source: HiSusy/trunk/Pythia8/pythia8170/xmldoc/OniaProcesses.xml @ 1

<chapter name="Onia Processes">

<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, <ei>(2S+1) L J</ei>, followed by 
<ei>(1)</ei> for colour-singlet states and <ei>(8)</ei> 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by Stefan Wolf [unpublished].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  
<aloc href="TimelikeShowers">final-state radiation</aloc>
is in this case based on some further model assumptions.

<p/>
Most of the processes below are divergent in the limit <ei>pT -> 0</ei>, 
and therefore a <ei>pTmin</ei> scale should be set. Comparisons with 
data indicate that this divergence can be tamed the same way as for 
the normal QCD <ei>2 -> 2</ei> cross sections <ref>Bar06,Kra08</ref>, 
which makes sense, since they are all dominated by the same kind of 
<ei>t</ei>-channel gluon exchange. It is therefore possible to use the 
<aloc href="UserHooks">SuppressSmallPT</aloc> user hook to impose a 
reweighting that cancels the low-<ei>pT</ei> divergence.

<p/>
An eikonalized description of these processes is included in the 
multiparton-interactions framework. Here the low-<ei>pT</ei> 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-<ei>pT</ei> limit.

<h3>Charmonium</h3>

<flag name="Charmonium:all" default="off">
Common switch for the group of charmonium production.
</flag>

<flag name="Charmonium:gg2QQbar[3S1(1)]g" default="off">
<ei>g g -> ccbar[3S1(1)] g</ei>.
Code 401.
</flag>

<flag name="Charmonium:gg2QQbar[3P0(1)]g" default="off">
<ei>g g -> ccbar[3P0(1)] g</ei>.
Code 402.
</flag>

<flag name="Charmonium:gg2QQbar[3P1(1)]g" default="off">
<ei>g g -> ccbar[3P1(1)] g</ei>.
Code 403.
</flag>

<flag name="Charmonium:gg2QQbar[3P2(1)]g" default="off">
<ei>g g -> ccbar[3P2(1)] g</ei>.
Code 404.
</flag>

<flag name="Charmonium:qg2QQbar[3P0(1)]q" default="off">
<ei>q g -> ccbar[3P0(1)] q</ei>.
Code 405.
</flag>

<flag name="Charmonium:qg2QQbar[3P1(1)]q" default="off">
<ei>q g -> ccbar[3P1(1)] q</ei>.
Code 406.
</flag>

<flag name="Charmonium:qg2QQbar[3P2(1)]q" default="off">
<ei>q g -> ccbar[3P2(1)] q</ei>.
Code 407.
</flag>

<flag name="Charmonium:qqbar2QQbar[3P0(1)]g" default="off">
<ei>q qbar -> ccbar[3P0(1)] g</ei>.
Code 408.
</flag>

<flag name="Charmonium:qqbar2QQbar[3P1(1)]g" default="off">
<ei>q qbar -> ccbar[3P1(1)] g</ei>.
Code 409.
</flag>

<flag name="Charmonium:qqbar2QQbar[3P2(1)]g" default="off">
<ei>q qbar -> ccbar[3P2(1)] g</ei>.
Code 410.
</flag>

<flag name="Charmonium:gg2QQbar[3S1(8)]g" default="off">
<ei>g g -> ccbar[3S1(8)] g</ei>.
Code 411.
</flag>

<flag name="Charmonium:gg2QQbar[1S0(8)]g" default="off">
<ei>g g -> ccbar[3S1(8)] g</ei>.
Code 412.
</flag>

<flag name="Charmonium:gg2QQbar[3PJ(8)]g" default="off">
<ei>g g -> ccbar[3S1(8)] g</ei>.
Code 413.
</flag>

<flag name="Charmonium:qg2QQbar[3S1(8)]q" default="off">
<ei>q g -> ccbar[3S1(8)] q</ei>.
Code 414.
</flag>

<flag name="Charmonium:qg2QQbar[1S0(8)]q" default="off">
<ei>q g -> ccbar[3S1(8)] q</ei>.
Code 415.
</flag>

<flag name="Charmonium:qg2QQbar[3PJ(8)]q" default="off">
<ei>q g -> ccbar[3S1(8)] q</ei>.
Code 416.
</flag>

<flag name="Charmonium:qqbar2QQbar[3S1(8)]g" default="off">
<ei>q qbar -> ccbar[3S1(8)] g</ei>.
Code 417.
</flag>

<flag name="Charmonium:qqbar2QQbar[1S0(8)]g" default="off">
<ei>q qbar -> ccbar[3S1(8)] g</ei>.
Code 418.
</flag>

<flag name="Charmonium:qqbar2QQbar[3PJ(8)]g" default="off">
<ei>q qbar -> ccbar[3S1(8)] g</ei>.
Code 419.
</flag>

<h3>Bottomonium</h3>

<flag name="Bottomonium:all" default="off">
Common switch for the group of charmonium production.
</flag>

<flag name="Bottomonium:gg2QQbar[3S1(1)]g" default="off">
<ei>g g -> bbbar[3S1(1)] g</ei>.
Code 501.
</flag>

