From IceCube: “IceCube aims for neutron astronomy”

icecube
IceCube South Pole Neutrino Observatory

20 Jul 2016
Sílvia Bravo

Cosmic-ray studies with IceCube have provided the first measurement of the anisotropy in the Southern Hemisphere. We have also measured the cosmic-ray flux, searching for signatures that can tell us about the transition from galactic to extragalactic sources and the chemical composition of cosmic rays.

And now it’s the neutron’s turn to reveal what it can tell us about galactic cosmic ray sources. The IceCube Collaboration presents results from a search for sources of high-energy neutrons using four years of data from IceTop, the surface detector array.

2
IceTop

Researchers have not found any evidence for astrophysical neutrons, but the results have allowed the collaboration to set new limits that constrain the possible galactic neutron sources. These results have just been submitted to the Astrophysical Journal.

1
Equatorial polar skymap of flux upper limit values for each search window. Image: IceCube Collaboration.

Neutrons cannot be accelerated by shock waves like cosmic-ray protons and other charged nuclei, but they can be produced in the interactions of cosmic rays with matter in and nearby the sources. They would then propagate in a straight line until they decay, travelling distances of about 10 pc per every PeV of energy.

These high-energy neutrons produce a shower of particles when they reach the Earth’s atmosphere—a cascade of particles very similar to the one produced by charged cosmic rays—and could be detected by IceTop in the energy range of around a few PeV and above.

The search for galactic astrophysical neutrons in IceTop looked for point sources in the cosmic ray anisotropy. Neutrons are not deflected by magnetic fields and will point back to their sources, which allows performing neutron astronomy at increasing distances with higher energy neutrons. However, to date, no experiment has been able to measure a source of astrophysical neutrons.

IceCube researchers performed two different analyses. The first one searched for hot spots anywhere in the southern sky, while the second one searched for correlations with known galactic sources, assuming that many or all these high-energy photon sources also emit neutrons.

The results show no significant clustering of proton-like air showers in IceTop, which could be an indication of a neutron contribution to the cosmic-ray anisotropy. The lack of neutron sources allows setting the first neutron flux upper limits in the Southern Hemisphere for energies between 10 PeV and 1 EeV.

The absence of PeV neutrons in IceTop data could be an indication of galactic neutron sources farther away, or it could be a hint that sources with GeV-TeV photon emission don’t produce neutrons. What these results definitely tell is that there is still plenty to learn before we can claim neutron astronomy as a reality.

Science paper:
Search for Sources of High Energy Neutrons with Four Years of Data from the IceTop Detector,” The IceCube Collaboration: M.G.Aartsen et al, Submitted to the Astrophysical Journal, arxiv.org/abs/1607.05614

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.

#basic-research, #icecube-experiment, #icetop, #neutrons

From AAS NOVA: “IceCube’s Search for Neutrinos from Gamma-Ray Bursts”

AASNOVA

Amercan Astronomical Society

29 June 2016
Susanna Kohler

cosmic-ray accelerator hidden
Cosmic-ray accelerator hidden, Bill Saxton at NRAO/AUI/NSF, modified by Kohta Murase at Penn State University

In a cubic kilometer of volume of ice under Antarctica, an observatory called IceCube is taking measurements that may help us to determine what causes the ultra-high-energy cosmic rays (UHECRs) we occasionally observe from Earth. A recent study reports on its latest results.

Atomic Baseballs

Cosmic rays are high-energy radiation primarily composed of protons and atomic nuclei. When these charged and extremely energetic particles impact the Earth’s atmosphere on their journey through space, they generate showers of secondary particles that we then detect.

A UHECR is any cosmic-ray particle with a kinetic energy exceeding 1018 eV — and some have been detected with energies of more than 1020 eV! In practical terms, this is an atomic nucleus with the same kinetic energy as a baseball pitched at 60mph. These unbelievably energetic particles are quite rare, but we’ve observed them for decades. Yet in spite of this, the source of UHECRs is unknown.

