Cosmic-muon flux and annual modulation in Borexino at 3800 m water-equivalent depth

Abstract

Abstract. We have measured the muon flux at the underground Gran Sasso National Laboratory (3800 m w.e.) to be (3.41 ± 0.01) · 10 −4 m −2 s −1 using four years of Borexino data. A modulation of this signal is observed with a period of (366±3) days and a relative amplitude of (1.29 ± 0.07)%. The measured phase is (179 ± 6) days, corresponding to a maximum on the 28 th of June. Using the most complete atmospheric data models available, muon rate fluctuations are shown to be positively correlated with atmospheric temperature, with an effective coefficient α T = 0.93 ± 0.04. This result represents the most precise study of the muon flux modulation for this site and is in good agreement with expectations.

Results from the first use of low radioactivity argon in a dark matter search

“…The rate of muons crossing both the LSV and the WCV was found to be 380 ± 5 day-1, in good agreement with the expected rate of 370 muon/day extrapolated from the measurement of the muon rate in the Hall C of LNGS performed in Borexino [37].…”

“…The muon flux at the 3800 m.w.e. depth of the LNGS, although reduced from that at the Earth's surface by a factor -106, is of the order of 1.1 muons/(m2-hr) [37]. This corresponds to about 2000 muons per day crossing the WCV, about 380 muons per day crossing the LSV, and about 4 muons per day crossing the LAr TPC.…”

Bulk NaI(Tl) scintillation low energy events selection with the ANAIS-0 module

“…Active plastic scintillator vetoes were installed on top of the ANAIS-0 shielding to reject the residual cosmic muon flux contribution to the background of ANAIS, and also to monitor the muon rate in the laboratory at the shielding position in order to evaluate any possible seasonal variation. A good comprehension of the muon related events in the ANAIS experiment is required because the annual modulation in the muon rate is well known [71][72][73], and it should be discarded as responsible of any modulation observed in the very low energy events rate. This issue has been discussed in the frame of the DAMA/LIBRA experiment [36,37,42,43], and is even more important for the ANAIS experiment because residual muon flux at LSC is about one order of magnitude larger than at Gran Sasso Laboratory, given the smaller rock overburden.…”

Atmospheric muons: experimental aspects

“…The dashed curve is the prediction using the pion-only model Ambrosio et al (1997c). The points correspond (from top to bottom): Ambrosio et al (1997c), Bouchta (1999), Grashorn et al (2010), Selvi (2009), Bellini (2012, Desiati (2011), Andreyev et al (1991, Cutler et al (1981), Sherman (1954), Barrett et al (1954). temperature T eff , defined by the weighted average of temperatures from the surface to the top of the atmosphere, is useful to describe the situation. T eff approximates the atmosphere as an isothermal body, weighting each pressure layer according to its relevance to muon production in atmosphere.…”

“…The dashed curve is the prediction using the pion-only model (Ambrosio et al, 1997c). The points correspond (from top to bottom): Ambrosio et al (1997c), Bouchta (1999), Adamson et al (2010), Selvi (2009), Bellini (2012, Desiati (2011), Andreyev et al (1991, Cutler et al (1981), Sherman (1954), Barrett et al (1954).…”