, Ee

GeV

150-250

150

50

Ne/bunch

-

3x1010

8x109

1x1010

Nbunch/pulse

-

2820

190

1

Pulses/s

Hz

5

120

30

Undulator Type

-

planar

helical

helical

Undulator Parameter, K

-

1

1

0.17

Undulator Periodu

cm

1.4

1.0

0.24

1st Harmonic Cutoff, Ec10

MeV

9-25

11

9.6

dN/dL

photons/m/e-

1

2.6

0.37

Undulator Length, L

m

135

132

1

Target Material

-

Ti-alloy

Ti-alloy

Ti-alloy, W

Target Thickness

r.l.

0.4

0.5

0.5

Yield

%

1-5

1.8

0.5

Capture Efficiency

%

25

20

-

N+/pulse

-

8.5x1012

1.5x1012

2x107

N+/bunch

-

3x1010

8x109

2x107

Positron Polarization

%

-

40-70

40-70

*TESLA baseline design; TESLA polarized e+ parameters (undulator and polarization) are the same as for the NLC/USLCSG

Including the effect of photon collimation at = 1.414.

Table 3: FFTB Helical Undulator System Parameters

Parameter

Units

Value

Number of Undulators

-

1

Length

m

1.0

Inner Diameter

mm

0.89

Period

mm

2.4

Field

kG

7.6

Undulator Parameter, K

-

0.17

Current

Amps

2300

Peak Voltage

Volts

540

Pulse Width

s

30

Inductance

H

0.9x10-6

Wire Type

-

Cu

Wire Diameter

mm

0.6

Resistance

ohms

0.110

Repetition Rate

Hz

30

Power Dissipation

W

260

T/pulse

0C

2.7