annika vauth spin 2014, beijing · annika vauth spin 2014, beijing. introductionphysics...

Beam Polarisation at the ILC:Physics Case and Realisation.

Annika VauthSPIN 2014, Beijing

Introduction Physics case Realisation Conclusion

Introduction: the ILC

Physics case for beam polarisation

Realisation at the ILC

Conclusion


Introduction: the ILC.

Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 1 / 24


Motivation for a linear lepton collider.

Electron positron collidersI pointlike particlesI well defined initial stateI precision machinesI discovery potential

e+e− → HZAdvantage of linear colliderI no energy loss due to synchrotron radiationI extendable (length→ energy)



ILC history.

Since early 90s different LC studiesTESLA (SCRF)

NLC/JLC (normal conducting)

2004 technology decision: SCRF

2004 ILC Global Design Effort founded

2007 ILC Reference Design Report

2009 LOI for detector concepts

2012/13 ILC Technical Design Report

since 2012/13: Linear Collider CollaborationI ILC: Higgs/Top factory

possible realisation in JapanI CLIC: multi-TeV, on longer timescale

(next energy frontier project in Europe?)

2013

2011

2007

2009



ILC in Japan.

Japanese HEP community put the ILC high on their roadmap

Japanese government is interested to host ILC in Japan:

I Support for ILC in Japanese parliament (Diet) is multi-partisanI government has started international initiativeI MEXT has assigned 50 MJPY project money to ILC

2010: two candidate sites (Sefuri and Kitakami)

August 2013: Kitakami site chosen

北上Kitakami



ILC overview.

I Planned e+e− collider (length ≈ 30 km)I Energy up to

√s = 500 GeV , potential upgrade to 1 TeV

I Technology: superconducting RF-cavities

damping rings IR & detectors e+ bunchcompressor

e- source

central region5 km

positron main linac

11 km

electron main linac

11 km2 km

e- bunchcompressor

e+ source

2 km

[ILC

TDR

vol.

1,20

13]



Detectors for physics measurements.

[line

arco

llide

r.org

]

Two detector concepts: ILD and SiD

Use push-pull system at interaction region

Both detectors use particle flow algorithm:I measure each particle type in the

most appropriate subdetector(charged particles→ tracker,photons→ ECAL,neutral hadrons→ HCAL)

I low material budget for thevertex detector and tracker

I high granularity calorimeters



Physics case for beam polarisation.



Precision physics at ILC.

ä Cleanliness calculability

ä Tune-able center-of-mass energy

ä Polarised beams: P(e+) & 30%, P(e−) ≈ 80%

I polarisation asymmetry as observable

I enhanced rates and background suppression fore−L e+R (Standard Model) or e−R e+L (new physics searches)

I access to chirality of new particles

e⁻ he- he+ cross section

J=0

e⁺

-1

+1

+1

-1

σLL

σRR

σRL

σLR

J=0

J=1

J=1

-1

+1

-1

+1

[LC

-RE

P-2

013-

017]



ILC physics program.

Polarisation benefits for major physics studies:

Energy Reaction Physics Goal91 GeV e+e− → Z ultra-precision electroweak160 GeV e+e− → WW ultra-precision W mass250 GeV e+e− → Zh precision Higgs couplings350 - 400 GeV e+e− → t t̄ top quark mass and couplings

e+e− → WW precision W couplingse+e− → νν̄h precision Higgs couplings

500 GeV e+e− → f f̄ precision search for Z’e+e− → tth Higgs coupling to tope+e− → Zhh Higgs self-couplinge+e− → χ̃χ̃ search for supersymmetrye+e− → AH,H+H− search for extended Higgs states

700 - 1000 GeV e+e− → νν̄hh Higgs self-couplinge+e− → νν̄VV composite Higgs sectore+e− → νν̄t t̄ composite Higgs and tope+e− → t̃ t̃∗ search for supersymmetry [IL

CTD

Rvo

l.2,

2013

]

polarisation asymmetry as observable opposite polarisations enhance luminositySM: e+

R e−L enhance rates / suppress BG NP: e+L e−R enhance rates / suppress BG



Top electroweak coupling.

