[u/mrichter/AliRoot.git] / PYTHIA8 / pythia8170 / htmldoc / SUSYProcesses.html

<html>
<head>
<title>SUSY Processes</title>
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<link rel="shortcut icon" href="pythia32.gif"/>
</head>
<body>

<h2>SUSY</h2>
<p>
Here is collected processes involving supersymmetric particle 
production, with the exception of the (extended) Higgs sector.
Since the number of separate but closely related processes is so big,
there will not be switches for each separate process but only for a
reasonable set of subgroups. However, the general 
switches <code>SUSY:idA</code> and <code>SUSY:idB</code> may be used in
conjunction with any of these groups to provide some additional
flexibility to concentrate on processes involving only specific (s)particle
final states, see below. 
</p>

<p>
Most of the SUSY implementation in PYTHIA 8 has been written by
N. Desai, in combination with an MCnet studentship at CERN in
2010, with further work having been carried out during 2011. 
The implementation is documented in [<a href="Bibliography.html" target="page">Des11</a>]. Please give due
credit to external contributions to PYTHIA 8, such as this one, by
including the original work in your list of references when using this
implementation. 
</p>

<p>Since the implementation of SUSY processes was only recently
completed [<a href="Bibliography.html" target="page">Des11</a>], case-by-case validations against other codes 
are still recommended. In all cases, a set of default validations have 
already been carried out by the authors. These validations compared to 
the PYTHIA 6 SUSY implementation, using an sps1a spectrum. Most of the
SLHA2-specific extensions have  not been explicitly validated,
however, with the exception of the R-parity violating single-sparticle
production cross sections.
</p>

<br/><b>Important Note on SLHA:</b> 
In order to simulate SUSY processes it is required to read in the 
couplings and masses relevant for the scenario to be studied. This 
is done with the help of the SUSY Les Houches Accord (SLHA), including
the SLHA2 extensions and generalizations. (Internally, the SLHA2
conventions are used. SLHA1 spectra are automatically translated into
SLHA2 notation during initialization.) The 
reading of a relevant SLHA file <b>must</b> be set up, as described 
on <a href="SUSYLesHouchesAccord.html" target="page">the SLHA page</a>. 
Attempting to generate SUSY processes without a properly initialized
SLHA spectrum is strongly discouraged and may lead to unexpected
results. Always check for warnings and errors reported by the SLHA
reader during the initialization stage. 

<h3>SUSY Processes</h3>

<br/><b>Note 1:</b> Decays of SUSY particles are described
separately <a href="#decays">below</a>. 

<br/><b>Note 2:</b> One special possibility is that the gluino or 
some squark(s) are sufficiently long-lived to hadronize. See 
<a href="RHadrons.html" target="page">the R-hadrons page</a> for further details.

<br/><b>Note 3:</b> lepton- and photon-initial states are not yet available. 
Only quark/gluon-initiated <i>2 -> 2</i> and <i>2 -> 1</i> (RPV) 
processes have been implemented. Likewise, direct slepton production 
has not yet been implemented (i.e., <i>2 -> 2</i> processes
involving sleptons in the final state). Sleptons will of course still be
produced through cascade decays of heavier (s)particles. 

<br/><b>Note 4:</b> cross sections will be correctly folded with open
branching fractions of cascade decays, but at present any difference between
particle and antiparticle decay tables is not taken into account. This
possibility will be included in a future update. 

<p/><code>flag&nbsp; </code><strong> SUSY:all &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Common switch for production of supersymmetric particles, i.e. 
particles with R-parity -1. 
  

<p/><code>mode&nbsp; </code><strong> SUSY:idA &nbsp;</strong> 
 (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)<br/>
Option to limit the sum over possible outgoing states in SUSY
<i>2 -> 2</i> processes to ones including a specific particle 
identity code. The default corresponds to summing over all possible 
indices. A non-zero value of <code>SUSY:idA</code> selects only processes 
that contain the state corresponding to that particular particle identity 
code in the fundamental <i>2 -> 2</i> scattering process (symmetrized 
over particle/antiparticle). It is the user's responsibility to ensure 
that (a subset of) the processes be to simulated actually include this 
particle at the <i>2 -> 2</i> level; thus, asking for the lightest 
neutralino (code 1000021) to be present in a squark-squark production 
process will give no match. 
  

