]>
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 |