[u/mrichter/AliRoot.git] / PYTHIA8 / pythia8130 / xmldoc / ElectroweakProcesses.xml

<chapter name="Electroweak Processes">

<h2>Electroweak Processes</h2>

This page contains processes involving Prompt-photon, <ei>gamma^*/Z^0</ei> 
and <ei>W^+-</ei> production, plus a few with <ei>t</ei>-channel boson 
exchange. 

<h3>Prompt photon processes</h3>

This group collects the processes where one or two photons are
produced by the hard process. Additional sources of photons 
include parton showers and hadron decays. A <ei>pT</ei> cut
is required to stay away from the unphysical low-<ei>pT</ei> region.
An eikonalized description, intended to be valid at all <ei>pT</ei>,
is included as part of the multiple-interactions framework.

<flag name="PromptPhoton:all" default="off">
Common switch for the group of all prompt photon processes, 
as listed separately in the following.
</flag>

<flag name="PromptPhoton:qg2qgamma" default="off">
Scattering <ei>q g -> q gamma</ei>.
Code 201.
</flag>

<flag name="PromptPhoton:qqbar2ggamma" default="off">
Scattering <ei>q qbar -> g gamma</ei>.
Code 202.
</flag>

<flag name="PromptPhoton:gg2ggamma" default="off">
Scattering <ei>g g -> g gamma</ei>.
<note>Note:</note> This is a box graph. The full quark-mass dependence 
in the loop leads to very complicated expressions. The current 
implementation is based on assuming five massless quarks (see below), 
and thus is questionable at small (<ei>pT &lt; m_b</ei>) or large 
(<ei>pT > m_t</ei>) transverse momenta.
Code 203.
</flag>

<flag name="PromptPhoton:ffbar2gammagamma" default="off">
Scattering <ei>q qbar -> gamma gamma</ei>.
Code 204.
</flag>

<flag name="PromptPhoton:gg2gammagamma" default="off">
Scattering <ei>g g -> gamma gamma</ei>.
<note>Note:</note> This is a box graph. The full quark-mass dependence 
in the loop leads to very complicated expressions. The current 
implementation is based on assuming five massless quarks (see below), 
and thus is questionable at small (<ei>pT &lt; m_b</ei>) or large 
(<ei>pT > m_t</ei>) transverse momenta.
Code 205.
</flag>

<modeopen name="PromptPhoton:nQuarkLoop" default="5" min="3" max="6">
Number of quark flavours included in the box graphs resposible for 
<ei>g g -> g gamma</ei> and <ei>g g-> gamma gamma</ei> processes.
Owing to the complexity if the massive expressions, quarks are treated 
as massless. The default value should be applicable in the range of 
transverse momenta above the <ei>b</ei> mass but below the <ei>t</ei> one.
</modeopen>

<h3>Weak boson processes</h3>

Under this heading we group processes involving the production
of a single electroweak gauge boson, i.e. a <ei>gamma^*/Z^0</ei>
or a <ei>W^+-</ei>, or a pair of them, or one of them in 
combination with a parton. Since the three sets are partly 
conflicting, each is associated with its own group flag.
In addition, <ei>t</ei>-channel exchange of such a boson 
between two fermions form a separate group.

<p/>
There is one flag that can be used to influence the <ei>gamma^*/Z^0</ei>
structure in all the processes below where it is produced, unless 
otherwise stated. 
<modepick name="WeakZ0:gmZmode" default="0" min="0" max="2">
Choice of full <ei>gamma^*/Z^0</ei> structure or not in relevant 
processes.
<option value="0">full <ei>gamma^*/Z^0</ei> structure,
with interference included.</option>
<option value="1">only pure <ei>gamma^*</ei> contribution.</option>
<option value="2">only pure <ei>Z^0</ei> contribution.</option>
<note>Note</note>: irrespective of the option used, the particle produced 
will always be assigned code 23 for <ei>Z^0</ei>, and open decay channels
is purely dictated by what is set for the <ei>Z^0</ei>. 
</modepick>

<h4>Boson exchange</h4>

The two processes in this subgroup is included as part of the 
multiple-interactions framework.

