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Polarisation at Linear Colliders. Achim Stahl Zeuthen 15.Oct.03. Polarisation at Linear Colliders. Contents. Physics Motivation Polarisation Measurement Creation of Polarised Beams. Single Particle: Helicity. Particle Bunch: Polarisation. Definitions. 4 Beam Configurations.

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slide1

Polarisation at

Linear Colliders

Achim Stahl

Zeuthen 15.Oct.03

slide2

Polarisation at

Linear Colliders

Contents

  • Physics Motivation
  • Polarisation Measurement
  • Creation of Polarised Beams
slide3

Single Particle: Helicity

Particle Bunch: Polarisation

Definitions

slide4

4 Beam Configurations

  • Unpolarised Beams
  • Long. Polarisation: Electrons only
  • Long. Polarisation: Both Beams
  • Transverse Polarisation
slide5

Pol: -90% / 60%

J = 0

6 %

J = 1

4 %

J = 0

36 %

J = 1

54 %

QM States:

slide6

Physics Motivation

Understanding Matter, Energy, Space and Time

http://blueox.uoregon.edu/~lc/wwwstudy/

slide7

Electron Polarisation

TDR assumes polarised electron beam (~80 %)

Higgs-W coupling from:

For mH = 120 GeV:

slide8

~

~

Positron Polarisation I:

known

to be discovered

~

~

but which is which ?

slide9

~

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

slide10

Positron Polarisation II:

Giga – Z option needs positron polarisation

109 Z0 in 100 days

sin2θeff from ALR

Δsin2θeff: ≈ 10-5

ΔALR: 8 10-5

slide11

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-

slide12

2 (1 – 4 sin2θeff)

L - R

ALR = =

L + R

1 + (1 – 4 sin2θeff)2

Positron Polarisation II:

Klaus Mönig

slide13

Positron Polarisation III:

gravitons into

extra dimensions

e+e- G 

main background

e+e- νν

enhance signal

suppress background

slide14

~

~

e+e- Χ0Χ0

Positron Polarisation III:

enhance signal

suppress background

slide15

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)

slide16

Positron Polarisation:

effective polarisation

in contact interactions

(by Sabine Riemann)

slide17

c,b

e+

G

e-

c,b

Transverse Polarisation:

transverse asymmetry

indicate Spin-2 exchange

trans. polarisation asymmetries

need both beams polarised

slide18

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

slide19

Precision

Polarimetry

slide20

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:

slide21

Møller Polarimeter:

JLab Polarimeter

slide22

N- - N+

N- + N+

Compton Polarimeter:

pol. Laser

electron beam

slide24

Compton Polarimeter:

main beam

  • large -background near beam
  • Čerenkov detectors only

sensitive to electrons

  • light guides allow PMT behind

schielding

slide25

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

slide26

Compton Polarimeter:

precision: ΔP/P

slide27

Polarised

e+e- Sources

slide28

Static e- Source:

Photoeffect on GaAs crystal

Acceleration of electrons by static electrical field

slide29

Polarised e- source:

simple model

+ spin-orbital momentum

coupling

+ anisotropy of crystal

slide30

Polarised e- source:

Negative Electron Affinity

surface

electrons drift to surface

L < 100 nm to avoid depolarisation

slide31

But Problem:

charge saturation

100 nm GaAs

Polarised e- source:

SLC source:

<P> = 77 % (97/98)

slide32

Polarised e- source:

New Development: Strained Super Lattice

slide33

Polarised e- source:

New Development: Strained Super Lattice

  • charge limit overcome
slide34

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)

slide35

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 (?)
slide36

Conventional e+ source:

NLC baseline design

high power needs

3 targets

+1 spare

slide37

Polarised e+ source:

TESLA baseline design: Undulator based source

Idea by

Balakin and

Michailichenko

(1979)

slide38

Proof-of-principle

Test-experiment at the SLC FFTB beam line

joint experiment between JLC / NLC / TESLA

slide39

Ø 0.89 mm

E166 prototype

prototype of TESLA undulator

The Helical Undulator

rotating magnetic field

creates circularly polarised photons

slide40

The Helical Undulator

rotating magnetic field

creates circularly polarised photons

similar spectrum

much smaller power

E166

LC

slide41

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)

slide44

Positron Spectrometer

select positron energy

for polarisation analysis

includes “capture prob.“

slide45

Transmission Polarimeter

Positron beam not collimated

 conventional polarimeter methods fail

Solution: transmission polarimeter

1st step: convert e+  (bremsstrahlung)

2nd step: measure -Pol in transmission

slide47

Transmission Polarimeter

  • Positron beam
  • not collimated
  • transmission

polarimeter

slide49

Photon Calorimeter

array of 16 CsI crystals

crystals Dresden + SLAC

photodiodes Dresden

preamp SLAC

receiver U Mass

ADCs SLAC (SLD)

mechanics HU

slide52

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

slide53

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

slide54

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

slide55

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