Electroweak Processes
 
  - Prompt photon processes
- Weak boson processes
-  Photon Collision Processes
-  Photon-Parton Processes
This page contains processes involving Prompt-photon, gamma^*/Z^0 
and W^+- production, plus a few with t-channel boson 
exchange.Prompt photon processes
 
 
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 pT cut 
is required to stay away from the unphysical low-pT region. 
An eikonalized description, intended to be valid at all pT, 
is included as part of the multiparton-interactions framework. 
 
flag   PromptPhoton:all   
 (default = off)
Common switch for the group of all prompt photon processes, 
as listed separately in the following. 
   
 
flag   PromptPhoton:qg2qgamma   
 (default = off)
Scattering q g → q gamma. 
Code 201. 
   
 
flag   PromptPhoton:qqbar2ggamma   
 (default = off)
Scattering q qbar → g gamma. 
Code 202. 
   
 
flag   PromptPhoton:gg2ggamma   
 (default = off)
Scattering g g → g gamma. 
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 (pT < m_b) or large 
(pT > m_t) transverse momenta. 
Code 203. 
   
 
flag   PromptPhoton:ffbar2gammagamma   
 (default = off)
Scattering q qbar → gamma gamma. 
Code 204. 
   
 
flag   PromptPhoton:gg2gammagamma   
 (default = off)
Scattering g g → gamma gamma. 
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 (pT < m_b) or large 
(pT > m_t) transverse momenta. 
Code 205. 
   
 
mode   PromptPhoton:nQuarkLoop   
 (default = 5; minimum = 3; maximum = 6)
Number of quark flavours included in the box graphs responsible for 
g g → g gamma and g g→ gamma gamma 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 b mass but below the t one. 
   
 
 
Weak boson processes
 
 
Under this heading we group processes involving the production 
of a single electroweak gauge boson, i.e. a gamma^*/Z^0 
or a W^+-, 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, t-channel exchange of such a boson 
between two fermions form a separate group. 
 
 
Note that the Z^0 and W^+- decay modes generated with 
the processes below only include those Standard-Model ones that are 
allowed for on-shell decays. Thus several other processes that receive 
contributions from off-shell resonances are listed separately, e.g. 
for top or 
fourth generation fermions. 
 
 
There is one flag that can be used to influence the gamma^*/Z^0 
structure in all the processes below where it is produced, unless 
otherwise stated. 
mode   WeakZ0:gmZmode   
 (default = 0; minimum = 0; maximum = 2)
Choice of full gamma^*/Z^0 structure or not in relevant 
processes. 
option  0 : full gamma^*/Z^0 structure, 
with interference included.   
option  1 : only pure gamma^* contribution.   
option  2 : only pure Z^0 contribution.   
Note: irrespective of the option used, the particle produced 
will always be assigned code 23 for Z^0, and open decay channels 
is purely dictated by what is set for the Z^0. 
   
 
Boson exchange
 
 
The two processes in this subgroup encode the standard Deeply Inelastic 
Scattering (DIS) of lepton-hadron collisions. In the latter context, 
it is useful to recall that the traditional Q^2 facorization 
and renormalization scales need be set explicitly by 
SigmaProcess:factorScale2 = 6 and 
SigmaProcess:renormScale2 = 6. The special phase space 
cut PhaseSpace:Q2Min may be more convenient than the 
traditional pT cut; to cover the phase space edges it may also 
be relevant to reduce PhaseSpace:pTHatMinDiverge. 
 
 
The processes are also included as part of the multiparton-interactions 
framework in hadron-hadron collisions. 
 
flag   WeakBosonExchange:all   
 (default = off)
Common switch for the group of gamma^*/Z^0 
or W^+- exchange between two fermions. 
   
 
flag   WeakBosonExchange:ff2ff(t:gmZ)   
 (default = off)
Scattering f f' → f f' via gamma^*/Z^0 
t-channel exchange, with full interference 
between the gamma^* and Z^0. 
Code 211. 
   
 
flag   WeakBosonExchange:ff2ff(t:W)   
 (default = off)
Scattering f_1 f_2 → f_3 f_4 via W^+- 
t-channel exchange. 
Code 212. 
   
