DESY Summer Program 2011 Gudrid Moortgat-Pick 1 Physics at e + e - Colliders Gudrid Moortgat-Pick...

DESY Summer Program 2011 Gudrid Moortgat-Pick

Physics at ePhysics at e++ee-- Colliders Colliders

Gudrid Moortgat-Pick

Hamburg University, 17.8.2011

• Introduction

• Achievements with LEP, SLC

• Physics beyond the Standard Model: supersymmetry

• Techniques at the high-energy e+e- collider

• ILC physics potential in view of LHC expectations

• Summary and some literature for further studies

Few words before …• You heard already a lot about

– how e+e- colliders work– how they are limited– how the physics is detected– how we describe the physics theoretically– summary on physics issues

I do not want to repeat the things, therefore I will focus on only a few

physics topics (top, Higgs, SUSY, ED) and a few technical tools

(threshold scans, continuums measurements, beam polarization)– Discussions: any time, please feel free to ask questions….

Introduction

Characteristics of pp collider:composite particles collideE(CM) < 2 E(beam)strong interaction in initial statesuperposition with spectator

jetsLHC: √s = 7 14TeV, used ŝ = x1x2s few TeVsmall fraction of events

analyzedmultiple triggers`no' polarization applicable

Large potential fordirect discoveries

and of the e +e-(γe, γ γ) collider:pointlike particles collideE(CM) = 2 E(beam)well defined initial stateclean final stateILC: √s = 90 GeV -- 1 TeV, tunableCLIC: √s=3 TeVmost events in detector analyzedno triggers requiredpolarized initial beams possible

Large potential for direct dis-coveries and via high

precision

Discoveries at e+e- colliders

• Some examples of direct discoveries at e+e- colliders:

• J/ Ѱ at SPEAR at SLAC (1974)

• Gluons at PETRA at DESY (1979)

• famous ‘3 jet events’

DESY Summer Program 2011 Gudrid Moortgat-Pick 5

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.

Prediction of the top quark mass

• Predicted discovery of the top quark at the Tevatron 1995!

• Predicted discoveries: e+, n, π, q, g,W, Z, c, b, t• Future examples: Higgs, SUSY ??? -- see later

Some LEP data• Circumference 27 km• √s 91.2 GeV (LEP1) to 209 GeV(LEP2)• Accelerating Gradient Up to 7MV/m

(Superconducting cavities)• Number of Bunches 4 × 4• Current per Bunch ≈ 750 μA• Luminosity at LEP1 24 × 1030 cm−2 s−1 (≈ 1 Z0/s)• Luminosity at LEP2 50 × 1030 cm−2 s−1 (≈ 3 W+W−/h)• Interaction regions 4 (ALEPH,DELPHI,L3,OPAL)• Energy calibration < 1MeV (at Z0)

LEP data1990 – ≈ 91 GeV1995 5 Million Z0/exp.1995 Test phase forLEP2 130GeV1996 161 − 172 GeVWW-Threshold1997 183 − 209 GeV2000 10 000 WW-pairs/exp.Searches fornew physics0 (?) Higgs bosonsLEP was shut down and dismantled to make room for LHC in Nov. 2000

Integrated Luminosities

LEP measured sin2θeff= from AFB(had)

SLC data and featuresSLC data and features• Stanford Linear Collider

– e+e- at √s=91.26 GeV: the ‘Z’ pole– Luminosity ~ 3 x 1030 cm-2s-1

– Special feature:highly polarized e--beam !

P(e-)~78%

– Best single measurement of weak mixing angle:

sin2θeff= 0.23098 ± 0.00026 from ALR(l)• Higher precision although lower luminosity!!!• More examples fort use of polarization, see later …

Back to LEP1: the Basic Process

• Z0 lineshape: Z0 mass, Z0/γ-interference • Number of neutrinos, etc.• Precision tests of the QFD: forward-backward asymmetries• Precision tests of QCD: Confirmation of SU(3)• Together with mW: Prediction of the top quark mass• Many other precision tests of the SM• Very successful: more than 2400 publications from 4 collaborations !