<flag name="WeakBosonExchange:all" default="off">
Common switch for the group of <ei>gamma^*/Z^0</ei>
or <ei>W^+-</ei> exchange between two fermions.
</flag>

<flag name="WeakBosonExchange:ff2ff(t:gmZ)" default="off">
Scattering <ei>f f' -> f f'</ei> via </ei>gamma^*/Z^0</ei>
<ei>t</ei>-channel exchange, with full interference
between the <ei>gamma^*</ei> and <ei>Z^0</ei>.
Code 211.
</flag>

<flag name="WeakBosonExchange:ff2ff(t:W)" default="off">
Scattering <ei>f_1 f_2 -> f_3 f_4</ei> via </ei>W^+-</ei>
<ei>t</ei>-channel exchange.
Code 212.
</flag>

<h4>Single boson</h4>

<flag name="WeakSingleBoson:all" default="off">
Common switch for the group of a single <ei>gamma^*/Z^0</ei>
or <ei>W^+-</ei> production.
</flag>

<flag name="WeakSingleBoson:ffbar2gmZ" default="off">
Scattering <ei>f fbar -> gamma^*/Z^0</ei>, with full interference
between the <ei>gamma^*</ei> and <ei>Z^0</ei>.
Code 221.
</flag>

<flag name="WeakSingleBoson:ffbar2W" default="off">
Scattering <ei>f fbar' -> W^+-</ei>.
Code 222.
</flag>

<flag name="WeakSingleBoson:ffbar2ffbar(s:gm)" default="off">
Scattering <ei>f fbar -> gamma^* -> f' fbar'</ei>. Subset of 
process 221, but written as a <ei>2 -> 2</ei> process, so that 
<ei>pT</ei> can be used as ordering variable, e.g. in multiple 
interactions. Hardcoded for the final state being either of the 
five quark flavours or three lepton ones. Not included in the 
<code>WeakSingleBoson:all</code> set, but included in the 
multiple-interactions framework. 
Code 223.
</flag>

<h4>Boson pair</h4>

<flag name="WeakDoubleBoson:all" default="off">
Common switch for the group of pair production of <ei>gamma^*/Z^0</ei>
and <ei>W^+-</ei>.
</flag>
 
<flag name="WeakDoubleBoson:ffbar2gmZgmZ" default="off">
Scattering <ei>f fbar' -> gamma^*/Z^0 gamma^*/Z^0</ei>. 
Code 231.
</flag>

<flag name="WeakDoubleBoson:ffbar2ZW" default="off">
Scattering <ei>f fbar' -> Z^0 W^+-</ei>. Note that here the 
<ei>gamma^*</ei> contribution is not (currently) included.
Code 232.
</flag>
 
<flag name="WeakDoubleBoson:ffbar2WW" default="off">
Scattering <ei>f fbar -> W^+ W^-</ei>.
Code 233.
</flag>

<h4>Boson and parton</h4>

<flag name="WeakBosonAndParton:all" default="off">
Common switch for the group of production of a single electroweak 
gauge boson, i.e. a <ei>gamma^*/Z^0</ei> or a <ei>W^+-</ei>, in 
association with a parton, i.e. a quark, gluon, photon or lepton.
These processes give first-order corrections to the ones in the
<code>WeakSingleBoson</code> class, and both sets cannot be used
simultaneously without unphysical doublecounting. The current class
should only be used to study the high-<ei>pT</ei> tail of the 
gauge-boson production processes (for LHC applications at least
<ei>pT</ei> > 20 GeV), while the ones in <code>WeakSingleBoson</code> 
should be used for inclusive production.
</flag>
 
