# Observation of seasonal variation of atmospheric multiple-muon events in the NOvA Near Detector

## TL;DR

This study reports a seasonal variation in atmospheric multiple-muon events detected by NOvA, showing an opposite phase to atmospheric temperature changes, with the variation strength increasing with muon multiplicity.

## Contribution

First observation of seasonal variation in multiple-muon events with an opposite phase to atmospheric temperature in the NOvA Near Detector.

## Key findings

- Seasonal variation in multiple-muon event rates observed.
- Variation strength increases with muon multiplicity.
- No dependence on muon zenith angle or spatial separation.

## Abstract

Using two years of data from the NOvA Near Detector at Fermilab, we report a seasonal variation of cosmic ray induced multiple-muon event rates which has an opposite phase to the seasonal variation in the atmospheric temperature. The strength of the seasonal multipl$ increase as a function of the muon multiplicity. However, no significant dependence of the strength of the seasonal variation of the multiple-muon variation is seen as a function of the muon zenith angle, or the spatial or angular separation between the correlated muons.