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MadGraph5Processes.php @ 1

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first import of structure, PYTHIA8 and DELPHES
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1	<html>
2	<head>
3	<title>MadGraph 5 Processes</title>
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7	<body>
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28	<form method='post' action='MadGraph5Processes.php'>
29
30	<h2>MadGraph 5 Processes</h2>
31
32	By far the easiest way to implement new processes into PYTHIA 8 is
33	by using the matrix-element generator MadGraph 5. This program has
34	an option to output the results of a matrix-element calculation
35	as a set of PYTHIA 8 C++ classes (plus further auxiliary code),
36	that can then be linked and used as
37	<?php $filepath = $_GET["filepath"];
38	echo "<a href='SemiInternalProcesses.php?filepath=".$filepath."' target='page'>";?>semi-internal</a> processes,
39	meaning they are handled identically with normal internal ones.
40	This way, MadGraph 5 can be used to implement processes from
41	any model that can be written in terms of a Lagrangian. Any
42	<i>2 -> 1</i>, <i>2 -> 2</i> and <i>2 -> 3</i> processes
43	can be implemented, the limit being set by the absence of efficient
44	phase space generator algorithms for higher multiplicities in
45	PYTHIA. Features such as <i>s</i>-channel resonances are
46	automatically implemented in the process classes. Besides the process
47	library and necessary model files, also an example main program is
48	generated for each set of processes, which can be easily modified to
49	perform the desired analyses.
50
51	<p/>
52	In order to create a PYTHIA 8 process library with MadGraph 5, first
53	download the MadGraph 5 package from
54	<a href="https://launchpad.net/madgraph5" target="page">
55	https://launchpad.net/madgraph5</a>, and untar the package. You can
56	then specify the location of your <code>pythia81xx</code> directory
57	in the file <code>input/mg5_configuration.txt</code>:
58	<br/><code>pythia8_path = ./pythia81xx</code>
59	<br/>The location can be either relative (to the directory
60	<code>MadGraph5_v_x_x_x/.</code>) or absolute.
61
62	<p/>
63	For any model that is already implemented in the MadGraph 5 package,
64	you can directly use the model. Start the MadGraph 5 interface
65	<code>bin/mg5</code>, and do:
66	<pre>
67	import model model_name
68	generate your_process_in_mg5_syntax
69	add process your_next_process_in_mg5_syntax
70	...
71	output pythia8 [path_to_pythia81xx_directory]
72	</pre>
73
74	<p/>
75	For examples of MG5 process syntax, please see
76	<a href="http://madgraph.phys.ucl.ac.be/EXAMPLES/example_mg5.html"
77	target="page">http://madgraph.phys.ucl.ac.be/EXAMPLES/example_mg5.html</a>
78	or type <code>help generate</code>. If you specified the path to the
79	<code>pythia81xx</code> directory in the <code>mg5_configuration</code>
80	file, you do not need to enter it in the <code>output</code> command.
81
82	<p/>
83	If your preferred model is found on the FeynRules model wiki page,
84	<a href="http://feynrules.irmp.ucl.ac.be/wiki/ModelDatabaseMainPage"
85	target="page">http://feynrules.irmp.ucl.ac.be/wiki/ModelDatabaseMainPage</a>,
86	download the UFO (Universal FeynRules Output) tar file for the model,
87	untar in the <code>models/</code> directory, and use as above.
88
89	<p/>
90	If you want to implement a new model which has not yet been implemented,
91	you can do this either using the Mathematica package FeynRules (see
92	<a href="http://feynrules.irmp.ucl.ac.be/" target="page">
93	http://feynrules.irmp.ucl.ac.be/</a>) or directly edit the UFO model
94	files of the most similar model in the <code>models/</code> directory.
95
96	<p/>
97	The resulting output from the <code>output pythia8</code> command is:
98	<ul>
99	<li>A process directory <code>Processes_modelname</code> with the
100	model information and the files needed for all processes defined for
101	this model, placed in the <code>pythia81xx</code> main directory.
102	The model files are <code>Parameters_modelname.h/cc</code> and
103	<code>HelAmps_modelname.h/cc</code>, and the process files for each
104	process class (with the same mass, spin and color of the initial/final
105	state particles) are called <code>Sigma_modelname_processname.h/cc</code>.
106	The directory also contains a <code>makefile</code> and a model parameter
107	file <code>param_card_modelname.dat</code>.</li>
108	<li>An example main program in the directory <code>examples/</code>
109	(in the <code>pythia81xx</code> main directory) called
110	<code>main_modelname_N.cc</code> and a corresponding makefile
111	<code>Makefile_modelname_N</code>. This main program links in the
112	process classes in the process directory described above. To run the
113	example main program, just go to the <code>examples/</code>
114	directory and run
115	<br/><code>make -f Makefile_modelname_N</code>
116	<br/>or run <code>launch</code> directly inside the MadGraph 5
117	command line interface.</li>
118	</ul>
119
120	<p/>
121	Note that in order for PYTHIA 8 to be able to automatically decay any
122	new particles, it is necessary to specify the branching ratios of the
123	particles in the <code>param_card</code> file, see
124	[<a href="Bibliography.php" target="page">Ska04,Alw07</a>] for details.
125
126	<p/>
127	For further technical details, please see the MadGraph 5 release paper
128	[<a href="Bibliography.php" target="page">Alw11</a>] and the
129	<?php $filepath = $_GET["filepath"];
130	echo "<a href='SemiInternalProcesses.php?filepath=".$filepath."' target='page'>";?>semi-internal</a> processes page.
131
132	<p/>
133	Of course, as with MadGraph 4, MadGraph 5 can also output
134	files of parton-level events according to the
135	<?php $filepath = $_GET["filepath"];
136	echo "<a href='LesHouchesAccord.php?filepath=".$filepath."' target='page'>";?>LHEF</a> standard,
137	that can be read in and processed further by PYTHIA 8.
138	The advantage is that then the MadGraph 5 phase space generator
139	can be used, which opens up for processes with more than three
140	particles in the final state. The disadvantages are that it is less
141	easy to mix and match with existing PYTHIA processes, and that one
142	needs to regenerate and store large LHEF files for different
143	kinematics cuts or parameter values.
144
145	<p/>
146	Please cite the MadGraph 5 release paper [<a href="Bibliography.php" target="page">Alw11</a>] if you use
147	MadGraph 5 to generate process libraries for PYTHIA 8.
148
149	</body>
150	</html>
151
152	<!-- Copyright (C) 2012 Torbjorn Sjostrand -->

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