Transcript Polarized Positrons at a Linear Collider and FFTB (SLAC E-166) Abstract Polarized positrons in addition to polarized electrons are a highly desirable feature.

Polarized Positrons at a Linear Collider
and FFTB (SLAC E-166)
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.
A.W. Weidemann, University of South Carolina, Columbia, SC 29208, USA
For the E-166 Collaboration*
At LC:
At
FFTB:
Motivation
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 (sin2θW )
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
Can’t do without positron polarization
E-166
• 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. 2005
•
•
•
Undulator
Table 3: FFTB Helical Undulator System Parameters
Parameter
Number of Undulators
Length
Inner Diameter
Period
Field
Undulator Parameter, K
Current
Peak Voltage
Pulse Width
Inductance
Wire Type
Wire Diameter
Resistance
Repetition Rate
Power Dissipation
T/pulse
Units
m
mm
mm
kG
Amps
Volts
s
H
mm
ohms
Hz
W
0
C
Value
1
1.0
0.89
2.4
7.6
0.17
2300
540
30
0.9x10-6
Cu
0.6
0.110
30
260
2.7
Ec10  24  MeV 
dN
dL

Parameter
Units
TESLA* NLC
E-166
GeV
150-250
150
50
Beam Energy, Ee
10
9
10
3x10
8x10
1x10
Ne/bunch
2820
190
1
Nbunch/pulse
Hz
5
120
30
Pulses/s
planar
helical
helical
Undulator Type
1
1
0.17
Undulator Parameter, K
cm
1.4
1.0
0.24
Undulator Periodu
MeV
9-25
11
9.6
1st Harmonic Cutoff, Ec10
photons/m/e
1
2.6
0.37
dN/dL
m
135
132
1
Undulator Length, L
Ti-alloy Ti-alloy Ti-alloy, W
Target Material
r.l.
0.4
0.5
0.5
Target Thickness
%
1-5
1.8†
0.5
Yield
%
25
20
Capture Efficiency
8.5x1012 1.5x1012
2x107
N+/pulse
3x1010
8x109
2x107
N+/bunch
%
40-70
40-70
Positron Polarization
*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.
E
e
50 GeV 
u  mm 1  K 2 
2
 9.6 MeV
Polarimetry
Photon Transmission Polarimetry:


 comp 
 phot   comp   pair
 0  P Pe  P
30.6
K2
photons / m / e  0.37 photons / e
u  mm 1  K 2
Measure Asymmetry d (when changing Iron Magnetization;
Pe  0.07
Pe=7% ); analysing Power A (from calculation, Geant3;
Pe / Pe  0.05
energy / number weighted), P(gamma)= d / (Pe * A)
!
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/)
More Information: http://www.slac.stanford.edu/exp/e166
Table 1: TESLA, NLC/USLCSG, E-166 Polarized Positron Parameters
Positron Polarimetry:Two-Step:
Photon Number Spectrum
Photon Polarization
Spectrum
Positron polarization (blue),
energy spectrum (red histogram
Work supported by the U.S. Department of Energy under contract DE-AC03-76SF00515(SLAC) and grant DE-FG02-95ER40910.
-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
[email protected]