SUSY Studies @Hadron Colliders

1. SUSY Studies @Hadron Colliders • MSSM and need for models e.g. SUGRA. • Limits from Tevatron. • SUSY studies at LHC: • inclusive analysis and discovery limits. • exclusive analysis and precision measurements. • Gauge Mediated SB models • R parity violating models. • SUSY Higgs sector • Conclusions SUSY course T. Weidberg

2. SUSY Models • MSSM: • R parity conservation  LSP stable • LSP is neutral from cosmology • LSP is weakly interacting (why?) • ~ 100 free parameters!  unified models eg SUGRA, GMSB. • R Parity violating models. SUSY course T. Weidberg

3. Minimal SUper GRAvity • SUSY breaking communicated through flavour-blind gravitational interactions. • 5 Parameters assuming unified masses & couplings at GUT scale: • Scalars have mass m0, • gauginos and higgsinos m1/2, • trilinear terms A0, • ratio of vacuum expectation values of Higgs doublets β (yields bilinear couplings and higgsino mass parameter μ2), • sign of the higgs mass term sign(μ). • Non-minimal: > 100 parameters. • LSP is neutralino or sneutrino. SUSY course T. Weidberg

4. How to shape our expectation? Masses in SUGRA: • Predictions very dependent on SUSY models and parameters used. • Use different Monte Carlo generators (ISAJET, SPYTHIA). • Different approximations in the generators require careful tuning and comparison. • Slight variations can have dramatic change in behaviour (channels open up or close). • Typically multi-dimensional parameter space, hard to cover everything by simulation. → Select benchmark parameter sets (e.g. ‘ATLAS 1-5’) to allow estimate of the search capacity of future experiments. Different parameter sets SUSY course T. Weidberg

5. SUSY course T. Weidberg

6. Examples of SUSY Searches at Tevatron • Jets + Missing Et (Why missing Et?) • Tri-leptons SUSY course T. Weidberg

7. Tevatron tri-leptons D0 • Final state: • Leptons are e, μ. • Low SM background: ‘Golden’ SUSY channel • Cuts: • 2e: pT> 15 GeV/c • 10 < Mee< 70 • MT(e,ET)>15 • Track isolation • ET> 15 GeV • D0 Run II (42pb-1): No events observed (0.0±1.4 expected). SUSY course T. Weidberg

8. Squarks and Gluinos • Produced through SU(3)C couplings to q and g. • Due to subsequent decays signatures like neutralinos and charginos, but with more jets. • Final states depend on exact decay channels, but again typically involve ET and multiplicity of jets and/or leptons. • Cleanest: di-lepton (from chargino/neutralino decays), especially same-sign (possible in gluino decays as gluino is Majorana particle). D0 limits in m0/m1/2 plane for different SUGRA parameters SUSY course T. Weidberg

9. SUSY @ LHC • Discovery: jets+ Missing Et • Precision studies depend on models for SUSY breaking. • Measure combinations of masses, reconstruct mass differences or absolute masses. • Branching ratios. • Lifetimes. • Cross-sections. SUSY course T. Weidberg

10. QCD jets ttbar W+jets Z+jets S/N > 10:1 Where does SM background come from? SUSY course T. Weidberg

11. SM Background • QCD NLO calculation gives much bigger background than Pythia. • Why? • Need to measure SM background from data. SUSY course T. Weidberg

12. Reach for SUSY signal at LHC • Final states: • Jets and missing ET (0l). • Missing ET and 1 lepton (1l). • Opposite sign leptons (OS). • Same charge leptons (SS). • Three leptons (3l). • Reach depends on tan b and sign m SUSY course T. Weidberg

13. SUSY course T. Weidberg

14. Supersymmetric Decay Cascades • Heavier supersymmetric particles decay in cascades ending in LSP. • Neutralinos & charginos: Typically 2 body decays when kinematically allowed, otherwise 3 body decay ( ) through virtual gauge bosons or sleptons/squarks. • Charginos (for example from ) can decay through with an isolated lepton in the final state. • Long decay chains → several high pT daughters. • Spherical events. • Gluino is Majorana fermion → can decay to either ℓ+ or ℓ-. Possibility to have same-charge decay chains on both sides. • Simplest signatures for SUSY: • Multiple jets (some of them hard) + missing ET. • Several leptons + missing ET. SUSY course T. Weidberg

15. Chargino and Neutralino Production at Hadron Colliders • Indirectly: • Result of decay chain of heavier sparticles. • Directly: • Through EW couplings to squarks, g, W, Z. • s-channel gauge boson production • t-channel squark exchange • interference SUSY course T. Weidberg

16. Precision Measurements • Measurements of sparticle masses. • . • Select bb with mbb around h mass, add hard jet in event → mbbj, depends on mq. • Endpoint of dilepton (same flavour) mass spectrum: measurement of mass difference. • Combination allows model independent way to establish sparticle masses. • After 1y ATLAS (10 fb-1) expect: ~ SUSY course T. Weidberg

17. higgs • hbbar + Etmiss • Needs b-tagging. SUSY course T. Weidberg

18. Min M(bbj)=>m(squark) SUSY course T. Weidberg

19. Lepton Pairs End point M(ll) gives mass difference SUSY course T. Weidberg

20. Squark Masses • End point  SUSY course T. Weidberg

21. Search for MSSM Stop • 3rd generation left-right mixing → stop can be light (accessible at Tevatron). • Production rate 10% of rate for t of same mass. • Signature: Di-lepton • Other possible stop decays: or with decay signatures bbℓ±jjET and bbjjjjET. SUSY course T. Weidberg

