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

Brian Rebel promoted to full professor

profile photo of Brian Rebel
Brian Rebel

The Department of Physics is happy to announce that Professor Brian Rebel has been promoted to full professor.

Rebel is a high energy experimentalist whose research focuses on accelerator-based neutrino physics. He joined the department as an associate professor with a joint appointment at Fermilab in 2018, where he is now a senior scientist.

“Professor Rebel is a leader in neutrino science, making major contributions to DUNE experiments and having published recently on four different neutrino collaborations,” says Mark Eriksson, physics department chair. “The department is thrilled about his promotion to full professor.”

Rebel has established himself as a leader in the Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE). DUNE is an international experiment for neutrino science and proton decay studies that consists of two neutrino detectors — one near Fermilab in Illinois, and one in South Dakota. The experiment will be installed in LBNF, which will produce the neutrino beam. Rebel is currently the DUNE Anode Plane Assembly (APA) consortium manager, and has previously led Fermilab’s DUNE Science Group.

Since 2005, Rebel has also been involved in Fermilab’s NOvA experiment, which uses precision measurements to investigate the flavor oscillations of neutrinos that are not predicted by the Standard Model. He is currently serving as the co-convener of the analysis group searching for oscillations of active neutrino flavors into a sterile neutrino.

Rebel is currently training three graduate students and two postdoctoral scholars, and expects to graduate his first UW–Madison doctoral student soon. Additionally, he supervised several trainees at Fermilab before he came to UW–Madison. He has enjoyed teaching both introductory physics as well as physics courses for non-majors, and is an effective and engaging teacher.

Congrats, Prof. Rebel, on this well-deserved recognition!

 

 

Machine Learning meets Physics

Machine learning and artificial intelligence are certainly not new to physics research — physicists have been using and improving these techniques for several decades.

In the last few years, though, machine learning has been having a bit of an explosion in physics, which makes it a perfect topic on which to collaborate within the department, the university, and even across the world. 

“In the last five years in my field, cosmology, if you look at how many papers are posted, it went from practically zero to one per day or so,” says assistant professor Moritz Münchmeyer. “It’s a very, very active field, but it’s still in an early stage: There are almost no success stories of using machine learning on real data in cosmology.”

Münchmeyer, who joined the department in January, arrived at a good time. Professor Gary Shiu was a driving force in starting the virtual seminar series “Physics ML” early in the pandemic, which now has thousands of people on the mailing list and hundreds attending the weekly or bi-weekly seminars by Zoom. As it turned out, physicists across fields were eager to apply their methods to the study of machine learning techniques. 

“So it was natural in the physics department to organize the people who work on machine learning and bring them together to exchange ideas, to learn from each other, and to get inspired,” Münchmeyer says. “Gary and I decided to start an initiative here to more efficiently focus department activities in machine learning.”

Currently, that initiative includes Münchmeyer, Shiu, Tulika Bose, Sridhara Dasu, Matthew Herndon, and Pupa Gilbert, and their research group members. They watch the Physics ML seminar together, then discuss it afterwards. On weeks that the virtual seminar is not scheduled, the group hosts a local speaker — from physics or elsewhere on campus — who is doing work in the realm of machine learning. 

In the next few years, the Machine Learning group in physics looks to build on the momentum the field currently has. For example, they hope to secure funding to hire postdoctoral fellows who can work within a group or across groups in the department. Also, the hiring of Kyle Cranmer — one of the best-known researchers in machine learning for physics — as Director of the American Family Data Science Institute and as a physics faculty member, will immediately connect machine learning activities in this department with those in computer sciences, statistics, and the Information School, as well other areas on campus.

“There are many people [on campus] actively working on machine learning for the physical sciences, but there was not a lot of communication so far, and we are trying to change that,” Münchmeyer says.

Machine Learning Initiatives in the Department (so far!)

Kevin Black, Tulika Bose, Sridhara Dasu, Matthew Herndon and the CMS collaboration at CERN use machine learning techniques to improve the sensitivity of new physics searches and increase the accuracy of measurements.

Pupa Gilbert uses machine learning to understand patterns in nanocrystal orientations (detected with her synchrotron methods) and fracture mechanics (detected at the atomic scale with molecular dynamics methods developed by her collaborator at MIT).

Moritz Münchmeyer develops machine learning techniques to extract information about fundamental physics from the massive amount of complicated data of current and upcoming cosmological surveys. 

