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<title>Hadron Scattering</title>
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<h2>Hadron Scattering</h2>
A simple hadron scattering model. It is intended to take into account
that the overlap of multiple strings at low transverse dimensions
is likely to lead to some collective effects, not unlike those
observed in heavy-ion collisions, even if not quite as pronounced.
Specifically, it is assumed that the hadrons produced can scatter
against each other on the way out, before the fragmenting system
has had time to expand enough that the hadrons get free. Thereby
heavier particles are shifted to higher transverse momenta, at the
expense of the lighter ones.
<br/><b>Warning:</b> This is still at an experimental level,
and should not be used unless you know what you are doing.
<p/><code>flag </code><strong> HadronScatter:scatter </strong>
(<code>default = <strong>off</strong></code>)<br/>
Master flag for hadron scattering.
<p/><code>flag </code><strong> HadronScatter:afterDecay </strong>
(<code>default = <strong>off</strong></code>)<br/>
Perform hadron scattering before or after first round of decays,
involving very short-lived particles like the <i>rho</i>.
The default is to perform scattering directly after the
string fragmentation, before any decays.
<p/><code>flag </code><strong> HadronScatter:allowDecayProd </strong>
(<code>default = <strong>off</strong></code>)<br/>
Allow two hadrons with same parent hadron to scatter.
<p/><code>flag </code><strong> HadronScatter:scatterRepeat </strong>
(<code>default = <strong>off</strong></code>)<br/>
Allow hadrons which have already scattered to scatter again.
Even if switched on, the same pair can not scatter off each
other twice.
<h3>Hadron selection</h3>
<p/><code>mode </code><strong> HadronScatter:hadronSelect </strong>
(<code>default = <strong>0</strong></code>; <code>minimum = 0</code>; <code>maximum = 0</code>)<br/>
Probability that a hadron is soft enough to scatter.
(A high-<i>pT</i> hadron presumably being part of a jet,
and thus produced away from the high-particle-density region
at small transverse dimensions.)
<br/><code>option </code><strong> 0</strong> :
<i>P = N exp(-pT^2 / 2 / sigma^2) /
( (1 - k) exp(-pT^2 / 2 / sigma^2) + k pT0^p / (pT0^2 + pT^2)^(p/2), </i>
with <i>sigma = 2 StringPT:sigma</i> and <i>pT0</i> the same as that
used in <i>MultipartonInteractions</i>.
<p/><code>parm </code><strong> HadronScatter:N </strong>
(<code>default = <strong>1.0</strong></code>; <code>minimum = 0.01</code>; <code>maximum = 1.0</code>)<br/>
<i>N</i> parameter as above.
<p/><code>parm </code><strong> HadronScatter:k </strong>
(<code>default = <strong>1.0</strong></code>; <code>minimum = 0.01</code>; <code>maximum = 1.0</code>)<br/>
<i>k</i> parameter as above.
<p/><code>parm </code><strong> HadronScatter:p </strong>
(<code>default = <strong>6</strong></code>; <code>minimum = 2</code>; <code>maximum = 30</code>)<br/>
<i>p</i> parameter as above.
<h3>Scattering probability</h3>
<p/><code>mode </code><strong> HadronScatter:scatterProb </strong>
(<code>default = <strong>0</strong></code>; <code>minimum = 0</code>; <code>maximum = 2</code>)<br/>
Probability for a pair of hadrons to scatter.
<br/><code>option </code><strong> 0</strong> : All hadrons scatter with probability
<i>j max(0, 1 - dR^2 / rMax^2)</i>. Angular distribution
is picked flat in <i>cos(theta).</i>
<br/><code>option </code><strong> 1</strong> : As option 0, above, but only <i>pi-pi</i>,
<i>pi-K</i> and <i>pi-p</i> scatterings are considered.
<br/><code>option </code><strong> 2</strong> : Only <i>pi-pi</i>, <i>pi-K</i> and
<i>pi-p</i> scatterings are considered, with probability
given by <i>(1 - exp(-j sigEl)) max(0, 1 - dR^2 / rMax^2)</i>.
The elastic cross sections and angular distributions are taken
from the partial-wave distributions.
<p/><code>parm </code><strong> HadronScatter:j </strong>
(<code>default = <strong>0.5</strong></code>; <code>minimum = 0.0</code>; <code>maximum = 10.0</code>)<br/>
<i>j</i> parameter as above.
<p/><code>parm </code><strong> HadronScatter:rMax </strong>
(<code>default = <strong>0.5</strong></code>; <code>minimum = 0.1</code>; <code>maximum = 2.0</code>)<br/>
<i>rMax</i> parameter as above.
<p/><code>flag </code><strong> HadronScatter:tile </strong>
(<code>default = <strong>off</strong></code>)<br/>
Use tiling in <i>(eta, phi)</i> to reduce number of pairwise tests.
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