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  • richardmitnick 8:00 pm on September 17, 2014 Permalink | Reply
    Tags: , , , , IceCube Experiment   

    From IceCube: “An improved measurement of the atmospheric neutrino flux in IceCube “ 

    IceCube South Pole Neutrino Observatory

    17 Sep 2014
    Silvia Bravo

    Cosmic neutrinos in IceCube are the vogue these days, but atmospheric neutrinos are the popular ones if we look at the number of hits in the detector. Those neutrinos, created by the interaction of cosmic rays in the Earth’s atmosphere, are the main background in searches for astrophysical neutrinos.

    The IceCube Collaboration has submitted a paper today to the European Physical Journal C describing a new analysis scheme for the measurement of the atmospheric neutrino spectrum with the IceCube detector. The analysis was performed using data from May 2009 to May 2010, when the detector was running with a configuration of 59 of the final 86 strings.

    The spectrum was measured introducing a novel unfolding technique in the energy range from 100 GeV to 1 PeV, extending previous results of AMANDA by almost an order of magnitude. The new analysis also uses an improved selection, with results that showed a reduced atmospheric muon background contamination of 5 to 6 orders of magnitude and an 8% increase in the signal efficiency.

    The unfolded atmospheric neutrino spectrum agrees with both previous experimental results and the current theoretical models. The new method reduces the impact of the systematic uncertainties on the measured flux, but at high energies they are still too large to allow for conclusive results about a prompt and/or an astrophysical component of the overall flux.

    Comparison of the unfolding result obtained using IceCube in the 59-string configuration to previous experiments. Theoretical models are shown for comparison. Image: IceCube Collaboration.

    The analysis scheme presented in this paper introduces a machine learning algorithm for the final event selection that uses 25 event variables to distinguish between atmospheric muon tracks and tracks produced by neutrino-induced muons.

    “IceCube is a great detector for measuring atmospheric
    muon neutrinos. Those are, in fact, the vast majority of the neutrinos we detect. And by using tools and algorithms from data mining we can detect even more,” explains Tim Ruhe, a researcher at TU Dortmund University, in Germany.

    For every neutrino detected by IceCube, about a million atmospheric muons are observed. A common way to look for neutrinos in this huge muon background consists of selecting only upgoing muon tracks, since muons created by the interaction of cosmic rays with the atmosphere will be absorbed by the Earth when approaching IceCube from below. Thus, if the event reconstruction and selection were perfect, the remaining muon tracks would have been created by the interaction of a neutrino with the ice in or around the IceCube detector.

    However, previous to this analysis, the muon background rejection in IceCube was only 99.9% efficient because about 1,000 originally downgoing muons per every neutrino seen by IceCube were falsely reconstructed as upgoing tracks. With the new selection algorithm, IceCube researchers were able to reject 99.9999% of the incoming background events.

    + Info “Development of a General Analysis and Unfolding Scheme and its Application to Measure the Energy Spectrum of Atmospheric Neutrinos with IceCube,” IceCube Collaboration: M.G. Aartsen et al. Submitted to The European Physical Journal C, arXiv.org:1409.4535

    See the full article here.

    ICECUBE neutrino detector

    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

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  • richardmitnick 1:30 pm on April 30, 2014 Permalink | Reply
    Tags: , , IceCube Experiment,   

    From Symmetry: “Possible expansion for South Pole detector” 


    April 30, 2014
    Kathryn Jepsen

    Physicists hope to seek out the source of cosmic neutrinos by expanding the IceCube neutrino detector to 10 times its current size.
    ICECUBE neutrino detector
    IceCube Neutrino Detector at South Pole

    The detectors of the IceCube experiment have so far caught about 100 cosmic neutrinos, dozens of which came from outside our galaxy.

    The exact provenance of these particle cosmonauts is a mystery. That’s one reason IceCube scientists would like to expand their experiment, which covers a cubic kilometer of ice at the South Pole, to a volume 10 times as large.

    University of Wisconsin physicist Francis Halzen and colleagues made the case for the expansion at a workshop in Virginia on April 24.

    It’s as if the IceCube experiment is a giant digital camera, Halzen says, and every neutrino spotted is a pixel. “The more you have, the clearer the picture gets,” he says. “To see several neutrinos come from the same source, you are likely to need well above one thousand.”

