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  • richardmitnick 11:29 am on September 25, 2017 Permalink | Reply
    Tags: , , , , , , U Wisconsin IceCube   

    From U Wisconsin IceCube: “Looking for new physics in the neutrino sector” 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    25 Sep 2017
    Sílvia Bravo

    ICECUBE neutrino detector

    Neutrinos are intriguing in more ways than one. And although the fact that they have such tiny mass explains their quirky behavior, their allure remains intact. The issue is that neutrino masses are not predicted by the Standard Model; thus, on its own, the existence of a neutrino with mass is an indication of new physics. And that’s what scientists around the world, including at IceCube, want to learn: what type of new physics are neutrinos pointing to?

    New physics could appear in the form of a new type of neutrino or it could help us understand the nature of dark matter. The possibilities are endless. In a new search for nonstandard neutrino interactions, the IceCube Collaboration has tested theories that introduce heavy bosons, such as some Grand Unified Theories. These heavy bosons would explain, for example, why neutrinos have masses much smaller than their lepton partners. The study resulted in new constraints on these models, which are among the world’s best limits for nonstandard interactions in the muon-tau neutrino sector. These results have just been submitted to Physical Review D.

    1
    Confidence limits from this analysis are shown as solid vertical red lines. The light blue and light green vertical lines show previous limits by Super-Kamiokande and another study using IceCube data at higher energy. Credit: IceCube Collaboration.

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    The flavor of neutrinos oscillates as they travel through matter or empty space, a quantum effect on macroscopic scales that proves that they have mass. When atmospheric neutrinos reach IceCube after crossing the Earth, they have often morphed from muon into tau neutrinos. If TeV-scale bosons predicted by nonstandard theories exist, they will modify the probability that a given type of neutrino oscillates into other types. The result is that the disappearance pattern of muon neutrinos in IceCube will change, with effects that span a large range of energies.

    In IceCube, for studies using atmospheric neutrinos that sail through the Earth, these nonstandard interactions (NSIs) can be parametrized in terms of the strength of muon neutrino to tau neutrino morphing due to an NSI, a parameter called .

    IceCube researchers have analyzed three years of data, using the same neutrino sample used for a recent measurement of the neutrino oscillation parameters, but with an additional selection criterion to improve the signal purity. The remaining 4,625 candidate neutrino events were used to fit the oscillation parameters, including the NSI contribution.

    The best fit of muon to tau NSI oscillations was consistent with no nonstandard interactions. “Even though no new physics was shown by this study, it narrows in on the possible existence of new neutrino interactions with regular matter” says Carlos Argüelles, an IceCube researcher from MIT. “It also showcases the advantages of having a very broad energy range, so experiments like IceCube can look for new oscillation physics with neutrinos, which are 10 to 1000 times more energetic than the average proton.”

    The 90% confidence level upper limit on the NSI parameter is consistent with previous measurements by Super-Kamiokande, which at that time had set the world’s best limits. The new IceCube measurement slightly improves Super-Kamiokande’s measurements, also extending the energy range. A more recent study using published IceCube data at even higher energies has also set limits on the parameter, which in turn were slightly more stringent than the ones of the present study.

    Albrecht Karle, a professor of physics at UW–Madison, comments that “the results shown here are based on only a relatively small set of muon neutrinos available.” IceCube is collecting more than 100,000 muon neutrinos per year, which are yet to be mined for physics beyond the Standard Model. “With almost a million atmospheric neutrinos, IceCube has an incredible data set for investigating even small deviations from Standard Model physics.”

    And keeping in mind that it’s not all about the detector, Melanie Day, another IceCube researcher and co-author on this paper, adds, “Not enough is said about the value of teamwork and collaboration over individual contributions to scientific results. But without that, this result would not have been possible.”

    See the full article here .