Top quark production at ILC throughelectroweak processesno competing QCD production

→ small theoretical errors

Polarised beams allow to testchiral structure at ttX vertex

I cross sectionsI forward-backward asymmetryI helicity angle distribution

→ precision on form factorssensitive to new physics

)hel

θcos(-1 -0.5 0 0.5 1

0

0.2

0.4

0.6

0.8

1R+e

L-e

L+e

R-e

Generator - Whizard

Reconstructed

1V

γF~

1VZF~

2V

γF~

2VZF~

1AZF~

Unce

rtainty

-310

-210

-110

1ILC (preliminary)

LHC (hep-ph/0601112)

[LC

-RE

P-2

013-

007]



Trilinear gauge boson couplings (TGC).

Current experimental statuson charged TGCs in WW production:few percent precision from single parameter fits (LEP & LHC)

Study of WWZ and WW γ at ILC:

Beam polarisation increases sensitivity to deviations from thestandard model & allows to disentangle couplings→ resolutions of few 10−4 in simultaneous fit

γ Z⁰

W⁺

W⁻

W⁺

W⁻

aTGC Parameter Limit

[hep

-ex/

1406

.773

1]pol+30% epol

-80% e

[LC

-DE

T-20

09-0

03]



Model distinction.

Polarisation can improve distinction between physics models.

Example: R-parity violating SUSY (spin 0) or Z’ (spin 1)?

Ñ ×

Î ℄

Ø

Ó

Ø

Ô

Ô

℄

¼ ¼ ââ ¼ ¼¼ ¼ ¼¼ ¼ ¼¼ ¼ ¼¼ ¼ â¼ ¼

â

â

¿

¾

½

¼

600 620 640 660 680 700

√s �GeV�

σto

t�pb�

e+ e− → ν̃τ → µ+ µ− e+ e− → Z’ → µ+ µ−

500

√s �GeV�800600 700

0

10

20

5

15

25

σto

t�pb�

0

1

5

2

3

4

(-80%, +60%)

(P , Pe- e+ )

(-80%, -60%)

(-80%, +60%)

(P , Pe- e+ )

(-80%, -60%)

Z’

[hep

-ph/

0509

099]



Precision observables.

What if nothing beyond the standard model is found?sin2 θeff can be crucial quantity to reveal effects of new physics

LEP:sin2 θeff(Ab

FB) = 0.23221± 0.00029

SLC:sin2 θeff(ALR) = 0.23098± 0.00026

World average:sin2 θeff = 0.23153± 0.00016

Goal ILC “GigaZ” (√

91 GeV):∆ sin2 θ = 1.3 · 10−5

[hep

-ph/

1310

.670

8]

Precision measurement via left-right cross-section asymmetry

ALR =

√(σRR + σRL − σLR − σLL)(−σRR + σRL − σLR + σLL)

(σRR + σRL + σLR + σLL)(−σRR + σRL + σLR − σLL)



Realisation at the ILC.



Electron source.

Requirements: 1312 bunches of 3 · 1010 electrons at 5 Hzwith polarisation >80 %

Polarisation, charge & lifetime already reached at SLC in the past

photocathodes with GaAs/GaAsPstrain-compensated superlatticeat least 85% polarisation,

quantum efficiency typically >0.4%

Active Region

GaAs0.64P0.36

Buffer

GaAs(1-x)Px

Graded Layer

GaAs Substrate

GaAsP

strained GaAs

GaAsP

GaAsP

strained GaAs

strained GaAs

30 Å

40 Å

1000 Å

25μm

25μm

[ILC

TDR

vol.

3.2,

2013

]

Primary challenges at ILC:I long bunch train→ laser system developementI high RF-power on the normal-conducting pre-accelerator

both demonstrated in R&D prototypes



Positron source.

Electromagnetic showers to generate positrons:multi-MeV photon beam onto thin metal targetalternative: e− driven source (“300 Hz scheme”), but no polarisation

Options for generation of the photons:I Compton backscatteringI Helical undulator - generates circularly polarised photons,

which in turn generate longitudinally polarised positrons147 m long undulator, space reserved for upgrade

[ILC

TDR

vol.

1,20

13]



Positron source (2).

Positron yieldI requirement Y = 1.5 e+/e−

I polarisation and yield stronglycoupled to e− beam energy

I below 150 GeV: “10 Hz scheme”with dedicated drive beam(tuning of undulator and collimator parameters -

possible to go to 120 GeV without this)

Polarisation upgradeI nominal design ∼ 30 % e+ polI for 60 %: 73.5 m longer undulator &

photon beam collimation

[ILC

TDR

vol.

3.2,

2013

][IL

CTD

Rvo

l.3,

2,20

13]

R&D work remains (e.g. target design, photon collimator)Beam Polarisation @ ILC | A. Vauth | Spin2014, 20.10.14 14 / 24


Spin rotators.

