Fine structure in the energy spectrum of cosmic ray protons at 50 GeV?

The recently published precise spectrum of cosmic ray protons from the Alph a Magnetic Spectrometer has been examined in some detail from the standpoin t of a search for deviations from a smooth, simple, power law. We find a si gnificant excess (similar or equal to 10% over similar to 0.3 interval in l og E) centered on 50 GeV in the published data. It is possible that the 'un folding technique' adopted by the experimenters causes an ova estimate of t he excess but it is difficult to reduce it much below about (5 +/- 2)%. We have examined other recent data, too, There is also evidence here, for a n excess in the same energy region, although of only (1.6 +/- 0.9)%. A valu e of (3 +/- 1.5)% would be consistent with all the data. There are hints of similar excesses for heavier nuclei and electrons. Possible explanations are put forward for an excess, should it prove to be genuine. (C) 2000 Elsevier Science B.V, All rights reserved.