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Higgs to WW

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Higgs to WW

Monte Carlo Tools and Cuts

Monte-Carlo tools

CMS

- 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)

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)

- For the considered backgrounds, the cross-sections are computed at NLO with MCFM

Rebeca Gonzalez Suarez (19/9/2010)

- 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)

- 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)

Sequential Cut-based analysis

ATLAS – CMS

- 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

- CMS:

Rebeca Gonzalez Suarez (19/9/2010)

- Initialstep of theanalysis
- Withoutaccountingforthespecificqualitycuts, bothaskforopposite-signleptonpairswithsubstantial PTwithintheacceptance
- CMS:
- PT > 10, 20
- η < 2.4

- ATLAS:
- PT > 15
- η < 2.5

- CMS:
- And eventswith a thirdlepton are vetoed

Rebeca Gonzalez Suarez (19/9/2010)

- 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)

Rebeca Gonzalez Suarez (19/9/2010)

µµ/ee/eµ

CutonMll > 12 included in the pre-selectionstep

Rebeca Gonzalez Suarez (19/9/2010)

Rebeca Gonzalez Suarez (19/9/2010)

*W+jets, Z+jets no eventsremainafterallthecuts

Rebeca Gonzalez Suarez (19/9/2010)

- 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)

- 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)