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Physics with CMS

Physics with CMS. Paolo Meridiani (INFN Roma1). Outline. Lecture 1 Is SM satisfactory? Open questions in the SM? LHC: the answer to unanswered questions? CMS Detector: a challenging detector for a challenging machine CMS Commissioning: how much time is required to make it work? Lecture 2

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Physics with CMS

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  1. Physics with CMS Paolo Meridiani (INFN Roma1) Paolo Meridiani - INFN Roma1

  2. Outline • Lecture 1 • Is SM satisfactory? Open questions in the SM? • LHC: the answer to unanswered questions? • CMS Detector: a challenging detector for a challenging machine • CMS Commissioning: how much time is required to make it work? • Lecture 2 • CMS early physics: what can be done at the beginning? • SM physics with CMS: known physics can be done better in CMS? • Higgs Physics with CMS: if it’s there we will catch it! • Lecture 3 • Beyond the SM physics at CMS: hunting new theories Paolo Meridiani - INFN Roma1

  3. Hunting new physics • Recall: • Why do we think about extending the SM? • Gravity is not incorporated • Hierarchy problem • Unification of couplings (GUT) • Flavour/ number of families beg for explanation • ... • Many candidate theories: • Supersimmetry • Extradimensions • ..... • I do not have the time to go deeply into all of them, but I would like you to have a feeling of the strategy and things to be controlled for new physics discoveries in CMS Paolo Meridiani - INFN Roma1

  4. Features of SuperSimmetry • SuperSimmetry: achieved in theory where lagrangian is invariant with respect to • What this brings: Cancellation of quadratic divergences • Unification of couplings • Provides a candidate for cold dark matter (in case of R-parity conservation) • Easy to accomodate EW precision data Paolo Meridiani - INFN Roma1

  5. MSSM • Minimal Supersimmetric extension of the SM • Introduce super-partners s = ½ for each SM particle • Two Higgs doublets with <vev> and superpartners. After EW simmetry breaking 5 Higgs bosons: h, H, A, H remain • Supersimmetry should be broken: no superpartner observed to date • Additional ingredient: R-parity a new conserved quantum number Paolo Meridiani - INFN Roma1

  6. MSSM physical spectrum Mass are not predicted but usually charginos and neutralinos are lighter than squarks/spletons/gluinos Paolo Meridiani - INFN Roma1

  7. Breaking SUSY • In MSSM supersimmetry is broken with explicit terms (105 free parameters) then reduced to 15-20 imposing phenomenological constraints • Since SUSY cannot be broken spontaneously, idea is to postulate an hidden sector of interactions Most of the following analysis will be shown in the mSUGRA scenario Paolo Meridiani - INFN Roma1

  8. Producing SUSY @ LHC Paolo Meridiani - INFN Roma1

  9. SUSY signatures In the assumption that R-parity is conserved: Paolo Meridiani - INFN Roma1

  10. Search strategy Paolo Meridiani - INFN Roma1

  11. Benchmark points • Basis of detailed studies in the mSUGRA context • Low mass points for early LHC running but outside Tevatron reach • High mass points for ultimate LHC reach Paolo Meridiani - INFN Roma1

  12. Inclusive search: jets + MET • Most powerfull way to observe SUSY excess • CMS Example: • MET>200 GeV + Clean-up • 3 jets: • ET> 180, 110, 30 GeV • Indirect lepton veto • Cuts on  between jets and MET • HT/Meff=ET1+ET2+ET3+MET>500 GeV • CMS Results: • LM1 efficiency is 13%, S/B ~ 26 • ~6 pb-1 for 5 discovery Paolo Meridiani - INFN Roma1

  13. Same sign muons • Even cleaner signature with low background due to same-sign requirement • Concentrate here on isolating the SUSY diagrams giving prompt muons with strong muon isolation & tight quality cuts • Cuts (optimize @ LM1): • 2 SS isolated muons • pT > 10 GeV • MET > 200 GeV • 3 jets: • ET1>175 GeV • ET2>130 GeV • ET3>55 GeV 65% efficient at identifying SUSY diagrams, 90% pure Paolo Meridiani - INFN Roma1

  14. Inclusive MET + Z0 CMS • Catch • Mostly from q, g decays • Z0 gives extra handle against non-resonant dilepton bkg • Cuts (optimize @ LM4): • MET > 230 GeV • 2 OS SF leptons • pT(e) > 17 GeV, or • pT(µ) > 7 GeV • 81 < Mll < 96.5 GeV •  < 2.65 rad • Background (10 fb-1) • SM: 200  40 (t-tbar+diboson) • Systematic uncertainty 20% • LM4 Signal (10 fb-1) • 1550  30 e+e– Sensitive here Paolo Meridiani - INFN Roma1

