<p><a href=“http://www.nytimes.com/2006/04/18/science/18find.html?_r=1&oref=slogin[/url]”>http://www.nytimes.com/2006/04/18/science/18find.html?_r=1&oref=slogin</a></p>
<p>Physicists at the Fermi National Accelerator Laboratory reported what would seem to set a new standard for vacillation last week: a subatomic particle that reverses identity three trillion times a second, switching into its upside-down mirror-image evil-twin antimatter opposite and then back again.</p>
<p>The measurement of this yin-yang dance was a triumph for Fermilab’s Tevatron, which smashes together trillion-volt protons and antiprotons to create fireballs of primordial energy, and for the so-called Standard Model, a suite of theories that explains all that is known to date about elementary particles and their interactions.</p>
<p>Young-Kee Kim of the University of Chicago, a spokeswoman for the Collider Detector Facility collaboration, said, “Our real hope was for something bizarre.” Nature is tough, she said, but physicists are pretty tough, too. “We keep fighting,” Dr. Kim said.</p>