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econte |
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#include "Alignment/TwoBodyDecay/interface/TwoBodyDecayLinearizationPointFinder.h"
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#include "DataFormats/CLHEP/interface/AlgebraicObjects.h"
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#include "Alignment/TwoBodyDecay/interface/TwoBodyDecayModel.h"
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const TwoBodyDecayParameters
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TwoBodyDecayLinearizationPointFinder::getLinearizationPoint( const std::vector< RefCountedLinearizedTrackState > & tracks,
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const double primaryMass,
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const double secondaryMass ) const
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{
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GlobalPoint linPoint = tracks[0]->linearizationPoint();
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PerigeeLinearizedTrackState* linTrack1 = dynamic_cast<PerigeeLinearizedTrackState*>( tracks[0].get() );
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GlobalVector firstMomentum = linTrack1->predictedState().momentum();
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PerigeeLinearizedTrackState* linTrack2 = dynamic_cast<PerigeeLinearizedTrackState*>( tracks[1].get() );
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GlobalVector secondMomentum = linTrack2->predictedState().momentum();
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AlgebraicVector secondaryMomentum1( 3 );
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secondaryMomentum1[0] = firstMomentum.x();
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secondaryMomentum1[1] = firstMomentum.y();
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secondaryMomentum1[2] = firstMomentum.z();
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AlgebraicVector secondaryMomentum2( 3 );
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secondaryMomentum2[0] = secondMomentum.x();
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secondaryMomentum2[1] = secondMomentum.y();
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secondaryMomentum2[2] = secondMomentum.z();
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AlgebraicVector primaryMomentum = secondaryMomentum1 + secondaryMomentum2;
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TwoBodyDecayModel decayModel( primaryMass, secondaryMass );
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AlgebraicMatrix rotMat = decayModel.rotationMatrix( primaryMomentum[0], primaryMomentum[1], primaryMomentum[2] );
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AlgebraicMatrix invRotMat = rotMat.T();
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double p = primaryMomentum.norm();
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double pSquared = p*p;
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double gamma = sqrt( pSquared + primaryMass*primaryMass )/primaryMass;
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double betaGamma = p/primaryMass;
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AlgebraicSymMatrix lorentzTransformation( 4, 1 );
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lorentzTransformation[0][0] = gamma;
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lorentzTransformation[3][3] = gamma;
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lorentzTransformation[0][3] = -betaGamma;
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double p1 = secondaryMomentum1.norm();
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AlgebraicVector boostedLorentzMomentum1( 4 );
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boostedLorentzMomentum1[0] = sqrt( p1*p1 + secondaryMass*secondaryMass );
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boostedLorentzMomentum1.sub( 2, invRotMat*secondaryMomentum1 );
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AlgebraicVector restFrameLorentzMomentum1 = lorentzTransformation*boostedLorentzMomentum1;
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AlgebraicVector restFrameMomentum1 = restFrameLorentzMomentum1.sub( 2, 4 );
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double perp1 = sqrt( restFrameMomentum1[0]*restFrameMomentum1[0] + restFrameMomentum1[1]*restFrameMomentum1[1] );
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double theta1 = atan2( perp1, restFrameMomentum1[2] );
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double phi1 = atan2( restFrameMomentum1[1], restFrameMomentum1[0] );
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double p2 = secondaryMomentum2.norm();
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AlgebraicVector boostedLorentzMomentum2( 4 );
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boostedLorentzMomentum2[0] = sqrt( p2*p2 + secondaryMass*secondaryMass );
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boostedLorentzMomentum2.sub( 2, invRotMat*secondaryMomentum2 );
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AlgebraicVector restFrameLorentzMomentum2 = lorentzTransformation*boostedLorentzMomentum2;
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AlgebraicVector restFrameMomentum2 = restFrameLorentzMomentum2.sub( 2, 4 );
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double perp2 = sqrt( restFrameMomentum2[0]*restFrameMomentum2[0] + restFrameMomentum2[1]*restFrameMomentum2[1] );
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double theta2 = atan2( perp2, restFrameMomentum2[2] );
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double phi2 = atan2( restFrameMomentum2[1], restFrameMomentum2[0] );
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double pi = 3.141592654;
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double relSign = -1.;
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if ( phi1 < 0 ) phi1 += 2*pi;
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if ( phi2 < 0 ) phi2 += 2*pi;
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if ( phi1 > phi2 ) relSign = 1.;
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double momentumSquared1 = secondaryMomentum1.normsq();
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double energy1 = sqrt( secondaryMass*secondaryMass + momentumSquared1 );
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double momentumSquared2 = secondaryMomentum2.normsq();
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double energy2 = sqrt( secondaryMass*secondaryMass + momentumSquared2 );
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double sumMomentaSquared = ( secondaryMomentum1 + secondaryMomentum2 ).normsq();
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double sumEnergiesSquared = ( energy1 + energy2 )*( energy1 + energy2 );
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double estimatedPrimaryMass = sqrt( sumEnergiesSquared - sumMomentaSquared );
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AlgebraicVector linParam( TwoBodyDecayParameters::dimension, 0 );
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linParam[TwoBodyDecayParameters::x] = linPoint.x();
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linParam[TwoBodyDecayParameters::y] = linPoint.y();
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linParam[TwoBodyDecayParameters::z] = linPoint.z();
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linParam[TwoBodyDecayParameters::px] = primaryMomentum[0];
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linParam[TwoBodyDecayParameters::py] = primaryMomentum[1];
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linParam[TwoBodyDecayParameters::pz] = primaryMomentum[2];
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linParam[TwoBodyDecayParameters::theta] = 0.5*( theta1 - theta2 + pi ) ;
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linParam[TwoBodyDecayParameters::phi] = 0.5*( phi1 + phi2 + relSign*pi );
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linParam[TwoBodyDecayParameters::mass] = estimatedPrimaryMass;
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return TwoBodyDecayParameters( linParam );
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}
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