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First discoveries?

First discoveries?. Alan Barr University of Oxford. Disclaimers. I haven’t done a year of analysis of 14 TeV data . Few of us have. I haven’t done a “new physics” search at the Tevatron LEP, HERA or SPPS. Acutely aware that many others have!. Few have claimed “new” physics.

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First discoveries?

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  1. First discoveries? Alan Barr University of Oxford

  2. Disclaimers I haven’t done a year of analysis of 14 TeV data  Few of us have I haven’t done a “new physics” search at the Tevatron LEP, HERA or SPPS Acutely aware that many others have! Few have claimed “new” physics My best credentials… “I haven’t made a claim I’d seen new physics which later turned out to be false” Alan Barr, Cosener's House

  3. Let’s get it out of the way… Stuck Magnetic Monopoles After sorting out cabling map … Alan Barr, Cosener's House

  4. Cross-sections etc • What can we find with 100 pb-1 to 1 fb-1? • Reasonable cross-section • Low backgrounds • Easily reconstructed • Limited detector understanding? • Some things should “stick out like a sore thumb” • Others need more careful analysis • Much relies on topics already covered “Rediscover” Lower backgrounds WW ZZ “Discover” Higher backgrounds Alan Barr, Cosener's House

  5. Taught to “rediscover” • Z’s W’s and tops are not just used for “detector calibration” • MC validation • Build confidence in analysis methods • Need to be measured as backgrounds to new physics no b-tag b-tag +W masswindow Getting started… can see top with “no” b-tagging Tagging clearly helps though! Reconstructed top mass/GeV Alan Barr, Cosener's House

  6. After bosons … di-bosons • Again – an important background for various studies: • Higgs -> VV • Vector boson rescattering • Slepton/gaguino • SUSY trilepton searches • … Then Tribosons?c.f. Campbell Alan Barr, Cosener's House

  7. Good news: If you are aware of the problem it’sten times easier… • Wire bonds • Cosmic commission early … What needs to be working? Some components calibrated • Resonances • Continuum signals • Missing energy • Complex topologies Harder? Some backgrounds understood All components calibrated All backgrounds understood • A lot of the well-motivated stuff lies towards the bottom of this list: • much of SUSY, complex Higgs decays, … • How quickly can we get there? C.f. Chris Hill Bad news: We’ll most likely have a wholedifferent stack of new problems • “Missing energy takes (took) 3 years” • “Leptons first, Jets later” • Involate? Alan Barr, Cosener's House

  8. Rapidly exceed Tevatron reach for new gauge bosons 10 fb-1 “Sore thumb” territoryNeed e.g. ECAL cross-calibration & scaleEvents triggered & read out (trigger efficiency for high energy leptons?) Alan Barr, Cosener's House

  9. Continuum distributions: dijets Strategy for poorly known systematics? Normalise in “outer” rapidity region Measure in “inner” rapidity Try to factor out e.g. energy scale Decreasing scale of new contact interaction 1fb-1 Alan Barr, Cosener's House

  10. SUSY and so on • RP conserving SUSY makes Jets, Leptons and missing transverse momentum • Cascade decays • Complicated events • Difficult background estimation Alan Barr, Cosener's House

  11. Those exclusion plots Statistical-only coverage if background already known! Often assume good knowledge of very complex final states E.g. “6 jets + 1 lepton + missing energy > 200 GeV” + … Alan Barr, Cosener's House

  12. First attack missing ET Started already with MC studies – e.g. punch-through, cracks etc. Alan Barr, Cosener's House

  13. Typical requirements CMS physics TDR Tracker, ECAL, HCAL, muons, FCAL all “needed” Cross-calibration of HCAL clearly important Missing energy in there… of course Alan Barr, Cosener's House

  14. Background normalisation… • Getting backgrounds wrong makes a big difference • Design analysis to reduce them • Measure them in situ • Independent extraction of different backgrounds needed • Preferably unbiased by any new physics CMS Alan Barr, Cosener's House

  15. 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 • Measure in Z -> μμ • Use in Z -> νν R: Z -> nn B: Estimated n n Backgrounds from data… Alan Barr, Cosener's House

  16. Measuring QCD jets backgrounds to SUSY? Control sample has large missing ET close to one jet Assume this jet has fluctuated to cause METUse this to measure tails of the jet resolution Assume jets are independent Apply the resolution function to all jets in sample of events with initially small missing ET Estimate of QCD BG Method describesthe QCD BGwell in the tailregion which it has been designed for Alan Barr, Cosener's House

  17. SIGNAL topology BACKGROUND topology (QCD) Keep it simple? Small Njets + ET • Select a small number of high PT jets • Large signal cross-section • Large control statistics • Relatively well known SM backgrounds • Relatively “model independent” • Does not rely on leptonic cascades • Does not rely on hadronic cascades • Use kinematics rather than “busyness of event” to pick out SUSY Alan Barr, Cosener's House

  18. ATLAS Geant4 1 fb-1 Jets-only measurement • Keeping it simple • >=2 jets • ET (J1,2) > 150 GeV; |η1,2| < 2.5 • Plot MT2 • N.B. MT2→ 0 if: • ET→ 0 • ET parallel to either jet • Jet ET → 0 Designed for mass measurements Useful for searches? Violates the Tevatron “leptons first rule” – problem? Alan Barr, Cosener's House

