AttenuationTool.h

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/*
 * AttenuationTool.h
 *
 *  Tool to calculate the attenuation length for direct and reflectec light in a scintillating fibre.
 *
 *  Created on 03 Mar 2020
 *      Author: Valerio Formato (based on code by Junjing Wang)
 */

/*
 * Some definitions:
 *  - ShortAttenuationLength: Distance along the fibre to divide the light amplitude by a factor e : short component
 *  - LongAttenuationLength: Distance along the fibre to divide the light amplitude by a factor e : long component
 *  - FractionShort: Fraction of short attenuation at SiPM
 */

#ifndef HERD_ATTENUATIONTOOL_H_
#define HERD_ATTENUATIONTOOL_H_

#include <limits>
#include <math.h>
#include <utility>

// this in c++17 will become
// namespace Herd::FitDigitizationTools {
namespace Herd {
namespace FitDigitizationTools {

namespace AttenuationTool {

double m_matLength = std::numeric_limits<double>::min();

namespace {
constexpr double m_shortAttenuationLength = 20; //"Attenuation length of the light along the fibre: short component"
constexpr double m_longAttenuationLength = 470; //"Attenuation length of the light along the fibre: long component"
constexpr double m_fractionShort = 0.18;        //"Fraction of short attenuation at SiPM"
constexpr double m_reflectionCoefficient = 0.7; // "Reflection coefficient of the fibre mirrored side, from 0 to 1"

inline double calcAtt(const double l) {
  return (m_fractionShort * exp(-l / m_shortAttenuationLength) +
          (1 - m_fractionShort) * exp(-l / m_longAttenuationLength));
}

// here we assume SiPM array is located in +m_matLength/2.
// and the coordinates system is local coordinates
inline double calcAttDir(const double y) {
  double Len = m_matLength / 2. - y;
  return calcAtt(Len);
}

inline double calcAttRef(const double y) {
  double Len_dir = y - (-m_matLength / 2.);
  return calcAtt(Len_dir) * m_reflectionCoefficient * calcAtt(m_matLength);
}
} // namespace

std::pair<double, double> attenuation(const double hitYPosition) {
  return std::make_pair(calcAttDir(hitYPosition), calcAttRef(hitYPosition));
}

} // namespace AttenuationTool
} // namespace FitDigitizationTools
} // namespace Herd
#endif