From U Wisconsin IceCube Collaboration: “What can cascade events tell us about neutrino sources?”

U Wisconsin ICECUBE neutrino detector at the South Pole

From From U Wisconsin IceCube Collaboration

13 Nov 2019
Madeleine O’Keefe

On a dark, clear night, you can look up and see the Milky Way galaxy: billions of stars shining in visible light. But we also expect our galaxy to “shine” in neutrinos, elusive particles whose origins are still mysterious. There are cosmic-ray sources within our galaxy, so these sources must also produce neutrinos.

Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

We cannot see neutrinos with our eyes, but the IceCube Neutrino Observatory can detect them. IceCube “sees” with 5,160 optical sensors buried deep in glacial ice at the South Pole.

When neutrinos pass through IceCube, they will sometimes leave signals, known as “events,” primarily as either tracks or cascades. The former occur when a neutrino collides with matter in or near IceCube, resulting in a high-energy muon that travels a long distance, leaving an elongated “track” of signals in its wake. Cascades happen when all or most of the neutrino’s energy is deposited in a small region and results in a nearly spherical event, making it hard to measure the direction from which the parent neutrino came.

Cascades are more difficult to reconstruct than tracks, which are usually used in searches for astrophysical neutrino sources, but they have their own advantages, including providing a better measurement of neutrino energy. By studying cascade events, researchers enhance IceCube’s sensitivity to possible neutrino sources in the southern sky, including the Galactic Center.

In a paper published today in The Astrophysical Journal, the IceCube Collaboration outlined recent results from a source search that used seven years of data from cascade events. While they did not find any statistically significant sources of neutrino emissions, this work is an improvement on the previous source search with cascades.

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Results from the all-sky scan for neutrino point sources, with the center and plane of the Milky Way shown by the grey dot and curve, respectively. No statistically significant emission was identified. Credit: IceCube Collaboration

Cascades have the advantage that atmospheric backgrounds are small and relatively uniform throughout the sky. IceCube collaborators previously used two years of cascades in a similar analysis. The current work is an improvement on that analysis in three ways: the use of seven years of data, greatly improved directional reconstruction, and the added emphasis on testing for possible sources within the Milky Way.

To perform their analysis, IceCube scientists first improved the directional reconstruction by using a deep convolutional neural network inspired by recent work in image recognition, rather than the traditional statistical approach. “In principle, the traditional approach should perform better,” says Mike Richman, a postdoctoral researcher at Drexel University and the lead on the analysis, “but in practice, our model of the glacial ice is sufficiently complex that it’s difficult to guarantee that method converges on the optimal result.”

Richman credits fellow IceCube collaborator Mirco Huennefeld of Universität Dortmund for his extensive work on the angular reconstruction used in the analysis. “Mirco has trained a model with an implicit understanding of the detector and the ice, and it’s able to obtain good results without resorting to expensive numerical scans.”

Armed with this improved reconstruction applied to seven years of data, the researchers performed two types of analysis: searches for point sources and searches for broad emission regions in our galaxy. The point source searches included a scan of the whole sky, a scan over 74 preselected potential sources, and a test for sum-total emission from three short lists of interesting supernova remnants. The broad emission regions included gas and dust distributed throughout the Milky Way and the giant “Fermi bubbles” near the center of our galaxy. Many of these tests were the most sensitive performed to date by any experiment.

Ultimately, the researchers did not find evidence for neutrino emission. However, they did acknowledge an interesting trend: As the Milky Way measurements become more sensitive (from using just IceCube tracks, to IceCube tracks and ANTARES events [The Astrophysical Journal Letters], and now to just IceCube cascades), the result becomes increasingly significant. Furthermore, the galactic neutrino energy spectrum suggested by the cascade data agrees with previous IceCube work with tracks. While not conclusive, this is consistent with emission that is just below the sensitivity of analyses done so far.

This work solidifies the importance of using all neutrino flavors to search for sources—at least with current-generation detectors. Going forward, Richman says they plan to improve the cascade analysis by applying the latest reconstructions to data collected over more time and extending to even lower energies (below 1 TeV). They expect data from the IceCube Upgrade to reduce systematic uncertainties, leading to still better sensitivity.

In the future, the plan is to study additional source types, including ones with time-dependent—and potentially very short-lived—emission. They also plan to combine IceCube tracks and cascades and ultimately to perform a “global” analysis that includes all event types from all available data.

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.

IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

Lunar Icecube

IceCube DeepCore annotated

IceCube PINGU annotated


DM-Ice II at IceCube annotated

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From Fermi National Accelerator Lab: “Gotta catch ’em all: new NOvA results with neutrinos and antineutrinos”

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FNAL Art Image by Angela Gonzales

From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

November 7, 2019
Steven Calvez
Erika Catano Mur

The latest results from the Fermilab NOvA experiment are taking us closer to describing the most basic properties of the mysterious neutrino — the most abundant particle of matter in the universe.

Neutrinos appear in a variety of natural processes, from formidable supernova explosions and nuclear reactions in the sun to radioactive decays in your banana. They are also produced in abundance in nuclear reactors and particle accelerators. Yet neutrinos barely interact with matter: a light-year of lead would hardly stop your average neutrino. Their elusive nature makes them extremely challenging to study, which explains both why we still know very little about their properties and why many scientists and experiments around the world have so much fun hunting them down.

