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Discovering (and understanding) SUSY at the LHC…

Discovering (and understanding) SUSY at the LHC…. Alan Barr University of Oxford. … an introduction (with apologies to the many people who’s work I have included unreferenced and to those whom I have left out). LHC physics is about to get very interesting!. ATLAS control room.

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Discovering (and understanding) SUSY at the LHC…

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  1. Discovering (and understanding) SUSY at the LHC… Alan BarrUniversity of Oxford … an introduction (with apologies to the many people who’s work I have included unreferenced and to those whom I have left out)

  2. LHC physics is about to get very interesting!

  3. ATLAS control room

  4. Have lots of cosmics events(these from much earlier)

  5. Last chance to visit LHC Relatively well-known German physicist takes her chance

  6. 1/α +SUSY Log10 (μ / GeV) The value of prejudice rapidly diminishing Visible mass Invisible mass stop higgs higgs Motivational arguments

  7. How to make a discovery? • Which way to search? cMSSM Who knows what? Other SUSY? ExtraDimensions? Explorer/experimentalists rule: Try to COVER ALL BASES

  8. Astro/cosmo motivation for model-independent signatures We’re pretty sure there are WIMPs out there LHC produces Dark Matter + something visible Invisible particle could be: Lightest SUSY particle Lightest KK particle Lightest generic parity-odd particle Signature: Missing energy + Xvis + Xvis Benefit: Same search finds multiple different models Drawback: You ain’t so sure what you’ve got when you find it Signature-based hunts • Experiments see: • Jets, leptons, missing energy, b-jets

  9. Example SUSY search Mass (GeV) • Assume R-parity • Look for: • Jets from squark & gluino decays • Leptons from gaugino & slepton decays • Missing energy from (stable) LSPs “Typical” SUSY spectrum

  10. SUSY event Missing transverse momentum Heavy quarks Jets Leptons

  11. Cross-sections etc “Rediscover” Lower backgrounds WW ZZ “Discover” Higher backgrounds

  12. Precise measurement of SM backgrounds: the problem • SM backgrounds are not that small • There are uncertainties in • Cross sections • Kinematical distributions • Detector response

  13. Signal BG Typical search: inclusive distributions • Trigger on jets + missing energy • Plot “effective mass” • Look for non-SM physics at high mass

  14. Example: SUSY BG Missing energy + jets from Z0 to neutrinos Measure in Z -> μμ Use for Z ->  Good match Useful technique Statistics limited Go on to use W => μ to improve m m n n Standard Model backgrounds: measure from LHC DATA • Measure in Z -> μμ • Use in Z -> νν R: Z -> nnB: EstimatedR: Estimated

  15. Estimating the backgrounds Good match to “true” background Search region Control Region More from Davide Costanzolater in this session

  16. Et(miss) Lesson from the Tevatron Importance of detailed detector understanding • Simulation shows events with large fake missing energy • Jets falling in “crack” region • Calorimeter punch-through • Vital to remove these in missing energy tails • Large effort in physics commissioning

  17. ’Focus point' region: annihilation to gauge bosons Reach in cMSSM? mSUGRA A0=0, tan(b) = 10, m>0 Slepton Co-annihilation region Rule out with 1fb-1 'Bulk' region: t-channel slepton exchange WMAP constraints

  18. Multiple channels for discovery Below the lines = discovered Differentfinalstates

  19. Assume we have MSSM-like SUSY with m(squark)~m(gluino)~600 GeV See excesses in these distributions Can’t say “we have discovered SUSY” Can say some things: Undetectedparticles produced missing energy Some particles have mass ~ 600 GeV, with couplings similar to QCD Meff & cross-section Some of the particles are coloured jets Some of the particles are Majorana excess of like-sign lepton pairs Lepton flavour~ conserved in first two generations e vs mu numbers Possibly Yukawa-like couplings excess of third generation Some particles containlepton quantum numbers opposite sign, same family dileptons … What might we then know? Slide based on Polesello

  20. Mapping out the new world • Some measurements make high demands on: • Statistics ( time) • Understanding of detector • Clever experimental techniques

  21. SUSY mass measurements Tryvariousdecaychains Look forsensitive variables (many of them) • Extracting parameters of interest • Difficult problem • Lots of competing channels • Can be difficult to disentangle • Ambiguities in interpretation • Example method shown here • Alternatives also on the market • Comparable precision Extractmasses

  22. Stransverse mass (MT2) method

  23. Measuring the shapes • Better precision possible than for endpoints • Systematic uncertinties need to be controlled Much work here recently…

  24. The defining property of supersymmetry Distinguish from e.g. similar-looking Universal Extra Dimensions Difficult to measure @ LHC No polarised beams Missing energy Inderminate initial state from pp collision Nevertheless, we have some very good chances… ~ l+ _ q q θ ~ l- SUSY spin measurements Slepton spin from angles in Drell-Yan production Neutralino spin from angles in decay chains + lots of other recent work in this area

  25. Vector Gluino Fermion Scalar Squark Other ways of measuring spin • Cross-section depends on spin • If mass scale can be measured then spin can be inferred

  26. Use LHC measurements to “predict” relic density of observed LSPs Caveats: Cant tell about lifetimes beyond detector (need direct search) Studies done so far in optimistic case (light sparticles) To remove mSUGRA assumption need extra constraints: All neutralino masses Use as inputs to gaugino & higgsino content of LSP Lightest stau mass Is stau-coannihilation important? Heavy Higgs boson mass Is Higgs co-annihilation important? More work is in progress Probably not all achievable at LHC ILC would help lots (if in reach) mSUGRA assumed Dark matter relic density?