<flag name="WeakBosonAndParton:qqbar2gmZg" default="off">
Scattering <ei>q qbar -> gamma^*/Z^0 g</ei>.
Code 241.
</flag>
 
<flag name="WeakBosonAndParton:qg2gmZq" default="off">
Scattering <ei>q g -> gamma^*/Z^0 q </ei>.
Code 242.
</flag>
 
<flag name="WeakBosonAndParton:ffbar2gmZgm" default="off">
Scattering <ei>f fbar -> gamma^*/Z^0 gamma</ei>.
Code 243.
</flag>
 
<flag name="WeakBosonAndParton:fgm2gmZf" default="off">
Scattering <ei>f gamma ->  gamma^*/Z^0 f</ei>.
Code 244.
</flag>
 
<flag name="WeakBosonAndParton:qqbar2Wg" default="off">
Scattering <ei>q qbar -> W^+- g</ei>.
Code 251.
</flag>
 
<flag name="WeakBosonAndParton:qg2Wq" default="off">
Scattering <ei>q g -> W^+- q</ei>.
Code 252.
</flag>
 
<flag name="WeakBosonAndParton:ffbar2Wgm" default="off">
Scattering <ei>f fbar -> W^+- gamma</ei>.
Code 253.
</flag>
 
<flag name="WeakBosonAndParton:fgm2Wf" default="off">
Scattering <ei>f gamma -> W^+- f</ei>.
Code 254.
</flag>

