source: HiSusy/trunk/Pythia8/pythia8170/src/SigmaLeptoquark.cc @ 1

Last change on this file since 1 was 1, checked in by zerwas, 11 years ago

first import of structure, PYTHIA8 and DELPHES

File size: 8.9 KB
Line 
1// SigmaLeptoquark.cc is a part of the PYTHIA event generator.
2// Copyright (C) 2012 Torbjorn Sjostrand.
3// PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
4// Please respect the MCnet Guidelines, see GUIDELINES for details.
5
6// Function definitions (not found in the header) for the
7// leptoquark simulation classes.
8
9#include "SigmaLeptoquark.h"
10
11namespace Pythia8 {
12
13//==========================================================================
14
15// Sigma1ql2LeptoQuark class.
16// Cross section for q l -> LQ (leptoquark state).
17
18//--------------------------------------------------------------------------
19
20// Initialize process.
21 
22void Sigma1ql2LeptoQuark::initProc() {
23
24  // Store LQ mass and width for propagator.
25  mRes     = particleDataPtr->m0(42);
26  GammaRes = particleDataPtr->mWidth(42);
27  m2Res    = mRes*mRes;
28  GamMRat  = GammaRes / mRes;
29
30  // Yukawa coupling strength.
31  kCoup    = settingsPtr->parm("LeptoQuark:kCoup");
32
33  // Set pointer to particle properties and decay table.
34  LQPtr    = particleDataPtr->particleDataEntryPtr(42);
35
36  // Read out quark and lepton the LQ couples to.
37  idQuark  = LQPtr->channel(0).product(0);
38  idLepton = LQPtr->channel(0).product(1);
39
40} 
41
42//--------------------------------------------------------------------------
43
44// Evaluate sigmaHat(sHat), part independent of incoming flavour.
45
46void Sigma1ql2LeptoQuark::sigmaKin() { 
47
48  // Incoming width for correct quark-lepton pair.
49  widthIn  = 0.25 * alpEM * kCoup * mH;
50
51  // Set up Breit-Wigner.
52  sigBW    = 4. * M_PI/ ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); 
53
54}
55
56//--------------------------------------------------------------------------
57
58// Evaluate sigmaHat(sHat) for specific incoming flavours.
59
60double Sigma1ql2LeptoQuark::sigmaHat() { 
61
62  // Identify whether correct incoming flavours.
63  int idLQ = 0;
64  if      (id1 ==  idQuark && id2 ==  idLepton) idLQ =  42;
65  else if (id2 ==  idQuark && id1 ==  idLepton) idLQ =  42;   
66  else if (id1 == -idQuark && id2 == -idLepton) idLQ = -42;   
67  else if (id2 == -idQuark && id1 == -idLepton) idLQ = -42;   
68  if (idLQ == 0) return 0.;
69
70  // Outgoing width and total sigma. Done.
71  return widthIn * sigBW * LQPtr->resWidthOpen(idLQ, mH);   
72
73}
74
75//--------------------------------------------------------------------------
76
77// Select identity, colour and anticolour.
78
79void Sigma1ql2LeptoQuark::setIdColAcol() {
80
81  // Flavours.
82  int idq  = (abs(id1) < 9) ? id1 : id2;
83  int idLQ = (idq > 0) ? 42 : -42;
84  setId( id1, id2, idLQ);
85
86  // Colour flow topology.
87  if (id1 == idq) setColAcol( 1, 0, 0, 0, 1, 0);
88  else            setColAcol( 0, 0, 1, 0, 1, 0);
89  if (idq < 0) swapColAcol();
90
91}
92
93//==========================================================================
94
95// Sigma2qg2LeptoQuarkl class.
96// Cross section for q g -> LQ l (leptoquark state).
97
98//--------------------------------------------------------------------------
99
100// Initialize process.
101 
102void Sigma2qg2LeptoQuarkl::initProc() {
103
104  // Store LQ mass and width for propagator.
