不惑

真相の宝庫に、暗黒物質のヒントが

December 18, 2009
At a Mine’s Bottom, Hints of Dark Matter
By DENNIS OVERBYE
An international team of physicists working in the bottom of an old iron mine in Minnesota
said Thursday that they might have registered the first faint hints of a ghostly sea of
subatomic particles known as dark matter long thought to permeate the cosmos.

The particles showed as two tiny pulses of heat deposited over the course of two years in
chunks of germanium and silicon that had been cooled to a temperature near absolute zero.
But, the scientists said, there was more than a 20 percent chance that the pulses were caused by fluctuations in the background radioactivity of their cavern, so the results were
tantalizing, but not definitive.

Gordon Kane, a physicist from the University of Michigan, called the results “inconclusive,
sadly,” adding, “It seems likely it is dark matter detection, but no proof.”

Dr. Kane said results from bigger and thus more sensitive experiments would be available in
a couple of months.

The team, known as the Cryogenic Dark Matter Search, announced its results in a pair of
simultaneous talks by Jodi Cooley from Southern Methodist University at the SLAC National
Acceleratory Laboratory in California and by Lauren Hsu of the Fermi National Accelerator
Laboratory in Illinois at Fermilab, and they say they plan to post a paper on the Internet.

The stakes for astronomy and physics could hardly be greater. If the particles are confirmed
by tests at other detectors, it would mean that, after more than half a century of
speculation, astronomers are zeroing in on the identity of the invisible material that
accounts for 25 percent of the universe and determines the architecture of the visible
universe.

Confirmation of the particles would also constitute the first evidence for a new feature of
nature, called supersymmetry, that physicists have been seeking as avidly as the astronomers
have been seeking dark matter. It is central to theoretical efforts like string theory,
which unify all of the forces of nature into one mathematical expression.

The report ended weeks of speculation on physics blogs and in laboratory cafeterias around
the world. At the Kavli Institute for Theoretical Physics in Santa Barbara, Calif., where
dark matter experts who had gathered for a two-week workshop watched the talks on the Web,
Dr. Kane, who was present, described the mood at the workshop as “a high level of serious
hysteria.”

Dark matter became a serious issue in the 1970s, when Vera Rubin of the Carnegie Institution
of Washington and her colleagues charted the rotation speeds of galaxies and found that they
seemed to be enveloped in halos of dark matter, then called missing mass.

A wide range of astrophysical and cosmological measurements have subsequently converged on an intimidating recipe for the cosmos of 4 percent atoms, 25 percent dark matter and 70 percent a mysterious energy that has been called dark energy and has nothing to do with the news on
Thursday.

The cryogenic experiment is nearly half a mile underground in an old iron mine in Soudan,
Minn., to shield it from cosmic rays. It consists of a stack of germanium and silicon
detectors, cooled to one-hundredth of a degree Kelvin. When a particle hits one of the
detectors, it produces an electrical charge and deposits a small bit of energy in the form
of heat, each of which are independently measured.

By comparing the amounts of charge and heat left behind, the collaboration’s physicists can
tell so-called wimps from more mundane particles like neutrons, which are expected to flood
the underground chamber from radioactivity in the rocks around it.

The team is planning a larger detector, called SuperCDMS. In the meantime, Elena Aprile of
Columbia, who was also present in Santa Barbara, said the results would be tested soon by her own detector, called Xenon, filled with liquid xenon, which just began working this fall
under the Alps in Italy.

“All eyes will be on Xenon,” she said in an interview a few days before, explaining that her detector, which is bigger, should see more events, adding, “Otherwise there will be a big
clash.”

木星の１０倍以上、巨大惑星２つの撮影成功

木星の１０倍以上、巨大惑星２つの撮影成功
12月4日4時10分配信 読売新聞


拡大写真
光の中心部の黒い部分が主星。丸で囲った２つが巨大惑星（国立天文台提供）
　国立天文台などの研究チームは３日、太陽と同じような大きさの主星（恒星）の周囲をまわる二つの巨大惑星を、すばる望遠鏡（米ハワイ島）を使って直接撮影したと発表した。

　惑星は、いずれも木星の１０倍以上の大きさで、太陽と同程度の星が、これほどの巨大惑星を持つことは考えにくく、惑星誕生の新しい理論の構築への糸口になりそうだ。

　巨大惑星は、こと座の方向に約５０光年離れた場所で見つかった。主星と惑星の位置どりを太陽系に例えると、太陽から遠く離れた天王星や海王星ほどだという。

　こうした惑星は通常、主星の明るさに隠れて地球から見えないが、今回は特殊な装置で主星の光を遮り、撮影に成功したという。

　惑星は恒星の周囲を取り囲むガスやちりが集まってできたと考えられている。このため、恒星から離れた場所では、惑星の材料となるガスやちりの密度が低く、巨大な惑星はできないとされている。

陽子光線

November 21, 2009
Proton Beams Are on Track at Collider
By DENNIS OVERBYE
Physicists returned to their future on Friday. About 10 p.m. outside Geneva, scientists at CERN, the European Center for Nuclear Research, succeeded in sending beams of protons clockwise around the 17-mile underground magnetic racetrack known as the Large Hadron Collider, the world’s biggest and most expensive physics experiment.

For physicists, the event was a milestone on the way back from disaster and the resumption of a 15-year, $9 billion quest to investigate laws and forces that prevailed when the universe was less than a trillionth of a second old.

The collider was designed to accelerate protons to energies of seven trillion electron volts apiece and smash them together in tiny fireballs in an effort to replicate and study the conditions of the Big Bang.

The first time protons circled the collider, on Sept. 10, 2008, the event was celebrated with Champagne and midnight pajama parties around the world. But the festivities were cut short a few days later when an electrical connection between a pair of the collider’s giant superconducting electromagnets vaporized.

Subsequent work revealed that the machine was riddled with thousands of connections unable to handle the high currents required to run the collider at its intended energy.

Physicists and engineers have spent the past year testing and making repairs. While they have not replaced all the faulty connections, they have patched things up enough to allow the collider to run at less than full speed.

Calling the past year’s work a “Herculean effort,” CERN’s director for accelerators, Steve Myers, said the engineers had learned from painful experience and understood the collider far better than they had before.

CERN’s director, Rolf Heuer, said in a statement, “It’s great to see beam circulating in the LHC again,” but he and others cautioned that there was a long way to go before the collider started producing the physics it was designed for.

When the collider begins to do real physics next year, it will run at half its original design energy, with protons of 3.5 trillion electron volts. The energy will be increased gradually during the year, but it could be years, physicists say, before the machine reaches its full potential.

Thousands of the troublesome junctions will have to be rebuilt during a yearlong shutdown in 2011, and engineers have to figure out why several dozen of the superconducting magnets seem to have lost their ability to operate at high intensities.

The delay has given new life to the collider’s main rival, the Tevatron at the Fermi National Accelerator Laboratory in Illinois.

If all goes well, CERN says, the protons will start colliding at low energies in about a week.

Those first collisions will occur at the so-called injection energy of 450 billion electron volts. The machine will then quickly step up to 1.1 trillion electron volts, which is just above the energy of the Tevatron.

CERN is hoping to achieve that landmark as a symbolic Christmas present before a short holiday shutdown.