Abstract. The SLIM experiment was a large array of nuclear track detectors located at the Chacaltaya high altitude Laboratory (5230 m a.s.l.). The detector was in particular sensitive to intermediate mass magnetic monopoles, with masses 10

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The SLIM experiment at the Chacaltaya high altitude laboratory was sensitive to nuclearites and Q-balls, which could be present in the cosmic radiation as possible Dark Matter components. It was sensitive also to strangelets, i.e. small lumps of Strange Quark Matter predicted at such altitudes by various phenomenological models. The analysis of 427 m 2 of Nuclear Track Detectors exposed for 4.22 years showed no candidate event. New upper limits on the flux of downgoing nuclearites and Q-balls at the 90% C.L. were established. The null result also restricts models for strangelets propagation through the Earth atmosphere.

New calibrations of CR39 and Makrofol nuclear track detectors have been obtained using 158 A GeV P b 82+ and In 49+ ions; a new method for the bulk etch rate determination, using both cone height and base diameter measurements was developed. The CR39 charge resolution based on the etch-pit base area measurement is adequate to identify nuclear fragments in the interval 7 ≤ Z/β ≤ 49. For CR39 the detection threshold is at REL ∼ 50 MeV cm 2 g −1 , corresponding to a nuclear fragment with Z/β ∼ 7. Base cone area distributions for Makrofol foils exposed to P b 82+ ions have shown for the first time all peaks due to nuclear fragments with Z > 50; the distribution of the etched cone heights shows well separated individual peaks for Z/β = 78 ÷ 83 (charge pickup). The Makrofol detection threshold is at REL ∼ 2700 MeV cm 2 g −1 , corresponding to a nuclear fragment with Z/β ∼ 50.