H W W l l l l Chiara Rovelli Univ.Milano Bicocca -- - - PowerPoint PPT Presentation

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H W W l l l l Chiara Rovelli Univ.Milano Bicocca -- - - PowerPoint PPT Presentation

Jun 30, 2023 872 likes •1.05k views

A first look at the channel + + H W W l l l l Chiara Rovelli Univ.Milano Bicocca -- LLR, E.Polytechnique 1 Outline Introduction of the channel different approaches event topologies and

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SLIDE 1

1

A first look at the channel

Chiara Rovelli Univ.Milano Bicocca -- LLR, E.Polytechnique

l l

H W W l l ν ν

+ − + −

→ →

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SLIDE 2

2

Outline

  • Introduction of the channel
  • different approaches
  • event topologies and selections
  • background studies
  • very preliminary results at the fast simulation level
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SLIDE 3

3

l l

H W W l l ν ν

+ − + −

→ →

Past analyses demonstrated that this could be a very fast channel for the discovery of the SM Higgs in the intermediate mass region 130 GeV< MH < 2MZ filling the gap of * BR ( H ZZ 4l ). It can be very useful also for lower mass ( 120 GeV )

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SLIDE 4

4

Possible approaches

  • study of the general kinematics of the channel without any

specific requirements on the Higgs production mechanism

  • study of the vector boson fusion channel for the Higgs

production to exploit its characteristic 2 jet signature In the past two different kinds of analysis have been performed: In both cases, because of the 2 , it is impossible to distinguish a peak in the invariant mass distribution not easy counting channel the precise knowledge of all possible backgrounds processes is fundamental

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SLIDE 5

5

Vector Boson Fusion

Production cross section is 20% ( 4pb)

  • f the total for mH=120GeV

The signal can be described as the scattering of q via t-channel W and Z exchange with the Higgs radiated off this weak bosons

the signal contains two forward quark jets in addition to

HWW 2l2 decay products. Backgrounds: any process resulting in 2 jets, 2 charged leptons and missing energy ( ttjj, WWjj, ….)

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SLIDE 6

6

Vector Boson Fusion

Extra event tags : * Two high PT forward jets in opposite hemisphere with large dijet invariant mass * Charged leptons between the tagging jets * Little jet activity in the central region ( no color flow; suppression of QCD background )

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Inclusive analysis

Signature: 2 leptons and missing momentum Possible backgrounds: WW non resonant, tt pair production single t production ( pp Wtb ) ZZ, Z/* bb pair production Up to now (very beginning) : preliminary analysis including the qq WW background (tt & t back. at a qualitative level) and considering l = e,

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SLIDE 8

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The WW nr background, I

Signal : Higgs scalar, W vectors => to have JTot= 0 spin wave function

must be:

        − + − + − + =

− + − + − +

LL W W TT W W TT W W WW

z z z z z z z

) ( ) ( ) ( ) ( ) ( ) ( 3 1 ) , (

TL coupling not allowed

Case TT: each lepton has the same SZ of the mother and must be produced

with definite elicity => max prob to have the leptons emitted in the same direction

Case LL: again max prob to have leptons emitted in the same direction

WWnr:

Unpolarized initial state => TL coupling is allowed and @ MWW~160 half

  • f the production rate

Case TL: no correlation in leptons emission

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SLIDE 9

9

Spin correlation

between the two leptons

in the transverse plane

  • f the first leptons

Vs of the second one

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SLIDE 10

10

The WW nr background, II

WWnr events more boosted along the beam More isotropic signal leptons spatial distribution

γz~10

Higgs produced mainly via g-g fusion WWnr mainly produced by qq

2 1 2 1

4 x x x x

z

+ = γ

Z boost

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SLIDE 11

11

Analysis

  • Search for relatively central events with isolated charged

leptons (e: PT > 20 GeV; : PT > 10 GeV; || < 2; leptons separated in space by more than 10 ° . and isolated in the calorimeter) .

.

  • Missing PT cut: MPT > 20 GeV/c .
  • Invariant mass cut: M(ll) < 80 GeV .

(to reject leptons from Z peak ) . Signal and backgrounds generated using PYTHIA and TOPREX (for t/tt back) and the fast simulation for CMS (CMSJET) Selections:

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SLIDE 12

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Analysis

  • Jet veto: rejected events with
  • ne jet with PT > 20 GeV

and || < 2.4

  • 10° < < 45°

(spin correlation)

  • |cos (ll)| < 0.8

(boost of WW background)

  • MT(WW) > 140

Selections:

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SLIDE 13

13

Summary & next steps

  • This analysis showed that channel H WW ll can be a

potential and quite fast channel for the Higgs discovery at the LHC

  • quantitative study of all the backgrounds source to find the

significance signal/noise

  • inclusion of the l = channel, considering both leptonics

and hadronic decays

  • study of this channel with the full simulation chain

Our goals:

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Signal

9998 0.182 MH=160 9999 0.104 MH=200 9997 0.114 MH=140 9999 0.036 MH=120 events in the sample x-sec (pb)

µ µ

ν µ ν µ

− + − +

→ → W W H 0

Reference sample

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SLIDE 15

15

WWnr is the main bkgr, with the same final states but reducible (next slides)

s Background

36990 17991 49489 48471 17599 N events 5,5 5,5 3,3 7,7 5,5 Ptmin O( fb-1 ) 29, 12 29 pb-1 621 49 nb-1 106 3.5 nb-1 (1.4)·107 (Pthard>20) 0.2 fb-1 77 L x-sec (pb) Process

µ µ

ν µ ν µ

− + − +

→ → W W q q X Z + →

− +µ

µ γ* / X t t + →

− +µ

µ X ZZ ZW + → µµ , X b b + →

− +µ

µ

Not yet considered:

  • Single top ( )
  • µ

µ

ν µ ν µ

− + − +

→ → W W gg X Wtb pp + → →

− +µ

µ

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SLIDE 16

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Statistical Results

88 22 Background 138 35 Signal Nev @ 20fb-1 Nev @ 5fb-1 MH=160

14.7 7.4 σ

Results for other masses:

21 4.9 2.5 2.7 MH=200 14 6.0 3.0 3.2 MH=140 390 1.1 0.5 1.9 MH=120 L5σ(fb-1) σ @ 20fb-1 σ @ 5fb-1 Eff (%)

MH=120: not viable; other H production processes like Vector Bosons Fusion can be used

(CMS Note 2002/26: pp->jjH, H->WW->llνν)

MH=200: different kinematic (e.g. no so effective spin correlation) different selections should

be used