3 <title>Electroweak Processes</title>
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30 <h2>Electroweak Processes</h2>
32 This page contains processes involving Prompt-photon, <i>gamma^*/Z^0</i>
33 and <i>W^+-</i> production, plus a few with <i>t</i>-channel boson
36 <h3>Prompt photon processes</h3>
38 This group collects the processes where one or two photons are
39 produced by the hard process. Additional sources of photons
40 include parton showers and hadron decays. A <i>pT</i> cut
41 is required to stay away from the unphysical low-<i>pT</i> region.
42 An eikonalized description, intended to be valid at all <i>pT</i>,
43 is included as part of the multiparton-interactions framework.
45 <br/><br/><strong>PromptPhoton:all</strong> <input type="radio" name="1" value="on"><strong>On</strong>
46 <input type="radio" name="1" value="off" checked="checked"><strong>Off</strong>
47 (<code>default = <strong>off</strong></code>)<br/>
48 Common switch for the group of all prompt photon processes,
49 as listed separately in the following.
52 <br/><br/><strong>PromptPhoton:qg2qgamma</strong> <input type="radio" name="2" value="on"><strong>On</strong>
53 <input type="radio" name="2" value="off" checked="checked"><strong>Off</strong>
54 (<code>default = <strong>off</strong></code>)<br/>
55 Scattering <i>q g -> q gamma</i>.
59 <br/><br/><strong>PromptPhoton:qqbar2ggamma</strong> <input type="radio" name="3" value="on"><strong>On</strong>
60 <input type="radio" name="3" value="off" checked="checked"><strong>Off</strong>
61 (<code>default = <strong>off</strong></code>)<br/>
62 Scattering <i>q qbar -> g gamma</i>.
66 <br/><br/><strong>PromptPhoton:gg2ggamma</strong> <input type="radio" name="4" value="on"><strong>On</strong>
67 <input type="radio" name="4" value="off" checked="checked"><strong>Off</strong>
68 (<code>default = <strong>off</strong></code>)<br/>
69 Scattering <i>g g -> g gamma</i>.
70 <br/><b>Note:</b> This is a box graph. The full quark-mass dependence
71 in the loop leads to very complicated expressions. The current
72 implementation is based on assuming five massless quarks (see below),
73 and thus is questionable at small (<i>pT < m_b</i>) or large
74 (<i>pT > m_t</i>) transverse momenta.
78 <br/><br/><strong>PromptPhoton:ffbar2gammagamma</strong> <input type="radio" name="5" value="on"><strong>On</strong>
79 <input type="radio" name="5" value="off" checked="checked"><strong>Off</strong>
80 (<code>default = <strong>off</strong></code>)<br/>
81 Scattering <i>q qbar -> gamma gamma</i>.
85 <br/><br/><strong>PromptPhoton:gg2gammagamma</strong> <input type="radio" name="6" value="on"><strong>On</strong>
86 <input type="radio" name="6" value="off" checked="checked"><strong>Off</strong>
87 (<code>default = <strong>off</strong></code>)<br/>
88 Scattering <i>g g -> gamma gamma</i>.
89 <br/><b>Note:</b> This is a box graph. The full quark-mass dependence
90 in the loop leads to very complicated expressions. The current
91 implementation is based on assuming five massless quarks (see below),
92 and thus is questionable at small (<i>pT < m_b</i>) or large
93 (<i>pT > m_t</i>) transverse momenta.
97 <br/><br/><table><tr><td><strong>PromptPhoton:nQuarkLoop </td><td></td><td> <input type="text" name="7" value="5" size="20"/> (<code>default = <strong>5</strong></code>; <code>minimum = 3</code>; <code>maximum = 6</code>)</td></tr></table>
98 Number of quark flavours included in the box graphs resposible for
99 <i>g g -> g gamma</i> and <i>g g-> gamma gamma</i> processes.
100 Owing to the complexity if the massive expressions, quarks are treated
101 as massless. The default value should be applicable in the range of
102 transverse momenta above the <i>b</i> mass but below the <i>t</i> one.
105 <h3>Weak boson processes</h3>
107 Under this heading we group processes involving the production
108 of a single electroweak gauge boson, i.e. a <i>gamma^*/Z^0</i>
109 or a <i>W^+-</i>, or a pair of them, or one of them in
110 combination with a parton. Since the three sets are partly
111 conflicting, each is associated with its own group flag.
112 In addition, <i>t</i>-channel exchange of such a boson
113 between two fermions form a separate group.