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    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 5:57 pm on July 25, 2017 Permalink | Reply
    Tags: , , , U Wisconsin IceCube   

    From U Wisconsin IceCube: “Improved measurements of neutrino oscillations with IceCube” 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    25 Jul 2017
    Sílvia Bravo

    A denser and smaller array of sensors at the bottom of the IceCube Neutrino Observatory, the DeepCore detector, enables the detection of neutrinos produced by the interaction of cosmic rays with the atmosphere down to energies of only a few GeVs. On their way to IceCube, many of the neutrinos produced in the Northern Hemisphere will morph into other neutrinos due to a well-known quantum effect: neutrino oscillations

    n 2013, IceCube reported its first measurement of the neutrino oscillation parameters. This was the first time that neutrino oscillations were measured with precision at energies between 20 and 100 GeV. The results were compatible with those from devoted neutrino experiments, but now the model was tested at higher energies, although uncertainties were still larger. A year later, the collaboration presented a second analysis with three years of data that improved the precision by a factor of ten. This week, the IceCube Collaboration presents a new measurement of the oscillation parameters that for the first time is competitive with the best measurements to date. These results have just been submitted to Physical Review Letters.

    1
    The oscillations parameters measured in this work compared to best results from other experiments. The cross marks the IceCube best-fit point. The 90% confidence level contours were calculated using the approach of Feldman and Cousins. The outer plots show the results of the 1-D projections of the 68% confidence level contours. Credit: IceCube Collaboration

    Long-baseline experiments, such as T2K or NOvA, observe much lower energy events.

    T2K Experiment


    T2K map

    FNAL NOvA Near Detector


    FNAL/NOvA experiment map

    Understanding neutrino oscillations at higher energies tests systematic uncertainties but also places constraints on different new physics models in the neutrino sector.

    The current measurement has improved the selection of neutrino events by a factor ten. The IceCube sensors immediately surrounding DeepCore are used as a veto against muons produced in the same atmospheric cosmic ray interactions, keeping only events that start inside the DeepCore instrumented volume.

    “The event reconstruction is a significant improvement of this analysis,” explains João Pedro Athayde Marcondes de André, an IceCube researcher at Michigan State University (MSU) and a coleader of this analysis. “We now take into account the properties of the ice to reconstruct all types of events, even those with a substantial energy deposition at the beginning of the event, where the interaction of the incoming neutrino with the Antarctic ice takes place,” adds A. M. de André.

    “IceCube is the first experiment using atmospheric neutrinos to measure the oscillation parameters with a similar precision to long-baseline experiments,” says Joshua Hignight, also an IceCube researcher at MSU and a coleader of this work. “But we measure them in a different energy range and with different baselines,” states Hignight.

    The best fit oscillation parameters point to a maximal mixing scenario, in agreement with results from the T2K experiment and in tension with measurements from the NOvA experiment. In the maximal mixing scenario, one of the neutrino quantum states is a precise equal mix of two different flavor neutrinos. Although this could be just a coincidence, it could also be a hint to new physics.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    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.

     
  • richardmitnick 10:03 am on July 24, 2017 Permalink | Reply
    Tags: , , , , U Wisconsin IceCube, Where are the IceCube neutrinos coming from? (part 2)   

    From astrobites: “Where are the IceCube neutrinos coming from? (part 2)” 

    Astrobites bloc

    Astrobites

    Jul 24, 2017

    Title: Constraints on Galactic Neutrino Emission with Seven Years of IceCube Data.
    Authors: The IceCube Collaboration

    U Wisconsin ICECUBE neutrino detector at the South Pole


    Status: Submitted to The Astrophysical Journal, [open access]

    Back in 2013, the IceCube Collaboration published a paper [Science November 22nd] announcing their discovery of astrophysical neutrinos, i.e. ones that have an origin outside our Solar System (Astrobites coverage). Since this discovery, scientists have been busily working to develop theories as to the origin of these neutrinos. The original paper noted some clustering in the area of the center of our Galaxy, but it was not statistically significant. Since then, both Galactic and extragalactic origins have been proposed. Star-forming galaxies have been suggested as one possible origin, which Astrobites has covered papers arguing both for and against (here and here). Other theories involve radio galaxies, transients, and dark matter.

