Performance of tracking stations of the underground cosmic-ray detector array EMMA

The new cosmic-ray experiment EMMA operates at the depth of 75 m (50 GeV cutoff energy for vertical muons; 210 m.w.e.) in the Pyhäsalmi mine, Finland. The underground infrastructure consists of a network of eleven stations equipped with multi-layer, position-sensitive detectors. EMMA is designed for cosmic-ray composition studies around the energy range of the knee, i.e., for primary particles with energies between 1 and 10 PeV. In order to yield significant new results EMMA must be able to record data in the full configuration for about three years. The key to the success of the experiment is the performance of its tracking stations. In this paper we describe the layout of EMMA and construction of the two main detector types used for muon tracking: the high-resolution drift chambers and fast scintillation detector arrays. We also show the measured tracking efficiencies, position and angular resolutions, and sensitivity of drift chambers to the air pressure. The measured angular muon distributions are well reproduced by CORSIKA simulations folded with the known density distribution of the overburden. The single muon flux at the depth of 210 m.w.e. is (1.29  ±  0.06) m−2s−1. This value was determined from the reconstructed tracks registered by a six-layer array of position-sensitive drift chambers.