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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.

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).

Differential evolution (DE) is an efficient algorithm to solve global optimization problems. It has a simple internal structure and uses a few control parameters. In this paper we incorporate crossover based on adaptive correlation matrix into Asynchronous differential evolution (ADE). Thanks to the proposed crossover the novel algorithm automatically adapts to the landscape of the optimized objective function. Combined with an adaptive scheme for the mutation scale factor and an automatic inflation of the population size this results in quasi parameter-free algorithm from the user's point of view. The performance of the Asynchronous differential evolution with adaptive correlation matrix is reported on the set of BBOB-2012 benchmark functions.

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