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-<h2>QCD Processes</h2>
-
-This section is subdivided into soft and hard QCD processes, with
-open charm and bottom production set aside as a special part of the
-latter, and three-jet topologies as a special subset. Kindly note
-that there is a considerable amount of overlap between the soft and
-hard process classes, so that you are likely to doublecount
-if you include both in a run.
-
-<h3>Soft QCD processes</h3>
-
-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.
-
-<p/>
-We here use the "minimum bias" expression as a shorthand for
-inelastic, nondiffractive 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 in PYTHIA classified as diffractive,
-especially (high-mass) double diffractive.
-
-<p/>
-Some options to modify these cross sections are found on the
-<a href="TotalCrossSections.html" target="page">Total Cross Sections</a> page.
-
-<p/><code>flag </code><strong> SoftQCD:all </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Common switch for the group of all soft QCD processes,
-as listed separately in the following.
-
-
-<p/><code>flag </code><strong> SoftQCD:minBias </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Minimum-bias events, based on an <a href="MultipartonInteractions.html" target="page">
-eikonalized description</a> of all the hard QCD processes, so
-includes them in combinationation with low-<i>pT</i> events.
-Code 101.<br/>
-Since the current description is handled by the multiparton-interactions
-machinery as part of the parton-level processing, no hard process at
-all is defined at the process-level part of the event generation.
-Fortunately, in this case a special
-<code><a href="EventInformation.html" target="page">codeSub()</a></code>
-method provides information on the first, i.e. hardest, subprocess
-selected by the multiparton-interactions machinery.
-
-
-
-<p/><code>flag </code><strong> SoftQCD:elastic </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Elastic scattering <i>A B -> A B</i>.
-Code 102. It is possible to include <a href="TotalCrossSections.html" target="page">
-Coulomb corrections</a>, but by default this is off.
-
-
-<p/><code>flag </code><strong> SoftQCD:singleDiffractive </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Single diffractive scattering <i>A B -> X B</i> and
-<i>A B -> A X</i>. See page on <a href="Diffraction.html" target="page">
-Diffraction</a> for details. Codes 103 and 104.
-
-
-<p/><code>flag </code><strong> SoftQCD:doubleDiffractive </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Double diffractive scattering <i>A B -> X_1 X_2</i>.
-See page on <a href="Diffraction.html" target="page">Diffraction</a>
-for details. Code 105.
-
-
-<p/><code>flag </code><strong> SoftQCD:centralDiffractive </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Central diffractive scattering <i>A B -> A X B</i>
-(a.k.a. double-Pomeron exchange, DPE). See pages on
-<a href="TotalCrossSections.html" target="page">Total Cross Sections</a>
-and on <a href="Diffraction.html" target="page">Diffraction</a> for details.
-In particular note the <code>SigmaTotal:zeroAXB</code> flag,
-which is off in most tunes, and that therefore would need to
-be reset to on after the selection of a tune (even the default one).
-Code 106.
-
-
-<h3>Hard QCD processes</h3>
-
-This group contains the processes for QCD jet production above
-some minimum <i>pT</i> threshold. The <i>pT_min</i> cut cannot be put
-too low, or else unreasonably large jet cross sections will be obtained.
-This is because the divergent perturbative QCD cross section is used
-in this process group, without any regularization modifications.
-An eikonalized description, intended to be valid at all <i>pT</i>,
-is instead included as part of the multiparton-interactions framework,
-specifically in <code>SoftQCD:minBias</code> above.
-<br/><b>Warning 1</b>: you <b>must</b> remember to set the
-<code>PhaseSpace:pTHatMin</code> value if you use any of these
-processes; there is no sensible default.
-<br/><b>Warning 2</b>: you <b>must not</b> mix processes from the
-<code>SoftQCD</code> and <code>HardQCD</code> process groups, since
-this is likely to lead to doublecounting.
-
-<p/><code>flag </code><strong> HardQCD:all </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Common switch for the group of all hard QCD processes,
-as listed separately in the following.
-
-
-<p/><code>flag </code><strong> HardQCD:gg2gg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>g g -> g g</i>.
-Code 111.
-
-
-<p/><code>flag </code><strong> HardQCD:gg2qqbar </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>g g -> q qbar</i>, where <i>q</i> by default
-is a light quark (<i>u, d, s</i>) (see below).
-Code 112.
-
-
-<p/><code>flag </code><strong> HardQCD:qg2qg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q g -> q g</i> and <i>qbar g -> qbar g</i>.
-Code 113.
-
-
-<p/><code>flag </code><strong> HardQCD:qq2qq </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q q' -> q q'</i>, <i>q qbar' -> q qbar'</i>,
-<i>qbar qbar' -> qbar qbar'</i>, where <i>q'</i> and <i>q</i>
-may agree, but the outgoing flavours equals the incoming ones
-Code 114.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2gg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> g g</i>.
-Code 115.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2qqbarNew </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> q' qbar'</i>, where <i>q'</i>
-by default is a light quark (<i>u, d, s</i>) (see below).
-Code 116.