Spin rotators before / after damping rings to preserve polarisation

Fest helicity reversal→ cancellation of time-dependent effects

ä Electron polarisation: switch at source by changing laser polarity

ä Positron polarisation:I depends on direction of undulator windingsI helicity reversal: use spin flipper near the damping ringI beam is kicked into one of two parallel transport lines

Kicker magnet

Dipole + FODO

Solenoidspin

directionfrom polarised

positron sourceB=+Bo

B=-Bo

to damping ring

line with positive solenoid field

line with negative solenoid field

[LC

-RE

P-2

013-

016]



Polarimetry concept.

ILC polarimetry: per mille level precision by combining

1650m

150m

e⁻ e⁺spin tracking

e⁺e⁻collisionsupstream

polarimeter

downstreampolarimeter

ä Compton polarimeter measurements upstream anddownstream of the e+e− interaction point

ä Spin tracking studies to relate these measurements to thepolarization at the e+e− interaction point

ä Long-term average determined from e+e− collision data asabsolute scale calibration



Compton polarimeters.

I O(103) Compton scatterings/bunchI Energy spectrum of scattered e+/e− depends on polarisationI Magnetic chicane: energy distribution→ position distributionI Measure number of e+/e− per detector channel

Upstream polarimeter:

e⁺/e⁻ IP

125 GeV

25 GeV2

4 c

m

inout

LaserIP

Dipole 2 Dipole 3

Dipole 4Dipole 1

total length: ~75 m

250 GeV

[JIN

ST

4(20

09),

1001

5]



Compton polarimeters (2).Downstream Polarimeter

I located at secondary focusI 6-magnet chicane kicks Compton e± out of synchrotron fan

15 c

m27

.4 c

m

z~46.8m1E

3Ez~55.2m

vacuumchamber

+dz=20m2P 4P

+dz=20m+dz=12m

1G

+dz=10m2G

+dz=10m

Polarimeter Chicane3P

z~175m

SR− limit forCherenkov detector

250 GeV

44 GeV

25 GeV

Cherenkov Det.

Energy Chicane

7Ez~68.8m

10 m

10 c

m

Horizontal BendMagnets z~147.7m, y=15.3cm

Synchrotron Strip Detectorz~147.7m, y=−19.9cm

2mrad energy stripes

z~120.7m1P

z~52.2m z~65.7m

SR−shielding forCherenkov det.

Synchrotron Strip Detector

energycollimator

[JIN

ST

4(20

09),

1001

5]



Polarimeter detectors.

Simple, robust, fast: Cherenkov detectorsI Cherenkov light emission proportional to number of electronsI independent of electron energy (once relativistic)I successfully used in best polarimeter sofar at SLCI gas or quartz option for Cherenkov medium

Goal: total uncertainty ∆P/P ≈ 0.25 %, of whichI laser: 0.1 %I analysing power (i.e. asymmetry at P = 1 ): 0.2 %I detector linearity: 0.1 %



Cross-calibration of Polarimeters.

Polarimeter locations 1650 m before and 150 m after the IP

Spin tracking studies to understand spin transport in-between

Without collisions: cross-calibration of polarimeters

effect on P[10−3]Beam and detector alignment at polarimeters 0.72(∆θbunch = 50 mrad,∆θpol = 25 mrad)Beam parameter variations (10% in emittances) 0.03Bunch rotation to compensate crossing angle < 0.01Longitudinal precession in detector magnets 0.01Emission of synchrotron radiation 0.005random misalignments (10 µm) 0.35Total 0.80

JIN

ST

9(2

014)

P07

003



Collision Effects.

zlo

ng. p

olar

izat

ion

P

0.79

0.795

0.8 ]-3

rela

tive

ch

ang

e [1

0

-10

-5

0

UPbefore collisionlumi-weightedafter collisionDP(0.1/0.2/0.5/1.0 mm) -e

w/o collisions

w/o beamstr.

with coll. effects

I beamstrahlung (energy loss, radiative depolarisation):difference downstream measurement vs. 〈P〉IP increases

I energy loss limits refocusing of the beam:laser spot at the polarimeter affects measurement



Polarisation Average from Collision Data.