105  mRes     = particleDataPtr->m0(42);
106  GammaRes = particleDataPtr->mWidth(42);
107  m2Res    = mRes*mRes;
108  GamMRat  = GammaRes / mRes;
109
110  // Yukawa coupling strength.
111  kCoup    = settingsPtr->parm("LeptoQuark:kCoup");
112
113  // Read out quark and lepton the LQ couples to.
114  ParticleDataEntry* LQPtr = particleDataPtr->particleDataEntryPtr(42);
115  idQuark  = LQPtr->channel(0).product(0);
116  idLepton = LQPtr->channel(0).product(1);
117
118   // Secondary open width fraction.
119  openFracPos = LQPtr->resOpenFrac( 42);
120  openFracNeg = LQPtr->resOpenFrac(-42);
121
122} 
123
124//--------------------------------------------------------------------------
125
126// Evaluate sigmaHat(sHat), part independent of incoming flavour.
127
128void Sigma2qg2LeptoQuarkl::sigmaKin() { 
129
130  //  Evaluate cross section.
131  sigma0 = (M_PI / sH2) * kCoup * (alpS * alpEM / 6.) * (-tH / sH)
132    * (uH2 + s3 * s3) / pow2(uH - s3);
133
134}
135
136//--------------------------------------------------------------------------
137
138// Evaluate sigmaHat(sHat) for specific incoming flavours.
139
140double Sigma2qg2LeptoQuarkl::sigmaHat() { 
141
142  // Check that correct incoming flavour.
143  if (abs(id1) != idQuark && abs(id2) != idQuark) return 0.;
144
145  // Answer, with secondary width correction.
146  double sigma = sigma0;
147  sigma *= (id1 == idQuark || id2 == idQuark) ? openFracPos : openFracNeg; 
148  return sigma;
149
150}
151
152//--------------------------------------------------------------------------
153
154// Select identity, colour and anticolour.
155
156void Sigma2qg2LeptoQuarkl::setIdColAcol() {
157
158  // Flavour set up for q g -> H q.
159  int idq = (id2 == 21) ? id1 : id2;
160  int idLQ = (idq > 0) ? 42 : -42;
161  int idlp = (idq > 0) ? -idLepton : idLepton;
162  setId( id1, id2, idLQ, idlp);
163
164  // tH defined between f and f': must swap tHat <-> uHat if q g in.
165  swapTU = (id2 == 21); 
166
167  // Colour flow topologies. Swap when antiquarks.
168  if (id2 == 21) setColAcol( 1, 0, 2, 1, 2, 0, 0, 0);
169  else           setColAcol( 2, 1, 1, 0, 2, 0, 0, 0);
170  if (idq < 0) swapColAcol();
171
172}
173
174//==========================================================================
175
176// Sigma2gg2LQLQbar class.
177// Cross section for g g -> LQ LQbar (leptoquark state).
178
179//--------------------------------------------------------------------------
180
181// Initialize process.
182 
183void Sigma2gg2LQLQbar::initProc() {
184
185  // Store LQ mass and width for propagator.
186  mRes     = particleDataPtr->m0(42);
187  GammaRes = particleDataPtr->mWidth(42);
188  m2Res    = mRes*mRes;
189  GamMRat  = GammaRes / mRes;
190
191   // Secondary open width fraction.
192  openFrac = particleDataPtr->resOpenFrac(42, -42);
193
194} 
195
196//--------------------------------------------------------------------------
197
198// Evaluate sigmaHat(sHat), part independent of incoming flavour.
199
200void Sigma2gg2LQLQbar::sigmaKin() { 
201
202  // Average outgoing masses and adjust kinematics accordingly.
203  double delta = 0.25 * pow2(s3 - s4) / sH;
204  double m2avg = 0.5 * (s3 + s4) - delta;
205  double tHavg = tH - delta;
206  double uHavg = uH - delta;
207
208  //  Evaluate cross section. Secondary width for G*.
