IceCube shows Milky Way galaxy is a neutrino desert

a red-lit IceCube lab (a metal modern-looking lab building stationed at the south pole) with the white swirl of the Milky Way behind it is in a photo, with an artists rendering of a stream of neutrinos (greek letter nu) streams out of the center of the Milky Way

The Milky Way galaxy is an awe-inspiring feature of the night sky, dominating all wavelengths of light and viewable with the naked eye as a hazy band of stars stretching from horizon to horizon. Now,

In a June 30 article in the journal Science, the IceCube Collaboration — an international group of more than 350 scientists — presents this new evidence of high-energy neutrino emission from the Milky Way. The findings indicate that the Milky Way produces far fewer neutrinos than the average distant galaxies.

“What’s intriguing is that, unlike the case for light of any wavelength, in neutrinos, the universe outshines the nearby sources in our own galaxy,” says Francis Halzen, a professor of physics at the University of Wisconsin–Madison and principal investigator at IceCube.

The IceCube search focused on the southern sky, where the bulk of neutrino emission from the galactic plane is expected near the center of the galaxy. However, until now, a background of neutrinos and other particles produced by cosmic-ray interactions with the Earth’s atmosphere made it difficult to parse out neutrinos originating from galactic sources — a significant challenge compounded by relatively sparse neutrino production in general.

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Ke Fang earns NSF CAREER award

profile photo of Ke Fang
Ke Fang

Congrats to Ke Fang, assistant professor of physics, WIPAC faculty member, and HAWC spokesperson, on earning an NSF CAREER award! CAREER awards are NSF’s most prestigious awards in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization.

Fang’s award is sponsored by the NSF Windows on the Universe: Multimessenger Astrophysics program. In multimessenger astrophysics, scientists search for multiple high energy signals to identify their sources and learn more about the makeup of our universe. WIPAC hosts both the IceCube neutrino telescope and the HAWC gamma ray telescope, and Fang says she is excited to have access to high-quality data from both. In her NSF proposal, she plans to use that data in two ways.

“One is evolving novel data analysis techniques to study the problems that remain outstanding, such as the source of high-energy neutrinos,” Fang says. “The second part is once we have these data analysis results, then we’ll use numerical simulations to understand our observations.”

In addition to an innovative research component, NSF proposals require that the research has broader societal impacts, such as working toward greater inclusion in STEM or increasing public understanding of science. Once again, Fang finds herself well-positioned at WIPAC, where the outreach team has developed Master Classes, a one-day event where high school students come to WIPAC, spend time with scientists, and learn about topics not typically covered in high school physics class. Currently, the students learn about IceCube’s instrumentation and how to analyze the complex detector data.

“The course is already well designed, but from my perspective, I use a lot of numerical simulation in my research, so one thing I proposed to do is that I would design a module that would incorporate some of these modern numerical study techniques into the master class,” Fang says. “The students will now learn how to study physics using supercomputers, using numerical simulations.”

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

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.

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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.

Does the behavior of the Higgs boson match the expectations?

Note: This story has been modified slightly from the original, which was published by the CMS Collaboration. Their version has some nice interactive graphics to check out, too!

The standard model of particle physics is our current best theory to describe the most basic building blocks of the universe, the elementary particles, and the interactions among them. At the heart of the standard model is a hypothesis describing how all the elementary particles acquire mass. Importantly, this scheme also envisages the existence of a new type of particle, called the Higgs boson.  It took nearly 50 years, since its postulation, to observe the Higgs boson at the LHC experiments at CERN. It is strongly believed that the Higgs boson, the only scalar particle known to date, is a key to answer some of the questions that standard model cannot answer. Thus a detailed study of the properties of the Higgs boson is the order of the day. Often, specially at the LHC, one of the essential observables concerns the probability that a certain unstable particle is produced momentarily, albeit obeying the laws of nature. In experiments this production cross section is estimated using a specific decay final state of this transient particle in terms of the number of events over a given amount of time. The standard model predicts the cross section for the Higgs boson production as well as the decay rates very precisely. The frequency distribution of a given type of event, as a function of some of the measured variables in the experiment, helps us understand better various aspects of the interactions involved; they are typically lost in the summed or total cross section. Hence measurement of this differential cross section is a powerful tool to vindicate the standard model; also any deviation from the standard model predictions in data would indicate presence of a New Physics.

The Higgs boson is roughly about 125 times more massive than a proton and decays to lighter particles including cascade processes in some cases. Physicists typically use the signatures of stable particles in the detector to trace back suitable decay chains of the Higgs boson. The tau lepton is the heaviest lepton known so far, and as such it is the lepton with strongest ties to the Higgs boson. The probability of a Higgs boson decaying to a pair of tau leptons is reasonably high (about 6%), when compared, for example, to a pair of muons (about 0.02%). But the tau lepton is also an unstable particle and decays quickly to lighter particles always accompanied by its partner, the tau neutrino. Often the decay products from the tau lepton are hadrons producing a shower of particles or jet in the calorimeter system. The tau neutrino goes undetected affecting the accuracy of measurement of the tau lepton energy. It is interesting to study the detailed characteristics of the Higgs boson events using the decay to tau leptons which possess a rest mass of only about 1.4% that of the parent.

profile photo of Andrew Loeliger
Andrew Loeliger

A recent study from the CMS Collaboration, focuses on the events where the Higgs boson decays into a pair of tau leptons using data collected by the experiment between 2016 and 2018. The analysis measures the Higgs boson production cross section as a function of three key variables: the Higgs boson momentum in the direction transverse to the beam, the number of jets produced along with the Higgs boson, and the transverse momentum of the leading jet. New Physics could manifest in excess of events in the frequency distribution of these variables when compared with the standard model predictions.

