Research, teaching and outreach in Physics at UW–Madison
High Energy
New NOvA results add to mystery of neutrinos
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The international NOvA collaboration presented new results at the Neutrino 2024 conference in Milan, Italy, on June 17. The collaboration doubled their neutrino data since their previous release four years ago, including adding a new low-energy sample of electron neutrinos. The new results are consistent with previous NOvA results, but with improved precision. The data favor the “normal” ordering of neutrino masses more strongly than before, but ambiguity remains around the neutrino’s oscillation properties.
At UW–Madison, the NOvA collaboration includes physics professor Brian Rebel, postdoc Adam Lister, former postdoc Tom Carroll, and grad student Anna Cooleybeck.
The latest NOvA data provide a very precise measurement of the bigger splitting between the squared neutrino masses and slightly favor the normal mass ordering. That precision on the mass splitting means that, when coupled with data from other experiments performed at nuclear reactors, the data favor the normal ordering at almost 7:1 odds. This suggests that neutrinos adhere to the normal ordering, but physicists have not met the high threshold of certainty required to declare a discovery.
Two physics students win presentation awards at APS April Meeting
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Elias Mettner and Nadia Talbi, both conducting research in high energy physics at UW–Madison, won undergraduate presenter awards at the American Physical Society’s April Meeting.
The meeting, held in Sacramento April 3-6, included seven undergraduate oral presentation sessions with six to eight students in each session. The top two students from each session earned “Top Presenter” awards. Mettner and Talbi were the only two UW–Madison students who gave oral presentations, and both won awards.
Elias Mettner
Mettner is a physics major working with scientist Abdollah Mohammadi. His talk was titled “Pair Production and Hadron Photoproduction Backgrounds at the Cool Copper Collider.”
The Cool Copper Collider is a proposed electron-positron collider that will help scientists to explore the Higgs boson even further. The electron-positron beam will have some natural decay that converts into particles and is recorded by the detector. Mettner’s research asks how this beam background will impact the detector.
“The detector will record this background, and it could take the place of the data we want or make it harder to reconstruct data,” Mettner says. “It’s important to make sure that the backgrounds that will come into the detector using this new design will not cause any issues, otherwise the benefits of this collider design cannot be put to their maximum use.”
Mettner had been interested in physics from a young age and comes from a family of teachers who encouraged him to explore his academic interests. Upon entering UW–Madison, he jumped at the chance to conduct research in particle physics. He joined the UW CMS Collaboration in his freshman year through the Undergraduate Research Scholars program and began his project with the Cool Copper Collider soon after. He was also awarded the Sophomore Research Fellowship for his junior year and the Hilldale Research Fellowship for his upcoming senior year.
Nadia Talbi presents at APS April Meeting
Talbi is an astronomy-physics major working in physics professor Tulika Bose’s group and mentored by postdoc Charis Koraka. Her talk, “A Search for Vector-Like Leptons: Compact Analysis,” covered work she has done through a Thaxton Fellowship.
“Bosons are force particles, and basically every boson except for the Higgs — the photon, the gluon — is a vector boson. Leptons are electrons, muons, neutrinos, stuff like that,” Talbi explains. “Vector-like leptons are a hypothetical particle, we don’t know whether or not they exist.”
Talbi was drawn to astronomy because she has long had an interest in the fundamental nature of the universe. As a child, she read an article on Dark Matter and, later, a friend gave her a book on the Standard Model. She was hooked. When she applied for the Thaxton Fellowship, a departmental program that was started to provide more equitable access to undergraduate research in physics, she discussed her interest in particle physics and the research at CERN, which landed her in Bose’s group.
“So before I even had any formal education in physics, where things can be very black and white, I’ve had the opportunity to understand the beautiful things within the field,” Talbi says. “Studying physics, I think, gives you some of the most fundamental understanding of our existence.”
Both Metter and Talbi say that attending conference was overall a very worthwhile experience — even if they both had to take an E+M exam remotely before presenting. (“It was a good bonding experience,” Talbi says.)
“The conference was a lot of fun, and worth it to go and make some connections and experience a bunch of really interesting research from people all in different stages of their careers,” Mettner says.
Adds Talbi: “There were so many undergraduates there, I met so many, I made a lot of friends. It felt like there was a community.”
Both students were also invited to present their award-winning talks to the Physics Board of Visitors spring meeting.
UW–Madison physicist Francis Halzen elected to National Academy of Sciences
Halzen directs the UW–Madison Institute for Elementary Particle Physics Research and is the principal investigator of the IceCube Neutrino Observatory.