Gamma-Ray Burst Fireballs

One proposed source that could accelerate particles to these energies is a gamma-ray burst (GRB). In some models for GRBs, the explosion is envisioned as a relativistically expanding fireball of electrons, photons and protons. Internal shock fronts accelerate electrons and protons within the fireball, generating UHECRs, gamma rays, and neutrinos in the process.

Because the charged cosmic-ray particles can be easily deflected as they travel, it’s difficult to identify where they came from. Neutrinos and photons, on the other hand, both travel largely undeflected through the universe. As a result, if we detect high-energy neutrinos that are correlated with gamma-ray photons from a GRB, this would provide strong support for GRB fireball models for UHECR production.

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

Heading Under the Ice

How do we search for these neutrinos? Enter IceCube, an neutrino observatory that consists of a cubic kilometer of detectors lying deep under the Antarctic ice. This observatory is designed to detect the by-products of the rare interactions neutrinos passing through the Earth might have with molecules of water in the ice.

In a recently published study by the IceCube Collaboration, the team performed a three-year search for neutrinos that were correlated with the locations and times of more than 800 known GRBs during that period.

3
Three different fireball models for GRBs, and the predicted neutrino flux from each. The neutrinos potentially detectable by IceCube are shown with solid segments. IceCube’s detections (and lack thereof) place new constraints on these models. [Aartsen et al. 2016]

New Constraints

From three years of data, the collaboration reports the detection of five low-significance events correlated with five GRBs. But these events are also consistent with the background of charged particles generated in Earth’s atmosphere. What does this mean? These detections could indicate a small number of real neutrinos generated by GRBs — or they could just be background noise.

Either way, these results from IceCube provide a new upper limit on the association of neutrinos with gamma-ray bursts. This constrains which production mechanisms are possible, eliminating some models for UHECR acceleration by GRB fireballs.

What’s next? The collaboration indicates that the next generation IceCube-Gen2 detector, planned for the future, will be even more sensitive — which will either result in the detection of more subtle neutrino events associated with GRBs, or it will further disfavor GRBs as the production mechanism for UHECRs.

Citation

M. G. Aartsen et al 2016 ApJ 824 115. doi:10.3847/0004-637X/824/2/115

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

#aas-nova, #basic-research, #icecube-experiment, #neutrinos-from-gamma-ray-bursts

From IceCube: “Searching for dark matter using IceCube cascades”

icecube
IceCube South Pole Neutrino Observatory

02 Jun 2016
Sílvia Bravo

IceCube searches for dark matter in the galactic center and halo have shown competitive results with other neutrino telescopes. IceCube has also searched for dark matter annihilations in the Sun that resulted in the world’s best limits for masses of around 100-200 GeV.

The IceCube Collaboration presents a new search for dark matter annihilation from the galactic center and halo using cascade events, i.e., particle showers created by the interaction of electron and tau neutrinos and Z-boson mediated muon neutrinos. Scientists searched for interactions starting in the DeepCore subarray between May 2011 and May 2012 and found no neutrino excess with respect to the background-only hypothesis, which allowed them to derive upper limits on dark matter candidates with masses between 30 GeV and 10 TeV. These results have been submitted today to the European Physical Journal C.

1
Comparison of upper limits on the velocity-averaged WIMP self-annihilation cross section versus WIMP mass. This work (IC86 Halo Casc.) is compared to ANTARES and previous IceCube searches with different detector configurations. Also shown are upper limits from gamma-ray searches from dwarf spheroidal galaxies (dSphs) by FermiLAT, MAGIC and VERITAS, as well as a recent limit from the combination of FermiLAT and MAGIC results. The three shaded areas indicate allowed regions if the electron+positron flux excess seen by FermiLAT, H.E.S.S. and the positron excess seen by PAMELA (3 sigma in dark green, 5 sigma in light green and gray area, respectively) would be interpreted as originating from dark-matter annihilations. The natural scale denotes the minimum value of the velocity-averaged cross section needed for WIMPs to be the solution to the dark matter problem as thermal relics. Image: IceCube Collaborartion.

