Is This a Quark I See Before Me?

A group at the University of Sydney has found five tracks in high‐energy cosmic‐ray air showers whose “appearance was that expected for a quark of charge $\text{2/3\hspace{0.17em}e.}$” The group, headed by Charles B. A. McCusker, used an array of scintillation counters, which triggered four delayed‐expansion cloud chambers when an extensive air shower arrived. Each chamber is expanded 100 millisec after the shower arrives, and the vapor trail is photographed 200 millisec later.

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