1 <chapter name="Onia Processes">
3 <h2>Onia Processes</h2>
5 Production of J/psi or Upsilon, directly and via chi states and the
6 colour-octet mechanism.
7 In each process the square-bracketed expression specifies the state
8 in spectroscopic notation, <ei>(2S+1) L J</ei>, followed by
9 <ei>(1)</ei> for colour-singlet states and <ei>(8)</ei> for
13 The original Fortran code for these processes has been contributed
14 by Stefan Wolf [unpublished]. For the C++ version only the unpolarized
15 expressions are retained, since the theoretical predictions of the
16 colour-octet model anyway do not agree with the experimental
17 observations. Furthermore, the polarization effects are modest,
18 so isotropic decay is not a bad starting point. Such an event sample
19 can afterwards be reweighted at will by the user, to test various
24 <aloc href="TimelikeShowers">final-state radiation</aloc>
25 is in this case based on some further model assumptions.
28 Most of the processes below are divergent in the limit
29 <ei>pT -> 0</ei>, and therefore a <ei>pTmin</ei> scale should
30 be set. Comparisons with data indicate that this divergence
31 can be tamed the same way as for the normal QCD <ei>2 -> 2</ei> cross
32 sections, which makes sense, since they are all dominated by the
33 same kind of <ei>t</ei>-channel gluon exchange. It is therefore
34 possible to use the <aloc href="UserHooks">SuppressSmallPT</aloc>
35 user hook to impose a reweighting that cancels the low-<ei>pT</ei>
39 An eikonalized description of these processes is included in the
40 multiple-interactions framework. Here the low-<ei>pT</ei> dampening
41 is automatic, and additionally the framework is more consistent
42 (e.g. with respect to energy-momentum constraints and the
43 impact-parameter description) for events where the onium production
44 is not the hardest subprocess, as would often be the case in the
45 low-<ei>pT</ei> limit.
49 <flag name="Charmonium:all" default="off">
50 Common switch for the group of charmonium production.
53 <flag name="Charmonium:gg2QQbar[3S1(1)]g" default="off">
54 <ei>g g -> ccbar[3S1(1)] g</ei>.
58 <flag name="Charmonium:gg2QQbar[3P0(1)]g" default="off">
59 <ei>g g -> ccbar[3P0(1)] g</ei>.
63 <flag name="Charmonium:gg2QQbar[3P1(1)]g" default="off">
64 <ei>g g -> ccbar[3P1(1)] g</ei>.
68 <flag name="Charmonium:gg2QQbar[3P2(1)]g" default="off">
69 <ei>g g -> ccbar[3P2(1)] g</ei>.
73 <flag name="Charmonium:qg2QQbar[3P0(1)]q" default="off">
74 <ei>q g -> ccbar[3P0(1)] q</ei>.
78 <flag name="Charmonium:qg2QQbar[3P1(1)]q" default="off">
79 <ei>q g -> ccbar[3P1(1)] q</ei>.
83 <flag name="Charmonium:qg2QQbar[3P2(1)]q" default="off">
84 <ei>q g -> ccbar[3P2(1)] q</ei>.
88 <flag name="Charmonium:qqbar2QQbar[3P0(1)]g" default="off">
89 <ei>q qbar -> ccbar[3P0(1)] g</ei>.
93 <flag name="Charmonium:qqbar2QQbar[3P1(1)]g" default="off">
94 <ei>q qbar -> ccbar[3P1(1)] g</ei>.
98 <flag name="Charmonium:qqbar2QQbar[3P2(1)]g" default="off">
99 <ei>q qbar -> ccbar[3P2(1)] g</ei>.
103 <flag name="Charmonium:gg2QQbar[3S1(8)]g" default="off">
104 <ei>g g -> ccbar[3S1(8)] g</ei>.
108 <flag name="Charmonium:gg2QQbar[1S0(8)]g" default="off">
109 <ei>g g -> ccbar[3S1(8)] g</ei>.
113 <flag name="Charmonium:gg2QQbar[3PJ(8)]g" default="off">
114 <ei>g g -> ccbar[3S1(8)] g</ei>.
118 <flag name="Charmonium:qg2QQbar[3S1(8)]q" default="off">
119 <ei>q g -> ccbar[3S1(8)] q</ei>.
123 <flag name="Charmonium:qg2QQbar[1S0(8)]q" default="off">
124 <ei>q g -> ccbar[3S1(8)] q</ei>.
128 <flag name="Charmonium:qg2QQbar[3PJ(8)]q" default="off">
129 <ei>q g -> ccbar[3S1(8)] q</ei>.
133 <flag name="Charmonium:qqbar2QQbar[3S1(8)]g" default="off">
134 <ei>q qbar -> ccbar[3S1(8)] g</ei>.
138 <flag name="Charmonium:qqbar2QQbar[1S0(8)]g" default="off">
139 <ei>q qbar -> ccbar[3S1(8)] g</ei>.
143 <flag name="Charmonium:qqbar2QQbar[3PJ(8)]g" default="off">
144 <ei>q qbar -> ccbar[3S1(8)] g</ei>.
150 <flag name="Bottomonium:all" default="off">
151 Common switch for the group of charmonium production.
154 <flag name="Bottomonium:gg2QQbar[3S1(1)]g" default="off">
155 <ei>g g -> bbbar[3S1(1)] g</ei>.