Direct extraction from collision data:any abundant, well-known, polarisation dependent process

〈| Pe± |〉IP =

√(σ−+ + σ+− − σ−− − σ++)(±σ−+ ∓ σ+− + σ−− − σ++)

(σ−+ + σ+− + σ−− + σ++)(±σ−+ ∓ σ+− − σ−− + σ++)

(assumes P+(e−) = −P−(e−) and P+(e+) = −P−(e+) )

Methods studied so farI total cross-sections:

WW at 500 GeV and 1 TeVI single-differential cross-sections:

WW at 500 GeV and 1 TeVI double-differential cross-sections:

WW at 1 TeV1Luminosity fb

0 200 400 600 800 1000 1200

% e

rro

r p

ola

riza

tio

n

0

0.2

0.4

0.6

0.8

1 pol

pol 80% e

+30% e

positron Blondel

electron Blondel

positron Fit

electron Fit

[LC

-DE

T-20

09-0

03]



Impact of Polarimeter Precision.

What happens if P+(e−) 6= −P−(e−) and P+(e+) 6= −P−(e+)?I let all P vary independently⇒ δP/P in percent regimeI better: difference to ±δP/P|pol = 0.25% with polarimetersI limits ultimate precision on P(e−)!

Luminosity [fb⁻¹]0 200 400 600 800 10000

1

0.2

0.4

0.6

0.8

error on polarisation [%]

80% e⁻ pol30% e⁺ pol

e⁻ (with polarimeters)e⁺ (with polarimeters)

e⁺ fit (2 parameters)e⁻ fit (2 parameters)

[thes

isI.

Mar

ches

ini2

011]

→ need polarimetry at permille-level and fast helicity reversal



Conclusion.



Conclusion.

I Beam polarisation is a key ingredientfor ILC physics studies

I Polarised electron and positron sourcesmore R&D on e+ source necessary, no show-stoppers

I Permille-level polarimetry from acombination of

I up- and downstream polarimetersI spin tracking, collision effectsI scale calibration from e+e− data

I Site for ILC selected,government negotiations ongoing

⇒ Exciting times ahead!

Backup Slides.

Push-Pull concept.

Beam delivery system(Accelerator tunnel)

Access to damping ring

SiD detector(parked)

ILD detector(on beamline)

ILD garage

[ILC

TDR

vol.

1,20

13]

Possible construction schedule.

[ILC

TDR

vol.

1,20

13]

Beam size.

[AFT

2]

44 nm reached in July 2014(different beam energy→ 37 nm at ATF will correspond to < 5 nm at ILC)

Sin Theta.

Connection between ALR and sin2 θeff:

ALR =1〈Peff〉

σL − σR

σL + σR=

2veae

v2e + a2

c

ve

ae= 1− 4 sin2 θeff

Peff =Pe+ + Pe−

1 + Pe+Pe−

With positron polarisation:

ALR =

√(σRR + σRL − σLR − σLL)(−σRR + σRL − σLR + σLL)

(σRR + σRL + σLR + σLL)(−σRR + σRL + σLR − σLL)

0LRA

0.10 0.12 0.14 0.16

92

93

94-95

96

97-98

Average

SLD

resu

lts[h

ep-e

x/05

0900

8]

Electron source parameters.

Parameter Symbol Value UnitsElectrons per bunch (at gun exit) N− 3×1010 NumberElectrons per bunch (at DR injection) N− 2×1010 NumberNumber of bunches nb 1312 NumberBunch repetition rate f b 1.8 MHzBunch train repetition rate f r ep 5 (10) HzFW Bunch length at source ∆ t 1 nsPeak current in bunch at source I avg 3.2 AEnergy stability σE /E <5 % rmsPolarization Pe 80 (min) %Photocathode Quantum Ef ciency QE 0.5 %Drive laser wavelength λ 790±20 (tunable) nmSingle bunch laser energy ub 5 µJ

[ILC

TDR

vol.

3.2,

2013

]

Electron source system.

SC e- LINAC (5.0 GeV)

Damping Ring

L-band (b = 0.75) TW Bunching

and Pre-Acceleration

DC Gun (2x)

DriveLaser

(aboveGround)

Spin Rotation

Faraday Cupand Mott

Polarimeter(13.5W)NC tune-up dump

(11.3 kW)

SC tune-up dump (311 kW)

3.2 nC

140 keV - 76 MeV76 MeV - 5.0 GeV

Energy Collimation(Vertical Chicane)

10 MW8 x 10 MW 10 MW

325

MH

z

325

MH

z

5 nC

Energy Compression

10 MWSPARE

SHB

2 x 5 MW(1 + 1 spare)

[ILC

TDR

vol.

3.2,

2013

]

Positron source parameters.