There are several theoretical models that predict the effects of the self-annihilation of WIMPs (weakly interacting massive particles), the dark matter candidate type tested in this study, in the Milky Way. A search using all neutrino flavors is more sensitive to models in which WIMPs annihilate preferably to leptons, i.e., creating a flux of electron and tau neutrinos. However, all-flavor searches can also test other WIMPs models.

IceCube researchers have used one year of data to test a new channel for dark matter searches, which resulted not only in an independent measurement but also improved previous IceCube searches for masses above 200 GeV and previous results from other neutrino telescopes ffor masses below 1 TeV. “This is another example of the rich physics possibilities that the DeepCore extension brought to IceCube,” says Carlos Pérez de los Heros, an IceCube researcher at Uppsala University and a corresponding author of this work.

The study is based on events that start inside the DeepCore subarray, which are selected by using surrounding IceCube strings as a veto region. This selection eliminates most of the atmospheric muon background. By using cascade-like events, the atmospheric neutrino background—made up of only muon neutrinos, which usually show up as a track—is also greatly reduced.

IceCube results, like those from other neutrino telescopes, are not yet competitive with atmospheric Cherenkov telescopes and gamma-ray satellites.

Cherenkov Telescope Array, http://www.isdc.unige.ch/cta/
Cherenkov Telescope Array, http://www.isdc.unige.ch/cta/

NASA/Fermi Telescope
NASA/Fermi Telescope

ESA/Integral.
ESA/Integral

However, neutrinos provide an alternative way to search for dark matter that is also much less dependent on the underlying dark matter distribution. Thus, IceCube results are more robust, and they also probe channels, e.g., the direct annihilation to neutrinos, that are not available to gamma-based detectors.

+ Info “All-flavour Search for Neutrinos from Dark Matter Annihilations in the Milky Way with IceCube/DeepCore,” The IceCube Collaboration: M.G.Aartsen et al, Submitted to European Physical Journal C, arxiv.org/abs/1606.00209

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.

#basic-research, #icecube-experiment, #neutrinos, #searching-for-dark-matter-using-icecube-cascades

From Business Insider via IceCube: “Step inside some of the biggest, coolest experiments in the world”

icecube
U Wisconsin IceCube South Pole Neutrino Observatory

Business Insider logo

May 19, 2016,
Ali Sundermier

Scientists call it the “ghost particle.”

It has almost no mass, travels at essentially the speed of light, and has evaded scientific confirmation for three decades.

Meet the neutrino, which scientists hope will help them answer dozens of critical questions about the universe, including why it’s full of matter.

Neutrinos are produced when radioactive elements decay. They gush out of the sun, other stars, and even our own bodies. They also travel through huge amounts of matter without even flinching.

So how do you study a particle that can pass through a light-year of lead without being stopped? With some really big experiments. Take a look:

1
The GERmanium Detector Array (GERDA) looks for neutrinos by monitoring the electrical activity inside pure Germanium crystals isolated deep under a mountain in Italy. The scientists who operate GERDA are hoping to spot a very rare type of radioactive decay.

When the Big Bang gave birth to our universe 13.7 billion years ago, it should have produced equal amounts of matter and antimatter, scientists say. And when matter and antimatter collide, they destroy each other, leaving behind nothing but energy.

And yet, here we are.

If the scientists are able to spot the decay they’re looking for, it could imply that a neutrino can be both a particle and an antiparticle at the same time, which would explain why the universe favored matter and why you’re here today.

2
The Canadian Sudbury Neutrino Observatory (SNO) is buried roughly a mile underground. It was originally built in the 1980s but was recently repurposed to form SNO+.

SNO+ will investigate neutrinos from Earth, the sun, and even supernovae. At its heart is a huge plastic sphere filled with 800 tons of a special fluid called liquid scintillator. The sphere is surrounded by a shell of water and held in place by ropes. It’s monitored by an array of about 10,000 extremely sensitive light detectors called photomultiplier tubes (PMTs).

