Measurement of the atmospheric muon charge ratio with the OPERA detector

Abstract

The OPERA detector at the Gran Sasso underground laboratory (LNGS) was used to measure the atmospheric muon charge ratio R μ = N μ + /N μ − in the TeV energy region. We analyzed 403069 atmospheric muons corresponding to 113.4 days of livetime during the 2008 CNGS run. We computed separately the muon charge ratio for single and for multiple muon events in order to select different energy regions of the primary cosmic ray spectrum and to test the R μ dependence on the primary composition. The measured R μ values were corrected taking into account the charge-misidentification errors. Data have also been grouped in five bins of the "vertical surface energy" E μ cos θ . A fit to a simplified model of muon production in the atmosphere allowed the determination of the pion and kaon charge ratios weighted by the cosmic ray energy spectrum.

Measurement of the TeV atmospheric muon charge ratio with the complete OPERA data set

“…Details on atmospheric muon event selection, reconstruction and analysis can be found in Refs. [7,9].…”

“…The main physics goal of the experiment is the first observation of neutrino oscillations in direct appearance mode in the ν μ → ν τ channel [4][5][6]. OPERA already reported a first measurement of the atmospheric muon charge ratio at TeV surface energies using the 2008 Run data [7]. Here we present the final results obtained with the complete statistics.…”

“…[7], we used the momentum and charge reconstruction obtained via the Precision Trackers (PT) of the OPERA spectrometers [8]. Layers of vertical drift tubes are arranged in PT stations instrumenting the two identical dipole magnets.…”

Experimental results on the atmospheric muon charge ratio

“…Data were collected with both magnetic field polarities in order to minimize systematic errors due to misalignment. OPERA reported a first measurement of the atmospheric muon charge ratio using the 2008 Run data [7] and the final results using the complete statistics from 2008 up to 2012 [8]. In the latter analysis the two data sets collected with opposite magnet polarities were combined reaching the most accurate measurement to date of R in the TeV energy region.…”

“…Recent results were obtained by the CMS [4], MINOS [5,6] and OPERA [7,8] experiments that measured the muon charge ratio R around vertical surface energy E cos ∼ 1 TeV. MINOS and OPERA are long-baseline neutrino experiments located deep underground, while CMS is a collider experiment located at shallow depth but provided with an intense magnetic field.…”