The Quest for Supersymmetry Sabine Kraml CERN AW

The Quest for Supersymmetry Sabine Kraml (CERN, ÖAW APART) Habilitationskolloquium 8 May 2007

Outline n Introduction ¨ The Standard Model of particle physics ¨ The hierarchy problem and need for New Physics n Supersymmetry (SUSY) ¨ ¨ What is SUSY The minimal supersymmetic model SUSY @ LHC SUSY dark matter n Conclusions S. Kraml The Quest for Supersymmetry 2

What is the world made of…. …. and what holds it together? S. Kraml The Quest for Supersymmetry 3

The Standard Model (SM) of elementary particle physics Masses O(Me. V) 175 Ge. V Interactions described as local gauge theories Matter: 3 families of quarks and leptons, spin ½ fermions. Forces mediated by spin 1 gauge bosons: g, Z 0, W±, g Gauge group: x x SU(3) c SU(2) Y strong int. , weak Lint. , U(1) hypercharge massless ~100 Ge. V c. f. mass of proton ~ 1 Ge. V Q=T -Y/2 3 Arbitrary inclusion Generate masses through of masses gauge-invariant spoils renormalizability dynamics S. Kraml The Quest for Supersymmetry 4

The Standard Model (SM) of elementary particle physics Higgs field Matter: 3 families of quarks and leptons, spin ½ fermions. Forces mediated by spin 1 gauge bosons: g, Z 0, W± <Φ>≠ 0 Gauge group: x Interaction with xscalar background “Higgs” field breaks SU(3) c SU(2)L U(1)Y the symmetry at ~100 Ge. V to SU(3)c x U(1)em → generation of particle masses S. Kraml The Quest for Supersymmetry 5

< 1973: theoretical foundations of the SM renormalizability of SU(2)x. U(1) with Higgs mech. for EWSB ¨ asymptotic freedom, QCD as gauge theory of strong force ¨ KM description of CP violation ¨ Followed by [more than] 30 years of consolidation ¨ experimental verification via discovery of n n ¨ experimental precision measurements of n n n ¨ S. Kraml gauge bosons: gluon, W, Z (Europe) matter fermions: charm, 3 rd family (USA) EW radiative corrections running of the strong coupling as CP violation in the 3 rd generation technical theoretical advances (higher-order calculations, . . ) The Quest for Supersymmetry 6

The development of particle physics has also led to significant progress in astrophysics and cosmology, in particular in our description of the Early Universe. E ~ 1 EMe. V ~ 100 ↔Ge. V T ~ 10 ↔ 10 K T ~↔ 10 t 15~ K 1 s↔ after t ~the 10− 10 Bigs. Bang (Nucleosynthesis) S. Kraml The Quest for Supersymmetry 7

The SM is tremendously successful; it continues to survive all experimental tests S. Kraml The Quest for Supersymmetry 8

Only missing piece: the Higgs! the particle most sought after … 2 fit of the Higgs boson mass from EW precision data as of Summer 2006 S. Kraml The Quest for Supersymmetry 9

Only missing piece: the Higgs! the particle most sought after … LEP Higgs search e+e− → ZH @ √s = 180 -208 Ge. V 2 s evidence of a 115 Ge. V Higgs until 2000, but then LEP had to stop operation ALEPH Transformed into lower limit of m. H > 114. 4 Ge. V Aleph, Delphi, L 3 and Opal collaborations and the LEP Higgs Working Group S. Kraml The Quest for Supersymmetry 10

The SM is tremendously successful. Nevertheless it can’t be the ultimate theory! S. Kraml The Quest for Supersymmetry 11

Grand Unified Theory ? n GUTs attempt to embed the SM gauge group SU(3)x. SU(2)x. U(1) into a larger simple group G only one single gauge coupling constant g. with n Moreover, the matter particles (quarks & leptons) should be combined into common multiplet representations of G. n Prediction: Unification of the strong, weak and electromagnetic interactions into one single force g at MGUT. NB: If MGUT is too low → problems with proton decay S. Kraml The Quest for Supersymmetry 12