  15. Convince yourself that you have observed something • If SUSY is there should be relatively easy to get an excess of events over the SM • But the real problem is convince yourself that this is a real excess • MET: key signature for SUSY in the assumption of R-parity conservation • But tuning MET will not be easy: Lesson from Tevatron: All the instrumental garbage go in MET Long and painstaking polishing phase is required Paolo Meridiani - INFN Roma1

  16. QCD Minbias MET in CMS • Sum mom. over calorimeter towers • MET is magnitude of imbalance • MET Resolution • Measure from data • Use min-bias and prescaled jet triggers to measure resolution • CMS stochastic term ~0.6–0.7 • Jet calibration crucial to improve resolution and reduce systematic uncertainty • Variety of techniques possible • -Jet balancing, di-jet balancing, • W mass constraint in tt events • CMS GOAL: Achieve <3% JES uncertainty for ET>50 GeV with 1–10 fb-1 Paolo Meridiani - INFN Roma1

  17. Example: MET SM Bkg normalization • Idea: use Zµµ + jets (>2) in data to normalize the Z (invisible) contribution and calibrate MET spectrum Paolo Meridiani - INFN Roma1

  18. Capability of observing a SUSY like excess in CMS with inclusive searches Paolo Meridiani - INFN Roma1

  19. The fun begins... • Assuming (hoping) to have observed an excess within 10 fb-1 what happens? • Need to demonstrate that: • Every particle has a superpartner with s=1/2 and same gauge quantum numbers • Mass relations predicted by SUSY holds • Observables: • Masses • BR’s • Production cross-sections • Angular decay distributions Paolo Meridiani - INFN Roma1

  20. p b b p ~ q SUSY spectroscopy • With stable 10 cannot fullyreconstruct squark or gluinodecay chains in general • Kinematical endpoints in invariant massdistributions give accesson sparticle masses • Start from dileptons from 20 (mll) • Add quark jet to get squark (mllq) • Add another jet to get gluino (mllqq) • These and other combinations (e.g. mlq) have endpoints thatare functions of the sparticle masses Kinematic end points (MC) in Dalitz plot of Mll and Mllq Paolo Meridiani - INFN Roma1

  21. Endpoint analysis Paolo Meridiani - INFN Roma1

  22. Example m(l+l-) at CMS • Measure invariant mass distribution of same-flavor opposite-sign (SFOS) leptons as evidence for • or • Striking signature: probably first and clearest signal of SUSY • LM1 with 1 fb-1, fit result: Subtract different flavor leptons Paolo Meridiani - INFN Roma1

  23. Alternative SUSY models: GMSB Actual phenomenology depens on neutralino life-time Paolo Meridiani - INFN Roma1

  24. And apart from SUSY? 1976 Nobel Discovery of the J/Psi Ting 1984 Nobel Discovery of W&Z Rubbia & Van der Meer Di-something resonances: Paolo Meridiani - INFN Roma1

  25. Di-something resonances Leptons and photons are the cleanest signature Paolo Meridiani - INFN Roma1

  26. Extended gauge simmetries Paolo Meridiani - INFN Roma1

  27. The Randall-Sundrum model Paolo Meridiani - INFN Roma1

  28. Experimental facts in reconstructing high energy objects in CMS • Very High Energy Electrons and Photons • Saturation in CMS ECAL (limited electronics range) above 1.7 TeV barrel, 3 TeV endcaps; mass resolution barrel 0.6 % (7%) with (without) saturation correction (based on non saturating adjacent crystals) • Very High Energy Muon • Misalignment + multiple scattering dominate • Muon bremsstrahlung • In general resolution of high energy electrons/photons better than muons p/p  p E/E  constant  0.5% Paolo Meridiani - INFN Roma1

  29. Searching for Z’ resonances • Discovery potential even with less than 1fb-1 Paolo Meridiani - INFN Roma1

  30. RS gravitons Paolo Meridiani - INFN Roma1

  31. Distinguishing RS graviton from Z’ • Angular distribution of lepton in the boosted rest frame of the heavy mass particle Paolo Meridiani - INFN Roma1

  32. Not only resonances but also continuum... Paolo Meridiani - INFN Roma1

  33. ADD model MD << MPl Constraints: MD<10 TeV n>1 (Newton law tested up to 200 m) Paolo Meridiani - INFN Roma1

  34. ADD graviton Signature: Single high pT in central region High missing pT back-to-back photon Main SM bkg: Z+→ +  Normalization from Z+→ +  Discovery reach MD< 3 TeV for 30fb-1 Paolo Meridiani - INFN Roma1

  35. High multiplicity/spherical events Paolo Meridiani - INFN Roma1

  36. Black Holes hunting... Paolo Meridiani - INFN Roma1

  37. Do not forget that... • Before any discovery we need to understand SM background that we know is there + control well our detector Paolo Meridiani - INFN Roma1

  38. CMS discovery path Paolo Meridiani - INFN Roma1

  39. THE END Paolo Meridiani - INFN Roma1

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