<p/><code>mode&nbsp; </code><strong> SUSY:idB &nbsp;</strong> 
 (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)<br/>
As for <code>SUSY:idA</code>, but requires an additional particle
with PDG code <code>SUSY:idB</code> to be present in the <i>2 -> 2</i>
process. Thus, using  <code>SUSY:idA</code> and  <code>SUSY:idB</code> 
a specific subprocess can be selected. Again only the absolute sign is 
used, i.e. the summation over particle and antiparticle is retained.
  

<p/><code>mode&nbsp; </code><strong> SUSY:sin2thetaWMode &nbsp;</strong> 
 (<code>default = <strong>2</strong></code>; <code>minimum = 1</code>; <code>maximum = 3</code>)<br/>
The value of <i>sin2(thetaW)</i> should be taken from
<br/><code>option </code><strong> 1</strong> : SM value, defined at <i>M_Z</i>, taken from
PYTHIA's <code>StandardModel:sin2thetaW</code> parameter.  
<br/><code>option </code><strong> 2</strong> : SUSY value, defined at <i>M_SUSY</i>, derived from the
running gauge couplings in <code>BLOCK GAUGE</code> in the SLHA
file. Note: if no such block is present in the input file, this option
will default back to option 1 above, i.e., the SM value.  
<br/><code>option </code><strong> 3</strong> : Pole value, defined by <i>1 - M_W^2/M_Z^2</i>, 
using the pole masses stored in the SLHA <code>BLOCK MASS</code>, or, 
alternatively, PYTHIA's internal pole masses if no such block is 
present.  
  

<h4>Gluino Pair Production</h4>

<p/><code>flag&nbsp; </code><strong> SUSY:gg2gluinogluino &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of gluinos by gluon-gluon initial states. 
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2gluinogluino &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of gluinos by quark-antiquark annihilation and
<i>t</i>-channel squark exchange. So far, these cross sections assume the
squark CKM is aligned with the quark CKM and that all quantities are
real, so effects of non-minimal flavour violation and/or CP violation
are not yet included.
  

<h4>Associated Squark-Gluino Production</h4>

<p/><code>flag&nbsp; </code><strong> SUSY:qg2squarkgluino &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Associated production of a squark with a gluino. Only implemented for the
flavor-diagonal case. So far, these cross sections assume the
squark CKM is aligned with the quark CKM and that all quantities are
real, so effects of non-minimal flavour violation and/or CP violation
are not yet included.
  

<h4>Squark Pair Production</h4>

<p/><code>flag&nbsp; </code><strong> SUSY:gg2squarkantisquark &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of a scalar quark together with a scalar antiquark by
gluon annhilation via <i>s</i>-channel gluon exhange, <i>t</i>- and 
<i>u</i>-channel squark exchange, and the direct 4-point coupling. 
The cross section expression follows [<a href="Bibliography.html" target="page">Boz07</a>]. 
Validation of the FLV and CPV cases has not yet been completed.
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2squarkantisquark &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of a scalar quark together with a scalar antiquark 
by quark-antiquark annihilation. 
For same-isospin <i>~q~q*</i> production (i.e., <i>~u~u*</i>, 
<i>~u~c*</i>, ...), the <i>s</i>-channel gluon, photon, and 
<i>Z</i> and <i>t</i>-channel gluino contributions have so far 
been implemented (i.e., the <i>t</i>-channel neutralino contributions 
are neglected). For opposite-isospin <i>~q~q*</i> production 
(<i>~u~d*</i>, <i>~u~s*</i>, ...), the <i>s</i>-channel <i>W</i> 
and <i>t</i>-channel gluino contributions have been implemented 
(i.e., the <i>t</i>-channel neutralino contributions are neglected). 
The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>]. 
Validation of the FLV and CPV cases has not yet been completed.
(Note to PYTHIA 6 users: 
in older PYTHIA 6 versions, a bug caused the <i>~t1~t2*</i> cross to be
overcounted by a factor of 2. Starting from version 6.4.24, that
generator now agrees with the implementation here.)
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2squarkantisquark:onlyQCD &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
When switched <code>on</code> this flag switches off all but the 
<i>s</i>-channel gluon contribution in the
calculation of same-isospin squark-antisquark production cross
sections. Intended for reference only. For the most
accurate physics simulation, leave this flag in the <code>off</code>
position.  
  

