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Exploiting spin effects to unravel the structure of NP at a future LC

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### Exploiting spin effects to unravel the structure of NP at a future LC

- ‘Big’ HEP questions
- Physics case for polarized beams
- Requirements to a Linear Collider
- Requirements to a Z-factory
- Summary

GudridMoortgat-Pick

Hamburg University

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

‘Big’ questions …and possible answers

- Shortcomings of the Standard Model
- Establish electroweak symmetry breaking LC
- Hierarchy problem?
- Unification of all interactions?
- Embedding of gravity in field theory?
- Baryon asymmetry in Universe?
- Content of dark matter
- Neutrino mixing and masses
- Why is new physics expected at TeVscale?
- Protect hierarchy between mweak and mplanck
- Dark matter consistent with sub-TeV scale WIMPs

Higgs mass with respect to large quantum corrections:

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

‘Big’ questions …and possible answers

- Shortcomings of the Standard Model
- Establish electroweak symmetry breaking LC
- Hierarchy problem? LHC, LC
- Unification of all interactions? LC
- Embedding of gravity in field th? cosmo,LHC, LC
- Baryon asymmetry in Universe? v-, cosmo, LHC, LC
- Content of dark matter?v-, cosmo, LHC, LC
- Neutrino mixing and masses v-, cosmo-exp.

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

‘Big’ questions …and possible answers

- Shortcomings of the Standard Model
- Establish electroweak symmetry breaking LC
- Hierarchy problem? LHC, LC
- Unification of all interactions? LC
- Embedding of gravity in field theory? cosmo,LHC, LC
- Baryon asymmetry in Universe? v-, cosmo, LHC, LC
- Content of dark matterv-, cosmo, LHC, LC
- Neutrino mixing and masses v-, cosmo-exp.
- Goal of a Linear Collider?
- observe, determine and precisely reveal the structure of the underlying physics model !

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Required features at LHC & ILC

LC, today only

LHC, LC: CP e.g.

LC, partially LHC

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

Characteristics of pp collider

composite particles collide

E(CM) < 2 E(beam)

strong interaction in initial state

`no' polarization applicable

LHC: √s = 14TeV,

used ŝ = x1x2s few TeV

small fraction of events analyzed

multiple triggers

superposition with spectator jets

Large potential for

direct discovery

and of the e +e-(γe, γ γ) collider

Pointlike particles collide

Known E(CM) = 2 E(beam)

well defined initial state

polarized initial e- and e+ beams

ILC: √s = 500 GeV -- 1 TeV, tunable

most events in detector analyzed

no triggers required

clean +fully reconstructable events

Large potential for discovery also via high precision

Why a linear collider?SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

The unique advantage of e+e-

- Their clean signatures allow precision measurements
- Sensitive to the theory at quantum level (i.e. contributions of virtual particles, ‘higher orders’)!
- Such measurements allow predictions for effects of still undiscovered particles, but whose properties are defined by theory.

Enables powerful discoveries and/or consistency checks and the determination of the underlying structure!

t

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Requirements for such`precision frontier’

ICFA Parameter Group for a future LC:

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Why are polarized beams required?

- Please remember: excellent e- polarization ~78% at SLC:
- led to best measurement of sin2θ=0.23098±0.00026

on basis of L~1030 cm-2s-1

- Compare with results from unpolarized beams at LEP:
- sin2θ=0.23221±0.00029 but with L~1031cm-2s-1

See importance and more details later when discussing ‘Z-factory’

- Comprehensive list of physics examples with polarized beams at a LC: GMP et al., Physics Rept., hep-ph/0507011
- Only few examples here, has to be weighted wrt LHC expectations!

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Beam polarization at HEP colliders

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Beams polarization at linear colliders

- Polarized e- beams:
- strained photocathode technologies (SLC, etc. )
- see talks at PESP@Bonn, W. Hillert
- expected for the LC P(e-)~80-90%
- Polarized e+ beams: e+ polarization is an absolute novelty!

- Expected at ILC P(e+) ~ 60%
- in RDR baseline already ~30% achievable
- see talks by A. Schaelicke, K. Laihem
- Measurement via Compton polarimetry: ΔP/P<0.25% exp.
- see talks by M. Beckmann, D. Kaefer

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Short overview: e+ sources at ILC

-200m

e+ yield and polarization depends on beam energy and undulator length

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Short overview: e+ sources at ILC

s

-200m

- in general: demanding challenges for the e+ source!

e+ yield and polarization depends on beam energy and undulator length

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Physics: pol.cross sections in general

Polarized cross sections can be subdivided in:

σRR, σLL, σRL, σLR are contributions with fully polarized L, R beams.

In case of a vector particle only (LR) and (RL) configurations contribute:

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Relation between Peffand ALR

- How are Peffand ALR related?
- That means:
- With pure error propagation (and errors uncorrelated), one obtains:
- With

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Gain in accuracy due to P(e+)

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

P(e±) sensitive to interaction structure

Definition: Helicityλ=s * p/|p| ‘projection of spin’

Chirality= handedness is equal to helicity only of m=0!