The observation that neutrinos are able to change type — a behavior called oscillation — proved that neutrinos have masses, albeit very small. This phenomenon explains how neutrinos that are produced in one of the three “flavor” states (electron neutrino, muon neutrino or tau neutrino) transition in and out of these types as they travel a certain distance and may be detected as a different type. The probability of these transitions depends on a number of factors: the energy of the neutrino, the distance between the particle beam source and the detector, the differences in neutrino masses, the amount of blending between neutrino types, which scientists describe with three “mixing” angles, and additional complex phases.

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Fermilab’s NOvA neutrino experiment studies neutrino oscillations using a powerful neutrino beam produced by the lab’s accelerator complex. The beam, made of muon neutrinos, is sent to NOvA’s two detectors — one located at Fermilab and one located about 800 kilometers away in Minnesota, pictured here.

Fermilab’s NOvA neutrino experiment studies neutrino oscillations using the powerful NuMI neutrino beam produced by the lab’s accelerator complex. The beam, made of muon neutrinos, is sent to NOvA’s two detectors — one located at Fermilab and one located about 800 kilometers away in Minnesota. The NOvA far detector looks to identify the fraction of muon neutrinos in the NuMI beam that oscillated into electron neutrinos (called electron neutrino appearance) and the fraction of muon neutrinos that oscillated to a different flavor (called muon neutrino disappearance).

The NuMI beam is generally described as a muon neutrino beam, but it can also be made of muon antineutrinos. The antineutrino is the antiparticle of the neutrino. Just as muon neutrinos can oscillate into electron neutrinos, muon antineutrinos can oscillate into electron antineutrinos.

Experimentalists can use information from the combination of the measurements of electron and muon neutrinos, as well as their antiparticle equivalents, to draw their conclusions. For example, if the oscillation rates of antineutrinos compared to those of neutrinos are different, the implication could be a violation of a symmetry called charge parity, commonly called CP. The existence of this type of CP violation is one of the great unknowns in particle physics that NOvA is investigating.

NOvA’s latest measurements of neutrino oscillation parameters have been published in Physical Review Letters. The data were recorded between 2014 and 2019 and correspond to 8.85 x 1020 protons-on-target of neutrino beam and 12.33 x 1020 protons-on-target of antineutrino beam. This represents a 78% increase in the amount of antineutrino data compared to NOvA’s previous results, presented at the Neutrino 2018 conference.

NOvA identified 27 electron antineutrino candidate events in the NOvA far detector, compared to the 10.3 events expected if muon antineutrinos did not oscillate into electron antineutrinos. This remains the strongest evidence (4.4 sigma) of electron antineutrino appearance in a muon antineutrino beam for a long-baseline experiment. (In particle physics, 3 sigma is usually considered “strong evidence” that the conclusions of the data analysis are unlikely to be a fluke, while 5 sigma means that the experimental results qualify as a discovery.)

In addition to those 27 electron antineutrino events, 102 surviving muon antineutrino candidates were detected in the far detector, where 476 events would have been expected if muon antineutrinos did not oscillate at all. NOvA scientists combined these new events with previously recorded neutrino data and analyzed them jointly. Pictures of such neutrino and antineutrino events as recorded by the NOvA far detector are shown below.

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Four events observed in the NOvA far detector, classified as muon (left) or electron (right) neutrino interactions, with the beam in neutrino (top) or antineutrino (bottom) mode. Each panel shows two views of the same event, and the color represents the energy deposited by particles that emerged from the interaction. The latest NOvA results comprise four data samples with 113 muon neutrino to muon neutrino, 58 muon neutrino to electron neutrino, 102 muon antineutrino to muon antineutrino and 27 muon antineutrino to electron antineutrino candidates.

The results help scientists chip away another problem in neutrino physics: the ordering of the three neutrino masses — which of the three is the lightest? NOvA’s combined neutrino-antineutrino appearance and disappearance fit shows a preference (1.9 sigma) for what is called normal mass ordering: The three neutrino mass states are ordered m1 ≤ m2 ≤ m3.

NOvA is also working to measure one of the least known oscillation parameters, θ23, that governs the degree of flavor mixing in the third mass state. The fit shows a slight preference (1.6 sigma) for the value of this angle to be in the upper octant (θ23 > 45 degrees) and therefore points towards an absence of symmetry in the way muon and tau neutrino flavors contribute to the third neutrino mass state. The data recorded thus far does not allow us to draw conclusions about CP violation in neutrino interactions.

The experiment is scheduled to collect new data until 2025. NOvA collaborators are continually working to improve the experiment and analysis techniques to potentially provide a definitive statement about the neutrino mass ordering, the value of θ23, and strong constraints on the CP-violating phase. These measurements are paramount if we want to understand the neutrino properties and the role they played in the formation of the universe as we know it.

This work is supported in part by the DOE Office of Science and the National Science Foundation.

See the full here.


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Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
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From Symmetry: “ARAPUCA: Let there be light traps”

Symmetry Mag
From Symmetry<

10/24/19
Lauren Biron

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

Latin American institutions are instrumental in creating photon detectors for the Deep Underground Neutrino Experiment.

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

It started with a drive.

Physicists Ana Machado and Ettore Segreto trundled their car along an Italian road, headed from Gran Sasso National Laboratory on a 40-minute trip to pick up their son from kindergarten. As was often the case, physics was on their minds—in particular, the topic of light.

Light is a key tool in the physicist’s bag of tricks, able to give glimpses of far-off galaxies or streaks of subatomic particles. For physicists such as Machado and Segreto, it’s a crucial component in reconstructing the interactions of elusive particles called neutrinos. Neutrinos rarely interact, making every quantum of light—called a photon—released when they do a precious piece of data. How, the scientists wondered, could detectors more efficiently capture those gems of light?

