Searching for the Higgs at ATLAS with the channel t t H 0 (H 0 ->b b )

Searching for the Higgs at ATLAS with the channel

ttH0(H0->bb)

Lily Asquith

UCL HEP XMAS TALKS

18th December 2007

NIKOS

Nikos Konstantinidis:

Level 2 Trigger guru

ATLANTIS event display overlord

ALEPH Higgs Hunter

NIKOS SIMON

Simon Dean:

ATLFast fast simulation software.

Principal developer of the UCL ttH(H->bb) analysis code

NIKOS SIMON SEBASTIAN

Sebastian Boeser:

Main developer for HepMCVisual

ATLANTIS developer

Athena-kit installation man

ttH(H->bb) combinatorics

NIKOS SIMON SEBASTIAN CATRIN

Catrin Bernius:

ttH(H->bb) Trigger

ttH(H->bb) background shape- analysis

NIKOS SIMON SEBASTIAN CATRIN LILY

Lily Asquith:

ttH(H->bb) cut-based analysis

Jets: detector effects + b-tagging

NIKOS SIMON SEBASTIAN CATRIN LILY

ATLAS detector at CERN’s Large Hadron Collider

Should start running Spring 2008

Proton-proton, 14TeV

14TeV

14TeV

‘our’ mass range

‘our’ mass range

H0->bb

t->Wb

We have 4 b quarks

‘our’ mass range

Require one W to decay leptonically

We have a ‘trigger’ lepton

Largest background: tt plus jets and W plus jets: reducible with b-tagging

Irreducible background:ttbb

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Background swamps signal by ~2000:1

Trigger

Trigger reduces vast amount of data to manageable rate.

Electron(muon) Pt> 25(20)GeV, ID track, isolation in calorimeter

Catrin: lepton trigger efficiency ~ 83%

Pre-selection

Need at least 6 jets (>20GeV) in order to reconstruct the event

Old ‘pre-selection’ : at least 4 jets b-tagged

New pre-selection: at least 4 jets b-taggable (central in eta)

Event Reconstruction

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Event Reconstruction

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Cut on mass 30GeV

Event Reconstruction

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.Estimate from fit to reco mass distributions

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Cut on mass 30GeV

Hadronic W

>3 b-tagged

>1 untagged

Tops and Higgs

Hadronic W

JETS

BUT b-tagging efficiency here ~ 60% per b-jet:: 13% for all four…

34% of our events lost just through jet segregation.

Hadronic W

Hadronic W

JETS

Use All

Not top N b-weighted

None with b-weight >n

Fewer Jets excluded from W reco=

More likely to get the W right BUT more incorrect combinations…

Have a nice holiday!