 
Single boson
 
 
flag   WeakSingleBoson:all   
 (default = off)
Common switch for the group of a single gamma^*/Z^0 
or W^+- production. 
   
 
flag   WeakSingleBoson:ffbar2gmZ   
 (default = off)
Scattering f fbar → gamma^*/Z^0, with full interference 
between the gamma^* and Z^0. 
Code 221. 
   
 
flag   WeakSingleBoson:ffbar2W   
 (default = off)
Scattering f fbar' → W^+-. 
Code 222. 
   
 
flag   WeakSingleBoson:ffbar2ffbar(s:gm)   
 (default = off)
Scattering f fbar → gamma^* → f' fbar'. Subset of 
process 221, but written as a 2 → 2 process, so that 
pT can be used as ordering variable, e.g. in multiparton 
interactions. Hardcoded for the final state being either of the 
five quark flavours or three lepton ones. Not included in the 
WeakSingleBoson:all set, but included in the 
multiparton-interactions framework. 
Code 223. 
   
 
flag   WeakSingleBoson:ffbar2ffbar(s:gmZ)   
 (default = off)
Scattering f fbar → gamma^*/Z^0 → f' fbar'. Equivalent 
to process 221, but written as a 2 → 2 process, so that 
pT could be used as cut or ordering variable. Final-state 
flavour selection is based on the Z^0 allowed decay modes, 
and the WeakZ0:gmZmode options are implemented. 
Not included in the WeakSingleBoson:all set. 
Code 224. 
   
 
flag   WeakSingleBoson:ffbar2ffbar(s:W)   
 (default = off)
Scattering f_1 fbar_2 → W+- → f_3 f_4. Almost equivalent 
to process 222, but written as a 2 → 2 process, so that 
pT could be used as cut or ordering variable. Final-state 
flavour selection is based on the W allowed decay modes. 
There are two simplifications relative to the implementation in 
process 222. Firstly, it is not possible to set different decay modes 
for the W^+ and the W^-; instead the allowed 
W^+ ones will be used throughout, with charge conjugation 
for the W^-. Secondly, quark mass corrections are neglected 
in the decay angular distribution. 
Not included in the WeakSingleBoson:all set. 
Code 225. 
   
 
Boson pair
 
 
Note that, in the decay of the two vector bosons produced by an 
f fbar → V V process, the full four-fermion correlations 
from the leading-order f fbar → V V → 4f matrix elements 
are included [Gun86] (with some extensions by the authors). 
The matrix elements are provided in the double-resonant approach, i.e. 
excludes graph like 
f fbar → V → f fbar → f fbar V → 4f. 
 
flag   WeakDoubleBoson:all   
 (default = off)
Common switch for the group of pair production of gamma^*/Z^0 
and W^+-. 
   
 
flag   WeakDoubleBoson:ffbar2gmZgmZ   
 (default = off)
Scattering f fbar' → gamma^*/Z^0 gamma^*/Z^0. 
Code 231. 
   
 
flag   WeakDoubleBoson:ffbar2ZW   
 (default = off)
Scattering f fbar' → Z^0 W^+-. Note that here the 
gamma^* contribution is not (currently) included. 
Code 232. 
   
 
flag   WeakDoubleBoson:ffbar2WW   
 (default = off)
Scattering f fbar → W^+ W^-. 
Code 233. 
   