</chapter>

<!-- Copyright (C) 2008 Torbjorn Sjostrand -->
Commit	Line	Data
5ad4eb21	1	<chapter name="Electroweak Processes">
	2
	3	<h2>Electroweak Processes</h2>
	4
	5	This page contains processes involving Prompt-photon, <ei>gamma^*/Z^0</ei>
	6	and <ei>W^+-</ei> production, plus a few with <ei>t</ei>-channel boson
	7	exchange.
	8
	9	<h3>Prompt photon processes</h3>
	10
	11	This group collects the processes where one or two photons are
	12	produced by the hard process. Additional sources of photons
	13	include parton showers and hadron decays. A <ei>pT</ei> cut
	14	is required to stay away from the unphysical low-<ei>pT</ei> region.
	15	An eikonalized description, intended to be valid at all <ei>pT</ei>,
	16	is included as part of the multiple-interactions framework.
	17
	18	<flag name="PromptPhoton:all" default="off">
	19	Common switch for the group of all prompt photon processes,
	20	as listed separately in the following.
	21	</flag>
	22
	23	<flag name="PromptPhoton:qg2qgamma" default="off">
	24	Scattering <ei>q g -> q gamma</ei>.
	25	Code 201.
	26	</flag>
	27
	28	<flag name="PromptPhoton:qqbar2ggamma" default="off">
	29	Scattering <ei>q qbar -> g gamma</ei>.
	30	Code 202.
	31	</flag>
	32
	33	<flag name="PromptPhoton:gg2ggamma" default="off">
	34	Scattering <ei>g g -> g gamma</ei>.
	35	<note>Note:</note> This is a box graph. The full quark-mass dependence
	36	in the loop leads to very complicated expressions. The current
	37	implementation is based on assuming five massless quarks (see below),
	38	and thus is questionable at small (<ei>pT < m_b</ei>) or large
	39	(<ei>pT > m_t</ei>) transverse momenta.
	40	Code 203.
	41	</flag>
	42
	43	<flag name="PromptPhoton:ffbar2gammagamma" default="off">
	44	Scattering <ei>q qbar -> gamma gamma</ei>.
	45	Code 204.
	46	</flag>
	47
	48	<flag name="PromptPhoton:gg2gammagamma" default="off">
	49	Scattering <ei>g g -> gamma gamma</ei>.
	50	<note>Note:</note> This is a box graph. The full quark-mass dependence
	51	in the loop leads to very complicated expressions. The current
	52	implementation is based on assuming five massless quarks (see below),
	53	and thus is questionable at small (<ei>pT < m_b</ei>) or large
	54	(<ei>pT > m_t</ei>) transverse momenta.
	55	Code 205.
	56	</flag>
	57
	58	<modeopen name="PromptPhoton:nQuarkLoop" default="5" min="3" max="6">
	59	Number of quark flavours included in the box graphs resposible for
	60	<ei>g g -> g gamma</ei> and <ei>g g-> gamma gamma</ei> processes.
	61	Owing to the complexity if the massive expressions, quarks are treated
	62	as massless. The default value should be applicable in the range of
	63	transverse momenta above the <ei>b</ei> mass but below the <ei>t</ei> one.
	64	</modeopen>
65
66	<h3>Weak boson processes</h3>
67
68	Under this heading we group processes involving the production
69	of a single electroweak gauge boson, i.e. a <ei>gamma^*/Z^0</ei>
70	or a <ei>W^+-</ei>, or a pair of them, or one of them in
71	combination with a parton. Since the three sets are partly
72	conflicting, each is associated with its own group flag.
73	In addition, <ei>t</ei>-channel exchange of such a boson
74	between two fermions form a separate group.
75
76	<p/>
77	There is one flag that can be used to influence the <ei>gamma^*/Z^0</ei>
78	structure in all the processes below where it is produced, unless
79	otherwise stated.
80	<modepick name="WeakZ0:gmZmode" default="0" min="0" max="2">
81	Choice of full <ei>gamma^*/Z^0</ei> structure or not in relevant
82	processes.
83	<option value="0">full <ei>gamma^*/Z^0</ei> structure,
84	with interference included.</option>
85	<option value="1">only pure <ei>gamma^*</ei> contribution.</option>
86	<option value="2">only pure <ei>Z^0</ei> contribution.</option>
87	<note>Note</note>: irrespective of the option used, the particle produced
88	will always be assigned code 23 for <ei>Z^0</ei>, and open decay channels
89	is purely dictated by what is set for the <ei>Z^0</ei>.
90	</modepick>
91
92	<h4>Boson exchange</h4>
93
94	The two processes in this subgroup is included as part of the
95	multiple-interactions framework.
96
97	<flag name="WeakBosonExchange:all" default="off">
98	Common switch for the group of <ei>gamma^*/Z^0</ei>