Tulika Bose honored with Vilas Distinguished Achievement Professorship
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Vilas Distinguished Achievement Professor Tulika Bose
Sixteen professors, including physics professor Tulika Bose, were named to Vilas Distinguished Achievement Professorships, an award recognizing distinguished scholarship as well as standout efforts in teaching and service. The 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. The awards are supported by the estate of professor, U.S. Senator and UW Regent William F. Vilas (1840-1908).
Wasikul Islam wins 2024 WISL award for communicating science
Wasikul Islam, a postdoctoral researcher with Sau Lan Wu’s group
For this award, postdocs write a short article that describes their research for the general public. Interested postdocs apply to submit an article, then receive guidelines and editorial assistance to improve accessibility. Approved articles are posted on the WISL website, and the author receives a $250 award.
Islam’s article, “Navigating Anomalies in the Pursuit of New Physics” shares how particle physicists study the fundamental building blocks of the universe, exploring the complex behaviors of subatomic particles that shape our world.
“As a postdoctoral researcher, my journey is not limited to research alone,” Islam says in the article. “It comes with an important responsibility to share the wonders and experiences of scientific research with diverse communities.”
The dual mission of the Wisconsin Initiative for Science Literacy is to promote literacy in science, mathematics and technology among the general public and to attract future generations to careers in research, teaching and public service. WISL is directed by Professor Bassam Z. Shakhashiri of the University of Wisconsin-Madison Chemistry Department. Programs draw on the concepts developed by Dr. Shakhashiri during many years of innovative work in science education.
Federal physics advisory panel — including Profs. Bose and Cranmer — announces particle physics recommendations
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Earlier this year, physics professors Tulika Bose and Kyle Cranmer were selected to serve on the Particle Physics Project Prioritization Panel, or P5, a group of High Energy Physics experts that advises the Department of Energy Office of Science and the National Science Foundation’s Division of Physics on high energy and particle physics matters.
One recommendation is to move forward with a planned expansion of the IceCube Neutrino Observatory, an international scientific collaboration operated by the UW–Madison at the South Pole. Other recommendations include support for a separate neutrino experiment based in Illinois (the Deep Underground Neutrino Experiment, or DUNE); continuing investment in the Large Hadron Collider in Switzerland and the Rubin Observatory in Chile; and expanding involvement in the Cherenkov Telescope Array (CTA), a ground-based very-high-energy gamma ray observatory. UW–Madison physicists have leading roles in all of these research efforts.
Additional recommendations include the development of a next generation of ground-based telescopes to observe the cosmic microwave background and a direct dark matter detector experiment, among others.
Wasikul Islam honored with UW Postdoc Association Excellence in Service Award
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Wasikul Islam, a postdoc in Sau Lan Wu’s group, was recognized by the UW–Madison Postdoc Association with an Excellence in Service Award. He was nominated for his science outreach activities, promotion of basic sciences, volunteering and mentorship to undergrad Physics students through various non-profit organizations including the American Physical Society.
The Postdoc Excellence Awards recognize current postdocs on the UW-Madison campus that contribute their time, knowledge, energy, and enthusiasm to mentoring, teaching, and service. They were established to encourage and reward excellence, innovation, and effectiveness in the mentoring, teaching, and service of UW-Madison postdocs. The 2023 winners were honored at the Celebration of Postdoc Excellence on May 19.
Wasikul Islam receives his award at the 2023 Celebration of Postdoc Excellence, held May 19.
Department of Energy grant to train students at the interface of high energy physics and computer science
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To truly understand our physical world, scientists look to the very small, subatomic particles that make up everything. Particle physics generally falls under the discipline of high energy physics (HEP), where higher and higher energy collisions — tens of teraelectronvolts, or about ten trillion times the energy of visible light — lead to the detection and characterization of particles and how they interact.
These collisions also lead to the accumulation of inordinate amounts of data, and HEP is increasingly becoming a field where researchers must be experts in both particle physics and advanced computing technologies. HEP graduate students, however, rarely enter graduate school with backgrounds in both fields.
Physicists from UW–Madison, Princeton University, and the University of Massachusetts-Amherst are looking to address the science goals of the HEP experiments by training the next generation of software and computing experts with a 5-year, ~$4 million grant from the U.S. Department of Energy (DOE) Office of Science, known as Training to Advance Computational High Energy Physics in the Exascale Era, or TAC-HEP.
“The exascale era is upon us in HEP and the complexity, computational needs and data volumes of current and future HEP experiments will increase dramatically over the next few years. A paradigm shift in software and computing is needed to tackle the data onslaught,” says Tulika Bose, a physics professor at UW–Madison and TAC-HEP principal investigator. “TAC-HEP will help train a new generation of software and computing experts who can take on this challenge head-on and help maximize the physics reach of the experiments.”
Tulika Bose
In total, DOE announced $10 million in funding today for three projects providing classroom training and research opportunities in computational high energy physics to train the next generation of computational scientists and engineers needed to deliver scientific discoveries.
