Partial Generation
Sometimes it may be convenient to omit certain aspects of the event
generation chain. This cannot be motivated in a full-blown production
run, but can often be convenient for own understanding and for
debug purposes. The flags on this page allow just that.
The event generation is subdivided into three levels: the process
level, the parton level and the hadron level, and flags are grouped
accordingly.
Process Level
The ProcessLevel
class administrates the initial step of
the event generation, wherein the basic process is selected. Currently
this is done either using some of the internal processes, or with
Les Houches Accord input, or from the Fortran PYTHIA 6.4 code,
the latter also using the Les Houches Accord standard.
Since there cannot be any event at all without an initial process,
there is no possibility to switch off this part of the story. It is
possible, however, to stop the generation immediately after the
basic process has been selected:
flag name="Pythia:afterProcessLevel" default="on"
If off then stop the generation after the hard process has been
generated, but before the parton-level and hadron-level steps.
The process
record is filled, but the event
one is not.
PartonLevel
The PartonLevel
class administrates the middle step of the
event generation, i.e. the evolution from an input (hard) process from
ProcessLevel
, containing a few partons only, to a complete
parton-level configuration to be handed on to HadronLevel
.
This step involves the application of initial- and final-state radiation,
multiple interactions and the structure of beam remnants.
Some parts of the event generation on this level may be switched off
individually:
flag name="PartonLevel:MI" default="on"
Master switch for multiple interactions; on/off = true/false.
Further options are found
here.
flag name="PartonLevel:ISR" default="on"
Master switch for initial-state radiation; on/off = true/false.
Further options are found
here.
flag name="PartonLevel:FSRinProcess" default="on"
Master switch for final-state radiation in association with the
hard process itself; on/off = true/false.
Further options are found
here.
flag name="PartonLevel:FSRinResonances" default="on"
Master switch for final-state radiation in any resonance decays
subsequent to the hard process itself; on/off = true/false.
Further options are found
here.
It is also possible to stop the generation immediately after this step:
flag name="Pythia:afterPartonLevel" default="on"
If off then stop the generation after the hard process and
parton-level activity has been generated, but before the
hadron-level steps.
HadronLevel
The HadronLevel
class administrates the final step of the
event generation, wherein the partonic configuration from
PartonLevel
is hadronized, including string fragmentation
and secondary decays.
Most of the code in this class deals with subdividing the partonic
content of the event into separate colour singlets, that can be
treated individually by the string fragmentation machinery. When a
junction and an antijunction are directly connected, it also breaks
the string between the two, so that the topology can be reduced back
to two separate one-junction systems, while still preserving the
expected particle flow in the junction-junction string region(s).
Some parts of the event generation on this level may be switched off
individually:
flag name="HadronLevel:Hadronize" default="on"
Master switch for hadronization; on/off = true/false.
Further options are found
here.
flag name="HadronLevel:Decay" default="on"
Master switch for decays; on/off = true/false.
Further options are found
here.