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Posts Tagged ‘Discovery’

Born in the hearts of stars and nuclear reactors, almost undetectable, nearly as fast as light, able to pass unhindered through everything from planets to people, and confirmed shapeshifters. That role call describes what makes the particles known as neutrinos both exciting and perpetually challenging for physicists on the hunt.

A series of brilliant experiments designed and executed since the 1950s have managed to detect these slippery subatomic wonders, revealing much about their origins, travels, and presence as one of the most abundant particles in the cosmos.

Earlier this week, an international collaboration led by China and the United States at the Daya Bay Reactor Neutrino Experiment in the south of China pinpointed the action behind one of the neutrino’s signature magic tricks: its ability to seemingly vanish entirely. The disappearing act is the product of neutrino oscillations, and the Daya Bay team calculated the final unknown transformation type. The 5-sigma discovery not only helps demystify the neutrino, but it will also guide future experiments in exposing more fundamental mysteries – such as how we exist.

Photomultiplier tubes on the Daya Bay walls.

Sensitive photomultiplier tubes line the Daya Bay detector walls, designed to amplify and record the faint flashes that signify an antineutrino interaction. (Courtesy of Roy Kaltschmidt, Lawrence Berkeley National Laboratory)

“It’s surprising and exciting that this result came so quickly and precisely,” said Brookhaven Lab’s Steve Kettell, who is Chief Scientist for the U.S. at Daya Bay. “It has been very gratifying to be able to work with such an outstanding international collaboration at the world’s most sensitive reactor neutrino experiment.” (more…)

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Higgs for the Holidays

Friday, December 23rd, 2011

 —  By Theorist David Morrissey & Particle Physicist Anadi Canepa

 Last week we hosted two particle physics workshops at TRIUMF – an ATLAS Canada collaboration meeting and a joint meeting for theorists and experimentalists to study new LHC results.  Everything went smoothly, no participants were lost to the wilds of Vancouver, and we had some really great discussions and seminars.  During one of these presentations, it occurred to me that these kinds of scientific meetings are not so different from a typical holiday gathering.  In both situations, you frequently run into people you know but that you haven’t seen in a long time.  You catch up, you gossip, and you eat too much food at the coffee breaks.  There’s usually a large group dinner where you often meet new people and strike up conversations about future work.  And every so often one of the participants has too much holiday cheer.

Despite these similarities, most scientific meetings don’t involve gifts.  But this time around we were really lucky, and our workshops had a gift exchange of sorts as well.  In this case, the gifts were the presentations by the ATLAS and CMS collaborations of exciting new results from their searches for the Higgs boson particle.  On top of the live streaming presentations from CERN in the early hours of the morning, we were treated to a longer seminar in the afternoon at TRIUMF by Rob McPherson.  His talk was standing-room only, and we had a great time bombarding him with questions about the ATLAS analysis.

The reason for all this excitement over a single particle is that the Higgs boson, first proposed nearly fifty years ago, is central to our current understanding of all known elementary particles, called the Standard Model.  (See here, here, and here for more details.)   In this theory, the Higgs is responsible for creating the masses of nearly all elementary particles and for making the weak force much weaker than electromagnetism.  Even though we have not yet seen the Higgs directly, we have indirect evidence for it from precision measurements of the weak and electromagnetic forces.  Discovering the Higgs boson would confirm the Standard Model, while not finding it would force us to drastically rethink our description of elementary particles and fundamental forces, which would perhaps be an even greater discovery.

 

Excitement about finding the Higgs has been building since the summer, when it became clear that the LHC would be able to collect enough data by the end of the year to possibly find it.  In the past few weeks the level has gone through the roof as rumours started to appear that the LHC experiments would soon release a significant result.  What we learned this week is that these latest searches did not discover the Higgs boson, but that they do suggest that it might be there with a mass close to 133 times that of a proton (125 GeV).  Finding a Higgs is hard work, and its delicate characteristic signal must be extracted from a huge amount of background noise.  What we have at the moment is an intersting bump, as you can see in the figure above taken from the ATLAS search, where we see more signal events than would typically be expected from the background alone for a candidate Higgs mass of about 125 GeV.  We just don’t have enough data right now to confirm that this bump is from a Higgs boson, and not just an especially unlucky spike in the background noise.  Fortunately, the ATLAS and CMS collaborations will be taking much more data in the new year.

So, for this year all we get is a gift-wrapped box that we’re allowed to shake and prod.  But if we’re good, we’ll get to open the box and find what’s inside at some point in 2012.  Dear Santa…


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