First Z - event

• e+e- -> Z -> q q (13.8.89 !)– Tracking chambers not yet fully operational,

therefore only ECAL

Total cross section

• Z0 gives a dramatic resonance

• cross section well described (at quantum level, not only at tree level!)

Z0 Mass Measurement

• Very important input to SM fits !• Uncertainty is only ∆mZ~2.1MeV• Important to understand systematics of the beam energy

measurement!

Systematics: Beam Energy Measurement

• Uncertainty is only 1MeV !• Further systematics have been: water level, tides, TGV• Remark: polarization not used for physics, but for calibration!

Z0 branching ratios: neutrinos

– measure ‘invisible’ events ! (also important for SUSY, see later)

Counting neutrinos via photons!

• Using radiative neutrino production:

– leads to signal only in ECAL

Fitting the cross section:

• Fit prefers 3 families

• but rather large error

• Some theory assumptions

• but better than nothing…

Other method for counting neutrinos

• Measuring the total width of the Z (‘life-time’)

Exploiting further observables:

angular distributions!• linear dependence on scattering angle cosθ:

Measuring Z0 couplings

• Vector- and axial-vector couplings:

– gVl=T3l-2 e sin2θW

– gAl=T3l

T3l=weak isospin

=-1/2 for e

Measuring the ew mixing angle

• Measuring the AFB

can be interpreted

as measuring sin2θW

• Result (only LEP):

sin2θW=0.23221±0.00029– Result improved by inclusion

of other experiments, e.g.

SLD (see later)

– Discrepancy between AFB and

ALR -> impact on Higgs tests !

Top mass prediction

So far we have done …

• Discussion of LEP1 results, only as an example• Because of time: rarely mentioned details from

other e+e- experiments– SLD: very important also for sin2θW (used polarized

beams, see later)– LEP2: but also very rich program, as e.g. precision W

mass measurement, searches for the Higgs boson, but also for new physics

• But why do we need physics beyond the SM and what are the experimental challenges?

Open questions …and possible Open questions …and possible answersanswers

LHC2FC@CERN 02/09 Gudrid Moortgat-Pick

• Shortcomings of the Standard Model

•Unification of all interactions?

ILC,CLIC

•Hierarchy problem?

LHC,ILC

•Establish electroweak symmetry breaking

ILC,CLIC

•Embedding of gravity

cosmo,LHC/ILC

•Neutrino mixing and masses v-,

cosmo-exp.

•Baryon asymmetry in Universe? v-, cosmo,

LHC, ILC

•Dark matter v-,

cosmo, LHC, ILC

• Why TeV scale?

• Protect hierarchy between mweak and mplanck

• Dark matter consistent with sub-TeV scale WIMPs

Shortcomings of the Standard Model

•doesn't contain gravity

•doesn't explain neutrino masses

•doesn't have candidate for dark matter 23% of universe is cold dark matter!

•no unification of gauge couplings possible

•further problem: `hierachy problem'Higgs mass unstable w.r.t. largequantum corrections:

The Hierarchy Problem

Hierarchy Problem 2Hierarchy Problem 2

Hierarchy Problem 3

Hierarchy Problem 4

Supersymmetry – intro 1

Soft SUSY Breaking

Free parameters in the MSSM

Unconstrained MSSMUnconstrained MSSM

• No particular SUSY breaking mechanism is assumed– 105 parameters, but no quadratic divergencies

• Constrained models (4 to 5 parameters only): assumptions

• New quantum number: R-parity=(-1)3B+L+2S (SM=+1, SUSY=-1)– If conserved: lightest particle is stable ….’dark matter candidate’– Most general and renormalizable superpotential

Particle content in the MSSM

Properties of SUSY - Unification

Prospects of SUSY at future colliders

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

• Unravelling 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!DESY Summer Program 2011 Gudrid Moortgat-Pick

Beam polarization at colliders

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

Electron polarization

Polarized positrons

How to describe the spin?

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

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

General remarks, cont.

Start: Statistical arguments for P(e+)

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:

Statistics 2

• Polarized cross section reads:

• With effective luminosity

Statistics 3 Effective polarization:

Statistics 4

Statistics 5How are Peff and ALR related?

