Polarisation at

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Polarisation at Linear Colliders
Achim Stahl Zeuthen 15.Oct.03
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Polarisation at Linear Colliders
Contents

• Physics Motivation
• Polarisation Measurement
• Creation of Polarised Beams

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Definitions
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4 Beam Configurations

• Unpolarised Beams
• Long. Polarisation Electrons only
• Long. Polarisation Both Beams
• Transverse Polarisation

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QM States
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Physics Motivation
Understanding Matter, Energy, Space and Time
http//blueox.uoregon.edu/lc/wwwstudy/
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Electron Polarisation
TDR assumes polarised electron beam (80 )
Higgs-W coupling from
For mH 120 GeV
? on gHWW
no pol. 2.8
e- pol. 0.8
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Positron Polarisation I
known
to be discovered


eL eR eL eR
µL µR µL µR

but which is which ?
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Positron Polarisation I
J 1
eL
J 0,1
e-L
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Positron Polarisation II
Giga Z option needs positron polarisation
109 Z0 in 100 days sin2?eff from ALR ?sin2?eff
10-5 ?ALR 8 10-5
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Positron Polarisation II
needs ?P/P 10-4
Positron
Elektron
4 Measurements 4 Unknown ?L, ?R, P, P-
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Positron Polarisation II
Klaus Mönig
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Positron Polarisation III
gravitons into extra dimensions ee- ? G
? main background ee- ? ? ? ?
enhance signal suppress background
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Positron Polarisation III
enhance signal suppress background
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Positron Polarisation IV
effective polarisation
for any s-channel J1 process
? (1 PP-) ?0 ( 1 Peff ALR)
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Positron Polarisation
effective polarisation in contact
interactions (by Sabine Riemann)
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Transverse Polarisation
transverse asymmetry indicate Spin-2 exchange
trans. polarisation asymmetries need both beams
polarised
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Transverse Polarisation
Triple Gauge Couplings trans. asym. dominated by
WLWL
trans. polarisation asymmetries need both beams
polarised
Jegerlehner / Fleischer / Kolodziej
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Precision Polarimetry
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Phys. Processes for Polarimetry
e Nucleon spin-orbital mom. coupling measures
trans. pol. energy 1 MeV
Mott Scattering
e e polarised iron foils destructive
measurement cross check _at_ LC
Møller Scattering
e ? polarised laser target non-invasive main
polarimeter _at_ LC
Compton Scattering
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Møller Polarimeter
JLab 1 6 GeV 1.4
E143 16/29 GeV 3.7
SLD 45 GeV 4.2
TESLA 250 GeV 1.0
JLab Polarimeter
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Compton Polarimeter
pol. Laser
electron beam
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Compton Polarimeter
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Compton Polarimeter
main beam

• large ?-background near beam
• Cerenkov detectors only
• sensitive to electrons
• light guides allow PMT behind
• schielding

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Optimal Position ?
Polarimeter electron source
Polarimeter positron source
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Compton Polarimeter
precision ?P/P
SLC 0.52 achieved
NLC 0.25 goal
TESLA 0.5 goal
Mike Woods lt 0.1 optimist
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Polarised ee- Sources
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Static e- Source
Photoeffect on GaAs crystal
Acceleration of electrons by static electrical
field
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Polarised e- source
simple model
spin-orbital momentum coupling
anisotropy of crystal
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Polarised e- source
Negative Electron Affinity surface
electrons drift to surface L lt 100 nm to avoid
depolarisation
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Polarised e- source
SLC source ltPgt 77 (97/98)
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Polarised e- source
New Development Strained Super Lattice
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Polarised e- source
New Development Strained Super Lattice

• charge limit overcome

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Polarised e- source
New Development Strained Super Lattice

• charge limit overcome

• high polarisation

SLC ltPgt 74 E158 ltPgt 86 LC
spec ltPgt 80 Goal ltPgt 90
but ...
GaAs crystals are very sensitive ? need UHV (lt
10-11 Torr)
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Polarised e- source
static source medium emittance / excellent
vacuum RF-gun excellent emittance / good
vacuum
GaAs crystals are very sensitive ? need UHV (lt
10-11 Torr)
LC baseline design static source damping ring

• New developments
• improve emittance of static source SLAC / KEK
• improve vacuum of RF-guns FermiLab
• more robust crystal (chalcopyrite) PITZ II (?)

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Conventional e source
NLC baseline design
high power needs 3 targets 1 spare
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Polarised e source
TESLA baseline design Undulator based source
Idea by Balakin and Michailichenko (1979)
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Proof-of-principle
Test-experiment at the SLC FFTB beam line
joint experiment between JLC / NLC / TESLA
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The Helical Undulator
rotating magnetic field
creates circularly polarised photons
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The Helical Undulator
rotating magnetic field
creates circularly polarised photons
similar spectrum much smaller power
E166
LC
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Positron Production
100 polarised photons
pair production on 0.5 X0 Ti-W alloy target
polarised photons ? polarised positrons
x capture prob. (LC only)
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Experimental Setup
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Positron Polarimeter
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Positron Spectrometer
select positron energy for polarisation analysis
includes capture prob.
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Transmission Polarimeter

• Positron beam not collimated
• ? conventional polarimeter methods fail
• Solution transmission polarimeter
• 1st step convert e ? ? (bremsstrahlung)
• 2nd step measure ?-Pol in transmission

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Conversion e ? ?
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Transmission Polarimeter

• Positron beam
• not collimated
• transmission
• polarimeter

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Transmission Polarimeter
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Photon Calorimeter
array of 16 CsI crystals
crystals Dresden SLAC photodiodes Dresden preamp
SLAC receiver U Mass ADCs SLAC
(SLD) mechanics HU
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Experimental Setup
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Expected Sensitivity
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E166 Collaboration
Undulator based production of polarised positrons
45 Collaborators / 15 Institutions
Brunel CERN Cornell DESY Durham
Thomas Jefferson Lab HU-Berlin KEK
Princeton South Carlolina SLAC Tel
Aviv Tokyo Metropoliten Tennessee Waseda
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E166 Status
Conditionally approved in June 2003 by SLAC
test-run in Feb. 2004 need to demonstrate
tolerable background levels
full run in early 2005 measure energy
spectrum and polarisation of undulator
photons and positrons
Summer 2005 conversion of SLC into XFEL
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Our Contribution

• DESY Z Humboldt
• CsI calorimeter
• Monte Carlo simulation
• data analysis

• DESY HH
• polarimeter concept
• analyzing magnets
• Monte Carlo simulation

Hermann Kolanoski Achim Stahl Sabine
Riemann Klaus Mönig Karim Laihem
Thomas Lohse Nikolaj Pavel Michael
Jablonski Thomas Schweizer
Peter Schüler Vahagn Gharibyan Klaus
Flöttmann Ties Behnke Norbert Meyners Roman Pöschl
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Conclusions

• Physics case for positron polarisation
• long. polarisation strong physics case
• trans. polarisation unclear

• Polarimetry
• achievable precision 0.5 0.05 ?
• before IP / After IP / Both ?
• expreimental improvements ?

• Sources
• electrons good perspective (90 )
• positrons undulators better than conventional
• demonstrate develop

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the end