/usr/share/doc/pythia8-doc/html/BeamParameters.html is in pythia8-doc-html 8.1.86-1.2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 | <html>
<head>
<title>Beam Parameters</title>
<link rel="stylesheet" type="text/css" href="pythia.css"/>
<link rel="shortcut icon" href="pythia32.gif"/>
</head>
<body>
<h2>Beam Parameters</h2>
The settings on this page relate to the beam identities and energies,
to a beam momentum spread and to a beam interaction spot.
As always, momenta and energies are to be given in units of GeV,
and of space and time in mm.
<h3>Incoming beams</h3>
There are two ways to set the identities and energies of the two incoming
beam particles. One is to use the <code>init()</code> method with no
arguments. Then the settings variables below will be read and used. The
alternative is to call <code><a href="ProgramFlow.html" target="page">init(...)</a></code>
with arguments that provide this information. Then you need not use the
variables below (although it would still be possible). Note that, if nothing
is done, you will default to LHC at 14 TeV.
<p/>
Currently the beam particles must be either a hadron pair or a lepton
pair. In the former category <i>p p</i> and <i>pbar p</i>
combinations dominate, but it is also possible to combine with
<i>pi^+</i>, <i>pi^-</i> and <i>pi^0</i>. In the latter
<i>e^+ e^-</i> and <i>mu^+ mu^-</i> would be the most useful
combinations, but also others should work if combined with an
appropriate hard process.
<p/><code>mode </code><strong> Beams:idA </strong>
(<code>default = <strong>2212</strong></code>)<br/>
The PDG <code>id</code> code for the first incoming particle.
Allowed codes include
<br/><i>2212 = p</i>, <i>-2212 = pbar</i>,
<br/><i>2112 = n</i>, <i>-2112 = nbar</i>,
<br/><i>211 = pi^+</i>, <i>-211 = pi^-</i>, <i>111 = pi^0</i>,
<br/><i>990 = Pomeron</i> (used in diffractive machinery;
here mainly for debug purposes),
<br/><i>11 = e^-</i>, <i>-11 = e^+</i>,
<br/><i>13 = mu^-</i>, <i>-13 = mu^+</i>,
<br/>and a few more leptons/neutrinos in a few combinations.
<p/><code>mode </code><strong> Beams:idB </strong>
(<code>default = <strong>2212</strong></code>)<br/>
The PDG <code>id</code> code for the second incoming particle.
<p/><code>mode </code><strong> Beams:frameType </strong>
(<code>default = <strong>1</strong></code>; <code>minimum = 1</code>; <code>maximum = 5</code>)<br/>
Choice of frame for the two colliding particles. For options
1 - 3 the beam identities are specified above, while they are
obtained by the Les Houches information for options 4 and 5.
<br/><code>option </code><strong> 1</strong> : the beams are colliding in their CM frame,
and therefore only the CM energy needs to be provided, see
<code>Beams:eCM</code> below.
<br/><code>option </code><strong> 2</strong> : the beams are back-to-back, but with different energies,
see <code>Beams:eA</code> and <code>Beams:eB</code> below.
This option could also be used for fixed-target configurations.
<br/><code>option </code><strong> 3</strong> : the beams are not back-to-back, and therefore the
three-momentum of each incoming particle needs to be specified, see
<code>Beams:pxA</code> through <code>Beams:pzB</code> below.
<br/><code>option </code><strong> 4</strong> : the beam and event information is stored in a
<a href="LesHouchesAccord.html" target="page">Les Houches Event File</a>,
see <code>Beams:LHEF</code> below.
<br/><code>option </code><strong> 5</strong> : the beam and event information is obtained by a
pointer to an <code><a href="LesHouchesAccord.html" target="page">LHAup</a></code>
class instance.
<p/><code>parm </code><strong> Beams:eCM </strong>
(<code>default = <strong>14000.</strong></code>; <code>minimum = 10.</code>)<br/>
Collision CM energy, to be set if <code>Beams:frameType</code> = 1.
<p/><code>parm </code><strong> Beams:eA </strong>
(<code>default = <strong>7000.</strong></code>; <code>minimum = 0.</code>)<br/>
The energy of the first incoming particle, moving in the
<i>+z </i>direction, to be set if <code>Beams:frameType</code> = 2.
If the particle energy is smaller than its mass
it is assumed to be at rest.
<p/><code>parm </code><strong> Beams:eB </strong>
(<code>default = <strong>7000.</strong></code>; <code>minimum = 0.</code>)<br/>
The energy of the second incoming particle, moving in the
<i>-z</i> direction, to be set if <code>Beams:frameType</code> = 2.
