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Linear collider makes a Z.

Linear collider makes a Z

The Stanford Linear Collider, a unique high-energy accelerator for probing the structure of matter, last week finally produced its first Z[deg.] particle. An electron moving at nearly the speed of light collided head-on with an equally fast positron, an electron's antimatter counterpart, to produce a Z[deg.] particle, which decayed almost immediately into a quark-antiquark pair. The Z[deg.] particle is one of three carriers of the weak nuclear force, which governs certain kinds of radioactive decay.

The feat marks the first time researchers have detected the decay of a Z[deg.] particle into quarks, which are thought to be the fundamental building blocks of nuclear matter. "This is the most clear evidence that the Z decays into two quarks," says Jonathan M. Dorfan of the Stanford Linear Accelerator Center at Stanford University. "This is what we'd expect to see first."

Delayed more than a year by a variety of technical problems, the collider required close to $1 million in repairs and improvements to get the necessary stability and reliability for particle creation (SN: 9/10/88, p.167). Collider personnel also had to find a way of getting rid of muons, particles similar to electrons but with a mass 200 times as large, created when stray electrons and positrons strike the collider's walls. The muons accompanied the electrons and positrons down the accelerator, obscuring anything that happened when the electron and positron beams collided. The solution was to install special magnets to spread out any muons present, keeping them out of the collision zone.

The modifications considerably enhanced the collider's efficiency, and within a week of the first sighting, researchers detected at least two more Z[deg.] particles. "In order to start the physics program, we need to accumulate many more of these events," Dorfan says. "The significance of the first few is that the machine is now working and holding together."
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Title Annotation:Z particle
Publication:Science News
Date:Apr 22, 1989
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