They imagined a slender box that contained a silicon photomultiplier: a small detector that could count single photons. The box would contain a transparent top that light could easily pass through when entering, paired with a film that could shift the light to a different, visible wavelength. The transformed light, unable to escape through the same opening, would reflect inside the box until it was absorbed and detected by the silicon photomultiplier.

Later, Machado would liken the design to a bird trap and christen it with a name from the indigenous Guaraní word for “a trap to catch birds.” ARAPUCA was born.

With only a few months before the pair left Italy for new jobs at the University of Campinas in Machado’s home country of Brazil, they hurried to test their idea. After some internet shopping to find what filters and components they could purchase commercially (with their own money), they contacted a mechanic at Gran Sasso to help them build a box and install a silicon sensor. The simple prototype was a mere 3.3-square-centimeter container made of Teflon—but it proved the concept.

They had no idea then that their technology would soon unite scientists from across Latin America.

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

Back in Brazil
Flushed with success, the couple started their new jobs in Brazil with a focus on ARAPUCA technology and how it could be used in the international Deep Underground Neutrino Experiment (DUNE), an enormous undertaking supported by the US Department of Energy’s Office of Science and hosted by Fermi National Accelerator Laboratory near Chicago.

The massive project was beginning to take shape, with plans to construct some of the world’s largest neutrino detectors and install them 1.5 kilometers (about a mile) deep in a former-mine-turned-underground-laboratory. Shielded from extraneous signals, the detectors would then be bombarded with the world’s most intense high-energy neutrino beam.

The goal of DUNE is to unlock some of the mysteries of neutrinos, including the answer to the biggest question of all: whether they are part of the reason matter as we know it exists. To reach their aims, scientists would need to gather immense amounts of data from neutrino interactions—including the light.

At a 2015 conference in Albany, New York, Machado and Segreto presented the ARAPUCA design publicly for the first time. The reception was positive, and further tweaks and tests with Fermilab and new collaborators at Colorado State University showed a technology that was quickly maturing. The results were so good, Machado says, that they proposed installing 32 ARAPUCA modules in the first ProtoDUNE detector—a house-sized prototype to test technology for the even bigger final detectors of DUNE.

Even with the construction start-date looming, the collaboration accepted their proposal. The summer of 2017 found Machado and Segreto back in Europe, this time at CERN to install many of the ARAPUCA detectors over the course of six months. When the ProtoDUNE detector turned on in 2018, ARAPUCA’s success was clear: The technology worked, the light was there, and the tracks were beautiful.

“It’s fun to think that everything started from that moment during that long drive,” Segreto says.

“We never had the idea that ARAPUCA would become what it is now,” Machado adds. “We never thought that this idea would become a reality. Everything that has happened for us has been such a surprise.”

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

Spreading across the continent
Back in Brazil, Machado and Segreto found themselves at the center of a rapidly growing group.

ARAPUCA had become an important piece of technology for neutrino experiments, but it was still but one of a thousand parts needed to build DUNE. ARAPUCA would need to connect to cold electronics: the hardware that sits inside the liquid argon that makes up the bulk of the neutrino detector, hovering around a frosty negative 184 degrees Celsius (negative 300 degrees Fahrenheit). Those cold electronics would need to interface with DUNE’s warm electronics, which sit outside the detector at room temperature. Along with simulations and testing, there was plenty of work to do—and a growing number of people to lend a hand.

Scientific tendrils snaked their way from the University of Campinas to other universities in Brazil and on to other Latin American countries, binding together a Latin American consortium focused on the detection of light. Machado made many of the connections personally. She reached out to fellow physicists, some of whom she knew from her PhD program, and encouraged them to join with their teams.

That was how Jorge Molina, a scientist in the engineering school at the National University of Asunción in Paraguay, got involved. The school doesn’t have a postgraduate program in physics, but the engineers excel at instrumentation, so they joined to work on the electronics in 2017.

“This is a great opportunity,’” Molina says. “We’ve never been delegated a huge project like this. It’s a chance to demonstrate we can do it, and do it well. This will be the door for the next big project that comes.”

Sometimes, a lack of scientific infrastructure in the country—which has a population of 7 million, about the same as Massachusetts—means Molina’s group has to take their science on the road. Paraguay sent one researcher to Fermilab to test electronics in cryogenic temperatures at the ICEBERG testbed earlier this year.

For many partners, participating in ARAPUCA is a chance to expand their skills. The Colombian team joined to work on the warm electronics, building on their decade of experience with running simulations for the ATLAS experiment at the Large Hadron Collider at CERN and digitizing signals for small neutrino experiments.

“The difference between ATLAS and DUNE, and something that I like a lot, is that when we started on ATLAS, the detector was already designed,” says Deywis Moreno Lopez, a scientist at Colombia’s University of Antonio Nariño. “With DUNE, we have the opportunity to participate directly in the design and construction of the components. It’s a very nice opportunity to get the universities involved and make a closer contact with industry.”

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

Industrial partners will be vital for producing the hundreds upon hundreds of pieces necessary to instrument the large detectors of DUNE. Each of the four far-detector modules will hold 17,000 tons of liquid argon inside a container four stories high. Accelerator operators at Fermilab will send trillions of neutrinos from the accelerator complex in Illinois straight through the earth, no tunnel required, to the detectors in South Dakota. The fraction of neutrinos that interact will produce additional particles, including electrons and light, that will be captured by the electronics, processed by computing algorithms, and stored for data analysis. The invisible will become visible.

