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Exploring the Mysteries of the Standard Model at the LHC

Learn about the role of the top quark and the search for new physics at the LHC. Discover the mysteries of the Standard Model and the potential breakthroughs in particle physics.

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Exploring the Mysteries of the Standard Model at the LHC

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  1. Preparing for first physics at the LHC “the role of the top quark” Ivo van Vulpen (Nikhef) Complex SMEarly tops SUSY Extra dimensions Early physics Now Calibrations Detector commissioning

  2. The famous top quark Paris Hilton Top Quark … everybody constantly talking about them … they are troublemakers, famous, important … buy why again ?

  3. Complex SMEarly tops SUSY Extra dimensions Early physics Now[6 slides] Calibrations Detector commissioning The Standard Model … and what’s wrong with it

  4. Particles Forces 1) Electromagnetism2) Weak nuclear force3) Strong nuclear force Quarks Leptons The Standard Model: Describes all measurements down to distances of 10-19 m

  5. Limits on mh from theoryLimits on mh from exper. “We know everything about the Higgs boson except its mass” Higgs mass (GeV) Triviality Vacuum stability Λ (GeV) Electroweak Symmetry breaking Electro-Weak Symmetry Breaking:(Higgs mechanism)- Weak gauge bosons and particles have mass- Regulate WW/ZZ scattering

  6. The standard model … boring ? “All measurements in HEP can be explained using the SM” “The Higgs boson will be discovered at the LHC at ~ 140 GeV” No. … there are many mysteries left!

  7. The big questions: • What explains (extreme) tuning of parameters: hierarchy problem ? • What is dark matter made of ? • Why is gravity so different ?

  8. The mysteries of the SM • Why is gravity not a part of the Standard Model ? • What is the origin of particle mass ? (Higgs mechanism) • In how many dimensions do we live ? • Are the quarks and leptons really the fundamental particles ? • Are there new symmetries in nature ? • Why are there only 3 families of fermions ? • Are protons really stable ? • Why is electric charged quantized ? • Why is there more matter than anti-matter in our universe ? • What is the nature of dark matter and dark energy ? • Do quantum corrections explodeat higher energies ? • Why are neutrino masses so small ?

  9. Extra dimensions ? Super-Symmetry ? String theory ? Edward Witten’s latest insight ?  Standard Model is an ‘approximation’ of a more fundamental one.  Model breaks down at 1-10 TeV New phenomena will appear at distances ~ 10-19 m 2009

  10. Complex SMEarly tops SUSY Extra dimensions Early physics Now Calibrations Detector commissioning [9 slides] • The LHC accelerator • The ATLAS detector (testbeam, cosmics, beam)

  11. The LHC machine Center-of-mass energy: 14 TeV Energy limited by bending power dipoles 1232 dipoles with B= 8.4 T working at 1.9k Search for particles with mass up to 4 TeV Luminosity: 1033-1034 cm-2s-1 Phase 1: (low luminosity) 2009-2010 Integrated luminosity ~ 10 fb-1/year Phase 2: (high luminosity) 2010-20xx Integrated luminosity ~ 100 fb-1/year  Search for rare processes 7 x Tevatron 100 x LEP & Tevatron

  12. P. Jenny, SUSY2009 Towards physics: LHC’s point of view 2009 2010 2011 j f m a m j j a s o n d j f m a m j j a s o n d j f m a m j j a s o n d Weltmeister ! - Start LHC operation Oct. 2009 - Run over winter shutdown - 10 TeV collisions first year shutdown physics LHC operators: “44 days from first injection to physics run” ATLAS/CMS: Analysis potential with ~100 pb-1 (ATLAS’ CSC-note)

  13. The ATLAS detector • Tracking (||<2.5, B=2T) : • Silicon, pixels and strips • Transition Radiation Detector (e/ separation) • Calorimetry(||<5) : • EM : Pb-LAr • HAD: barrel: Fe/scintillator forward: Cu/W-LAr • Muon Spectrometer (||<2.7) : • air-core toroids with muon chambers ~1000 charged particles produced over ||<2.5 at each crossing.

