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BreitWigner.h

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#ifndef PhysicsTools_Utilities_ZMuMu_BreitWigner_h
#define PhysicsTools_Utilities_ZMuMu_BreitWigner_h
#include "PhysicsTools/Utilities/interface/Parameter.h"
#include <boost/shared_ptr.hpp>
#include <cmath>

namespace funct {
  const double twoOverPi = 2./M_PI;
  
  struct BreitWigner {
    BreitWigner(const Parameter& m, const Parameter& g):
      mass(m.ptr()), width(g.ptr()) { }
    BreitWigner(boost::shared_ptr<double> m, boost::shared_ptr<double> g): 
      mass(m), width(g) {}
    BreitWigner(double m, double g): 
      mass(new double(m)), width(new double(g)) {}
    double operator()(double x) const {
      double m2 = *mass * (*mass); 
      double g2 = *width * (*width);
      double g2OverM2 = g2/m2;
      double s = x*x;
      double deltaS = s - m2;
      double lineShape = 0;
      if (fabs(deltaS/m2)<16) {
        double prop = deltaS*deltaS + s*s*g2OverM2;
        lineShape = twoOverPi * (*width) * s/prop;
      }
      return lineShape;
    }
    boost::shared_ptr<double> mass, width;
  };

}

#endif

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