Measurements of integrated muon intensity at large zenith angles
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EMENTARY PARTICLES AND FIELDS Experiment
Measurements of Integrated Muon Intensity at Large Zenith Angles А. N. Dmitrieva* , R. P. Kokoulin, K. G. Kompaniets, А. А. Petrukhin, O. Saavedra1), D. А. Timashkov, D. V. Chernov, V. V. Shutenko, and I. I. Yashin Moscow Engineering Physics Institute (State University), Kashirskoe sh. 31, Moscow, 115409 Russia Received June 29, 2005; in final form, November 14, 2005
Abstract—Data from the DECOR coordinate detector on the integrated intensity of muons that have a threshold energy of 1.2 to 2 GeV are analyzed over the zenith-angle interval 60◦ −90◦ . Experimental results in these intervals of zenith angles and threshold energies were obtained for the first time. In the interval θ ≤ 80◦ , the integrated intensity at Emin = 1.5 GeV as a function of the cosine of the zenith angle is described by a power-law function characterized by an exponent value of n = 1.884 ± 0.005, which is close to the value obtained in earlier experiments. PACS numbers : 95.85.Ry DOI: 10.1134/S1063778806050097
1. INTRODUCTION Investigations of the angular and the energy dependence of the muon flux at the Earth’s surface provide important information both about muongeneration processes in the atmosphere and about primary cosmic rays. Experimental data on the muon flux are used to normalize and test models of cosmicray propagation through the atmosphere. Measurements of the muon flux at large zenith angles up to 90◦ are especially important since, at such angles, mean energies higher than those in the vertical direction correspond to primary particles. By convention, experiments devoted to studying the muon flux at large zenith angles near the Earth’s surface can be broken down into two groups, that in which the energy threshold is below 1 GeV [1–7] and that in which the energy threshold ranges between 10 GeV and 25 TeV (for an overview, see [8]; see also [9–12]). The regions in which the muon spectra were measured at large zenith angles are displayed in Fig. 1. As can be seen from the figure, experiments have not yet been performed at threshold energies of 1 to 10 GeV and zenith angles in the range 60◦ ≤ θ ≤ 90◦ , so that the muon flux has not been measured in this region. In order to study in detail nearly horizontal muon fluxes in the above energy range, one needs a detector that is able to measure muon fluxes at various energy thresholds with a high angular precision in recording
tracks. The NEVOD–DECOR complex arranged at the Moscow Engineering Physics Institute (MEPI) is a large-scale detector deployed on the Earth’s surface. It enables one to study atmospheric muons over a broad interval of zenith angles up to 90◦ at threshold energies of 1 to 7 GeV. In Fig. 1, the cross-hatched regions cover threshold-energy and zenith-angle values accessible to the coordinate detectors of the NEVOD–DECOR Zenith angle, deg 50
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90 10–1
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101 102 Threshold energy, GeV
Fig. 1. Regions of measurements of muon spectra at large zenith angles: measurements of the integrated intensity that were performed by () W
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