When neutrinos interact with other particles in the detector, they produce light in the liquid scintillator, which the PMTs are designed to pick up.

Thanks to the original SNO detector, scientists now know there at least three different kinds, or “flavors,” of neutrinos, which they change back and forth between as they speed through space.

3
IceCube neutrino detector interior
Meet the largest neutrino detector in the world. IceCube, located at the South Pole, uses 5,160 sensors distributed over a billion tons of ice to spot high-energy neutrinos from extremely violent cosmic sources like exploding stars, black holes, and neutron stars.

When neutrinos crash into water molecules in the ice, they release high-energy eruptions of subatomic particles that can stretch as far as six city blocks, Symmetry reports. These particles move so quickly that they emit a brief cone of light, called Cherenkov radiation. That’s what IceCube’s detectors pick up.

The scientists hope to use this information to reconstruct the path of the neutrinos and identify their source.

3
Daya Bay is a neutrino experiment that uses three experimental halls buried in the hills of Daya Bay, China. Six cylindrical detectors, each containing 20 tons of liquid scintillator, are clustered in the halls and surrounded by close to 1,000 PMTs. They are submerged in pools of pure water to block out any surrounding radiation.

A nearby group of six nuclear reactors churns out “millions of quadrillions of harmless electron antineutrinos every second.” This stream of antineutrinos interacts with the liquid scintillator to emit brief flashes of light, which are picked up by the PMTs.

Daya Bay is built to investigate neutrino oscillations. Just like neutrinos, antineutrinos change between different flavors. Scientists at Daya Bay are trying to figure out how many antineutrinos evade detection at the farthest detector because they’ve changed flavors.

4
Super-Kamiokande (Super K) is a neutrino observatory a little over 3,000 feet underground beneath the mountains of western Japan. The massive detector contains 50,000 tons of pure water surrounded by about 11,200 PMTs, which staff must fix by boat.

Similar to IceCube, Super K detects neutrinos using Cherenkov radiation. And Super K beat SNO to the punch in 1998 by being the first observatory to find strong evidence of neutrinos oscillating between flavors, which also showed that the tiny particles have mass.

Now, its researchers are shooting an underground, 180-mile-long beam of neutrinos at the detector to further investigate these oscillations. For another upcoming experiment, Deep Underground Neutrino Experiment (DUNE), scientists plan to send a beam of neutrinos roughly five times that distance.
SEE ALSO: How scientists use a giant telescope in Antarctica to study the strangest particle in the universe
DON’T MISS: The neutrino: a guide to the invisible particle that has astronomers so excited

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.

#basic-research, #business-insider, #icecube-experiment, #neutrinos

From IceCube: “IC86-2016, or a new physics run for IceCube”

icecube
IceCube South Pole Neutrino Observatory

27 May 2016
Sílvia Bravo

1
The IceCube Lab at the South Pole collects data from over 5,000 light sensors. Around one terabyte (TB) of data is recorded every day, which is then filtered, cleaned, and sent to the north over satellite. Image: Sven Lidstrom, IceCube/NSF

“On behalf of the operations group, I’m happy to report that as of run 127950 on 2016-05-20, 20:38:47 UTC, we have started the IC86-2016 physics run.” With these words, every IceCuber learned that we were entering a new year of data for IceCube. The mail was sent by John Kelley, who manages the detector operations in IceCube.

But what makes a new physics run special when IceCube is already taking data 99% of the time every day of the year? Well, data samples are delivered to IceCube researchers for analysis in one-year blocks. When the IceCube Collaboration searches for cosmic neutrinos or measures neutrino oscillations, it uses at least one year of data. Sure, scientists may sometimes use two or more years of data, too, but they will never use 1.5 years.

