Physics at a future Linear Collider

Pre-SUSY, Bonn, 19-21.8.2010 Gudrid Moortgat-Pick

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Physics at a future Physics at a future Linear ColliderLinear Collider

Gudrid Moortgat-Pick Hamburg University, 20.8.2010

• ‘Big’ HEP questions•LC technical requirements• LC physics in view of LHC results• Techniques at the high-energy e+e- collider• Summary and some literature for further studies

Sceptical thoughts Sceptical thoughts before….before….• Many options and ideas for experiments

– Most are expensive, some ‘rather’ cheap– Should cost be a criteria? Or diversity of the physics

programme?• Priority lists are needed

– Many lists exist (CERN strategy group, P5, UK roadmaps, German roadmaps…)

• But big experiments require long term planning– To which extent are physics needs in advance

predictable? Particle scales? Physics Models? …• Can we really weight today all options?

– ILC, SLHC, LHeC, CLIC, ν-fact, DLHC, μ-collider,…. Pre-SUSY, Bonn, 19-21.8.2010 Gudrid Moortgat-Pick

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(My ) Pragmatic (My ) Pragmatic approachapproach

• Physics: what are the ‘big’ questions?– Define steps ... ‘physics milestones’– Identify which models tic which question– Common feature requirements: measure masses,

couplings, spin, quantum numbers … ‘verify at quantum level’

• Machine: next physics milestone achievable?– Technical requirements for a LC have been defined– Synergy with other experiments– Some degree of flexibility required: ‘the unexpected’


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‘‘Big’ questions …and possible Big’ questions …and possible answersanswers


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• Shortcomings of the Standard Model•Establish electroweak symmetry breaking LC •Hierarchy problem? •Unification of all interactions? •Embedding of gravity •Baryon asymmetry in Universe? •Dark matter •Neutrino mixing and masses

• Why TeV scale?• Protect hierarchy between mweak and mplanck

• Dark matter consistent with sub-TeV scale WIMPs

Higgs mass with respect to large quantum corrections:



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





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



Why a Linear Collider?

Key features of the e +e-( and γe, γ γ) collider:– Precisely defined and known cms energy of hard process (machine requirements: low beam energy spread, low beamstrahlung)– Tunable cms energy (machine requirements: flexibility, high luminosity)– Polarized initial beams (machine and detector requirements: – Clean and fully reconstructable events (hadronic, invisible) (detector requirements: jet, lepton reconstruction, full hermiticity)– Moderate backgrounds: no trigger required! rather unbiased physics….

Large potential for direct discoveries and via high precision !Pre-SUSY, Bonn, 19-21.8.2010 Gudrid Moortgat-Pick

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Pre-SUSY, Bonn, 19-21.8.2010 Gudrid Moortgat-Pick 8

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.

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At the precision frontier: the LC


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ICFA Parameter Group

Synergy effects: LHC2FC@CERN 2/09

Questions from early LHC data ( ~10 fb-1 )• ‘Famous’ 3 cases (cf. CERN strategy

documents) :

– LHC not detected anything

– LHC only detected SM-like Higgs

– LHC detected some new physics

• What could the LC do – in first ILC stage of 90 up to 500 GeV?

– in LC upgrades?

– in multi-TeV CLIC option?Pre-SUSY, Bonn, 19-21.8.2010 Gudrid Moortgat-Pick

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Nothing found at (early) LHC

• Interpretation for ILC?– ‘Top’ physics

– indirect searches in bb, cc, l l ( large ED, CI)

– ew precision runs from Z-pole data

• But is then really 500 GeV as first ILC stage needed?– or better 350 GeV? High-lumi Z-factory?


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Physics up to sqrt(s)=500 GeV: top

mtop= 173.3 +- 1.1 GeV

Top mass


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•We expect at the LC:

• From running at tt threshold:• Measurement of a ‘threshold mass parameter’’ with high precision: < 20 MeV •+transition to suitably defined (short-distance) top-quark mass, e.g. MS mass

δmtexp<100 MeV (dominated by theory

uncertainty)

Importance of ‘top’ mass


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EW precision measurements

• GigaZ option at the ILC: – high-lumi running on Z-pole/WW– 109 Z in 50-100 days of running– Needs machine changes (bypass in the current

outline)

• High precision needs polarized beams

• Provides measurement of sin2θW with unprecedented precision!

Electroweak precision data


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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 !

mW vs. central value sin2θeff


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→ Consistent with SM and SUSY

mW vs. SLD-value sin2θeff


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→ not consistent with the SM

mW vs. LEP -value sin2θeff


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→ not consistent with neither SM nor SUSY


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Blondel scheme for GigaZ


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Relevance in worst case scenariosRelevance 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


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SUSY Constraints from GigaZ

What’s needed? What’s needed? ….polarized beams….polarized beams


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e+ polarization is an absolute novelty! Expected P(e+) ~ 60%


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Polarized positrons


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Polarized 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:


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Effective polarization Effective polarization:


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Relation between Peff and ALRHow are Peff and ALR related?

