DESY Summer Program 2011 Gudrid Moortgat-Pick 1 Physics at e Physics at e + + e e - - 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
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DESY Summer Program 2011 Gudrid Moortgat-Pick
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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
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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….
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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
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
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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’
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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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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
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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)
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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 …
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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 !
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First Z - event
• e+e- -> Z -> q q (13.8.89 !)– Tracking chambers not yet fully operational,
therefore only ECAL
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Total cross section
• Z0 gives a dramatic resonance
• cross section well described (at quantum level, not only at tree level!)
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Z0 Mass Measurement
• Very important input to SM fits !• Uncertainty is only ∆mZ~2.1MeV• Important to understand systematics of the beam energy
measurement!
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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!
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Z0 branching ratios: neutrinos
– measure ‘invisible’ events ! (also important for SUSY, see later)
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Counting neutrinos via photons!
• Using radiative neutrino production:
– leads to signal only in ECAL
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Fitting the cross section:
• Fit prefers 3 families
• but rather large error
• Some theory assumptions
• but better than nothing…
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Other method for counting neutrinos
• Measuring the total width of the Z (‘life-time’)
•
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Exploiting further observables:
angular distributions!• linear dependence on scattering angle cosθ:
– n
– n
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Measuring Z0 couplings
• Vector- and axial-vector couplings:
– gVl=T3l-2 e sin2θW
– gAl=T3l
T3l=weak isospin
=-1/2 for e
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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 !
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Top mass prediction
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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
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• 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
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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:
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The Hierarchy Problem
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Hierarchy Problem 2Hierarchy Problem 2
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Hierarchy Problem 3
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Hierarchy Problem 4
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Supersymmetry – intro 1
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Supersymmetry – intro 2
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Supersymmetry – intro 3
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Supersymmetry – intro 4
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Supersymmetry – intro 5
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Supersymmetry – intro 6
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Soft SUSY Breaking
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Free parameters in the MSSM
Unconstrained MSSMUnconstrained MSSM
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• 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
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Particle content in the MSSM
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Properties of SUSY - Unification
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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
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Beam polarization at colliders
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e+ polarization is an absolute novelty! Expected P(e+) ~ 60%
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Electron polarization
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Polarized positrons
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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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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:
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Statistics 2
• Polarized cross section reads:
• With effective luminosity
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Statistics 3 Effective polarization:
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Statistics 4
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Statistics 5How are Peff and ALR related?
That means:
With pure error propagation (and errors uncorrelated), one obtains:
With
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Statistics 6
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Background suppression
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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
LHC input for optimal choices of running scenarios !
Higgs spin
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Higgs mass at ILC
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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!
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Higgs properties
SUSY expectations
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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
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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
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Status LHC results, cont.Status LHC results, cont.• ATLAS-result:
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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!
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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….
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New SUSY breaking New SUSY breaking developmentsdevelopments
• For instance, hybrid models: flavourful anomaly-gravity mediation
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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
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Is this the only solution?Is this the only solution?• Or take AMSB scenarios:
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• 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
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Or remember good ‘old’ Or remember good ‘old’ examplesexamples
• Have a look on GMSB scenarios (`SPS7’):
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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,
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Back to work: discovery of SUSY
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SUSY mass determinations at the LHC
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SUSY mass measurement im continuum
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Mass measurement of the LSP mass
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Test off spin quantum number at ILC
• Clean signatures, known initial state, tunable
energy:
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One more SUSY Test at the ILC
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Chiral quantum numbers, 2
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LHC/ILC interplay
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Indirect searches: extra dimensions
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Extra dimensions
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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!