DeltaSlopeZoverS.h

/**************************************************************************
 * basf2 (Belle II Analysis Software Framework)                           *
 * Author: The Belle II Collaboration                                     *
 *                                                                        *
 * See git log for contributors and copyright holders.                    *
 * This file is licensed under LGPL-3.0, see LICENSE.md.                  *
 **************************************************************************/
 
#pragma once
 
#include <tracking/trackFindingVXD/filterMap/filterFramework/SelectionVariable.h>
#include <tracking/trackFindingVXD/filterMap/threeHitVariables/CircleCenterXY.h>
#include <tracking/trackFindingVXD/filterMap/threeHitVariables/CircleRadius.h>
#include <tracking/trackFindingVXD/filterMap/twoHitVariables/CosDirectionXY.h>
#include <framework/geometry/B2Vector3.h>
#include <cmath>
 
#define DELTASLOPEZOVERS_NAME DeltaSlopeZoverS
 
namespace Belle2 {

  template <typename PointType >
  class DELTASLOPEZOVERS_NAME : public SelectionVariable< PointType, 3, double > {
  public:

    PUT_NAME_FUNCTION(DELTASLOPEZOVERS_NAME);

    static double value(const PointType& outerHit, const PointType& centerHit, const PointType& innerHit)
    {
 
      B2Vector3D cCenter = CircleCenterXY<PointType>::value(outerHit, centerHit, innerHit);
      double circleRadius = CircleRadius<PointType>::calcAvgDistanceXY(outerHit, centerHit, innerHit, cCenter);
      B2Vector3D vecOuter2cC((outerHit.X() - cCenter.X()),
                             (outerHit.Y() - cCenter.Y()),
                             (outerHit.Z() - cCenter.Z()));
      B2Vector3D vecCenter2cC((centerHit.X() - cCenter.X()),
                              (centerHit.Y() - cCenter.Y()),
                              (centerHit.Z() - cCenter.Z()));
      B2Vector3D vecInner2cC((innerHit.X() - cCenter.X()),
                             (innerHit.Y() - cCenter.Y()),
                             (innerHit.Z() - cCenter.Z()));
 
      // WARNING: this is only approximately S (valid in the limit of small angles) but might be OK for this use!!!
      //  want to replace id with 2*sin ( alfa ) * circleRadius
      double alfaOCr = acos(CosDirectionXY<B2Vector3D>::value(vecOuter2cC, vecCenter2cC)) * circleRadius ;
      double alfaCIr = acos(CosDirectionXY<B2Vector3D>::value(vecCenter2cC, vecInner2cC)) * circleRadius ;
 
      // Beware of z>r!:
      double result = (asin(double(outerHit.Z() - centerHit.Z()) / alfaOCr)) - asin(double(centerHit.Z() - innerHit.Z()) / alfaCIr);
 
      return (std::isnan(result) || std::isinf(result)) ? double(0) : result;
    }
  };

}