<flag name="Bottomonium:gg2QQbar[3P0(1)]g" default="off">
<ei>g g -> bbbar[3P0(1)] g</ei>.
Code 502.
</flag>

<flag name="Bottomonium:gg2QQbar[3P1(1)]g" default="off">
<ei>g g -> bbbar[3P1(1)] g</ei>.
Code 503.
</flag>

<flag name="Bottomonium:gg2QQbar[3P2(1)]g" default="off">
<ei>g g -> bbbar[3P2(1)] g</ei>.
Code 504.
</flag>

<flag name="Bottomonium:qg2QQbar[3P0(1)]q" default="off">
<ei>q g -> bbbar[3P0(1)] q</ei>.
Code 505.
</flag>

<flag name="Bottomonium:qg2QQbar[3P1(1)]q" default="off">
<ei>q g -> bbbar[3P1(1)] q</ei>.
Code 506.
</flag>

<flag name="Bottomonium:qg2QQbar[3P2(1)]q" default="off">
<ei>q g -> bbbar[3P2(1)] q</ei>.
Code 507.
</flag>

<flag name="Bottomonium:qqbar2QQbar[3P0(1)]g" default="off">
<ei>q qbar -> bbbar[3P0(1)] g</ei>.
Code 508.
</flag>

<flag name="Bottomonium:qqbar2QQbar[3P1(1)]g" default="off">
<ei>q qbar -> bbbar[3P1(1)] g</ei>.
Code 509.
</flag>

<flag name="Bottomonium:qqbar2QQbar[3P2(1)]g" default="off">
<ei>q qbar -> bbbar[3P2(1)] g</ei>.
Code 510.
</flag>

<flag name="Bottomonium:gg2QQbar[3S1(8)]g" default="off">
<ei>g g -> bbbar[3S1(8)] g</ei>.
Code 511.
</flag>

<flag name="Bottomonium:gg2QQbar[1S0(8)]g" default="off">
<ei>g g -> bbbar[3S1(8)] g</ei>.
Code 512.
</flag>

<flag name="Bottomonium:gg2QQbar[3PJ(8)]g" default="off">
<ei>g g -> bbbar[3S1(8)] g</ei>.
Code 513.
</flag>

<flag name="Bottomonium:qg2QQbar[3S1(8)]q" default="off">
<ei>q g -> bbbar[3S1(8)] q</ei>.
Code 514.
</flag>

<flag name="Bottomonium:qg2QQbar[1S0(8)]q" default="off">
<ei>q g -> bbbar[3S1(8)] q</ei>.
Code 515.
</flag>

<flag name="Bottomonium:qg2QQbar[3PJ(8)]q" default="off">
<ei>q g -> bbbar[3S1(8)] q</ei>.
Code 516.
</flag>

<flag name="Bottomonium:qqbar2QQbar[3S1(8)]g" default="off">
<ei>q qbar -> bbbar[3S1(8)] g</ei>.
Code 517.
</flag>

<flag name="Bottomonium:qqbar2QQbar[1S0(8)]g" default="off">
<ei>q qbar -> bbbar[3S1(8)] g</ei>.
Code 518.
</flag>

<flag name="Bottomonium:qqbar2QQbar[3PJ(8)]g" default="off">
<ei>q qbar -> bbbar[3S1(8)] g</ei>.
Code 519.
</flag>

<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 <ref>Nas00</ref>; see also <ref>Bar06</ref>. 

<parm name="Charmonium:OJpsi3S11" default="1.16" min="0.0">
<ei>&lt;O(J/psi)[3S1(1)]&gt;</ei>.
</parm>

<parm name="Charmonium:OJpsi3S18" default="0.0119" min="0.0">
<ei>&lt;O(J/psi)[3S1(8)]&gt;</ei>.
</parm>

<parm name="Charmonium:OJpsi1S08" default="0.01" min="0.0">
<ei>&lt;O(J/psi)[1S0(8)]&gt;</ei>.
</parm>

<parm name="Charmonium:OJpsi3P08" default="0.01" min="0.0">
<ei>&lt;O(J/psi)[3P0(8)]&gt;/m_c^2</ei>.
</parm>

<parm name="Charmonium:Ochic03P01" default="0.05" min="0.0">
<ei>&lt;O(chi_c0)[3P0(8)]&gt;/m_c^2</ei>.
</parm>

<parm name="Bottomonium:OUpsilon3S11" default="9.28" min="0.0">
<ei>&lt;O(Upsilon)[3S1(1)]&gt;</ei>.
</parm>

<parm name="Bottomonium:OUpsilon3S18" default="0.15" min="0.0">
<ei>&lt;O(Upsilon)[3S1(8)]&gt;</ei>.
</parm>

<parm name="Bottomonium:OUpsilon1S08" default="0.02" min="0.0">
<ei>&lt;O(Upsilon)[1S0(8)]&gt;</ei>.
</parm>

<parm name="Bottomonium:OUpsilon3P08" default="0.02" min="0.0">
<ei>&lt;O(Upsilon)[3P0(8)]&gt;/m_b^2</ei>.
</parm>

<parm name="Bottomonium:Ochib03P01" default="0.085" min="0.0">
<ei>&lt;O(chi_b0)[3P0(8)]&gt;/m_b^2</ei>.
</parm>


</chapter>

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