Version 1 (modified by trac, 7 years ago) (diff)

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## Higgs phenomenology at hadron colliders

#### 1. Decays of the Higgs boson

• A light SM Higgs boson mostly decays into % %. Compute the decay rate for % %.
• For a Higgs mass of around 160 !GeV, the main decay mode is % %. Compute the decay rate.

The Higgs branching ratios can be found here.

You may also have a look at the following Mathematica notebook.

#### 2. Gluon fusion and Higgs effective field theory

The computation of the leading order cross-section of a Higgs boson via gluon fusion involves the computation of a top quark loop. In the large top mass limit, the gluon fusion production of a Higgs boson can be described by an effective field theory where the Higgs couples directly to the gluons,

% %,

where % % is an effective (dimensionful) coupling constant and % % denotes the gluon field strength tensor.

For details on the calculation of the top loop and the effective theory, see the notes and/or check the following Mathematica notebooks (which actually contain much more information):

1. pp>H at LO (1-loop): details of the calculation (Mathematica Notebook) HiggsGG-LO-mtfinite.nb
2. pp>H at NLO: details of the calculation (Mathematica Notebook) higgsGG-NLO.nb
3. pp>H at NLO: cross section evaluation for the LHC (Mathematica Notebook+PDF libraries to be compiled) phenHiggs.tar.gz.

Exercise (DIFFICULT but interesting!!): Use the all the material above to derive the EFT description of a pseudo-scalar Higgs, A,

% %,

where % % is an effective (dimensionful) coupling constant and % % denotes the gluon field strength tensor and % % is its dual. Compute the loop amplitude, derive the Feynman rules in the large top mass limit and calculate the LO and NLO cross sections at the LHC.

#### 3. Discover the SM Higgs at the LHC

• Find the best prediction for Higgs production at the LHC here.

Choose a channel and investigate signal and background:

1. The 4 lepton final state: % %
1. The 2 lepton + missing Et final state: % %
2. Top associated production % % with % %

#### 4. Gluon fusion vs. weak boson fusion

• Use the web interface of MadGraph/MadEvent to generate the cross-sections for H+2jets at the LHC via gluon fusion and weak boson fusion. Hint: For the gluon fusion, you need to use the Higgs efective field theory (heft) in MadGraph/MadEvent.
• Plot the rapidities of the two jets for boson production channels.
• What do you observe? What do you conclude?
• What happens to this picture when a third jet is added?

-- Main.FabioMaltoni - 28 Aug 2008