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Higgs to WW

Higgs to WW. Monte Carlo Tools and Cuts. Monte-Carlo tools. CMS. Monte Carlo generators. PYTHIA (LO): Event generator for a large number of physic processes: hard/soft interactions, parton distributions, initial/final state parton showers, multiple interactions, fragmentation and decay

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Higgs to WW

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  1. Higgs to WW Monte Carlo Tools and Cuts

  2. Monte-Carlo tools CMS

  3. Monte Carlo generators • PYTHIA (LO): Event generator for a large number of physic processes: hard/soft interactions, parton distributions, initial/final state parton showers, multiple interactions, fragmentation and decay • MC@NLO (NLO): Fortran package. Monte Carlo event generator that provides Next-to-Leading-Order calculations of rates for QCD processes. It uses the Fortran HERWIG event generator • Alpgen: Hard multiparton processes. Produces matrix element (ME) level events to be passed to a parton shower (PS) / hadronization code (Pythia/HERWIG). The best Monte Carlo prediction of multi-jet final states • TopReX: Provides processes not implemented in PYTHIA, that can be later accessed from PYTHIA as external processes. Also stand alone event generator (partonic final states before showering) • MadGraph/MadEvent: Software that allows to generate amplitudes and events for any process (with up to 9 external particles) in any model Rebeca Gonzalez Suarez (19/9/2010)

  4. Background Samples 14TeV 7TeV POWHEG samples are also available in the official production of CMS, we tested them in V + jets processes 10 TeV *POWHEG: The POWHEG method is a prescription for interfacing NLO calculations with parton shower generators, covers several processes, Higgs included (no negative weights) Rebeca Gonzalez Suarez (19/9/2010)

  5. Background Cross-sections • For the considered backgrounds, the cross-sections are computed at NLO with MCFM Rebeca Gonzalez Suarez (19/9/2010)

  6. Higgs Signal Samples • Higgs signal samples (to WW to 2 leptons) generated with PYTHIA • The differential Higgs boson transverse momentum distribution, PTH, is sensitive to higher order corrections • Differential reweighting technique has been applied: the leading order (LO) PYTHIA Higgs boson transverse momentum spectrum is reweighted to match the MC@NLO differential distribution, as MC@NLO incorporates next-to-leading order (NLO) matrix element calculations • The reweighting is done by means of PT dependant k-factors Rebeca Gonzalez Suarez (19/9/2010)

  7. Higgs Cross-sections • The cross-sections have been calculated at different orders in perturbative QCD for the four main Higgs production mechanism at the LHC, using dedicated tools: • Associated production with Z/W:calculated at NLO using V2HV • Associated production with a top pair:at LO using HQQ • Vector-Boson fusion: at NLO using VV2H • Gluon-Fusion: (N)NLO using HIGLU and HggTotal • The Branching ratios of the SM Higgs are computed with the tool HDECAY http://people.web.psi.ch/spira/proglist.html Rebeca Gonzalez Suarez (19/9/2010)

  8. Sequential Cut-based analysis ATLAS – CMS

  9. Twodifferentstyles • CMS and ATLAS havedifferentstrategiesforthe HWW analysisbasedonsequentialcuts: • CMS: • 0 jet bin • 3 final states (ee, eµ, µµ) • Mass-dependentapproach (differentcuts Vs mH) • ATLAS: • 0j, 1j, 2j • (one) CutmHdependant Rebeca Gonzalez Suarez (19/9/2010)

  10. Leptonselection • Initialstep of theanalysis • Withoutaccountingforthespecificqualitycuts, bothaskforopposite-signleptonpairswithsubstantial PTwithintheacceptance • CMS: • PT > 10, 20 • η < 2.4 • ATLAS: • PT > 15 • η < 2.5 • And eventswith a thirdlepton are vetoed Rebeca Gonzalez Suarez (19/9/2010)

  11. Things in common • Jets: Same ET and η thresholds (details like JEC unknown in ATLAS, they just say “ET”) • Anti k-t calorimeter jets • Parameter size of 0.5 (CMS) • |η| < 3 / ET > 20 (RAW), 30 (corrected) • Use of: • MET • ΔΦll • Mll • PT of theleptons • But ATLAS uses more variables Rebeca Gonzalez Suarez (19/9/2010)

  12. Variables Used Rebeca Gonzalez Suarez (19/9/2010)

  13. CMS: Cuts µµ/ee/eµ CutonMll > 12 included in the pre-selectionstep Rebeca Gonzalez Suarez (19/9/2010)

  14. ATLAS: Cuts Rebeca Gonzalez Suarez (19/9/2010)

  15. 0 jet bin, µµ Comparison *W+jets, Z+jets no eventsremainafterallthecuts Rebeca Gonzalez Suarez (19/9/2010)

  16. Possible set of commoncuts • Selecteventswith 2 leptons : • |η| < 2.5 • PT > 10, 20 • Oppositecharge • Veto eventswith a thirdlepton • Jets: PT > 20 |η| < 3 → Loosecuts Eachexperiment, final state and jet binappliesthentheirownon top Rebeca Gonzalez Suarez (19/9/2010)

  17. Possible set of common cuts (GEN) • Events with 2 leptons (tau included in the simulation) : • |η| < 2.5 • PT > 10/10 (5/5 or 0/0 if possible) If the cuts are goint to be made at generation level, we should go for something looser, to not risk ‘problematic regions (low mass) Rebeca Gonzalez Suarez (19/9/2010)

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