Flux Modulations seen by the Muon Veto of the GERDA Experiment

TL;DR

The GERDA muon veto system detects seasonal and beam-related muon flux modulations, with measured rates aligning with other deep underground experiments, revealing secondary effects from neutrino beams and atmospheric temperature changes.

Contribution

This study provides the first detailed measurement of muon flux modulations in the GERDA experiment, identifying secondary effects from neutrino beams and atmospheric temperature variations.

Findings

Muon flux shows seasonal modulation.

Secondary muons from CNGS neutrino beam contribute 2.2%.

Atmospheric temperature causes 1.4% modulation.

Abstract

The GERDA experiment at LNGS of INFN is equipped with an active muon veto. The main part of the system is a water Cherenkov veto with 66~PMTs in the water tank surrounding the GERDA cryostat. The muon flux recorded by this veto shows a seasonal modulation. Two effects have been identified which are caused by secondary muons from the CNGS neutrino beam (2.2 %) and a temperature modulation of the atmosphere (1.4 %). A mean cosmic muon rate of $I^0_{\mu} = (3.477 \pm 0.002_{\textrm{stat}} \pm 0.067_{\textrm{sys}}) \times 10^{-4}$/(s$\cdot$m$^2$) was found in good agreement with other experiments at LNGS at a depth of 3500~meter water equivalent.