The reason is that updates to the data-taking system as well as detector calibrations are done yearly and need to be taken into account when analyzing the data. “It’s exciting that after more than five years since the completion of IceCube, we’re still expanding the physics reach of the detector by deploying new trigger and filter algorithms,” said Kelley when talking about the start of the IC86-2016 physics run.

But before detailing the updates, let’s summarize the IC86-2015 physics run in three numbers: 8,810 hours of data, 99.8% detector uptime and 97.9% analysis-ready data, also called clean uptime. Take a look at the numbers of the 2014 run. Since detector performance is so high, continued improvements by the IceCube operations group yield only small changes now. Still, they provided an extra 52 hours of interesting astrophysical data. As you know, very high energy neutrinos are rare—very rare, in fact. So every hour counts!

So, now let’s talk about the updates implemented for this new physics run. Detectorwise, four new surface detectors, which were deployed during the 2015 polar season, are now fully integrated into the data acquisition system. “These add to the previous IceTop tanks and increase the efficiency to veto atmospheric background events when searching for astrophysically interesting events,” says Matt Kauer, who is the IceCube run coordinator. More surface detectors are planned for deployment in the upcoming seasons.

2
The IceCube team at the South Pole deploying the surface scintillation detectors. Image: Delia Tosi, IceCube/NSF

Also related to the surface component of IceCube, our team in Delaware developed a new IceTop trigger that has now been deployed. It uses the closely-spaced infill tanks at the center of the detector to detect low-energy cosmic ray air showers.

Other important updates include targeting an improvement for multimessenger searches within the international astrophysics and astronomy community. The quality of the event selection for track-like neutrino events has been enhanced. The very high energy alerts, which use events that start within the detector and throughgoing tracks, are now based on better online reconstructions. IceCube is currently generating about one event alert each month and about four per day at lower energy thresholds.

More significant changes have been made to the optical and gamma-ray follow-up systems, which analyze neutrinos for clustering in space or time and send alerts to other telescopes in case of an interesting coincidence. These systems had previously run at the South Pole, “but this year, neutrino events are transferred to the northern hemisphere over an Iridium satellite link and are typically available for analysis within 30 seconds after they are recorded,” describes Jim Braun, a software developer in the IceCube detector operations team. Advantages of analyzing these events using systems at UW-Madison include the ability to view sky maps in real-time, easier maintenance of analysis algorithms, and the ability to send alerts to other telescopes in a straightforward manner.

Still another interesting update is the new monopole filter, designed to search for hypothetical magnetic monopoles with moderate velocities (0.1 to 0.75 times the speed of light) and developed by our team in Wuppertal.

If the last run provided about 13 very high energy neutrinos detected—we have not yet looked at the data, but by now we know more or less what nature will provide us—, the new efforts to improve IceCube contributions to multimessenger campaigns across experiments will boost their impact. “In order to track down the source of these astrophysical neutrino events, it’s important to get the information from these events in the hands of the scientific community as quickly as possible so they can quickly look for a counterpart signal in their telescopes,” explains Erik Blaufuss, who is the IceCube analysis coordinator.

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.

#basic-research, #ic86-2016-physics-run, #icecube-experiment, #neutrinos

From IceCube: “A first search for sterile neutrinos in IceCube”

icecube
IceCube South Pole Neutrino Observatory

09 May 2016
Sílvia Bravo

IceCube studies of neutrino physics usually happen in the low-energy regime, where the inner and more dense DeepCore is the most relevant subdetector of the Antarctic observatory. However, searches for new physics beyond the Standard Model can also use the main IceCube array when the signature signal is expected at energies above 100 GeV.

The Standard Model of elementary particles , with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
The Standard Model of elementary particles , with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

This is the case for searches for light sterile neutrinos with IceCube. Sterile neutrinos could be a fourth type of neutrino that only interacts gravitationally and is able to answer questions such as why neutrinos have mass or if neutrinos are important contributors to the dark matter pool in the universe. A typical signature of light sterile neutrinos, those with mass around 1 eV, is expected to produce a strong disappearance of atmospheric muon neutrinos crossing the Earth. This effect results in a depletion at energies of a few TeV due to matter effects in neutrino oscillations.

