update theta0 calculation to use the radiation length in light water

Previously I was using the radiation length in light water but scaling it by
the density of heavy water, which isn't correct. Since the radiation length in
heavy and light water is almost identical, we just use the radiation length in
light water.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/pdg.c b/src/pdg.c
index 780fbc8..a3eb2d5 100644
--- a/src/pdg.c
+++ b/src/pdg.c
@@ -1,7 +1,8 @@
 #include "pdg.h"
 #include "math.h"
+#include "sno.h"
 
-double get_scattering_rms(double x, double p, double beta, double z, double rho)
+double get_scattering_rms(double x, double p, double beta, double z)
 {
     /* Returns the RMS width of the scattering angle for a particle deflected
      * by many small-angle scatters after a distance `x`. `p` is the momentum
@@ -22,5 +23,5 @@ double get_scattering_rms(double x, double p, double beta, double z, double rho)
      * See Equation 33.15 in
      * http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf. */
     if (x == 0.0) return 0.0;
-    return (13.6/(beta*p))*z*sqrt(x*rho/RADIATION_LENGTH)*(1+0.038*log((x*z*z)/(RADIATION_LENGTH*beta*beta/rho)));
+    return (13.6/(beta*p))*z*sqrt(x*WATER_DENSITY/RADIATION_LENGTH)*(1+0.038*log((x*z*z)/(RADIATION_LENGTH*beta*beta/WATER_DENSITY)));
 }