1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433
|
// SigmaGeneric.cc is a part of the PYTHIA event generator.
// Copyright (C) 2012 Johan Bijnens, Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.
// Function definitions (not found in the header) for various generic
// production processes, to be used as building blocks for some BSM processes.
// Currently represented by QCD pair production of colour triplet objects,
// with spin either 0, 1/2 or 1.
// Cross sections are only provided for fixed m3 = m4, so do some gymnastics:
// i) s34Avg picked so that beta34 same when s3, s4 -> s34Avg.
// ii) tHQ = tH - mQ^2 = -0.5 sH (1 - beta34 cos(thetaH)) for m3 = m4 = mQ,
// but tH - uH = sH beta34 cos(thetaH) also for m3 != m4, so use
// tH, uH selected for m3 != m4 to derive tHQ, uHQ valid for m3 = m4.
#include "SigmaGeneric.h"
namespace Pythia8 {
//==========================================================================
// Sigma2gg2qGqGbar class.
// Cross section for g g -> qG qGbar (generic quark of spin 0, 1/2 or 1).
//--------------------------------------------------------------------------
// Initialize process.
void Sigma2gg2qGqGbar::initProc() {
// Number of colours. Anomalous coupling kappa - 1 used for vector state.
nCHV = settingsPtr->mode("HiddenValley:Ngauge");
kappam1 = settingsPtr->parm("HiddenValley:kappa") - 1.;
hasKappa = (abs(kappam1) > 1e-8);
// Secondary open width fraction.
openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew);
}
//--------------------------------------------------------------------------
// Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour.
void Sigma2gg2qGqGbar::sigmaKin() {
// Modified Mandelstam variables for massive kinematics with m3 = m4.
double delta = 0.25 * pow2(s3 - s4) / sH;
double s34Avg = 0.5 * (s3 + s4) - delta;
double tHavg = tH - delta;
double uHavg = uH - delta;
double tHQ = -0.5 * (sH - tH + uH);
double uHQ = -0.5 * (sH + tH - uH);
double tHQ2 = tHQ * tHQ;
double uHQ2 = uHQ * uHQ;
// Evaluate cross section for spin 0 colour triplet.
if (spinSave == 0) {
sigSum = 0.5 * ( 7. / 48. + 3. * pow2(uHavg - tHavg) / (16. * sH2) )
* ( 1. + 2. * s34Avg * tHavg / pow2(tHavg - s34Avg)
+ 2. * s34Avg * uHavg / pow2(uHavg - s34Avg)
+ 4. * pow2(s34Avg) / ((tHavg - s34Avg) * (uHavg - s34Avg)) );
// Equal probability for two possible colour flows.
sigTS = 0.5 * sigSum;
sigUS = sigTS;
}
// Evaluate cross section for spin 1/2 colour triplet.
else if (spinSave == 1) {
double tumHQ = tHQ * uHQ - s34Avg * sH;
sigTS = ( uHQ / tHQ - 2.25 * uHQ2 / sH2 + 4.5 * s34Avg * tumHQ
/ ( sH * tHQ2) + 0.5 * s34Avg * (tHQ + s34Avg) / tHQ2
- s34Avg*s34Avg / (sH * tHQ) ) / 6.;
sigUS = ( tHQ / uHQ - 2.25 * tHQ2 / sH2 + 4.5 * s34Avg * tumHQ
/ ( sH * uHQ2) + 0.5 * s34Avg * (uHQ + s34Avg) / uHQ2
- s34Avg*s34Avg / (sH * uHQ) ) / 6.;
sigSum = sigTS + sigUS;
}
// Evaluate cross section for spin 1 colour triplet.
else {
double tmu = tHavg - uHavg;
double s34Pos = s34Avg / sH;
double s34Pos2 = s34Pos * s34Pos;
double s34Neg = sH / s34Avg;
double s34Neg2 = s34Neg * s34Neg;
sigSum = pow2(tmu) * sH2 * (241./1536. - 1./32. * s34Pos
+ 9./16. * s34Pos2)
+ pow4(tmu) * (37./512. + 9./64. * s34Pos)
+ pow6(tmu) * (9./512. / sH2)
+ sH2 * sH2 * (133./1536. - 7./64. * s34Pos + 7./16. * s34Pos2);
// Anomalous coupling.
if (hasKappa)
sigSum += pow2(tmu) * sH2 * (kappam1 * (143./384. - 7./3072 * s34Neg)
+ pow2(kappam1) * (- 1./768. * s34Neg + 185./768.)
