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 observation of the [Formula: see text] structure in [Formula: see text] decays produced in [Formula: see text] collisions at [Formula: see text] TeV is reported with a statistical significance greater than 5 standard deviations. A fit to the [Formula: see text] mass spectrum is performed assuming the presence of a Breit–Wigner resonance. The fit yields a signal of [Formula: see text] resonance events, and resonance mass and width of [Formula: see text] and [Formula: see text], respectively. The parameters of this resonance-like structure are consistent with values reported from an earlier CDF analysis.

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.