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<head>
<title>Onia Processes</title>
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<body>
<h2>Onia Processes</h2>
Production of J/psi or Upsilon, directly and via chi states and the
colour-octet mechanism.
In each process the square-bracketed expression specifies the state
in spectroscopic notation, <i>(2S+1) L J</i>, followed by
<i>(1)</i> for colour-singlet states and <i>(8)</i> for
colour-octet ditto.
<p/>
The original Fortran code for these processes has been contributed
by Stefan Wolf [unpublished]. For the C++ version only the unpolarized
expressions are retained, since the theoretical predictions of the
colour-octet model anyway do not agree with the experimental
observations. Furthermore, the polarization effects are modest,
so isotropic decay is not a bad starting point. Such an event sample
can afterwards be reweighted at will by the user, to test various
assumptions.
<p/>
The description of
<a href="TimelikeShowers.html" target="page">final-state radiation</a>
is in this case based on some further model assumptions.
<p/>
Most of the processes below are divergent in the limit <i>pT -> 0</i>,
and therefore a <i>pTmin</i> scale should be set. Comparisons with
data indicate that this divergence can be tamed the same way as for
the normal QCD <i>2 -> 2</i> cross sections [<a href="Bibliography.html" target="page">Bar06,Kra08</a>],
which makes sense, since they are all dominated by the same kind of
<i>t</i>-channel gluon exchange. It is therefore possible to use the
<a href="UserHooks.html" target="page">SuppressSmallPT</a> user hook to impose a
reweighting that cancels the low-<i>pT</i> divergence.
<p/>
An eikonalized description of these processes is included in the
multiparton-interactions framework. Here the low-<i>pT</i> dampening
is automatic, and additionally the framework is more consistent
(e.g. with respect to energy-momentum constraints and the
impact-parameter description) for events where the onium production
is not the hardest subprocess, as would often be the case in the
low-<i>pT</i> limit.
<h3>Charmonium</h3>
<p/><code>flag </code><strong> Charmonium:all </strong>
(<code>default = <strong>off</strong></code>)<br/>
Common switch for the group of charmonium production.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[3S1(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3S1(1)] g</i>.
Code 401.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[3P0(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3P0(1)] g</i>.
Code 402.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[3P1(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3P1(1)] g</i>.
Code 403.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[3P2(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3P2(1)] g</i>.
Code 404.
<p/><code>flag </code><strong> Charmonium:qg2QQbar[3P0(1)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> ccbar[3P0(1)] q</i>.
Code 405.
<p/><code>flag </code><strong> Charmonium:qg2QQbar[3P1(1)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> ccbar[3P1(1)] q</i>.
Code 406.
<p/><code>flag </code><strong> Charmonium:qg2QQbar[3P2(1)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> ccbar[3P2(1)] q</i>.
Code 407.
<p/><code>flag </code><strong> Charmonium:qqbar2QQbar[3P0(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> ccbar[3P0(1)] g</i>.
Code 408.
<p/><code>flag </code><strong> Charmonium:qqbar2QQbar[3P1(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> ccbar[3P1(1)] g</i>.
Code 409.
<p/><code>flag </code><strong> Charmonium:qqbar2QQbar[3P2(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> ccbar[3P2(1)] g</i>.
Code 410.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[3S1(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3S1(8)] g</i>.
Code 411.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[1S0(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3S1(8)] g</i>.
Code 412.
<p/><code>flag </code><strong> Charmonium:gg2QQbar[3PJ(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> ccbar[3S1(8)] g</i>.
Code 413.
<p/><code>flag </code><strong> Charmonium:qg2QQbar[3S1(8)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> ccbar[3S1(8)] q</i>.
Code 414.
<p/><code>flag </code><strong> Charmonium:qg2QQbar[1S0(8)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> ccbar[3S1(8)] q</i>.
Code 415.
<p/><code>flag </code><strong> Charmonium:qg2QQbar[3PJ(8)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> ccbar[3S1(8)] q</i>.
Code 416.
<p/><code>flag </code><strong> Charmonium:qqbar2QQbar[3S1(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> ccbar[3S1(8)] g</i>.
Code 417.
<p/><code>flag </code><strong> Charmonium:qqbar2QQbar[1S0(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> ccbar[3S1(8)] g</i>.
Code 418.
<p/><code>flag </code><strong> Charmonium:qqbar2QQbar[3PJ(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> ccbar[3S1(8)] g</i>.
Code 419.
<h3>Bottomonium</h3>
<p/><code>flag </code><strong> Bottomonium:all </strong>
(<code>default = <strong>off</strong></code>)<br/>
Common switch for the group of charmonium production.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[3S1(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3S1(1)] g</i>.