+ pow3(kappam1) * (- 7./3072. * s34Neg2
- 25./3072. * s34Neg + 67./1536.)
+ pow4(kappam1) * (- 37./49152. * s34Neg2
- 25./6144. * s34Neg + 5./1536.) )
+ pow4(tmu) * (kappam1 * 3./32.
+ pow2(kappam1) * (7./6144. * s34Neg2 - 7./768. * s34Neg + 3./128.)
+ pow3(kappam1) * (7./6144. * s34Neg2 - 7./1536. * s34Neg)
+ pow4(kappam1) * (- 1./49152. * s34Neg2 + 5./6144. * s34Neg) )
+ pow6(tmu) * pow4(kappam1) * 13./49152. / pow2(s34Avg)
+ sH2 * sH2 * ( kappam1 * 77./384.
+ pow2(kappam1) * (7./6144. * s34Neg2 + 1./96.* s34Neg + 39./256.)
+ pow3(kappam1) * (7./6144. * s34Neg2 + 13./1024. * s34Neg + 61./1536.)
+ pow4(kappam1) * (25./49152. * s34Neg2 + 5./1536. * s34Neg + 1./512.)
);
// Equal probability for two possible colour flows.
sigSum /= pow2( (uHavg-s34Avg) * (tHavg-s34Avg) );
sigTS = 0.5 * sigSum;
sigUS = sigTS;
}
// Final answer, with common factors.
sigma = (M_PI / sH2) * pow2(alpS) * sigSum * nCHV * openFracPair;
}
//--------------------------------------------------------------------------
// Select identity, colour and anticolour.
void Sigma2gg2qGqGbar::setIdColAcol() {
// Flavours trivial.
setId( 21, 21, idNew, -idNew);
// Two colour flow topologies.
double sigRand = sigSum * rndmPtr->flat();
if (sigRand < sigTS) setColAcol( 1, 2, 2, 3, 1, 0, 0, 3);
else setColAcol( 1, 2, 3, 1, 3, 0, 0, 2);
}
//==========================================================================
// Sigma2qqbar2qGqGbar class.
// Cross section for q qbar -> qG qGbar (generic quark of spin 0, 1/2 or 1).
//--------------------------------------------------------------------------
// Initialize process.
void Sigma2qqbar2qGqGbar::initProc() {
// Number of colours. Coupling kappa used for vector state.
nCHV = settingsPtr->mode("HiddenValley:Ngauge");
kappa = settingsPtr->parm("HiddenValley:kappa");
// Secondary open width fraction.
openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew);
}
//--------------------------------------------------------------------------
// Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour.
void Sigma2qqbar2qGqGbar::sigmaKin() {
// Modified Mandelstam variables for massive kinematics with m3 = m4.
double delta = 0.25 * pow2(s3 - s4) / sH;
double s34Avg = 0.5 * (s3 + s4) - delta;
double tHavg = tH - delta;
double uHavg = uH - delta;
double tHQ = -0.5 * (sH - tH + uH);
double uHQ = -0.5 * (sH + tH - uH);
double tHQ2 = tHQ * tHQ;
double uHQ2 = uHQ * uHQ;
// Evaluate cross section for spin 0 colour triplet.
if (spinSave == 0) {
sigSum = (1./9.) * (sH * (sH - 4. * s34Avg)
- pow2(uHavg - tHavg)) / sH2;
}
// Evaluate cross section for spin 1/2 colour triplet.
else if (spinSave == 1) {
sigSum = (4./9.) * ((tHQ2 + uHQ2) / sH2 + 2. * s34Avg / sH);
}
// Evaluate cross section for spin 1 colour triplet.
else {
double tuH34 = (tHavg + uHavg) / s34Avg;
sigSum = (1./9.) * (
pow2(1. + kappa) * sH * s34Avg * (pow2(tuH34) - 4.)
