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5ad4eb21 | 1 | <chapter name="Beam Parameters"> |
2 | ||
3 | <h2>Beam Parameters</h2> | |
4 | ||
5 | The settings on this page relate to the beam identities and energies, | |
6 | to a beam momentum spread and to a beam interaction spot. | |
7 | As always, momenta and energies are to be given in units of GeV, | |
8 | and of space and time in mm. | |
9 | ||
10 | <h3>Incoming beams</h3> | |
11 | ||
12 | There are two ways to set the identities and energies of the two incoming | |
13 | beam particles. One is to use the <code>init()</code> method with no | |
14 | arguments. Then the settings variables below will be read and used. The | |
15 | alternative is to call <code>init(...)</code> with arguments that provide | |
16 | this information. Then you need not use the variables below (although it | |
17 | would still be possible). Note that, if nothing is done, you will default | |
18 | to LHC at the nominal energy. | |
19 | ||
20 | <modeopen name="Beams:idA" default="2212"> | |
21 | The PDG <code>id</code> code for the first incoming particle. | |
22 | </modeopen> | |
23 | ||
24 | <modeopen name="Beams:idB" default="2212"> | |
25 | The PDG <code>id</code> code for the second incoming particle. | |
26 | </modeopen> | |
27 | ||
28 | <modepick name="Beams:frameType" default="1" min="1" max="4"> | |
29 | Choice of frame for the two colliding particles. | |
30 | <option value="1">the beams are colliding in their cm frame, | |
31 | and therefore only the cm energy needs to be provided, see | |
32 | <code>Beams:eCM</code> below. | |
33 | </option> | |
34 | <option value="2">the beams are back-to-back, but with different energies, | |
35 | see <code>Beams:eA</code> and <code>Beams:eB</code> below. | |
36 | This option could also be used for fixed-target configurations. | |
37 | </option> | |
38 | <option value="3">the beams are not back-to-back, and therefore the | |
39 | three-momentum of each incoming particle needs to be specified, see | |
40 | <code>Beams:pxA</code> through <code>Beams:pzB</code> below. | |
41 | </option> | |
42 | <option value="4">the beam and event information is stored in a | |
43 | Les Houches Event File, see <code>Beams:LHEF</code> below. | |
44 | </option> | |
45 | </modepick> | |
46 | ||
47 | <parm name="Beams:eCM" default="14000." min="10."> | |
48 | Collision CM energy, to be set if <code>Beams:frameType</code> = 1. | |
49 | </parm> | |
50 | ||
51 | <parm name="Beams:eA" default="7000." min="0."> | |
52 | The energy of the first incoming particle, moving in the | |
53 | <ei>+z </ei>direction, to be set if <code>Beams:frameType</code> = 2. | |
54 | If the particle energy is smaller than its mass | |
55 | it is assumed to be at rest. | |
56 | </parm> | |
57 | ||
58 | <parm name="Beams:eB" default="7000." min="0."> | |
59 | The energy of the second incoming particle, moving in the | |
60 | <ei>-z</ei> direction, to be set if <code>Beams:frameType</code> = 2. | |
61 | If the particle energy is smaller than its mass | |
62 | it is assumed to be at rest. | |
63 | </parm> | |
64 | ||
65 | <parm name="Beams:pxA" default="0."> | |
66 | The <ei>p_x</ei> component of the first incoming particle, | |
67 | to be set if <code>Beams:frameType</code> = 3. | |
68 | </parm> | |
69 | ||
70 | <parm name="Beams:pyA" default="0."> | |
71 | The <ei>p_y</ei> component of the first incoming particle, | |
72 | to be set if <code>Beams:frameType</code> = 3. | |
73 | </parm> | |
74 | ||
75 | <parm name="Beams:pzA" default="7000."> | |
76 | The <ei>p_z</ei> component of the first incoming particle, | |
77 | to be set if <code>Beams:frameType</code> = 3. | |
78 | </parm> | |
79 | ||
80 | <parm name="Beams:pxB" default="0."> | |
81 | The <ei>p_x</ei> component of the second incoming particle, | |
82 | to be set if <code>Beams:frameType</code> = 3. | |
