BBBrem Class Reference

Generator for low scattering angle radiative Bhabha events (Beam-Beam Bremsstrahlung). More...

#include <BBBrem.h>

Public Member Functions
	BBBrem ()
	Constructor.
	~BBBrem ()
	Destructor.
void	init (double cmsEnergy, double minPhotonEFrac, bool unweighted=true, double maxWeight=2000.0, int densitymode=1, double densityparameter=1.68e-17)
	Initializes the generator.
double	generateEvent (MCParticleGraph &mcGraph, ROOT::Math::XYZVector vertex, ROOT::Math::LorentzRotation boost)
	Generates one single event.
double	getCrossSection ()
	Returns the total cross section of the generated process in millibarn.
double	getCrossSectionError ()
	Returns the error on the total cross section of the generated process in millibarn.
double	getCrossSectionOver ()
	Returns the total overweight bias cross section of the generated process in millibarn.
double	getCrossSectionErrorOver ()
	Returns the error on the total overweight bias cross section of the generated process in millibarn.
double	getMaxWeightDelivered ()
	Returns the maximum weight given by the BBBrem generation.
double	getSumWeightDelivered ()
	Returns the sum of all weights returned by the BBBrem generation.
void	term ()
	Terminates the generator.

Protected Member Functions
void	calcOutgoingLeptonsAndWeight ()
	Calculate the outgoing leptons and the event weight for one single radiative Bhabha scattering.
void	storeParticle (MCParticleGraph &mcGraph, const double *mom, int pdg, ROOT::Math::XYZVector vertex, ROOT::Math::LorentzRotation boost, bool isVirtual=false, bool isInitial=false)
	Store a single generated particle into the MonteCarlo graph.

Protected Attributes
int	m_eventCount
	Internal event counter.
bool	m_unweighted
	True if BBBrem should produce unweighted events.
long	m_weightCount
	Internal weighted event counter.
long	m_weightCountOver
	Internal overweighted event counter.
double	m_maxWeight
	The maximum weight.
double	m_maxWeightDelivered
	The maximum weight given by the BBBrem generation.
double	m_sumWeightDelivered
	The sum of all weights returned by the BBBrem generation.
double	m_sumWeightDeliveredSqr
	The square of the sum of all weights returned by the BBBrem generation.
double	m_sumWeightDeliveredOver
	The sum of all overweights.
double	m_sumWeightDeliveredSqrOver
	The square of the sum of all overweights.
double	m_cmsEnergy
	Center of mass energy (sqrt(s)).
double	m_photonEFrac
	Minimum photon energy fraction.
double	m_crossSection
	The cross-section in millibarns.
double	m_crossSectionError
	The error on the cross-section in millibarns.
double	m_crossSectionOver
	The overweight bias cross-section in millibarns.
double	m_crossSectionErrorOver
	The overweight bias error on the cross-section in millibarns.
int	m_densityCorrectionMode
	Mode for bunch density correction.
double	m_densityCorrectionParameter
	Density correction parameter tc.

Private Attributes
double	alpha
	variable
double	rme
	in MeV
double	s
	variable
double	rme2
	variable
double	rme2s
	variable
double	rls
	variable
double	z0
	variable
double	a1
	variable
double	a2
	variable
double	ac
	variable
double	sigapp
	variable
double	eb
	variable
double	pb
	variable
double	rin2pb
	variable
double	p1 [4]
	variable
double	p2 [4]
	variable
double	q1 [4]
	variable
double	q2 [4]
	variable
double	qk [4]
	variable
double	weight
	variable

Static Private Attributes
static constexpr double	tomb = 3.8937966e5 / 1e6
	Conversion factor (hc)^2.
static constexpr double	twopi = 2.0 * M_PI
	2*pi.

Detailed Description

Generator for low scattering angle radiative Bhabha events (Beam-Beam Bremsstrahlung).

Based on the FORTRAN source code from R. Kleiss. In order to be consistent with the original source code, the variable names are kept and might therefore violate the coding conventions.