If the particle energy is smaller than its mass
it is assumed to be at rest.
<p/><code>parm </code><strong> Beams:pxA </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>p_x</i> component of the first incoming particle,
to be set if <code>Beams:frameType</code> = 3.
<p/><code>parm </code><strong> Beams:pyA </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>p_y</i> component of the first incoming particle,
to be set if <code>Beams:frameType</code> = 3.
<p/><code>parm </code><strong> Beams:pzA </strong>
(<code>default = <strong>7000.</strong></code>)<br/>
The <i>p_z</i> component of the first incoming particle,
to be set if <code>Beams:frameType</code> = 3.
<p/><code>parm </code><strong> Beams:pxB </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>p_x</i> component of the second incoming particle,
to be set if <code>Beams:frameType</code> = 3.
<p/><code>parm </code><strong> Beams:pyB </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>p_y</i> component of the second incoming particle,
to be set if <code>Beams:frameType</code> = 3.
<p/><code>parm </code><strong> Beams:pzB </strong>
(<code>default = <strong>-7000.</strong></code>)<br/>
The <i>p_z</i> component of the second incoming particle,
to be set if <code>Beams:frameType</code> = 3.
<p/><code>word </code><strong> Beams:LHEF </strong>
(<code>default = <strong>void</strong></code>)<br/>
The name of a Les Houches Event File,
to be set if <code>Beams:frameType</code> = 4.
<p/><code>word </code><strong> Beams:LHEFheader </strong>
(<code>default = <strong>void</strong></code>)<br/>
As some information in a Les Houches Event File init block is only known
at the end of generation, some programs choose to output this as a
separate file. If <code>Beams:LHEFheader</code> is given, information up
till the end of the init block is read from this file, with
the events themselves read as usual from the file given in
<code>Beams:LHEF</code>.
<p/><code>flag </code><strong> Beams:newLHEFsameInit </strong>
(<code>default = <strong>off</strong></code>)<br/>
Allow to begin reading events from a new LHEF or or a new
<code>LHAup</code> instance without a completely new initialization.
Only useful when <code>Beams:frameType</code> = 4 or 5.
<p/><code>flag </code><strong> Beams:readLHEFheaders </strong>
(<code>default = <strong>on</strong></code>)<br/>
Read in LHEF header blocks and store them in the
<a href="EventInformation.html" target="page">Info</a> class. See also
<a href="LesHouchesAccord.html" target="page">LHAupLHEF</a> for more information.
<p/><code>mode </code><strong> Beams:nSkipLHEFatInit </strong>
(<code>default = <strong>0</strong></code>)<br/>
Skip the first <i>nSkip</i> events of the input stream
(cf. the <code>LHAup::skipEvent(nSkip)</code> method).
Only used when <code>Beams:frameType</code> = 4 or 5.
<h3>Beam momentum spread</h3>
This framework currently is intended for a modest beam spread, such as
experienced at hadron colliders. Thus it can be safely assumed that the
physics does not change over the CM energy range probed, so that the
parameters of the physics initialization at the nominal energy can be
used as is. Currently it can <b>not</b> be used for the more extensive
energy spread expected at linear <i>e^+ e^-</i> colliders. Also,
any attempt to combine it with external Les Houches input of
parton-level events is at own risk.
<p/>
On this page you can set the momentum spread according to a simple
Gaussian distribution. If you instead want a more sophisticated
parametrization, you can write and link your own
<code><a href="BeamShape.html" target="page">BeamShape</a></code> class.
<p/><code>flag </code><strong> Beams:allowMomentumSpread </strong>
(<code>default = <strong>off</strong></code>)<br/>
Allow the beam momenta to be smeared around their initialization
nominal values.
<p/><code>parm </code><strong> Beams:sigmaPxA </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>p_x</i> spread of the
first incoming particle.
<p/><code>parm </code><strong> Beams:sigmaPyA </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>p_y</i> spread of the
first incoming particle.
<p/><code>parm </code><strong> Beams:sigmaPzA </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>p_z</i> spread of the
first incoming particle.
<p/><code>parm </code><strong> Beams:maxDevA </strong>
(<code>default = <strong>5.</strong></code>; <code>minimum = 0.</code>)<br/>
The triply Gaussian distribution <i>(p_x, p_y, p_z)</i> is restricted to
a maximal total deviation from the nominal values <i>(p_x0, p_y0, p_z0)</i>
for the first incoming particle, like
<br/><i>
(p_x - p_x0)^2/sigma_px^2 + (p_y - p_y0)^2/sigma_py^2 +
(p_z - p_z0)^2/sigma_pz^2 < maxDev^2
</i><br/>
(Note the absence of a factor 2 in the denominator, unlike the Gaussians
used to pick <i>(p_x, p_y, p_z)</i>.)