“This is something that is almost science fiction,” says Cesar Castromonte, a physicist at Peru’s National University of Engineering and part of the group from Peru that began working on ARAPUCA earlier this year. “People are totally surprised most of the time when I talk about neutrinos—and surprised that there are Peruvian people working on this kind of stuff.”

That “stuff” for DUNE includes hunting for an explanation as to why matter exists in our universe, trying to determine whether protons decay, and working to better understand exploding stars and the formation of black holes. They’re giant science goals using the biggest detector of its kind, and collaborators know they need to bring the best technological solutions in their arsenals. Not long after the initial ARAPUCA tests were successful, the team began working on upgrades to the design to make the equipment even better.

The new X-ARAPUCA rolled in additional light guides within the box that funneled photons toward the sensor. Tests showed even more light captured than before, and scientists decided to incorporate 200 of the newly designed modules into the plans for the Short-Baseline Near Detector (SBND) at Fermilab—another neutrino experiment and another good test for DUNE technologies. Machado says she expects the electronic boards, filters and mechanical structures to be shipped to Fermilab, assembled and installed in SBND around December.

With DUNE test detectors running, cavern preparation for the massive far detectors at Sanford Lab underway, and a recent groundbreaking for Fermilab’s new accelerator upgrades, teams around the world are pushing their pieces of DUNE forward quickly and aiming to start up the experiment around 2026.

“We are very excited,” Castromonte says. “It’s a once-in-a-lifetime chance.

See the full article here .


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From WIRED: “Physicists Get Close to Knowing the Mass of the Neutrino”

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From WIRED

10.27.2019

The KATRIN experiment is working to “weigh the ghost,” which could point to new laws of particle physics and reshape theories of cosmology.

KATRIN experiment aims to measure the mass of the neutrino using a huge device called a spectrometer (interior shown)Karlsruhe Institute of Technology, Germany

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Photograph: Forschungszentrum Karlsruhe

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The main spectrometer of the KATRIN experiment being transported to the Karlsruhe Research Center in Germany in 2006. Photograph: Forschungszentrum Karlsruhe

Of all the known particles in the universe, only photons outnumber neutrinos. Despite their abundance, however, neutrinos are hard to catch and inspect, as they interact with matter only very weakly. About 1,000 trillion of the ghostly particles pass through your body every second—with nary a flinch from even a single atom.

The fact that they’re ubiquitous, yet we don’t even know what they weigh, is kind of crazy,” said Deborah Harris, a physicist at the Fermi National Accelerator Laboratory near Chicago and York University in Toronto.

Physicists have long tried to weigh the ghost. And in September, after 18 years of planning, building and calibrating, the Karlsruhe Tritium Neutrino (KATRIN) experiment in southwestern Germany announced its first results: It found that the neutrino can’t weigh more than 1.1 electron-volts (eV), or about one-five-hundred-thousandth the mass of the electron.

This initial estimate, from only one month’s worth of data, improves on previous measurements using similar techniques that placed the upper limit on the neutrino mass at 2 eV. As its data accrues, KATRIN aims to nail the actual mass rather than giving an upper bound.

Why Mass Matters

Mass is one of the most basic and important characteristics of fundamental particles. The neutrino is the only known particle whose mass remains a mystery. Measuring its mass would help point toward new laws of physics beyond the Standard Model, the remarkably successful yet incomplete description for how the universe’s known particles and forces interact. Its measured mass would also serve as a check on cosmologists’ theories for how the universe evolved.

“Depending on what the mass of the neutrino turns out to be, it may lead to very exciting times in cosmology,” said Diana Parno, a physicist at Carnegie Mellon University and a member of the KATRIN team.

Until about two decades ago, neutrinos—which were theoretically predicted in 1930 and discovered in 1956—were presumed to be massless. “When I was in grad school, my textbooks all said neutrinos didn’t have mass,” Harris said.

That changed when, in a discovery that would win the 2015 Nobel Prize, physicists found that neutrinos could morph from one kind to another, oscillating between three “flavor” states: electron, muon and tau. These oscillations can only happen if neutrinos also have three possible mass states, where each flavor has distinct probabilities of being in each of the three mass states. The mass states travel through space differently, so by the time a neutrino goes from point A to point B, this mix of probabilities will have changed, and a detector could measure a different flavor.

If there are three different mass states, then they can’t all be zero—thus, neutrinos have mass. According to recent neutrino oscillation data (which reveals the differences between the mass states rather than their actual values), if the lightest mass state is zero, the heaviest must be at least 0.0495 eV.

Still, that’s so light compared to the mass of other particles that physicists aren’t sure how neutrinos get such tiny masses. Other particles in the Standard Model acquire mass by interacting with the Higgs field, a field of energy that fills all space and drags on massive particles. But for neutrinos, “the mass is so small, you need some additional theory to explain that,” Parno said.

Figuring out how neutrinos acquire mass may resolve other, seemingly related mysteries, such as why there is more matter than antimatter in the universe. Competing theories for the mass-generating mechanism predict different values for the three mass states. While neutrino oscillation experiments have measured the differences between the mass states, experiments like KATRIN home in on a kind of average of the three. Combining the two types of measurements can reveal the value of each mass state, favoring certain theories of neutrino mass over others.

