1 // SigmaLeptoquark.cc is a part of the PYTHIA event generator.
2 // Copyright (C) 2008 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.
6 // Function definitions (not found in the header) for the
7 // leptoquark simulation classes.
9 #include "SigmaLeptoquark.h"
13 //**************************************************************************
15 // Sigma1ql2LeptoQuark class.
16 // Cross section for q l -> LQ (leptoquark state).
20 // Initialize process.
22 void Sigma1ql2LeptoQuark::initProc() {
24 // Store LQ mass and width for propagator.
25 mRes = ParticleDataTable::m0(42);
26 GammaRes = ParticleDataTable::mWidth(42);
28 GamMRat = GammaRes / mRes;
30 // Yukawa coupling strength.
31 kCoup = Settings::parm("LeptoQuark:kCoup");
33 // Set pointer to particle properties and decay table.
34 LQPtr = ParticleDataTable::particleDataPtr(42);
36 // Read out quark and lepton the LQ couples to.
37 idQuark = LQPtr->decay[0].product(0);
38 idLepton = LQPtr->decay[0].product(1);
44 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
46 void Sigma1ql2LeptoQuark::sigmaKin() {
48 // Incoming width for correct quark-lepton pair..
49 widthIn = 0.25 * alpEM * kCoup * mH;
51 // Set up Breit-Wigner.
52 sigBW = 4. * M_PI/ ( pow2(sH - m2Res) + pow2(sH * GamMRat) );
58 // Evaluate sigmaHat(sHat) for specific incoming flavours.
60 double Sigma1ql2LeptoQuark::sigmaHat() {
62 // Identify whether correct incoming flavours.
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.;
70 // Outgoing width and total sigma. Done.
71 return widthIn * sigBW * LQPtr->resWidthOpen(idLQ, mH);
77 // Select identity, colour and anticolour.
79 void Sigma1ql2LeptoQuark::setIdColAcol() {
82 int idq = (abs(id1) < 9) ? id1 : id2;
83 int idLQ = (idq > 0) ? 42 : -42;
84 setId( id1, id2, idLQ);
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();
93 //**************************************************************************
95 // Sigma2qg2LeptoQuarkl class.
96 // Cross section for q g -> LQ l (leptoquark state).
100 // Initialize process.
102 void Sigma2qg2LeptoQuarkl::initProc() {
104 // Store LQ mass and width for propagator.
105 mRes = ParticleDataTable::m0(42);
106 GammaRes = ParticleDataTable::mWidth(42);
108 GamMRat = GammaRes / mRes;
110 // Yukawa coupling strength.
111 kCoup = Settings::parm("LeptoQuark:kCoup");
113 // Read out quark and lepton the LQ couples to.
114 ParticleDataEntry* LQPtr = ParticleDataTable::particleDataPtr(42);
115 idQuark = LQPtr->decay[0].product(0);
116 idLepton = LQPtr->decay[0].product(1);
118 // Secondary open width fraction.
119 openFracPos = LQPtr->resOpenFrac( 42);
120 openFracNeg = LQPtr->resOpenFrac(-42);
126 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
128 void Sigma2qg2LeptoQuarkl::sigmaKin() {
130 // Evaluate cross section.
131 sigma0 = (M_PI / sH2) * kCoup * (alpS * alpEM / 6.) * (-tH / sH)
132 * (uH2 + s3 * s3) / pow2(uH - s3);
138 // Evaluate sigmaHat(sHat) for specific incoming flavours.
140 double Sigma2qg2LeptoQuarkl::sigmaHat() {
142 // Check that correct incoming flavour.
143 if (abs(id1) != idQuark && abs(id2) != idQuark) return 0.;
145 // Answer, with secondary width correction.
146 double sigma = sigma0;
147 sigma *= (id1 == idQuark || id2 == idQuark) ? openFracPos : openFracNeg;
154 // Select identity, colour and anticolour.
156 void Sigma2qg2LeptoQuarkl::setIdColAcol() {
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);
164 // tH defined between f and f': must swap tHat <-> uHat if q g in.
165 swapTU = (id2 == 21);
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();
174 //**************************************************************************
176 // Sigma2gg2LQLQbar class.
177 // Cross section for g g -> LQ LQbar (leptoquark state).
181 // Initialize process.
183 void Sigma2gg2LQLQbar::initProc() {
185 // Store LQ mass and width for propagator.
186 mRes = ParticleDataTable::m0(42);
187 GammaRes = ParticleDataTable::mWidth(42);
189 GamMRat = GammaRes / mRes;
191 // Secondary open width fraction.
192 openFrac = ParticleDataTable::resOpenFrac(42, -42);
198 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
200 void Sigma2gg2LQLQbar::sigmaKin() {
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;
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)) );
220 // Select identity, colour and anticolour.
222 void Sigma2gg2LQLQbar::setIdColAcol() {
225 setId( 21, 21, 42, -42);
227 // Colour flow topologies: random choice between two mirrors.
228 if (Rndm::flat() < 0.5) setColAcol( 1, 2, 2, 3, 1, 0, 0, 3);
229 else setColAcol( 1, 2, 3, 1, 3, 0, 0, 2);
233 //**************************************************************************
235 // Sigma2qqbar2LQLQbar class.
236 // Cross section for q qbar -> LQ LQbar (leptoquark state).
240 // Initialize process.
242 void Sigma2qqbar2LQLQbar::initProc() {
244 // Store LQ mass and width for propagator.
245 mRes = ParticleDataTable::m0(42);
246 GammaRes = ParticleDataTable::mWidth(42);
248 GamMRat = GammaRes / mRes;
250 // Yukawa coupling strength.
251 kCoup = Settings::parm("LeptoQuark:kCoup");
253 // Read out quark and lepton the LQ couples to.
254 ParticleDataEntry* LQPtr = ParticleDataTable::particleDataPtr(42);
255 idQuark = LQPtr->decay[0].product(0);
257 // Secondary open width fraction.
258 openFrac = ParticleDataTable::resOpenFrac(42, -42);
264 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
266 void Sigma2qqbar2LQLQbar::sigmaKin() {
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;
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;
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);
285 sigmaDiff *= openFrac;
286 sigmaSame *= openFrac;
292 // Select identity, colour and anticolour.
294 void Sigma2qqbar2LQLQbar::setIdColAcol() {
297 setId( id1, id2, 42, -42);
299 // tH defined between f and LQ: must swap tHat <-> uHat if qbar q in.
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);
308 //**************************************************************************
310 } // end namespace Pythia8