159 <flag name="Bottomonium:gg2QQbar[3P0(1)]g" default="off">
160 <ei>g g -> bbbar[3P0(1)] g</ei>.
164 <flag name="Bottomonium:gg2QQbar[3P1(1)]g" default="off">
165 <ei>g g -> bbbar[3P1(1)] g</ei>.
169 <flag name="Bottomonium:gg2QQbar[3P2(1)]g" default="off">
170 <ei>g g -> bbbar[3P2(1)] g</ei>.
174 <flag name="Bottomonium:qg2QQbar[3P0(1)]q" default="off">
175 <ei>q g -> bbbar[3P0(1)] q</ei>.
179 <flag name="Bottomonium:qg2QQbar[3P1(1)]q" default="off">
180 <ei>q g -> bbbar[3P1(1)] q</ei>.
184 <flag name="Bottomonium:qg2QQbar[3P2(1)]q" default="off">
185 <ei>q g -> bbbar[3P2(1)] q</ei>.
189 <flag name="Bottomonium:qqbar2QQbar[3P0(1)]g" default="off">
190 <ei>q qbar -> bbbar[3P0(1)] g</ei>.
194 <flag name="Bottomonium:qqbar2QQbar[3P1(1)]g" default="off">
195 <ei>q qbar -> bbbar[3P1(1)] g</ei>.
199 <flag name="Bottomonium:qqbar2QQbar[3P2(1)]g" default="off">
200 <ei>q qbar -> bbbar[3P2(1)] g</ei>.
204 <flag name="Bottomonium:gg2QQbar[3S1(8)]g" default="off">
205 <ei>g g -> bbbar[3S1(8)] g</ei>.
209 <flag name="Bottomonium:gg2QQbar[1S0(8)]g" default="off">
210 <ei>g g -> bbbar[3S1(8)] g</ei>.
214 <flag name="Bottomonium:gg2QQbar[3PJ(8)]g" default="off">
215 <ei>g g -> bbbar[3S1(8)] g</ei>.
219 <flag name="Bottomonium:qg2QQbar[3S1(8)]q" default="off">
220 <ei>q g -> bbbar[3S1(8)] q</ei>.
224 <flag name="Bottomonium:qg2QQbar[1S0(8)]q" default="off">
225 <ei>q g -> bbbar[3S1(8)] q</ei>.
229 <flag name="Bottomonium:qg2QQbar[3PJ(8)]q" default="off">
230 <ei>q g -> bbbar[3S1(8)] q</ei>.
234 <flag name="Bottomonium:qqbar2QQbar[3S1(8)]g" default="off">
235 <ei>q qbar -> bbbar[3S1(8)] g</ei>.
239 <flag name="Bottomonium:qqbar2QQbar[1S0(8)]g" default="off">
240 <ei>q qbar -> bbbar[3S1(8)] g</ei>.
244 <flag name="Bottomonium:qqbar2QQbar[3PJ(8)]g" default="off">
245 <ei>q qbar -> bbbar[3S1(8)] g</ei>.
249 <h3>Onium matrix elements</h3>
251 The implementation of charmonium and bottomonium production, including
252 the colour-octet production mechanism, requires information on NRQCD
253 matrix elements for the various wavefunctions involved. Default values
254 for these are encoded in the following ten variables. They
255 are taken from <ref>Nas00</ref>; see also <ref>Bar06</ref>.
257 <parm name="Charmonium:OJpsi3S11" default="1.16" min="0.0">
258 <ei><O(J/psi)[3S1(1)]></ei>.
261 <parm name="Charmonium:OJpsi3S18" default="0.0119" min="0.0">
262 <ei><O(J/psi)[3S1(8)]></ei>.
265 <parm name="Charmonium:OJpsi1S08" default="0.01" min="0.0">
266 <ei><O(J/psi)[1S0(8)]></ei>.
269 <parm name="Charmonium:OJpsi3P08" default="0.01" min="0.0">
270 <ei><O(J/psi)[3P0(8)]>/m_c^2</ei>.
273 <parm name="Charmonium:Ochic03P01" default="0.05" min="0.0">
274 <ei><O(chi_c0)[3P0(8)]>/m_c^2</ei>.
277 <parm name="Bottomonium:OUpsilon3S11" default="9.28" min="0.0">
278 <ei><O(Upsilon)[3S1(1)]></ei>.
281 <parm name="Bottomonium:OUpsilon3S18" default="0.15" min="0.0">
282 <ei><O(Upsilon)[3S1(8)]></ei>.
285 <parm name="Bottomonium:OUpsilon1S08" default="0.02" min="0.0">
286 <ei><O(Upsilon)[1S0(8)]></ei>.
289 <parm name="Bottomonium:OUpsilon3P08" default="0.48" min="0.0">
290 <ei><O(Upsilon)[3P0(8)]>/m_b^2</ei>.
293 <parm name="Bottomonium:Ochib03P01" default="0.09" min="0.0">
294 <ei><O(chi_b0)[3P0(8)]>/m_b^2</ei>.
300 <!-- Copyright (C) 2010 Torbjorn Sjostrand -->