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Register a new userMeasurement of the atmospheric muon charge ratio with the OPERA detector
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The OPERA detector at the Gran Sasso underground laboratory (LNGS) was used to measure the atmospheric muon charge ratio 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 charge ratio dependence on the primary composition. The measured charge ratio values were corrected taking into account the charge-misidentification errors. Data have also been grouped in five bins of the vertical surface energy. 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.
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The OPERA detector, designed to search for $ u_{mu} to u_{tau}$ oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. For the analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio $R_{mu} equiv N_{mu^+}/N_{mu^-}$ was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1-20 TeV investigated by OPERA, $R_{mu}$ is well described by a parametric model including only pion and kaon contributions to the muon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to $200$ TeV/nucleon primary energy.
This paper describes a new measurement of the flux ratio of positive and negative muons from cosmic-ray interactions in the atmosphere, using data collected by the CMS detector at ground level and in the underground experimental cavern. The excellent performance of the CMS detector allowed detection of muons in the momentum range from 3 GeV to 1 TeV. For muon momenta below 100 GeV the flux ratio is measured to be a constant $1.2766 pm 0.0032(stat) pm 0.0032(syst)$, the most precise measurement to date. At higher momenta an increase in the charge asymmetry is observed, in agreement with models of muon production in cosmic-ray showers and compatible with previous measurements by deep-underground experiments.
The charge ratio ${k equiv mu^+/mu^-}$ for atmospheric muons has been measured using Large Volume Detector (LVD) in the INFN Gran Sasso National Laboratory, Italy (minimal depth is 3000 m w.e.). To reach this depth muons should have the energy at the sea level greater than 1.3 TeV. The muon charge ratio was defined using the number of the decays of stopping positive muons in the LVD iron structure and the decays of positive and negative muons in scintillator. We have obtained the value of the muon charge ratio ${k}$ ${= 1.26 pm 0.04(stat) pm 0.11(sys)}$.
The charge ratio, $R_mu = N_{mu^+}/N_{mu^-}$, for cosmogenic multiple-muon events observed at an under- ground depth of 2070 mwe has been measured using the magnetized MINOS Far Detector. The multiple-muon events, recorded nearly continuously from August 2003 until April 2012, comprise two independent data sets imaged with opposite magnetic field polarities, the comparison of which allows the systematic uncertainties of the measurement to be minimized. The multiple-muon charge ratio is determined to be $R_mu = 1.104 pm 0.006 {rm ,(stat.)} ^{+0.009}_{-0.010} {rm ,(syst.)} $. This measurement complements previous determinations of single-muon and multiple-muon charge ratios at underground sites and serves to constrain models of cosmic ray interactions at TeV energies.
The OPERA experiment discovered muon neutrino into tau neutrino oscillations in appearance mode, detecting tau leptons by means of nuclear emulsion films. The apparatus was also endowed with electronic detectors with tracking capability, such as scintillator strips and resistive plate chambers. Because of its location, in the underground Gran Sasso laboratory, under 3800 m.w.e., the OPERA detector has also been used as an observatory for TeV muons produced by cosmic rays in the atmosphere. In this paper the measurement of the single muon flux modulation and of its correlation with the seasonal variation of the atmospheric temperature are reported.
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