UW–Madison physicists key in revealing neutrinos emanating from galactic neighbor with a gigantic black hole

On Earth, billions of subatomic particles called neutrinos pass through us every second, but we never notice because they rarely interact with matter. Because of this, neutrinos can travel straight paths over vast distances unimpeded, carrying information about their cosmic origins.

Although most of these aptly named “ghost” particles detected on Earth originate from the Sun or our own atmosphere, some neutrinos come from the cosmos, far beyond our galaxy. These neutrinos, called astrophysical neutrinos, can provide valuable insight into some of the most powerful objects in the universe.

For the first time, an international team of scientists has found evidence of high-energy astrophysical neutrinos emanating from the galaxy NGC 1068 in the constellation Cetus.

The detection was made by the National Science Foundation-supported IceCube Neutrino Observatory, a 1-billion-ton neutrino telescope made of scientific instruments and ice situated 1.5-2.5 kilometers below the surface at the South Pole.

These new results, to be published tomorrow (Nov. 4, 2022) in Science, were shared in a presentation given today at the Wisconsin Institute for Discovery.

“One neutrino can single out a source. But only an observation with multiple neutrinos will reveal the obscured core of the most energetic cosmic objects,” says Francis Halzen, a University of Wisconsin–Madison professor of physics and principal investigator of the IceCube project. “IceCube has accumulated some 80 neutrinos of teraelectronvolt energy from NGC 1068, which are not yet enough to answer all our questions, but they definitely are the next big step toward the realization of neutrino astronomy.”

For the full story, please visit https://news.wisc.edu/uw-madison-scientists-and-staff-key-in-revealing-neutrinos-emanating-from-galactic-neighbor-with-a-gigantic-black-hole/

 

The future of particle physics is also written from the South Pole

This post was originally published by the IceCube collaboration. Several UW–Madison physicists are part of the collaboration and are featured in this story

A month ago, the Seattle Community Summer Study Workshop—July 17-26, 2022, at the University of Washington—brought together over a thousand scientists in one of the final steps of the Particle Physics Community Planning Exercise. The meetings and accompanying white papers put the cherry on top of a period of collaborative work setting a vision for the future of particle physics in the U.S. and abroad. Later this year, the final report identifying research priorities in this field will be presented. Its main purpose is to advise the Department of Energy and the National Science Foundation on research for their agendas during the next decade.

As new and old detectors once again prepare to expand the frontiers of knowledge, we asked some IceCube collaborators about the role the South Pole neutrino observatory should play in the bright future that lies ahead for particle physics.

Q: What type of neutrinos are currently detected in IceCube? And will that change with the future extensions?

The vast majority of the neutrinos we detect are generated in the atmosphere by cosmic rays, but we also have on the order of 1,000 cosmic neutrinos at energies above 10 TeV. We use the atmospheric neutrinos for a wide range of science, first of all to study the neutrinos themselves.

IceCube has detected more than a million neutrinos to date. That’s already a big number for neutrino scientists, and we will detect even more in the future. The deployment of the IceCube Upgrade, an extension of our facility targeting neutrinos at lower energies, will increase the density of sensors in IceCube’s inner subdetector, DeepCore, by a factor of 10. And a second, larger extension is also in the works. With IceCube-Gen2, we will improve the detection at the highest energies, too: the IceCube volume will increase by almost a factor of 10, and our event rate for high-energy cosmic neutrinos will also grow by an order of magnitude.

Albrecht Karle, IceCube associate director for science and instrumentation and a professor of physics at the University of Wisconsin–Madison

Q: Are the futures of IceCube and that of particle physics intrinsically linked?

Absolutely! Many open questions in particle physics have neutrinos at the center. What’s their mass? What is the behavior of neutrino flavor mixing? Are there right-handed (sterile) neutrinos? Neutrinos are particularly attractive in the search for new physics. We can answer all these questions, to varying levels, within IceCube and especially moving forward with the IceCube Upgrade and IceCube-Gen2.