-
-
-<p/><code>mode </code><strong> HardQCD:nQuarkNew </strong>
- (<code>default = <strong>3</strong></code>; <code>minimum = 0</code>; <code>maximum = 5</code>)<br/>
-Number of allowed outgoing new quark flavours in the above
-<i>g g -> q qbar</i> and <i>q qbar -> q' qbar'</i> processes,
-where quarks are treated as massless in the matrix-element expressions
-(but correctly in the phase space). It is thus assumed that <i>c cbar</i>
-and <i>b bbar</i> are added separately with masses taken into account,
-using the processes below. A change to 4 would also include <i>c cbar</i>
-in the massless approximation, etc. In order to avoid doublecounting
-the processes below should then not be used simultaneously.
-
-
-<h3>Hard QCD processes: heavy-flavour subset</h3>
-
-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 <i>pT -> 0</i> limit, but at
-high energies one may still question the validity of the expressions
-at low <i>pT</i> values, like for the other hard-QCD processes.
-Also as above, an eikonalized description, intended to be valid at all
-<i>pT</i>, is included as part of the multiparton-interactions framework.
-<br/>Note that the processes below only represent the "tip of the iceberg"
-of charm and bottom production at high energies, where flavour excitation
-and shower branchings provide major additional sources. All these sources
-come together in the descriptions offered by <code>SoftQCD:minBias</code>
-and <code>HardQCD:all</code>.
-
-<p/><code>flag </code><strong> HardQCD:gg2ccbar </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>g g -> c cbar</i>.
-Code 121.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2ccbar </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> c cbar</i>.
-Code 122.
-
-
-<p/><code>flag </code><strong> HardQCD:gg2bbbar </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>g g -> b bbar</i>.
-Code 123.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2bbbar </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> b bbar</i>.
-Code 124.
-
-
-<h3>Hard QCD three-parton processes</h3>
-
-Three-parton final states are generated by showers off two-parton
-processes. Topologies then cannot be specified beforehand, beyond
-what is provided by the two-parton hard process. For some checks
-it may be convenient to have access to the dedicated three-parton
-final states, which is what this set of processes allows.
-Cross sections have been taken from [<a href="Bibliography.html" target="page">Ber81</a>].
-<br/>Note that the processes in this section are <it>not</it>
-affected by the <code>HardQCD:all</code> switch. In fact, it would
-be doublecounting to include both the <code>HardQCD:all</code> and
-the <code>HardQCD:3parton</code> processes in a run or study.
-<br/><b>Warning:</b> this section is still incomplete, e.g. the
-selection of colour flow is very simple, and so it should only
-be used with caution.
-
-<p/><code>flag </code><strong> HardQCD:3parton </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Common switch for the group of all hard QCD processes with three
-partons in the final state, as listed separately in the following.
-
-
-<p/><code>flag </code><strong> HardQCD:gg2ggg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>g g -> g g g</i>.
-Code 131.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2ggg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> g g g</i>.
-Code 132.
-
-
-<p/><code>flag </code><strong> HardQCD:qg2qgg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q g -> q g g</i> and <i>qbar g -> qbar g g</i>.
-Code 133.
-
-
-<p/><code>flag </code><strong> HardQCD:qq2qqgDiff </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q q' -> q q' g</i>, <i>q qbar' -> q qbar' g</i>,
-and <i>qbar qbar' -> qbar qbar' g</i>.
-Code 134.
-
-
-<p/><code>flag </code><strong> HardQCD:qq2qqgSame </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q q -> q q g</i> and
-<i>qbar qbar -> qbar qbar g</i>
-(<i>q qbar -> q qbar g</i> scatterings are considered separately
-below, see <code>HardQCD:qqbar2qqbargSame</code>).
-Code 135.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2qqbargDiff </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> q' qbar' g</i>, where <i>q'</i>
-by default is a light quark (<i>u, d, s</i>)
-(see <code>HardQCD:nQuarkNew</code> above).
-Code 136.
-
-
-<p/><code>flag </code><strong> HardQCD:qqbar2qqbargSame </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q qbar -> q qbar g</i>.
-Code 137.
-
-
-<p/><code>flag </code><strong> HardQCD:gg2qqbarg </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>g g -> q qbar g</i>, where <i>q</i> by
-default is a light quark (<i>u, d, s</i>)
-(see <code>HardQCD:nQuarkNew</code> above).
-Code 138.
-
-
-<p/><code>flag </code><strong> HardQCD:qg2qqqbarDiff </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q g -> q q' qbar'</i> and
-<i>qbar g -> qbar qbar' q'</i>, where <i>q'</i>
-by default is a light quark (<i>u, d, s</i>)
-(see <code>HardQCD:nQuarkNew</code> above).
-Code 139.
-
-
-<p/><code>flag </code><strong> HardQCD:qg2qqqbarSame </strong>
- (<code>default = <strong>off</strong></code>)<br/>
-Scatterings <i>q g -> q q qbar</i> and
-<i>qbar g -> qbar qbar q</i>.
-Code 140.
-
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