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1	<html>
2	<head>
3	<title>Onia 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>Onia Processes</h2>
10
11	Production of J/psi or Upsilon, directly and via chi states and the
12	colour-octet mechanism.
13	In each process the square-bracketed expression specifies the state
14	in spectroscopic notation, <i>(2S+1) L J</i>, followed by
15	<i>(1)</i> for colour-singlet states and <i>(8)</i> for
16	colour-octet ditto.
17
18	<p/>
19	The original Fortran code for these processes has been contributed
20	by Stefan Wolf [unpublished]. For the C++ version only the unpolarized
21	expressions are retained, since the theoretical predictions of the
22	colour-octet model anyway do not agree with the experimental
23	observations. Furthermore, the polarization effects are modest,
24	so isotropic decay is not a bad starting point. Such an event sample
25	can afterwards be reweighted at will by the user, to test various
26	assumptions.
27
28	<p/>
29	The description of
30	<a href="TimelikeShowers.html" target="page">final-state radiation</a>
31	is in this case based on some further model assumptions.
32
33	<p/>
34	Most of the processes below are divergent in the limit <i>pT -> 0</i>,
35	and therefore a <i>pTmin</i> scale should be set. Comparisons with
36	data indicate that this divergence can be tamed the same way as for
37	the normal QCD <i>2 -> 2</i> cross sections [<a href="Bibliography.html" target="page">Bar06,Kra08</a>],
38	which makes sense, since they are all dominated by the same kind of
39	<i>t</i>-channel gluon exchange. It is therefore possible to use the
40	<a href="UserHooks.html" target="page">SuppressSmallPT</a> user hook to impose a
41	reweighting that cancels the low-<i>pT</i> divergence.
42
43	<p/>
44	An eikonalized description of these processes is included in the
45	multiparton-interactions framework. Here the low-<i>pT</i> dampening
46	is automatic, and additionally the framework is more consistent
47	(e.g. with respect to energy-momentum constraints and the
48	impact-parameter description) for events where the onium production
49	is not the hardest subprocess, as would often be the case in the
50	low-<i>pT</i> limit.
51
52	<h3>Charmonium</h3>
53
54	<p/><code>flag  </code><strong> Charmonium:all  </strong>
55	(<code>default = <strong>off</strong></code>)<br/>
56	Common switch for the group of charmonium production.
57
58
59	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[3S1(1)]g  </strong>
60	(<code>default = <strong>off</strong></code>)<br/>
61	<i>g g -> ccbar[3S1(1)] g</i>.
62	Code 401.
63
64
65	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[3P0(1)]g  </strong>
66	(<code>default = <strong>off</strong></code>)<br/>
67	<i>g g -> ccbar[3P0(1)] g</i>.
68	Code 402.
69
70
71	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[3P1(1)]g  </strong>
72	(<code>default = <strong>off</strong></code>)<br/>
73	<i>g g -> ccbar[3P1(1)] g</i>.
74	Code 403.
75
76
77	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[3P2(1)]g  </strong>
78	(<code>default = <strong>off</strong></code>)<br/>
79	<i>g g -> ccbar[3P2(1)] g</i>.
80	Code 404.
81
82
83	<p/><code>flag  </code><strong> Charmonium:qg2QQbar[3P0(1)]q  </strong>
84	(<code>default = <strong>off</strong></code>)<br/>
85	<i>q g -> ccbar[3P0(1)] q</i>.
86	Code 405.
87
88
89	<p/><code>flag  </code><strong> Charmonium:qg2QQbar[3P1(1)]q  </strong>
90	(<code>default = <strong>off</strong></code>)<br/>
91	<i>q g -> ccbar[3P1(1)] q</i>.
92	Code 406.
93
94
95	<p/><code>flag  </code><strong> Charmonium:qg2QQbar[3P2(1)]q  </strong>
96	(<code>default = <strong>off</strong></code>)<br/>
97	<i>q g -> ccbar[3P2(1)] q</i>.