    In today’s paper, the IceCube Collaboration has analyzed more of their data and set limits on the percentage of the diffuse neutrino flux that can come from Galactic sources. Theoretically, some neutrinos should be created in the Galactic plane: we know that this area emits gamma rays from pion decay, and neutrinos are created in the same types of interactions that create the gamma rays.

    The collaboration used an unbinned maximum likelihood method as the main analysis technique in this paper. This is a standard technique used in astrophysics; it takes a model and finds the values of all the parameters of that model that give the best likelihood of getting the data that has been observed. (A second, separate technique was used as a cross-check). They used five different catalogs of Galactic sources expected to emit neutrinos to determine where to search. Sources included pulsar wind nebulae and supernovae interacting with molecular clouds. The upper limits on the flux from our galaxy can be seen below.

    1
    Figure 1: Upper limits on the neutrino flux from the Galaxy, assuming a three-flavor neutrino flux and a certain emission model known as the KRA-gamma model. The red limits are from this paper (with the grey showing how the limits change if other emission models are used); the blue are from ANTARES, which is another neutrino experiment. For comparison, the measured overall neutrino flux is also shown (black data points and the yellow band). The green band is from the data, but only data from the northern sky is used. IceCube is more sensitive in the Northern hemisphere. (Source: Figure 2 of the paper.)

    It turns out that, under these assumptions, Galactic contributions can’t be more than 14% of the diffuse neutrino flux. However, the authors note that there are still scenarios where the flux could originate in/near the Galaxy. This paper focused on emission in the Galactic plane, but cosmic ray interactions in a gas halo far from the plane, and/or dark matter annihilation or decay would change the emission templates that were used here. They also mention that the limits could be made stronger by doing a joint analysis with ANTARES.

    Anteres Neutrino Telescope Underwater, a large area water Cherenkov detector in the deep Mediterranean Sea, 40 km off the coast of Toulon, Fr

    Since IceCube and ANATARES are located in different hemispheres, they are most sensitive in different areas of the sky. The mystery continues…

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 7:02 am on July 1, 2017 Permalink | Reply
    Tags: , , , , , U Wisconsin IceCube, Week 25 at the Pole   

    From U Wisconsin IceCube: “Week 25 at the Pole” 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    30 Jun 2017
    Jean DeMerit

    1
    Martin Wolf, IceCube/NSF

    Last week the IceCube detector had almost perfect uptime. They survived a mid-week 90-second power outage with no interruption to data taking, but then a power supply failure just at the end of the week ruined the perfect performance. The third round in the poker tournament, however, didn’t ruin winterover Martin’s standing—he’s still in the lead going into the finals. It was Martin’s birthday last week, so the galley staff made a nice cake to celebrate. The aurora in the bottom image seems to be ushering in the upcoming 4th of July celebrations.

    2
    James Casey, IceCube/NSF

    3
    James Casey, IceCube/NSF

    4
    James Casey, IceCube/NSF

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.

     
  • richardmitnick 2:07 pm on June 27, 2017 Permalink | Reply
    Tags: , , , , , , U Wisconsin IceCube   

    From Symmetry: “The rise of LIGO’s space-studying super-team” 

    Symmetry Mag

    Symmetry

    06/27/17
    Troy Rummler

    The era of multi-messenger astronomy promises rich rewards—and a steep learning curve.

    NASA/Fermi LAT

    Sometimes you need more than one perspective to get the full story.

    Scientists including astronomers working with the Fermi Large Area Telescope have recorded brief bursts of high-energy photons called gamma rays coming from distant reaches of space. They suspect such eruptions result from the merging of two neutron stars—the collapsed cores of dying stars—or from the collision of a neutron star and a black hole.