Gary Shiu develops data science methods to tackle computationally complex systems in cosmology, string theory, particle physics, and statistical mechanics. His work suggests that Topological Data Analysis (TDA) can be integrated into machine learning approaches to make AI interpretable — a necessity for learning physical laws from complex, high dimensional data.

Study of high-energy particles leads PhD student Alex Wang to Department of Energy national lab

This story, by Meghan Chua, was originally published by the Graduate School

In 2012, scientists at CERN’s Large Hadron Collider announced they had observed the Higgs boson particle, verifying many of the theories of physics that rely on its existence.

profile photo of Alex Wang
Alex Wang

Since then, scientists have continued to search for the properties of the Higgs boson and for related particles, including an extremely rare case where two Higgs boson particles appear at the same time, called di-Higgs production.

“We’ve had some searches for di-Higgs right now, but we don’t see anything significant yet,” said Alex Wang, a PhD student in experimental high energy physics at UW­–Madison. “It could be because it doesn’t exist, which would be interesting. But it also could just be because, according to the Standard Model theory, it’s very rare.”

Wang will have a chance to aid in the search for di-Higgs production in more ways than one. Starting in November, he will spend a year at the SLAC National Accelerator Laboratory as an awardee in the Department of Energy Office of Science Graduate Student Research Program.

The program funds outstanding graduate students to pursue thesis research at Department of Energy (DOE) laboratories. Students work with a DOE scientist on projects addressing societal challenges at the national and international scale.

At the SLAC National Accelerator Laboratory, Wang will primarily work on hardware for a planned upgrade of the ATLAS detector, one of the many detectors that record properties of collisions produced by the Large Hadron Collider. Right now, ATLAS collects an already massive amount of data, including some events related to the Higgs boson particle. However, Higgs boson events are extremely rare.

In the future, the upgraded High-Luminosity Large Hadron Collider (HL-LHC) will enable ATLAS to collect even more data and help physicists to study particles like the Higgs boson in more detail. This will make it more feasible for researchers to look for extremely rare events such as di-Higgs production, Wang said. The ATLAS detector itself will also be upgraded to adjust for the new HL-LHC environment.

a black background with orange cones and small yellow box-like dots indicate the signal events
This image of a signal-like event in the ATLAS detector comes from one of the Higgs boson-related analyses Wang works on. The red cones and cyan towers indicate particles which may have originated from the decay of two Higgs boson particles. (Photo credit: ATLAS Experiment © 2021 CERN)

“I’m pretty excited to go there because SLAC is essentially where they’ll be assembling the innermost part of the ATLAS detector for the future upgrade,” Wang said. “So, I think it’s going to be a really central place in the future years, at least for this upgrade project.”

Increasing the amount of data a sensor collects can also cause problems, such as radiation damage to the sensors and more challenges sorting out meaningful data from background noise. Wang will help validate the performance of some of the sensors destined for the upgraded ATLAS detector.

“I’m also pretty excited because for the data analysis I’m doing right now, it’s mainly working in front of a computer, so it will be nice to have some experience working with my hands,” Wang said.

At SLAC, he will also spend time searching for evidence of di-Higgs production.

Wang’s thesis research at UW–Madison also revolves around the Higgs boson particle. He sifts through data from the Large Hadron Collider to tease out which events are “signals” related to the Higgs boson, versus events that are “backgrounds” irrelevant to his work.

One approach Wang uses is to predict how many signal events researchers expect to see, and then determine if the number of events recorded in the Large Hadron Collider is consistent with that prediction.

“If we get a number that’s consistent with our predictions, then that supports the existing model of physics that we have,” Wang said. “But for example, if you see that the theory predicts we’d have 10 events, but in reality, we see 100 events, then that could be an indication that there’s some new physics going on. So that would be a potential for discoveries.”

The Department of Energy formally approved the U.S. contribution to the High-Luminosity Large Hadron Collider accelerator upgrade project earlier this year. The HL-LHC is expected to start producing data in 2027 and continue through the 2030s. Depending on what the future holds, Wang may be able to use data from the upgraded ATLAS detector to find evidence of di-Higgs production. If that happens, he also will have helped build the machine that made it possible.

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.

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/

CMS Group publishes new study on Lepton flavor in Higgs boson decays

Neutrinos mix and transform from one flavor to the other. So do quarks. However, electron and its heavier cousins, the muon and the tau, seem to conserve their flavor identity. This accidental conservation of charged lepton flavor must have a profound reason, or low-levels of violation of that conservation principle should occur at high energy scales. However, evidence for any charged lepton flavor violation remains elusive.

