Process Selection
By default all processes are switched off. You should switch on
those you want to simulate. This may be done at two levels, either
for each individual process or for a group of processes. That is,
a process is going to be generated either if its own flag or its
group flag is on. There is no built-in construction to switch on
a group and then switch off a few of its members.
Each process is assigned an integer code. This code is not used in
the internal administration of events (so having the same code for
two completely different processes would not be a problem), but only
intended to allow a simpler user separation of different processes.
Also the process name is available, as a string.
Soft QCD processes
As a rule, the processes in this class should not be mixed with
the simulation of other processes. All by themselves, they are
intended to represent the total cross section of hadron collisions,
with the exception of the "rare processes" that one wishes to study
separately. In particular, jet physics at all scales occurs as part
of the minimum-bias description.
flag name="SoftQCD:all" default="off"
Common switch for the group of all soft QCD processes,
as listed separately in the following.
flag name="SoftQCD:minBias" default="off"
Minimum-bias events, based on an eikonalized description of all the
hard QCD processes, so includes them in combinationation with
low-pT events. Strictly speaking, "minimum bias" represents
an experimental procedure of accepting "everything", with some
non-universal cuts to exclude elastic and diffractive topologies.
In practice, the experimental mimimum-bias sample may then contain
some contamination of what is here classified as diffractive,
especially (high-mass) double diffractive. Note that, since the
current description is handled by the multiple-interactions machinery
as part of the parton-level processing, no hard subprocess at all
is defined at the process-level part of the event generation.
Code 101.
flag name="SoftQCD:elastic" default="off"
Elastic scattering A B -> A B.
Code 102.
flag name="SoftQCD:singleDiffractive" default="off"
Single diffractive scattering A B -> X B and
A B -> A X.
Codes 103 and 104.
flag name="SoftQCD:doubleDiffractive" default="off"
Double diffractive scattering A B -> X_1 X_2.
Code 105.
Hard QCD processes
This group contains the processes for QCD jet production above
some minimum pT threshold, as opposed to the minimum-bias
process above, where all pT scales can be probed.
The pT_min cut cannot be put too low, or else unreasonably
large jet cross sections will be obtained.
flag name="HardQCD:all" default="off"
Common switch for the group of all hard QCD processes,
as listed separately in the following.
flag name="HardQCD:gg2gg" default="off"
Scatterings g g -> g g.
Code 111.
flag name="HardQCD:gg2qqbar" default="off"
Scatterings g g -> q qbar.
Code 112.
flag name="HardQCD:qg2qg" default="off"
Scatterings q g -> q g and qbar g -> qbar g.
Code 113.
flag name="HardQCD:qq2qq" default="off"
Scatterings q q' -> q q', q qbar' -> q qbar',
qbar qbar' -> qbar qbar', where q' and q
may agree, but the outgoing flavours equals the incoming ones
Codes 114, 115 and 116.
flag name="HardQCD:qqbar2qqbarNew" default="off"
Scatterings q qbar -> q' qbar', where the outgoing flavours
are different from the incoming ones.
Code 117.
flag name="HardQCD:qqbar2gg" default="off"
Scatterings q qbar -> g g.
Code 118.
Hard QCD processes: heavy-flavour subset
These processes form a natural part of the above class, but can
also be generated separately. Formally the heavy-quark mass makes
these matrix elements finite in the pT -> 0 limit, but at
high energies one may still question the validity of the expressions
at low pT values, like for the other hard-QCD processes.
flag name="HardQCD:gg2ccbar" default="off"
Scatterings g g -> c cbar.
Code 121.
flag name="HardQCD:qqbar2ccbar" default="off"
Scatterings q qbar -> c cbar.
Code 122.
flag name="HardQCD:gg2bbbar" default="off"
Scatterings g g -> b bbar.
Code 123.
flag name="HardQCD:qqbar2bbbar" default="off"
Scatterings q qbar -> b bbar.
Code 124.
Prompt photon processes
This group collects the processes where one or two photons are
produced by the hard process. Additional sources of photons
include parton showers and hadron decays. Again a pT cut
is required to stay away from the unphysical low-pT region.
flag name="PromptPhoton:all" default="off"
Common switch for the group of all prompt photon processes,
as listed separately in the following.
flag name="PromptPhoton:qg2qgamma" default="off"
Scattering q g -> q gamma.
Code 131.
flag name="PromptPhoton:qqbar2ggamma" default="off"
Scattering q qbar -> g gamma.
Code 132.
flag name="PromptPhoton:gg2ggamma" default="off"
Scattering g g -> g gamma.
Note: This is a box graph. The full quark-mass
dependence in the loop leads to very complicated expressions.
The current implementation is based on assuming five massless
quarks, and thus is questionable at small (pT < m_b)
or large (pT > m_t) transverse momenta.
Code 133.
flag name="PromptPhoton:qqbar2gammagamma" default="off"
Scattering q qbar -> gamma gamma.
Code 134.
flag name="PromptPhoton:gg2gammagamma" default="off"
Scattering g g -> gamma gamma.
Note: This is a box graph. The full quark-mass
dependence in the loop leads to very complicated expressions.
The current implementation is based on assuming five massless
quarks, and thus is questionable at small (pT < m_b)
or large (pT > m_t) transverse momenta.
Code 135.
Weak boson processes
Under this heading we group processes involving the production
of a single electroweak gauge boson, i.e. a gamma^*/Z^0
or a W^+-, or a pair of them, or one of them in
combination with a jet or a photon. Since the three sets are
partly conflicting, each is associated with its own group flag.
flag name="WeakSingleBoson:all" default="off"
Common switch for the group of a single gamma^*/Z^0
or W^+- production.
flag name="WeakSingleBoson:ffbar2Z" default="off"
Scattering f fbar' -> gamma^*/Z^0, with full interference
between the gamma^* and Z^0.
Code 151.
flag name="WeakSingleBoson:ffbar2W" default="off"
Scattering f fbar' -> W^+-.
Code 152.