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1<html>
2<head>
3<title>Hadron Scattering</title>
4<link rel="stylesheet" type="text/css" href="pythia.css"/>
5<link rel="shortcut icon" href="pythia32.gif"/>
6</head>
7<body>
8
9<h2>Hadron Scattering</h2>
10
11A simple hadron scattering model. It is intended to take into account
12that the overlap of multiple strings at low transverse dimensions
13is likely to lead to some collective effects, not unlike those
14observed in heavy-ion collisions, even if not quite as pronounced. 
15Specifically, it is assumed that the hadrons produced can scatter
16against each other on the way out, before the fragmenting system
17has had time to expand enough that the hadrons get free. Thereby
18heavier particles are shifted to higher transverse momenta, at the
19expense of the lighter ones.
20
21<br/><b>Warning:</b> This is still at an experimental level,
22and should not be used unless you know what you are doing.
23
24<p/><code>flag&nbsp; </code><strong> HadronScatter:scatter &nbsp;</strong> 
25 (<code>default = <strong>off</strong></code>)<br/>
26Master flag for hadron scattering.
27 
28
29<p/><code>flag&nbsp; </code><strong> HadronScatter:afterDecay &nbsp;</strong> 
30 (<code>default = <strong>off</strong></code>)<br/>
31Perform hadron scattering before or after first round of decays,
32involving very short-lived particles like the <i>rho</i>.
33The default is to perform scattering directly after the
34string fragmentation, before any decays.
35 
36
37<p/><code>flag&nbsp; </code><strong> HadronScatter:allowDecayProd &nbsp;</strong> 
38 (<code>default = <strong>off</strong></code>)<br/>
39Allow two hadrons with same parent hadron to scatter.
40 
41
42<p/><code>flag&nbsp; </code><strong> HadronScatter:scatterRepeat &nbsp;</strong> 
43 (<code>default = <strong>off</strong></code>)<br/>
44Allow hadrons which have already scattered to scatter again.
45Even if switched on, the same pair can not scatter off each
46other twice.
47 
48
49<h3>Hadron selection</h3>
50
51<p/><code>mode&nbsp; </code><strong> HadronScatter:hadronSelect &nbsp;</strong> 
52 (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>; <code>maximum = 0</code>)<br/>
53Probability that a hadron is soft enough to scatter.
54(A high-<i>pT</i> hadron presumably being part of a jet,
55and thus produced away from the high-particle-density region
56at small transverse dimensions.)
57<br/><code>option </code><strong> 0</strong> :
58<i>P = N exp(-pT^2 / 2 / sigma^2) /
59  ( (1 - k) exp(-pT^2 / 2 / sigma^2) + k pT0^p / (pT0^2 + pT^2)^(p/2), </i>
60with <i>sigma = 2 StringPT:sigma</i> and <i>pT0</i> the same as that
61used in <i>MultipartonInteractions</i>.
62 
63 
64
65<p/><code>parm&nbsp; </code><strong> HadronScatter:N &nbsp;</strong> 
66 (<code>default = <strong>1.0</strong></code>; <code>minimum = 0.01</code>; <code>maximum = 1.0</code>)<br/>
67<i>N</i> parameter as above.
68 
69<p/><code>parm&nbsp; </code><strong> HadronScatter:k &nbsp;</strong> 
70 (<code>default = <strong>1.0</strong></code>; <code>minimum = 0.01</code>; <code>maximum = 1.0</code>)<br/>
71<i>k</i> parameter as above.
72 
73<p/><code>parm&nbsp; </code><strong> HadronScatter:p &nbsp;</strong> 
74 (<code>default = <strong>6</strong></code>; <code>minimum = 2</code>; <code>maximum = 30</code>)<br/>
75<i>p</i> parameter as above.
76 
77
78<h3>Scattering probability</h3>
79
80<p/><code>mode&nbsp; </code><strong> HadronScatter:scatterProb &nbsp;</strong> 
81 (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>; <code>maximum = 2</code>)<br/>
82Probability for a pair of hadrons to scatter.
83<br/><code>option </code><strong> 0</strong> : All hadrons scatter with probability
84<i>j max(0, 1 - dR^2 / rMax^2)</i>. Angular distribution
85is picked flat in <i>cos(theta).</i> 
86<br/><code>option </code><strong> 1</strong> : As option 0, above, but only <i>pi-pi</i>,
87<i>pi-K</i> and <i>pi-p</i> scatterings are considered.
88 
89<br/><code>option </code><strong> 2</strong> : Only <i>pi-pi</i>, <i>pi-K</i> and
90<i>pi-p</i> scatterings are considered, with probability
91given by <i>(1 - exp(-j sigEl)) max(0, 1 - dR^2 / rMax^2)</i>.
92The elastic cross sections and angular distributions are taken
93from the partial-wave distributions.
94 
95 
96
97<p/><code>parm&nbsp; </code><strong> HadronScatter:j &nbsp;</strong> 
98 (<code>default = <strong>0.5</strong></code>; <code>minimum = 0.0</code>; <code>maximum = 10.0</code>)<br/>
99<i>j</i> parameter as above.
100 
101<p/><code>parm&nbsp; </code><strong> HadronScatter:rMax &nbsp;</strong> 
102 (<code>default = <strong>0.5</strong></code>; <code>minimum = 0.1</code>; <code>maximum = 2.0</code>)<br/>
103<i>rMax</i> parameter as above.
104 
105
106<p/><code>flag&nbsp; </code><strong> HadronScatter:tile &nbsp;</strong> 
107 (<code>default = <strong>off</strong></code>)<br/>
108Use tiling in <i>(eta, phi)</i> to reduce number of pairwise tests.
109 
110
111</body>
112</html>
113
114<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
115
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