  14. Towards physics: ATLAS’ point of view Subdetector Installation Cosmics commissioning Testbeam Single beams First LHC collissions First physics runs 2005 2006 2007 2008

  15. Muons in the ATLAS cavern ~ 20 million muons enter cavern per hour Simulation ATLAS cavern 0.01 seconds Collected statistics: ATLAS Preliminary Cosmics : tracks in Pixels+SCT+TRT Debugging, first alignment studies

  16. Muons in the ATLAS cavern ~ 20 million muons enter cavern per hour Simulation ATLAS cavern 0.01 seconds origin Collected statistics: ATLAS Preliminary

  17. Cosmics: alignments & checks Alignment SCT barrel Energy loss in calorimeter After alignment Before alignment x residual [mm] p(ID) – p(MS) [GeV/c] Expected 3 GeV loss M Aleksa, P. Jenny, O. Jinnouchi SUSY2009

  18. Cosmics: EM Calorimeter Electromagnetic calorimeter Electromagnetic calorimeter Test-beam data Test-beam data Entries Muons ATLAS Preliminary Relative Energy Noise Energy GeV Eta (module) A muon deposit ~ 300 MeV in ECAL cell (S/N~ 7) Check (+ correct) ECAL responseuniformity vs  to ~ 0.5%

  19. Single beams in LHC Beam gas + beam halo: • 5 TeV protons on residual gas in vacuum • tracks accompanying the beam First beam event in ATLAS

  20. Complex SMEarly tops SUSY Extra dimensions Early physics Now Calibrations [4 slides] • Planning road to new physics • Simple SM topologies (collecting pieces of the puzzle) Detector commissioning

  21. Look for new physicsin ATLAS at 10 TeV 3 Higgs/SUSY 2 Understand SM+ATLASin complex topologies Top quark pairs 1 Understand SM+ATLAS in simple topologies W/Z 0 Understand ATLAS Testbeam/cosmics LHC start-up programme Integrated luminosity 1 fb–1 100 pb–1 10 pb–1 Andreas Hoecker Time LHC startup

  22. ATLAS detector performance on day-1 - Reconstruct (high-level) physics objects: Electrons/photons: Electromagnetic Energy scale Quarks/Gluons: Jet Energy scale + b-tagging Neutrino’s/LSP?: Missing Energy reconstruction Expected detector performance from ATLAS(based on Testbeam and simulations) Performance Expected day-1 Physics samples to improve ECAL uniformity 1% Min. bias, Ze+e- (105 in a few days)e/γ scale 1-2% Ze+e-HCAL uniformity 2-3% single pions, QCD jetsJet scale <10% γ/Z (Zl+l-) + 1 jet or Wjj in ttTracking alignment 20-500 μm Rφ Generic tracks, isol. muons, Zμ+μ-

  23. Plan-de-campagne during first year Process #events 10 fb-1 First year:A new detectorANDa new energy regime Understand ATLAS using cosmics 0 1 1 Understand SM+ATLAS in simple topolgies 2 2 Understand SM+ATLASin complex topologies 3 3 Look for new physicsin ATLAS at 10 TeV

  24. Early SM peaks: di-lepton resonances J/ Y 160 4200 Number of events Number of events 800 ATLAS preliminary, 1 pb-1 ATLAS preliminary, 10 pb-1 Mμμ (GeV) Mμμ (GeV) Events per day at a Luminosity of 1031 Reconstruction efficiencies, Muon spectrometer alignment, Detector and trigger performance, Tracking momentum scale, ECAL uniformity, E/p scale, …

  25. Top quarks: • As weird member of SM family • As a calibration tool in complex topologies • As a window to new physics Complex SMEarly tops SUSY Extra dimensions Early physics Now Calibrations Detector commissioning

  26. The top quark: ‘old-physics’ We know already a lot about the top quark u c t s b d Mass(difference), Electric charge (⅔), Spin, Isospin, Br(t  Wb), V-A decay, FCNC, Top Width, Yukawa coupling, ... The LHC offers an opportunity for precision measurements The top quark is a trouble maker

  27. Top quark production at the LHC 400,000/800,000 tt events per year at 10/14 TeV Cross section LHC = 100 x TevatronBackground LHC = 10 x Tevatron 90% 10% t t bbqqqq 4/9bbqqlv 4/9bblvlv 1/9 1) Top most complex SM candle Clear signal on early data 2) Top signal important background for most new physics searches

