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Among the secondary particles produced in a high energy jet shower and observed by emulsion chambers exposed to cosmic rays, a possible decay in flight of a new type particle was found.A new type of emulsion chamber!) with local producing layer of jet shower was designed in order to investigate super high energy jet showers in full detail by combining information about secondary charged particles at or near an origin of jet shower as well as r rays. Exposure of new type chambers for about 500 hours at about 260 gr/cm 2 was performed using a Jet Cargo Aeroplane of Japan Air Lines.One of the jet showers observed in this type of chamber, Event "6B-23 ", was fortunately produced in the emulsion of lower surface of a plate in the middle of the producing layer which is a pile of 49 nuclear emulsion plates with a 50 p.m coating on both sides of metaacryl base with a thickness of 800 p.m. Therefore, this type of jet shower was observed as (19+70)n. Schematical view of this jet shower is shown in Fig. 1.In Fig. 2 is shown the relation of energy to lg. tg (} for r rays with log. tg (} distribution of charged secondary particles. The most impressive feature of this jet shower is that 2r rays with energy by nearly one order higher than others are emitted very closely in the center region of shower.The total sum of their energy is estimated as 3.2±0.4 TeV, and relative distance between them is 3.4 p.m at the target plane 5.14 em down from jet shower origin. Coupling them into a n° meson, the estimated production height is 3.8±0.5 em above the target plane, and it does not reach the jet shower origin. There emitted 4 charged particles very near to these r rays. We drew a precise target diagram of tracks of these 4 particles A, B, C and D at each emulsion surface in the producing layer, and then reconstructed three-dimensional view of tracks of these particles and n° meson. X, Y and Z projections of these tracks are shown in Figs. 3(a), (b) and (c). We adopted the Z axis parallel to the emitted direction of track B.As you can see from X and Y projections, tracks B and C have knees at 1.38 em and 4.88 em, respectively, from the origin of jet shower. Angles of direction change of tracks are 1.07X10-3 radian and 1.50x1o-s radian, respectively.Looking at the Z projection, you can easily recognize that the two cascade cores from the n° meson appear just in the opat University of

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