The IceCube Collaboration has performed two independent searches, both with one year of data, searching for sterile neutrinos in the energy range between approximately 320 GeV and 20 TeV. IceCube has not found any anomalous disappearance of muon neutrinos and has placed new exclusion limits on the parameter space of the 3+1 model, a scenario with only one sterile neutrino. These results* have been submitted today to Physical Review Letters.

Results from the IceCube search. The 90% (orange solid line) CL contour is shown with bands containing 68% (green) and 95% (yellow) of the 90% contours in simulated pseudo-experiments, respectively. The contours and bands are overlaid on 90% CL exclusions from previous experiments, and the MiniBooNE / LSND 90% CL allowed region. Image: IceCube Collaboration.
Results from the IceCube search. The 90% (orange solid line) CL contour is shown with bands containing 68% (green) and 95% (yellow) of the 90% contours in simulated pseudo-experiments, respectively. The contours and bands are overlaid on 90% CL exclusions from previous experiments, and the MiniBooNE / LSND 90% CL allowed region. Image: IceCube Collaboration.

IceCube has proven to be a great tool for the study of neutrino oscillations, i.e., their change from one flavor to another, in the energy regime from a few GeV up to 50 GeV. But the detailed properties of neutrinos have not yet been fully revealed, and the international scientific community is working on several experiments that will shed new light on what neutrinos can tell us about the universe.

We know that neutrinos traveling through matter will change their oscillation pattern because of interactions with atomic electrons and nucleons. These interactions, which depend on the energy of the neutrinos and on the density of the medium, create matter enhanced oscillations that can result in a strong disappearance of antineutrinos at specific energies.

Following the first observations of neutrino oscillations back in 1998, several experiments have measured oscillations patterns at different energies and for different neutrino types. And a few of them, including LSND and MiniBooNE, have found anomalies that cannot be explained with the current model of three neutrinos.

LSND Experiment University of California
LSND Experiment University of California

FNAL/MiniBooNE
FNAL/MiniBooNE

However, theories that postulate the existence of sterile neutrinos could accommodate these results. Sterile neutrinos only interact gravitationally, and they would be harder to detect than the currently known neutrinos.

During the last few years, several experiments have been searching for sterile neutrinos. These searches have not been successful so far and have every time further constrained the sterile neutrino parameter space, namely, the relative mass and mixing angle of sterile neutrinos with the other three active neutrinos.

The sterile neutrino search announced by IceCube today used throughgoing neutrino-induced muon events, which are neutrinos that reach the detector after crossing the Earth, from the first year of data with the full detector, i.e., with 86 strings of sensors, and its results are confirmed by an independent study using the so-called IC59 data, or data taken when the detector was running with 59 strings. IceCube researchers selected atmospheric neutrinos with energies between 320 GeV and 20 TeV, which includes the energies where the existence of sterile neutrinos would introduce a new resonance effect in matter neutrino oscillations.

Sterile neutrino models predict a strong disappearance of muon antineutrinos for energies around a few TeV. And, although IceCube cannot differentiate neutrino and antineutrino interactions, if sterile neutrinos exist, it should be able to measure a significant disappearance in the total number of atmospheric muon neutrinos and antineutrinos reaching the South Pole after sailing through the Earth.

“IceCube’s search for sterile neutrinos is an example of something that experimental physicists strive for: taking a phenomenon that is weak and difficult to study and examining it using a method where its effects would be amplified,” says Ben Jones, who co-led this study while a graduate student at MIT. “By not seeing sterile neutrinos in this way, we have excluded much of the parameter space that has been inaccessible to previous sterile neutrino experiments,” adds Jones.

In fact, IceCube’s null result also excludes the allowed parameter space region for several experiments that had observed anomalies in the oscillation patterns, which were interpreted as hints of sterile neutrinos, at approximately the 99% confidence level.