209  sigma = (M_PI / sH2) * 0.5 * pow2(alpS) 
210    * ( 7. / 48. + 3. * pow2(uHavg - tHavg) / (16. * sH2) )
211    * ( 1. + 2. * m2avg * tHavg / pow2(tHavg - m2avg) 
212    + 2. * m2avg * uHavg / pow2(uHavg - m2avg)
213    + 4. * m2avg * m2avg / ((tHavg - m2avg) * (uHavg - m2avg)) );
214  sigma *= openFrac;
215
216}
217
218//--------------------------------------------------------------------------
219
220// Select identity, colour and anticolour.
221
222void Sigma2gg2LQLQbar::setIdColAcol() {
223
224  // Flavours trivial.
225  setId( 21, 21, 42, -42);
226
227  // Colour flow topologies: random choice between two mirrors.
228  if (rndmPtr->flat() < 0.5) setColAcol( 1, 2, 2, 3, 1, 0, 0, 3);
229  else                       setColAcol( 1, 2, 3, 1, 3, 0, 0, 2);
230
231}
232
233//==========================================================================
234
235// Sigma2qqbar2LQLQbar class.
236// Cross section for q qbar -> LQ LQbar (leptoquark state).
237
238//--------------------------------------------------------------------------
239
240// Initialize process.
241 
242void Sigma2qqbar2LQLQbar::initProc() {
243
244  // Store LQ mass and width for propagator.
245  mRes     = particleDataPtr->m0(42);
246  GammaRes = particleDataPtr->mWidth(42);
247  m2Res    = mRes*mRes;
248  GamMRat  = GammaRes / mRes;
249
250  // Yukawa coupling strength.
251  kCoup    = settingsPtr->parm("LeptoQuark:kCoup");
252
253  // Read out quark and lepton the LQ couples to.
254  ParticleDataEntry* LQPtr = particleDataPtr->particleDataEntryPtr(42);
255  idQuark  = LQPtr->channel(0).product(0);
256
257   // Secondary open width fraction.
258  openFrac = particleDataPtr->resOpenFrac(42, -42);
259
260} 
261
262//--------------------------------------------------------------------------
263
264// Evaluate sigmaHat(sHat), part independent of incoming flavour.
265
266void Sigma2qqbar2LQLQbar::sigmaKin() { 
267
268  // Average outgoing masses and adjust kinematics accordingly.
269  double delta = 0.25 * pow2(s3 - s4) / sH;
270  double m2avg = 0.5 * (s3 + s4) - delta;
271  double tHavg = tH - delta;
272  double uHavg = uH - delta;
273
274  // Evaluate cross section for quark of different flavour than LQ.
275  sigmaDiff = (M_PI / sH2) * (pow2(alpS) / 9.)
276    * ( sH * (sH - 4. * m2avg) - pow2(uHavg - tHavg) ) / sH2;
277
278  // Evaluate cross section for quark of same flavour as LQ.
279  sigmaSame = sigmaDiff + (M_PI / sH2) * (pow2(kCoup * alpEM) / 8.)
280    * (-sH * tHavg - pow2(m2avg-tHavg)) / pow2(tHavg) 
281    + (M_PI / sH2) * (kCoup * alpEM * alpS / 18.) * ( (m2avg - tHavg) 
282    * (uHavg - tHavg) + sH * (m2avg + tHavg) ) / (sH * tHavg);
283
284  // Open fraction.
285  sigmaDiff *= openFrac;
286  sigmaSame *= openFrac;
287
288}
289
290//--------------------------------------------------------------------------
291
292// Select identity, colour and anticolour.
293
294void Sigma2qqbar2LQLQbar::setIdColAcol() {
295
296  // Flavours trivial.
297  setId( id1, id2, 42, -42);
298
299  // tH defined between f and LQ: must swap tHat <-> uHat if qbar q in.
300  swapTU = (id1 < 0); 
301
302  // Colour flow topologies.
303  if (id1 > 0) setColAcol( 1, 0, 0, 2, 1, 0, 0, 2);
304  else         setColAcol( 0, 2, 1, 0, 1, 0, 0, 2);
305
306}
307
308//==========================================================================
309
310} // end namespace Pythia8
Note: See TracBrowser for help on using the repository browser.