98	Code 407.
99
100
101	<p/><code>flag  </code><strong> Charmonium:qqbar2QQbar[3P0(1)]g  </strong>
102	(<code>default = <strong>off</strong></code>)<br/>
103	<i>q qbar -> ccbar[3P0(1)] g</i>.
104	Code 408.
105
106
107	<p/><code>flag  </code><strong> Charmonium:qqbar2QQbar[3P1(1)]g  </strong>
108	(<code>default = <strong>off</strong></code>)<br/>
109	<i>q qbar -> ccbar[3P1(1)] g</i>.
110	Code 409.
111
112
113	<p/><code>flag  </code><strong> Charmonium:qqbar2QQbar[3P2(1)]g  </strong>
114	(<code>default = <strong>off</strong></code>)<br/>
115	<i>q qbar -> ccbar[3P2(1)] g</i>.
116	Code 410.
117
118
119	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[3S1(8)]g  </strong>
120	(<code>default = <strong>off</strong></code>)<br/>
121	<i>g g -> ccbar[3S1(8)] g</i>.
122	Code 411.
123
124
125	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[1S0(8)]g  </strong>
126	(<code>default = <strong>off</strong></code>)<br/>
127	<i>g g -> ccbar[3S1(8)] g</i>.
128	Code 412.
129
130
131	<p/><code>flag  </code><strong> Charmonium:gg2QQbar[3PJ(8)]g  </strong>
132	(<code>default = <strong>off</strong></code>)<br/>
133	<i>g g -> ccbar[3S1(8)] g</i>.
134	Code 413.
135
136
137	<p/><code>flag  </code><strong> Charmonium:qg2QQbar[3S1(8)]q  </strong>
138	(<code>default = <strong>off</strong></code>)<br/>
139	<i>q g -> ccbar[3S1(8)] q</i>.
140	Code 414.
141
142
143	<p/><code>flag  </code><strong> Charmonium:qg2QQbar[1S0(8)]q  </strong>
144	(<code>default = <strong>off</strong></code>)<br/>
145	<i>q g -> ccbar[3S1(8)] q</i>.
146	Code 415.
147
148
149	<p/><code>flag  </code><strong> Charmonium:qg2QQbar[3PJ(8)]q  </strong>
150	(<code>default = <strong>off</strong></code>)<br/>
151	<i>q g -> ccbar[3S1(8)] q</i>.
152	Code 416.
153
154
155	<p/><code>flag  </code><strong> Charmonium:qqbar2QQbar[3S1(8)]g  </strong>
156	(<code>default = <strong>off</strong></code>)<br/>
157	<i>q qbar -> ccbar[3S1(8)] g</i>.
158	Code 417.
159
160
161	<p/><code>flag  </code><strong> Charmonium:qqbar2QQbar[1S0(8)]g  </strong>
162	(<code>default = <strong>off</strong></code>)<br/>
163	<i>q qbar -> ccbar[3S1(8)] g</i>.
164	Code 418.
165
166
167	<p/><code>flag  </code><strong> Charmonium:qqbar2QQbar[3PJ(8)]g  </strong>
168	(<code>default = <strong>off</strong></code>)<br/>
169	<i>q qbar -> ccbar[3S1(8)] g</i>.
170	Code 419.
171
172
173	<h3>Bottomonium</h3>
174
175	<p/><code>flag  </code><strong> Bottomonium:all  </strong>
176	(<code>default = <strong>off</strong></code>)<br/>
177	Common switch for the group of charmonium production.
178
179
180	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[3S1(1)]g  </strong>
181	(<code>default = <strong>off</strong></code>)<br/>
182	<i>g g -> bbbar[3S1(1)] g</i>.
183	Code 501.
184
185
186	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[3P0(1)]g  </strong>
187	(<code>default = <strong>off</strong></code>)<br/>
188	<i>g g -> bbbar[3P0(1)] g</i>.
