Searching for the Higgs boson at the LHC via Hb anti-b

Dan HertzA Examination

Physics DepartmentCornell University

5/4/05

Why are we looking?

● Standard Model– Higgs mechanism, Electroweak Symmetry-Breaking

(EWSB)

– requires existence of Higgs boson

● Beyond the SM– Usually include Higgs, e.g. MSSM

● Expected mass range ~130 GeV

The CMS Detector

ATLAS

Cross sections and branching fractions

Decay Modes for the Higgs

How to make a Higgs boson (and how to lose it)

● Direct production– gluon fusion: gg H

● Associated Production– q anti-q WH

– gg,q anti-qt anti-tH

– gg, q anti-q

● Decay modes– Light

● H ● H b anti-b

– Heavy● H WW(*)l+E

Tmiss

● H*)l

Let's take a look at that in detail...

Lowest order contributing diagrams

gg t anti-t Hq anti-qW H

WH -> lb anti-b

● Trigger

– lepton, ET miss

– 2 b jets

● Reconstruction– jet veto

– lepton veto

– MT(l) < 100 GeV

t anti-t H –> qq'b anti-b b anti-b l

● Triggers

– lepton, ET miss

– at least 6 jets● 4 b jets● 2 non-b jets

● Reconstruction– top

● W from l● match b jet

– top● W from qq'● match b jet

– Higgs from b-jets.

You call that a peak?

Results, almost...

Pure signal peaks Signal + Background

So do we see something or not?CMS

ATLAS