Original authors: r. Kleiss and h. Burkhardt Reference: [arXiv:hep-ph/9401333v1]

Definition at line 31 of file BBBrem.h.

Constructor & Destructor Documentation

BBBrem()

BBBrem ( )

inline

Constructor.

Definition at line 37 of file BBBrem.h.

             :
      m_eventCount(0),
      m_unweighted(true),
      m_weightCount(0),
      m_weightCountOver(0),
      m_maxWeight(0.0),
      m_maxWeightDelivered(0.0),
      m_sumWeightDelivered(0.0),
      m_sumWeightDeliveredSqr(0.0),
      m_sumWeightDeliveredOver(0.0),
      m_sumWeightDeliveredSqrOver(0.0),
      m_cmsEnergy(10.58),
      m_photonEFrac(0.000001),
      m_crossSection(0.0),
      m_crossSectionError(0.0),
      m_crossSectionOver(0.0),
      m_crossSectionErrorOver(0.0),
      m_densityCorrectionMode(0),
      m_densityCorrectionParameter(0.0),
      alpha(0.0),
      rme(0.0),
      s(0.0),
      rme2(0.0),
      rme2s(0.0),
      rls(0.0),
      z0(0.0),
      a1(0.0),
      a2(0.0),
      ac(0.0),
      sigapp(0.0),
      eb(0.0),
      pb(0.0),
      rin2pb(0.0),
      weight(0.0)
    {for (int i = 0; i < 4; i++) p1[i] = p2[i] = q1[i] = q2[i] = qk[i] = 0.0;}

~BBBrem()

~BBBrem ( )

inline

Destructor.

Definition at line 77 of file BBBrem.h.

{};

Member Function Documentation

calcOutgoingLeptonsAndWeight()

void calcOutgoingLeptonsAndWeight ( )

protected

Calculate the outgoing leptons and the event weight for one single radiative Bhabha scattering.

The main method. A direct translation from the BBBrem Fortran source code.

Definition at line 155 of file BBBrem.cc.

{
  //Generate z
  double z;
  if (gRandom->Uniform() < ac) {
    double temp1 = gRandom->Uniform();
//     z = 1.0 / (temp1 * (exp(a1 * gRandom->Uniform()) - 1.0));
// Expression 'exp(x) - 1' is replaced by 'expm1(x)' to avoid loss of precision.
    z = 1.0 / (temp1 * (expm1(a1 * gRandom->Uniform())));
  } else {
    z = z0 / gRandom->Uniform();
  }
 
  //Bounds on t
  double y = rme2s * z;
  double q0 = eb * y;
  double temp1 = pb * pb - eb * q0;
  double temp2 = temp1 * temp1 - rme2 - q0 * q0;
 
  //If temp2<0 (very very rare): set weight to 0
  if (temp2 < 0.0) {
    B2WARNING("BBBrem: y too large: delta_t^2 = " << temp2 << " !!!");
    weight = 0.0;
  } else {
    double tmin = -2.0 * (temp1 + sqrt(temp2));
    double tmax = rme2 * s * y * y / tmin;
 
    //Generate t
    double sy = s * y;
    double w2 = sy + rme2;
    temp1 = sy + tmax;
    double rlamx = sqrt(temp1 * temp1 - 4.0 * w2 * tmax);
 
    if (temp1 <= 0.0) {
      temp1 = rlamx - temp1;
    } else {
      temp1 = -4.0 * w2 * tmax / (rlamx + temp1);
    }
 
    double t = 0.0;
    do {
      double b;
// b = exp(gRandom->Uniform() * log(1.0 + 2.0 * sy / temp1));
// Expression 'log(1 + x)' is replaced by 'log1p(x)' to avoid loss of precision.
      b = exp(gRandom->Uniform() * log1p(2.0 * sy / temp1));
      t = -b * z * z * rme2 / ((b - 1) * (b * z + b - 1));
    } while (t <= tmin);
 