189	Code 502.
190
191
192	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[3P1(1)]g  </strong>
193	(<code>default = <strong>off</strong></code>)<br/>
194	<i>g g -> bbbar[3P1(1)] g</i>.
195	Code 503.
196
197
198	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[3P2(1)]g  </strong>
199	(<code>default = <strong>off</strong></code>)<br/>
200	<i>g g -> bbbar[3P2(1)] g</i>.
201	Code 504.
202
203
204	<p/><code>flag  </code><strong> Bottomonium:qg2QQbar[3P0(1)]q  </strong>
205	(<code>default = <strong>off</strong></code>)<br/>
206	<i>q g -> bbbar[3P0(1)] q</i>.
207	Code 505.
208
209
210	<p/><code>flag  </code><strong> Bottomonium:qg2QQbar[3P1(1)]q  </strong>
211	(<code>default = <strong>off</strong></code>)<br/>
212	<i>q g -> bbbar[3P1(1)] q</i>.
213	Code 506.
214
215
216	<p/><code>flag  </code><strong> Bottomonium:qg2QQbar[3P2(1)]q  </strong>
217	(<code>default = <strong>off</strong></code>)<br/>
218	<i>q g -> bbbar[3P2(1)] q</i>.
219	Code 507.
220
221
222	<p/><code>flag  </code><strong> Bottomonium:qqbar2QQbar[3P0(1)]g  </strong>
223	(<code>default = <strong>off</strong></code>)<br/>
224	<i>q qbar -> bbbar[3P0(1)] g</i>.
225	Code 508.
226
227
228	<p/><code>flag  </code><strong> Bottomonium:qqbar2QQbar[3P1(1)]g  </strong>
229	(<code>default = <strong>off</strong></code>)<br/>
230	<i>q qbar -> bbbar[3P1(1)] g</i>.
231	Code 509.
232
233
234	<p/><code>flag  </code><strong> Bottomonium:qqbar2QQbar[3P2(1)]g  </strong>
235	(<code>default = <strong>off</strong></code>)<br/>
236	<i>q qbar -> bbbar[3P2(1)] g</i>.
237	Code 510.
238
239
240	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[3S1(8)]g  </strong>
241	(<code>default = <strong>off</strong></code>)<br/>
242	<i>g g -> bbbar[3S1(8)] g</i>.
243	Code 511.
244
245
246	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[1S0(8)]g  </strong>
247	(<code>default = <strong>off</strong></code>)<br/>
248	<i>g g -> bbbar[3S1(8)] g</i>.
249	Code 512.
250
251
252	<p/><code>flag  </code><strong> Bottomonium:gg2QQbar[3PJ(8)]g  </strong>
253	(<code>default = <strong>off</strong></code>)<br/>
254	<i>g g -> bbbar[3S1(8)] g</i>.
255	Code 513.
256
257
258	<p/><code>flag  </code><strong> Bottomonium:qg2QQbar[3S1(8)]q  </strong>
259	(<code>default = <strong>off</strong></code>)<br/>
260	<i>q g -> bbbar[3S1(8)] q</i>.
261	Code 514.
262
263
264	<p/><code>flag  </code><strong> Bottomonium:qg2QQbar[1S0(8)]q  </strong>
265	(<code>default = <strong>off</strong></code>)<br/>
266	<i>q g -> bbbar[3S1(8)] q</i>.
267	Code 515.
268
269
270	<p/><code>flag  </code><strong> Bottomonium:qg2QQbar[3PJ(8)]q  </strong>
271	(<code>default = <strong>off</strong></code>)<br/>
272	<i>q g -> bbbar[3S1(8)] q</i>.
273	Code 516.
274
275
276	<p/><code>flag  </code><strong> Bottomonium:qqbar2QQbar[3S1(8)]g  </strong>
277	(<code>default = <strong>off</strong></code>)<br/>
278	<i>q qbar -> bbbar[3S1(8)] g</i>.