+ (tHavg * uHavg - pow2(s34Avg)) * (8. + 2. * (1. - pow2(kappa)) * tuH34
+ pow2(kappa) * pow2(tuH34)) ) / sH2;
}
// Final answer, with common factors.
sigma = (M_PI / sH2) * pow2(alpS) * sigSum * nCHV * openFracPair;
}
//--------------------------------------------------------------------------
// Select identity, colour and anticolour.
void Sigma2qqbar2qGqGbar::setIdColAcol() {
// Flavours trivial.
setId( id1, id2, idNew, -idNew);
// tH defined between f and qG: must swap tHat <-> uHat if qbar q in.
swapTU = (id1 < 0);
// Colour flow topologies.
if (id1 > 0) setColAcol( 1, 0, 0, 2, 1, 0, 0, 2);
else setColAcol( 0, 2, 1, 0, 1, 0, 0, 2);
}
//==========================================================================
// Sigma2ffbar2fGfGbar class.
// Cross section for f fbar -> qG qGbar (generic quark of spin 0, 1/2 or 1)
// via gamma^*/Z^* s-channel exchange. Still under development!! ??
//--------------------------------------------------------------------------
// Initialize process.
void Sigma2ffbar2fGfGbar::initProc() {
// Charge and number of colours. Coupling kappa used for vector state.
if (settingsPtr->flag("HiddenValley:doKinMix"))
eQHV2 = pow2(settingsPtr->parm("HiddenValley:kinMix"));
else
eQHV2 = pow2( particleDataPtr->charge(idNew) );
nCHV = settingsPtr->mode("HiddenValley:Ngauge");
kappa = settingsPtr->parm("HiddenValley:kappa");
// Coloured or uncoloured particle.
hasColour = (particleDataPtr->colType(idNew) != 0);
colFac = (hasColour) ? 3. : 1.;
// Secondary open width fraction.
openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew);
}
//--------------------------------------------------------------------------
// Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour.
void Sigma2ffbar2fGfGbar::sigmaKin() {
// Modified Mandelstam variables for massive kinematics with m3 = m4.
double delta = 0.25 * pow2(s3 - s4) / sH;
double s34Avg = 0.5 * (s3 + s4) - delta;
double tHavg = tH - delta;
double uHavg = uH - delta;
double tHQ = -0.5 * (sH - tH + uH);
double uHQ = -0.5 * (sH + tH - uH);
double tHQ2 = tHQ * tHQ;
double uHQ2 = uHQ * uHQ;
// Evaluate cross section for spin 0 colour triplet.
if (spinSave == 0) {
sigSum = 0.5 * (sH * (sH - 4. * s34Avg) - pow2(uHavg - tHavg)) / sH2;
}
// Evaluate cross section for spin 1/2 colour triplet.
else if (spinSave == 1) {
sigSum = 2. * ((tHQ2 + uHQ2) / sH2 + 2. * s34Avg / sH);
}
// Evaluate cross section for spin 1 colour triplet.
else {
double tuH34 = (tHavg + uHavg) / s34Avg;
sigSum = 0.5 * ( pow2(1. + kappa) * sH * s34Avg * (pow2(tuH34) - 4.)
+ (tHavg * uHavg - pow2(s34Avg)) * (8. + 2. * (1. - pow2(kappa)) * tuH34
+ pow2(kappa) * pow2(tuH34)) ) / sH2;
}
// Final-state charge factors.
sigSum *= colFac * eQHV2 * (1. + alpS / M_PI);
// Final answer, except for initial-state weight
sigma0 = (M_PI / sH2) * pow2(alpEM) * sigSum * nCHV * openFracPair;
}
//--------------------------------------------------------------------------
// Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence.
double Sigma2ffbar2fGfGbar::sigmaHat() {
// Charge and colour factors.