    //Generate cgam
    double rlam = sqrt((sy - t) * (sy - t) - 4 * rme2 * t);
    double eps = 4 * rme2 * w2 / (rlam * (rlam + w2 + rme2 - t));
    double rl = log((2 + eps) / eps);
//     double vgam = eps * (exp(gRandom->Uniform() * rl) - 1.0);
// Expression 'exp(x) - 1' is replaced by 'expm1(x)' to avoid loss of precision.
    double vgam = eps * (expm1(gRandom->Uniform() * rl));
    double cgam = 1.0 - vgam;
    double sgam = sqrt(vgam * (2 - vgam));
 
    //Generate azimuthal angles
    double phi  = twopi * gRandom->Uniform();
    double phig = twopi * gRandom->Uniform();
 
    //Construct momentum transfer q(mu)
    double ql = (2.0 * eb * q0 - t) * rin2pb;
    double qt = sqrt((tmax - t) * (t - tmin)) * rin2pb;
    double q[4];
    q[0] = qt * sin(phi);
    q[1] = qt * cos(phi);
    q[2] = ql;
    q[3] = q0;
 
    //Construct momentum of outgoing positron in lab frame
    q2[0] = q1[0] - q[0];
    q2[1] = q1[1] - q[1];
    q2[2] = q1[2] - q[2];
    q2[3] = q1[3] - q[3];
 
    //Find euler angles of p1(mu) in cm frame
    double r0 = eb + q0;
    double w = sqrt(w2);
    double rin2w = 0.5 / w;
    double rinr0w = 1.0 / (r0 + w);
    double eta = -(sy + 2 * w * q0 + t) * rin2w * rinr0w;
    double phat1 = -q[0] * (1 + eta);
    double phat2 = -q[1] * (1 + eta);
    double phat3 = pb * eta - ql * (1 + eta);
    double phatl = rlam * rin2w;
    double phatt = sqrt(phat1 * phat1 + phat2 * phat2);
    double sfhat = phat1 / phatt;
    double cfhat = phat2 / phatt;
    double sthat = phatt / phatl;
    double vthat;
    if (phat3 > 0.0) {
      vthat = sthat * sthat / (1 - sqrt(1 - sthat * sthat));
    } else {
      vthat = sthat * sthat / (1 + sqrt(1 - sthat * sthat));
    }
    double cthat = vthat - 1.0;
 
    //Rotate using these euler angles to get the qk direction in the cm
    double sfg = sin(phig);
    double cfg = cos(phig);
    temp1 = sgam * sfg;
    temp2 = cthat * sgam * cfg + sthat * cgam;
    double veg = vthat + vgam - vthat * vgam - sthat * sgam * cfg;
    double qkhat[4];
    qkhat[3] = sy * rin2w;
    qkhat[0] = qkhat[3] * (cfhat * temp1 + sfhat * temp2);
    qkhat[1] = qkhat[3] * (-sfhat * temp1 + cfhat * temp2);
    qkhat[2] = qkhat[3] * (veg - 1.0);
 
    //Boost the photon momentum to the lab frame
    temp1 = pb * qkhat[2];
    if (temp1 > 0.0) {
      temp2 = (rme2 * qkhat[3] * qkhat[3] + pb * pb * (qkhat[0] * qkhat[0] + qkhat[1] * qkhat[1])) / (eb * qkhat[3] + temp1);
    } else {
      temp2 = eb * qkhat[3] - temp1;
    }
 
    qk[3] = (temp2 + qkhat[3] * q[3] + qkhat[0] * q[0] + qkhat[1] * q[1] + qkhat[2] * q[2]) / w;
    temp1 = (qk[3] + qkhat[3]) * rinr0w;
    qk[0] = qkhat[0] + temp1 * q[0];
    qk[1] = qkhat[1] + temp1 * q[1];
    qk[2] = qkhat[2] + temp1 * (-pb + ql);
 
    //Construct p2 by momentum conservation
    p2[0] = -q2[0] - qk[0];
    p2[1] = -q2[1] - qk[1];
    p2[2] = -q2[2] - qk[2];
    p2[3] = -q2[3] - qk[3] + m_cmsEnergy;
 