That means:

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

Statistics 6

Background suppression

Back to the ILC physics case…

• But since the ILC can not start before 2020, all physics issues have to be seen in view of expected LHC results

• In the following we discuss several physics topics, starting at 500 GeV, 1TeV, multi-TeV

• Applying the mentioned tools, threshold scans, beam polarization, precision measurements

• But only a personal selection of examples ……

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

mtop= 173.3 +- 1.1 GeV

Top mass 3

We expect at the LC:

Importance of ‘top’ mass

Electroweak symmetry breaking / Higgs

Mh<185 GeV

Currently LHC: maybe mH~120-140 GeV ???

Determination of Higgs properties

LHC input for optimal choices of running scenarios !

Higgs spin

Higgs mass at ILC

Higgs mass, 2

• Use Higgsstrahlung: due to well-known initial state and well-observed Z-decays– Derive Higgs mass independently from decay

– Only possible at a LC!

Higgs properties

SUSY expectations

Status LHC resultsStatus LHC results• First LHC results based on L=35pb-1:

– Exclusion bounds in mSUGRA for couloured spectrum

• Remember talks from EPS conference

From: pp -> 2 jets +MTE

• mSUGRA scenario• coloured g,q > 500 GeV

Interpretation in mSUGRA• electroweak sector: mχ0

2~200 GeV still rather light…

CMS, arXiv: 1101.1628

Status LHC results, cont.Status LHC results, cont.• ATLAS-result:

From: pp -> 2 jets +MTE

• mSUGRA scenario• q,g > 700-800 GeV

Interpretation in mSUGRA• electroweak sector: mχ0

2~300 GeV SPS1a `excluded’• many particles out of kinematical range for √s=500 GeV• but remember, that’s just in mSUGRA!

News see talk by G. Weiglein next week….

But – is mSUGRA the full But – is mSUGRA the full truth?truth?

• Remember: we have 105 new SUSY parameters (instead of only 4) …– `everything’ is possible– but the full MSSM is a more long-term goal– No ‘real’ fitting option

• Relation between particles depends crucially on the SUSY breaking scenario – Study different breaking scenarios with also only a

few parameters – Get a feeling whether we walk on the right interpretation

path….

69DESY Summer Program 2011 Gudrid Moortgat-Pick

New SUSY breaking New SUSY breaking developmentsdevelopments

• For instance, hybrid models: flavourful anomaly-gravity mediation

C. Gross, G. Hiller, arXiv: 1101.5352

• heavy coloured sector• ‘light’ electroweak sector

Further advantages:• no tachions due to flavour dependence• heavy gravitino: benefitial for cosmology

Very interesting model

Is this the only solution?Is this the only solution?• Or take AMSB scenarios:

• Similar feature: heavy coloured but also light uncoloured spectrum

•Technical challenge:

•Mass degeneration

•Only few pheno LC studies performed in the past

Uli Martyn, Nabil Ghodbane, hep-ph/0201233

Or remember good ‘old’ Or remember good ‘old’ examplesexamples

• Have a look on GMSB scenarios (`SPS7’):

Again: •a heavy couloured spectrum is natural in this scenario• but also a rather light electroweak sector…..

But: technical challenges• many т’s, etc.• still many detailed ILC studies missing! ……Uli Martyn, Nabil Ghodbane,

hep-ph/0201233DESY Summer Program 2011 Gudrid Moortgat-Pick

Back to work: discovery of SUSY

SUSY mass determinations at the LHC

SUSY mass measurement im continuum

Mass measurement of the LSP mass

Test off spin quantum number at ILC

• Clean signatures, known initial state, tunable

energy:

One more SUSY Test at the ILC

Chiral quantum numbers, 2

LHC/ILC interplay

Indirect searches: extra dimensions

Extra dimensions

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 test 2

Electroweak precision Electroweak precision observablesobservables

• EWPO: α, GF, MZ, MW, Гl , sin2θeff, gμ-2, …– One example: precise measurement of

MW = 80.399±0.023 GeV

• accuracy of 0.3‰• leading to sensitivity to 1- and 2-loop quantum effects …

• Previous experimental results at the Z-pole:• LEP: very precise measurement of MZ, ГZ, AFB(l), AFB(b,c),…

• SLD: ALR(e), ALR(μ), …

• Of particular interest: sin2θeff = 1-MW2/M2

Z + loop effects• Determined from AFB , A LR

High sensitivity to effects of new physics !85DESY Summer Program 2011 Gudrid Moortgat-Pick

Physics gain of polarized Physics gain of polarized beam(s)beam(s)

• Past experience: – excellent e- polarization ~78% at SLC:– led to best single 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

polarization can even compensate order of magnitude in

luminosity for specific observables !

