Tag: muons

Antarctic Particle Detector Buried in Ice Records Cosmic Ray Weirdness

By Joseph Calamia | August 3, 2010 1:35 pm

icecube_skymap_22string09Detectors buried thousands of feet under the Antarctic ice recently confirmed a mysterious cosmic lopsidedness. Though it might seem reasonable for our planet to receive energetic particles, called cosmic rays, on average from all directions equally, more cosmic rays’ seem to approach Earth from certain preferred directions.

The IceCube Neutrino Observatory, which is still under construction, confirmed these odd cosmic ray preferences, previously detected in the northern hemisphere.

Cosmic rays–energetic particles flung from as nearby as the sun and light years away–are the extra “noise” in the observatory’s experiments; to filter out this noise, researchers needed to map where the cosmic rays are coming from. In a paper published earlier this month in The Astrophysical Journal they confirmed that more cosmic rays seem to come from certain directions–an observation known as anisotropy–in the Earth’s southern hemisphere too.

[T]hey used IceCube to study a longstanding puzzle: whether the distribution of cosmic ray arrivals is uneven across the southern sky, as scientists have previously observed in the northern hemisphere. Indeed, the team found, IceCube detected a disproportionate number of cosmic rays arriving from some parts of the sky. But the reason for this uneven distribution remains unclear. [ScienceNOW]

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CATEGORIZED UNDER: Physics & Math, Space

A Particle Physics First: Researchers Watch Neutrinos Change Flavors

By Joseph Calamia | June 1, 2010 4:28 pm

detectorFor the first time, physicists say they have witnessed a subatomic particle change its “flavor.” Physicists at OPERA, run by Italy’s national nuclear physics institute, announced yesterday that they have observed one neutrino change its type, or flavor, spontaneously. The experiment solves a 50-year-old physics mystery, and may uncover some of the universe’s hidden mass.

The Mystery

Neutrinos, which come in three different flavors, can have fairly violent births: they can come into the world via nuclear reactions in the sun, particle decay, or collisions in particle accelerators. But, once formed, they seem to ignore almost everything around them, including magnetic fields, electric fields, and matter. In fact, there are trillions of them zipping through each of us every second; they go right through our bodies and keep on moving through the planet itself.

The mystery of “neutrino oscillations” began with the number of neutrinos that should be coming from the sun. Theory predicted a certain number of various flavors to arrive, but observation showed much less:

The neutrino puzzle began with a pioneering and ultimately Nobel Prize winning experiment conducted by US scientist Ray Davis beginning in the 1960s. He observed far fewer neutrinos arriving at the Earth from the Sun than solar models predicted: either solar models were wrong, or something was happening to the neutrinos on their way. [CERN]

In 1969, Bruno Pontecorvo and Vladimir Gribov theorized that the neutrinos weren’t disappearing, they were changing their flavors mid-journey. Though physicists were looking for one type, they weren’t finding what they ordered.

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In the Universe’s Decisive Battle, Why Did Matter Prevail Over Antimatter?

By Andrew Moseman | May 21, 2010 11:13 am

TevatronAs opposed to simply energy, the universe is also made of stuff. Not a whole lot of stuff, mind you, at least if you compare the matter we experience to the vast emptiness of space or the preponderance of dark matter. But enough.

The continued prevalence of matter has long been one of my favorite attributes of the universe, given that it allows for the existence of galaxies, and Guinness. However, it’s the source of confusion to physicists. In short, there should have been equal amounts of matter and antimatter present at the creation of the universe, which doesn’t make sense:

If matter and antimatter had come out even in those first moments, they would have instantly destroyed each other, leaving nothing but energy behind [TIME].

But they didn’t; as sure as I’m sitting here, matter won out. And this week, at the Tevatron particle smasher in Illinois, a new clue to the problem has emerged. In a study for Physical Review D, physicist Dmitri Denisov and his colleagues explain that in long-running proton-antiproton collisions (nearly 8 years of them), they saw a slight favoritism toward normal matter in a particular place:

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Ghost in the Machine? Physicists May Have Detected a New Particle at Fermilab

By Eliza Strickland | November 5, 2008 4:00 pm

TevatronStrange things are afoot at the Tevatron particle collider at Fermilab, and the aging U.S. particle smasher is getting an unexpected moment in the spotlight while physicists wait for the repairs of the Large Hadron Collider in Switzerland. Researchers say experiments at the Tevatron have produced particles that they are unable to explain using the standard model of physics, and say it’s possible that they’ve detected a previously unknown particle. If the result does turn out to be due to some unexpected new process, it would be the most significant discovery in particle physics for decades [Physics World].

Bloggers and theorists are already lining up explanations that involve unseen particles, hypothetical strings, or modifications of conventional physics. The finding is so controversial that about one-third of the 600-person experiment that detected it are refusing to put their names on the 69-page paper purporting its discovery [Nature News], which was posted in advance of publication on the server arXiv.

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