    //Impose cut on the photon energy: qk[3]>eb*rk0
    if (qk[3] < eb * m_photonEFrac) {
      weight = 0.0;
    } else {
      //The event is now accepted: compute matrix element and weight
      //Compute fudge factor c1
//       double c1 = log(1 + z) / log((2 + eps) / eps);
//       Expression 'log(1 + x)' is replaced by 'log1p(x)' to avoid loss of precision.
      double c1 = log1p(z) / log((2.0 + eps) / eps);
 
      //Compute fudge factor c2
      temp1 = sy - tmax;
      double vnumx = sqrt(temp1 * temp1 - 4.0 * rme2 * tmax) + temp1;
      temp1 = sy + tmax;
 
      double vdenx;
      if (temp1 < 0.0) {
        vdenx = sqrt(temp1 * temp1 - 4.0 * w2 * tmax) - temp1;
      } else {
        vdenx = -4.0 * w2 * tmax / (sqrt(temp1 * temp1 - 4.0 * w2 * tmax) + temp1);
      }
      temp1 = sy - tmin;
      double vnumn = sqrt(temp1 * temp1 - 4.0 * rme2 * tmin) + temp1;
      temp1 = sy + tmin;
 
      double vdenn;
      if (temp1 < 0.0) {
        vdenn = sqrt(temp1 * temp1 - 4.0 * w2 * tmin) - temp1;
      } else {
        vdenn = -4.0 * w2 * tmin / (sqrt(temp1 * temp1 - 4.0 * w2 * tmin) + temp1);
      }
      double c2 = 2.0 * rls / log((vnumx * vdenn) / (vdenx * vnumn));
 
      //Compute vector (small) r in cm frame, and (big) z
      double rlabl = (t - 2.0 * rme2 * y) * rin2pb;
      double rhat4 = -(2.0 * rme2 * y + (1 - y) * t) * rin2w;
      double etar = rhat4 * rinr0w;
      double rhat1 = -q[0] * (1 + etar);
      double rhat2 = -q[1] * (1 + etar);
      double rhat3 = rlabl + (pb - ql) * etar;
      double zz = s * (rhat4 * qkhat[3] - rhat1 * qkhat[0] - rhat2 * qkhat[1] - rhat3 * qkhat[2]);
 
      //The other invariants
      double s1 = 4.0 * eb * (eb - qk[3]);
      double d1 = sy * rlam * (eps + vgam) * rin2w * rin2w;
      double d2 = 0.5 * sy;
 
      //The exact matrix element
      //Kleiss-burkhardt cross section multiplied by t^2
      double rind1 = 1.0 / d1;
      double rind12 = rind1 * rind1;
      double rind2 = 1.0 / d2;
      double rind22 = rind2 * rind2;
      temp1 = s + t - 2 * d2;
      temp2 = s1 + t + 2 * d1;
      double aa0 = (s * s + s1 * s1 + temp1 * temp1 + temp2 * temp2) * rind1 * rind2 * (-t);
      double aa1 = -4.0 * rme2 * zz * zz * rind12 * rind22;
      double aa2 = -8.0 * rme2 * (d1 * d1 + d2 * d2) * rind1 * rind2;
      double aa3 = 16.0 * rme2 * rme2 * (d1 - d2) * zz * rind12 * rind22;
      double aa4 = -16.0 * rme2 * rme2 * rme2 * (d1 - d2) * (d1 - d2) * rind12 * rind22;
      double rmex = aa0 + aa1 + aa2 + aa3 + aa4;
 
      //The approximate matrix element without c1,2, multiplied by t^2
      double rmap = 4.0 * s * s * rind1 * rind2 * (-t) * c1 * c2;
 
      //The weight
      weight = rmex / rmap * sigapp;
 
      //Isnan check (not sure if this is ok)
      if (std::isnan(weight)) {
        B2WARNING("BBBrem: Weight is nan! Setting the weight to zero.");
        weight = 0.0;
      }
 
 
      //========================================================
      // beam size effect (or density effect)
      // ref: arxiv:hep-ph/9401333
 