Says Andrew Loeliger, a UW–Madison physics grad student and one of the lead authors on the study:

The Higgs Boson is the most recent addition to the standard model of particle physics, discovered jointly between the CMS and ATLAS collaborations in 2012, so a big goal of the High Energy Physics field is to make very detailed measurements of its properties, to understand if our predictions are all confirmed, or if there is some kind of new physics or strange properties that might foreshadow or necessitate further discoveries. This work provides, what amounts to, a very fine grained consistency check (alternatively, a search for deviations in the amount) that the Higgs Boson is produced with the amounts/strengths we would expect when categorizing alongside some second interesting property (the transverse momentum of the Higgs Boson is a big one). This type of analysis had not been performed before using the particles we used, so it may open the door for far more precise measurements in places we may not have been able to do before, and a better overall confirmation of the Higgs Boson’s properties.

Other UW–Madison researchers involved in the study include former postdoc Cecile Caillol and Profs. Tulika Bose and Sridhara Dasu.

The analysis employs deep neural networks to exploit simultaneously a variety of tau lepton properties for identifying them with high efficiency. Eventually, to ensure that the selected tau lepton pair is produced from the decay of the Higgs boson and discard those from other processes, such as Z boson decay, the mass of the selected tau pair (m𝝉𝝉 ) is scrutinized. Reconstruction of m𝝉𝝉 , after taking into account the neutrinos involved in the decay as mentioned earlier, required a dedicated algorithm which computes, for each event, a  likelihood function P(m𝝉𝝉) to quantify the level of compatibility of a Higgs boson process.

yellow and orange cones radiate from a common center, with green dots around them
Higgs boson produced in vector boson fusion and decay to tau pair | credit: CMS Collaboration

The Higgs boson typically has more transverse momentum or boost when produced in conjunction with jet(s), compared to the case when it is produced singly. One such event, collected by the CMS detector in 2018 and shown in Figure 1, could correspond to such a boosted Higgs boson decaying to two tau leptons which, in turn, decay hadronically. However, several other less interesting processes could also be the cause of such an event and pose as backgrounds. Such contributions have been measured mostly from the data itself by carefully studying the properties of the jets. Figure 2 shows the good agreement in the m𝝉𝝉 distribution between the prediction and data collected by the CMS experiment for the events with the transverse momentum of the Higgs boson below 45 GeV. The contribution from the Higgs boson process is hardly noticeable due to the overwhelming background.  On the other hand, Figure 3 presents m𝝉𝝉 distribution for the events with highly boosted Higgs boson, when its transverse momentum is above 450 GeV.  Selecting only events with high boost reduces a lot the total number of available events, but  the fraction of the signal events in the collected sample is significantly improved. The data agrees with the sum of predicted contributions from the Higgs boson and all the standard model background processes.

This CMS result presents the first-ever measurement of the differential cross sections for the Higgs boson production decaying to a pair of tau leptons. Run 2 data is allowing us to scrutinize the Higgs boson in the tau lepton decay channel which was only observed a few years back. Future comparison and combination of all Higgs boson decay modes will offer better insights on the interactions of the Higgs boson to different standard model particles. But the story does not end here! The Run 3 of the LHC machine is just around the corner and looking into the future, the high luminosity operation (the HL-LHC) will offer a huge increase in data volume. That could perhaps provide hints of the question if the discovered Higgs boson is the one as predicted by the standard model or if there is any new interaction depicting another fundamental particle contributing to such measurements. That will indeed point to New Physics!

Yang Bai promoted to full professor

Profile photo of Yang Bai
Yang Bai

The Department of Physics is pleased to announce that Prof. Yang Bai has been promoted to the rank of full professor.

“It is my pleasure and honor as Dean to approve Prof. Yang Bai’s promotion to Full Professor. His creativity and impressive breadth in particle physics research make him a leader not only on dark matter, but also more generally on Beyond-the-Standard-Model Physics,” says Eric Wilcots, Dean of the College of Letters & Science. “He is also a valued teacher, appreciated by students especially at the graduate level. Graduate students and junior researchers in Madison are in good hands.”

Bai joined the department in 2012, and was promoted to associate professor in 2017. In addition to his robust and well-funded research program, he has trained several successful graduate students, taught all levels of departmental courses, and served on several departmental and university committees.

“Professor Yang Bai is widely recognized as one of the leading theoretical particle physicists of his generation with a broad and vigorous research program, covering both the collider-related frontiers and the cosmic frontier. His work includes significant contributions in essentially every area related to dark matter,” says Sridhara Dasu, professor and department chair. “The Physics Department very strongly endorses the promotion of Yang Bai to Full Professor.”

Congrats, Prof. Bai on this well-earned recognition!

 

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/