Code 501.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[3P0(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3P0(1)] g</i>.
Code 502.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[3P1(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3P1(1)] g</i>.
Code 503.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[3P2(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3P2(1)] g</i>.
Code 504.
<p/><code>flag </code><strong> Bottomonium:qg2QQbar[3P0(1)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> bbbar[3P0(1)] q</i>.
Code 505.
<p/><code>flag </code><strong> Bottomonium:qg2QQbar[3P1(1)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> bbbar[3P1(1)] q</i>.
Code 506.
<p/><code>flag </code><strong> Bottomonium:qg2QQbar[3P2(1)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> bbbar[3P2(1)] q</i>.
Code 507.
<p/><code>flag </code><strong> Bottomonium:qqbar2QQbar[3P0(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> bbbar[3P0(1)] g</i>.
Code 508.
<p/><code>flag </code><strong> Bottomonium:qqbar2QQbar[3P1(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> bbbar[3P1(1)] g</i>.
Code 509.
<p/><code>flag </code><strong> Bottomonium:qqbar2QQbar[3P2(1)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> bbbar[3P2(1)] g</i>.
Code 510.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[3S1(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3S1(8)] g</i>.
Code 511.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[1S0(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3S1(8)] g</i>.
Code 512.
<p/><code>flag </code><strong> Bottomonium:gg2QQbar[3PJ(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>g g -> bbbar[3S1(8)] g</i>.
Code 513.
<p/><code>flag </code><strong> Bottomonium:qg2QQbar[3S1(8)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> bbbar[3S1(8)] q</i>.
Code 514.
<p/><code>flag </code><strong> Bottomonium:qg2QQbar[1S0(8)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> bbbar[3S1(8)] q</i>.
Code 515.
<p/><code>flag </code><strong> Bottomonium:qg2QQbar[3PJ(8)]q </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q g -> bbbar[3S1(8)] q</i>.
Code 516.
<p/><code>flag </code><strong> Bottomonium:qqbar2QQbar[3S1(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> bbbar[3S1(8)] g</i>.
Code 517.
<p/><code>flag </code><strong> Bottomonium:qqbar2QQbar[1S0(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> bbbar[3S1(8)] g</i>.
Code 518.
<p/><code>flag </code><strong> Bottomonium:qqbar2QQbar[3PJ(8)]g </strong>
(<code>default = <strong>off</strong></code>)<br/>
<i>q qbar -> bbbar[3S1(8)] g</i>.
Code 519.
<h3>Onium matrix elements</h3>
The implementation of charmonium and bottomonium production, including
the colour-octet production mechanism, requires information on NRQCD
matrix elements for the various wavefunctions involved. Default values
for these are encoded in the following ten variables. They
are taken from [<a href="Bibliography.html" target="page">Nas00</a>]; see also [<a href="Bibliography.html" target="page">Bar06</a>].
<p/><code>parm </code><strong> Charmonium:OJpsi3S11 </strong>
(<code>default = <strong>1.16</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(J/psi)[3S1(1)]></i>.
<p/><code>parm </code><strong> Charmonium:OJpsi3S18 </strong>
(<code>default = <strong>0.0119</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(J/psi)[3S1(8)]></i>.
<p/><code>parm </code><strong> Charmonium:OJpsi1S08 </strong>
(<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(J/psi)[1S0(8)]></i>.
<p/><code>parm </code><strong> Charmonium:OJpsi3P08 </strong>
(<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(J/psi)[3P0(8)]>/m_c^2</i>.
<p/><code>parm </code><strong> Charmonium:Ochic03P01 </strong>
(<code>default = <strong>0.05</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(chi_c0)[3P0(8)]>/m_c^2</i>.
<p/><code>parm </code><strong> Bottomonium:OUpsilon3S11 </strong>
(<code>default = <strong>9.28</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(Upsilon)[3S1(1)]></i>.
<p/><code>parm </code><strong> Bottomonium:OUpsilon3S18 </strong>
(<code>default = <strong>0.15</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(Upsilon)[3S1(8)]></i>.
<p/><code>parm </code><strong> Bottomonium:OUpsilon1S08 </strong>
(<code>default = <strong>0.02</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(Upsilon)[1S0(8)]></i>.
<p/><code>parm </code><strong> Bottomonium:OUpsilon3P08 </strong>
(<code>default = <strong>0.02</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(Upsilon)[3P0(8)]>/m_b^2</i>.
<p/><code>parm </code><strong> Bottomonium:Ochib03P01 </strong>
(<code>default = <strong>0.085</strong></code>; <code>minimum = 0.0</code>)<br/>
<i><O(chi_b0)[3P0(8)]>/m_b^2</i>.
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