116 There is one flag that can be used to influence the <i>gamma^*/Z^0</i>
117 structure in all the processes below where it is produced, unless
119 <br/><br/><table><tr><td><strong>WeakZ0:gmZmode </td><td> (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>; <code>maximum = 2</code>)</td></tr></table>
120 Choice of full <ei>gamma^*/Z^0</ei> structure or not in relevant
123 <input type="radio" name="8" value="0" checked="checked"><strong>0 </strong>: full <ei>gamma^*/Z^0</ei> structure, with interference included.<br/>
124 <input type="radio" name="8" value="1"><strong>1 </strong>: only pure <ei>gamma^*</ei> contribution.<br/>
125 <input type="radio" name="8" value="2"><strong>2 </strong>: only pure <ei>Z^0</ei> contribution.<br/>
126 <br/><b>Note</b>: irrespective of the option used, the particle produced
127 will always be assigned code 23 for <ei>Z^0</ei>, and open decay channels
128 is purely dictated by what is set for the <ei>Z^0</ei>.
130 <h4>Boson exchange</h4>
132 The two processes in this subgroup is included as part of the
133 multiparton-interactions framework.
135 <br/><br/><strong>WeakBosonExchange:all</strong> <input type="radio" name="9" value="on"><strong>On</strong>
136 <input type="radio" name="9" value="off" checked="checked"><strong>Off</strong>
137 (<code>default = <strong>off</strong></code>)<br/>
138 Common switch for the group of <i>gamma^*/Z^0</i>
139 or <i>W^+-</i> exchange between two fermions.
142 <br/><br/><strong>WeakBosonExchange:ff2ff(t:gmZ)</strong> <input type="radio" name="10" value="on"><strong>On</strong>
143 <input type="radio" name="10" value="off" checked="checked"><strong>Off</strong>
144 (<code>default = <strong>off</strong></code>)<br/>
145 Scattering <i>f f' -> f f'</i> via </i>gamma^*/Z^0</i>
146 <i>t</i>-channel exchange, with full interference
147 between the <i>gamma^*</i> and <i>Z^0</i>.
151 <br/><br/><strong>WeakBosonExchange:ff2ff(t:W)</strong> <input type="radio" name="11" value="on"><strong>On</strong>
152 <input type="radio" name="11" value="off" checked="checked"><strong>Off</strong>
153 (<code>default = <strong>off</strong></code>)<br/>
154 Scattering <i>f_1 f_2 -> f_3 f_4</i> via </i>W^+-</i>
155 <i>t</i>-channel exchange.
159 <h4>Single boson</h4>
161 <br/><br/><strong>WeakSingleBoson:all</strong> <input type="radio" name="12" value="on"><strong>On</strong>
162 <input type="radio" name="12" value="off" checked="checked"><strong>Off</strong>
163 (<code>default = <strong>off</strong></code>)<br/>
164 Common switch for the group of a single <i>gamma^*/Z^0</i>
165 or <i>W^+-</i> production.
168 <br/><br/><strong>WeakSingleBoson:ffbar2gmZ</strong> <input type="radio" name="13" value="on"><strong>On</strong>
169 <input type="radio" name="13" value="off" checked="checked"><strong>Off</strong>
170 (<code>default = <strong>off</strong></code>)<br/>
171 Scattering <i>f fbar -> gamma^*/Z^0</i>, with full interference
172 between the <i>gamma^*</i> and <i>Z^0</i>.
176 <br/><br/><strong>WeakSingleBoson:ffbar2W</strong> <input type="radio" name="14" value="on"><strong>On</strong>
177 <input type="radio" name="14" value="off" checked="checked"><strong>Off</strong>
178 (<code>default = <strong>off</strong></code>)<br/>
179 Scattering <i>f fbar' -> W^+-</i>.
183 <br/><br/><strong>WeakSingleBoson:ffbar2ffbar(s:gm)</strong> <input type="radio" name="15" value="on"><strong>On</strong>
184 <input type="radio" name="15" value="off" checked="checked"><strong>Off</strong>
185 (<code>default = <strong>off</strong></code>)<br/>
186 Scattering <i>f fbar -> gamma^* -> f' fbar'</i>. Subset of
187 process 221, but written as a <i>2 -> 2</i> process, so that
188 <i>pT</i> can be used as ordering variable, e.g. in multiparton
189 interactions. Hardcoded for the final state being either of the
190 five quark flavours or three lepton ones. Not included in the
191 <code>WeakSingleBoson:all</code> set, but included in the
192 multiparton-interactions framework.