Erin O’Sullivan, an associate professor of physics at Uppsala University

IceCube, the Icecube Upgrade, and IceCube-Gen2 can all uniquely contribute to the study of particle physics, in particular, neutrino physics, beyond Standard Model (BSM) physics, and indirect searches of dark matter. The IceCube Upgrade provides complementary and independent measurements of neutrino oscillation in addition to the long-baseline experiments. And IceCube-Gen2 will be crucial to exploring the BSM features, such as sterile neutrinos and secret neutrino interactions, at an energy that cannot be reached by the underground facilities. It will also be a discovery machine for heavy dark matter particles.

Ke Fang, an assistant professor of physics at the University of Wisconsin–Madison

Q: Talking about discoveries, now that both IceCube and Super-Kamiokande have reported definitive observations of tau neutrinos in atmospheric and astrophysical neutrino data, why should the international particle physics community continue to improve their detection?  

The tau neutrino was discovered at Fermilab in an emulsion experiment where they observed double-bang events with a distance on the order of 1 mm separating production and decay. Since they represent the least studied neutrino and, in fact, one of the least studied particles, improved measurements of tau properties may reveal that the 3×3 matrix is not unitary and expose the first indication of physics beyond the 3-flavor oscillation scenario.

Francis Halzen, IceCube PI and a professor of physics at the University of Wisconsin–Madison

We are the only experiment operating currently (and in the foreseeable future) that is able to identify tau neutrinos on an event-by-event basis. We can do so by looking at the distinct morphological features they produce in our data at the highest energies. And with the IceCube Upgrade, we will also be the experiment that collects the most tau neutrinos.  I suspect that these neutrinos will surprise us again and point us towards new physics.

Carlos Argüelles, an assistant professor of physics at Harvard University.  

Four hundred years from now, people may see IceCube the way we see Galileo’s telescope, not as an end but as the beginning of a new branch of science. The astrophysical observation of tau neutrinos is but one piece in a large number of studies that IceCube can conduct, including the study of fundamental physics using astrophysical neutrinos.

Ignacio Taboada, IceCube spokesperson and a professor of physics at the Georgia Institute of Technology

Q: In 2019, the Wisconsin IceCube Particle Astrophysics Center joined the Interactions Collaboration, which includes all major particle physics laboratories around the globe. The IceCube letter of introduction to this community detailed some of the most accurate results to date in neutrino physics. What’s unique about IceCube neutrino science?

One unique aspect of IceCube is the breadth of neutrino energy that we can measure, all the way down to the MeV energy scale in the case of a galactic supernova and up to as far as a few PeV neutrinos, which are the highest energy neutrinos ever detected. Therefore, IceCube provides us with different windows to study the neutrino and understand its properties. Especially in the context of searching for new physics, this is important as these processes can manifest at a particular energy scale but not be visible at other energy scales.

Erin O’Sullivan, an associate professor of physics at Uppsala University

Q:  Let’s focus on high-energy neutrinos for a moment. What are the needs for their detection and why is the South Pole ice the perfect place for those searches? 

The highest energy neutrinos can be directly linked to the most powerful accelerators in the universe but also allow us to test the Standard Model at energies inaccessible to current or future planned colliders.

And why the South Pole? Well, what makes the South Pole such an optimal location are the exceptional optical and radio properties of its ice sheet, which is also the largest pool of ice on Earth. Neutrino event rates are very low at these energies and, thus, we need a huge detector to measure them.

Deep-ice Cherenkov optical sensors have already been proven as high-performing detectors for TeV and PeV neutrinos when deployed at depths of 1.4 km and greater below the surface. And radio technology is promising because radio waves can travel much further than optical photons in the ice, plus they work at shallow depths. So, when searching for the highest energy neutrinos using the South Pole ice sheet, radio neutrino detectors might be the only solution that scales up. Radio waves are able to travel further in the South Pole than in Greenland, for example. It’s a gift from nature to have this giant, pure block of ice to catch elusive neutrinos from the most powerful accelerators.

Lu Lu, an assistant professor of physics at the University of Wisconsin–Madison

Q: And what about the lowest energies? How does IceCube perform there? 

IceCube’s DeepCore detector was especially designed for that: a more dense layout of photodetectors embedded in the center of IceCube and located at about 2 km depth, it uses the surrounding IceCube sensors to eliminate essentially all background from the otherwise dominant cosmic ray muons. This means that DeepCore can now be analyzed as if it was at 10 km depth, deeper than any mine on Earth. In the near future, the IceCube Upgrade will add seven strings of new sensors inside DeepCore, which will hugely increase its precision for neutrino properties.