The CMS group recently published a new study on Lepton flavor in Higgs boson decays. At UW–Madison, the effort was led by Sridhara Dasu and postdoctoral researcher Varun Sharma, building off of work done by former postdoctoral researcher Maria Cepeda and former graduate student Aaron Levine.

The international CMS collaboration recently published a news story about this new study. Please read the full story here.

a cylindrical shape made up of blue lines has a cone of red lines emanating from its center within the cylinder, like it's heading toward exiting out the base of the cylinder
An event similar to the lepton flavor violating decay of the Higgs boson, produced with the gluon fusion production mechanism. The red track corresponds to a muon, while the red cone along with its corresponding calorimeter deposits is the tau lepton. | CMS Collaboration

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

Welcome, Professor Ke Fang!

By Madeleine O’Keefe, WIPAC

When you think of scientific meccas throughout the world, Madison, Wisconsin might not be the first place that comes to mind. But for astroparticle physicist Ke Fang, Madison is the place to be. That’s because it’s home to the Wisconsin IceCube Particle Astrophysics Center (WIPAC): the “leader of particle astrophysics in the world,” according to Fang. “Throughout the years, there have been all kinds of meetings and workshops that drive people in this field to Madison because it’s the center for particle astrophysics,” she says.

Ke Fang

Originally from Huangshan, China, Fang earned a B.S. in physics from the University of Science and Technology of China. Afterward, Fang moved to the United States for graduate school and earned her PhD in astrophysics from the University of Chicago in 2015. Following that, she went to the University of Maryland and the Goddard Space Flight Center for a Joint Space-Science Institute fellowship. Most recently, Fang was a NASA Einstein Fellow at Stanford University in California.

Now, Fang has joined WIPAC and the UW–Madison Physics Department as an assistant professor. To welcome Fang and learn more about her, we met up on—where else?—Zoom for an interview.

 Can you summarize your research? 

I use both experiments and theory to understand extreme activities of our universe. We receive multiple types of messengers from the universe—all the way from optical light to gamma rays, cosmic rays, neutrinos, and gravitational waves. These messengers can be emitted by a common source, such as a binary neutron star merger. Specifically, I use theoretical models to understand how these astrophysical events produce different messengers, whether theoretical models explain the data, and how the data compare with theoretical models. I also use the HAWC Observatory, the IceCube Neutrino Observatory, and the Fermi Large Area Telescope (Fermi-LAT) to observe or to find sources directly. For example, I jointly analyze the Fermi-LAT and HAWC data to observe gamma-ray sources from 0.1 GeV to 100 TeV—across six orders of magnitude. Studies using multiple messengers and wavelengths are rewarding because they help us get a full picture of what these astrophysical sources look like.

How did you get into your field of research?

When I started graduate school, high-energy astrophysics was rather new; it’s a field that has quickly grown in the past decade or so. High-energy astrophysics traditionally refers to astrophysics with X-ray observations, because X-rays are higher in energy compared to the optical band that astronomers traditionally use. But in the last few years, high-energy astrophysics has had another burst of delving into even higher energies. When we move up in energy, by millions or billions, we see many new sources that were previously not observable in the X-ray band, or different aspects of sources that were previously seen at lower energies. And there are so many unknowns in this field; we can see surprising things at the highest energies, and many of those observations are discoveries. I think that’s really intriguing.

 What attracted you to UW–Madison and WIPAC? 

I think it’s pretty fair to say that WIPAC—with IceCube, CTA, HAWC, Fermi-LAT, ARA, and IceCube-Gen2—is now the leader of particle astrophysics in the world. I think there’s a close match between my expertise and what is currently being done at WIPAC, and I’m excited about joining the department and joining these explorations of higher and higher energy neutrinos and gamma rays.

What’s one thing you hope students who take a class with you will come away with?

The content you learn from a class is limited, but the contexts where you could apply the knowledge are unlimited.

 What is your favorite particle?

Neutrino. If I have to pick one, neutrino is the one that I have in my heart.

What hobbies/other interests do you have?

 Cooking! I like to explore different things. I come from China, so Chinese cuisine is what I started from when I just moved to the United States. But after all these years, I’m getting more exposed to different types of cuisines and starting to explore more, like with Thai and Italian. When I go to nice restaurants, I try to remember the name of the dish and find the recipe online.