Cosmic Questions

Neutrino mass is also of cosmic importance. Despite their minuscule mass, so many neutrinos were born during the Big Bang that their collective gravity influenced how all the matter in the universe clumped together into stars and galaxies. About a second after the Big Bang, neutrinos were flying around at almost light speed—so fast that they escaped the gravitational pull of other matter. But then they started to slow, which enabled them to help corral atoms, stars and galaxies. The point at which neutrinos began to slow down depends on their mass. Heavier neutrinos would have decelerated sooner and helped make the universe clumpier.

By measuring the cosmic clumpiness, cosmologists can infer the neutrino’s mass. But this indirect method hinges on the assumption that models of the cosmos are correct, so if it gives a different answer than direct measurements of the neutrino mass, this might indicate that cosmological theories are wrong.

So far, the indirect cosmological approach has been more sensitive than direct mass measurements by experiments like KATRIN. Recent cosmological data from the Planck satellite suggests that the sum of the three neutrino mass states can’t be greater than 0.12 eV, and in August, another analysis of cosmological observations [Physical Review Letters] found that the lightest mass must be less than 0.086 eV. These all fall well below KATRIN’s upper bound, so there’s no contradiction between the two approaches yet. But as KATRIN collects more data, discrepancies could arise.

What’s Next

The long-awaited KATRIN experiment weighs neutrinos by using tritium, a heavy isotope of hydrogen. When tritium undergoes beta decay, its nucleus emits an electron and an electron-flavored neutrino. By measuring the energy of the most energetic electrons, physicists can deduce the energy—and thus the mass (or really, a weighted average of the three contributing masses)—of the electron neutrino.

If KATRIN finds a mass of around 0.2 or 0.3 eV, cosmologists will have a hard time reconciling their observations, said Marilena Loverde, a cosmologist at Stony Brook University. One possible explanation would be some new phenomenon that causes the cosmological influence of the neutrino’s mass to wane over time. For instance, maybe the neutrino decays into even lighter unknown particles, whose near-light speeds render them incapable of clumping matter together. Or maybe the mechanism that gives mass to neutrinos has changed over cosmic history.

If, on the other hand, the neutrino mass is close to what cosmological observations predict, KATRIN won’t be sensitive enough to measure it. It can only weigh neutrinos down to 0.2 eV. If neutrinos are lighter than that, physicists will need more sensitive experiments to close in on its mass and resolve the particle physics and cosmology questions. Three potentially more sensitive projects—Project 8, Electron Capture on Holmium, and HOLMES—are already taking data with proof-of-concept instruments.

See the full article here .

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From U Wisconsin IceCube Collaboration: “New all-sky search reveals potential neutrino sources”

U Wisconsin ICECUBE neutrino detector at the South Pole

From From U Wisconsin IceCube Collaboration

21 Oct 2019
Madeleine O’Keefe

For over a century, scientists have been observing very high energy charged particles called cosmic rays arriving from outside Earth’s atmosphere. The origins of these particles are very difficult to pinpoint because the particles themselves do not travel on a straight path to Earth. Even gamma rays, a type of high-energy photon that offers a little more insight, are absorbed when traversing long distances.

The IceCube Neutrino Observatory, an array of optical modules buried in a cubic kilometer of ice at the South Pole, hunts for cosmic-ray sources inside and outside our galaxy—extending to galaxies more than billions of light years away—using hints from elusive particles called neutrinos. These neutrinos are expected to be produced by cosmic-ray collisions with gas or radiation near the sources.

Unlike cosmic rays, neutrinos are not absorbed or diverted on their way to Earth, making them a practical tool for locating and understanding cosmic accelerators. If scientists can find a source of high-energy astrophysical neutrinos, this would be a smoking gun for a cosmic-ray source.

After 10 years of searching for origins of astrophysical neutrinos, a new all-sky search provides the most sensitive probe of time-integrated neutrino emission of point-like sources. The IceCube Collaboration presents the results of this scan in a paper submitted recently to Physical Review Letters.

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The pre-trial probability of the observed signal being due to background in a 5×5 degree window around the most significant point in the Northern Hemisphere (the hottest spot); the black cross marks the Fermi-3FGL coordinates of the galaxy NGC 1068. Credit: IceCube Collaboration

Tessa Carver led this analysis under the supervision of Teresa Montaruli in the Département de Physique Nucléaire et Corpusculaire at the University of Geneva in Switzerland. “IceCube has already observed an astrophysical flux of neutrinos, so we know they exist and are detectable—we just don’t know exactly where they come from,” says Carver, now a postdoc at Cardiff University. “It is only a matter of time and precision until we can identify the sources behind this neutrino flux.”

The principle challenge in searching for astrophysical neutrino sources with IceCube is the overwhelming background of events induced by cosmic-ray interactions in our atmosphere. The signal of faint neutrino sources needs to be extracted via sophisticated statistical analysis techniques.

Using these methods, Carver and her collaborators “scanned” across the entire sky to look for point-like neutrino sources at arbitrary locations. This scanning method is able to identify very bright neutrino sources that could be invisible in gamma rays, which are also produced in cosmic-ray collisions.

In order to be sensitive to dimmer sources, they also analyzed 110 galactic and extragalactic source candidates, which have been observed via gamma rays. They then combined the results obtained for individual sources in this list in a “population analysis,” which looks for a higher-than-expected rate of significant results from the individual source list search. This allows researchers to find significant neutrino emission, even if sources in the list are too weak to be observed individually.

Researchers also employed a “stacking search” for three catalogs of gamma-ray sources within our galaxy. This search layers together all the emission from groups of known objects of the same type under the assumption that they have well-known emission properties. While it can significantly reduce the per-source emission required to observe a large excess of signal over the background, this search is limited in that it requires more knowledge of the sources in the catalog.

