a Search for Fractionally Charged Particles.

An ion-source and a charge spectrometer have been built which make it possible to search in solid stable matter for particles with non-integral charge. The ion -source uses a beam of magnetically analyzed 30 keV Ar('+) ions to sputter the sample in an ultra high vacuum environment. The charge spectrometer comprises a 3 MV Pelletron tandem accelerator followed by a 0.2% resolution electrostatic analysis system and a (DELTA)E-E detector system. The entire apparatus has been constructed to be independent of mass over a mass range of 0.2 GeV/c('2) to 250 GeV/c('2). It is assumed that the fractionally charged particle is able to bind an electron. A search has been carried out in samples of niobium and tungsten for fractionally charged particles (FCP) with fractional charge modulo 1/3. In particular, we have looked for Z = N + 1/3 ; N = 0,1... and Z = N + 2/3; N = 0,1. Upper limits have been obtained for the FCP concentration per target atom. These upper limits vary between 1 x 10(' -16) and 3 x 10('--9) depending on the material searched and the charge state examined. Some interesting events have been seen. These are FCP candidates, but they can also be explained as improbable integrally charged events.