Offshell interference effects

This page describes step by step how to get the interference between signal and background for the WW > vlqq' and ZZ fully leptonic decay in the SM and some extended model within MG_aMC@NLO

Authors : Benoît Hespel ​email and Eleni Vryonidou ​email

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SM

You can download a modified version of the loop_sm model (loop_sm_modif​) where we made simple changes in the couplings orders to be able to get the pieces (signal, background, interference) separately.

ZZ > ll l'l'

After you imported it inside the MG_2.3.1 loop_induced version, use the following syntax to get the different pieces for the ZZ > e+ e- µ+ µ- for example:

Signal :

generate g g > e+ e- mu+ mu- / e+ e- mu+ mu- [QCD] NP^2==2

Interference :

generate g g > e+ e- mu+ mu- / e+ e- mu+ mu- [QCD] NP^2==1

Total :

generate g g > e+ e- mu+ mu- / e+ e- mu+ mu- [QCD] NP=1

Background :

generate g g > e+ e- mu+ mu- / e+ e- mu+ mu- [QCD] NP=0

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WW > vl qq'

For the WW > ve e+ d u~ process for example, use:

Signal:

generate g g > e+ ve d u~ / e+ e- d u~ [QCD] NP^2==2

Interference:

generate g g > e+ ve d u~ / e+ e- d u~ [QCD] NP^2==1

Total:

generate g g > e+ ve d u~ / e+ e- d u~ [QCD] NP=1

Background:

generate g g > e+ ve d u~ / e+ e- d u~ [QCD] NP=0

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Additional heavy scalar

Then we extended the scalar sector of the SM by adding one additional particle called Y⁰. Via 2 parameters in the param_card, this particle can be set to be either a scalar (gSu33=1 & gPu33=0), a pseudoscalar (gSu33=0 & gPu33=1) or a mixed state (gSu33=x & gPu33=1-x).

The model can be downloaded here Scalar_simp_NLO_UFO​ and allows you to get the different pieces separately via the same commands as before.