Current experimental Current experimental situationsituation

LEP:sin2θeff(AFB

b)= 0.23221±0.00029

SLC:sin2θeff(ALR)= 0.23098±0.00026

World average:sin2θeff = 0.23153±0.00016

Discrepancy between the two most precise measurementsCentral value has large impact on physics predictions!

Theory vs. experiment: MTheory vs. experiment: MWW – world av. – world av. of sinof sin22θθeffeff

→ Consistent with Standard Model and MSSM (unconstrained)

Heinemeyer, Weiglein

MMWW - A - ALRLR(SLD)-value sin(SLD)-value sin22θθeffeff

→ large deviation from the Standard Model

MMWW - A - AFBFB(LEP )-value sin(LEP )-value sin22θθeffeff

→ large deviation from both, the Standard Model and the MSSM Precise sin2θeff-measurement has the potential to rule out both models !

sinsin22θθeffeff at the Z-factoryat the Z-factory

• Measure both AFB and ALR in same experiment !

with improved precision w.r.t. LEP and SLC:

• ALR: large gain from polarization of both beams and higher luminosity

• AFB: gain from higher luminosity, better b-tagging, etc.

resolve unclear situation: • New physics affecting AFB(b) and ALR(l) in different ways?

• Resolution of experimental discrepancy:

reliable central value+ improved precision

large impact on interpretation of LHC results!

Which precision should one aim for Which precision should one aim for NOW?NOW?

• Theoretical uncertainties: Δsin2θeffho~5x10-5 (currently)

• Uncertainties from input parameters: ΔmZ, Δαhad , mtop

• ΔmZ=2.1 MeV: Δsin2θeffpara~1.4x10-5

• Δαhad~10 ( 5 future) x 10-5 : Δsin2θeffpara~3.6 (1.8 future )x10-5

• Δmtop~1 GeV (LHC): Δsin2θeffpara~3x10-5

• Δmtop~0.1 GeV (ILC): Δsin2θeffpara~0.3x10-5

If Δsin2θeff ~ 3x10-5 achievable: already big physics impact

Davier, ’10:

Possible result of a Z-factory : Possible result of a Z-factory : ΔΔsinsin22θθeff eff ~ ~ 3x103x10-5-5

would unambiguously rule out SM+MSSM !

Higher precision mandatory to fix central value!

• What’s the benefit of higher precision?Heinemeyer, Weiglein

Blondel scheme for GigaZ @ILC

Would be ultimate precision…..

SUSY Constraints from GigaZ

Only Higgs @LHCNo hints for SUSY

• Deviations in

sin2θeff

– hints for SUSY

• Powerful test!– Do not miss it

Help in worst case scenarios ?

Physics up to 1 TeV

•Direct search for extra dimensions

Direct search for extra dimensions

Multi-TeV option at CLIC - Higgs

Summary• e+e- physics has been the core of high precision

physics over the last decade• Results from LEP, SLD, B-factories provide tests of the

SM at quantum level!• We expect a fascinating future in the next years: LHC

will shed first light on the mysteries of EW symmetry breacking

• Rich program and high physics potential of the ILC will unravel the new physics and enter a new precision frontier!

Stay tuned for the LHC and (I)LC!

( Klaus Desch @CERN 02/09)

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

• Supersymmetry: introduction

M. Drees, hep-ph/9611409, S. Martin, hep-ph/9709356

• Polarization+Spin: GMP, POWER report, Phys. Rept. 460,131 (2008), hep-ph/0507011

webpage: www.ippp.dur.ac.uk/LCsources

DESY Summer Program 2011 Gudrid Moortgat-Pick 1 Physics at e + e - Colliders Gudrid Moortgat-Pick...

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