279	Code 517.
280
281
282	<p/><code>flag  </code><strong> Bottomonium:qqbar2QQbar[1S0(8)]g  </strong>
283	(<code>default = <strong>off</strong></code>)<br/>
284	<i>q qbar -> bbbar[3S1(8)] g</i>.
285	Code 518.
286
287
288	<p/><code>flag  </code><strong> Bottomonium:qqbar2QQbar[3PJ(8)]g  </strong>
289	(<code>default = <strong>off</strong></code>)<br/>
290	<i>q qbar -> bbbar[3S1(8)] g</i>.
291	Code 519.
292
293
294	<h3>Onium matrix elements</h3>
295
296	The implementation of charmonium and bottomonium production, including
297	the colour-octet production mechanism, requires information on NRQCD
298	matrix elements for the various wavefunctions involved. Default values
299	for these are encoded in the following ten variables. They
300	are taken from [<a href="Bibliography.html" target="page">Nas00</a>]; see also [<a href="Bibliography.html" target="page">Bar06</a>].
301
302	<p/><code>parm  </code><strong> Charmonium:OJpsi3S11  </strong>
303	(<code>default = <strong>1.16</strong></code>; <code>minimum = 0.0</code>)<br/>
304	<i><O(J/psi)[3S1(1)]></i>.
305
306
307	<p/><code>parm  </code><strong> Charmonium:OJpsi3S18  </strong>
308	(<code>default = <strong>0.0119</strong></code>; <code>minimum = 0.0</code>)<br/>
309	<i><O(J/psi)[3S1(8)]></i>.
310
311
312	<p/><code>parm  </code><strong> Charmonium:OJpsi1S08  </strong>
313	(<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/>
314	<i><O(J/psi)[1S0(8)]></i>.
315
316
317	<p/><code>parm  </code><strong> Charmonium:OJpsi3P08  </strong>
318	(<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/>
319	<i><O(J/psi)[3P0(8)]>/m_c^2</i>.
320
321
322	<p/><code>parm  </code><strong> Charmonium:Ochic03P01  </strong>
323	(<code>default = <strong>0.05</strong></code>; <code>minimum = 0.0</code>)<br/>
324	<i><O(chi_c0)[3P0(8)]>/m_c^2</i>.
325
326
327	<p/><code>parm  </code><strong> Bottomonium:OUpsilon3S11  </strong>
328	(<code>default = <strong>9.28</strong></code>; <code>minimum = 0.0</code>)<br/>
329	<i><O(Upsilon)[3S1(1)]></i>.
330
331
332	<p/><code>parm  </code><strong> Bottomonium:OUpsilon3S18  </strong>
333	(<code>default = <strong>0.15</strong></code>; <code>minimum = 0.0</code>)<br/>
334	<i><O(Upsilon)[3S1(8)]></i>.
335
336
337	<p/><code>parm  </code><strong> Bottomonium:OUpsilon1S08  </strong>
338	(<code>default = <strong>0.02</strong></code>; <code>minimum = 0.0</code>)<br/>
339	<i><O(Upsilon)[1S0(8)]></i>.
340
341
342	<p/><code>parm  </code><strong> Bottomonium:OUpsilon3P08  </strong>
343	(<code>default = <strong>0.02</strong></code>; <code>minimum = 0.0</code>)<br/>
344	<i><O(Upsilon)[3P0(8)]>/m_b^2</i>.
345
346
347	<p/><code>parm  </code><strong> Bottomonium:Ochib03P01  </strong>
348	(<code>default = <strong>0.085</strong></code>; <code>minimum = 0.0</code>)<br/>
349	<i><O(chi_b0)[3P0(8)]>/m_b^2</i>.
350
351
352
353	</body>
354	</html>
355
356	<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
357

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