Emilio Segrè Visual Archives

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Lawrence Berkeley National Laboratory H16

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Lawrence Berkeley National Laboratory H16

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Image title: 
Antiproton entering the 72-inch hydrogen bubble chamber at the University of California's Lawrence Radiation Laboratory
Credit line: 
Lawrence Berkeley National Laboratory, courtesy of AIP Emilio Segrè Visual Archives

Antiproton entering the 72-inch hydrogen bubble chamber at the University of California's Lawrence Radiation Laboratory, Berkeley (currently known as the Lawrence Berkeley National Laboratory). The four-pronged 'star' is formed when an antiproton, generated by the Bevatron, comes close to a proton, the nucleus of ordinary hydrogen atom, in the chamber. The process is called annihilation, and is visualized by the profusion of tracks forming the star. The tracks forming the 'star' are made by pions, particles of lower mass into which the primary particle disintegrates. Not all of the particles are seen -- the neutral ones (those with no electrical charge) make no tracks. It had been theoretically postulated that the Omega meson is composed of three pi mesons (pions), and is neutrally charged.

Elaborate analysis of the star showed that an Omega meson has been born in the annihilation. The complex sequence is as follows: the antiproton breaks up into two pions (the two tracks in the middle of the four-pronged star) and an Omega meson; the Omega exists only briefly, then breaks up into two pions (the tracks at far left and far right in the four-pronged star) and a neutral pion which makes no track.

The discovery was made by means of three-part high energy particle research system at Berkeley: the 6.2 billion electron volt (Bev-"atom-smashing" Bevatron; the giant 72-inch liquid hydrogen bubble chamber in which particle tracks are photographed; and an extensive analytical complex which includes specially developed, semi-automatic measuring machines, and an IBM 709 computer. The fundamental research program in the Laboratory in financed by the Atomic Energy Commission.

Original format: 
2 photographic prints (black and white; 10 x 8 inches)
Lawrence Berkeley National Laboratory