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LorentzVector.cc
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LorentzVector.cc
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/**
* \authors The HEJ collaboration (see AUTHORS for details)
* \date 2020
* \copyright GPLv2 or later
*/
#include "HEJ/LorentzVector.hh"
#include <cmath>
#include <utility>
namespace HEJ {
namespace {
using COM = std::complex<double>;
COM perp(CLHEP::HepLorentzVector const & p) {
return COM{p.x(), p.y()};
}
void angle_aux(CLHEP::HepLorentzVector const & p, COM & perp_hat, double & p_plus, double & p_minus) {
const COM p_perp = perp(p);
if(p_perp == COM{0., 0.}){
perp_hat = -1.;
if(std::abs(std::abs(p.z())/p.t() - 1.) > 1e-9){
throw std::invalid_argument("zero pT particle with |pz| != E");
}
if(p.z() > 0){
p_plus = p.plus();
p_minus = 0.;
}else{
p_plus = 0.;
p_minus = p.minus();
}
}else{
perp_hat = p_perp/std::abs(p_perp);
p_plus = p.plus();
p_minus = p.minus();
}
}
} // anonymous namespace
// "angle" product angle(pi, pj) = <i j>
// see eq. (53) (\eqref{eq:angle_product}) in developer manual
COM angle(
CLHEP::HepLorentzVector const & pi,
CLHEP::HepLorentzVector const & pj
) {
COM pi_perp_hat;
COM pj_perp_hat;
double pi_plus = NAN;
double pi_minus = NAN;
double pj_plus = NAN;
double pj_minus = NAN;
angle_aux(pi, pi_perp_hat, pi_plus, pi_minus);
angle_aux(pj, pj_perp_hat, pj_plus, pj_minus);
return
+ std::sqrt(pi_minus*pj_plus)*pi_perp_hat
- std::sqrt(pi_plus*pj_minus)*pj_perp_hat;
}
// "square" product square(pi, pj) = [i j]
// see eq. (54) (\eqref{eq:square_product}) in developer manual
COM square(
CLHEP::HepLorentzVector const & pi,
CLHEP::HepLorentzVector const & pj
) {
return -std::conj(angle(pi, pj));
}
// see eq:P_massive, eq:P_massive_p, eq:P_massive_q, , eq:P_massive_plus,
// eq:P_massive_minus in the developer manual
std::pair<CLHEP::HepLorentzVector, CLHEP::HepLorentzVector>
split_into_lightlike(CLHEP::HepLorentzVector const & P) {
const double pt = P.perp();
if(P.plus() > 0){
const double y = std::log(P.plus()/pt);
const double E = P.m2()/(2.*P.plus());
return std::make_pair(
CLHEP::HepLorentzVector{P.x(), P.y(), pt*std::sinh(y), pt*std::cosh(y)},
CLHEP::HepLorentzVector{0., 0., -E, E}
);
}
const double y = std::log(pt/P.minus());
const double E = P.m2()/(2.*P.minus());
return std::make_pair(
CLHEP::HepLorentzVector{P.x(), P.y(), pt*std::sinh(y), pt*std::cosh(y)},
CLHEP::HepLorentzVector{0., 0., +E, E}
);
}
} // namespace HEJ

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