Albrecht Karle, IceCube associate director for science and instrumentation and a professor of physics at the University of Wisconsin–Madison 

IceCube’s low energies are what all other neutrino experiments would call high energies. This is a regime where the neutrino interactions are well predicted from accelerator experiments, which means that if deviations are found in the data we can claim new physics. Thus, IceCube and the upcoming IceCub Upgrade results are not only going to yield some of the most precise measurements on the neutrino oscillation parameters but also—and more importantly—test the neutrino oscillation framework.

Carlos Argüelles, an assistant professor of physics at Harvard University  

Q: And, last but not least, we should think about the people that will make all this possible. What efforts are underway to diversify who does science and make the field more equitable?

Four years ago, IceCube invited a few collaborations to join efforts to increase equity, diversity, inclusion, and accessibility (DEIA) in multimessenger astrophysics. With support from NSF, this was the birth of the Multimessenger Diversity Network (MDN). This network now includes a dozen participating collaborations, which is an indication of the growing awareness and action to increase DEIA across the field. Set up as a community of practice, where people share their knowledge and experiences with each other, the MDN is a reproducible and scalable model for other fields. We are excited to see this community of practice grow, to contribute with resources and experiences, and to learn from others.

For the first time in an official capacity, DEIA efforts were included in the Snowmass planning process and were also incorporated into the Astro2020 Decadal Survey. One take-away from these processes is that more resources and accountability are needed to speed up DEIA efforts.

Ellen Bechtol, MDN community manager and an outreach specialist at the Wisconsin IceCube Particle Astrophysics Center

Read more about IceCube and its future contributions to particle physics

  • Snowmass Neutrino Frontier: NF04 Topical Group Report. Neutrinos from natural sources. (Jul 2022)
  • CF7. Cosmic Probes of Fundamental Physics. Topical Group Report (Jul  2022).
  • “High-Energy and Ultra-High-Energy Neutrinos: A Snowmass White Paper”, M.Ackermann et al. arxiv.org/abs/2203.08096
  • “Tau Neutrinos in the Next Decade: from GeV to EeV,” R. S. Abraham et al. arxiv.org/abs/2203.05591
  • “Snowmass White Paper: Beyond the Standard Model effects on Neutrino Flavor,” C. Argüelles et al. arxiv.org/abs/2203.10811
  • “Snowmass 2021 White Paper: Cosmogenic Dark Matter and Exotic Particle Searches in Neutrino Experiments,” J. Berger et al. arxiv.org/abs/2207.02882
  • “White Paper on Light Sterile Neutrino Searches and Related Phenomenology,” M. A. Acero et al, arxiv.org/abs/2203.07323
  • “Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers,” A. Coleman, arxiv.org/abs/2205.05845
  • “Advancing the Landscape of Multimessenger Science in the Next Decade,” K. Engle et al. arxiv.org/abs/2203.10074

Search for neutrino emission associated with LIGO/Virgo gravitational waves

Gravitational waves (GWs) are a signature for some of the most energetic phenomena in the universe, which cause ripples in space-time that travel at the speed of light. These events, spurred by massive accelerating objects, act as cosmic messengers that carry with them clues to their origins. They are also probable sources for highly energetic neutrinos, nearly massless cosmic messengers hurtling through space unimpeded. Because neutrinos rarely interact with surrounding matter, they can reveal phenomena that are otherwise unobserved with electromagnetic waves. These high-energy neutrinos are detected by the IceCube Neutrino Observatory, a cubic-kilometer detector enveloped in Antarctic ice at the South Pole.

Both GWs and neutrinos are recently introduced messengers in astronomy and have yet to be detected by the same source. Such a major discovery would not only shed light on the sources of cosmic rays but would also help in understanding the most energetic processes in the universe. By coordinating traditional observations (from radio to gamma rays) with these new messengers, researchers can gain deeper insights into astrophysical sources that were unobtainable before.