<p/><code>flag&nbsp; </code><strong> SUSY:qq2squarksquark &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of scalar quarks (squark-squark and its charge
conjugate process; for squark-antisquark production see above) 
by <i>t</i>- and <i>u</i>-channel gluino, neutralino, and 
chargino exchange. The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>]. 
Validation of the FLV and CPV cases has not yet been completed.
(Note to PYTHIA 6 users: PYTHIA 6 only included the gluino exchange
contribution, which typically dominates due to the size of the strong
coupling; for counterchecks, 
the flag <code>SUSY:qq2squarksquark:onlyQCD</code>
below can be switched on to eliminate the chargino and neutralino
contributions.)
  

<p/><code>flag&nbsp; </code><strong> SUSY:qq2squarksquark:onlyQCD &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
When switched <code>on</code> this flag causes the <i>t</i>- or 
<i>u</i>-channel neutralino and chargino contributions to be 
ignored in the calculation of squark pair production cross sections. 
Intended for reference only. For the most accurate physics simulation, 
leave this flag in the <code>off</code> position.  
  

<h4>Neutralino and Chargino Pair Production</h4>

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2chi0chi0 &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of neutralinos by quark-antiquark annihilation. With
four neutralino species this gives ten separate processes, codes 
1201 - 1210. The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
Validation of the FLV and CPV cases has not yet been completed.
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2chi+-chi0 &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Associated chargino-neutralino production by quark-antiquark
annihilation. With four neutralino species, two chargino ones, and
maintaining charge conjugate proceeses separate, this gives 16 
separate processes, codes 1221 - 1236. The cross section expressions 
follow [<a href="Bibliography.html" target="page">Boz07</a>].
Validation of the FLV and CPV cases has not yet been completed.
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2chi+chi- &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of charginos by quark-antiquark annihilation. With
two chargino species and maintaining mutually charge conjugate
processes separate, this gives four separate processes, codes 
1241 - 1244. The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>]. 
Validation of the FLV and CPV cases has not yet been completed.
  

<h4>Associated Neutralino/Chargino + Squark/Gluino Production</h4>

<p/><code>flag&nbsp; </code><strong> SUSY:qg2chi0squark &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Pair production of neutralinos from quark-gluon initial states.
The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
Validation of the FLV and CPV cases has not yet been completed.
  

<p/><code>flag&nbsp; </code><strong> SUSY:qg2chi+-squark &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Associated chargino-squark production from quark-gluon initial states.
annihilation. The cross section expressions
follow [<a href="Bibliography.html" target="page">Boz07</a>].
Validation of the FLV and CPV cases has not yet been completed.
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2chi0gluino &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Associated neutralino-gluino production by quark-antiquark
annihilation. Status: not implemented yet.
  

<p/><code>flag&nbsp; </code><strong> SUSY:qqbar2chi+-gluino &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Associated chargino-gluino production by quark-antiquark
annihilation. Status: not implemented yet.
  

<h4>Slepton Production</h4>

No 2->2 slepton pair production or associated slepton production 
cross sections have been implemented yet. 

<h4>R-parity violating squark production</h4>

<p/><code>flag&nbsp; </code><strong> SUSY:qq2antisquark &nbsp;</strong> 
 (<code>default = <strong>off</strong></code>)<br/>
Resonant squark production via R-parity violating UDD couplings. The
couplings must be input using the SLHA2 structure. 
  

