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<chapter name="Master Switches">
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<h2>Master Switches</h2>
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Sometimes it may be convenient to omit certain aspects of the event
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generation chain. This cannot be motivated in a full-blown production
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run, but can often be convenient for own understanding and for
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debug purposes. The flags on this page allow just that.
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The event generation is subdivided into three levels: the process
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level, the parton level and the hadron level, and flags are grouped
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<h3>Process Level</h3>
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The <code>ProcessLevel</code> class administrates the initial step of
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the event generation, wherein the basic process is selected. Currently
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this is done either using some of the internal processes, or with
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Les Houches Accord input.
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There could not be a complete event without an initial process, so
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it would not be a normal action to switch off this step. Furthermore,
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without a process set, it is also not possible to carry out the tasks
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on the parton level. It is still possible, however, to hadronize
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a parton-level configuration provided by some external program.
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<flag name="ProcessLevel:all" default="on">
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If off, do not attempt to carry out any generation at all on the
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process level. For the parton level only final-state radiation
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is possible, using the <code>Pythia::forceTimeShower(...)</code> method.
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Do allow parton configurations stored in the event record to hadronize
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and hadrons to decay, however, as set by the <code>HadronLevel</code>
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switches. Further details are found
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<aloc href="HadronLevelStandalone">here</aloc>.
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For <code>ProcessLevel:all = on</code> one part of the event generation
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on this level may be switched off individually:
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<flag name="ProcessLevel:resonanceDecays" default="on">
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Master switch to allow resonance decays; on/off = true/false.
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Normal hadrons and leptons do not count as resonances, so this is
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aimed specifically towards <ei>Z^0, W^+-, t, h^0</ei> and similar
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objects beyond the Standard Model. Do not use this option if you
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may produce coloured resonances and intend to allow hadronization,
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since currently the program would not know how to handle this.
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It is possible to stop the generation immediately after the basic
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process has been selected, see <code>PartonLevel:all</code> below.
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The <code>PartonLevel</code> class administrates the middle step of the
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event generation, i.e. the evolution from an input (hard) process from
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<code>ProcessLevel</code>, containing a few partons only, to a complete
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parton-level configuration to be handed on to <code>HadronLevel</code>.
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This step involves the application of initial- and final-state radiation,
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multiparton interactions and the structure of beam remnants.
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<flag name="PartonLevel:all" default="on">
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If off then stop the generation after the hard process has been
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generated, but before the parton-level and hadron-level steps.
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The <code>process</code> record is filled, but the <code>event</code>
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For <code>PartonLevel:all = on</code> some parts of the event generation
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on this level may be switched off individually:
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<flag name="PartonLevel:MPI" default="on">
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Master switch for multiparton interactions; on/off = true/false.
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Further options are found <aloc href="MultipartonInteractions">here</aloc>.
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<flag name="PartonLevel:ISR" default="on">
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Master switch for initial-state radiation; on/off = true/false.
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Further options are found <aloc href="SpacelikeShowers">here</aloc>.
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<flag name="PartonLevel:FSR" default="on">
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Master switch for initial-state radiation; on/off = true/false.
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Further options are found <aloc href="TimelikeShowers">here</aloc>.
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If you leave this switch on, the following two switches allow
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more detailed control to switch off only parts of the showers.
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<flag name="PartonLevel:FSRinProcess" default="on">
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Switch for final-state radiation in association with the hard process
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itself; on/off = true/false. In addition <code>PartonLevel:FSR</code>
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must be on for these emissions to occur.
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<flag name="PartonLevel:FSRinResonances" default="on">
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Master switch for final-state radiation in any resonance decays
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subsequent to the hard process itself; on/off = true/false. In addition
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<code>PartonLevel:FSR</code> must be on for these emissions to occur.
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Switching off all the above MPI/ISR/FSR switches is <b>not</b> equivalent
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to setting <code>PartonLevel:all = off</code>. In the former case a
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minimal skeleton of parton-level operations are carried out, such as
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tying together the scattered partons with the beam remnants into colour
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singlets, and storing this information in the <code>event</code> record.
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It is therefore possible to go on and hadronize the event, if desired.
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In the latter case <b>no</b> operations at all are carried out on the
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parton level, and therefore it is also not possible to go on to the
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<flag name="PartonLevel:Remnants" default="on">
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Master switch for addition of beam remnants; on/off = true/false.
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Only intended for very special applications, and cannot be used to
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generate complete events. Specifically, unlike the other switches above,
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the program will complain and possibly crash unlike you also set
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<code>HadronLevel:all = off</code> and <code>Check:event = off</code>.
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It is possible to stop the generation immediately after the parton level
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has been set up, see <code>HadronLevel:all</code> below.
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The <code>HadronLevel</code> class administrates the final step of the
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event generation, wherein the partonic configuration from
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<code>PartonLevel</code> is hadronized, including string fragmentation
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and secondary decays.
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Most of the code in this class itself deals with subdividing the partonic
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content of the event into separate colour singlets, that can be
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treated individually by the string fragmentation machinery. When a
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junction and an antijunction are directly connected, it also breaks
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the string between the two, so that the topology can be reduced back
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to two separate one-junction systems, while still preserving the
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expected particle flow in the junction-junction string region(s).
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<flag name="HadronLevel:all" default="on">
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If off then stop the generation after the hard process and
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parton-level activity has been generated, but before the
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For <code>HadronLevel:all = on</code> some parts of the event generation
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on this level may be switched off individually:
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<flag name="HadronLevel:Hadronize" default="on">
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Master switch for hadronization; on/off = true/false.
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Further options are found <aloc href="Fragmentation">here</aloc>.
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<flag name="HadronLevel:Decay" default="on">
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Master switch for decays; on/off = true/false.
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Further options are found <aloc href="ParticleDecays">here</aloc>.
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<flag name="HadronLevel:BoseEinstein" default="off">
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Master switch for the simulation of Bose-Einstein effects;
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on/off = true/false. Further options are found
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<aloc href="BoseEinsteinEffects">here</aloc>.
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<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
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