Polarisation at Linear Colliders Achim Stahl Zeuthen 15.Oct.03.
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Transcript of Polarisation at Linear Colliders Achim Stahl Zeuthen 15.Oct.03.
Polarisation atLinear Colliders
Achim StahlZeuthen 15.Oct.03
Polarisation atLinear Colliders
Physics Motivation
Polarisation Measurement
Creation of Polarised Beams
Contents
DefinitionsSingle Particle: Helicity
Particle Bunch: Polarisation
4 Beam Configurations
Unpolarised Beams
Long. Polarisation: Electrons only
Long. Polarisation: Both Beams
Transverse Polarisation
QM States:
J = 0
J = 1
J = 0
J = 1
Pol: -90% / 60%
6 %
4 %
36 %
54 %
Understanding Matter, Energy, Space and Time
Physics Motivation
http://blueox.uoregon.edu/~lc/wwwstudy/
Electron PolarisationTDR assumes polarised electron beam (~80 %)
Higgs-W coupling from:
For mH = 120 GeV:
on gHWW
no pol. 2.8 %
e- pol. 0.8 %
Positron Polarisation I:
known
to be discovered
but which is which ?
eL eR eL eR
μL μR μL μR
… …
~ ~
~ ~
Positron Polarisation I:
e+~e+
e- e-~
, Z
e+L
e-L
e+L
~
e-L
~
ν~
e+L
~e-
L
~
e+R
~e-
R
~and
e+L
~e-
L
~
e+R
~e-
R
~or
J = 1
J = 0,1
Positron Polarisation II:Giga – Z option needs positron polarisation
109 Z0 in 100 days
sin2θeff from ALR
Δsin2θeff: ≈ 10-5
ΔALR: 8 10-5
Positron Polarisation II:
Elektron Positron
ALR = =L - R
L + R
2 (1 – 4 sin2θeff)
1 + (1 – 4 sin2θeff)2
needsΔP/P ≈ 10-4
4 Measurements4 Unknown L, R, P+, P-
Positron Polarisation II:
ALR = =L - R
L + R
2 (1 – 4 sin2θeff)
1 + (1 – 4 sin2θeff)2
Klaus Mönig
Positron Polarisation III:
enhance signalsuppress background
gravitons intoextra dimensions e+e- G main background e+e- ν ν
Positron Polarisation III:
e+e- Χ0Χ0~ ~ enhance signalsuppress background
Positron Polarisation IV:
= (1 – P+P-) 0 ( 1 + Peff ALR)
effective polarisation
Peff = P+ - P-
1 - P+ P-
for any s-channel J=1 process
Positron Polarisation:effective polarisation
in contact interactions(by Sabine Riemann)
Transverse Polarisation:c,be+
e- c,b
Gtransverse asymmetryindicate Spin-2 exchange
trans. polarisation asymmetriesneed both beams polarised
Transverse Polarisation:
trans. polarisation asymmetriesneed both beams polarised
e
e
, Z
W
W
TGC
e
e
W
W
ν
Jegerlehner / Fleischer / Kołodziej
Triple Gauge Couplings trans. asym. dominated by WLWL
Precision Polarimetry
Phys. Processes for Polarimetry:
Mott Scattering: e – Nucleonspin-orbital mom. couplingmeasures trans. pol. energy ≤ 1 MeV
Møller Scattering: e – epolarised iron foilsdestructive measurement cross check @ LC
Compton Scattering: e – polarised laser targetnon-invasive main polarimeter @ LC
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
Compton Polarimeter:
pol. Laser
electron beam
N- - N+
N- + N+
Compton Polarimeter:
Compton Polarimeter:
main beam
large -background near beam
Čerenkov detectors only sensitive to electrons
light guides allow PMT behind schielding
Optimal Position ?
Polarimeter:electron source
Polarimeter:positron source
Polarimeter:at the IP
Polarimeter:before the IP
Polarimeter:before the IP
beam depolarises duringcollision by ≈ 1 %
Compton Polarimeter:
precision: ΔP/P
SLC 0.52 % achieved
NLC 0.25 % goal
TESLA 0.5 % goal
Mike Woods < 0.1 % optimist
Polarised e+e- Sources
Static e- Source:Photoeffect on GaAs crystal
Acceleration of electrons by static electrical field
Polarised e- source:
simple model
+ spin-orbital momentum coupling
+ anisotropy of crystal
Polarised e- source:Negative Electron Affinity
surface
electrons drift to surfaceL < 100 nm to avoid depolarisation
Polarised e- source:
100 nm GaAs
SLC source: <P> = 77 % (97/98)
But Problem: charge saturation
Polarised e- source:New Development: Strained Super Lattice
Polarised e- source:New Development: Strained Super Lattice
charge limit overcome
Polarised e- source:New Development: Strained Super Lattice
charge limit overcome
high polarisation
SLC: <P> = 74 %E158: <P> = 86 %LC spec: <P> = 80 %Goal: <P> = 90 %
but ...GaAs crystals are very sensitive need UHV (< 10-11 Torr)
Polarised e- source:
GaAs crystals are very sensitive need UHV (< 10-11 Torr)
static source: medium emittance / excellent vacuumRF-gun: excellent emittance / good vacuum
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 (?)
Conventional e+ source:NLC baseline design
high power needs 3 targets
+1 spare
Polarised e+ source:TESLA baseline design: Undulator based source
Idea byBalakin andMichailichenko(1979)
Proof-of-principle
Test-experiment at the SLC FFTB beam line
joint experiment between JLC / NLC / TESLA
The Helical Undulator
rotating magnetic field
creates circularly polarised photons
prototype of TESLA undulatorE166 prototype
Ø 0.89 mm
The Helical Undulator
rotating magnetic field
creates circularly polarised photons
E166 LCsimilar spectrummuch smaller power
Positron Production
pair production on0.5 X0 Ti-W alloy target
polarised photons polarised positrons
100 % polarised photons
E166: -spec. x -pol. x pair x e+-pol.x capture prob. (LC only)
Experimental Setup
Positron Polarimeter
Positron Spectrometer
select positron energyfor polarisation analysis
includes “capture prob.“
Transmission PolarimeterPositron beam not collimated conventional polarimeter methods failSolution: transmission polarimeter 1st step: convert e+ (bremsstrahlung) 2nd step: measure -Pol in transmission
Conversion e+
Transmission Polarimeter
Positron beam not collimated transmission polarimeter
Transmission Polarimeter
Photon Calorimeterarray of 16 CsI crystals
crystals Dresden + SLACphotodiodes Dresdenpreamp SLACreceiver U MassADCs SLAC (SLD)mechanics HU
Experimental Setup
Expected Sensitivity
E166 Collaboration Undulator based production of polarised positrons
45 Collaborators / 15 Institutions
Brunel CERN Cornell DESY Durham Thomas Jefferson LabHU-Berlin KEK Princeton South Carlolina SLAC Tel AvivTokyo Metropoliten Tennessee Waseda
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
Our Contribution:
DESY HH polarimeter concept analyzing magnets Monte Carlo simulation
DESY Z + Humboldt CsI calorimeter Monte Carlo simulation data analysis
Peter SchülerVahagn GharibyanKlaus FlöttmannTies BehnkeNorbert MeynersRoman Pöschl
Hermann KolanoskiAchim StahlSabine RiemannKlaus MönigKarim Laihem
Thomas LohseNikolaj PavelMichael JablonskiThomas Schweizer
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
the end