HadXSUtils.h

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//____________________________________________________________________________
/*!

\namespace  genie::utils::hadxs

\brief      Simple functions and data for computing hadron interaction xsecs

\author     Costas Andreopoulos <constantinos.andreopoulos \at cern.ch>
            University of Liverpool & STFC Rutherford Appleton Laboratory

\created    March 11, 2004

\cpright    Copyright (c) 2003-2020, The GENIE Collaboration
            For the full text of the license visit http://copyright.genie-mc.org            
*/
//____________________________________________________________________________

#ifndef _HADXS_UTILS_H_
#define _HADXS_UTILS_H_

namespace genie {
namespace utils {

namespace hadxs
{
  // The inelastic pion-nucleon cross section used in Rein-Sehgal coherent pi0
  // production xsec: D.Rein and L.M.Sehgal,Nucl.Phys.B223:29-144 (1983).
  // The data used here are coming from CERN-HERA 79-01, 1979, 'Compilation of
  // cross sections I - pi- and pi+ induced reactions'. Also, look at the
  // Fig.3 in Rein-Sehgal's paper.
  // However, the actual values I am using are copied from Hugh Gallagher's
  // NeuGEN inel() function which is adapted here.
  static const int    kInelNDataPoints = 60;
  static const double kInelMinLog10P   = -0.975;
  static const double kIneldLog10P     =  0.05;
  static const double kInelSig[kInelNDataPoints] = {
         1.596,   3.192,   5.692,   5.596,   3.788,   6.528,
        22.931,  43.462,  55.580,  36.761,  19.754,  12.588,
        12.914,  12.500,  13.707,  15.082,  19.671,  16.860,
        21.708,  29.128,  21.752,  22.444,  23.698,  23.847,
        23.067,  25.336,  25.366,  25.273,  24.646,  24.003,
        23.636,  23.615,  23.029,  22.667,  22.434,  21.901,
        21.763,  22.235,  20.177,  21.707,  20.827,  21.102,
        21.028,  21.155,  20.932,  20.577,  20.865,  21.122,
        21.193,  21.081,  20.611,  20.788,  20.591,  20.514,
        20.796,  20.813,  20.425,  20.460,  20.495,  20.530
  };

  // Total pion nucleon cross section data
  // Data from Hugh Gallagher's NeuGEN total() function.
  static const int    kTotNDataPoints = 60;
  static const double kTotMinLog10P   = -0.975;
  static const double kTotdLog10P     =  0.05;
  static const double kTotSig[kTotNDataPoints] = {
         3.252,   6.504,  12.316,  18.314,  22.600,  31.435,
        53.933,  84.872, 102.626,  87.084,  60.234,  39.922,
        32.804,  28.935,  27.952,  29.439,  36.824,  31.814,
        35.152,  50.062,  39.079,  35.741,  37.390,  35.575,
        34.043,  34.363,  34.171,  32.990,  32.110,  31.316,
        30.621,  29.918,  29.134,  28.461,  27.985,  27.208,
        26.749,  27.111,  25.047,  26.357,  25.393,  25.777,
        25.467,  25.305,  25.008,  24.814,  24.662,  24.481,
        24.453,  24.336,  24.099,  24.098,  24.010,  23.908,
        23.992,  24.058,  23.805,  23.808,  23.811,  23.815
  };

  // Previous (2.8) default has been to treat pions as charged for purposes of mass.
  double InelasticPionNucleonXSec (double Epion, bool isChargedPion=true);
  double TotalPionNucleonXSec     (double Epion, bool isChargedPion=true);


  // Pion-Nucleon cross-sections as implemented by C. Berger for re-implementation
  // of the Rein-Sehgal coherent pion production model, and provided to D. Cherdack.
  //
  // C. Berger & L. Sehgal
  // "PCAC and coherent pion production by low energy neutrinos"
  // http://arxiv.org/abs/0812.2653
  namespace berger
  {
    double InelasticPionNucleonXSec (double Epion, bool isChargedPion=true);
    double TotalPionNucleonXSec     (double Epion, bool isChargedPion=true);
    double PionNucleonXSec     (double Epion, bool get_total, bool isChargedPion=true);
    //Pion-Nucleus xsec extrapolated from pion-Carbon data
    int    PionNucleusXSec(double tpi, double ppistar, double t_new, double A, double &tpilow, double &siglow, double &tpihigh, double &sighigh);
                           //Input: the pion kinetic energy,
                           //       the pion CMS momentum,
                           //       the square if the 4-p transfer from the pion to the nucleus, and
                           //       the number of nucleons in teh target nucleus
                           //Also pass pointers to varaibles which store the output:
                           //       the data points (xsec -vs- tpi) above and below the input tpi
                           //       an interpolation algorithm must be used to determine the xsec from this information
  }
}      // hadxs namespace
}      // utils namespace
}      // genie namespace

#endif // _HADXS_UTILS_H_