    But gamma rays alone can’t tell them that. The story of the dense, crashing cores would be more convincing if astronomers saw a second signal coming from the same event—for example, the release of ripples in space-time called gravitational waves.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    “The Fermi Large Area Telescope detects a few short gamma ray bursts per year already, but detecting one in correspondence to a gravitational-wave event would be the first direct confirmation of this scenario,” says postdoctoral researcher Giacomo Vianello of the Kavli Institute for Particle Astrophysics and Cosmology, a joint institution of SLAC National Accelerator Laboratory and Stanford University.

    Scientists discovered gravitational waves in 2015 (announced in 2016). Using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, they detected the coalescence of two massive black holes.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    LIGO scientists are now sharing their data with a network of fellow space watchers to see if any of their signals match up. Combining multiple signals to create a more complete picture of astronomical events is called multi-messenger astronomy.​

    Looking for a match

    “We had this dream of finding astronomical events to match up with our gravitational wave triggers,” says LIGO scientist Peter Shawhan of the University of Maryland. ​

    But LIGO can only narrow down the source of its signals to a region large enough to contain roughly 100,000 galaxies.

    Searching for contemporaneous signals within that gigantic volume of space is extremely challenging, especially since most telescopes only view a small part of the sky at a time. So Shawhan and his colleagues developed a plan to send out an automatic alert to other observatories whenever LIGO detected an interesting signal of its own. The alert would contain preliminary calculations and the estimated location of the source of the potential gravitational waves.

    “Our early efforts were pretty crude and only involved a small number of partners with telescopes, but it kind of got this idea started,” Shawhan says. The LIGO Collaboration and the Virgo Collaboration, its European partner, revamped and expanded the program while upgrading their detectors. Since 2014, 92 groups have signed up to receive alerts from LIGO, and the number is growing.

    LIGO is not alone in latching onto the promise of multi-messenger astronomy. The Supernova Early Warning System (SNEWS) also unites multiple experiments to look at the same event in different ways.

    Neutral, rarely interacting particles called neutrinos escape more quickly from collapsing stars than optical light, so a network of neutrino experiments is prepared to alert optical observatories as soon as they get the first warning of a nearby supernova in the form of a burst of neutrinos.

    National Science Foundation Director France Córdova has lauded multi-messenger astronomy, calling it in 2016 a bold research idea that would lead to transformative discoveries.​

    The learning curve

    Catching gamma ray bursts alongside gravitational waves is no simple feat.

    The Fermi Large Area Telescope orbits the earth as the primary instrument on the Fermi Gamma-ray Space Telescope.

    NASA/Fermi Telescope

    The telescope is constantly in motion and has a large field of view that surveys the entire sky multiple times per day.

    But a gamma-ray burst lasts just a few seconds, and it takes about three hours for LAT to complete its sweep. So even if an event that releases gravitational waves also produces a gamma-ray burst, LAT might not be looking in the right direction at the right time. It would need to catch the afterglow of the event.

    Fermi LAT scientist Nicola Omodei of Stanford University acknowledges another challenge: The window to see the burst alongside gravitational waves might not line up with the theoretical predictions. It’s never been done before, so the signal could look different or come at a different time than expected.

    That doesn’t stop him and his colleagues from trying, though. “We want to cover all bases, and we adopt different strategies,” he says. “To make sure we are not missing any preceding or delayed signal, we also look on much longer time scales, analyzing the days before and after the trigger.”

    Scientists using the second instrument on the Fermi Gamma-ray Space Telescope have already found an unconfirmed signal that aligned with the first gravitational waves LIGO detected, says scientist Valerie Connaughton of the Universities Space Research Association, who works on the Gamma-Ray Burst Monitor. “We were surprised to find a transient event 0.4 seconds after the first GW seen by LIGO.”

    While the event is theoretically unlikely to be connected to the gravitational wave, she says the timing and location “are enough for us to be interested and to challenge the theorists to explain how something that was not expected to produce gamma rays might have done so.”

