1 <chapter name="Process Selection">
3 <h2>Process Selection</h2>
5 There is no way PYTHIA could contain all processes of interest,
6 neither in terms of potential physics topics nor in terms of
7 high-multiplicity final states. What exists is a reasonably
8 complete setup of all <ei>2 -> 1</ei> and <ei>2 -> 2</ei>
9 processes within the Standard Model, plus some examples of
10 processes beyond that, again for low multiplicities. Combined with
11 the PYTHIA parton showers, this should be enough to get a flying
12 start in the study of many physics scenarios.
13 Other processes could be fed in via the
14 <aloc href="LesHouchesAccord">Les Houches Accord</aloc>
15 or be implemented as a
16 <aloc href="SemiInternalProcesses">Semi-Internal Process</aloc>.
17 In the latter case the existing processes would act as obvious
21 By default all processes are switched off. You should switch on
22 those you want to simulate. This may be done at two (occasionally
23 three) levels, either for each individual process or for a group of
24 processes. That is, a process is going to be generated either if its
25 own flag or its group flag is on. There is no built-in construction
26 to switch on a group and then switch off a few of its members.
29 Each process is assigned an integer code. This code is not used in
30 the internal administration of events (so having the same code for
31 two completely different processes would not be a problem), but only
32 intended to allow a simpler user separation of different processes.
33 Also the process name is available, as a string.
36 To ease navigation, the list of processes has been split into several
37 separate pages, by main topic. The classification is hopefully
38 intuitive, but by no means unambiguous. For instance, essentially
39 all processes involve QCD, so the "QCD processes" are the ones that
40 only involve QCD. (And also that is not completely true, once one
41 includes all that may happen in multiple interactions.) On these
42 separate pages also appear the settings that are completely local
43 to that particular process class, but not the ones that have a
46 <h3><aloc href="QCDProcesses">QCD Processes</aloc></h3>
48 QCD processes fall in two main categories: soft and hard. The soft ones
49 contain elastic, diffractive and "minimum-bias" events, together
50 covering the total cross section. Hard processea are the normal
51 <ei>2 -> 2</ei> ones, including charm and bottom production.
52 <br/>Reserved code range: 101 - 199.
54 <h3><aloc href="ElectroweakProcesses">Electroweak Processes</aloc></h3>
56 Prompt-photon, <ei>gamma^*/Z^0</ei> and <ei>W^+-</ei> production,
57 plus a few processes with <ei>t</ei>-channel boson exchange.
58 <br/>Reserved code range: 201 - 299.
60 <h3><aloc href="OniaProcesses">Onia Processes</aloc></h3>
62 Colour singlet and octet production of charmonium and bottomonium.
63 <br/>Reserved code range: 401 - 499 for charmonium and
64 501 - 599 for bottomonium.
66 <h3><aloc href="TopProcesses">Top Processes</aloc></h3>
68 Top production, singly or doubly.
69 <br/>Reserved code range: 601 - 699.
71 <h3><aloc href="FourthGenerationProcesses">Fourth-Generation
74 Production of hypothetical fourth-generation fermions.
75 <br/>Reserved code range: 801 - 899.
77 <h3><aloc href="HiggsProcesses">Higgs Processes</aloc></h3>
79 Higgs production, within or beyond the Standard Model.
80 See section on Left-Right-Symmetry processes for doubly charged Higgses.
81 <br/>Reserved code range: 901 - 999 for a Standard Model Higgs
82 and 1001 - 1199 for MSSM Higgses.
84 <h3><aloc href="SUSYProcesses">SUSY Processes</aloc></h3>
86 Production of supersymmetric particles, currently barely begun.
87 <br/>Reserved code range: 1001 - 2999. (Whereof 1001 - 1199
88 for Higgses; see above.)
90 <h3><aloc href="NewGaugeBosonProcesses">New-Gauge-Boson
93 Production of new gauge bosons such as <ei>Z'</ei> and <ei>W'</ei>.
94 <br/>Reserved code range: 3001 - 3099.
96 <h3><aloc href="LeftRightSymmetryProcesses">Left-Right-Symmetry
99 Production of righthanded <ei>Z_R</ei> and <ei>W_R</ei> bosons and of
100 doubly charged Higgses.
101 <br/>Reserved code range: 3101 - 3199.
103 <h3><aloc href="LeptoquarkProcesses">Leptoquark Processes</aloc></h3>
105 Production of a simple scalar leptoquark state.
106 <br/>Reserved code range: 3201 - 3299.
108 <h3><aloc href="CompositenessProcesses">Compositeness Processes</aloc></h3>
110 Production of excited fermion states and contact-interaction modification
111 to interactions between fermions (excluding technicolor; see below).
112 <br/>Reserved code range: 4001 - 4099.
114 <h3>Technicolor Processes</h3>
116 Production of technicolor particles and modifications of QCD processes
117 by technicolor interactions. Does not exist yet.
118 <br/>Reserved code range: 4101 - 4199.
120 <h3><aloc href="HiddenValleyProcesses">Hidden Valley Processes</aloc></h3>
121 A scenario for the pair prodiction of new particles with couplings
122 under a new gauge group, with invisible gauge bosons. Radiation of
123 these gauge bosons is included in the standard final-state parton
125 <br/>Reserved code range: 4901 - 4999.
127 <h3><aloc href="ExtraDimensionalProcesses">Extra-Dimensional
128 Processes</aloc></h3>
130 A vast area, here represented by the production of a Randall-Sundrum
131 excited graviton state and a Kaluza-Klein gluon, a Kaluza-Klein tower
132 of <ei>gamma/Z^0</ei> excitations in one TeV^- sized extra dimension,
133 several Large Extra Dimension processes, and a few related Unparticle
135 <br/>Reserved code range: 5001 - 5099.
139 <!-- Copyright (C) 2010 Torbjorn Sjostrand -->