S. Kraml The Quest for Supersymmetry 13

The hierarchy problem To break the electroweak symmetry and give masses to the SM particles, some scalar background field must acquire a non-zero VEV. Elementary scalar “Higgs” boson of mass m. H. However, ^m. H=O(m. W) ^dm. H 2 ≤ m. H 2 where L is the scale (=cut-off) up to which theory is valid. MGUT? MPlanck? S. Kraml The Quest for Supersymmetry 14

Beyond the SM (BSM) n The need to stabilize the electroweak scale, dm. H 2 < m. H 2, lets us expect new physics at Te. V energies The search for this new physics is the genuine motivation to build the LHC n Besides, neutrino masses as well as the dark matter and the baryon asymmetry of the Universe provide concrete experimental evidence for BSM physics. S. Kraml The Quest for Supersymmetry 15

Supersymmetry (SUSY) S. Kraml The Quest for Supersymmetry 16

What is SUSY? { Supersymmetry (SUSY) is a symmetry between fermions and bosons. { The SUSY generator Q changes a fermion into a boson & vice versa { Extension of space-time to include anticommuting coordinates xm → (xm, qa) with {qa, qb} = eab This combines the relativistic “external” symmetries (such as Lorentz invariance) with the “internal” symmetries such as weak isospin. { Actually the unique extension of the Poincare algebra * * (the algebra of space-time translations, rotations and boosts) S. Kraml The Quest for Supersymmetry 17

. . . predicts a partner particle for every SM state S. Kraml The Quest for Supersymmetry 18

. . . predicts a partner particle for every SM state Minimal supersymmetric standard model (MSSM) gauge structure SU(3)x. SU(2)x. U(1) S. Kraml The Quest for Supersymmetry 19

Compare: space-time symmetry (special relativity) doubling of the spectrum Antiparticles Superpartners space-time supersymmetry S. Kraml The Quest for Supersymmetry 20

If SUSY exacttheory symmetry, SUSY as were a localan gauge includes a spin-2 state, the graviton (!) and its superpartner the equal gravitino. SM particles and their superpartners would have mass. This is obviously not the case (no superpartners found so far), so SUSY must be broken S. Kraml The Quest for Supersymmetry 21

Back to the hierarchy problem. . . In SUSY, every fermion has a bosonic partner (and vice versa) S. Kraml The Quest for Supersymmetry 22

. . . the SUSY solution + XX − XX solves the hierachy problem XX provided M < O(1) Te. V ! SUSY S. Kraml The Quest for Supersymmetry 23

Gauge coupling unification SM SUSY Again requires SUSY masses of < O(1) Te. V! S. Kraml The Quest for Supersymmetry 24

MSSM particle spectrum SM particles quarks leptons gauge bosons spin Superpartners 1/2 squarks 1/2 sleptons 1 gauginos Higgs bosons 0 spin 0 0 1/2 higgsinos gauginos + higgsinos mix to 2 charginos ± 4 neutralinos 0 Lightest neutralino 01 = lightest SUSY particle (LSP) 2 Higgs doublets → 5 physical Higgs bosons: R 3 parity: symmetry under which SM particles neutral states: scalar h, H; pseudoscalar A are even SUSY are odd. − 2 charged while states: H+, Hparticles If RP is conserved, superpartners can only be produced in pairs and every spuperpartner will cascade-decay to the LSP, which is stable dark matter candidate! S. Kraml The Quest for Supersymmetry 25

SUSY breaking S. Kraml The Quest for Supersymmetry 26

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Minimal supergravity (m. SUGRA) Universal boundary conditions @ GUT scale gluinos, squarks Heavy top effect, drives m. H 2 < 0 Radiative electroweak symmetry breaking! charginos, neutralinos, sleptons S. Kraml univ. gaugino mass univ. scalar mass The Quest for Supersymmetry 28

A light Higgs tanb = v 2/v 1 S. Kraml The Quest for Supersymmetry 29

The beauties of SUSY { Unique extension of relativistic symmetries { Solution to gauge hierarchy problem { Radiative EW symmetry breaking, light Higgs { Gauge coupling unification { Ingredient of string theories { Very rich collider phenomenology { Cold dark matter candidate {. . . . S. Kraml The Quest for Supersymmetry 30

SUSY @ the LHC S. Kraml The Quest for Supersymmetry 31

Large Hadron Collider New accelerator currently built at CERN, scheduled to go in operation this year n n pp collisions at 14 Te. V Searches for Higgs and new physics beyond the Standard Model n n „discovery machine“, typ. precisions O(few%) S. Kraml The Quest for Supersymmetry 32

