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