    From the ground up

    It’s not just space-based experiments looking for signals that align with LIGO alerts. A working group called DESgw, members of the Dark Energy Survey with independent collaborators, have found a way to use the Dark Energy Camera, a 570-Megapixel digital camera mounted on a telescope in the Chilean Andes, to follow up on gravitational wave detections.​


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    “We have developed a rapid response system to interrupt the planned observations when a trigger occurs,” says DES scientist Marcelle Soares-Santos of Fermi National Accelerator Laboratory. “The DES is a cosmological survey; following up gravitational wave sources was not originally part of the DES scientific program.”

    Once they receive a signal, the DESgw collaborators meet to evaluate the alert and weigh the cost of changing the planned telescope observations against what scientific data they could expect to see—most often how much of the LIGO source location could be covered by DECam observations.

    “We could, in principle, put the telescope onto the sky for every event as soon as night falls,” says DES scientist Jim Annis, also of Fermilab. “In practice, our telescope is large and the demand for its time is high, so we wait for the right events in the right part of the sky before we open up and start imaging.”

    At an even lower elevation, scientists at the IceCube neutrino experiment—made up of detectors drilled down into Antarctic ice—are following LIGO’s exploits as well.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    Lunar Icecube

    IceCube DeepCore

    IceCube PINGU

    DM-Ice II at IceCube

    “The neutrinos IceCube is looking for originate from the most extreme environment in the cosmos,” says IceCube scientist Imre Bartos of Columbia University. “We don’t know what these environments are for sure, but we strongly suspect that they are related to black holes.”

    LIGO and IceCube are natural partners. Both gravitational waves and neutrinos travel for the most part unimpeded through space. Thus, they carry pure information about where they originate, and the two signals can be monitored together nearly in real time to help refine the calculated location of the source.

    The ability to do this is new, Bartos says. Neither gravitational waves nor high-energy neutrinos had been detected from the cosmos when he started working on IceCube in 2008. “During the past few years, both of them were discovered, putting the field on a whole new footing.”

    Shawhan and the LIGO collaboration are similarly optimistic about the future of their program and multi-messenger astronomy. More gravitational wave detectors are planned or under construction, including an upgrade to the European detector Virgo, the KAGRA detector in Japan, and a third LIGO detector in India, and that means scientists will home in closer and closer on their targets.​


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    IndIGO LIGO in India

    IndIGO in India

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:54 pm on May 31, 2017 Permalink | Reply
    Tags: , , , , , U Wisconsin IceCube   

    From U Wisconsin IceCube: “A model-independent observation of an astrophysical neutrino flux 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    30 May 2017
    Sílvia Bravo

    The astrophysical neutrino flux observed by IceCube has been the focus of many studies, by both the IceCube Collaboration and other scientists around the world. The collaboration announces today a new study that finds an excess of muon neutrinos at energies above 126 TeV, which is compatible with recent measurements of the astrophysical neutrino flux and constitutes the first model-independent measurement of this flux. These results have been submitted recently to the European Physical Journal C.

    1
    Comparison of the unfolded overall spectrum of muon neutrinos to a likelihood analysis of six years of IceCube data. Credit: IceCube Collaboration

    The muon neutrino flux has two main components: atmospheric neutrinos, created by cosmic ray showers in the atmosphere, and extraterrestrial neutrinos, also called astrophysical neutrinos. Most searches are based on models using specific values for the spectral shape of each component that feed Monte Carlo simulations, which are later compared to data.

    However, this energy spectrum can also be extracted from experimental data using less strict assumptions of the cosmic ray composition or any spectral shape, which allows the direct comparison of data and theoretical predictions. To do that, one needs to compute the energy spectrum of the incoming muon neutrinos from the energy spectrum of the reconstructed muons—created by the interaction of neutrinos with the ice—which usually produce tracks only partially contained in the detector. This the so-called unfolding process.

    IceCube researchers have performed this unfolding using one year of data taken with the IC79 configuration, i.e., the last year before the completion of the detector. The unfolded spectrum covers an energy range from 125 GeV to 3.2 PeV, extending IceCube’s reach by a factor of 3 compared to previous studies using smaller instrumented volumes—IC40 and IC59.