Previously, the IceCube Collaboration looked for joint emission of GWs and high-energy neutrinos with data collected by IceCube, the Laser Interferometer Gravitational-Wave Observatory (LIGO), and the Virgo gravitational wave detector. These results were from GWs observed during the first two observing runs (O1 and O2) of LIGO and Virgo. IceCube researchers from the University of Wisconsin–Madison and Columbia University conducted an updated analysis of GWs from the third observing run (O3) of the LIGO/Virgo detectors. The increased number of GWs improved the researchers’ overall analysis. Their findings were recently submitted to The Astrophysical Journal.

Read the full story by WIPAC

Study led by UW–Madison researcher confirms star wreck as source of extreme cosmic particles

Astronomers have long sought the launch sites for some of the highest energy protons in our galaxy. Now, a study using 12 years of data from NASA’s Fermi Gamma-ray Space Telescope (Fermi) confirms that a remnant of a supernova, or star explosion, is just such a place, solving a decade-long cosmic mystery.

a mostly black image of space, with some small white-ish out-of-focus stars, and a large fuzzy pink blob partially overlapping a green-hued amorphous apparition
The newly discovered PeVatron (in pink) is hosted by a supernova remnant (in green) called G106.3+2.7. The supernova remnant is believed to have formed together with the pulsar (in magenta) about 10,000 years ago. Particles accelerated by the shock waves of the supernova remnant interact with the gas in the interstellar medium, producing high-energy gamma-ray emission. Credit: Jayanne English, University of Manitoba, NASA/Fermi/Fang et al. 2022, and Canadian Galactic Plane Survey/DRAO.

Previously, Fermi has shown that the shock waves of exploded stars boost particles to speeds comparable to that of light. Called cosmic rays, these particles mostly take the form of protons, but can include atomic nuclei and electrons. Because they all carry an electric charge, their paths become scrambled as they whisk through our galaxy’s magnetic field, which masks their origins. But when these particles collide with interstellar gas near the supernova remnant (SNR), they produce a telltale glow in gamma rays—the highest-energy light there is.

“Theorists think the highest energy cosmic ray protons in the Milky Way reach a million billion electron volts, or PeV energies,” said Ke Fang, an assistant professor of physics at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), a research center at the University of Wisconsin–Madison. “The precise nature of their sources, which we call PeVatrons, has been difficult to pin down.”

Fang, who led the study, performed the data analysis and developed the theory models. The research team identified a few suspected PeVatrons, including one at the center of our galaxy. Naturally, SNR top the list of candidates. Yet out of about 300 known remnants, only a few have been found to emit gamma rays with sufficiently high energies.

Read the full story

Design and performance of the prototype Schwarzschild-Couder telescope camera

The debut of a new detector has many “firsts”: the first assembly, the first shift, the first light, the first detection… But if there’s one thing that makes a debut official—sort of like a detector’s birth certificate—it’s the detailed description of how the detector was built and how it performs.

And this is achieved in a new paper by members of the Cherenkov Telescope Array Consortium, published in the Journal of Astronomical Telescopes, Instruments and Systems. The paper documents the design of the camera of the prototype Schwarzschild-Couder Telescope (pSCT), a medium-sized candidate telescope for the Cherenkov Telescope Array (CTA). The paper also includes performance metrics that show its potential as a very-high-energy gamma-ray detector and that have already been used to plan an upgrade, a project which is now well underway. Very high energy gamma rays are the highest energy photons in the universe and can unveil the physics of extreme objects, including black holes and possibly dark matter.

The pSCT uses novel dual-mirror optics, rather than more traditional single-mirror optics, and relies on high-speed electronics to cover CTA’s middle energy range from 80 GeV to 50TeV. This camera was developed by a team spanning multiple universities and co-led by UW–Madison physics professor Justin Vandenbroucke, who has been working on this project since 2009.

Read the full story

Francis Halzen named Vilas Research Professor

Francis Halzen

UW–Madison physics professor Francis Halzen has been named a Vilas Research Professor. Created “for the advancement of learning,” Vilas Research Professorships are granted to faculty with proven research ability and unusual qualifications and promise. The recipients of the award have contributed significantly to the research mission of the university and are recognized both nationally and internationally.

