Research options in the Pyhäsalmi Underground Facility

Abstract

The Pyhasalmi Mine is the deepest operational base-metal mine in Europe. The existing caverns in the old mine at levels 95 m – 1080 m can be used for scientific purposes. The new mine extends down to 1440 metres where the mining goes on, probably until the year 2017. It is technically possible to construct very large laboratory caverns at 1400 – 1500 levels (4000 – 4200 m.w.e.), at reasonable cost. The stable bedrock, modern infrastructure, and good traffic conditions all around the year give excellent opportunities for the research of underground physics. The CUPP project (Centre for Underground Physics in Pyhasalmi) aims at establishing an underground research facility in the mine. It is run by the University of Oulu, and it receives funding from the Regional Development Fund of the EU. The first major experiment [1] will measure the multiplicity and the lateral distribution of cosmicray muons. The measured data are used to obtain information on the composition of cosmic rays at the knee region (10 – 10 eV), with the purpose to clarify the origin of cosmic rays and the kink in the spectrum. The experiment consists of large drift chambers used previously at DELPHI, and plastic scintillators as auxiliary underground detectors and surface array. The prototype is under construction at the 210 m level. Smaller experiments have been carried out in the mine. The measurements of the backgrounds, like muon fluxes and rock radioactivity at different depths, will be continued, with the permanent monitoring of the fluxes being the aim. The facility is suitable for neutrino experiments. Low-cost supernova neutrino experiments are under consideration, to be located in the available caverns at the 660 m level. These detectors may be also used for other purposes like monitoring the muon and neutron fluxes. The proposed new laboratory at 1500 m level could host very large experiments that cannot be located elsewhere. Several initiatives are around, one of the most interesting being the LENA (Low Energy Neutrino Astronomy)[2] experiment. It is an international initiative to build a large-volume liquid scintillation detector to observe solar neutrinos, supernova neutrinos, geoneutrinos, and to search for proton decay. The size of the detector would be about 90 metres (length) times 20 metres (diameter) and the mass about 30 ktons. The Pyhasalmi mine is considered as one of the possible locations of the detector. In the next decade, the Pyhasalmi mine might host the far detector for a possible neutrino factory at CERN. The distance is interestingly 2288 km. Other baselines and sources are also possible and provide their own physical goals. Simulations of neutrino oscillations related to long baseline experiments are being done[3].