<a name="decays"></a>
<h3>Decays of SUSY Particles</h3>

Based on the parameters read in from the SLHA, PYTHIA 8 will normally 
compute the decay modes of SUSY particles automatically, using the 
<code>SusyResonanceDecays</code> class(es). Essentially all tree-level
2-body decays in the MSSM  
have been implemented this way, excepting so far only those involving
Higgs bosons (either in the in- or out-state) or gravitinos. 
Available channels so far include:
<ul>
<li>~q &rarr; q + ~chi</li>
<li>~q &rarr; ~q + W/Z</li>
<li>~q &rarr; q + q (RPV UDD)</li>
<li>~q &rarr; l + q (RPV LQD)</li>
<li>~g &rarr; ~q + q</li>
<li>~chi &rarr; ~chi + Z/W</li>
<li>~chi &rarr; ~q + q</li>
<li>~chi &rarr; ~l/~nu + l/nu</li>
<li>~chi0 &rarr; q + q + q (RPV UDD)</li>
<li>~l/~nu &rarr; l/nu + ~chi</li>
<li>~l/~nu &rarr; ~l/~nu + W/Z</li>
</ul>
All channels are still undergoing validation, so this
implementation should be considered preliminary.
Still missing but to be included in a forthcoming update
are: 3-body decays of charginos (via RPV), and 2-body decays of squarks and
gauginos with Higgs as one of the decay products. 

