Boost.h

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// SPDX-License-Identifier: LGPL-3.0-or-later
// Copyright (C) 2022 Wouter Deconinck, Barak Schmookler
 
#pragma once
 
#include "Math/Vector4D.h"
using ROOT::Math::PxPyPzEVector;
 
#include "Math/LorentzRotation.h"
#include "Math/LorentzVector.h"
#include "Math/RotationX.h"
#include "Math/RotationY.h"
#include "Math/Boost.h"
 
namespace Jug::Base::Boost {
 
  using ROOT::Math::LorentzRotation;
 
  inline LorentzRotation determine_boost(PxPyPzEVector ei, PxPyPzEVector pi) {
 
    using ROOT::Math::RotationX;
    using ROOT::Math::RotationY;
    using ROOT::Math::Boost;
 
    // Step 1: Find the needed boosts and rotations from the incoming lepton and hadron beams
    // (note, this will give you a perfect boost, in principle you will not know the beam momenta exactly and should use an average)
 
    // Define the Boost to make beams back-to-back
    const auto cmBoost = (ei + pi).BoostToCM();
 
    const Boost boost_to_cm(-cmBoost);
 
    // This will boost beams from a center of momentum frame back to (nearly) their original energies
    const Boost boost_to_headon(cmBoost); // FIXME
 
    // Boost and rotate the incoming beams to find the proper rotations TLorentzVector
 
    // Boost to COM frame
    boost_to_cm(pi);
    boost_to_cm(ei);
    // Rotate to head-on
    RotationY rotAboutY(-1.0*atan2(pi.Px(), pi.Pz())); // Rotate to remove x component of beams
    RotationX rotAboutX(+1.0*atan2(pi.Py(), pi.Pz())); // Rotate to remove y component of beams
 
    LorentzRotation tf;
    tf *= boost_to_cm;
    tf *= rotAboutY;
    tf *= rotAboutX;
    tf *= boost_to_headon;
    return tf;
  }
 
  inline PxPyPzEVector apply_boost(const LorentzRotation& tf, PxPyPzEVector part) {
 
    // Step 2: Apply boosts and rotations to any particle 4-vector
    // (here too, choices will have to be made as to what the 4-vector is for reconstructed particles)
  
    // Boost and rotate particle 4-momenta into the headon frame
    tf(part);
    return part;
  }
 
} // namespace Jug::Base::Boost