# Using UFO Models¶

In addition to the wide range of internal BSM models it is possible to use most models using the UFO format with Herwig. Herwig can currently only handle the perturbative Lorentz structures which arise in the coupling of particles but in most cases this is sufficient.

There are a wide range of models available in the FeynRules Model database

While many of these models contain both the UFO files need to use the model with Herwig a number only contain the FeynRules Mathematica files which can be used to generate the UFO files required by Herwig.

We will use the $$W'$$ model as a simple example. The model is available here

First we need to either download the ufo file using a web browser, or directly get it using wget

wget https://feynrules.irmp.ucl.ac.be/raw-attachment/wiki/Wprime/weff.ufo.tgz


Then extract the files

tar xzf weff.ufo.tgz


The files can then be processes to produce the C++ code needed by Herwig using the converter script supplied with Herwig

ufo2herwig WEff_UFO


This produces a number of C++ files and an example input file. We first need to compile the C++ code using the Makefile which has been automatically generated

make -j8


In this model as the main feature is the existence of the $$W'$$ resonance instead of using the general HPConstructor we will use the ResonantProcessConstructor just to construct the resonant processes and make use of the Inclusive option for the processes. The can be achieved by editing the example LHC-FRModel.in

insert ResConstructor:Incoming 0 /Herwig/Particles/u
insert ResConstructor:Incoming 0 /Herwig/Particles/ubar
insert ResConstructor:Incoming 0 /Herwig/Particles/d
insert ResConstructor:Incoming 0 /Herwig/Particles/dbar
insert ResConstructor:Incoming 0 /Herwig/Particles/g
#
insert ResConstructor:Intermediates 0 /Herwig/FRModel/Particles/Wp+
insert ResConstructor:Intermediates 0 /Herwig/FRModel/Particles/Wp-
#
set ResConstructor:Processes Inclusive


The standard read and run can then be read to generate events

Herwig read LHC-FRModel.in
Herwig run LHC-FRModel.run