fourvec.h

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//
//
// File: hitfit/fourvec.h
// Purpose: Define 3- and 4-vector types for the hitfit package, and
//          supply a few additional operations.
// Created: Jul, 2000, sss, based on run 1 mass analysis code.
//
// This file defines the types `Threevec' and `Fourvec' to be used
// in hitfit code.  These are based on the corresponding CLHEP classes.
// We also provide a handful of operations in addition to those that
// CLHEP has.
//
// CMSSW File      : interface/fourvec.h
// Original Author : Scott Stuart Snyder <snyder@bnl.gov> for D0
// Imported to CMSSW by Haryo Sumowidagdo <Suharyo.Sumowidagdo@cern.ch>
//

#ifndef HITFIT_FOURVEC_H
#define HITFIT_FOURVEC_H

#include "CLHEP/Vector/LorentzVector.h"

namespace hitfit {

  // Define the types that we want to use.
  typedef CLHEP::HepLorentzVector Fourvec;

  typedef CLHEP::Hep3Vector Threevec;

  // Adjust the 3-vector part of V (leaving the energy unchanged) so that
  // it has mass MASS.
  void adjust_p_for_mass(Fourvec& v, double mass);

  // Adjust the energy component of V (leaving the 3-vector part unchanged)
  // so that it has mass MASS.
  void adjust_e_for_mass(Fourvec& v, double mass);

  // Rotate V through polar angle THETA.
  void rottheta(Fourvec& v, double theta);

  // Rotate V through a polar angle such that its pseudorapidity changes by ETA.
  void roteta(Fourvec& v, double eta);

  // Conversions between pseudorapidity and polar angle.
  double eta_to_theta(double eta);
  double theta_to_eta(double theta);

  // Get the detector eta (D0-specific).  Needs a Z-vertex.
  double deteta(const Fourvec& v, double zvert);  // XXX

  //  Handle wraparound for a difference in azimuthal angles.
  double phidiff(double phi);

  // Find the distance in R between two four-vectors.
  double delta_r(const Fourvec& a, const Fourvec& b);

}  // namespace hitfit

#endif  // not HITFIT_FOURVEC_H