The LHC machine and experiments 100 m underground 27 km circumference pp collisions at 14 Te. V 8 pp collisions per High 10 Energy factor 7 increase w. r. t. present accelerators second, bunch spacing 24. 95 ns 6 GB/yr Highevent Luminosity section/time) tape: factor increase 33 size 1 (#events/cross MB, storage rate 1 Hz, data to 10100 The Quest for Supersymmetry S. Kraml

S. Kraml The Quest for Supersymmetry 34

SUSY searches at LHC Large cross sections ~100 events/day for M ~ 1 Te. V Spectacular signatures SUSY could be found early on q jet q 0 2 Z jets, l+l− Cascade decays into LSP lead to typical signature: multi-jets / multi-leptons plus large missing energy 0 1 missing energy S. Kraml From Meff peak first+fast measurement of SUSY mass scale to 20% (ca 10 fb-1) The Quest for Supersymmetry 35

Compare with Higgs search S. Kraml The Quest for Supersymmetry 36

Mass measurements: cascade decays ETmiss → no peaks → mass reconstruction through kinematic endpoints Typical precisions: a few % [ATLAS, G. Polesello] S. Kraml The Quest for Supersymmetry 37

If Te. V-scale SUSY is realized in Nature, the LHC will discover a wealth of new states: the superpartner world! would also revolutionize our understanding of space-time S. Kraml The Quest for Supersymmetry 38

SUSY dark matter S. Kraml The Quest for Supersymmetry 39

strong evidence for DM: large-scale structures rotation curves CMB dark matter from BSM? WMAP+SDSS: WCDMh 2 = 0. 105 ± 0. 004 [astro-ph/0608632] multipole moment (l) 0. 094 < WCDMh 2 < 0. 136 (95% CL) [astro-ph/0611582] S. Kraml The Quest for Supersymmetry 40

WIMPs n (weakly interacting massive particles) Dark matter (DM) should be stable, electrically neutral, weakly and gravitationally interacting n WIMPs are predicted by most BSM theories n Stable as result of new discrete symmetries n Thermal relic of the Big Bang n Testable at colliders! A neutralino LSP would indeed be an excellent dark matter candidate Neutralino, gravitino, axino, lightest KK state, T-odd little Higgs, etc. , . . . BSM-DM S. Kraml The Quest for Supersymmetry 41

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: Wh 2 ~ sv − 1 Thermally avaraged annihilation cross section S. Kraml The Quest for Supersymmetry 42

Neutralino relic density 0 LSP as thermal relic: relic density computed as thermally avaraged cross section of all annihilation channels → Wh 2 ~ sv − 1 0. 094 < Wh 2 < 0. 135 puts strong bounds on the parameter space S. Kraml The Quest for Supersymmetry 43

Neutralino relic density 0 LSP as thermal relic: relic density computed as thermally avaraged cross section of all annihilation channels → Wh 2 ~ sv − 1 m. SUGRA 0. 094 < Wh 2 < 0. 135 puts strong bounds on the parameter space S. Kraml The Quest for Supersymmetry 44

Prediction of sv from colliders ~~ ~~ Recall LHC: large cross sections, ~100 gg, gq, . . . events/day q jet q 0 jet 2 Z jets, l+l− 0 1 Abundant production missing energy of our DM candidate S. Kraml LHC as „DM factory“ The Quest for Supersymmetry 45

Prediction of sv from colliders: What do we need to measure? ü LSP mass and decomposition bino, wino, higgsino admixture ü Sfermion masses (bulk, coannhilation) or at least lower limits on them ü Higgs masses and widths: h, H, A ü tanb Required precisions investigated in, e. g. LHC precision most likely not sufficient precision measuremants of O(‰) ! • Need Allanach et al, 2004; • to SK, Pukhov, 2005; match WMAP/PLANCK accuracies Belanger, ILC: international e+e− linear collider • Baltz et al. , 2006 NB: determination of sv also gives a prediction of (in)direct detection rates S. Kraml The Quest for Supersymmetry 46

Direct detection rates Check by direct detection is indispensible to pin down the dark matter [H. Baer et al, hep-ph/0611387] S. Kraml The Quest for Supersymmetry 47