    2
    The obtained muon neutrino spectrum of this analysis compared to the unfolding analyses of AMANDA, ANTARES, and IceCube-59. The unfoldings can have slightly different zenith dependent sensitivities. In addition to the unfolding results the best fits and its uncertainties from an IceCube parameter fit, evaluated for the zenith dependent sensitivity of this work, are shown. Credit: IceCube Collaboration.

    The IC79 unfolded spectrum shows good compatibility with theoretical predictions for a purely atmospheric composition up to about 126 TeV. However, for the first time, at higher energies this unfolded spectrum shows an excess with respect to the atmospheric-only predictions and is in good agreement with recent measurements of the astrophysical neutrino flux. Earlier IC40 and IC59 unfolded measurements had not found any hint of a nonatmospheric component, which can be explained by the lower maximum energy and larger uncertainties of those analyses.

    The flattening observed above 126 TeV follows the trend observed in other measurements of the astrophysical flux with IceCube. When comparing the unfolded muon neutrino spectrum to theoretical predictions for the atmospheric neutrino flux, the excess in the energy range between 126 TeV and 1.8 PeV is up to 2.8 sigma. The exact value of the significance depends on the theoretical framework used to describe the atmospheric neutrino flux and interactions. At higher energies, the significance is reduced due to larger uncertainties.

    See the full article here .

    Please help promote STEM in your local schools.

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    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.

     
  • richardmitnick 1:40 pm on May 27, 2017 Permalink | Reply
    Tags: , , , , , U Wisconsin IceCube, WIPAC scientists lead UW2020: WARF Discovery Initiative award   

    From U Wisconsin IceCube- “WIPAC scientists lead UW2020: WARF Discovery Initiative award” 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    May 26, 2017
    Sílvia Bravo

    1
    Kael Hanson, WIPAC director and professor of physics at UW–Madison. Credit: WIPAC.

    Kael Hanson, WIPAC director and a professor of physics at UW–Madison, has been awarded a UW2020: WARF Discovery Initiative grant to explore the potential of the Askaryan radio detection method in the future upgrade of the IceCube Neutrino Observatory, the so-called IceCube-Gen2 facility.

    1
    U Wisconsin IceCube Gen 2

    High-energy neutrinos are a big deal for WIPAC scientists and staff. Under Hanson’s supervision, over sixty scientists and technicians work on the maintenance and operations activities of the IceCube Neutrino Observatory, a cubic-kilometer detector at the South Pole, including data taking and management. A smaller group of faculty, researchers, and students also works on data analysis and has produced outstanding IceCube results, including the discovery of astrophysical neutrinos. This team includes IceCube principal investigator Francis Halzen and IceCube associate director for science and instrumentation Albrecht Karle. Halzen and Karle are also professors of physics at UW–Madison.

    IceCube detects high-energy neutrinos by recording the bluish light, also called Cherenkov light, produced when neutrinos interact in the ice and emit showers of charged secondary particles. IceCube has instrumented a huge volume of ice to capture these rare neutrino events, whose flux decreases drastically with energy. As a result, IceCube’s sensitivity to neutrinos above 10 PeV is very limited.

    Consequently, the WIPAC team in conjunction with the worldwide IceCube-Gen2 Collaboration, is boosting efforts on IceCube-Gen2. The new facility will include a larger optical Cherenkov detector array, similar to the current in-ice detector, and will also feature other detectors to improve and broaden the science scope.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.

     
  • richardmitnick 1:22 pm on May 24, 2017 Permalink | Reply
    Tags: , , , , , U Wisconsin IceCube   

    From U Wisconsin IceCube: “IceCube sets new best limits for dark matter searches in neutrino detectors” 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    24 May 2017
    Sílvia Bravo

    Studies aimed at understanding the nature and origin of dark matter include experiments in astronomy, astrophysics and particle physics. Astronomical observations point to the existence of dark matter in large amounts and in many cosmic environments, including the Milky Way. However, at the same time, the international quest to detect a dark matter interaction has so far been unsuccessful.