  27. Covering all the bases… • Host of other searches: • Light stop squarks • R-parity violating models • Dileptons/trileptons with missing energy • Taus with jets & missing energy, … • Single photons • Diphoton resonances • Heavy l resonances • Heavy flavour excesses • Monojets • Same sign Stops • … See e.g.CMS Physics TDR II2006 ATLAS SUSYdiscovery chapter2008

  28. 10 TeV … LHC run 2008 10 TeV run need not be “just “commissioning” Lots of physics and discovery potential

  29. Conclusions

  30. Extra rations

  31. Signature depends on Next to Lightest SUSY Particle (NLSP) lifetime Interesting cases: Non-pointing photons Long lived staus Extraction of masses possible from full event reconstruction More detailed studies in progress by both detectors Gauge Mediated SUSY Breaking

  32. Motivated by e.g. “split SUSY” Heavy scalars Gluino decay through heavy virtual squark very suppressed R-parity conserved Gluinos long-lived Lots of interesting nuclear physics in interactions Charge flipping, mass degeneracy, … Importance here is that signal is very different from standard SUSY R-hadrons

  33. The ultimate test of electroweak symmetry breaking Not unitary above ~1 TeV if no new physics Reconstruct hadronic + leptonic W pair Require forward jets Veto jets in central region Exotic WW scattering BG BG signal Most difficult case: continuum signal 5- significance with 30 fb-1in most difficult case

  34. Dijet masses: Contact Interactions • Reduce systematics by using ratio à la DZero • New physics in the central region • “Calibration” sample at higher rapidity • Uncertainties from proton structure not negligible • Improve with LHC data? • Detector cross-calibration uncertainties to be determined from data • Estimates here

  35. Randall -Sudrum graviton spin e graviton p p θ e 1.5 TeV Randall-Sundrum graviton -» e+e- Graviton is spin-2 RS Gravitons & heavy bosons • Discovery • Find mass peak • Characterisation • Measure spin Angular distributions

  36. Large EDs Micro black hole decaying via Hawking radiation Photons + Jets + … We will certainly know something funny is happening Large multiplicities Large ET Large missing ET Highly spherical compared to BGs Theory uncertainty limits interpretation Geometrical information difficult to disentangle Spectacular states : micro Black Holes sphericity

  37. Black hole interpretation? Slide from Lester

  38. CMS Physics TDR, Volume II (recent) CERN-LHCC-2006-021 ATLAS Physics TDR (older) CERN-LHCC-99-015 Physics at the LHC 2006 Programme SLAC School 06 Polesello, Hinchliffe SUSY06 Polesello, Spiropulu Missing ET tails: Paige SM background Okawa et al, WMAP constraints Ellis et al SUSY mass extraction Gjelsten et al SUSY Spin: Barr Exotic SUSY Parker Dark Matter Nojiri et al R-hadrons Kraan et al Hellman et al WW scattering Stefanidis GMSB Zalewski, Prieur RS Graviton: Allanach et al,Traczyk Black Holes Charybdis, Tanaka, Brett, Lester WW scattering Stephanidis Some of the sources

  39. inclusivecross-sectionptmiss > 500 edges combined Combine with MarkovChain MC Constraining masses with cross-section information • Edges best for mass differences • Formulae contain differences in m2 • Overall mass- scale hard at LHC • Cross-section changes rapidly with mass scale • Use inclusive variables to constrain mass scale • E.g. >500 GeV ptmiss Lester, Parker, White hep-ph/0508143

  40. 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons ~ ~ c01 t ~ c01 l ~ t1 ~ ~ t1 g/Z/h lR ~ c01 l SUSY Dark Matter mSUGRA A0=0, tan(b) = 10, m>0 Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. Ellis et al. hep-ph/0303043 Disfavoured by BR (b  s) = (3.2  0.5)  10-4 (CLEO, BELLE) 'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. Also 'rapid annihilation funnel' at Higgs pole at high tan(b), stop co-annihilation region at large A0 0.094    h2  0.129 (WMAP)

  41. More on GMSB • Negligible contribution from the SM backgrounds (consistent with TDR)  Trigger efficiencies of the signal is crucial for the discovery potential (background rejection, rate estimates would be the next step) G1a (L=90TeV) G1a (L=90TeV) <After Requiring> Meff > 400GeV EtMiss>0.1Meff two leptons BG Total BG Total g1 g2 Leading Photon Pt (GeV) 2nd Leading Photon Pt (GeV)

  42. Baryonic R-Parity Violation Decay via allowed where m( ) > m() • Use extra information from leptons to decrease background. • Sequential decay of to through and producing Opposite Sign, Same Family (OSSF) leptons Test point

  43. Leptonic R-Parity Violation RPV has less missing EtNeutralino -> stau taustau -> tau mu qq Large rate of taus - smoking gun Stau LSP Phillips

  44. Light stops • Stop pair production: 412 pb (PROSPINO, NLO) • Dominant (~100%) stop decay: t → c+ b → c01 W* b • Final state is very similar to top pair production events. • 4 jets, 2 of which b-jets, one isolated lepton, missing energy • All of them softer (on average) than in top pair production • Invariant mass combinations will not check out with top, W masses M(bjj) 1.8 fb-1 M(bl) 1.8 fb-1 GeV GeV Points: simulated data Histograms: signal events (MC truth)

  45. New vector boson: W’ • Transverse mass plot for W’ => μ

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