That means:

With pure error propagation (and errors uncorrelated), one obtains:

With


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Gain in accuracy due to P(e+)

Only SM-like Higgs at early LHC• Interpretation for ILC

– best-suited for studying Higgs properties

– precise determination of couplings:

determination of Hbb is crucial!

– distinction: SM- versus SUSY Higgs– t t H and trilinear Higgs coup. challenging

• But is then really 500 GeV as 1st step needed?– Optimize running scenarios (tunable energy, polarization)


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Pre-SUSY, Bonn, 19-21.8.2010 Gudrid Moortgat-Pick 31

Determination of Higgs properties

LHC input for optimal choices of running scenarios !

→ Higgs spin


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Higgs physics at ILC• Higgs Strahlung WW fusion


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Higgs mass• Use Higgsstrahlung: due to well-known initial state

and well-observed Z-decays– Derive Higgs mass independently from decay !

– Only possible at a LC!


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Higgs properties

Something ‘new’ detected at early LHC• SUSY-like signals (many tics at big questions!)

– At least partial spectrum accessible at ILC – ‘light’ SUSY consistent with precision fits

• Extra gauge bosons and/or large extra dimensions (some tics at big questions!)– High precision in indirect searches allow

model distinction and couplings determination


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Goals and features at a Goals and features at a LCLC

• Direct production up to kinematical limit– tunable energy: threshold scans !

• Extremely clean signatures– polarized beams available– impressive potential also for indirect searches via

precision• Unraveling the structure of NP

– precise determination of underlying parameters– model distinction through model independent searches

• High precision measurements– test of the Standard Model (SM) with unprecedented

precision– even smallest hints of NP could be observed

Discovery of new phenomena via high energy and high precision!


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Discovery of SUSY


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SUSY mass measurement im continuum


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Masses and spin via threshold scans

• Assume LHC provides mass of a SUSY particle:


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Mass measurement of the LSP mass

Properties of WIMP’s: Properties of WIMP’s: mass+spinmass+spin

• Reconstruct the `invisible’:

– via recoil mass distribution


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Verify SUSY properties at ILC


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Slepton `chiral’ quantum numbers

Sensitivity to heavy SUSY Sensitivity to heavy SUSY particles particles

• Challenging scenarios: – multi-TeV sfermions, only few light

gauginos (‘focuspoint-like’) also very difficult for

LHC …– sensitivity to heavy sneutrinos in t-channel


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Suitable observable: Precise measurement of asymmetry copes with multi-TeV particles !


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Free parameters in the MSSM


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SUSY parameter determination

• Exploit just light SUSY particle spectrum at ILC and determine the parameters (see below)• Combine it with LHC results

via prediction of heavier states

SUSY multi-parameter fits: SUSY multi-parameter fits: LHCLHC


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SUSY multi parameter fits: SUSY multi parameter fits: LHC+ILCLHC+ILC


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Aside: Disney World of SUSY Aside: Disney World of SUSY scenariosscenarios


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Pure particle counting as justification of the energy scale -but what’s about the achievable precision? -but what can be learned via precisions observables at lower energies? (GigaZ, AFB,…)General feature: in order to be consistent with existing experimental bounds, e.g. with gμ-2:

a few gauginos have to be rather light ! ….sufficient as 1.step


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Indirect searches: extra dimensions


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Extra dimensions


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Physics up to 1 TeV

•Direct search for extra dimensions


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Direct search for extra dimensions


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Multi-TeV option at CLIC - Higgs


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Summary• e+e- physics (LEP, SLC, B-factories) has been the core

of high precision physics over the last decade • We expect a fascinating future in the next years: LHC

will shed first light on the mysteries of EW symmetry breaking

• Rich program and high physics potential of a LC: The LC will unravel the new physics and enter a new

precision frontier!– Thresholds scans and polarized beams mandatory

• Staged approach of a LC seems reasonable… Stay tuned for the LHC and the (I)LC!


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Some literature• ILC physics: TESLA TDR, physics part hep-ph/0106315 ILC RDR, arXiv:0712.1950

• LHC/ILC interplay: G. Weiglein, Phys. Rept. 426, 47 (2006), hep-ph/0410364

• Polarization+Spin: GMP, POWER report, Phys. Rept. 460,131 (2008), hep-ph/0507011 webpage: www.ippp.dur.ac.uk/LCsources


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Beam polarization at colliders


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Electron polarization


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How to describe the spin?


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Remarks about couplings structureDefinition: Helicity λ=s * p/|p| ‘projection of spin’

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


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General remarks, cont.


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Background suppression

Dark matter analysis at LC• High precision in parameter determination

required for reliable DM prediction– Parameter ranges where abrupt changes of neutralino character happen

– Precise determination of M1,M2….required


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V. Morton-Thurtle

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Physics at a future Linear Collider