Onia Processes
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, (2S+1) L J, followed by
(1) for colour-singlet states and (8) for
colour-octet ditto.
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by Stefan Wolf [unpublished].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.
The description of
final-state radiation
is in this case based on some further model assumptions.
Most of the processes below are divergent in the limit
pT -> 0, and therefore a pTmin scale should
be set. Comparisons with data indicate that this divergence
can be tamed the same way as for the normal QCD 2 -> 2 cross
sections, which makes sense, since they are all dominated by the
same kind of t-channel gluon exchange. It is therefore
possible to use the SuppressSmallPT
user hook to impose a reweighting that cancels the low-pT
divergence.
An eikonalized description of these processes is included in the
multiple-interactions framework. Here the low-pT 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-pT limit.
Charmonium
flag Charmonium:all
(default = off)
Common switch for the group of charmonium production.
flag Charmonium:gg2QQbar[3S1(1)]g
(default = off)
g g -> ccbar[3S1(1)] g.
Code 401.
flag Charmonium:gg2QQbar[3P0(1)]g
(default = off)
g g -> ccbar[3P0(1)] g.
Code 402.
flag Charmonium:gg2QQbar[3P1(1)]g
(default = off)
g g -> ccbar[3P1(1)] g.
Code 403.
flag Charmonium:gg2QQbar[3P2(1)]g
(default = off)
g g -> ccbar[3P2(1)] g.
Code 404.
flag Charmonium:qg2QQbar[3P0(1)]q
(default = off)
q g -> ccbar[3P0(1)] q.
Code 405.
flag Charmonium:qg2QQbar[3P1(1)]q
(default = off)
q g -> ccbar[3P1(1)] q.
Code 406.
flag Charmonium:qg2QQbar[3P2(1)]q
(default = off)
q g -> ccbar[3P2(1)] q.
Code 407.
flag Charmonium:qqbar2QQbar[3P0(1)]g
(default = off)
q qbar -> ccbar[3P0(1)] g.
Code 408.
flag Charmonium:qqbar2QQbar[3P1(1)]g
(default = off)
q qbar -> ccbar[3P1(1)] g.
Code 409.
flag Charmonium:qqbar2QQbar[3P2(1)]g
(default = off)
q qbar -> ccbar[3P2(1)] g.
Code 410.
flag Charmonium:gg2QQbar[3S1(8)]g
(default = off)
g g -> ccbar[3S1(8)] g.
Code 411.
flag Charmonium:gg2QQbar[1S0(8)]g
(default = off)
g g -> ccbar[3S1(8)] g.
Code 412.
flag Charmonium:gg2QQbar[3PJ(8)]g
(default = off)
g g -> ccbar[3S1(8)] g.
Code 413.
flag Charmonium:qg2QQbar[3S1(8)]q
(default = off)
q g -> ccbar[3S1(8)] q.
Code 414.
flag Charmonium:qg2QQbar[1S0(8)]q
(default = off)
q g -> ccbar[3S1(8)] q.
Code 415.
flag Charmonium:qg2QQbar[3PJ(8)]q
(default = off)
q g -> ccbar[3S1(8)] q.
Code 416.
flag Charmonium:qqbar2QQbar[3S1(8)]g
(default = off)
q qbar -> ccbar[3S1(8)] g.
Code 417.
flag Charmonium:qqbar2QQbar[1S0(8)]g
(default = off)
q qbar -> ccbar[3S1(8)] g.
Code 418.
flag Charmonium:qqbar2QQbar[3PJ(8)]g
(default = off)
q qbar -> ccbar[3S1(8)] g.
Code 419.
Bottomonium
flag Bottomonium:all
(default = off)
Common switch for the group of charmonium production.
flag Bottomonium:gg2QQbar[3S1(1)]g
(default = off)
g g -> bbbar[3S1(1)] g.
Code 501.
flag Bottomonium:gg2QQbar[3P0(1)]g
(default = off)
g g -> bbbar[3P0(1)] g.
