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lunes, 29 de noviembre de 2010

Antimatter Matters: Fermilab Glimpses 'The Toe of God'

Everyone's abuzz these days about the Large Hadron Collider finally being up and running and collecting data like crazy, storing interesting "events" for future analysis. But did you miss the big news coming out of Fermilab last week? It seems that the D-Zero collaboration -- co-discovers of the top quark back in the 1990s -- analyzed data from a bunch of proton-anti-proton collisions and found a slight asymmetry in the number of muons produced compared to anti-muons: about 1% more.

While that might not sound like much, it a hint of greater things to come, should experiments at the LHC confirm these initial results. It's genuine "new physics," since the most likely culprit for this strange asymmetry is a new particle not predicted by the Standard Model (kind of the periodic table of elementary particle physics). Which is why the New York Times article on the result ends with this classic quote from Fermilab's Joe Lykken: "I would not say that this announcement is the equivalent of seeing the face of god, but it might turn out to be the toe of god."

A quick refresher course for those unfamiliar with the conundrum of matter/antimatter asymmetry in our universe. A long time ago, when our universe was still in its earliest birthing throes, matter and antimatter were colliding and annihilating each other out of existence constantly. This process slowed down as our universe gradually cooled, but there should have been equal parts matter and antimatter -- and there weren't. Instead, there were slightly more matter particles than antimatter.

We know this because we can see the remnants of the survivors of that cosmological Octagon all around us: every bit of matter in our observable universe, from galaxies to dust mites and everything in between, exists because matter won that long-ago war of attrition. And physicists have no idea why that asymmetry should have existed in the first place. It's one of the Big Questions they hope the LHC can help answer.

Technically, it's known as CP (charge-parity) violation, an effect first proposed by Russian physicist Andrei Sakharov, in which "when the charges and spins of particles are reversed, they should behave slightly differently." This isn't the first glimpse of CP violation in the subatomic realm, but prior observed asymmetries haven't been large enough to explain how our material world could exist. According to the New York Times' Dennis Overbye:

"The new effect hinges on the behavior of particularly strange particles called neutral B-mesons, which are famous for not being able to make up their minds. They oscillate back and forth trillions of times a second between their regular state and their antimatter state. As it happens, the meson,s created in the proton-anti-proton collisions, seem to go from their antimatter state to their matter state more rapidly than they go the other way around, leading to an eventual preponderance of matter over antimatter of about 1 percent, when they decay to muons."

Curiouser and curiouser! And not bad for a world-class accelerator that perhaps some perceive as being past its prime. We'll just have to wait and see if experimental results from the LHC give further evidence for this potential first glimpse of exciting new physics beyond the Standard Model.

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