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Skymap of -log10(plocal), where plocal is the local pre-trial p-value, for the area between ±82 degrees declination in equatorial coordinates. The Northern and Southern Hemisphere hotspots, defined as the most significant plocal in the given hemisphere, are indicated with black circles. Credit: IceCube Collaboration

While the different analyses did not discover steady neutrino sources, the results are nevertheless exciting: some of the objects in the catalog of known sources showed a higher neutrino flux than expected, with excesses at the 3σ-level. In particular, the all-sky scan revealed that the “hottest” location in the sky is just 0.35 degrees away from the starburst galaxy NGC 1068, which has a 2.9σ excess over background. NGC 1068 is one of the closest black holes to us; it is embedded in a star-forming region with lots of matter for neutrinos to interact with while the high-energy gamma rays are attenuated, as shown by Fermi and MAGIC measurements.

NASA/Fermi LAT


NASA/Fermi Gamma Ray Space Telescope

MAGIC Čerenkov telescopes at the Observatorio del Roque de los Muchachos (Garfia, La Palma, Spain)), Altitude 2,396 m (7,861 ft)

This is the most significant excess seen besides TXS 0506-056, the 2017 source that IceCube found to be coincident with a gamma ray flare. Still, these potential neutrino sources require more data with a more-sensitive detector, like IceCube-Gen2, to be confirmed.

The researchers also found that the Northern Hemisphere source catalog as a whole differed from background expectations with a significance of 3.3σ. Carver says these results demonstrate a strong motivation to continue to analyze the objects in the catalog. Time-dependent analyses, which search for flares of peaked emission, and the possibility of correlating neutrino emission with electromagnetic or gravitational wave observations for these and other sources may provide additional evidence of neutrino emission and insights into the neutrinos’ origin. With continued data-taking, more refined direction reconstruction, and the upcoming IceCube Upgrade, further improvements in sensitivity are on the horizon.

“We are lucky to have the unique opportunity to be the first people to map the universe with neutrinos, which provides a brand-new perspective,” says Carver. “Also, this progress in neutrino astronomy is accompanied by great strides in gravitational wave physics and cosmic-ray physics.”

Montaruli adds, “While we are at the dawn of a new era in astronomy that observes the universe not just with light, this is the first time we have begun to see potentially significant excesses of candidate neutrino events around interesting extragalactic objects in time-independent searches.”

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.

IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

Lunar Icecube

IceCube DeepCore annotated

IceCube PINGU annotated


DM-Ice II at IceCube annotated

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From Symmetry: “A partnership turns to neutrinos”

Symmetry Mag
From Symmetry<

10/16/19
Caitlyn Buongiorno

A collaboration with fewer than 100 members has played an important role in Fermilab’s ongoing partnership with Latin American scientists and institutions.

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

On the 12th floor of Wilson Hall, the central high-rise building at Fermi National Accelerator Laboratory outside Chicago, sit the offices and cubicles occupied by members of the MINERvA collaboration.

The MINERvA experiment—which studies how particles called neutrinos and their antimatter counterparts, antineutrinos, interact with different types of materials—finished collecting data in late February. But there is still analysis left to complete.

Scientists at Fermilab use the MINERvA to make measurements of neutrino interactions that can support the work of other neutrino experiments. Photo Reidar Hahn

The area is mostly quiet, but occasionally a conversation will carry down the hall, sometimes in English, sometimes in Spanish or Portuguese.

About a third of the scientists who have participated in the experiment since its inception in 2002 have come from countries in Latin America. Collaborating institutions include Pontifical Catholic University of Peru (PUCP); the National University of Engineering in Peru; the Federico Santa María Technical University in Chile; the University of Guanajuato in Mexico; and the Brazilian Center for Research in Physics (CBPF). The Center for Research and Advanced Studies of the National Polytechnic Insititute (CINVESTAV) in Mexico also recently joined MINERvA. More than 45 students from those institutions have earned or are in the process of earning a degree on the experiment—and some have even earned more than one.

The make-up of the experiment is in some ways a continuation of an effort begun by former Fermilab director and Nobel laureate Leon Lederman to reach out to physicists in Latin America. Most of the Latin American physicists who came to Fermilab in 1970s worked on accelerator-based experiments in specialized particle beam lines or at the laboratory’s particle collider, the Tevatron. Although many of them have moved on to similar experiments at the Large Hadron Collider at CERN, new generations of Latin American scientists are still coming to Fermilab, many of them to study neutrinos.

The large contingent of Latin American scientists on the MINERvA neutrino experiment has added a bilingual component to communication at Fermilab, both in announcing new results and in speaking with potential future physicists. And although MINERvA’s detector operation has come to an end, the partnership between Latin American institutions and Fermilab in neutrino research has only begun.

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

New life for an old partnership

Neutrinos are the most abundant matter particles in the universe. The nuclear fusion that causes the sun and other stars to shine is constantly producing them, as are other nuclear and subatomic processes. Despite this abudance, neutrinos are difficult to study because they rarely interact with other matter, which makes them hard to detect. About 100 trillion neutrinos pass through each person every second, day and night.

Physicist Wolfgang Pauli first postulated the existence of the neutrino in 1930 to explain an apparent anomaly in some types of nuclear decay. Since then scientists have learned much about these elusive partices.

Neutrinos come in three types, called flavors. The 2015 Nobel Prize was split between two scientists from the Super-Kamiokande experiment in Japan and Sudbury Neutrino Observatory in Canada, who in 1998 and 2001 showed that neutrinos change flavors as they move through the universe.

