We present evidence for the rst observation of electromagnetically bound π ± K ∓pairs (πK-atoms) with the DIRAC experiment at the CERN-PS. The πK-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the π ± and K ∓mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173 ± 54 πK-atoms. The mean life of πK-atoms is related to the s-wave πKscattering lengths, the measurement of which is the goal of the experiment. From these rst data we derive a lower limit for the mean life of 0.8 fs at 90% condence level.

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The results of a search for hydrogen-like atoms consisting of π ∓ K ± mesons are presented. Evidence for π K atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic π K pairs from their breakup in the same target (178 ± 49) as well as in terms of produced π K atoms (653 ± 42). Using these results, the analysis yields a first value for the π K atom lifetime of τ = (2.5 +3.0 −1.8 ) fs and a first measurement of the S-wave isospin-odd π K scattering length |a − 0 | = 1 3 |a 1/2 − a 3/2 | = (0.11 +0.09 −0.04 )M −1 π (a I for isospin I).

An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6  MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18)  s has been deduced for Z=120 from the measured x-ray multiplicity.

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