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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

Higgs to WW

Monte Carlo Tools and Cuts

monte carlo generators
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)

background samples
Background Samples



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)

background cross sections
Background Cross-sections
  • For the considered backgrounds, the cross-sections are computed at NLO with MCFM

Rebeca Gonzalez Suarez (19/9/2010)

higgs signal samples
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)

higgs cross sections
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


Rebeca Gonzalez Suarez (19/9/2010)

two different styles
  • 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)

lepton selection
  • 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)

things in common
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)

variables used
Variables Used

Rebeca Gonzalez Suarez (19/9/2010)

cms cuts
CMS: Cuts


CutonMll > 12 included in the pre-selectionstep

Rebeca Gonzalez Suarez (19/9/2010)

atlas cuts

Rebeca Gonzalez Suarez (19/9/2010)

0 jet bin comparison
0 jet bin, µµ Comparison

*W+jets, Z+jets no eventsremainafterallthecuts

Rebeca Gonzalez Suarez (19/9/2010)

possible set of common cuts
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)

possible set of common cuts gen
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)