99	or <ei>W^+-</ei> exchange between two fermions.
100	</flag>
101
102	<flag name="WeakBosonExchange:ff2ff(t:gmZ)" default="off">
103	Scattering <ei>f f' -> f f'</ei> via </ei>gamma^*/Z^0</ei>
104	<ei>t</ei>-channel exchange, with full interference
105	between the <ei>gamma^*</ei> and <ei>Z^0</ei>.
106	Code 211.
107	</flag>
108
109	<flag name="WeakBosonExchange:ff2ff(t:W)" default="off">
110	Scattering <ei>f_1 f_2 -> f_3 f_4</ei> via </ei>W^+-</ei>
111	<ei>t</ei>-channel exchange.
112	Code 212.
113	</flag>
114
115	<h4>Single boson</h4>
116
117	<flag name="WeakSingleBoson:all" default="off">
118	Common switch for the group of a single <ei>gamma^*/Z^0</ei>
119	or <ei>W^+-</ei> production.
120	</flag>
121
122	<flag name="WeakSingleBoson:ffbar2gmZ" default="off">
123	Scattering <ei>f fbar -> gamma^*/Z^0</ei>, with full interference
124	between the <ei>gamma^*</ei> and <ei>Z^0</ei>.
125	Code 221.
126	</flag>
127
128	<flag name="WeakSingleBoson:ffbar2W" default="off">
129	Scattering <ei>f fbar' -> W^+-</ei>.
130	Code 222.
131	</flag>
132
133	<flag name="WeakSingleBoson:ffbar2ffbar(s:gm)" default="off">
134	Scattering <ei>f fbar -> gamma^* -> f' fbar'</ei>. Subset of
135	process 221, but written as a <ei>2 -> 2</ei> process, so that
136	<ei>pT</ei> can be used as ordering variable, e.g. in multiple
137	interactions. Hardcoded for the final state being either of the
138	five quark flavours or three lepton ones. Not included in the
139	<code>WeakSingleBoson:all</code> set, but included in the
140	multiple-interactions framework.
141	Code 223.
142	</flag>
143
144	<h4>Boson pair</h4>
145
146	<flag name="WeakDoubleBoson:all" default="off">
147	Common switch for the group of pair production of <ei>gamma^*/Z^0</ei>
148	and <ei>W^+-</ei>.
149	</flag>
150
151	<flag name="WeakDoubleBoson:ffbar2gmZgmZ" default="off">
152	Scattering <ei>f fbar' -> gamma^/Z^0 gamma^/Z^0</ei>.
153	Code 231.
154	</flag>
155
156	<flag name="WeakDoubleBoson:ffbar2ZW" default="off">
157	Scattering <ei>f fbar' -> Z^0 W^+-</ei>. Note that here the
158	<ei>gamma^*</ei> contribution is not (currently) included.
159	Code 232.
160	</flag>
161
162	<flag name="WeakDoubleBoson:ffbar2WW" default="off">
163	Scattering <ei>f fbar -> W^+ W^-</ei>.
164	Code 233.
165	</flag>
166
167	<h4>Boson and parton</h4>
168
169	<flag name="WeakBosonAndParton:all" default="off">
170	Common switch for the group of production of a single electroweak
171	gauge boson, i.e. a <ei>gamma^*/Z^0</ei> or a <ei>W^+-</ei>, in
172	association with a parton, i.e. a quark, gluon, photon or lepton.
173	These processes give first-order corrections to the ones in the
174	<code>WeakSingleBoson</code> class, and both sets cannot be used
175	simultaneously without unphysical doublecounting. The current class
176	should only be used to study the high-<ei>pT</ei> tail of the
177	gauge-boson production processes (for LHC applications at least
178	<ei>pT</ei> > 20 GeV), while the ones in <code>WeakSingleBoson</code>
179	should be used for inclusive production.
180	</flag>
181
182	<flag name="WeakBosonAndParton:qqbar2gmZg" default="off">
183	Scattering <ei>q qbar -> gamma^*/Z^0 g</ei>.
184	Code 241.
185	</flag>
186
187	<flag name="WeakBosonAndParton:qg2gmZq" default="off">
188	Scattering <ei>q g -> gamma^*/Z^0 q </ei>.
189	Code 242.
190	</flag>
191
192	<flag name="WeakBosonAndParton:ffbar2gmZgm" default="off">
193	Scattering <ei>f fbar -> gamma^*/Z^0 gamma</ei>.
194	Code 243.
195	</flag>
196
197	<flag name="WeakBosonAndParton:fgm2gmZf" default="off">
198	Scattering <ei>f gamma -> gamma^*/Z^0 f</ei>.
199	Code 244.
200	</flag>
201
202	<flag name="WeakBosonAndParton:qqbar2Wg" default="off">
203	Scattering <ei>q qbar -> W^+- g</ei>.
204	Code 251.
205	</flag>
206
207	<flag name="WeakBosonAndParton:qg2Wq" default="off">
208	Scattering <ei>q g -> W^+- q</ei>.
209	Code 252.
210	</flag>
211
212	<flag name="WeakBosonAndParton:ffbar2Wgm" default="off">
213	Scattering <ei>f fbar -> W^+- gamma</ei>.
214	Code 253.
215	</flag>
216
217	<flag name="WeakBosonAndParton:fgm2Wf" default="off">
218	Scattering <ei>f gamma -> W^+- f</ei>.
219	Code 254.
220	</flag>
221
222	</chapter>
223
224	<!-- Copyright (C) 2008 Torbjorn Sjostrand -->
225