- Annihilation channel:

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Complete fixing of initial state via P(e+)

- Scattering channel: direct access to chirality of final state !

from SM processes

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Something ‘new’ detected at early LHC

- Supersymmetry-like signals
- New physics model with

high predictive power

- ‘light’ SUSY consis-

tent with precision fits

- Extra gauge bosons and/or large extra dimensions
- High precision in indirect searches allow model distinction and couplings determination

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Slepton `chiral’ quantum numbers

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Models with extra dimensions

- String theory: 10 or 11 dimensions of space-time
- Extra dimensions ‘compactified’, too small to be detected so far:

To a tightrope walker, the

tightrope is one-dimensional:

he can only move forward or

backward

But to an ant, the rope has an extra dimension: the ant can

travel around the rope as well !

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

Searches for extra dimensions

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Extra dimensions

Distinction between SM and different models of extra dimensions

- Detect and determine new kind of physics even in the multi-TeV range
- Transversely-polarized beams require P(e-) and P(e+) !

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Polarimetry requirements

- SLC experience: measured ΔP/P=0.5%
- Compton scattered e- measured in magnetic spectrometer
- Goal at ILC: measure ΔP/P≤0.25%
- Dedicated Compton polarimeters and Cherenkov detectors
- Use upstream and downstream polarimeters
- Machine feedback and access to luminosity-weighted polarization
- Use also annihilation data: `average polarization’
- Longterm absolute calibration scale, up to ΔP/P=0.1%

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Compton polarimetry at ILC

- Upstream polarimeter: use chicane system
- Can measure individual e± bunches
- Prototype Cherenkov detector tested at ELSA!
- Downstream polarimeter: crossing angle required
- Lumi-weighted polarization (via w/o collision)
- Spin-tracking simulations required

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Expected depolarization effects

- In general: two effects cause depolarization
- Largest Effects during beam-beam interaction
- Spin precession (T-BMT) and spin-flip (ST) effects
- Have been compared for ILC and CLIC:
- Theoretical updates due to strong field environment
- See also talk by A. Hartin
- Spin treatment in DR, spin rotators, BDS under work
- See also talks by D. Barber

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

EW precision measurements@Z-factory

- GigaZ option at the ILC:
- high-lumi running on Z-pole/WW
- 109 Z in 50-100 days of running
- Needs machine changes (e.g. bypass in the current outline)
- Dedicated Z-factory:
- fraction of GigaZ
- but strong physics case given already now!
- Both facilities need polarized e- and e+ beams
- Use of Blondel scheme required to get ΔP/P≤0.1%
- Measurement of e.g. sin2θW with unprecedented precision achievable!

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

Why electroweak precision data?

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

Relevance of ew data today

- Most sensitive observables: mW, sin2θeff,(g-2)μ,…
- Large discrepancy between ALR(l) and AFB(b)
- world average: sin2θeff=0.23153±0.00016

(central value, errors added in quadrature →brute force)

- Impact of this measurement ?

←in b’s

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

Measuring the ew mixing angle

- Measuring the AFB ,

ALR can be interpreted

as measuring sin2θW

- LEP result:

sin2θW=0.23221±0.00029

- SLC result:

sin2θW=0.23098±0.00026

- Discrepancy between AFB and

ALR -> impact on Higgs tests !

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

mW vs. central value sin2θeff

→ Consistent with SM and SUSY

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

mW vs. LEP -value sin2θeff

→ not consistent with neither SM nor SUSY

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

What’s the role of polarization?

- Statistical uncertainty of ALR
- If only polarized electrons:Δ ALR given by polarimeter uncertainty

→ depends on ΔσL, ΔσR, ΔP/P

→ main uncertainty at LC from ΔP/P~ 0.5 %→ 0. 25%...

- If both beams are polarized: Blondel scheme

→uncertainty depends on ΔσLL, ΔσLR, ΔσRL, ΔσRR not on ΔP/P !

→Some running in LL and RR required, about 10-20% of the time

SPIN2010, Jülich, 28.9.10 GudridMoortgat-Pick

Blondel scheme for GigaZ / Z-factory

—

- Measurement of sin2θ in e+e-→Z→f f :

- With Blondel Scheme at ILC:
- (80%,60%) : Δsin2θ= 1.3x10-5
- but Δmtop= 0.1 GeV required!

- With Blondel Scheme at a Z-factory:
- and still Δmtop~1 GeV (i.e. before ILC run): Δsin2θ= 1x10-4 useful!
- but polarized beams required, i.e. P(e+)≥ 20% !

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Summary

- Polarized e- and e+ beams to optimize LC physics potential
- Not only powerful for ‘chirality’ and couplings of new particles!
- Physics potential of either GigaZ or Z-factory a.s.a.p.
- Δsin2θ <1x10-4 seems reasonable now!
- Special care of machine design needed to exploit polarization
- High lumi source designs, spin rotators, precise spin tracking
- Precise Compton polarimetry (up- and downstream)

…. But polarization is these efforts worth ! …

- Further news on polarization at a LC
- Webpages: www.ippp.dur.ac.uk/LCsources
- Further spin effects under work, e.g. CP at LHC, LC, …..

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

Relevance in worst case scenarios

- Hints for new physics in worst case scenarios:
- Only Higgs @LHC
- No hints for SUSY
- Deviations at Zpole
- Hints for SUSY
- Discrepancy

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

- Further important input quantities: mass of top
- δsin2θ ~ 1 x 10-4 would be reasonable now (i.e. before ILC run) !

LHC

ILC

SPIN2010, Jülich, 28.9.10 Gudrid Moortgat-Pick

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