    IceCube has proven to be a champion detector for indirect searches of dark matter using neutrinos. As the amount of data grows and a better understanding of the detector allows making evermore precise measurements, the IceCube Collaboration continues exploring a vast range of dark matter energies and decay channels. In the most recent study, the collaboration sets the best limits on a neutrino signal from dark matter particles with masses between 10 and 100 GeV. These results have recently been submitted to the European Physical Journal C.

    2
    Comparison of upper limits on , i.e., the velocity averaged product of the dark matter self-annihilation cross section and the relative velocity of the dark matter particles, versus WIMP mass, for dark matter self-annihilating through taus to neutrinos. The ‘natural scale’ refers to the value that is needed for WIMPs to be a thermal relic. Credit: IceCube Collaboration.

    Searches for dark matter usually focus on a generic candidate, called a weakly interacting massive particle, or WIMP. Physicists expect WIMPs to interact with other matter particles or to self-annihilate, producing a cascade of known particles, which for many channels and energies include neutrinos that can be detected on Earth. If this is the case, a neutrino detector on Earth is expected to detect an excess of neutrinos related to the distribution of dark matter in our galaxy. A similar signal is expected for photons.

    “The enormous size of IceCube allows the rare detection of high-energy neutrinos, but it is also essential for the detection of neutrinos at lower energies as it serves to identify incoming muons produced in cosmic ray air showers, which is a major challenge in searching for a signal from the Southern Hemisphere,” explains Morten Medici, a PhD student at the Niels Bohr Institute in Denmark and corresponding author of this study.

    See the full article here .

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    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.

     
  • richardmitnick 2:53 pm on May 9, 2017 Permalink | Reply
    Tags: Astrophysical neutrinos, , , U Wisconsin IceCube   

    From U Wisconsin IceCube: “Searching for neutrino sources with IceCube cascade events” 

    icecube
    U Wisconsin IceCube South Pole Neutrino Observatory

    09 May 2017
    Sílvia Bravo

    Astrophysical neutrinos show up with two different signatures in IceCube: tracks and cascades. The direction of tracks, produced by muon neutrino charged interactions, can be reconstructed with an angular resolution of less than a degree. On the other hand, the direction of cascade events, produced by muon neutrino neutral interactions or electron and tau neutrino interactions, can only be reconstructed with a resolution of 10-20 degrees.

    Most IceCube efforts to identify the first sources of astrophysical neutrinos have concentrated on tracks, especially those with an origin in the Northern Hemisphere, where the atmospheric muon background is almost negligible. Now, the IceCube Collaboration presents the first search for neutrino sources using cascade events with an energy above 1 TeV. Although no significant clustering was observed, this method provides an independent technique to search for astrophysical neutrino sources. These results have just been submitted to The Astrophysical Journal.

    1
    Two-year starting cascade sky map in equatorial coordinates (J2000). The sky map shows pre-trial p-values for all locations in the sky. The grey curve indicates the galactic plane, and the grey dot indicates the galactic center.

    From May 2010 to May 2012, IceCube detected 263 cascades that started in the detector. Using those, researchers have looked for point-like sources anywhere in the sky, for neutrinos correlated with an a priori catalog, and for neutrinos associated with the galactic plane.

    The all-sky search looking for deviations from the isotropic expectation did not find any significant clustering, nor did the search for emission from the galactic plane. Researchers have also searched for neutrino emission correlated to catalog sources, which allowed setting upper limits on the flux from each object in the catalog.

    Even though no significant clustering was observed, the study shows that these cascades provide a better sensitivity to sources in the southern sky.

    “It is very challenging to obtain a high-purity selection of muon neutrino events from the southern sky in IceCube,” says Mike Richman, a researcher at Drexel University and a corresponding author of this paper. “Cascade events are easier to distinguish from the large cosmic ray muon background, which results in a much lower energy threshold for sources in the southern sky.”