“Not finding the characteristic depletion signal has allowed us to place constraints in some parameter regions that are an order of magnitude stronger than past experiments. This greatly increases the tension between experiments that claim observation and those that do not,” explains Carlos Argüelles, an IceCube researcher who received his PhD at UW–Madison working on this study. “IceCube results have changed the parameter space where sterile neutrinos may exist, calling their existence into question and impacting future search strategies,” adds Argüelles.

To sum up, sterile neutrinos are not yet ruled out, but their existence is now more remote than ever.

+ Info Searches for Sterile Neutrinos with the IceCube Detector, The IceCube Collaboration: M.G.Aartsen et al, Submitted to Physical Review Letters, arxiv.org/abs/1605.01990

*Science paper:
Searches for Sterile Neutrinos with the IceCube Detector

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

ICECUBE neutrino detector
IceCube neutrino detector interior

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.

#basic-research, #icecube-experiment, #sterile-neutrinos

From phys.org: “First high-energy neutrino traced to an origin outside of the Milky Way”

physdotorg
phys.org

1
a, The Fermi/LAT γ-ray light curve is shown as two-week binned photon fluxes between 100 MeV and 300 GeV (black), the Bayesian blocks light curve (blue), and the HESE-35 time stamp (red line). The HESE period (May 2010 to May 2013) and the included outburst time range are highlighted in colour. Only statistical uncertainties are considered and shown at a 1 sigma confidence level.

b, VLBI images show the core region at 8.4 GHz from 13 November 2011 (2011.87), 16 September 2012 (2012.71) and 14 March 2013 (2013.20) in uniform colour scale. 1 mas corresponds to about 8.3 pc. All contours start at 3.3 mJy beam−1 and increase logarithmically by factors of 2. The images were convolved with the enclosing beam from all three observations of 2.26 mas × 0.79 mas at a position angle of 9.5°, which is shown in the bottom left. The peak flux density increases from 1.95 Jy beam−1 (April 2011) to 5.62 Jy beam−1 (March 2013). Credit: Nature Physics (2016) doi:10.1038/nphys3715

An international team of researchers has spotted the first instance of a high-energy neutrino collision from a source outside of the Milky Way, marking what they describe as a significant discovery. In their paper* published in the journal Nature Physics, the team describes their work at the South Pole Neutrino Observatory, the details pertaining to the sighting and why they believe their discovery may lead to a new era in neutrino astrophysics.

U Wisconsin ICECUBE neutrino detector
IceCube neutrino detector interior
U Wisconsin ICECUBE neutrino detector

Neutrino’s are massless and have no charge and very seldom interact with other matter—the exception is when they collide head on with another particle. Scientists have been studying neutrinos for several years, believing that they may hold the key to understanding many parts of the universe that remain otherwise hidden from our view. To see evidence of them, researchers fill large underground tanks with different types of fluids and then use extremely sensitive sensors to capture very brief flashes of light which are emitted when a neutrino collides with something in the fluid. The team with this latest effort has taken a different approach, they have placed sensors around a kilometer sized ice cube 2.5 kilometers beneath the surface, in a location near the South Pole. The sensors capture the brief flashes that occur when neutrinos collide with particles in the ice.

Capturing evidence of collisions does not happen very often, but when it does, it sets off a chain of events that center around trying to ascertain where the neutrino came from—most come from the sun or cosmic rays striking our atmosphere. But back in 2012, the team captured evidence of what they described as the most powerful yet, registering two petavolts. Following that discovery, the team used data from radio telescopes, and in particular data from a galaxy that has been named KS B1424-418—astrophysicists have been studying it for several decades and it had been observed to undergo a change in shape during the time period 2011 to 2014. After much analysis, the team confirmed that the neutrino collision they observed was due to an emission from that very galaxy, making it the first neutrino collision to be traced back to a source outside of the Milky Way.

Science paper:
Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

About Phys.org in 100 Words

Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

#basic-research, #icecube-experiment, #neutrinos, #phys-org