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The Quest for SUSY : issues for collider physics and cosmology. S. Kraml (CERN) 1-3 Dec 2006. Supersymmetry (SUSY) is the leading candidate for physics beyond the Standard Model (SM). Symmetry between fermions and bosons Q a |fermion> = |boson>.
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The Quest for SUSY:issues for collider physics and cosmology S. Kraml (CERN) 1-3 Dec 2006
Supersymmetry (SUSY) is the leading candidate for physics beyond the Standard Model (SM). Symmetry between fermions and bosons Qa|fermion> = |boson> This combines the relativistic “external” symmetries (such as Lorentz invariance) with the “internal” symmetries such as weak isospin. unique extension of relativistic symmetries of space-time!
recall Arkani-Hamed‘s comments on the unification of space and time...
________________________________________________________ The motivations for TeV-scale SUSY include • the solution of the gauge hierachy problem • the cancellation of quadratic divergences • gauge coupling unification • a viable dark matter candidate ________________________________________________________ ... predicts a partner particle for every SM state
The search for SUSY is hence one of the primary objectives of the CERN Large Hadron Colider and a future int. e+e_ linear collider!
This talk • SM problems and SUSY cures • Naturalness and hierachy problems • Gauge coupling unification • The minimal supersymmetric standard model • Particle spectrum • Collider searches: LHC, ILC • The cosmology connection • Dark matter • EW phase transition and baryon asymmetry
SM problems and SUSY cures
The hierachy and naturalness problems • To break the electroweak symmetry and give masses to the SM particles, some scalar field must acquire a non-zero VEV. • In the SM, this field is elementary, leading to an elementary scalar `Higgs' boson of mass mH. However, where L is the scale (=cut-off) up to which the theory is valid.
These large corrections to the SM Higgs boson mass, which should be mH=O(mW), raise problems at two levels: • to arrange for mH to be many orders smaller than other fundamental mass scales, such as the GUT or the Planck scale ―the hierarchy problem, • to avoid corrections dmH2 which are much larger than mH2 itself ― the naturalness problem.
The supersymmetric solution XXX XXX
A light Higgs XXXX XXXX XXXX c.f. talk by W. Hollik
c2 fit of the Higgs boson mass from EW precision data as of Summer 2006
Radiative electroweak symmetry breaking Heavy top effect, drives mH2 < 0 EW scale GUT scale
Grand unification . • GUTs attempt to embed the SM gauge group SU(3)xSU(2)xU(1) into a larger simple group G with only one single gauge coupling constant g. • Moreover, the matter particles (quarks leptons) should be combined into common multiplet representations of G. • Prediction: Unification of the strong, weak and electro-magnetic interactions into one single force g at MX. NB: If MX is too low → problems with proton decay
1-loop renormalization group evolution of gauge couplings: • SM: • MSSM:
XX Can also be turned into a prediction of the weak mixing angle .....
1 superpartner for each d.o.f.: qL,R and lL,R L-R mixing ~Yukawas ~ ~ Minimal supersymmetric model MSSM = minimal supersymmetric standard model gauginos + higgsinos mix to 2 charginos + 4 neutralinos Lightest neutralino = LSP 2 Higgs doublets → 5 physical Higgs bosons: neutral states: scalar h, H; pseudoscalar A charged states: H+, H-
gluinos, squarks charginos, neutralinos, sleptons Minimal supergravity (mSUGRA) Universal boundary conditions @ GUT scale Heavy top effect, drives mH2 < 0 univ. gaugino mass univ. scalar mass
Recall: Light Higgs XXXX XXXX XXXX c.f. talk by W. Hollik
R parity: symmetry under which SM particles are even _ and SUSY particles are odd If R parity is conserved • SUSY particles can only be produced in pairs • Sparticles always decay to an odd number of sparticles • the lightest SUSY particle (LSP) is stable • any SUSY decay chain ends in the LSP, which is a dark matter candidate
Large Hadron Collider • New accelerator currently built at CERN, scheduled to go in operation in 2007 • pp collisions at 14 TeV • Searches for Higgs and new physics beyond the Standard Model • „discovery machine“, • typ. precisions O(few%)
Events for 10 fb-1 background signal Events for 10 fb-1 Tevatron reach ATLAS ET(j1) > 80 GeV ETmiss > 80 GeV signal background Spectacular and large signal From Meff peak first/fast measurement of SUSY mass scale to 20%(10 fb-1, mSUGRA) Caution: also other BSM models lead to missing energy signature → need spin determination
Compare with Higgs search c.f. talk by G. Dissertori
Mass measurements: cascade decays Mass reconstruction through kinematic endpoints [Allanach et al., hep-ph/0007009] Typical precisions: (a) few % [ATLAS, G. Polesello]
International Linear Collider • e+e- collisions at 0.5-1 TeV • Tunable beam energy and polarization • Clean experimental env. • Precision measurements of O(0.1%), c.f. LEP • Global initiative, next big accelerator after LHC?