<p/><code>parm </code><strong> Beams:sigmaPxB </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>p_x</i> spread of the
second incoming particle.
<p/><code>parm </code><strong> Beams:sigmaPyB </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>p_y</i> spread of the
second incoming particle.
<p/><code>parm </code><strong> Beams:sigmaPzB </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>p_z</i> spread of the
second incoming particle.
<p/><code>parm </code><strong> Beams:maxDevB </strong>
(<code>default = <strong>5.</strong></code>; <code>minimum = 0.</code>)<br/>
The triply Gaussian distribution <i>(p_x, p_y, p_z)</i> is restricted to
a maximal total deviation from the nominal values <i>(p_x0, p_y0, p_z0)</i>,
for the second incoming particle, like
<br/><i>
(p_x - p_x0)^2/sigma_px^2 + (p_y - p_y0)^2/sigma_py^2 +
(p_z - p_z0)^2/sigma_pz^2 < maxDev^2
</i><br/>
(Note the absence of a factor 2 in the denominator, unlike the Gaussians
used to pick <i>(p_x, p_y, p_z)</i>.)
<h3>Beam interaction vertex</h3>
On this page you can set the spread of the interaction vertex according to
a simple Gaussian distribution. If you instead want a more sophisticated
parametrization, you can write and link your own
<code><a href="BeamShape.html" target="page">BeamShape</a></code> class.
<p/><code>flag </code><strong> Beams:allowVertexSpread </strong>
(<code>default = <strong>off</strong></code>)<br/>
Allow the interaction vertex of the two colliding beams to be smeared.
If off, then the vertex is set to be the origin.
<p/><code>parm </code><strong> Beams:sigmaVertexX </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>x</i> location of the
interaction vertex.
<p/><code>parm </code><strong> Beams:sigmaVertexY </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>y</i> location of the
interaction vertex.
<p/><code>parm </code><strong> Beams:sigmaVertexZ </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the <i>z</i> location of the
interaction vertex.
<p/><code>parm </code><strong> Beams:maxDevVertex </strong>
(<code>default = <strong>5.</strong></code>; <code>minimum = 0.</code>)<br/>
The triply Gaussian distribution of interaction vertex position
<i>(x, y, z)</i> is restricted to a maximal total deviation from the
origin, like
<br/><i>
x^2/sigma_x^2 + y^2/sigma_y^2 + z^2/sigma_z^2 < maxDevVertex^2
</i><br/>
(Note the absence of a factor 2 in the denominator, unlike the Gaussians
used to pick <i>(x, y, z)</i>.)
<p/><code>parm </code><strong> Beams:sigmaTime </strong>
(<code>default = <strong>0.</strong></code>; <code>minimum = 0.</code>)<br/>
The width of a Gaussian distribution of the collision time (in units of
mm/c). Note that, if the above space parametrization is viewed as the
effect of two incoming beams along the <i>+-z</i> axis, with each beam
having a Gaussian spread, then the spread of the time would also become
a Gaussian with the same width as the <i>z</i> one (times the
velocity of the beams, which we expect is close to unity). For flexibility
we have not enforced any such relation, however.
<p/><code>parm </code><strong> Beams:maxDevTime </strong>
(<code>default = <strong>5.</strong></code>; <code>minimum = 0.</code>)<br/>
The collision time is restricted to be in the range
<i>|t| < sigma_t * maxDevTime</i>.
<p/>
The distributions above are all centered at the origin. It is also
possible to shift the above distributions to be centered around another
nominal position. You must have <code>Beams:allowVertexSpread = on</code>
to use this possibility.
<p/><code>parm </code><strong> Beams:offsetVertexX </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>x</i> location of the interaction vertex is centered at this value.
<p/><code>parm </code><strong> Beams:offsetVertexY </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>y</i> location of the interaction vertex is centered at this value.
<p/><code>parm </code><strong> Beams:offsetVertexZ </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The <i>z</i> location of the interaction vertex is centered at this value.
<p/><code>parm </code><strong> Beams:offsetTime </strong>
(<code>default = <strong>0.</strong></code>)<br/>
The time <i>t</i> of the interaction vertex is centered at this value.
</body>
</html>
<!-- Copyright (C) 2014 Torbjorn Sjostrand -->
|