  19. Electroweak symmetry breaking? • Not the easiest thing to attack quickly • Small couplings to most fermions • Large backgrounds and/or difficult final states • b-tagging/taus/missing energy • But clearly a high physics priority CMS Higgs-> γγwith 1 fb-1 Signal scaled by x10 ! Alan Barr, Cosener's House

  20. Any hope of a rapid Standard Model Higgs? ATLAS Low mass harder CMS H->γγ “simpler” than ttH ; H-> bb “Under the streetlight” is near 160 GeV with H->WW->lνlν Is this the Higgs we’re looking for? Alan Barr, Cosener's House

  21. H-> WW -> lν lν • Best chance for early discovery • No mass peak • Signal at small Δφ (spin correlations) • Control samples from high mll and large Δφ CMS Alan Barr, Cosener's House

  22. First discoveries at LHC may not come from General Purpose Detectors… …if flavour or CP violating C. Lazzeroni, IoP half day meeting, UCL, Oct ‘06 Alan Barr, Cosener's House

  23. Bump-hunting at LHCb… Alan Barr, Cosener's House

  24. Diversion

  25. Fun: Revisit the 2003 ATLAS blind data challenge • July 2003 • 450 pb-1 simulated data (GEANT) • Single lepton trigger • Collaboration told “something in the data” • Interesting why? • Which analysis strategies do we really employ? • Test our own confidence in what we see • Learn from mistakes! Much media interest in random numbers! No detector effects, halo, Miscalibration … Alan Barr, Cosener's House

  26. Checking the backgrounds mee • Does the MC match the “data”? • Is the detector calibrated? • Do we have a reasonable background estimate? mμμ Able to find which parts of oursimulation don’t match the “data”:Pink part is double counted in simulation Alan Barr, Cosener's House

  27. Confidence in our findings? Alan Barr, Cosener's House

  28. SUSY? • Excess of high mass stuff? • SUSY-like signatures… Leading jet ET Missingtransverse momentum In this case discrepancy was due to bias from generator PT distribution: low PT top quark generation lost in “Data” Alan Barr, Cosener's House

  29. “First discoveries” • “Easy” to reconstruct • Bumps on falling backgrounds! mμμ mee Alan Barr, Cosener's House

  30. Charged resonance • Excess at large transverse mass is not hard to pick out mT (muon) mT (electron) Alan Barr, Cosener's House

  31. Results: • No one had confidence enough to claim non-PDG Top mass • Some (far from complete) background validation achieved • Resonances were obvious to all • Properties of resonances could start to be uncovered • No one looked for Higgs Alan Barr, Cosener's House

  32. Back to reality… What would make us smile?

  33. Assume we have MSSM-like SUSY with m(squark)~m(gluino)~600 GeV • See excesses in “typical” distributions: • Missing transverse energy • Scalar sum ET • Dilepton spectrum (below) with edge Alan Barr, Cosener's House

  34. Can say some things: Undetected particles produced missing energy Some particles mass ~ 600 GeV, couplings similar to QCD “Effective mass” & 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 contain lepton quantum numbers opposite sign, same family dileptons … What might we have found out? There will be lots more to do after this! Alan Barr, Cosener's House Slide based on Giacomo’s

  35. Conclusions? • We don’t know what we will find • Value of prejudices rapidly decreases with data! • Sure to be hard work • It already has been for some time! • Terra Incognita in very many ways • Human as well as technical aspects • Opportunities abound “I find all this stuff simply fascinating!” “Jim of the Hog’s Bosun” (My retired neighbour) Alan Barr, Cosener's House

  36. Fin Alan Barr, Cosener's House

  37. Check for weirdos Well matched – gave somedegree of confidence in“new physics” invariantmasses Electron-muon invariant mass Alan Barr, Cosener's House

  38. W contribution to no-lepton BG Oe, Okawa, Asai • Use visible leptons from W’s to estimate background to no-lepton SUSY search Alan Barr, Cosener's House

  39. Normalising alone not necessarily good enough Distributions are biased by lepton selection  Alan Barr, Cosener's House

  40. Need to probe deeper… Alan Barr, Cosener's House

  41. Then possible to get it right… Similar story for other backgrounds – control needs careful selection Alan Barr, Cosener's House

  42. 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 Alan Barr, Cosener's House

  43. ~ c01 ~ G GMSB: non-pointing g event h cluster (1st layer – IP) h rec poiting (egamma obj) g Alan Barr, Cosener's House

  44. 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 Alan Barr, Cosener's House

  45. R-hadrons in detectors • Signatures: • High energy tracks (charged hadrons) • High ionisation in tracker (slow, charged) • Characteristic energy deposition in calorimeters • Large time-of-flight (muon chambers) • Charge may flip • Trigger: • Calorimeter: etsum or etmiss • Time-of-flight in muon system • Overall high selection efficiency • Reach up to mass of 1.8 TeV at 30 fb-1 GEANT simulation of pair of R-hadrons (gluino pair production) Alan Barr, Cosener's House

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