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A cosmic-ray event is described in which a negative cascade particle and two neutral heavy mesons appear to be produced in a single nuclear interaction above a cloud chamber. It is suggested that this event may be an example of the associated production of a S~ particle with two 0° particles according to the scheme of Gell-Mann. E XPERIMENTAL information concerning the associated production of unstable heavy particles was first obtained by Shutt and his collaborators at Brookhaven. 1 Using a hydrogen diffusion chamber in the 1.37-Bev ir~ beam, these researchers have found that neutral or charged hyperons may be produced with neutral or charged i£-mesons.Recent data have shown that associated production occurs to some extent in cloud chambers triggered on penetrating showers 2 and in nuclear emulsions exposed to cosmic rays. 3 Here again the evidence is that hyperons are produced associated with heavy mesons.In the 48-inch magnet cloud chambers operating in Pasadena (Fig. 1), we have obtained a photograph showing four V events (Fig. 2), all connected with a single penetrating shower origin. This event is produced by a primary particle of >4 Bev/c momentum and unknown sign of charge which enters from above and behind chamber 2. Only 6 mm above the top inside wall of chamber 3 the primary makes a high-energy nuclear interaction which produces the penetrating shower containing the four F-particles, all of which decay in chamber 3. There are no other tracks besides the primary in chambers 1 and 2, and all of the tracks in chambers 3 and 4 appear to result from the single interaction at the top of chamber 3.In Fig. 3, the various decays are shown in an isometric projection of the tangents to the pertinent tracks at their decay points. All decay secondaries pass through the front of the apparatus except for FH and IK which travel down through chamber 4.There are three V° decays, FGH, CDE, and UK. The planes of both FGH and UK pass through the origin within experimental error, the angles of noncoplanarity for O with respect to FGH and UK being 2.8db4° and 0.5zfcl.4° respectively. Moreover, the

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