    The sources of IceCube’s first 100 neutrinos could be exploding stars in distant galaxies. Or they could come from some other process, like the decay of dark matter particles in our galactic halo.

    “I can tell you what would be most exciting: if they came from something we haven’t seen before,” Halzen says.

    An expanded IceCube experiment could also include a bonus, smaller experiment called PINGU, which would detect lower-energy neutrinos to allow scientists to study their properties.

    Neutrinos are elementary particles that very rarely interact with other matter. To catch a thousand of them, IceCube scientists would need to run their current experiment for a decade, Halzen says.

    The IceCube experiment consists of more than 5000 detectors about the size and shape of a basketball, strung on 86 lines and lowered into holes in the ice. When a neutrino interacts with the ice, it releases a particle such as a muon. The small shockwave that follows the particle as it travels through the ice emits blue light in the form of Cherenkov radiation. The detectors catch this light.

    It turns out, the ice is even clearer than previously thought. The IceCube detectors built 15 years ago are located 125 meters apart from one another. If the scientists add new detectors, they’ll be able to double the spacing, which means they will be able to drastically expand the array without drastically increasing the number of detectors.

    “We can do this for about the same amount of money we spent on the original array,” Halzen says.

    The physicists would like to upgrade their hot-water ice drill, originally designed and built for IceCube at University of Wisconsin, and add 120 new strings of detectors, installing about 20 at a time over six years.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

    ScienceSprings is powered by MAINGEAR computers

  • richardmitnick 4:39 pm on November 8, 2013 Permalink | Reply
    Tags: , , , , IceCube Experiment, ,   

    From Symmetry: “Ultra-high-energy neutrinos” 

    November 08, 2013

    Scientists on the IceCube experiment discovered two extraterrestrial neutrinos with energies higher than any neutrino anyone had detected before.

    Kelen Tuttle

    Physicists on the IceCube experiment were in for a jolt. In processing data taken by their strings of more than 5000 light-sensitive detectors suspended under Antarctic ice, they discovered two particles called neutrinos with 1000 times more energy than the ones that regularly zip through IceCube’s detectors. They are the highest-energy neutrinos ever observed.

    Courtesy of IceCube collaboration

    Nearly all of the neutrinos that IceCube sees are produced in Earth’s atmosphere. These atmospheric neutrinos tend to have energies somewhere between 1 and 10—and occasionally as high as 100—trillion electronvolts. The two unusual neutrinos appear to have come from far out in space and carried an impressive 1000 trillion electronvolts of energy. Each one lit up hundreds of IceCube’s detectors.

    “These two neutrinos were discovered in an analysis that was optimized to see something else entirely—so they were quite the surprise,” says Kurt Woschnagg, an IceCube collaborator from the University of California, Berkeley.

    Since these were the most exciting particles IceCube had ever observed, collaborators spent much time talking and writing about them.

    “These events were originally named with long strings of numbers,” says graduate student Jakob van Santen. “But that was confusing—people would accidentally mix them up by transposing numbers.”

    So van Santen named them Bert and Ernie, after the Sesame Street characters that their event displays somewhat resembled. He named Bert because it came from a more horizontal direction, whereas Ernie was more vertical and slightly larger, sort of like the heads of each Muppet.

    “Unfortunately my memory of Sesame Street was a bit too dim, as was pointed out to me some time later: Bert is the one with the elongated head, and Ernie is the wide one,” van Santen says. “By that time it was too late; the names had stuck.”

    Through careful analysis of Bert and Ernie, the collaboration confirmed that they had seen extremely high-energy neutrinos produced not in the Earth’s atmosphere, but somewhere beyond. Because neutrinos interact rarely with matter, these neutrinos may serve as messengers, carrying clear information about the most powerful cosmic events, including gamma-ray bursts, black holes and the formation of stars. The collaboration is now refining and expanding their analysis to learn more about these two zingers while also hunting for additional high-energy extraterrestrial neutrinos. Where there’s a Bert and an Ernie, there may also be a Mr. Snuffleupagus and an Oscar the Grouch.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

    ScienceSprings is powered by MAINGEAR computers

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