  28. Top cross-section (theory) Fractional uncertainty mtop (GeV) Uncertainty due to PDF’s similar to W/Z Scale dependence: NLO (approxNNLO): μF and μR varied separately (together) Jianming Qian: http:// indico.cern.ch/conferenceDisplay.py?confId=54025

  29. Top cross-section (theory) Dependence on √s 883 pb Factor 2 401 pb bbqqqq 4/9bbqqlv 4/9bblvlv 1/9 √s (TeV) mt = 172.5 GeVm CTEQ 6.6 Topology: - high-PT (b-) jets, - isolated leptons - missing energy √s = 14 TeV: σapproxNNLO = 883 pb √s = 10 TeV: σapproxNNLO = 401 pb

  30. Top quark physics (with b-tag information) Top physics is ‘easy’ at the LHC Selection: Lepton + multiple jets+ 2 b-jetskills the dominant background from W+jets Systematic errors on Mtop (GeV)in semi-leptonic channel Nr of Evts/ 4 GeV Top signal W+jets Mjjb (GeV) Could we see top quarks when selection is not based on b-tag ?

  31. Di-lepton cross-section measurement (μμ) Trigger: Single muon, PT > 17 GeV Lepton ID: Two, isolated, opposite charge PT > 20 GeV Jets: ≥2 jets with PT > 20 GeV Missing ET: ET-miss > 35 GeV (+ cleaning) MZ-cut: |Mμμ–MZ| > 5 GeV Number of events Number of jets 200 pb-1 tt signal = 327 bckg = 87 S/√(S+B) = 16.1

  32. Single-lepton Top quark events (no b-tag information) • Robust selection cuts Missing ET > 20 GeV1 lepton PT > 20 GeV3 jets PT > 40 GeV4 jets with PT > 30 GeV W CANDIDATE Hadronic 3-jet mass • Assign jets to top decays TOP CANDIDATE Note: In 70% of events there is an extra jet with PT > 30 GeV jet pairings ? L=200 pb-1 Hadronic top: three jets with highest vector-sum pT Extra: Require a jj-pair in top quark candidate with |Mjj-80.4| < 10 Mjjj (GeV) 200 pb-1: few days of low-lumi LHC operation

  33. Single lepton cross-section measurement (μ) Data-driven estimate for W+jets from Z+jets 20% uncertainty reachable

  34. Top phase space ‘clean’ Top quark phase space Top precision measurements Calibrating ATLAS in multi-jet events

  35. A candle for complex topologies: Calibrate light jet energy scale Calibrate missing ET Obtain enriched b-jet sample Leptons & Trigger Top physics at the LHC “Top quark pair production has it all”: ≥4 jets, b-jets, neutrino, lepton several mass constraints for calibration 4/9 Note the 4 candles: - 2 W-bosons Mw = 80.4 GeV- 2 top quarks & Mt = Mt-bar

  36. MW(had) MW = 78.1±0.8 GeV Events / 5.1 GeV S/B = 0.5 Jet energy scale Determine Light-Jet energy scale (1) Abundant source of W decays into light jets • Invariant mass of (light-) jets should add up to well known W mass (80.4 GeV) Light jet energy scale calibration (1% for 1 pb-1) t t Pro:- Large event sample - Small physics backgrounds Con: - Only light quark jets - Limited Range in PT andη

  37. Using top quark events to obtain a clean sample of b-quarks Calibrate/test b-tagging in complex event topology (2) Abundant clean source of b-jets • 2 out of 4 jets in event are b-jets  ~50% a-priori purity (extra ISR/FSR jets) • The 2 light quark-jets can be identified (should form W mass) t t Conventional: - Rejection in di-jet sample - Efficiency using semi-lept. decays

  38. Estimating b-tag efficiency Jet counting Likelihood / Topological selection # jets with 0,1,2,3, 4 jets b-tags Configuration depends on εb, εcεl Fit templates to event characteristics 100 pb-1:Δεb ~5% Can also measure tt cross-section