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

Sudbury Neutrino Observatory, , no longer operating

The discovery had the surprising implication that neutrinos have at least a small amount of mass—something not predicted in the Standard Model of particle physics. Scientists still do not know where that mass comes from.

Understanding neutrinos could answer important questions about our galaxy and the universe. Neutrinos could play a vital role in the explosions of supernovae, which help galaxies form. They could also have played a role in what our universe is made of: Although the Big Bang should have produced an equal amount of matter and antimatter, which should have annihilated one another completely, somehow we exist in a universe dominated by matter.

The MINERvA experiment is an intermediate step, designed to answer the questions scientists need to ask before they can tackle those big mysteries: What happens when a neutrino interacts with the massive nucleus of an atom? What technology should scientists use to study these strange particles? What should they know about how they interact with different types of materials inside the detectors they might build? Prior to MINERvA, there was no experiment designed to use different materials placed in the same neutrino beamline to determine the best models of how neutrinos and antineutrinos interact with the nuclei of different atoms.

Founding co-spokespersons Jorge Morfín and Kevin McFarland first proposed MINERvA in 2002. The experiment was approved for construction in 2007 with support from the US Department of Energy’s Office of Science.

The MINERvA detector includes a series of hexagonal plates made of different solid materials and tanks of water and liquid helium, each one in the path of the neutrino beam. The active part of the detector is made of solid scintillator. Scientists built it at Fermilab about 100 meters underground, shielded from the interference of cosmic rays raining down from space, in the path of the world’s most intense beams of muon neutrinos and antineutrinos.

Morfín appreciated Lederman’s early efforts to partner with scientists in Latin America and decided to pick up the mantle of keeping those relationships going. Going country by country in 2005, he reached out to the contacts he’d made through working on other experiments at Fermilab. Gradually he convinced a group of Latin American scientists to join MINERvA, and to bring their students with them.

MINERvA started taking data in 2010. Over its nine years of operation, the experiment thoroughly mapped out neutrino interactions with polystyrene, carbon, iron, lead, water and helium.

“The Latin American students and collaborators, analyzing an array of physics topics, have been essential in determining how neutrinos interact with these nuclei,” Morfín says. “And the benefits go both ways.”

Taking part in this crucial step for future neutrino experiments has given students who started their careers on MINERvA a clear path forward.

José Bazo, now an associate professor at PUCP, was one of the first students on MINERvA. When he and fellow students joined the collaboration, the detector was still under construction, so they spent a one-year stint performing simulations. These simulations tested different theoretical models of how the neutrinos fired at the MINERvA detector would collide, depending on the design of the neutrino beam.

By joining MINERvA at the beginning, Bazo and his colleagues were able to shape how the experiment was set up.

MINERvA has continued to provide foundational learning experiences like these for students throughout the years.

Barbara Yaeggy of Chile’s Federico Santa María Technical University first joined the MINERvA collaboration in 2016. She says that at that time, she was overwhelmed. Prior to MINERvA, Yaeggy had only ever worked on theoretical physics, so she’d never had to consider the ins and outs of working with a real-life detector.

“It took me a long time to feel like I had a good idea of what I was doing,” she says. “But eventually you realize that the senior scientists don’t expect you to be an expert. They want you to develop ideas, take action and ask questions.”

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

Sharing the science

In 2013 MINERvA released its first scientific result—with a twist. For the first time, a Fermilab experiment added a summary of its result written in Spanish. (MINERvA scientists now also write summaries in Portuguese.)

“We wanted to make sure that the people in Latin America and Spanish-speakers in the US would get the important physics in their language,” Morfín says. “And the words are coming from Latin American students on MINERvA.”

Those students have also been instrumental in reaching out to Spanish-speaking communities in the United States, near Fermilab.

Since 2016 Fermilab scientist Minerba Betancourt, from Venezuela, has worked with an organization called “Dare to Dream” to bring middle school girls to Fermilab for an annual Latina STEM conference. These conferences enable the young girls to meet STEM professionals such as the students and scientists on MINERvA, who share their experiences through a Q&A, hands-on activities and a lab tour, given in Spanish.

The tour enables the girls and their parents, who may not speak English, to easily follow along, says Betancourt, who began regularly speaking English herself only after arriving in the United States for graduate school. “Plus, they see us as an example,” she says of the parents. “They see how the girls can be in the future.”

Betancourt sees it as an important opportunity for the young girls—and for the young scientists who work with them. The scientists are given the chance to teach and to practice their science communication skills.

In 2017, Fermilab also began offering a biennial Spanish-language version of its monthly “Ask a Scientist” program, in which scientists volunteer to chat with visitors to the laboratory about their science.

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Illustration by Sandbox Studio, Chicago with Pedro Rivas

Continuing the trend

MINERvA hasn’t been the only force drawing Latin American researchers to Fermilab. Around the same time that Morfín began approaching Latin American institutions to collaborate on MINERvA, Fermilab theorist Marcela Carena, from Argentina, began a student program in the Fermilab Theory Department. Since the program’s inception, 15 students from Argentina, Brazil, Chile, Mexico and Peru have gotten involved in theoretical physics at Fermilab.

And even though the MINERvA experiment has finished collecting data, Latin American participation in neutrino research at Fermilab remains strong with the detectors that make up the lab’s Short Baseline Neutrino program (SBN) as well as the international Deep Underground Neutrino Experiment (DUNE), hosted by Fermilab.

