h -> Z* Gamma

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

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

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 :

bzr branch lp:~maddevelopers/madgraph5/formfactor/

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.