1

Search of the Higgs Search of the Higgs boson in the WW boson in the WW (*)(*)

decay channel with the decay channel with the CMS experiment CMS experiment

We are ready to go !

18th - 23th February 2008 Alberta , Canada

Lake Louise Winter Lake Louise Winter Institute Institute

On behalf of the CMS collaboration

Ezio Torassa - INFN Ezio Torassa - INFN PadovaPadova

Lake Louise – February 2008 Ezio Torassa – INFN Padova 2

CMS Physics TDR Vol 2

Higgs production at the LHC

SM Higgs production cross section including NLO QCD corrections

Lake Louise – February 2008 Ezio Torassa – INFN Padova 3

Higgs branching ratios

The Higgs coupling constants to fermions and bosons are proportional to the particle masses:

For Higgs masses above 135 GeV the main decay modes are those

into WW(*) and ZZ(*)

(under 135 GeV b/c quarks and +-)

ff

fhfm

v

mg

WV

hVV Mv

mg

22

2GeV/c246sin

WWMv

CMS Physics TDR Vol 2

Lake Louise – February 2008 Ezio Torassa – INFN Padova 4

Signal and Backgrounds

Continuum production of WW pairs

Wt

The signal is characterized by:

- two high Pt isolated leptons - missing Et- no high energy Jet - angle correlation between WW

DYtt

Lake Louise – February 2008 Ezio Torassa – INFN Padova 5

Monte Carlo simulation

Higgs boson signal samples were generated using the LO PHYTIA Monte Carlo.The events were reweighted to match expectation from NLO. k(pT) factors were calculated with the MC@NLO Monte Carlo.

))((p

))((p

T

T

PYTHIALO

orderhigher)(pTk

The total NLO cross section is rescaled considering NLO calculations.The same procedure was used for the dominant irreducible WW background.

For the other backgrounds the inclusive k factor was used:

tt and Wt were produced using the TopRex Monte Carlo

kinc = ∫ k(pT) dpT

Lake Louise – February 2008 Ezio Torassa – INFN Padova 6

The CMS recent H→WW analysis

Standard Model Higgs Discovery Potential of CMS NOTE 2006/047CMS in the H→WW→ll channel

Systematic uncertainties of the top background CMS NOTE 2006/048In the H→WW channel

Physics study of the Higgs decay channel CMS NOTE 2006/055 H→WW(*)→22

Search for a Light Standard Model Higgs boson CMS NOTE 2006/114in the H→WW(*)→eechannel

Search for the Higgs boson in the WW(*) decay CMS PAS Hig_07_001Channel with the CMS experiment

CMS TDR vol II Cut based

CMS PAS Hig_07_001 Cut based + TMVA

Summary inside

CMS TDR vol II

Physics Performance

This report =>

Low Higgs Mass

optimization

Lake Louise – February 2008 Ezio Torassa – INFN Padova 7

H→WW analysis CMS PTDR vol. II

MET Ptmax

Ptmin

Isolation

IP < 3 for each muon

Jet Veto

Missing ET > 50 GeV

55 GeV > ptmax > 35 GeV

ptmin > 25 GeV

Inv. Mass < 50 GeV

between muons < 0.8

Inv. Mass

( L = 10 fb-1 )

The selection tools ( channel )

tt WW DY

Lake Louise – February 2008 Ezio Torassa – INFN Padova 8

H→WW analysis CMS PTDR vol. II

Angle between the leptons

Final selection + e + ee channels

l = e , , NLO x BR (pb) Rate / fb-1

H→WW→ll (160 GeV) 2.34 42

H→WW→ll (165 GeV) 2.36 46

H→WW→ll (170 GeV) 2.26 33

qq→WW→ll 11.7 12

gg→WW→ll 0.48 3.7

tt→WWbb→ll 86.2 9.8

tW→WWb→ll 3.4 1.4

ZW→lll 1.6 0.5

ZZ→ll 1.5 0.35

Sum backgrounds 105 28

Lake Louise – February 2008 Ezio Torassa – INFN Padova 9

control region signal region

H→WW analysis CMS PTDR vol. II

regcontrolMCregcontrol

MCregsignal

regsignal NN

NN _

_

__

JET veto removed

2 b-tagged jets

Background estimation from data

H→WW

tt

WW

control region

tt

tt

Systematic error estimation

Th. err. Det. sys. Stat. err.

Tot. errors @ L = 5 fb-1 16% 17%

regcontrolMCregcontrol

MCregsignal

MCregcontrol

MCregsignal

regcontrolMCregcontrol

MCregsignal

regsignal NNN

NN _

_

_

_

__

_

__

tt

tt WW

Lake Louise – February 2008 Ezio Torassa – INFN Padova 10

H→WW analysis CMS PTDR vol. II

Signal significance Luminosity for discovery at 5

Lake Louise – February 2008 Ezio Torassa – INFN Padova 11

H→WW analysis CMS PAS Hig_07_001

trigger + skim pre-selectionmultivariate

analysis

cut based analysis

Analysis strategy

one pair of leptons with opposite charge |η1| < 2.5, |η2| < 2.5 MET > 30 GeV m(ll) >= 12 GeV Njets central <= 2 (ET > 20 GeV)

ptmin > 10 GeV, ptmax

> 20 GeV

Lake Louise – February 2008 Ezio Torassa – INFN Padova 12

H→WW analysis CMS PAS Hig_07_001

Analysis strategy

- mass dependent cuts optimization- optimized significance defined as:

nσ (cuts) = NS / √[NB + (ΔNB)2]

- test of different Multivariate Techniques: boosted decision tree (BDT) neural network classifiers (NN)

Classifier output for the boosted decision tree analysis

Cut based analysis

Multivariate analysis

Lake Louise – February 2008 Ezio Torassa – INFN Padova 13

Conclusions

The Monte Carlo analysis preformed for the PTDR vol. II showed the SM Higgs boson could be discovered with: - less than 1 fb-1 if its mass is around 165 GeV - 10 fb-1 if its mass is between 150 GeV and 180 GeV

More detailed studies are showing that we can increase the sensibility in the low mass region with: - mass dependent cut based analysis - multivariate analysis techniques

Next results will provide exclusion limits with the 100 pb-1

misalignment scenario