JugBase/Utilities/Boost.h

0001 // SPDX-License-Identifier: LGPL-3.0-or-later
0002 // Copyright (C) 2022 Wouter Deconinck, Barak Schmookler
0003
0004 #pragma once
0005
0006 #include "Math/Vector4D.h"
0007 using ROOT::Math::PxPyPzEVector;
0008
0009 #include "Math/LorentzRotation.h"
0010 #include "Math/LorentzVector.h"
0011 #include "Math/RotationX.h"
0012 #include "Math/RotationY.h"
0013 #include "Math/Boost.h"
0014
0015 namespace Jug::Base::Boost {
0016
0017   using ROOT::Math::LorentzRotation;
0018
0019   inline LorentzRotation determine_boost(PxPyPzEVector ei, PxPyPzEVector pi) {
0020
0021     using ROOT::Math::RotationX;
0022     using ROOT::Math::RotationY;
0023     using ROOT::Math::Boost;
0024
0025     // Step 1: Find the needed boosts and rotations from the incoming lepton and hadron beams
0026     // (note, this will give you a perfect boost, in principle you will not know the beam momenta exactly and should use an average)
0027
0028     // Define the Boost to make beams back-to-back
0029     const auto cmBoost = (ei + pi).BoostToCM();
0030
0031     const Boost boost_to_cm(-cmBoost);
0032
0033     // This will boost beams from a center of momentum frame back to (nearly) their original energies
0034     const Boost boost_to_headon(cmBoost); // FIXME
0035
0036     // Boost and rotate the incoming beams to find the proper rotations TLorentzVector
0037
0038     // Boost to COM frame
0039     boost_to_cm(pi);
0040     boost_to_cm(ei);
0041     // Rotate to head-on
0042     RotationY rotAboutY(-1.0*atan2(pi.Px(), pi.Pz())); // Rotate to remove x component of beams
0043     RotationX rotAboutX(+1.0*atan2(pi.Py(), pi.Pz())); // Rotate to remove y component of beams
0044
0045     LorentzRotation tf;
0046     tf *= boost_to_cm;
0047     tf *= rotAboutY;
0048     tf *= rotAboutX;
0049     tf *= boost_to_headon;
0050     return tf;
0051   }
0052
0053   inline PxPyPzEVector apply_boost(const LorentzRotation& tf, PxPyPzEVector part) {
0054
0055     // Step 2: Apply boosts and rotations to any particle 4-vector
0056     // (here too, choices will have to be made as to what the 4-vector is for reconstructed particles)
0057
0058     // Boost and rotate particle 4-momenta into the headon frame
0059     tf(part);
0060     return part;
0061   }
0062
0063 } // namespace Jug::Base::Boost