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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 should be done at the beginning? • SM physics with CMS: known SM 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. How 2008 should look like... Paolo Meridiani - INFN Roma1

  4. What we should do at the begin? • New territory to be explored. 14 TeV is just an extrapolation from what we already know... • Pre-operations • Synchronization (all subdetectors) • Pre-Alignment (Tk + Muon) • Pre-calibration (HCAL & ECAL) • Next triggering on collision events • Next high rate events: from 10 mb to 1b • Minbias • Jets, dijet imbalance • Direct photons • Then from b to nb • W, Z, W/Z + jets, diphoton, dilepton Paolo Meridiani - INFN Roma1

  5. Pre-operations • Synchronization • Set relative timings to better than 1ns using lasers and pulsers checking with cosmic muons (should be achieved in cosmic global runs) • Pre-calibration • ECAL: intercalibration with cosmics (1.5%)+ TB intercalibrated SM (one quarter of EB at 0.3%) • HCAL: radioactive sources + TB 5% • Pre-alignment • Muon: Alignment with cosmic muons + optical alignement system (also MB w.r.t ME). Track motion when field on (already tested in Magnet test 2006) • Tracker: survey + optical alignment + cosmic muons Paolo Meridiani - INFN Roma1

  6. The collisions start... • We should first understand the trigger table Paolo Meridiani - INFN Roma1

  7. How to demonstrate that we are looking at collisions? • First thing than one wants to do is to demonstrate that trigger is selecting real beam-beam interactions. How to do this? • Look at position of the reconstructed vertex. • z position will give information on the bunch lenght. RMS should be compatible with the expected bunch lenght / 2. From tails background can be estimated • Transverse position will give information on transverse beam size and its stability Paolo Meridiani - INFN Roma1

  8. Measure dN/d, dN/dpT • Minbias are the events with the largest xsec • But minimum bias charge multiplicity known only at 50% • Few 104 events needed to get preliminary measurement of dN/d & dN/dpT • Acquire them with the special prescaled trigger • Probably less than half-hour of good data will be sufficient • Useful also to look for beam background • First inputs to start tuning MonteCarlo for pileup and set final trigger strategies (e.g. Isolation) • Probably first article published by CMS... Paolo Meridiani - INFN Roma1

  9. What else one can do with minimum bias events? • Useful to improve ECAL & HCAL calibrations • Charged pions will be used to improve tracker alignment Use the assumption that energy deposit is uniform in . Possibility to calibrate rings at same . Precision limited by tracker material which is not completely uniform in  Neutral pions will be another source for ECAL intercalibration Examples with ECAL Paolo Meridiani - INFN Roma1

  10. Next step: dijets • Start using prescaled trigger to try to measure jet-cross section • For example look at angular distribution, ratio 2J/J to extract trigger and reconstruction efficiency • Also possibility to intercalibrate the HCAL  rings, using the 2J balance • After that start investigating MET in dijets • MET is dijet is due to energy mismeasures • If tails are under control than b and t pairs should dominated for large (>100 GeV) MET values Paolo Meridiani - INFN Roma1

  11. Electrons, muons • Then move to nb processes at LHC, W/Z production. NLO Xsec known at 4-5% level • Many different uses: • Lepton energy scale from W & Z • Goal 0.1% can be achieved with 1fb-1 • Tune detector simulation (model Z mass and W transverse mass) • Efficiencies from Z (tag/probe) Paolo Meridiani - INFN Roma1

  12. We are starting to undestand detector, beam what we do... • We can start measuring SM xsec (W/Z), W mass, top mass but fundamental ingredients for precise meaurements are: Paolo Meridiani - INFN Roma1

  13. Precise measurement of MW Paolo Meridiani - INFN Roma1

  14. How to measure W mass? Paolo Meridiani - INFN Roma1

  15. Ingredients for precise W mass spectrum prediction Paolo Meridiani - INFN Roma1

  16. Rediscover the top • With 840pb LHC is a top pait factory • But also single top has a huge xsec • 250 pb t-channel, 62pb tW, 10 pb s-channel Paolo Meridiani - INFN Roma1

  17. Top physics: early analysis • Top as “commissioning tool” Paolo Meridiani - INFN Roma1

  18. Top: semileptonic Paolo Meridiani - INFN Roma1

  19. Top: leptonic + hadronic Paolo Meridiani - INFN Roma1

  20. Triple gauge boson couplings ZZ also irreducible bkg for H→4l searches Paolo Meridiani - INFN Roma1

  21. SM Higgs Paolo Meridiani - INFN Roma1

  22. Higgs production @ LHC Paolo Meridiani - INFN Roma1

  23. Higgs Searches • “Benchmark” channels: • Strongly tied to detector performance • H, HZZ(*)4l • Narrow peaks • Event counting • No peak • Need good control ofbackground normalization • HWW(*) • VBF • Take advantage of the special topology • HWW(*), H Paolo Meridiani - INFN Roma1

