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

Polarisation at Linear Colliders  Physics Motivation  Polarisation Measurement  Creation of Polarised Beams Contents

Definitions Single 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

Electron Polarisation TDR assumes polarised electron beam (~80 %) Higgs-W coupling from: For m H = 120 GeV:  on g HWW no pol.2.8 % e - pol.0.8 %

Positron Polarisation I: known to be discovered but which is which ? e L e R μ L μ R …… ~~ ~ ~

Positron Polarisation I: e+e+ ~ e+e+ e-e- e-e- ~ , Z e+Le+L e-Le-L e+Le+L ~ e-Le-L ~ ν ~ e+Le+L ~ e-Le-L ~ e+Re+R ~ e-Re-R ~ and e+Le+L ~ e-Le-L ~ e+Re+R ~ e-Re-R ~ or J = 1 J = 0,1

Positron Polarisation II: Giga – Z option needs positron polarisation 10 9 Z 0 in 100 days sin 2 θ eff from A LR Δsin 2 θ eff : ≈ ΔA LR :

Positron Polarisation II: Elektron Positron A LR = =  L -  R  L +  R 2 (1 – 4 sin 2 θ eff ) 1 + (1 – 4 sin 2 θ eff ) 2 needs ΔP/P ≈ Measurements 4 Unknown  L,  R, P +, P -

Positron Polarisation II: A LR = =  L -  R  L +  R 2 (1 – 4 sin 2 θ eff ) 1 + (1 – 4 sin 2 θ eff ) 2 Klaus Mönig

Positron Polarisation III: enhance signal suppress background gravitons into extra dimensions e + e -  G  main background e + e -  ν ν 

Positron Polarisation III: e+e-  Χ0Χ0e+e-  Χ0Χ0 ~~ enhance signal suppress background

Positron Polarisation IV:  = (1 – P + P - )  0 ( 1 + P eff A LR ) effective polarisation P eff = P + - P P + P - for any s-channel J=1 process

Positron Polarisation: effective polarisation in contact interactions (by Sabine Riemann)

Transverse Polarisation: c,b e+e+ e-e- G transverse asymmetry indicate Spin-2 exchange trans. polarisation asymmetries need both beams polarised

Transverse Polarisation: trans. polarisation asymmetries need both beams polarised e e , Z W W TGC e e W W ν Jegerlehner / Fleischer / Kołodziej Triple Gauge Couplings trans. asym. dominated by W L W L

Precision Polarimetry

Phys. Processes for Polarimetry: Mott Scattering: e – Nucleon spin-orbital mom. coupling measures trans. pol. energy ≤ 1 MeV Møller Scattering: e – e polarised iron foils destructive measurement cross LC Compton Scattering: e –  polarised laser target non-invasive main LC

Møller Polarimeter: JLab1 – 6 GeV1.4 % E14316/29 GeV3.7 % SLD45 GeV4.2 % TESLA250 GeV1.0 % JLab Polarimeter

Compton Polarimeter: pol. Laser electron beam N - - N + N - + N +

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 during collision by ≈ 1 %

Compton Polarimeter: precision: ΔP/P SLC0.52 %achieved NLC0.25 %goal TESLA0.5 %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 surface L < 100 nm to avoid depolarisation

Polarised e - source: 100 nm GaAs SLC source: = 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: = 74 % E158: = 86 % LC spec: = 80 % Goal: = 90 % but... GaAs crystals are very sensitive  need UHV (< Torr)

Polarised e - source: GaAs crystals are very sensitive  need UHV (< Torr) static source: medium emittance / excellent vacuum RF-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 by Balakin and Michailichenko (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 undulator E166 prototype Ø 0.89 mm

The Helical Undulator rotating magnetic field creates circularly polarised photons E166 LC similar spectrum much smaller power

Positron Production pair production on 0.5 X 0 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 energy for polarisation analysis includes “capture prob.“

Transmission Polarimeter Positron beam not collimated  conventional polarimeter methods fail Solution: transmission polarimeter 1 st step: convert e +   (bremsstrahlung) 2 nd step: measure  -Pol in transmission

Conversion e +  

Transmission Polarimeter Positron beam not collimated  transmission polarimeter

Transmission Polarimeter

Photon Calorimeter array of 16 CsI crystals crystalsDresden + SLAC photodiodesDresden preampSLAC receiverU Mass ADCsSLAC (SLD) mechanicsHU

Experimental Setup

Expected Sensitivity

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

E166 Status Conditionally approved in June 2003 by SLAC test-run in Feb 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 Schüler Vahagn Gharibyan Klaus Flöttmann Ties Behnke Norbert Meyners Roman Pöschl Hermann Kolanoski Achim Stahl Sabine Riemann Klaus Mönig Karim Laihem Thomas Lohse Nikolaj Pavel Michael Jablonski Thomas 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

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