 
Boson and parton
 
 
flag   WeakBosonAndParton:all   
 (default = off)
Common switch for the group of production of a single electroweak 
gauge boson, i.e. a gamma^*/Z^0 or a W^+-, in 
association with a parton, i.e. a quark, gluon, photon or lepton. 
These processes give first-order corrections to the ones in the 
WeakSingleBoson class, and both sets cannot be used 
simultaneously without unphysical double-counting. The current class 
should only be used to study the high-pT tail of the 
gauge-boson production processes (for LHC applications at least 
pT > 20 GeV), while the ones in WeakSingleBoson 
should be used for inclusive production. 
   
 
flag   WeakBosonAndParton:qqbar2gmZg   
 (default = off)
Scattering q qbar → gamma^*/Z^0 g. 
Code 241. 
   
 
flag   WeakBosonAndParton:qg2gmZq   
 (default = off)
Scattering q g → gamma^*/Z^0 q . 
Code 242. 
   
 
flag   WeakBosonAndParton:ffbar2gmZgm   
 (default = off)
Scattering f fbar → gamma^*/Z^0 gamma. 
Code 243. 
   
 
flag   WeakBosonAndParton:fgm2gmZf   
 (default = off)
Scattering f gamma →  gamma^*/Z^0 f. 
Code 244. 
   
 
flag   WeakBosonAndParton:qqbar2Wg   
 (default = off)
Scattering q qbar → W^+- g. 
Code 251. 
   
 
flag   WeakBosonAndParton:qg2Wq   
 (default = off)
Scattering q g → W^+- q. 
Code 252. 
   
 
flag   WeakBosonAndParton:ffbar2Wgm   
 (default = off)
Scattering f fbar → W^+- gamma. 
Code 253. 
   
 
flag   WeakBosonAndParton:fgm2Wf   
 (default = off)
Scattering f gamma → W^+- f. 
Code 254. 
   
 
 
 Photon Collision Processes
 
 
A few electroweak two-photon production processes are available. 
To use them, photon PDFs have to be defined for the incoming 
beam particles. This is the case for the internal NNPDF 2.3 QCD+QED 
sets, as well as some further ones available in the LHAPDF library, 
but not for all PDFs. 
 
flag   PhotonCollision:all   
 (default = off)
Common switch for the group of six processes presented below. 
   
 
flag   PhotonCollision:gmgm2qqbar   
 (default = off)
Scatterings gamma gamma → q qbar, where q 
is a light quark (u, d, s) . 
Code 261. 
   
 
flag   PhotonCollision:gmgm2ccbar   
 (default = off)
Scattering gamma gamma → c cbar. 
Code 262. 
   
 
flag   PhotonCollision:gmgm2bbbar   
 (default = off)
Scattering gamma gamma → b bbar. 
Code 263. 
   
 
flag   PhotonCollision:gmgm2ee   
 (default = off)
Scattering gamma gamma → e+ e-. 
Code 264. 
   
 
flag   PhotonCollision:gmgm2mumu   
 (default = off)
Scattering gamma gamma → mu+ mu-. 
Code 265. 
   
 
flag   PhotonCollision:gmgm2tautau   
 (default = off)
Scattering gamma gamma → tau+ tau-. 
Code 266. 
   
 
 
 Photon-Parton Processes
 
 
 
Photon-parton production processes. See comment related to PDFs above. 
Also relevant for direct-resolved processes in photon-photon collisions. 
Two instances of a given process are created when mixing processes where 
the direct photon can come from either side. In this case the process 
code in the parentheses is used when the direct photon is from side A. 
 
 
flag   PhotonParton:all   
 (default = off)
Common switch for the processes 271-274 (also 281-284 when relevant). 
   
 
flag   PhotonParton:ggm2qqbar   
 (default = off)
Scattering g gamma → q qbar, where q 
is a light quark (u, d, s). 
Code 271 (281). 
   
 
flag   PhotonParton:ggm2ccbar   
 (default = off)
Scattering g gamma → c cbar. 
Code 272 (282). 
   
 
flag   PhotonParton:ggm2bbbar   
 (default = off)
Scattering g gamma → b bbar. 
Code 273 (283). 
   
 
flag   PhotonParton:qgm2qg   
 (default = off)
Scattering q gamma → q g. 
Code 274 (284). 
   
 
flag   PhotonParton:qgm2qgm   
 (default = off)
Scattering q gamma → q gamma. 
Code 275 (285).