Halzen, the Gregory Breit and Hilldale Professor of Physics, joined the UW­­–Madison faculty in 1972. He has made pioneering contributions to particle physics and neutrino astrophysics, and he continues to be the driving force of the international IceCube Collaboration.

Early in his career, Halzen cofounded the internationally recognized phenomenology research institute in the UW–Madison Department of Physics to promote research at the interface of theory and experiment in particle physics. This institute is recognized for this research and for its leadership in the training of postdocs and graduate students in particle physics phenomenology.

The IceCube Neutrino Observatory is the culmination of an idea first conceived in the 1960s, and one in which Halzen has played an integral role in its design, implementation, and data acquisition and analysis for the past three decades. After initial experiments confirmed that the Antarctic ice was ultratransparent and established the observation of atmospheric neutrinos, IceCube was ready to become a reality. From 2004 to 2011, the South Pole observatory was constructed — the largest project ever assigned to a university and one led by Halzen.

After two years of taking data with the full detector, the IceCube Neutrino Observatory opened a new window onto the universe with its discovery of highly energetic neutrinos of extragalactic origin. This discovery heralded the beginning of the exploration of the universe with neutrino telescopes. The IceCube observation of cosmic neutrinos was named the 2013 Physics World Breakthrough of the Year.

Nationally and internationally renowned for this work, Halzen was awarded a 2014 American Ingenuity Award, a 2015 Balzan Prize, a 2018 Bruno Pontecorvo Prize, a 2019 Yodh Prize, and a 2021 Bruno Rossi Prize.

With the Vilas Research Professorship, Halzen is also recognized for his commitment to education and service in the department, university, and international science communities. He has taught everything from physics for nonscience majors to advanced particle physics and special topics courses at UW–Madison. He has actively participated on several departmental and university committees as well as advisory, review, and funding panels. His input is highly sought by committees and agencies that assess future priorities of particle and astroparticle physics research.

“Francis Halzen has had a prolific, internationally recognized research career, has shown excellence as an educator who is able to effectively communicate cutting-edge science on all levels, and has made tireless and valued contributions in service of the department,” says Sridhara Dasu, Physics Department chair. “He is one of the most creative and influential physicists of the last half century and worthy of the prestigious Vilas Research Professorship.”

Vilas awards are supported by the estate of professor, U.S. senator and UW Regent William F. Vilas (1840-1908). The Vilas Research Professorship provides five years of flexible funding — two-thirds of which is provided by the Office of the Provost through the generosity of the Vilas trustees and one-third provided by the school or college whose dean nominated the winner.

Halzen joins department colleagues Profs. Vernon Barger and Sau Lan Wu as recipients of this prestigious UW–Madison professorship.

Ke Fang receives prestigious Shakti Duggal Award

This article was originally published by WIPAC

Ke Fang, professor at the University of Wisconsin–Madison, has been selected as the recipient of the 2021 Shakti P. Duggal Award presented by the International Union of Pure and Applied Physics (IUPAP).

profile photo of Ke Fang
Ke Fang

The Duggal Award was established after cosmic-ray physicist Shakti Duggal’s untimely death in 1982. In honor of Shakti’s long association with cosmic ray physics and his many contributions to the field during his career, his namesake award is given biennially “to recognize an outstanding young scientist for contributions in any branch of cosmic ray physics.” The first Shakti P. Duggal Award was presented at the 19th International Cosmic Ray Conference at La Jolla in 1985. Previous Duggal Award winners have all achieved recognition and prominence in their careers.

Award winners receive a monetary award and, since 1991, an invitation to visit the Bartol Research Institute of the University of Delaware, where Shakti Duggal worked, to present a colloquium and discuss their work.

Fang’s research focuses on understanding the universe through its energetic messengers, including ultra-high-energy cosmic rays, gamma rays, and high-energy neutrinos. She runs numerical simulations to study theories of astroparticle sources and analyzes data from HAWC, Fermi-LAT, and IceCube. She joined WIPAC and the UW–Madison Physics Department as an assistant professor on January 1, 2021. You can learn more about Fang and her research in this Q&A.

