From a84cfbe584580f08ca0a88f176cb49cdf801665e Mon Sep 17 00:00:00 2001 From: tlatorre Date: Mon, 27 Aug 2018 10:59:31 -0500 Subject: fix how multiple Coulomb scattering is treated Previously I had been assuming that a particle undergoing many small angle Coulomb scatters had a track direction whose polar angle was a Gaussian. However, this was just due to a misunderstanding of the PDG section "Multiple scattering through small angles" in the "Passage of particles through matter" article. In fact, what is described by a Gaussian is the polar angle projected onto a plane. Therefore the distribution of the polar angle is actually: (1/(sqrt(2*pi)*theta0**2))*theta*exp(-theta**2/(2*theta0)) This commit updates the code in scattering.c to correctly calculate the probability that a photon is emitted at a particular angle. I also updated test-likelihood.c to simulate a track correctly. --- src/muon.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/muon.c') diff --git a/src/muon.c b/src/muon.c index 9a539de..7012214 100644 --- a/src/muon.c +++ b/src/muon.c @@ -262,5 +262,5 @@ double get_expected_charge(double x, double T, double T0, double *pos, double *d theta0 = get_scattering_rms(x,p0,beta0,z,rho); /* FIXME: add angular response and scattering/absorption. */ - return 2*omega*2*M_PI*FINE_STRUCTURE_CONSTANT*z*z*(1-(1/(beta*beta*n*n)))*get_probability(beta, cos_theta, theta0)/(sqrt(2*M_PI)*theta0); + return omega*FINE_STRUCTURE_CONSTANT*z*z*(1-(1/(beta*beta*n*n)))*get_probability(beta, cos_theta, theta0); } -- cgit