83 | </parm> | |
84 | ||
85 | <parm name="Beams:pyB" default="0."> | |
86 | The <ei>p_y</ei> component of the second incoming particle, | |
87 | to be set if <code>Beams:frameType</code> = 3. | |
88 | </parm> | |
89 | ||
90 | <parm name="Beams:pzB" default="-7000."> | |
91 | The <ei>p_z</ei> component of the second incoming particle, | |
92 | to be set if <code>Beams:frameType</code> = 3. | |
93 | </parm> | |
94 | ||
95 | <word name="Beams:LHEF" default="void"> | |
96 | The name of a Les Houches Event File, | |
97 | to be set if <code>Beams:frameType</code> = 4. | |
98 | </word> | |
99 | ||
100 | <h3>Beam momentum spread</h3> | |
101 | ||
102 | This framework currently is intended for a modest beam spread, such as | |
103 | experienced at hadron colliders. Thus it can be safely assumed that the | |
104 | physics does not change over the CM energy range probed, so that the | |
105 | parameters of the physics initialization at the nominal energy can be | |
106 | used as is. Currently it can <b>not</b> be used for the more extensive | |
107 | energy spread expected at linear <ei>e^+ e^-</ei> colliders. Also, | |
108 | any attempt to combine it with external Les Houches input of | |
109 | parton-level events is at own risk. | |
110 | ||
111 | <p/> | |
112 | On this page you can set the momentum spread according to a simple | |
113 | Gaussian distribution. If you instead want a more sophisticated | |
114 | parametrization, you can write and link your own | |
115 | <aloc href="BeamShape"><code>BeamShape</code></aloc> class. | |
116 | ||
117 | <flag name="Beams:allowMomentumSpread" default="off"> | |
118 | Allow the beam momenta to be smeared around their initialization | |
119 | nominal values. | |
120 | </flag> | |
121 | ||
122 | <parm name="Beams:sigmaPxA" default="0." min="0."> | |
123 | The width of a Gaussian distribution of the <ei>p_x</ei> spread of the | |
124 | first incoming particle. | |
125 | </parm> | |
126 | ||
127 | <parm name="Beams:sigmaPyA" default="0." min="0."> | |
128 | The width of a Gaussian distribution of the <ei>p_y</ei> spread of the | |
129 | first incoming particle. | |
130 | </parm> | |
131 | ||
132 | <parm name="Beams:sigmaPzA" default="0." min="0."> | |
133 | The width of a Gaussian distribution of the <ei>p_z</ei> spread of the | |
134 | first incoming particle. | |
135 | </parm> | |
136 | ||
137 | <parm name="Beams:maxDevA" default="5." min="0."> | |
138 | The triply Gaussian distribution <ei>(p_x, p_y, p_z)</ei> is restricted to | |
139 | a maximal total deviation from the nominal values <ei>(p_x0, p_y0, p_z0)</ei> | |
140 | for the first incoming particle, like | |
141 | <eq> | |
142 | (p_x - p_x0)^2/sigma_px^2 + (p_y - p_y0)^2/sigma_py^2 + | |
143 | (p_z - p_z0)^2/sigma_pz^2 < maxDev^2 | |
144 | </eq> | |
145 | (Note the absence of a factor 2 in the denominator, unlike the Gaussians | |
146 | used to pick <ei>(p_x, p_y, p_z)</ei>.) | |
147 | </parm> | |
148 | ||
149 | <parm name="Beams:sigmaPxB" default="0." min="0."> | |
150 | The width of a Gaussian distribution of the <ei>p_x</ei> spread of the | |
151 | second incoming particle. | |
152 | </parm> | |
153 | ||
154 | <parm name="Beams:sigmaPyB" default="0." min="0."> | |
155 | The width of a Gaussian distribution of the <ei>p_y</ei> spread of the | |
156 | second incoming particle. | |
157 | </parm> | |
158 | ||
159 | <parm name="Beams:sigmaPzB" default="0." min="0."> | |
160 | The width of a Gaussian distribution of the <ei>p_z</ei> spread of the | |
161 | second incoming particle. | |
162 | </parm> | |
163 | ||
164 | <parm name="Beams:maxDevB" default="5." min="0."> | |
165 | The triply Gaussian distribution <ei>(p_x, p_y, p_z)</ei> is restricted to | |
166 | a maximal total deviation from the nominal values <ei>(p_x0, p_y0, p_z0)</ei>, | |
167 | for the second incoming particle, like | |
168 | <eq> | |