</body>
</html>

<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
Commit	Line	Data
63ba5337	1	<html>
	2	<head>
	3	<title>SUSY Processes</title>
	4	<link rel="stylesheet" type="text/css" href="pythia.css"/>
	5	<link rel="shortcut icon" href="pythia32.gif"/>
	6	</head>
	7	<body>
	8
	9	<h2>SUSY</h2>
	10	<p>
	11	Here is collected processes involving supersymmetric particle
	12	production, with the exception of the (extended) Higgs sector.
	13	Since the number of separate but closely related processes is so big,
	14	there will not be switches for each separate process but only for a
	15	reasonable set of subgroups. However, the general
	16	switches <code>SUSY:idA</code> and <code>SUSY:idB</code> may be used in
	17	conjunction with any of these groups to provide some additional
	18	flexibility to concentrate on processes involving only specific (s)particle
	19	final states, see below.
	20	</p>
	21
	22	<p>
	23	Most of the SUSY implementation in PYTHIA 8 has been written by
	24	N. Desai, in combination with an MCnet studentship at CERN in
	25	2010, with further work having been carried out during 2011.
	26	The implementation is documented in [<a href="Bibliography.html" target="page">Des11</a>]. Please give due
	27	credit to external contributions to PYTHIA 8, such as this one, by
	28	including the original work in your list of references when using this
	29	implementation.
	30	</p>
	31
	32	<p>Since the implementation of SUSY processes was only recently
	33	completed [<a href="Bibliography.html" target="page">Des11</a>], case-by-case validations against other codes
	34	are still recommended. In all cases, a set of default validations have
	35	already been carried out by the authors. These validations compared to
	36	the PYTHIA 6 SUSY implementation, using an sps1a spectrum. Most of the
	37	SLHA2-specific extensions have not been explicitly validated,
	38	however, with the exception of the R-parity violating single-sparticle
	39	production cross sections.
	40	</p>
	41
	42	<br/><b>Important Note on SLHA:</b>
	43	In order to simulate SUSY processes it is required to read in the
	44	couplings and masses relevant for the scenario to be studied. This
	45	is done with the help of the SUSY Les Houches Accord (SLHA), including
	46	the SLHA2 extensions and generalizations. (Internally, the SLHA2
	47	conventions are used. SLHA1 spectra are automatically translated into
	48	SLHA2 notation during initialization.) The
	49	reading of a relevant SLHA file <b>must</b> be set up, as described
	50	on <a href="SUSYLesHouchesAccord.html" target="page">the SLHA page</a>.
	51	Attempting to generate SUSY processes without a properly initialized
	52	SLHA spectrum is strongly discouraged and may lead to unexpected
	53	results. Always check for warnings and errors reported by the SLHA
	54	reader during the initialization stage.
	55
	56	<h3>SUSY Processes</h3>
	57
	58	<br/><b>Note 1:</b> Decays of SUSY particles are described
	59	separately <a href="#decays">below</a>.
	60
	61	<br/><b>Note 2:</b> One special possibility is that the gluino or
	62	some squark(s) are sufficiently long-lived to hadronize. See
	63	<a href="RHadrons.html" target="page">the R-hadrons page</a> for further details.
	64
65	<br/><b>Note 3:</b> lepton- and photon-initial states are not yet available.
66	Only quark/gluon-initiated <i>2 -> 2</i> and <i>2 -> 1</i> (RPV)
67	processes have been implemented. Likewise, direct slepton production
68	has not yet been implemented (i.e., <i>2 -> 2</i> processes
69	involving sleptons in the final state). Sleptons will of course still be
70	produced through cascade decays of heavier (s)particles.
71
72	<br/><b>Note 4:</b> cross sections will be correctly folded with open
73	branching fractions of cascade decays, but at present any difference between
74	particle and antiparticle decay tables is not taken into account. This
75	possibility will be included in a future update.
76
77	<p/><code>flag  </code><strong> SUSY:all  </strong>
78	(<code>default = <strong>off</strong></code>)<br/>
79	Common switch for production of supersymmetric particles, i.e.
80	particles with R-parity -1.
81
82
83	<p/><code>mode  </code><strong> SUSY:idA  </strong>
84	(<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)<br/>
85	Option to limit the sum over possible outgoing states in SUSY
86	<i>2 -> 2</i> processes to ones including a specific particle
87	identity code. The default corresponds to summing over all possible
88	indices. A non-zero value of <code>SUSY:idA</code> selects only processes
89	that contain the state corresponding to that particular particle identity
90	code in the fundamental <i>2 -> 2</i> scattering process (symmetrized
91	over particle/antiparticle). It is the user's responsibility to ensure
92	that (a subset of) the processes be to simulated actually include this
93	particle at the <i>2 -> 2</i> level; thus, asking for the lightest
94	neutralino (code 1000021) to be present in a squark-squark production
95	process will give no match.
96
97
98	<p/><code>mode  </code><strong> SUSY:idB  </strong>
99	(<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)<br/>
100	As for <code>SUSY:idA</code>, but requires an additional particle
