diff options
| -rw-r--r-- | src/muon.c | 26 |
1 files changed, 14 insertions, 12 deletions
@@ -95,15 +95,20 @@ void muon_get_position_distribution_parameters(double T0, double *a, double *b) * * f(x) = x**(a-1)*exp(-x/b)/(Gamma(a)*b**a) * - * I determined the b parameter by simulating high energy muons using - * RAT-PAC and determined that it's roughly equal to the radiation length. - * To calculate the a parameter we use the formula from the PDG, i.e. + * I determined a and b by simulating high energy muons using + * RAT-PAC and fitting the histogram of the position of all photons as a + * function of the distance along the track length. * - * tmax = (a-1)/b = ln(E/E_C) - 0.5 + * Note: Unlike the case of a shower produced by an electron, the + * distribution of photons from high energy muons does not seem to follow a + * gamma distribution very well. In addition, the numbers I use here are + * really approximate. The b parameter was obtained by a single degree + * polynomial fit because it looked pretty good, but for the a parameter, I + * couldn't find any functional form that would describe it well as a + * function of energy and so I decided to just approximate it by a + * constant. * - * Therefore, we calculate a as: - * - * a = tmax*b+1. + * FIXME: Should update this in the future. * * `T` should be in units of MeV. * @@ -116,11 +121,8 @@ void muon_get_position_distribution_parameters(double T0, double *a, double *b) * See http://pdg.lbl.gov/2014/reviews/rpp2014-rev-passage-particles-matter.pdf. * * FIXME: Double check that this is correct for muons. */ - double tmax; - - *b = RADIATION_LENGTH; - tmax = log(T0/MUON_CRITICAL_ENERGY_D2O) - 0.5; - *a = fmax(1.1,tmax*(*b)/RADIATION_LENGTH + 1); + *b = -7.8 + 0.118928*T0; + *a = 1.5; } double muon_get_angular_distribution_alpha(double T0) |