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001 #include "AtlfastAlgs/BremBinData.h"
002 
003 namespace Atlfast 
004 {
005   /** @brief Class to hold smearing matrix data.
006    *
007    * The data is provided through the constructor
008    * in the format found in the flat file and the
009    * correlation matrix corresponding to the bin
010    * can be calculated and returned via public methods.
011    */
012 
013   //-----------------------------------------------
014   // PUBLIC - Constructor
015   //-----------------------------------------------
016   BremBinData::BremBinData( BinID& id,
017                             vector< ParameterResolutions* > startPoints,
018                             vector< ParameterResolutions* > slopes,
019                             vector< ParameterResolutions* > sigmas,
020                             int randSeed
021                           ) :
022                 m_id(id),
023                 m_startPoints(startPoints),    
024                 m_slopes(slopes),
025                 m_sigmas(sigmas)
026   {
027     m_randomEngine = new HepJamesRandom(randSeed);
028   }    
029   
030   
031   //-----------------------------------------------
032   // PUBLIC - Destructor
033   //-----------------------------------------------
034   BremBinData::~BremBinData()
035   {
036     for (size_t i = 0; i < m_startPoints.size(); i++)
037       delete m_startPoints[i];
038     for (size_t i = 0; i < m_slopes.size(); i++)
039       delete m_slopes[i];
040     for (size_t i = 0; i < m_sigmas.size(); i++)
041       delete m_sigmas[i];
042     delete m_randomEngine;
043   }  
044   
045   
046   //--------------------------------------------------------------------
047   // PUBLIC - TrackTrajectory getBremTrack
048   // returns smeared track parameters
049   //--------------------------------------------------------------------
050   TrackTrajectory BremBinData::getBremTrack( const TrackTrajectory& traj ) const
051   {
052     // data necessary to generate bremsstrahlung corrections
053     double x0[3], lambda[3], sigma[3];
054     for ( int i = 0; i < 3; i++ )
055     {
056       x0[i]     = std::abs( m_startPoints[i]->resolution(traj) );
057       lambda[i] = std::abs( m_slopes[i]->resolution(traj) );
058       sigma[i]  = m_sigmas[i]->resolution(traj);
059     }  
060     // range of power-function distribution [x0, xMax]
061     // for q/pT, 500MeV is the offline reconstruction cut
062     double xMax[3] = { 90 * sigma[0], 90 * sigma[1], 1.0 / (0.5*GeV) };
063 
064     double charge = double( traj.signOfCharge() );
065     // bremsstrahlung results in both pos and neg tails, depending on charge and parameter
066     double sign[3] = { -charge, charge, charge };
067      
068     double random[3];
069     random[0] = m_randomEngine->flat();
070     random[1] = random[0];  // introduce correlation (d0,phi0) 
071     random[2] = random[0];  // introduce correlation (d0,q/pT), (phi0,q/pT)
072 
073     double var[3];
074     for ( int i = 0; i < 3; i++ )
075     {
076       double denom = 1 - random[i] * ( 1 - std::pow( x0[i] / xMax[i], lambda[i] - 1 ) );
077       denom = std::pow( denom, 1.0 / ( lambda[i] - 1 ) );
078       var[i] = sign[i] * x0[i] / denom;   // normalised power-series distribution
079     }  
080    
081     // create output TrackTrajectory object: longitudinal parameters remain unchanged
082     // (small effects taken into account in double-Gaussian smearing in ElectronMatrixManager)
083     TrackParameters trkParam = traj.parameters();
084 
085     double impactParameter = var[0];
086     double zPerigee        = trkParam.zPerigee();
087     Phi phi                = var[1];
088     double cotTheta        = trkParam.cotTheta();
089     double invPtCharge     = var[2];
090 
091     double curvature = traj.curvature(); 
092     double pT = std::abs( 1. / invPtCharge );
093     Hep3Vector vec;
094     vec.setX( pT * std::cos(phi) );
095     vec.setY( pT * std::sin(phi) );
096     vec.setZ( pT * cotTheta );
097     
098     // Convert results to object
099     TrackTrajectory newTrajectory( TrackParameters( vec.pseudoRapidity(), 
100                                                     phi, pT, impactParameter,
101                                                     zPerigee, cotTheta,
102                                                     invPtCharge ), 
103                                    traj.startPoint(),
104                                    curvature );
105     return newTrajectory;
106   }
107   
108 } //namespace bracket
109
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