EMMA – an underground cosmic-ray experiment

A new cosmic-ray experiment is under construction in the Pyhäsalmi mine, Finland. It aims to study the (mass) composition of cosmic rays at and above the knee region. The array, called EMMA (Experiment with MultiMuon Array), will cover approximately 130 m 2 of detector area at a depth of 75 metres (~210 mwe). It is able to locate shower cores in an area of approximately 400 m 2 with an accuracy better than 6 metres. The array detects underground muons and the muon multiplicity, their lateral distribution and the arrival direction of the air shower can be determined. First scientific measurements can be started during the spring 2009 with a partial-size array. The full-size array is expected to be ready by autumn 2010. The full-size array consist of two type of detectors: drift chambers and plastic scintillation detectors. Besides the composition study, it is also expected that the array contributes on the study of high-multiplicity muon bundles that were observed at the cosmic-ray experiments at the LEP detectors.