Parameter Symbol Value UnitsPositrons per bunch at IP nb 2 × 1010 numberBunches per pulse Nb 1312 numberPulse Repetition Rate f r ep 5 HzPositron Energy (DR injection) E 0 5 GeVDR Dynamic Aperture γ(Ax + Ay ) <0.07 m radDR Energy Acceptance ∆ 0.75 %DR Longitudinal Acceptance Al 3.4 x 37.5 cm-MeVElectron Drive Beam Energy† Ee 150/175/250 GeVUndulator Period λ 1.15 cmUndulator Strength‡ K 0.92/0.75/0.45 -Undulator Type - Helical -Undulator Length L u 147 mPhoton Energy (1st harm cutof ) Ec10 10.1/16.2/42.8 MeVPhoton Beam Power Pγ 63.1/54.7/41.7 kWTarget Material - Ti-6%Al-4%V -Target Thickness L t 0.4 / 1.4 r.l. / cmTarget Absorption - 7 %Incident Spot Size on Target σi 1.4/1.2/0.8 mm, rmsPositron Polarisation P 31/30/29 %† For centre-of-mass energy below 300 GeV, the machine operates in 10 Hz mode where

a 5 Hz 150 GeV beam with parameters as shown in the table is a dedicated drive beampositron source.

‡ K is lowered for beam energies above 150 GeV to bring the polarisation back to 30 % with-out adding a photon collimator before the target. [IL

CTD

Rvo

l.3.

2,20

13]

Compton cross-subsection.

(dσ

dy

)Compton

=

(dσ

dy

)unpol

+2πro

x· λP · rx(1− 2r)(2− y)

Compton electron energy [GeV]

0 50 100 150 200 2500

1

2

3

4

Pλ=−1.0

Pλ=+1.0

Pλ= 0.0

[mb]

Compton

(dσ/d

E)

x =4E0ω0

m2 cos2(θ0/2), y = 1− EE0

, r =y

x(1− y),

(dσ

dy

)unpol

=2πro

x

[1

1− y+ 1− y − 4r(1− r)

]

Polarimetry - gas detector concept.

e⁻ beam

Čerenkovphotons

Photomultiplier

LED calibration system

gas-filled Al-channel

beam

aluminum tubes

photodetectors

LED calibration system

[arX

iv:1

011.

6314

]

Beam Energy Spectrum After Collision.

-1 -0.8 -0.6 -0.4 -0.2 0

# of

par

ticle

s

1

10

210

310

410

510

610

710

particle energy [GeV]0 50 100 150 200 250

before collisionafter collision

Downstream Polarimeter: y vs E .

-0.4 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

1

10

210

310

410

510

610

particle energy [GeV]160 180 200 220 240ve

rt. p

artic

le p

ositi

on y

[mm

]

-20

-10

0

10

-0.05 -0.04 -0.03 -0.02 -0.01 0

-0.4

-0.2

0

0.2

0.4

-310×

1

10

210

310

410

510

particle energy [GeV]238 240 242 244 246 248 250ve

rt. p

artic

le p

ositi

on y

[mm

]

-0.5

0

0.5

Blondel scheme.

Blondel scheme:

〈| Pe± |〉IP =

√(σ+− + σ−+ − σ−− − σ++)(∓σ−+ ± σ+− + σ−− − σ++)

(σ−+ + σ+− + σ−− + σ++)(∓σ−+ ∓ σ+− − σ−− + σ++)

included assumption:P+(e−) = −P−(e−) and P+(e+) = −P−(e+)

If not: assume | P | equal up to 2ε±

measure ε±with polarimeters.

Correction to modified Blondel scheme.

P+(e±) = P± + ε± and P−(e±) = P± − ε±

Correction to P(e+)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-0.06

-0.04

-0.02

0

0.02

0.04

0.06

ε-/%

ε+/%

Luminosity Sharing.

How much running time needed for ++ and −−?

I like-sign combinations less interesting for SM phyicsI 10% to 20% like-sign lumi rather close to optimum (50%)I even 2% halfs already total lumi needed for 0.2% precision

1Luminosity fb200 400 600 800 1000

pola

rization

%

err

or

e

0

0.2

0.4

0.6

0.8

1 pol

pol 80% e+60% e

0% ++

2% ++

5% ++

10% ++

20% ++

50% ++ [thes

isI.

Mar

ches

ini2

011]

annika vauth spin 2014, beijing · annika vauth spin 2014, beijing. introductionphysics...

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