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EvtBtoXsgammaAliGreub.cpp
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EvtBtoXsgammaAliGreub.cpp
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//--------------------------------------------------------------------------
//
//
// Copyright Information: See EvtGen/COPYRIGHT
//
// Environment:
// This software is part of the EvtGen package developed jointly
// for the BaBar and CLEO collaborations. If you use all or part
// of it, please give an appropriate acknowledgement.
//
// Module: EvtBtoXsgammaAliGreub.cc
//
// Description: Routine to perform two-body non-resonant B->Xs,gamma decays.
// It generates an X_s mass spectrum based on a parameterisation of the
// b->s,gamma photon spectrum of Ali-Greub. The resultant X_s particles may
// be decayed by JETSET.
//
// Modification history:
//
// Mark Ian Williams July 20, 2000 Module created
// Mark Ian Williams July 21, 2000 Module works
// Mark Ian Williams July 25, 2000 Works for all Xs modes
// Mark Ian Williams Aug 09, 2000 New values for mass minima
// Mark Ian Williams Sept 06, 2000 14 parameter M_Xs function
// Mark Ian Williams Sept 07, 2000 18 parameter M_Xs function
// Mark Ian Williams Sept 07, 2000 Tidied up the code
// Mark Ian Williams Sept 10, 2000 Updated parameters
// Mark Ian Williams Sept 11, 2000 Finalised code
// Jane Tinslay March 21, 2000 Separated from EvtBtoXsgamma
// class to allow choice of input models.
//------------------------------------------------------------------------
//
#include "EvtGenBase/EvtPatches.hh"
#include <stdlib.h>
#include "EvtGenBase/EvtRandom.hh"
#include "EvtGenModels/EvtBtoXsgammaAliGreub.hh"
#include <string>
#include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtReport.hh"
using std::endl;
EvtBtoXsgammaAliGreub::~EvtBtoXsgammaAliGreub(){}
void EvtBtoXsgammaAliGreub::init(int nArg, double* /*args*/){
if ((nArg - 1) != 0) {
report(ERROR,"EvtGen") << "EvtBtoXsgamma generator model "
<< "EvtBtoXsgammaAliGreub expected "
<< "zero arguments but found: "<<nArg-1<<endl;
report(ERROR,"EvtGen") << "Will terminate execution!"<<endl;
::abort();
}
}
double EvtBtoXsgammaAliGreub::GetMass(int Xscode) {
// The special lineshape for strange hadrons X_s in b -> s gamma:
// An 18 parameter function fitted to the theoretical mass spectrum
// of Ali & Greub for a B meson mass of 5.279 GeV; top quark mass of
// 174.3 GeV; strange quark mass of 0.48 GeV (tuned to give minimum
// M_Xs of 0.64 GeV) and Fermi momentum of 265 MeV for spectator quark
// mass of 150 MeV (from CLEO fit). Truncated at max on high side
// and min (just above K pi or KK thresold) on low side.
double min=0.64;
double max=4.5;
double xbox, ybox, alifit;
double mass=0.0;
double par[18];
if ((Xscode == 30343) || (Xscode == -30343) ||
(Xscode == 30353) || (Xscode == -30353)) { // Xsu or Xsd
min=0.6373; // Just above K pi threshold for Xsd/u
//min=0.6333; // K pi threshold for neutral Xsd
par[0]=-2057.2380371094;
par[1]=2502.2556152344;
par[2]=1151.5632324219;
par[3]=0.82431584596634;
par[4]=-4110.5234375000;
par[5]=8445.6757812500;
par[6]=-3034.1894531250;
par[7]=1.1557708978653;
par[8]=1765.9311523438;
par[9]=1.3730158805847;
par[10]=0.51371538639069;
par[11]=2.0056934356689;
par[12]=37144.097656250;
par[13]=-50296.781250000;
par[14]=27319.095703125;
par[15]=-7408.0678710938;
par[16]=1000.8093261719;
par[17]=-53.834449768066;
} else if ((Xscode == 30363) || (Xscode == -30363)) {
min = 0.9964; // Just above KK threshold for Xss
par[0]=-32263.908203125;
par[1]=57186.589843750;
par[2]=-24230.728515625;
par[3]=1.1155973672867;
par[4]=-12161.131835938;
par[5]=20162.146484375;
par[6]=-7198.8564453125;
par[7]=1.3783323764801;
par[8]=1995.1691894531;
par[9]=1.4655895233154;
par[10]=0.48869228363037;
par[11]=2.1038570404053;
par[12]=55100.058593750;
par[13]=-75201.703125000;
par[14]=41096.066406250;
par[15]=-11205.986328125;
par[16]=1522.4024658203;
par[17]=-82.379623413086;
} else {
report(DEBUG,"EvtGen") << "In EvtBtoXsgammaAliGreub: Particle with id " << Xscode << " is not a Xss particle"<<endl;
return 0;
}
double boxheight=par[8];
double boxwidth=max-min;
while ((mass > max) || (mass < min)){
xbox = EvtRandom::Flat(boxwidth)+min;
ybox=EvtRandom::Flat(boxheight);
if (xbox<par[3]) {
alifit=par[0]+par[1]*xbox+par[2]*pow(xbox,2);
} else if (xbox<par[7]) {
alifit=par[4]+par[5]*xbox+par[6]*pow(xbox,2);
} else if (xbox<par[11]) {
alifit=par[8]*exp(-0.5*pow((xbox-par[9])/par[10],2));
} else {
alifit=par[12]+par[13]*xbox+par[14]*pow(xbox,2)+par[15]*pow(xbox,3)+par[16]*pow(xbox,4)+par[17]*pow(xbox,5);
}
if (ybox>alifit) {
mass=0.0;
} else {
mass=xbox;
}
}
return mass;
}

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