double eNow = couplingsPtr->ef( abs(id1) );
double sigma = sigma0 * pow2(eNow);
if (abs(id1) < 9) sigma /= 3.;
// Answer.
return sigma;
}
//--------------------------------------------------------------------------
// Select identity, colour and anticolour.
void Sigma2ffbar2fGfGbar::setIdColAcol() {
// Flavours trivial.
setId( id1, id2, idNew, -idNew);
// tH defined between f and qG: must swap tHat <-> uHat if fbar f in.
swapTU = (id1 < 0);
// Colour flow topologies.
if (hasColour) {
if (id1 > 0 && id1 < 7) setColAcol( 1, 0, 0, 1, 2, 0, 0, 2);
else if (id1 > -7 && id1 < 0) setColAcol( 0, 1, 1, 0, 2, 0, 0, 2);
else setColAcol( 0, 0, 0, 0, 1, 0, 0, 1);
} else {
if (id1 > 0 && id1 < 7) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0);
else if (id1 > -7 && id1 < 0) setColAcol( 0, 1, 1, 0, 0, 0, 0, 0);
else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0);
}
}
//==========================================================================
// Sigma1ffbar2Zv class.
// Cross section for f fbar -> Zv, where Zv couples both to the SM and
// to a hidden sector. Primitive coupling structure.
//--------------------------------------------------------------------------
// Initialize process.
void Sigma1ffbar2Zv::initProc() {
// Store Zv mass and width for propagator.
idZv = 4900023;
mRes = particleDataPtr->m0(idZv);
GammaRes = particleDataPtr->mWidth(idZv);
m2Res = mRes*mRes;
GamMRat = GammaRes / mRes;
// Set pointer to particle properties and decay table.
particlePtr = particleDataPtr->particleDataEntryPtr(idZv);
}
//--------------------------------------------------------------------------
// Evaluate sigmaHat(sHat); first step when inflavours unknown.
void Sigma1ffbar2Zv::sigmaKin() {
// Breit-Wigner, including some (guessed) spin factors.
double sigBW = 12. * M_PI / ( pow2(sH - m2Res) + pow2(sH * GamMRat) );
// Outgoing width: only includes channels left open.
double widthOut = particlePtr->resWidthOpen(663, mH);
// Temporary answer.
sigOut = sigBW * widthOut;
}
//--------------------------------------------------------------------------
// Evaluate sigmaHat(sHat); second step when inflavours known.
double Sigma1ffbar2Zv::sigmaHat() {
// Incoming quark or lepton; for former need two 1/3 colour factors.
int id1Abs = abs(id1);
double widthIn = particlePtr->resWidthChan( mH, id1Abs, -id1Abs);
if (id1Abs < 6) widthIn /= 9.;
return widthIn * sigOut;
}
//--------------------------------------------------------------------------
// Select identity, colour and anticolour.
void Sigma1ffbar2Zv::setIdColAcol() {
// Flavours trivial.
setId( id1, id2, idZv);
// Colour flow topologies. Swap when antiquarks.
if (abs(id1) < 6) setColAcol( 1, 0, 0, 1, 0, 0);
else setColAcol( 0, 0, 0, 0, 0, 0);
if (id1 < 0) swapColAcol();
}
//--------------------------------------------------------------------------
// Evaluate weight for decay angles.
double Sigma1ffbar2Zv::weightDecay( Event& process, int iResBeg,
int iResEnd) {
// Identity of mother of decaying resonance(s).
int idMother = process[process[iResBeg].mother1()].idAbs();
// For Z' itself angular distribution as if gamma*.
if (iResBeg == 5 && iResEnd == 5) {
double mr = 4. * pow2(process[6].m()) / sH;
double cosThe = (process[3].p() - process[4].p())
* (process[7].p() - process[6].p()) / (sH * sqrtpos(1. - mr));
double wt = 1. + pow2(cosThe) + mr * (1. - pow2(cosThe));
return 0.5 * wt;
}
// For top decay hand over to standard routine.
if (idMother == 6)
return weightTopDecay( process, iResBeg, iResEnd);
// Else done.
return 1.;
}
//==========================================================================
} // end namespace Pythia8
|