    The source searches were performed with a sample of cascade events previously studied in the context of spectral measurements over the entire sky. The angular resolution is much better for tracks, but since the cascade channel benefits from a low rate of atmospheric backgrounds, it offers a complementary view of southern sources.

    The collaboration is now working on improvements that will reduce the angular resolution for IceCube cascades and provide a better understanding of the relevant systematics.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.

     
  • richardmitnick 2:01 pm on February 7, 2017 Permalink | Reply
    Tags: Anisotropies in Our Galaxy, , , , Origin and acceleration mechanisms of cosmic rays?, Tibet Air Shower experiment, U Wisconsin IceCube   

    From astrobites: ” Anisotropies in Our Galaxy” 

    Astrobites bloc

    Astrobites
    2.7.17
    Kelly Malone

    Title: Northern sky Galactic Cosmic Ray anisotropy between 10-1000 TeV with the Tibet Air Shower Array
    Authors: The Tibet AS Collaboration
    First Author’s Institution: Yale University
    Yale University bloc
    Status: Accepted to ApJ, open access

    1
    The Tibet Air Shower Array, located at over 14,000 ft in elevation, searches for signs of cosmic rays. [ICRR]

    One of the big unsolved mysteries in particle astrophysics is the origin and acceleration mechanisms of cosmic rays, or charged particles that are constantly bombarding the Earth. It is impossible to tell which astronomical source is the origin of any one particular cosmic ray. Because cosmic rays are charged particles, they are deflected on their way to Earth by our galactic magnetic field. Due to this effect, one might expect cosmic rays to arrive isotropically (in equal numbers in every direction), with slight anisotropy because of diffusion effects. However, that is not what is observed. Instead, there is a large-scale anisotropy with an energy-dependent amplitude. This causes problems for traditional diffusion models. Studying this anisotropy is important in learning more about cosmic rays.

    Today’s bite uses roughly five years of data from the Tibet Air Shower experiment, located at 4300 meters above sea level in Tibet, to provide an update in the study of the cosmic-ray anisotropy. The area of the sky they looked at is slightly larger than in their previous papers, and when combined with data from the IceCube experiment in Antarctica, allows us to have a complete picture of the entire sky in the energy range of a few hundred TeV.

    U Wisconsin ICECUBE neutrino detector at the South Pole
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector at the South Pole

    3
    Left: The anisotropy, as seen in 5 different energy bins. From top to bottom, the median energy is 15, 50, 100, 300 and 1000 TeV. Right: The 1D projection of the plot on the left. The blue curve is the first harmonic fit to the data. Note how the phase changes with energy. [Amenomori et al. 2017]

    Maps were binned according to energy and analyzed. A summary of results can be found below.

    In the map corresponding to a median energy of ~300 TeV, there are two regions that can be seen by eye: one area where there is an excess of cosmic rays, and another area where there is a deficit. Only the excess is statistically significant after taking trials into account. (For a description of what “trials” are in a statistical context, check out this page about the “look-elsewhere effect“). This result is consistent with what IceCube sees in a similar energy range. The authors looked to see if this anisotropy is due to the Compton-Getting effect (i.e. if it was caused by the motion of our solar system around the center of our Galaxy). The Compton-Getting effect predicts that we would see more cosmic rays coming from the direction that the Earth is moving toward, with a deficit coming from the other direction. They concluded that this particular excess is not related to the Compton-Getting effect.

    The anisotropy appears to be energy dependent. The maps in the 15–50 TeV range have completely different features than the maps at a few hundred TeV/1 PeV. (See the figure above for an illustration)

    These effects are not related to seasonal variations in the performance of the detector (atmospheric effects can affect experiments such as the Tibet Air Shower array, but it was shown to be negligible in this case).

    So what are the implications of this? Well, for one, studies like these give us some hints as to the origins of cosmic rays. For example, at a few hundred TeV, the most significant excess is coming from the direction of the Galactic center. However, the observed energy dependence shows that there is still a lot to learn about how cosmic rays diffuse. Changes in the anisotropy with energy may imply that the cosmic ray propagation parameters are evolving.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
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