      // tc = (hbarc/simga_y)^2
//       double tc = 1.68e-17;  //SuperKEKB LER (sigma_y*=48nm)
      //double tc = 9.81e-18;  //SuperKEKB HER (sigma_y*=63nm)
      double tc = m_densityCorrectionParameter;
//       int cutflag = 0 ;  // 0: no cut, 1: hard cut, 2: soft cut
      if (m_densityCorrectionMode == 1) {
        if (abs(t) < tc) weight = 0.0;
      } else if (m_densityCorrectionMode == 2) {
        if (t != tc) weight *= t * t / (t - tc) / (t - tc); // t<0<tc, always t!=tc
      }
      //========================================================
 
    }
  }
}

generateEvent()

double generateEvent	(	MCParticleGraph &	mcGraph,
		ROOT::Math::XYZVector	vertex,
		ROOT::Math::LorentzRotation	boost
	)

Generates one single event.

Parameters

mcGraph	Reference to the MonteCarlo graph into which the generated particles will be stored.
vertex	Production vertex.
boost	Lorentz boost vector.

Returns

Returns the weight of the event.

Definition at line 80 of file BBBrem.cc.

{
 
  if (m_unweighted) {
    double ran = 0.0;
    do {
      calcOutgoingLeptonsAndWeight();
      if (weight > m_maxWeightDelivered) m_maxWeightDelivered = weight;
      if (weight > m_maxWeight) {
        B2INFO("BBBrem: OVERWEIGHT, w=" << weight << ", nw=" << m_weightCountOver << ", sumw=" << m_sumWeightDeliveredOver);
        m_weightCountOver++;
        m_sumWeightDeliveredOver = m_sumWeightDeliveredOver + (weight - m_maxWeight);
        m_sumWeightDeliveredSqrOver = m_sumWeightDeliveredSqrOver + (weight - m_maxWeight) * (weight - m_maxWeight);
      }
      m_weightCount++;
      m_sumWeightDelivered += weight;
      m_sumWeightDeliveredSqr += weight * weight;
 
      ran = gRandom->Uniform();
    } while (weight <= ran * m_maxWeight);
  } else {
    calcOutgoingLeptonsAndWeight();
    if (weight > m_maxWeightDelivered) m_maxWeightDelivered = weight;
    m_weightCount++;
    m_sumWeightDelivered += weight;
    m_sumWeightDeliveredSqr += weight * weight;
  }
 
  //Store the incoming particles as virtual particles, the outgoing particles as real particles
  storeParticle(mcGraph, p1, 11, vertex, boost, false, true);
  storeParticle(mcGraph, q1, -11, vertex, boost, false, true);
 
  // BBBrem emits gammma only from electron(p1)
  // To emit gamma from positron we need to swap electron and positron here
  bool swapflag = (gRandom->Uniform() > 0.5) ? true : false;
  if (swapflag) {
    double tmp[4];
    for (int i = 0; i < 4; i++) tmp[i] = p2[i];
    for (int i = 0; i < 4; i++) p2[i]  = q2[i];
    for (int i = 0; i < 4; i++) q2[i] = tmp[i];
    p2[2] = -p2[2];
    q2[2] = -q2[2];
    qk[2] = -qk[2];
  }
 
  //Store the outgoing particles as real particles
  storeParticle(mcGraph, p2, 11, vertex, boost, false, false);
  storeParticle(mcGraph, q2, -11, vertex, boost, false, false);
  storeParticle(mcGraph, qk, 22, vertex, boost, false, false);
 
  if (!m_unweighted) return weight;
  return 1.0;
}

getCrossSection()

double getCrossSection ( )

inline

Returns the total cross section of the generated process in millibarn.

Returns

The total cross section.

Definition at line 101 of file BBBrem.h.

{ return m_crossSection; }

getCrossSectionError()

double getCrossSectionError ( )

inline

Returns the error on the total cross section of the generated process in millibarn.

Returns

The error on the total cross section.

Definition at line 106 of file BBBrem.h.

{ return m_crossSectionError; }

getCrossSectionErrorOver()

double getCrossSectionErrorOver ( )

inline

Returns the error on the total overweight bias cross section of the generated process in millibarn.

