Antoine Laureys

Centre for Cosmology, Particle Physics and Phenomenology (CP3)
Université Catholique de Louvain
Chemin du Cyclotron 2
1348 Louvain-La-Neuve, Belgium
mail : antoine.laureys@uclouvain.be
Last modification : 2012-11-05

## $\underline{ p p \rightarrow h^0 \rightarrow Z^{0*} \gamma }$

The rare Higgs decay, $h^0 \rightarrow Z^{0*} \gamma$, is implemented in the UFO model "h_ZGamma" (version v1.0) and allows the user to study the full Higgs production process, $p p \rightarrow h^0 \rightarrow Z^{0*} \gamma \rightarrow l^- l^+ \gamma$, since it includes,

• all tree-level Standard Model interactions
• the Higgs Effective Field Theory, i.e. interactions according to the following low-energy lagrangian,

$\mathcal{L}=\frac{\alpha_{\rm S}}{12\pi \rm v}G^{a\mu\nu}G^a_{\mu\nu}h$

• a local H-Z*-Gamma interaction allowing for an off-shell Z boson as calculated in Nucl.Phys. B259 (1985) 137 with the exact contribution from the W loop and from the massive bottom and top quarks.

The model described above has been tested in several ways,

• analytic formulae for the Higgs partial width from Nucl.Phys. B259 (1985) 137 and arXiv:hep-ph/0503172 have been cross checked against each other,
• the computed Higgs partial width has been cross checked with HDECAY, a program of Michael Spira implementing the partial width of reference arXiv:hep-ph/0503172,
• kinematical and differential jet rate distributions have been checked with matched samples up to 2 extra jets.

Please, notice that a specific version of MadGraph5 is dedicated to this process to support formfactors and is available here or via launchpad :

Once the right version of MadGraph5 is downloaded as well as the h_ZGamma model, extract the tarball h_zgamma.tar.gz in the directory "formfactor/models/" and run MadGraph5 as usual :

./bin/mg5
>import model h_Zgamma
>generate p p > h > z a
>output pp_h_za

Below, the reader can find matching plots (a,b,c) for $p p \rightarrow h^0 \rightarrow Z^{0*} \gamma$ samples with 0, 1 and 2 jets as well as an illustration of the pT distribution (d) of a Higgs boson of 125 GeV produced at the LHC running at 8 TeV.

Figure: (a) differential 0 -> 1 jet rate distribution using the matching of matrix elements and parton showers,
(b) differential 1 -> 2 jet rate distribution,
(c) differential 2 -> 3 jet rate distribution,
(d) Higgs (125 GeV) pT distribution of the matched pp -> h -> e- e+ a + 0,1 jet samples, LHC@8TeV.