ILC: Precision measurements with tunable beam energy and polarization [TESLA TDR] can reach O(0.1%) precision see talk by H.-U. Martyn
High-scale parameter determination c.f. talk by W. Porod
The cosmology connection Higgs? SUSY? • dark matter • dark energy • baryon asymmetry • inflation • .... 1 GeV ~ 1.3 * 1013 K
What is the Universe made of? • Cosmological data: • 4% ±0.4% baryonic matter • 23% ±4% dark matter • 73% ±4% dark energy • Particle physics: • SM is incomplete; expect new physics at the TeV scale • Hope that this new physics also provides the dark matter • Discovery at LHC, precision measurements at ILC ?
WIMPs (weakly interacting massive particles) • DM should be stable, electrically neutral, weakly and gravitationally interacting • WIMPs are predicted by most theories beyond the Standard Model (BSM) • Stable as result of discrete symmetries • Thermal relic of the Big Bang • Testable at colliders! Neutralino, gravitino, axion, axino, LKP, T-odd Little Higgs, branons, etc., ... BSM dark matter
Relic density of WIMPs (weakly interacting massive particles) • Early Universe dense and hot; WIMPs in thermal equilibrium • Universe expands and cools;WIMP density is reduced through pair annihilation; Boltzmann suppression: n~e-m/T • Temperature and densitytoo low for WIMP annihilation to keep up with expansion rate → freeze out Final dark matter density: Wh2 ~ 1/<sv> Thermally avaraged cross section of all annihilation channels
Neutralino LSP as dark matter candidate
Neutralino system Gaugino m´s Higgsino mass Neutralino mass eigenstates → LSP
Neutralino relic density c0 LSP as thermal relic: relic density computed as thermally avaraged cross section of all annihilation channels → Wh2 ~ 1/<sv> Wh2 = 0.1 with 10% acc. puts strong bounds on the parameter space
Annihilation into gauge bosons • cc→ WW / ZZ mainly through t-channel chargino / neutralino exchange; typically also some annihilation into Zh, hh • Does not occur for pure bino; LSP needs to be mixed bino-higgsino(or bino-wino) • Pure wino or higgsino LSP: • neutral and charged states are a mass-degenerate triplet, • (co)annihilation too efficient • Right relic density for • (|m|-M1)/M1 ~ 0.3, • (M2-M1)/M1 ~ 0.1 [hep-ph/0604150]
Coannihilations • Occur for small mass differences between LSP and next-to-lightest sparticle(s); efficient channel for a bino-like LSP • Typical case: coann. with staus • Key parameter is the mass difference DM = mNLSP−mLSP • Other possibilities: Coannihilation with stops (DM~20-30GeV), coann. with chargino and the 2nd neutralino (in non-unified models)
mSUGRA parameter space • GUT-scale boundary conditions: m0, m1/2, A0 [plus tanb, sgn(m)] • 4 regions with right Wh2 • bulk (excl. by mh from LEP) • co-annihilation • Higgs funnel (tanb ~ 50) • focus point (higgsino scenario)
Prediction of Wh2 from colliders: Requires precise measurements of • LSP mass and decomposition bino, wino, higgsino admixture • Sfermion masses (bulk, coannhilation) or at least lower limits on them • Higgs masses and widths: h,H,A • tanb Required precisions investigated in, e.g. Allanach et al, hep-ph/0410091 and Baltz et al., hep-ph/0602187 c.f. talks by H.U. Martyn & B. Allanach NB: determination of <sv> also gives a prediction of the (in)direct detection rates
For a precise prediction of Wh2 we need precision measurements of most of the SUSY spectrum (masses and couplings) → LHC+ILC ← LHC WMAP ILC