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Differential D36 Diff 134 src/EvtGenBase/EvtGenKine.cpp

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src/EvtGenBase/EvtGenKine.cpp

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#include "EvtGenBase/EvtGenKine.hh" #include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtConst.hh" #include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtPatches.hh" #include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtRandom.hh" #include "EvtGenBase/EvtRandom.hh"
#include "EvtGenBase/EvtReport.hh" #include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtVector4R.hh" #include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtParticle.hh"
#include <iostream> #include <iostream>
#include <math.h> #include <math.h>
using std::endl; using std::endl;
double EvtPawt( double a, double b, double c ) double EvtPawt( double a, double b, double c )
{ {
double temp = ( a * a - ( b + c ) * ( b + c ) ) * double temp = ( a * a - ( b + c ) * ( b + c ) ) *
▲ Show 20 Lines • Show All 299 Lines • ▼ Show 20 Lines// generate kinematics for 3 body decays, pole for the m1,m2 mass.
double gamma = EvtRandom::Flat( EvtConst::twoPi ); double gamma = EvtRandom::Flat( EvtConst::twoPi );
p4[0].applyRotateEuler( alpha, beta, gamma ); p4[0].applyRotateEuler( alpha, beta, gamma );
p4[1].applyRotateEuler( alpha, beta, gamma ); p4[1].applyRotateEuler( alpha, beta, gamma );
p4[2].applyRotateEuler( alpha, beta, gamma ); p4[2].applyRotateEuler( alpha, beta, gamma );
return 1.0 + a / ( m12sq * m12sq ); return 1.0 + a / ( m12sq * m12sq );
} }
/*
* Function which takes two invariant masses squared in 3-body decay and
* parent after makeDaughters() and generateMassTree() and
* calculates/generates momenta of daughters and sets those.
*/
void EvtGenKine::ThreeBodyKine( const double m12Sq, const double m23Sq,
EvtParticle* p )
{
const double mParent = p->mass();
EvtParticle* daug1 = p->getDaug( 0 );
EvtParticle* daug2 = p->getDaug( 1 );
EvtParticle* daug3 = p->getDaug( 2 );
const double mDaug1 = daug1->mass();
const double mDaug2 = daug2->mass();
const double mDaug3 = daug3->mass();
const double En1 = 0.5 * ( mParent * mParent + mDaug1 * mDaug1 - m23Sq ) /
mParent;
const double En3 = 0.5 * ( mParent * mParent + mDaug3 * mDaug3 - m12Sq ) /
mParent;
const double En2 = mParent - En1 - En3;
const double p1mag = std::sqrt( En1 * En1 - mDaug1 * mDaug1 );
const double p2mag = std::sqrt( En2 * En2 - mDaug2 * mDaug2 );
double cosPhi = 0.5 *
( mDaug1 * mDaug1 + mDaug2 * mDaug2 + 2 * En1 * En2 - m12Sq ) /
p1mag / p2mag;
tlathamUnsubmitted
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Have cross-checked all the expressions with LauKinematics and they agree.

I think it would be helpful to pre-calculate, e.g.
const double mParSq { mParent * mParent };
and similarly for the daughter masses squared since these products appear more than once.

I think also for a small efficiency gain it is better to pre-calculate:
const double invMPar { 1.0 / mParent };
and multiply by that wherever you currently divide by mParent.

Similarly, it should be better to divide by (p1mag * p2mag) rather than do the / p1mag / p2mag.

tlatham: Have cross-checked all the expressions with LauKinematics and they agree. I think it would be…
krepsAuthorUnsubmitted
Done
Inline Actions

All should be implemented here.

kreps: All should be implemented here.
double sinPhi = std::sqrt( 1 - cosPhi * cosPhi );
if ( EvtRandom::Flat( 0., 1. ) > 0.5 ) {
sinPhi *= -1;
}
const double p2x = p2mag * cosPhi;
const double p2y = p2mag * sinPhi;
const double p3x = -p1mag - p2x;
const double p3y = -p2y;
// Construct 4-momenta and rotate them randomly in space
EvtVector4R p1( En1, p1mag, 0., 0. );
EvtVector4R p2( En2, p2x, p2y, 0. );
EvtVector4R p3( En3, p3x, p3y, 0. );
const double euler1 = EvtRandom::Flat( 0., EvtConst::twoPi );
const double euler2 = std::acos( EvtRandom::Flat( -1.0, 1.0 ) );
const double euler3 = EvtRandom::Flat( 0., EvtConst::twoPi );
p1.applyRotateEuler( euler1, euler2, euler3 );
p2.applyRotateEuler( euler1, euler2, euler3 );
p3.applyRotateEuler( euler1, euler2, euler3 );
// set momenta for daughters
daug1->init( daug1->getId(), p1 );
daug2->init( daug2->getId(), p2 );
daug3->init( daug3->getId(), p3 );
return;
}