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.