198 Note that, in the decay of the two vector bosons produced by an
199 <i>f fbar -> V V</i> process, the full four-fermion correlations
200 from the leading-order <i>f fbar -> V V -> 4f</i> matrix elements
201 are included [<a href="Bibliography.php" target="page">Gun86</a>] (with some extensions by the authors).
202 The matrix elements are provided in the double-resonant approach, i.e.
203 excludes graph like <i>f fbar -> V -> f fbar -> f fbar V -> 4f</i>.
205 <br/><br/><strong>WeakDoubleBoson:all</strong> <input type="radio" name="16" value="on"><strong>On</strong>
206 <input type="radio" name="16" value="off" checked="checked"><strong>Off</strong>
207 (<code>default = <strong>off</strong></code>)<br/>
208 Common switch for the group of pair production of <i>gamma^*/Z^0</i>
212 <br/><br/><strong>WeakDoubleBoson:ffbar2gmZgmZ</strong> <input type="radio" name="17" value="on"><strong>On</strong>
213 <input type="radio" name="17" value="off" checked="checked"><strong>Off</strong>
214 (<code>default = <strong>off</strong></code>)<br/>
215 Scattering <i>f fbar' -> gamma^*/Z^0 gamma^*/Z^0</i>.
219 <br/><br/><strong>WeakDoubleBoson:ffbar2ZW</strong> <input type="radio" name="18" value="on"><strong>On</strong>
220 <input type="radio" name="18" value="off" checked="checked"><strong>Off</strong>
221 (<code>default = <strong>off</strong></code>)<br/>
222 Scattering <i>f fbar' -> Z^0 W^+-</i>. Note that here the
223 <i>gamma^*</i> contribution is not (currently) included.
227 <br/><br/><strong>WeakDoubleBoson:ffbar2WW</strong> <input type="radio" name="19" value="on"><strong>On</strong>
228 <input type="radio" name="19" value="off" checked="checked"><strong>Off</strong>
229 (<code>default = <strong>off</strong></code>)<br/>
230 Scattering <i>f fbar -> W^+ W^-</i>.
234 <h4>Boson and parton</h4>
236 <br/><br/><strong>WeakBosonAndParton:all</strong> <input type="radio" name="20" value="on"><strong>On</strong>
237 <input type="radio" name="20" value="off" checked="checked"><strong>Off</strong>
238 (<code>default = <strong>off</strong></code>)<br/>
239 Common switch for the group of production of a single electroweak
240 gauge boson, i.e. a <i>gamma^*/Z^0</i> or a <i>W^+-</i>, in
241 association with a parton, i.e. a quark, gluon, photon or lepton.
242 These processes give first-order corrections to the ones in the
243 <code>WeakSingleBoson</code> class, and both sets cannot be used
244 simultaneously without unphysical doublecounting. The current class
245 should only be used to study the high-<i>pT</i> tail of the
246 gauge-boson production processes (for LHC applications at least
247 <i>pT</i> > 20 GeV), while the ones in <code>WeakSingleBoson</code>
248 should be used for inclusive production.
251 <br/><br/><strong>WeakBosonAndParton:qqbar2gmZg</strong> <input type="radio" name="21" value="on"><strong>On</strong>
252 <input type="radio" name="21" value="off" checked="checked"><strong>Off</strong>
253 (<code>default = <strong>off</strong></code>)<br/>
254 Scattering <i>q qbar -> gamma^*/Z^0 g</i>.
258 <br/><br/><strong>WeakBosonAndParton:qg2gmZq</strong> <input type="radio" name="22" value="on"><strong>On</strong>
259 <input type="radio" name="22" value="off" checked="checked"><strong>Off</strong>
260 (<code>default = <strong>off</strong></code>)<br/>
261 Scattering <i>q g -> gamma^*/Z^0 q </i>.
265 <br/><br/><strong>WeakBosonAndParton:ffbar2gmZgm</strong> <input type="radio" name="23" value="on"><strong>On</strong>
266 <input type="radio" name="23" value="off" checked="checked"><strong>Off</strong>
267 (<code>default = <strong>off</strong></code>)<br/>
268 Scattering <i>f fbar -> gamma^*/Z^0 gamma</i>.
272 <br/><br/><strong>WeakBosonAndParton:fgm2gmZf</strong> <input type="radio" name="24" value="on"><strong>On</strong>
273 <input type="radio" name="24" value="off" checked="checked"><strong>Off</strong>