  39. Top group (all) ttH ‘clean’ Extra jets Exotics, SUSYTop group: High-PT low ‘ISR-FSR’ Top mass Cross-section or Large ET-miss Top quark phase space SUSY

  40. Intro to SUSY • SUSY parameter space (early discovery potential) • ATLAS’ SUSY reach Complex SMEarly tops SUSY [11 slides] Extra dimensions Early physics Now Calibrations Detector commissioning

  41. t W W t h h λtλt b Failure of radiative corr. in Higgs sector: Radiative corrections from top quark mh = 150 = 1354294336587235150–1354294336587235000 Λ2 The hierarchy problem in the SM The hierarchy problem Success of radiative corr. in the SM: predicted observed ? Hierarchy problem: ‘Conspiracy’ to get mh ~ MEW («MPL) Biggest troublemaker is the top quark!

  42. A new symmetry: supersymmetry Standard model particles New ‘partner’ particles Fermion-partnerswino’s, zino’s, fotino’s BosonsW,Z,photon Fermionsquarks/leptons Boson-partnerssquarks/sleptons SUSY: - Regulates quantum corrections (‘solves’ hierarchy problem) - Gauge Unification and dark matter candidate - a-priori not very predictive (many parameters) - many constraints from data (no sparticles, cosmology, … )

  43. A model: mSUGRA  R-parity conserved : - Stable Lightest Supersymmetric Particle: LSP - m0: universal scalar mass (sfermions) - m½: universal gaugino mass - A0: trilinear Higgs-sfermion coupling - sgn(μ): sign of Higgs mixing parameter - tan(β): ratio of 2 Higgs doublet v.e.v mSUGRA Evolution of masses Fixing parameters at 1016 GeV, the renormalization group equations will give you all sparticle masses at LHC! Running mass (GeV) m½ m0 1016 GeV Radiative EW symmetry breaking (thanks to top quark) Energy scale a.u.

  44. ATLAS 100 pb-1 mSUGRA parameter space Allowed mSUGRA space m0 = 100 GeV m1/2 = 250 GeV tan  = 10 800700600500400300200100 0 Mass spectrum mSUGRAtan(β)=10 gluino g-2 Particle mass (GeV) m0 (GeV) (WMAP) stau LSP m1/2 (GeV) Higgs boson(LEP) LSP (ΩDM) Constraints: - LEP: mh > 114.4 GeV - Cosmology: LSP neutral - Cosmology: limits on mLSP Allowed mSUGRA spaceVery different exper. signatures

  45. Cosmology and SUSY dark matter WMAP III: 0.121 < Ωmh2 = nLSP x mLSP < 0.135 ρLSP = Relic LSP density x LSP mass The relic LSP density depends on LSP mass:LSP stable, but they can annihilate, so density decreases when LSP annihilation cross section increases. lepton slepton(NLSP) lepton Upper AND lower limitson LSP mass

  46. ATLAS 100 pb-1 mSUGRA space: ATLAS reach Allowed mSUGRA space (post WMAP) ATLAS reach in mSUGRA space (1-lepton) mSUGRAtan(β)=10 M½ (GeV) g-2 m0 (GeV) (WMAP) stau LSP m1/2 (GeV) M0 (GeV) Allowed mSUGRA spaceVery different exper. signatures

  47. Production of SUSY particles at the LHC • Superpartners have same gauge quantum numbers as SM particles  interactions have same couplings αS αS • Gluino’s / squarks are produced copiously (rest SUSY particles in decay chain)

  48. Event topology jet lepton jet lepton Missing energy Missing energy Topology: ≥4 jets missing ET (large) leptons/photons jet jet SUSY events look like top events

  49. jet jet jet jet/lepton jet/lepton Common signature large fraction SUSY events LHC day 2: First to discover SUSY SUSY event topology Sensitive to hard scale SUSY Discovery # events/1 fb-1 SUSY SM SU(1) 232 tt 36 SU(2) 40 total 42 SU(3) 364 SU(4) 896 SU(5) 148 Meff (GeV) tt production dominant background

  50. Estimate tt background in SUSY region: big fit Top (sl) Top (fl) W+jets SUSY ET-miss MT mtop  20% uncertainty on W+jets and tt Vital for early claims of signs of breakdown SM

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