101	with PDG code <code>SUSY:idB</code> to be present in the <i>2 -> 2</i>
102	process. Thus, using <code>SUSY:idA</code> and <code>SUSY:idB</code>
103	a specific subprocess can be selected. Again only the absolute sign is
104	used, i.e. the summation over particle and antiparticle is retained.
105
106
107	<p/><code>mode  </code><strong> SUSY:sin2thetaWMode  </strong>
108	(<code>default = <strong>2</strong></code>; <code>minimum = 1</code>; <code>maximum = 3</code>)<br/>
109	The value of <i>sin2(thetaW)</i> should be taken from
110	<br/><code>option </code><strong> 1</strong> : SM value, defined at <i>M_Z</i>, taken from
111	PYTHIA's <code>StandardModel:sin2thetaW</code> parameter.
112	<br/><code>option </code><strong> 2</strong> : SUSY value, defined at <i>M_SUSY</i>, derived from the
113	running gauge couplings in <code>BLOCK GAUGE</code> in the SLHA
114	file. Note: if no such block is present in the input file, this option
115	will default back to option 1 above, i.e., the SM value.
116	<br/><code>option </code><strong> 3</strong> : Pole value, defined by <i>1 - M_W^2/M_Z^2</i>,
117	using the pole masses stored in the SLHA <code>BLOCK MASS</code>, or,
118	alternatively, PYTHIA's internal pole masses if no such block is
119	present.
120
121
122	<h4>Gluino Pair Production</h4>
123
124	<p/><code>flag  </code><strong> SUSY:gg2gluinogluino  </strong>
125	(<code>default = <strong>off</strong></code>)<br/>
126	Pair production of gluinos by gluon-gluon initial states.
127
128
129	<p/><code>flag  </code><strong> SUSY:qqbar2gluinogluino  </strong>
130	(<code>default = <strong>off</strong></code>)<br/>
131	Pair production of gluinos by quark-antiquark annihilation and
132	<i>t</i>-channel squark exchange. So far, these cross sections assume the
133	squark CKM is aligned with the quark CKM and that all quantities are
134	real, so effects of non-minimal flavour violation and/or CP violation
135	are not yet included.
136
137
138	<h4>Associated Squark-Gluino Production</h4>
139
140	<p/><code>flag  </code><strong> SUSY:qg2squarkgluino  </strong>
141	(<code>default = <strong>off</strong></code>)<br/>
142	Associated production of a squark with a gluino. Only implemented for the
143	flavor-diagonal case. So far, these cross sections assume the
144	squark CKM is aligned with the quark CKM and that all quantities are
145	real, so effects of non-minimal flavour violation and/or CP violation
146	are not yet included.
147
148
149	<h4>Squark Pair Production</h4>
150
151	<p/><code>flag  </code><strong> SUSY:gg2squarkantisquark  </strong>
152	(<code>default = <strong>off</strong></code>)<br/>
153	Pair production of a scalar quark together with a scalar antiquark by
154	gluon annhilation via <i>s</i>-channel gluon exhange, <i>t</i>- and
155	<i>u</i>-channel squark exchange, and the direct 4-point coupling.
156	The cross section expression follows [<a href="Bibliography.html" target="page">Boz07</a>].
157	Validation of the FLV and CPV cases has not yet been completed.
158
159
160	<p/><code>flag  </code><strong> SUSY:qqbar2squarkantisquark  </strong>
161	(<code>default = <strong>off</strong></code>)<br/>
162	Pair production of a scalar quark together with a scalar antiquark
163	by quark-antiquark annihilation.
164	For same-isospin <i>~q~q</i> production (i.e., <i>~u~u</i>,
165	<i>~u~c*</i>, ...), the <i>s</i>-channel gluon, photon, and
166	<i>Z</i> and <i>t</i>-channel gluino contributions have so far
167	been implemented (i.e., the <i>t</i>-channel neutralino contributions
168	are neglected). For opposite-isospin <i>~q~q*</i> production
169	(<i>~u~d</i>, <i>~u~s</i>, ...), the <i>s</i>-channel <i>W</i>
170	and <i>t</i>-channel gluino contributions have been implemented
171	(i.e., the <i>t</i>-channel neutralino contributions are neglected).
172	The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
173	Validation of the FLV and CPV cases has not yet been completed.
174	(Note to PYTHIA 6 users:
175	in older PYTHIA 6 versions, a bug caused the <i>~t1~t2*</i> cross to be
176	overcounted by a factor of 2. Starting from version 6.4.24, that
177	generator now agrees with the implementation here.)
178
179
180	<p/><code>flag  </code><strong> SUSY:qqbar2squarkantisquark:onlyQCD  </strong>
181	(<code>default = <strong>off</strong></code>)<br/>
182	When switched <code>on</code> this flag switches off all but the
183	<i>s</i>-channel gluon contribution in the
184	calculation of same-isospin squark-antisquark production cross
185	sections. Intended for reference only. For the most
186	accurate physics simulation, leave this flag in the <code>off</code>
187	position.
188
189
190	<p/><code>flag  </code><strong> SUSY:qq2squarksquark  </strong>
191	(<code>default = <strong>off</strong></code>)<br/>
192	Pair production of scalar quarks (squark-squark and its charge
193	conjugate process; for squark-antisquark production see above)
194	by <i>t</i>- and <i>u</i>-channel gluino, neutralino, and
195	chargino exchange. The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
196	Validation of the FLV and CPV cases has not yet been completed.
197	(Note to PYTHIA 6 users: PYTHIA 6 only included the gluino exchange
198	contribution, which typically dominates due to the size of the strong
