A 3-Dimensional Calculation of Atmospheric Neutrino Flux

TL;DR

This paper presents a comprehensive 3D Monte Carlo calculation of atmospheric neutrino flux, highlighting the inaccuracies of the 1D collinear approximation and its limited impact on experimental results due to detector smearing.

Contribution

It introduces a detailed 3D flux calculation using FLUKA and compares it to traditional 1D methods, assessing the approximation's impact on neutrino flux predictions.

Findings

1. 3D calculations show different angular distributions than 1D.

2. Experimental smearing reduces differences between models.

3. Collinear approximation does not significantly bias oscillation measurements.

Abstract

An extensive 3-dimensional Monte Carlo calculation of the atmospheric neutrino flux is in progress with the FLUKA Monte Carlo code. The results are compared to those obtained under the 1-dimensional approximation, where secondary particles and decay products are assumed to be collinear to the primary cosmic ray, as usually done in most of the already existing flux calculations. It is shown that the collinear approximation gives rise to a wrong angular distribution of neutrinos, essentially in the Sub-GeV region. However, the angular smearing introduced by the experimental inability of detecting recoils in neutrino interactions with nuclei is large enough to wash out, in practice, most of the differences between 3-dimensional and 1-dimensional flux calculations. Therefore, the use of the collinear approximation should have not introduced a significant bias in the determination of the flavor oscillation parameters in current experiments.