22. High tanβ • For tanβ > 8 final state leptons dominated by t. • Large tanβ is theoretically motivated & favoured by LEP2. • Tevatron standard trilepton search: • Improved t trigger and reconstruction in Run II. • ATLAS: reconstruct m (cuts on jet shape, isolation etc.), endpoint gives ∆m. t id ??? SUSY course T. Weidberg

23. Gauge mediated symmetry breaking (GMSB) • Gauge interactions mediate SUSY breaking. • 6 fundamental parameters: • Number of equivalent messenger fields N5, • scale factor for gravitino mass CGrav, • tanβ, • sign(μ), • messenger mass Mm, • Ratio of SUSY breaking scale to messenger scale Λ. • LSP is gravitino with mass «1GeV,Unlike SUGRA • NLSP either neutralino (small N5) or slepton (large N5). • Small tanβ: slepton masses degenerate, large tanβ: lightest slepton. • Lifetime model-dependent (c from μm to km). SUSY course T. Weidberg

24. GMSB with neutralino NLSP • Phenomenology as for SUGRA, but decay into lightest neutralino is followed by its subsequent decay yielding a photon and ET. • Production of pairs provides clear two-g signature (+ET). • SUSY masses can be determined from kinematics (combine same-flavour, opposite-charge leptons → mℓℓ, then pick smaller mℓℓ, and 2 mℓ distributions give 4 endpoints to determine 3 masses. • Decay length from Dalitz decays (2% of decays). Can be >1km for large Cgrav. SUSY course T. Weidberg

25. GSMB search at Tevatron • Signature (for long lifetime): two non-pointing g + missing ET. • Backgrounds: jets and e faking photons. Messenger mass scale Run II: Run I: SUSY course T. Weidberg

26. GSMB with slepton NLSP • Signature contains final state leptons & missing ET. • Dilepton mass spectrum has steps given by difference of slepton and neutralino mass. • N5>1, Cgrav = 5×103: NLSP is stau. Decay length 1km. Low velocity quasi-stable particles resemble muons: measure TOF in μ-detector. Study ATLAS slow SUSY course T. Weidberg

27. R-parity violation (RPV) • Can be broken into 3 distinct interaction terms with strengths λ, λ’ and λ”: • λ≠ 0: Nl violation in • λ’≠ 0: Nl violation in and • λ”≠ 0:NB violation in • To be consistent with proton lifetime: either lepton or baryon number violated. • Dilutes ET signature but λ andλ’ give multi-jet, multi-lepton events, which are easy to isolate. • Strategy: completely reconstruct LSP decay. SUSY course T. Weidberg

28. SM bounds on RPV opeators • (→en)/(→μn) • Br(D+→K0*μ+nμ)/ Br(D+→K0*e+ne) • nμ deep-inelastic scattering • Br(t→ nt) • Heavy nucleon decay • n - n oscillations • Charged-current universality • (t→enn)/(m→enn) • Bound on the mass of ne • Neutrino-less double-beta decay • Atomic parity violation • D0-D0 mixing • Rℓ→ had(Z0)/ℓ(Z0) All in remarkable agreement with SM predictions. SUSY course T. Weidberg

29. RPV with λ≠ 0 • >4ℓ Signature easy to detect. • Mass of neutralino from dilepton mass spectrum end point (LHC: σm ≈ 180MeV). • Combining candidates at edge with events in h→bb peak allow reconstruction of (LHC: σm ≈ 5GeV). Correct combinations End point Wrong combinations SUSY course T. Weidberg

30. RPV with λ’ ≠ 0 • Fully reconstructable with dilepton signature. • More diffcult. • Missing ET is less than in SUGRA. • Rely on additional leptons from cascade decays and large jet multiplicity. • di-gluinos produce like-sign fermions in 1/8 of time (+2j) CDF Run I: no events SUSY course T. Weidberg

31. Baryon number violating RPV • Most challenging, as decays like provide no signatures like missing ET, or special lepton or quark flavour (b) tags. • Look for dilepton signature from • Signature: minimum 6 jets (3 jets from other neutralino) + 2 leptons, typically around 12 jets (from cascade involving squarks and gluinos). • Then: combine triplets of jets and require two combinations/event within 20 GeV. Then combine with leptons and reconstruct decay fully. SUSY course T. Weidberg

32. 3 jet Mass Reconstruction SUSY course T. Weidberg

33. An indirect evidence for SUSY: H± • If light enough: produced in t→ bH+ • For small tanβ: H+ → cs, large tanβ: H+ → t+nt • CDF: • Direct search: excess over SM of events with t leptons • Indirect search: ‘dissappearance’, depletion of SM decay t → bW (less di-lepton and ℓ+j). SUSY course T. Weidberg

34. SUSY Higgs • MSSM depends on tan b and m(A). • Many decay modes important e.g. • h gg • A tt (enhanced cf SM). tt mass reconstruction? SUSY course T. Weidberg

35. hgg Q1: What is the reducible background? Q2: What is the irreducible background? SUSY course T. Weidberg

36. Att SUSY course T. Weidberg

37. SUSY course T. Weidberg

38. Summary of current SUSY analyses SUSY course T. Weidberg

39. Conclusions • Interesting existing limits from Tevatron • Run II @ Tevatron has chance to discover SUSY. • LHC will allow for discovery and precision SUSY PHYSICS. • Discovery or exclusion of low energy SUSY. • Precision measurements of masses, cross-sections and branching ratios. • Tests of unified theories (e.g. SUGRA). SUSY course T. Weidberg