199	coupling; for counterchecks,
200	the flag <code>SUSY:qq2squarksquark:onlyQCD</code>
201	below can be switched on to eliminate the chargino and neutralino
202	contributions.)
203
204
205	<p/><code>flag  </code><strong> SUSY:qq2squarksquark:onlyQCD  </strong>
206	(<code>default = <strong>off</strong></code>)<br/>
207	When switched <code>on</code> this flag causes the <i>t</i>- or
208	<i>u</i>-channel neutralino and chargino contributions to be
209	ignored in the calculation of squark pair production cross sections.
210	Intended for reference only. For the most accurate physics simulation,
211	leave this flag in the <code>off</code> position.
212
213
214	<h4>Neutralino and Chargino Pair Production</h4>
215
216	<p/><code>flag  </code><strong> SUSY:qqbar2chi0chi0  </strong>
217	(<code>default = <strong>off</strong></code>)<br/>
218	Pair production of neutralinos by quark-antiquark annihilation. With
219	four neutralino species this gives ten separate processes, codes
220	1201 - 1210. The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
221	Validation of the FLV and CPV cases has not yet been completed.
222
223
224	<p/><code>flag  </code><strong> SUSY:qqbar2chi+-chi0  </strong>
225	(<code>default = <strong>off</strong></code>)<br/>
226	Associated chargino-neutralino production by quark-antiquark
227	annihilation. With four neutralino species, two chargino ones, and
228	maintaining charge conjugate proceeses separate, this gives 16
229	separate processes, codes 1221 - 1236. The cross section expressions
230	follow [<a href="Bibliography.html" target="page">Boz07</a>].
231	Validation of the FLV and CPV cases has not yet been completed.
232
233
234	<p/><code>flag  </code><strong> SUSY:qqbar2chi+chi-  </strong>
235	(<code>default = <strong>off</strong></code>)<br/>
236	Pair production of charginos by quark-antiquark annihilation. With
237	two chargino species and maintaining mutually charge conjugate
238	processes separate, this gives four separate processes, codes
239	1241 - 1244. The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
240	Validation of the FLV and CPV cases has not yet been completed.
241
242
243	<h4>Associated Neutralino/Chargino + Squark/Gluino Production</h4>
244
245	<p/><code>flag  </code><strong> SUSY:qg2chi0squark  </strong>
246	(<code>default = <strong>off</strong></code>)<br/>
247	Pair production of neutralinos from quark-gluon initial states.
248	The cross section expressions follow [<a href="Bibliography.html" target="page">Boz07</a>].
249	Validation of the FLV and CPV cases has not yet been completed.
250
251
252	<p/><code>flag  </code><strong> SUSY:qg2chi+-squark  </strong>
253	(<code>default = <strong>off</strong></code>)<br/>
254	Associated chargino-squark production from quark-gluon initial states.
255	annihilation. The cross section expressions
256	follow [<a href="Bibliography.html" target="page">Boz07</a>].
257	Validation of the FLV and CPV cases has not yet been completed.
258
259
260	<p/><code>flag  </code><strong> SUSY:qqbar2chi0gluino  </strong>
261	(<code>default = <strong>off</strong></code>)<br/>
262	Associated neutralino-gluino production by quark-antiquark
263	annihilation. Status: not implemented yet.
264
265
266	<p/><code>flag  </code><strong> SUSY:qqbar2chi+-gluino  </strong>
267	(<code>default = <strong>off</strong></code>)<br/>
268	Associated chargino-gluino production by quark-antiquark
269	annihilation. Status: not implemented yet.
270
271
272	<h4>Slepton Production</h4>
273
274	No 2->2 slepton pair production or associated slepton production
275	cross sections have been implemented yet.
276
277	<h4>R-parity violating squark production</h4>
278
279	<p/><code>flag  </code><strong> SUSY:qq2antisquark  </strong>
280	(<code>default = <strong>off</strong></code>)<br/>
281	Resonant squark production via R-parity violating UDD couplings. The
282	couplings must be input using the SLHA2 structure.
283
284
285	<a name="decays"></a>
286	<h3>Decays of SUSY Particles</h3>
287
288	Based on the parameters read in from the SLHA, PYTHIA 8 will normally
289	compute the decay modes of SUSY particles automatically, using the
290	<code>SusyResonanceDecays</code> class(es). Essentially all tree-level
291	2-body decays in the MSSM
292	have been implemented this way, excepting so far only those involving
293	Higgs bosons (either in the in- or out-state) or gravitinos.
294	Available channels so far include:
295	<ul>
296	<li>~q → q + ~chi</li>
297	<li>~q → ~q + W/Z</li>
298	<li>~q → q + q (RPV UDD)</li>
299	<li>~q → l + q (RPV LQD)</li>
300	<li>~g → ~q + q</li>
301	<li>~chi → ~chi + Z/W</li>
302	<li>~chi → ~q + q</li>
303	<li>~chi → ~l/~nu + l/nu</li>
304	<li>~chi0 → q + q + q (RPV UDD)</li>
305	<li>~l/~nu → l/nu + ~chi</li>
306	<li>~l/~nu → ~l/~nu + W/Z</li>
307	</ul>
308	All channels are still undergoing validation, so this
309	implementation should be considered preliminary.
310	Still missing but to be included in a forthcoming update
311	are: 3-body decays of charginos (via RPV), and 2-body decays of squarks and
312	gauginos with Higgs as one of the decay products.
313
314	</body>
315	</html>
316
317	<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
318