Characterization of the varying flux of atmospheric muons measured with the Large Volume Detector for 24 years

Abstract

The Large Volume Detector (LVD), hosted in the INFN Laboratori Nazionali del Gran Sasso, is triggered by atmospheric muons at a rate of ∼ 0.1 Hz. The data collected over almost a quarter of century are used to study the muon intensity underground. The 50-million muon series, the longest ever exploited by an underground instrument, allows for the accurate longterm monitoring of the muon intensity underground. This is relevant as a study of the background in the Gran Sasso Laboratory, which hosts a variety of long-duration, low-background detectors. We describe the procedure to select muon-like events as well as the method used to compute the exposure. We report the value of the average muon flux measured from 1994 to 2017: I 0 µ = 3.35 ± 0.0005 stat ± 0.03 sys · 10 −4 m −2 s −1 . We show that the intensity is modulated around this average value due to temperature variations in the stratosphere. We quantify such a correlation by using temperature data from the European Center for Medium-range Weather Forecasts:we find an effective temperature coefficient α T = 0.94 ± 0.01 stat ± 0.01 sys , in agreement with other measurements at the same depth. We scrutinise the spectral content of the time series of the muon intensity by means of the Lomb-Scargle analysis. This yields the evidence of a 1-year periodicity, as well as the indication of others, both shorter and longer, suggesting that the series is not a pure sinusoidal wave. Consequently, and for the first time, we characterise the observed modulation in terms of amplitude and position of maximum and minimum on a year-by-year basis.When high-energy cosmic rays enter the atmosphere, they produce a large number of secondary particles, in a series of successive interactions with atmospheric nuclei, called extensive air showers (EAS). EAS particles produced in the upper atmosphere propagate longitudinally through the atmosphere: at ground level, the most abundant among them are muons, which are produced in the decay of short-lived mesons, namely charged pions and kaons. Thanks to their small energy loss, small cross-section and long lifetime, higher energy (above ∼ 1 TeV) muons can penetrate deeply underground. Thus, large acceptance instruments located underground, originally designed for, e.g., neutrino or proton decay studies, all have excellent capabilities for the study of high energy atmospheric muons.The Large Volume Detector (LVD) [1], located in the INFN Laboratori Nazionali del Gran Sasso (LNGS) at a minimal depth of 3100 m w.e., is one of such detectors. Despite the large amount of overhead rock, LVD is triggered by atmospheric muons at a rate of ∼ 0.1 Hz.Underground muons are exploited for a variety of physics analyses, most notably for the measurement of the flux and the composition of Galactic cosmic rays (see e.g., [2] and [3]) as well as for the search for anisotropies (see [4], [5] and [6]). Also, the study of muons underground allows for the measurement of the high-energy part (above 1 TeV) of the sea-level muon energy spectrum through the depth-intens...

Measurement of the cosmic muon annual and diurnal flux variation with the COSINE-100 detector

“…Here, the LNGS measurement is a weighted average of various Gran Sasso experiments taken from ref. [19]. The red solid line show predictions based on a meson production models for an atmospheric kaon/pion ratio of 0.149 [15,16].…”

“…High energy muons can penetrate to deep underground laboratories if their energy is above a threshold value, E thr , that depends on the depth level; lower energy muons are absorbed in the rock overburden. Numerous underground detectors have observed an annual modulation of the rates for high energy muons [16], including MACRO [17], LVD [18,19], BOREXINO [20,21], GERDA [22], OPERA [23], IceCube [24], MINOS [25,26], Double CHOOZ [27], and Daya Bay [28]. There was only one reported search for daily variations of muon rates in an underground laboratory by the MACRO experiment in Gran Sasso (LNGS) with a modulation amplitude ¡ 0.1% at the limit of detector statistics [29].…”

“…Various measurements from different experiments are listed: MINOS[26], Daya Bay[28], IceCube[24], AMANDA[48], and LNGS together with our Y2L measurement (blue filled circle). Here, the LNGS measurement is a weighted average of various Gran Sasso experiments taken from ref [19]…”

Challenges and Opportunities for Predicting Muons in Underground and Underwater Labs Using MUTE

“…The latter have had their depth values fitted to lie on the daemonflux curve, giving the laboratory's equivalent vertical depth. Experimental data is shown for WIPP [4], Y2L [5], Soudan [6], KamLAND [7], Boulby [8], SUPL [9], LNGS [10], LSM [11], SURF [12], SNOLAB [13], and Jinping [14]. For comparison, the curve from the parametric formula from [15] is also shown.…”

Science in Underground Laboratories and DULIA-Bio

“…This effect could induce a seasonal dependence of the atmospheric muon-induced backgrounds in DULs. A comprehensive study of the atmospheric muon flux and temperature correlation has been carried out by the LVD collaboration from data taken from 1994 to 2017 [2]. The comparison of measurements of the seasonal effect induced by atmospheric muons in DULs located in the Northern and Southern hemisphere is crucial, as an example, in the evaluation of the expected annual modulation of dark matter particle interaction rate, which is a model-independent signature of dark matter.…”