“I am very grateful for this special honor,” said Fang. “As a young researcher, I have received enormous support from my mentors and collaborators, to whom the award truly belongs. I look forward to continuing working on and contributing to cosmic ray physics as a member of the Duggal family.”

 

Celebrating IceCube’s first decade of discovery

It was the beginning of a grand experiment unlike anything the world had ever seen. Ten years ago today, the IceCube Neutrino Observatory fully opened its eyes for the first time.

Over the course of the previous seven years, dozens of intrepid technicians, engineers, and scientists had traveled to the South Pole—one of the coldest, driest, and most isolated places on Earth—to build the biggest, strangest telescope in the world. Crews drilled 86 holes nearly two-and-a-half kilometers deep and lowered a cable strung with 60 basketball-sized light detectors into each hole. The result was a hexagonal grid of sensors embedded in a cubic kilometer of ice about a mile below the surface of the Antarctic ice sheet. On December 18, 2010, the 5,160th light sensor was deployed in the ice, completing the construction of the IceCube Neutrino Observatory.

The purpose of the unconventional telescope was to detect signals from passing astrophysical neutrinos: mysterious, tiny, extremely lightweight particles created by some of the most energetic and distant phenomena in the cosmos. IceCube’s founders believed that studying these astrophysical neutrinos would reveal hidden parts of the universe. Over the course of the next decade, they would be proven right.

IceCube began full operations on May 13, 2011 — ten years ago today — when the detector took its first set of data as a completed instrument. Since then, IceCube has been watching the cosmos and collecting data continuously for a decade.

During its first few years of operation, IceCube accumulated vast amounts of data, but it wasn’t until 2013 that the observatory yielded its first major results.

For the full story, please visit https://icecube.wisc.edu/news/collaboration/2021/05/celebrating-icecubes-first-decade-of-discovery/

Highest-energy Cosmic Rays Detected in Star Clusters

For decades, researchers assumed the cosmic rays that regularly bombard Earth from the far reaches of the galaxy are born when stars go supernova — when they grow too massive to support the fusion occurring at their cores and explode.

Those gigantic explosions do indeed propel atomic particles at the speed of light great distances. However, new research suggests even supernovae — capable of devouring entire solar systems — are not strong enough to imbue particles with the sustained energies needed to reach petaelectronvolts (PeVs), the amount of kinetic energy attained by very high-energy cosmic rays.

And yet cosmic rays have been observed striking Earth’s atmosphere at exactly those velocities, their passage marked, for example, by the detection tanks at the High-Altitude Water Cherenkov (HAWC) observatory near Puebla, Mexico. Instead of supernovae, the researchers — including UW–Madison’s Ke Fang — posit that star clusters like the Cygnus Cocoon serve as PeVatrons — PeV accelerators — capable of moving particles across the galaxy at such high energy rates.

Their paradigm-shifting research provides compelling evidence for star forming regions to be PeVatrons and is published in two recent papers in Nature Astronomy and Astrophysical Journal Letters.

For the full news story, please visit https://www.mtu.edu/news/stories/2021/march/not-so-fast-supernova-highestenergy-cosmic-rays-detected-in-star-clusters.html.

 

IceCube detection of a high-energy particle proves 60-year-old theory

a colorized simulation of the detection event indicating where energies took place and were transferred

On Dec. 8, 2016, a high-energy particle hurtled to Earth from outer space at close to the speed of light. The particle, an electron antineutrino, smashed into an electron deep inside the ice sheet at the South Pole. This collision produced a particle that quickly decayed into a shower of secondary particles, triggering the sensors of the IceCube Neutrino Observatory, a massive telescope buried in the Antarctic glacier.

IceCube had seen a Glashow resonance event, a phenomenon predicted by Nobel laureate physicist Sheldon Glashow in 1960. With this detection, scientists provided another confirmation of the Standard Model of particle physics. It also further demonstrated the ability of IceCube, which detects nearly massless particles called neutrinos using thousands of sensors embedded in the Antarctic ice, to do fundamental physics. The result was published March 10 in Nature.

For the full story, please visit: https://news.wisc.edu/icecube-detection-of-high-energy-particle-proves-60-year-old-physics-theory/

For the study, please visit: https://www.nature.com/articles/s41586-021-03256-1