Returns

The error on the total overweight bias cross section.

Definition at line 116 of file BBBrem.h.

{ return m_crossSectionErrorOver; }

getCrossSectionOver()

double getCrossSectionOver ( )

inline

Returns the total overweight bias cross section of the generated process in millibarn.

Returns

The total overweight bias cross section.

Definition at line 111 of file BBBrem.h.

{ return m_crossSectionOver; }

getMaxWeightDelivered()

double getMaxWeightDelivered ( )

inline

Returns the maximum weight given by the BBBrem generation.

Returns

The maximum weight given by the BBBrem generation.

Definition at line 121 of file BBBrem.h.

{ return m_maxWeightDelivered; }

getSumWeightDelivered()

double getSumWeightDelivered ( )

inline

Returns the sum of all weights returned by the BBBrem generation.

Returns

The sum of all weights returned by the BBBrem generation.

Definition at line 126 of file BBBrem.h.

{ return m_sumWeightDelivered; }

init()

void init	(	double	cmsEnergy,
		double	minPhotonEFrac,
		bool	unweighted = true,
		double	maxWeight = 2000.0,
		int	densitymode = 1,
		double	densityparameter = 1.68e-17
	)

Initializes the generator.

Parameters

cmsEnergy	The center of mass energy in [GeV].
minPhotonEFrac	The minimum photon energy fraction. The min. photon energy is this fraction * beam energy.
unweighted	Set to true to generate unweighted events (e.g. for detector simulation), set to false for weighted events.
maxWeight	The maximum weight. Only required in the case of unweighted events.
densitymode	TODO
densityparameter	TODO

Definition at line 21 of file BBBrem.cc.

{
  m_cmsEnergy = cmsEnergy;
  m_photonEFrac = minPhotonEFrac;
 
  m_unweighted = unweighted;
  m_maxWeight = maxWeight;
  m_densityCorrectionMode = densitymode;
  m_densityCorrectionParameter = densityparameter;
 
  m_maxWeightDelivered = 0.0;
  m_sumWeightDelivered = 0.0;
  m_sumWeightDeliveredSqr = 0.0;
  m_weightCount = 0;
 
  if ((minPhotonEFrac <= 0.0) || (minPhotonEFrac >= 1.0)) {
    B2ERROR("BBBrem: The minimum photon energy fraction has to be in the range ]0,1[ !");
    return;
  }
 
  B2DEBUG(100, "BBBrem: Center of mass energy:     " << cmsEnergy);
  B2DEBUG(100, "BBBrem: Minimum photon energy:     " << minPhotonEFrac << " * beam energy");
 
  //Initialize the constants (in order to be consistent with the FORTRAN source code)
  alpha = Const::fineStrConst;
  rme = Const::electronMass;
 
  //Initialize the derived constants
  s     = cmsEnergy * cmsEnergy;
  rme2  = rme * rme;
  rme2s = rme2 / s;
  rls   = -log(rme2s);
  z0    =  minPhotonEFrac / (1.0 - minPhotonEFrac);
 
  //Approximate total cross section
  a1 = log((1.0 + z0) / z0);
//   a2 = (log(1.0 + z0)) / z0;
// Expression 'log(1 + x)' is replaced by 'log1p(x)' to avoid loss of precision.
  a2 = (log1p(z0)) / z0;
  ac = a1 / (a1 + a2);
  sigapp = 8.0 * (alpha * alpha * alpha) / rme2 * (-log(rme2s)) * (a1 + a2) * tomb;
  B2DEBUG(100, "BBBrem: Approximate cross section: " << sigapp << " millibarn");
 
  //Initial-state momenta
  eb     = 0.5 * cmsEnergy;
  pb     = sqrt(eb * eb - rme2);
  rin2pb = 0.5 / pb;
  p1[0] = 0.0;
  p1[1] = 0.0;
  p1[2] = -pb;
  p1[3] = eb;
  q1[0] = 0.0;
  q1[1] = 0.0;
  q1[2] = pb;
  q1[3] = eb;
}

storeParticle()

void storeParticle ( MCParticleGraph &  mcGraph, const double *  mom, int  pdg, ROOT::Math::XYZVector  vertex, ROOT::Math::LorentzRotation  boost, bool  isVirtual = false, bool  isInitial = false  )

protected

Store a single generated particle into the MonteCarlo graph.