274 (<code>default = <strong>off</strong></code>)<br/>
275 Scattering <i>f gamma -> gamma^*/Z^0 f</i>.
279 <br/><br/><strong>WeakBosonAndParton:qqbar2Wg</strong> <input type="radio" name="25" value="on"><strong>On</strong>
280 <input type="radio" name="25" value="off" checked="checked"><strong>Off</strong>
281 (<code>default = <strong>off</strong></code>)<br/>
282 Scattering <i>q qbar -> W^+- g</i>.
286 <br/><br/><strong>WeakBosonAndParton:qg2Wq</strong> <input type="radio" name="26" value="on"><strong>On</strong>
287 <input type="radio" name="26" value="off" checked="checked"><strong>Off</strong>
288 (<code>default = <strong>off</strong></code>)<br/>
289 Scattering <i>q g -> W^+- q</i>.
293 <br/><br/><strong>WeakBosonAndParton:ffbar2Wgm</strong> <input type="radio" name="27" value="on"><strong>On</strong>
294 <input type="radio" name="27" value="off" checked="checked"><strong>Off</strong>
295 (<code>default = <strong>off</strong></code>)<br/>
296 Scattering <i>f fbar -> W^+- gamma</i>.
300 <br/><br/><strong>WeakBosonAndParton:fgm2Wf</strong> <input type="radio" name="28" value="on"><strong>On</strong>
301 <input type="radio" name="28" value="off" checked="checked"><strong>Off</strong>
302 (<code>default = <strong>off</strong></code>)<br/>
303 Scattering <i>f gamma -> W^+- f</i>.
307 <h3> Photon Collision Processes</h3>
309 A few electroweak two-photon production processes are available.
310 To use them, photon PDFs have to be defined for the incoming
311 beam particles. For proton beams an appropriate set would be
312 MRST QED 2004 [<a href="Bibliography.php" target="page">Mar05</a>], available in the LHAPDF library.
314 <br/><br/><strong>PhotonCollision:all</strong> <input type="radio" name="29" value="on"><strong>On</strong>
315 <input type="radio" name="29" value="off" checked="checked"><strong>Off</strong>
316 (<code>default = <strong>off</strong></code>)<br/>
317 Common switch for the group of six processes presented below.
320 <br/><br/><strong>PhotonCollision:gmgm2qqbar</strong> <input type="radio" name="30" value="on"><strong>On</strong>
321 <input type="radio" name="30" value="off" checked="checked"><strong>Off</strong>
322 (<code>default = <strong>off</strong></code>)<br/>
323 Scatterings <i>gamma gamma -> q qbar</i>, where <i>q</i>
324 is a light quark (<i>u, d, s</i>) .
328 <br/><br/><strong>PhotonCollision:gmgm2ccbar</strong> <input type="radio" name="31" value="on"><strong>On</strong>
329 <input type="radio" name="31" value="off" checked="checked"><strong>Off</strong>
330 (<code>default = <strong>off</strong></code>)<br/>
331 Scattering <i>gamma gamma -> c cbar</i>.
335 <br/><br/><strong>PhotonCollision:gmgm2bbbar</strong> <input type="radio" name="32" value="on"><strong>On</strong>
336 <input type="radio" name="32" value="off" checked="checked"><strong>Off</strong>
337 (<code>default = <strong>off</strong></code>)<br/>
338 Scattering <i>gamma gamma -> b bbar</i>.
342 <br/><br/><strong>PhotonCollision:gmgm2ee</strong> <input type="radio" name="33" value="on"><strong>On</strong>
343 <input type="radio" name="33" value="off" checked="checked"><strong>Off</strong>
344 (<code>default = <strong>off</strong></code>)<br/>
345 Scattering <i>gamma gamma -> e+ e-</i>.
349 <br/><br/><strong>PhotonCollision:gmgm2mumu</strong> <input type="radio" name="34" value="on"><strong>On</strong>
350 <input type="radio" name="34" value="off" checked="checked"><strong>Off</strong>
351 (<code>default = <strong>off</strong></code>)<br/>
352 Scattering <i>gamma gamma -> mu+ mu-</i>.
356 <br/><br/><strong>PhotonCollision:gmgm2tautau</strong> <input type="radio" name="35" value="on"><strong>On</strong>
357 <input type="radio" name="35" value="off" checked="checked"><strong>Off</strong>
358 (<code>default = <strong>off</strong></code>)<br/>
359 Scattering <i>gamma gamma -> tau+ tau-</i>.
363 <input type="hidden" name="saved" value="1"/>
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560 <!-- Copyright (C) 2012 Torbjorn Sjostrand -->