  24. H • very clean signature in mH<140GeV/c2 region • low branching ratio (0.002) • signature: • two isolated high pT photons • narrow peak in di-photon invariant mass • backgrounds:pp→gg (irreducible) • pp→ g+jets, pp→jets (reducible) • experimental requirements: • very good g identification and isolation • aiming at 0.5% ECAL energy resolution signal: mH = 115 GeV/c2σxBR = 99.3fb mH = 140 GeV/c2 σxBR = 65.5fb backgrounds: pp → gg σ = 82pb pp → g +jets σ = 5x104pb pp → jets σ = 2.8x107pb Paolo Meridiani - INFN Roma1 photons (clusters in ECAL)

  25. H two approaches: cuts based analysis and neural network analysis signal: very small contribution to the total number of events (signal efficiency at 120 GeV/c2 ~ 30%) 30fb-1: discovery possible for masses < 140 GeV/c2 using 0.5% resolution background events normalized to 1fb-1 signalx10 Paolo Meridiani - INFN Roma1

  26. H→ZZ→4l • GOLDEN CHANNEL: cleanest discovery channel over mH>140GeV/c2 range • signature: • 2 pairs of opposite-charge, same flavour isolated leptons • from primary vertex • dileptons invariant mass ~ mZ • backgrounds: pp → ZZ(*) (irreducible, dominant) • pp→tt, pp→Zbb (reducible) • main experimental challenges: • lepton identification with • high efficiency and resolution • down to low (~ 5 GeV/c) pT • selection criteria: • requirements on vertex, pT(l), isolation, m(ll) 2e2μ final state 1fb-1 before selections after selections after cuts 1fb-1 Paolo Meridiani - INFN Roma1

  27. An event H→4e at CMS... Paolo Meridiani - INFN Roma1

  28. H→WW→2l2 • discovery channel in 2mW < mH < 2mZ • signature: • 2 charged leptons and missing energy • no jet activity in the central region • 2 neutrinos in the final state: • no mass peak, counting experiments → • accurate background estimate from data needed • main backgrounds: • WW(*) (irreducible, dominant) • pp→ tt, pp→ Wtb • pp→ W+jets, pp→ Z+jets • crucial for the analysis: • reconstruction tools for • charged leptons, missing • energy and jet veto • understanding !!! } (reducible) 2 opposite charge leptons no jet with ET > 15GeV, |η|<2.5 MET > 50 GeV 12 < m(ll) < 40 GeV 30 < pTmax < 55 GeV pTmin > 25 GeV ΔΦ(ll) < 45º cuts and counts analysis Paolo Meridiani - INFN Roma1

  29. H→WW→2l2 WW control region, no ΔΦ(ll) cut critical: precise background knowledge → control regions using data ie. WW: inverted kinematic cuts on ΔΦ(ll) and m(ll) ie. tt: extra b-tagged jets 10fb-1,em large S/B, 5σ with L<1fb-1 mH=165 GeV/c2 Paolo Meridiani - INFN Roma1

  30. Higgs in VBF and associated production • associated ttH, WH production: additional leptons/jets in the final state • vector boson fusion: two tagging jets, large Δηjj (>4.5), large m(jj) (>1TeV) • despite lower cross section wrt gg fusion • increased discriminating power against QCD jets background • better main vertex reconstruction • with large statistics: enhance the significance, measure of Higgs couplings • some examples in CMS: • VBF with H→tt →l+tjet+ ETmiss (5σ with L=60fb-1 if mH<140GeV/c2) • VBF with H→gg (3σ with L=60fb-1 if mH<150 GeV/c2) • ttH, WH with H→gg (3σ with L=100fb-1 if mH<150 GeV/c2) VBF with H→tt → l+tjet+ ETmiss ttH with H→gg Paolo Meridiani - INFN Roma1

  31. CMS Higgs discovery potential: if it’s there we will catch it 5fb-1 enough 140<mH<450GeV/c2 discovery with 30fb-1 in the full range all Higgs mass range: significance larger than 5σ with 30 fb-1 mH < 140 GeV/c2 discovery with L < 10 fb-1 mH > 140 GeV/c2 discovery with L < 5 fb-1 Paolo Meridiani - INFN Roma1

  32. Measure Higgs mass and width • Higgs mass precision: • better than 0.1% if mH<200 GeV/c2 • better than 2% up to 600 GeV/c2 • Higgs width precision: • detector effects dominate • if mH < 200 GeV/c2 • if mH > 200 GeV/c2 possible measurement with precision better 30% in ZZ channel Paolo Meridiani - INFN Roma1

  33. End of lecture 2 Paolo Meridiani - INFN Roma1

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