EvtBtoXsgammaAliGreub.cc

Go to the documentation of this file.

//--------------------------------------------------------------------------
//
//
// 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;
}