Parameters

mcGraph	Reference to the MonteCarlo graph into which the particle should be stored.
mom	The 3-momentum of the particle in [GeV].
pdg	The PDG code of the particle.
vertex	The vertex of the particle in [mm].
boost	Lorentz boost vector.
isVirtual	If the particle is a virtual particle, such as the incoming particles, set this to true.
isInitial	If the particle is a initial particle for ISR, set this to true.

Definition at line 382 of file BBBrem.cc.

{
 
  // RG 6/25/14 Add new flag for ISR "c_Initial"
  MCParticleGraph::GraphParticle& part = mcGraph.addParticle();
  if (isVirtual) {
    part.setStatus(MCParticle::c_IsVirtual);
  } else if (isInitial) {
    part.setStatus(MCParticle::c_Initial);
  }
 
  //all particles from a generator are primary
  part.addStatus(MCParticle::c_PrimaryParticle);
 
  //all non virtual photons from BBBREM are ISR or FSR
  if (pdg == 22 && !isVirtual) {
    part.addStatus(MCParticle::c_IsISRPhoton);
    part.addStatus(MCParticle::c_IsFSRPhoton);
  }
 
  part.setPDG(pdg);
  part.setFirstDaughter(0);
  part.setLastDaughter(0);
  part.setMomentum(ROOT::Math::XYZVector(mom[0], mom[1],
                                         -mom[2])); //Switch direction, because electrons fly into the +z direction at Belle II
  part.setEnergy(mom[3]);
  part.setMassFromPDG();
//   part.setDecayVertex(0.0, 0.0, 0.0);
 
  //set the production vertex of non initial particles
  if (!isInitial) {
    ROOT::Math::XYZVector v3 = part.getProductionVertex();
    v3 = v3 + vertex;
    part.setProductionVertex(v3);
    part.setValidVertex(true);
  }
 
  //If boosting is enable boost the particles to the lab frame
  ROOT::Math::PxPyPzEVector p4 = part.get4Vector();
  p4 = boost * p4;
  part.set4Vector(p4);
}

term()

void term

(

)

Terminates the generator.

Definition at line 135 of file BBBrem.cc.

{
  if (m_weightCount > 0.0) {
    m_crossSection          = m_sumWeightDelivered / m_weightCount;
    m_crossSectionError     = sqrt(m_sumWeightDeliveredSqr - m_sumWeightDelivered * m_sumWeightDelivered / m_weightCount) /
                              m_weightCount;
 
    if (m_unweighted) {
      m_crossSectionOver      = m_sumWeightDeliveredOver / m_weightCount;
      m_crossSectionErrorOver = sqrt(abs(((m_sumWeightDeliveredSqrOver) / m_weightCount - m_crossSectionOver * m_crossSectionOver) /
                                         m_weightCount));
    }
  }
}

Member Data Documentation

a1

double a1

private

variable

Definition at line 188 of file BBBrem.h.

a2

double a2

private

variable

Definition at line 189 of file BBBrem.h.

ac

double ac

private

variable

Definition at line 190 of file BBBrem.h.

alpha

double alpha

private

variable

Definition at line 181 of file BBBrem.h.

eb

double eb

private

variable

Definition at line 192 of file BBBrem.h.

m_cmsEnergy

double m_cmsEnergy

protected

Center of mass energy (sqrt(s)).

Definition at line 146 of file BBBrem.h.

m_crossSection

double m_crossSection

protected

The cross-section in millibarns.

Definition at line 149 of file BBBrem.h.

m_crossSectionError

double m_crossSectionError

protected

The error on the cross-section in millibarns.

Definition at line 150 of file BBBrem.h.

m_crossSectionErrorOver

double m_crossSectionErrorOver

protected

The overweight bias error on the cross-section in millibarns.

