EMMA experiment

EMMA experiment makes the first attempt in the world to conduct underground a dedicated study of cosmic ray composition. The construction started back in 2006 utilizing unused access tunnels in the Pyhäsalmi mine at the depth of about 75 meters below the ground. Working together with our colleagues from the University of Oulu we have constructed 11 measuring stations spread over the area of about 3600 m2. Measuring stations are equipped with drift chambers from the decommissioned DELPHI experiment at CERN and plastic scintillation detectors that were designed and build in collaboration with the physicists from the Russian Academy of Sciences. The total active area of the drift chambers is approximately 240 m2. The coverage of the scintillators is about 24 m2. Preparations are on the way to extend the instrumented area with 180 m2 of Limited Streamer Tubes previously used by the Kascade Grande experiment in Karlsruhe.

EMMA results are expected to be unique and relevant. Muon groups containing large number of muons were observed by several underground detectors at CERN (L3+Cosmics, DELPHI, CMS), as well as HiRes (USA) and Gran Sasso (MACRO). However, their origin is still the subject of a debate. During the last decade the situation with the muon groups became even more confusing. Two experiments: Pierre Auger Observatory and Yaku-SHAL indicate that there is an excess of muons in the extensive air shows (EAS) compared with their number expected from the most realistic theoretical models. On the other hand such experiments as Ice-Top and EAS-MSU did not find such excess. EMMA has the potential to clarify this discrepancy by yielding new data for the energies about the knee region.