= 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 [https://cp3.irmp.ucl.ac.be/Members/bhespel email] and Eleni Vryonidou [https://cp3.irmp.ucl.ac.be/Members/evryonidou email] '''

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== SM ==

You can download a modified version of the loop_sm model ([attachment:loop_sm_modif.tar.gz 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
}}}


----

=== 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 Y^0^. 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 [attachment:Scalar_simp_NLO_UFO_modif.tar.gz Scalar_simp_NLO_UFO] and allows you to get the different pieces separately via the same commands as before.