Definition at line 152 of file BBBrem.h.

m_crossSectionOver

double m_crossSectionOver

protected

The overweight bias cross-section in millibarns.

Definition at line 151 of file BBBrem.h.

m_densityCorrectionMode

int m_densityCorrectionMode

protected

Mode for bunch density correction.

Definition at line 154 of file BBBrem.h.

m_densityCorrectionParameter

double m_densityCorrectionParameter

protected

Density correction parameter tc.

Definition at line 155 of file BBBrem.h.

m_eventCount

int m_eventCount

protected

Internal event counter.

Used to calculate the cross-section.

Definition at line 136 of file BBBrem.h.

m_maxWeight

double m_maxWeight

protected

The maximum weight.

Used for the event rejection procedure to produce unweighted events.

Definition at line 140 of file BBBrem.h.

m_maxWeightDelivered

double m_maxWeightDelivered

protected

The maximum weight given by the BBBrem generation.

Definition at line 141 of file BBBrem.h.

m_photonEFrac

double m_photonEFrac

protected

Minimum photon energy fraction.

Definition at line 147 of file BBBrem.h.

m_sumWeightDelivered

double m_sumWeightDelivered

protected

The sum of all weights returned by the BBBrem generation.

Definition at line 142 of file BBBrem.h.

m_sumWeightDeliveredOver

double m_sumWeightDeliveredOver

protected

The sum of all overweights.

Definition at line 144 of file BBBrem.h.

m_sumWeightDeliveredSqr

double m_sumWeightDeliveredSqr

protected

The square of the sum of all weights returned by the BBBrem generation.

Definition at line 143 of file BBBrem.h.

m_sumWeightDeliveredSqrOver

double m_sumWeightDeliveredSqrOver

protected

The square of the sum of all overweights.

Definition at line 145 of file BBBrem.h.

m_unweighted

bool m_unweighted

protected

True if BBBrem should produce unweighted events.

Definition at line 137 of file BBBrem.h.

m_weightCount

long m_weightCount

protected

Internal weighted event counter.

Used to calculate the cross-section.

Definition at line 138 of file BBBrem.h.

m_weightCountOver

long m_weightCountOver

protected

Internal overweighted event counter.

Used to calculate the cross-section.

Definition at line 139 of file BBBrem.h.

p1

double p1[4]

private

variable

Definition at line 195 of file BBBrem.h.

p2

double p2[4]

private

variable

Definition at line 196 of file BBBrem.h.

pb

double pb

private

variable

Definition at line 193 of file BBBrem.h.

q1

double q1[4]

private

variable

Definition at line 197 of file BBBrem.h.

q2

double q2[4]

private

variable

Definition at line 198 of file BBBrem.h.

qk

double qk[4]

private

variable

Definition at line 199 of file BBBrem.h.

rin2pb

double rin2pb

private

variable

Definition at line 194 of file BBBrem.h.

rls

double rls

private

variable

Definition at line 186 of file BBBrem.h.

rme

double rme

private

in MeV

Definition at line 182 of file BBBrem.h.

rme2

double rme2

private

variable

Definition at line 184 of file BBBrem.h.

rme2s

double rme2s

private

variable

Definition at line 185 of file BBBrem.h.

s

double s

private

variable

Definition at line 183 of file BBBrem.h.

sigapp

double sigapp

private

variable

Definition at line 191 of file BBBrem.h.

tomb

constexpr double tomb = 3.8937966e5 / 1e6

staticconstexprprivate

Conversion factor (hc)^2.

Definition at line 177 of file BBBrem.h.

twopi

constexpr double twopi = 2.0 * M_PI

staticconstexprprivate

2*pi.

To keep things short.

Definition at line 178 of file BBBrem.h.

weight

double weight

private

variable

Definition at line 200 of file BBBrem.h.

z0

double z0

private

variable

Definition at line 187 of file BBBrem.h.

---

The documentation for this class was generated from the following files:

• generators/bbbrem/include/BBBrem.h
• generators/bbbrem/src/BBBrem.cc