Polarisation at Linear Colliders

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

2. Polarisation at Linear Colliders Contents • Physics Motivation • Polarisation Measurement • Creation of Polarised Beams

3. Single Particle: Helicity Particle Bunch: Polarisation Definitions

4. 4 Beam Configurations • Unpolarised Beams • Long. Polarisation: Electrons only • Long. Polarisation: Both Beams • Transverse Polarisation

5. Pol: -90% / 60% J = 0 6 % J = 1 4 % J = 0 36 % J = 1 54 % QM States:

6. Physics Motivation Understanding Matter, Energy, Space and Time http://blueox.uoregon.edu/~lc/wwwstudy/

7. Electron Polarisation TDR assumes polarised electron beam (~80 %) Higgs-W coupling from: For mH = 120 GeV:

8. ~ ~ Positron Polarisation I: known to be discovered ~ ~ but which is which ?

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

10. Positron Polarisation II: Giga – Z option needs positron polarisation 109 Z0 in 100 days sin2θeff from ALR Δsin2θeff: ≈ 10-5 ΔALR: 8 10-5

11. 2 (1 – 4 sin2θeff) L - R ALR = = L + R 1 + (1 – 4 sin2θeff)2 Positron Polarisation II: needs ΔP/P ≈ 10-4 Positron Elektron 4 Measurements 4 Unknown L, R, P+, P-

12. 2 (1 – 4 sin2θeff) L - R ALR = = L + R 1 + (1 – 4 sin2θeff)2 Positron Polarisation II: Klaus Mönig

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

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

15. P+ - P- Peff = 1 - P+ P- Positron Polarisation IV: for any s-channel J=1 process effective polarisation  = (1 – P+P-) 0 ( 1 + Peff ALR)

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

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

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

19. Precision Polarimetry

20. 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 @ LC Møller Scattering: e –  polarised laser target non-invasive main polarimeter @ LC Compton Scattering:

21. Møller Polarimeter: JLab Polarimeter

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

23. Compton Polarimeter:

24. Compton Polarimeter: main beam • large -background near beam • Čerenkov detectors only sensitive to electrons • light guides allow PMT behind schielding

25. Polarimeter: before the IP Polarimeter: at the IP Polarimeter: before the IP beam depolarises during collision by ≈ 1 % Optimal Position ? Polarimeter: electron source Polarimeter: positron source

26. Compton Polarimeter: precision: ΔP/P

27. Polarised e+e- Sources

28. Static e- Source: Photoeffect on GaAs crystal Acceleration of electrons by static electrical field

29. Polarised e- source: simple model + spin-orbital momentum coupling + anisotropy of crystal

30. Polarised e- source: Negative Electron Affinity surface electrons drift to surface L < 100 nm to avoid depolarisation

31. But Problem: charge saturation 100 nm GaAs Polarised e- source: SLC source: <P> = 77 % (97/98)

32. Polarised e- source: New Development: Strained Super Lattice

33. Polarised e- source: New Development: Strained Super Lattice • charge limit overcome

34. 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)

35. Polarised e- source: static source: medium emittance / excellent vacuum RF-gun: excellent emittance / good vacuum GaAs crystals are very sensitive  need UHV (< 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 (?)

36. Conventional e+ source: NLC baseline design high power needs 3 targets +1 spare

37. Polarised e+ source: TESLA baseline design: Undulator based source Idea by Balakin and Michailichenko (1979)

38. Proof-of-principle Test-experiment at the SLC FFTB beam line joint experiment between JLC / NLC / TESLA

39. Ø 0.89 mm E166 prototype prototype of TESLA undulator The Helical Undulator rotating magnetic field creates circularly polarised photons

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

41. E166: -spec. x -pol. x pair x e+-pol. Positron Production 100 % polarised photons pair production on 0.5 X0 Ti-W alloy target polarised photons  polarised positrons x capture prob. (LC only)

42. Experimental Setup

43. Positron Polarimeter

44. Positron Spectrometer select positron energy for polarisation analysis includes “capture prob.“

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

46. Conversion e+ 

47. Transmission Polarimeter • Positron beam • not collimated • transmission polarimeter

48. Transmission Polarimeter

49. Photon Calorimeter array of 16 CsI crystals crystals Dresden + SLAC photodiodes Dresden preamp SLAC receiver U Mass ADCs SLAC (SLD) mechanics HU

50. Experimental Setup