FNAL Short Baseline Neutrino Detector [SBND]

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

Scientists on SBN will use three detectors, placed at locations within 600 meters from the source of Fermilab’s second neutrino beamline, to study how neutrinos oscillate. Data collected by SBN will help scientists determine whether there are actually more than three types of neutrino, as some previous experiments have hinted.

Mexico’s Center for Research and Advanced Studies of the National Polytechnic Institute has joined the SBN collaboration. And Betancourt says she is encouraging members of the MINERvA collaboration to join as well. “I find the start of an experiment to be the most exciting,” she says. “And SBN will begin within the next year.”

Building the detectors for SBN will also help scientists prepare for Fermilab’s upcoming flagship experiment, DUNE.

DUNE will study the properties of neutrinos using a new Fermilab neutrino beamline and detectors placed both at a short distance, similar to SBN, and at a much longer one: DUNE’s “far detectors” will be located 1300 kilometers (about 800 miles) away from the laboratory in a former mine turned high-tech underground laboratory called the Sanford Underground Research Facility in Lead, South Dakota.

SURF-Sanford Underground Research Facility, Lead, South Dakota, USA

SURF DUNE LBNF Caverns at Sanford Lab

The four far detector modules, each 62 meters long and as high as a five-story building, will be the largest neutrino detectors ever built in the United States.

All of the Latin America-based institutions involved with MINERvA have already signed on to participate. “DUNE is now the fruit of all these efforts,” Morfín says. “There is now a concerted effort within Latin American countries to fully contribute to the success of DUNE.”

Perhaps among the young scientists who participate in SBN and DUNE will be the future advocates who will keep the relationships between Fermilab and Latin American institutions alive for generations to come.

See the full article here .


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Symmetry is a joint Fermilab/SLAC publication.


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From Fermi National Accelerator Lab: “Tests start at CERN for large-scale prototype of new technology to detect neutrinos”

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FNAL Art Image by Angela Gonzales

From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

October 9, 2019
Kurt Riesselmann

Scientists working at CERN have started tests of a new neutrino detector prototype, using a very promising technology called “dual phase.” If successful, this new technology will be used at a much larger scale for the international Deep Underground Neutrino Experiment, hosted by the U.S Department of Energy’s Fermilab.

Scientists began operating the dual-phase prototype detector at CERN at the end of August and have observed first tracks. Filled with 800 tons of argon, the detector is about the size of a three-story house.

The new technology would be used in addition to so-called single phase detectors that have been successfully operated during many years. But the new dual-phase technology may be game-changing, as it would significantly amplify the faint signals that particles create when moving through the detector.

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This picture shows a track made by a cosmic-ray muon observed in the dual-phase ProtoDUNE detector.

CERN Proto Dune

Cern ProtoDune

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Researcher Jae Yu checks components within the dual-phase ProtoDUNE detector. Photo by CERN

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The Deep Underground Neutrino Experiment is advancing technology commonly used in dark matter experiments—and scaling it up to record-breaking sizes. CERN

The ionization released by the muon track in liquid argon and by the correlated electromagnetic activity can be seen. Image: ProtoDUNE

“The single-phase technology is a proven method that will be used to build the first module for the DUNE detector,” said DUNE co-spokesperson Ed Blucher of the University of Chicago. “This new dual-phase technology provides a second method that has great potential to add to the DUNE detector’s capabilities.”

In a single-phase experiment, the particle detector is filled entirely with liquid argon. Wire planes and photo sensors submerged in the liquid argon record the faint signals caused when a neutrino smashes into an argon atom. The DUNE collaboration successfully began operating a large single-phase prototype detector at CERN in September 2018.

Scientists and engineers have now deployed on a large scale a dual-phase technology that uses liquid argon as target material and a layer of gaseous argon above the liquid to amplify faint particle signals before they arrive at sensors located at the top of the detector, inside the argon gas. Compared to the single-phase technology, this setup could yield stronger signals, which makes them stand out from background noise. It would thus enable scientists to look for lower-energy neutrino interactions.

Another advantage of the dual-phase technology: All the electronics for the data collection are located in the gas layer near the top of the detector and can be accessed via special chimneys that open from the outside, even as most of the detector is filled with argon, kept at a temperature below minus 184 degrees Celsius (minus 300 degrees Fahrenheit).

In contrast to the single-phase technology, the detector features a single active volume with no detector components in the middle of the liquid argon and a reduced number of readout elements at the top.

“This is a very elegant design that requires advances in high-voltage technology and argon purity,” said Fermilab Director Nigel Lockyer.

The prototype is a cube-shaped detector that is about six meters long in each direction. The collection of the electrons and readout of the signals is performed by innovative systems, each with a surface of nine square meters, individually suspended a few millimeters above the liquid level.

The dual-phase ProtoDUNE detector is but a small component of the detector the international DUNE collaboration plans to build in the United States over the next decade: a DUNE detector module will house the equivalent of 20 dual-phase prototype detectors and operate at a high voltage of up to 600,000 volts.

DUNE plans to build four full-size detector modules based on argon technology. They will be located a mile underground at the Sanford Underground Research Facility in South Dakota. Scientists will use it to discover whether neutrinos could be the reason that matter dominates over antimatter in our universe.

The outcomes of the test at CERN will help with the decision how many modules will feature the single-phase technology and how many will use the dual-phase technology.

The DUNE collaboration includes more than 1,000 scientists and engineers from over 30 countries in five continents: Africa, Asia, Europe, North America and South America.

See the full here.


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Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
collaborate at Fermilab on experiments at the frontiers of discovery.

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