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 parton. Since the three sets are partly
conflicting, each is associated with its own group flag.
In addition, t-channel exchange of such a boson
between two fermions form a separate group.
Boson exchange
flag name="WeakBosonExchange:all" default="off"
Common switch for the group of gamma^*/Z^0
or W^+- exchange between two fermions.
flag name="WeakBosonExchange:ff2ff9gmZ" default="off"
Scattering f f' -> f f' via gamma^*/Z^0
t-channel exchange, with full interference
between the gamma^* and Z^0.
Code 141.
flag name="WeakBosonExchange:ff2ff9W" default="off"
Scattering f_1 f_2 -> f_3 f_4 via W^+-
t-channel exchange.
Code 142.
Single boson
flag name="WeakSingleBoson:all" default="off"
Common switch for the group of a single gamma^*/Z^0
or W^+- production.
flag name="WeakSingleBoson:ffbar2gmZ" 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.
Boson pair
flag name="WeakDoubleBoson:all" default="off"
Common switch for the group of pair production of gamma^*/Z^0
and W^+-.
flag name="WeakDoubleBoson:ffbar2ZW" default="off"
Scattering f fbar' -> Z^0 W^+-. Note that here the
gamma^* is not included.
Code 162.
flag name="WeakDoubleBoson:ffbar2WW" default="off"
Scattering f fbar -> W^+ W^-.
Code 163.
Boson and parton
flag name="WeakBosonAndParton:all" default="off"
Common switch for the group of production of a single electroweak
gauge boson, i.e. a gamma^*/Z^0 or a W^+-, in
association with a parton, i.e. a quark, gluon, photon or lepton.
These processes give first-order corrections to the ones in the
WeakSingleBoson
class, and boths sets cannot be used
simultaneously without unphysical doublecounting. The current class
should only be used to study the high-pT tail of the
gauge-boson production processes, while the ones in
WeakSingleBoson
should be used for inclusive production.
flag name="WeakBosonAndParton:qqbar2Wg" default="off"
Scattering f fbar -> W^+- g.
Code 176.
flag name="WeakBosonAndParton:qg2Wq" default="off"
Scattering f g -> f W^+-.
Code 177.
flag name="WeakBosonAndParton:ffbar2Wgm" default="off"
Scattering f fbar -> W^+- gamma.
Code 178.
Top
Different ways to produce top quarks, singly or (more frequently)
in pairs.
flag name="Top:all" default="off"
Common switch for the group of top production.
flag name="Top:gg2ttbar" default="off"
Scatterings g g -> t tbar.
Code 181.
flag name="Top:qqbar2ttbar" default="off"
Scatterings q qbar -> t tbar.
Code 182.
flag name="Top:qq2tq9W" default="off"
Scatterings q q' -> t q" by t-channel exchange of W boson.
Code 183.
Supersymmetric processes
Here is collected all processes involving supersymmetric particle
production, with the exception of the (extended) Higgs sector.
Since the number of separate but closely related processes is so big,
there are not switches for each separate process but only for a
reasonable set of subgroups.
Important note:
In order to simulate SUSY processes it is required to read in the
couplings and masses relevant for the scenario to be studied. This
is done with the help of the SUSY Les Houches Accord (SLHA). The
reading of a relevant SLHA file must be set up, as described
on this page.
flag name="SUSY:all" default="off"
Common switch for production of supersymmetric particles, i.e.
particles with R-parity -1.
flag name="SUSY:qqbar2chi0chi0" default="off"
Pair production of neutralinos by quark-antiquark annihilation. With
four neutralino species this gives ten separate processes, codes 1001
- 1010. The current implementation is in a development stage and does
not include contributions from diagrams with intermediate squarks,
hence the correct answer is only obtained in the limit of infinitely heavy
squarks. As yet, there are also no sparticle decays implemented -
all neutralinos decay to Gravitino+photon.