Code 502.
flag Bottomonium:gg2QQbar[3P1(1)]g
(default = off)
g g -> bbbar[3P1(1)] g.
Code 503.
flag Bottomonium:gg2QQbar[3P2(1)]g
(default = off)
g g -> bbbar[3P2(1)] g.
Code 504.
flag Bottomonium:qg2QQbar[3P0(1)]q
(default = off)
q g -> bbbar[3P0(1)] q.
Code 505.
flag Bottomonium:qg2QQbar[3P1(1)]q
(default = off)
q g -> bbbar[3P1(1)] q.
Code 506.
flag Bottomonium:qg2QQbar[3P2(1)]q
(default = off)
q g -> bbbar[3P2(1)] q.
Code 507.
flag Bottomonium:qqbar2QQbar[3P0(1)]g
(default = off)
q qbar -> bbbar[3P0(1)] g.
Code 508.
flag Bottomonium:qqbar2QQbar[3P1(1)]g
(default = off)
q qbar -> bbbar[3P1(1)] g.
Code 509.
flag Bottomonium:qqbar2QQbar[3P2(1)]g
(default = off)
q qbar -> bbbar[3P2(1)] g.
Code 510.
flag Bottomonium:gg2QQbar[3S1(8)]g
(default = off)
g g -> bbbar[3S1(8)] g.
Code 511.
flag Bottomonium:gg2QQbar[1S0(8)]g
(default = off)
g g -> bbbar[3S1(8)] g.
Code 512.
flag Bottomonium:gg2QQbar[3PJ(8)]g
(default = off)
g g -> bbbar[3S1(8)] g.
Code 513.
flag Bottomonium:qg2QQbar[3S1(8)]q
(default = off)
q g -> bbbar[3S1(8)] q.
Code 514.
flag Bottomonium:qg2QQbar[1S0(8)]q
(default = off)
q g -> bbbar[3S1(8)] q.
Code 515.
flag Bottomonium:qg2QQbar[3PJ(8)]q
(default = off)
q g -> bbbar[3S1(8)] q.
Code 516.
flag Bottomonium:qqbar2QQbar[3S1(8)]g
(default = off)
q qbar -> bbbar[3S1(8)] g.
Code 517.
flag Bottomonium:qqbar2QQbar[1S0(8)]g
(default = off)
q qbar -> bbbar[3S1(8)] g.
Code 518.
flag Bottomonium:qqbar2QQbar[3PJ(8)]g
(default = off)
q qbar -> bbbar[3S1(8)] g.
Code 519.
Onium matrix elements
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 [Nas00]; see also [Bar06].
parm Charmonium:OJpsi3S11
(default = 1.16; minimum = 0.0)
<O(J/psi)[3S1(1)]>.
parm Charmonium:OJpsi3S18
(default = 0.0119; minimum = 0.0)
<O(J/psi)[3S1(8)]>.
parm Charmonium:OJpsi1S08
(default = 0.01; minimum = 0.0)
<O(J/psi)[1S0(8)]>.
parm Charmonium:OJpsi3P08
(default = 0.01; minimum = 0.0)
<O(J/psi)[3P0(8)]>/m_c^2.
parm Charmonium:Ochic03P01
(default = 0.05; minimum = 0.0)
<O(chi_c0)[3P0(8)]>/m_c^2.
parm Bottomonium:OUpsilon3S11
(default = 9.28; minimum = 0.0)
<O(Upsilon)[3S1(1)]>.
parm Bottomonium:OUpsilon3S18
(default = 0.15; minimum = 0.0)
<O(Upsilon)[3S1(8)]>.
parm Bottomonium:OUpsilon1S08
(default = 0.02; minimum = 0.0)
<O(Upsilon)[1S0(8)]>.
parm Bottomonium:OUpsilon3P08
(default = 0.48; minimum = 0.0)
<O(Upsilon)[3P0(8)]>/m_b^2.
parm Bottomonium:Ochib03P01
(default = 0.09; minimum = 0.0)
<O(chi_b0)[3P0(8)]>/m_b^2.