169 | (p_x - p_x0)^2/sigma_px^2 + (p_y - p_y0)^2/sigma_py^2 + | |
170 | (p_z - p_z0)^2/sigma_pz^2 < maxDev^2 | |
171 | </eq> | |
172 | (Note the absence of a factor 2 in the denominator, unlike the Gaussians | |
173 | used to pick <ei>(p_x, p_y, p_z)</ei>.) | |
174 | </parm> | |
175 | ||
176 | <h3>Beam interaction vertex</h3> | |
177 | ||
178 | On this page you can set the spread of the interaction vertex according to | |
179 | a simple Gaussian distribution. If you instead want a more sophisticated | |
180 | parametrization, you can write and link your own | |
181 | <aloc href="BeamShape"><code>BeamShape</code></aloc> class. | |
182 | ||
183 | <flag name="Beams:allowVertexSpread" default="off"> | |
184 | Allow the interaction vertex of the two colliding beams to be smeared. | |
185 | If off, then the vertex is set to be the origin. | |
186 | </flag> | |
187 | ||
188 | <parm name="Beams:sigmaVertexX" default="0." min="0."> | |
189 | The width of a Gaussian distribution of the <ei>x</ei> location of the | |
190 | interaction vertex. | |
191 | </parm> | |
192 | ||
193 | <parm name="Beams:sigmaVertexY" default="0." min="0."> | |
194 | The width of a Gaussian distribution of the <ei>y</ei> location of the | |
195 | interaction vertex. | |
196 | </parm> | |
197 | ||
198 | <parm name="Beams:sigmaVertexZ" default="0." min="0."> | |
199 | The width of a Gaussian distribution of the <ei>z</ei> location of the | |
200 | interaction vertex. | |
201 | </parm> | |
202 | ||
203 | <parm name="Beams:maxDevVertex" default="5." min="0."> | |
204 | The triply Gaussian distribution of interaction vertex position | |
205 | <ei>(x, y, z)</ei> is restricted to a maximal total deviation from the | |
206 | origin, like | |
207 | <eq> | |
208 | x^2/sigma_x^2 + y^2/sigma_y^2 + z^2/sigma_z^2 < maxDevVertex^2 | |
209 | </eq> | |
210 | (Note the absence of a factor 2 in the denominator, unlike the Gaussians | |
211 | used to pick <ei>(x, y, z)</ei>.) | |
212 | </parm> | |
213 | ||
214 | <parm name="Beams:sigmaTime" default="0." min="0."> | |
215 | The width of a Gaussian distribution of the collision time (in units of | |
216 | mm/c). Note that, if the above space parametrization is viewed as the | |
217 | effect of two incoming beams along the <ei>+-z</ei> axis, with each beam | |
218 | having a Gaussian spread, then the spread of the time would also become | |
219 | a Gaussian with the same width as the <ei>z</ei> one (times the | |
220 | velocity of the beams, which we expect is close to unity). For flexibility | |
221 | we have not enforced any such relation, however. | |
222 | </parm> | |
223 | ||
224 | <parm name="Beams:maxDevTime" default="5." min="0."> | |
225 | The collision time is restricted to be in the range | |
226 | <ei>|t| < sigma_t * maxDevTime</ei>. | |
227 | </parm> | |
228 | ||
229 | <p/> | |
230 | The distributions above are all centered at the origin. It is also | |
231 | possible to shift the above distributions to be centered around another | |
232 | nominal position. You must have <code>Beams:allowVertexSpread = on</code> | |
233 | to use this possibility. | |
234 | ||
235 | <parm name="Beams:offsetVertexX" default="0."> | |
236 | The <ei>x</ei> location of the interaction vertex is centered at this value. | |
237 | </parm> | |
238 | ||
239 | <parm name="Beams:offsetVertexY" default="0."> | |
240 | The <ei>y</ei> location of the interaction vertex is centered at this value. | |
241 | </parm> | |
242 | ||
243 | <parm name="Beams:offsetVertexZ" default="0."> | |
244 | The <ei>z</ei> location of the interaction vertex is centered at this value. | |
245 | </parm> | |
246 | ||
247 | <parm name="Beams:offsetTime" default="0."> | |
248 | The time <ei>t</ei> of the interaction vertex is centered at this value. | |
249 | </parm> | |
250 | ||
251 | </chapter> | |
252 | ||
253 | <!-- Copyright (C) 2008 Torbjorn Sjostrand --> |