S. Kraml (CERN)

1-3 Dec 2006

The Quest for SUSY :issues for collider physics and cosmology

Supersymmetry (SUSY)

is the leading candidate for physics

beyond the Standard Model (SM).

Symmetry between fermions and bosons

Q|fermion> = |boson>

unique extension of relativistic symmetries of space-time!This combines the relativistic “external” symmetries (such as Lorentz

invariance) with the “internal” symmetries such as weak isospin.

recall Arkani-Hamed‘s comments on the unification of space and time...

... predicts a partner particle for every SM state________________________________________________________

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

________________________________________________________

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

1. SM problems and SUSY cures Naturalness and hierachy problems Gauge coupling unification

2. The minimal supersymmetric standard model Particle spectrum Collider searches: LHC, ILC

3. 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 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 mH

2 which are much larger than mH

2 itself ― the naturalness problem.

The supersymmetric solution

XXXXXX

A light Higgs

XXXX

XXXX

XXXX

c.f. talk by W. Hollik

2 fit of the Higgs boson mass from EW precision data as of Summer 2006

Heavy top effect,

drives mH2 < 0

Radiative electroweak symmetry breaking

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:

One can also re-write this as

XX

Can also be turned into a prediction of the weak mixing angle .....

The MSSM

Minimal supersymmetric modelMSSM = minimal supersymmetric standard model

SM particles spin Superpartners spin

quarks 1/2 squarks 0

leptons 1/2 sleptons 0

gauge bosons 1 gauginos 1/2

Higgs bosons 0 higgsinos 1/2

gauginos +

higgsinos

mix to

2 charginos +

4 neutralinos

2 Higgs doublets → 5 physical Higgs bosons:

neutral states: scalar h, H; pseudoscalar A

charged states: H+, H-

Lightest neutralino = LSP

1 superpartner

for each d.o.f.:

qL,R and lL,R

L-R mixing

~Yukawas

~ ~

XXXX

Heavy top effect,

drives mH2 < 0

Minimal supergravity (mSUGRA)

charginos,

neutralinos,

sleptons

gluinos,

squarks

Universal

boundary

conditions

@ GUT scale

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

The scale of SUSY breaking

Goldstino and Gravitino

Gravitino mass

SUSY @ colliders

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%)

SUSY searches at LHC

Events for 10 fb-1 signalbackground

(GeV) )(jet p E M4

1iiT

missTeff

Tevatron reach

ET(j1) > 80 GeVET

miss > 80 GeV

signalEvents for 10 fb-1

background

(GeV) )(jet p E M4

1iiT

missTeff

ATLAS

From Meff peak first/fast measurement of SUSY mass scale to 20% (10 fb-1, mSUGRA)

Spectacular and large signal

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 decaysMass reconstruction through kinematic endpoints

[ATLAS, G. Polesello]

[Allanach et al., hep-ph/0007009]

Typical precisions: (a) few %

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

Higgs?

SUSY?

1 GeV ~ 1.3 * 1013 K

The cosmology connection

• dark matter• dark energy• baryon asymmetry• inflation• ....

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)

(1) Early Universe dense and hot; WIMPs in thermal equilibrium

(2) Universe expands and cools; WIMP density is reduced through pair annihilation; Boltzmann suppression: n~e-m/T

(3) Temperature and density too low for WIMP annihilation to keep up with expansion rate → freeze out

Final dark matter density: h2 ~ 1/<v>Thermally avaraged cross section of all annihilation channels

Neutralino LSP

as dark matter candidate

Neutralino system

Neutralino mass eigenstates

Gaugino m´s

Higgsino mass

→ LSP

Neutralino relic density

h2 = 0.1 with 10% acc. puts strong bounds on the parameter space

LSP as thermal relic: relic density computed as thermally avaraged

cross section of all annihilation channels → h2 ~ 1/<v>

Annihilation into gauge bosons → 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 (-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

= mNLSP−mLSP

Other possibilities: Coannihilation with stops (~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 tan, sgn()]

4 regions with right h2 bulk (excl. by mh from LEP)

co-annihilation Higgs funnel (tan ~ 50) focus point (higgsino scenario)

Prediction of h2 from colliders:Requires precise measurements of

LSP mass and decompositionbino, wino, higgsino admixture

Sfermion masses (bulk, coannhilation)or at least lower limits on them

Higgs masses and widths: h,H,A

tan

Required precisions investigated in, e.g. Allanach et al, hep-ph/0410091 andBaltz et al., hep-ph/0602187 c.f. talks by H.U. Martyn & B. Allanach

NB: determination of <v> also gives a prediction of the (in)direct detection rates

For a precise prediction of h2

we need precision measurements

of most of the SUSY spectrum

(masses and couplings)

→ LHC+ILC ←WMAP

LHC

ILC

Gravitinos

Recall:

If m3/2 > mLSP, the gravitino does not play any role in collider phenomenology

However, it is possible that the gravitino is the LSPPhenomenology as before, BUT all SUSY particles will cascade decay to the next-to-lightest sparticle (NLSP), which then decays to the gravitino LSP.

Note 1: the NLSP may be charged Note 2: since the couplings to the gravitino are very weak,

the NLSP can moreover be long-lived

→ Gravitino as dark matter candidate

→ Collider pheno characterized by the nature and lifetime of the NLSP

Implications from cosmology The most popular model for explaining the apparent baryon

asymmetry of the Universe is LEPTOGENESIS

→ out-of-equilibrium decays of heavy singlet neutrinos

Leptogenesis requires

a reheating temperature

TR > 109 GeV

At high TR an unstable G is

severely constrained by BBN

► Leptogenesis is OK

if the gravitino is the LSP

[Buchmüller et al]

~

Gravitino dark matter

• Neutralino NLSP is excluded by BBN• Best studied alternative: stau NLSP

• Need to confirm spin-3/2 [L. Covi et al]

c.f. talk by H.-U. Martyn

instead of conclusions ...

„Since its discovery some ten years ago, supersymmetry has fascinated many physicists“

Hans-Peter Nilles, Phys. Rept. 110 (1984)

„The discovery of supersymmetry is

tantamount to the discovery of

quantum dimensions of space-time“

David Gross, CERN Colloq., 2004

whether or not it is SUSY ....

The exploration of the TEV energy scale

at the LHC and a future ILC

will lead to

fundamental new insights on physics

at both the smallest and the largest scales.

PS: SUSY phenomenology is extremly rich,

and this talk could only scratch on the surface.

SUSY at this meeting:

MSSM predictions W. Hollik

Charginos at the ILC T. Robens

Parameter determination H.-U. Martyn, W. Porod

SUSY CP violation T. Kernreiter, K. Rolbiecki

Neutrino masses F. Deppisch

SUSY breaking N. Uekusa

SUSY dark matter A. Provenza, B. Allanach

backups

Assume we have found SUSY with

a neutralino LSP and made very precise

measurements of all relevant parameters:

What if the inferred

h2 is too high?

Solution 1:

Dark matter is superWIMP

e.g. gravitino or axino

Solution 2:

R-parity is violated after all

RPV on long time scales

Late decays of neutralino LSP reduce the number density; actual CDM is something else

Very hard to test at colliders

Astrophysics constraints?

Our picture of dark matter as a thermal relic

from the big bang may be to simple

Universe after Inflation radiation dominated?

Non-thermal production?

Assumptions in WMAP data ↔ h2 ?

Solution 3:

Cosmological assumptions are wrong