At UW–Madison, TAC-HEP will annually fund four-to-six two-year training positions for graduate students working on a computational HEP research project with Bose or physics professors Keith Bechtol, Kevin Black, Kyle Cranmer, Sridhara Dasu, or Brian Rebel. Their research must broadly fit into the categories of high-performance software and algorithms, collaborative software infrastructure, or hardware-software co-design.
Bose’s research group, for example, focuses on proton-proton collisions in the Compact Muon Solenoid (CMS) at the CERN Large Hadron Collider (LHC). The high luminosity run of the LHC, starting in 2029, will bring unprecedented physics opportunities — and computing challenges, challenges that TAC-HEP graduate students will tackle firsthand.
“The annual data volume will increase by 30 times while the event reconstruction time will increase by nearly 25 times, requiring modernization of the software and computing infrastructure to handle the demands of the experiments,” Bose says. “Novel algorithms using modern hardware and accelerators, such as Graphics Processing Units, or GPUs, will need to be exploited together with a transformation of the data analysis process.”
TAC-HEP will incorporate targeted coursework and specialized training modules that will enable the design and development of coherent hardware and software systems, collaborative software infrastructure, and high-performance software and algorithms. Structured R&D projects, undertaken in collaboration with DOE laboratories (Fermilab and Brookhaven National Lab) and integrated within the program, will provide students from all three participating universities with hands-on experience with cutting-edge computational tools, software and technology.
The training program will also include student professional development including oral and written science communication and cohort-building activities. These components are expected to help build a cohort of students with the goal of increasing recruitment and retention of a diverse group of graduate students.
“Future high energy physics discoveries will require large accurate simulations and efficient collaborative software,” said Regina Rameika, DOE Associate Director of Science for High Energy Physics. “These traineeships will educate the scientists and engineers necessary to design, develop, deploy, and maintain the software and computing infrastructure essential for the future of high energy physics.
Higgs @ Ten: UW–Madison physicists’ past and future roles
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Ten years ago, on July 4, 2012, the CMS and ATLAS collaborations at the Large Hadron Collider (LHC) at CERN — including many current and former UW–Madison physicists — announced they had discovered a particle that was consistent with predictions of the Higgs boson.
In the ten years since, scientists have confirmed the finding was the Higgs boson, but its discovery opened more avenues of discovery than it closed. Now, with the LHC back up and running, delivering proton collisions at unprecedented energies, high energy physicists are ready to investigate even more properties of the particle.
The Higgs discovery was published in Physics Letters B and received the cover
“The Higgs plays an incredibly important role in particle physics,” says Kevin Black, who previously worked on ATLAS before joining the UW–Madison physics department and is now part of CMS. “But for being such a fundamental particle, for giving mass to all elementary particles, for being deeply connected to flavor physics and why we have different generations of matter particles — we know a relatively small amount about it.”
Finding the Higgs particle had been one of the main goals of the LHC. The particle was first theorized by physicist Peter Higgs (amongst others, but his name was forever associated with it) in the 1960s.
“The basic idea was that if you just had electromagnetic and strong interactions, then the theory would have been fine if you just put a mass in by hand for the elementary particles,” explains Black. “The weak interaction spoils that, and it was a big question at the time of whether or not the whole structure of particle physics and of quantum field theory were actually going to be consistent.”
Higgs and others realized that there was a way to make it happen if they introduced a new field, which then became the Higgs field and the Higgs particle, that can interact with all other matter and give particles their mass. The Higgs particle, however, eluded experimental observation, leaving a gap in the Standard Model. In retrospect, one of the difficulties was that the mass of the Higgs — around 125 GeV — was much larger than the technology at the time could reach experimentally.
In earlier generations of experiments, UW–Madison physicist Sau Lan Wu participated in searches using the ALEPH experiment that placed a strong lower bound on the mass of the Higgs boson. Also at UW–Madison, Duncan Carlsmith, Matthew Herndon and their groups participated in searches at the CDF experiment that placed an upper bound on the mass of the Higgs boson and saw evidence of Higgs production in the region of mass where it was finally discovered.
Wesley Smith shows the electronics of the trigger system which led to the discovery of the Higgs Boson. Smith led the team that designed and developed the trigger system.
This research set the stage for the experiments that were perfectly designed to discover the Higgs boson: the world’s most powerful hadron collider, the LHC, and the most capable pair of high energy collider experiments ever built, CMS and ATLAS.
The UW–Madison CMS group had three major projects: the trigger project led by Wesley Smith (now emeritus faculty), and the end cap muon system led by Don Reeder (now emeritus faculty) and Dick Loveless (now emeritus scientist), and a computing project led by Sridhara Dasu, who is current head of the group. Having made essential detector contributions, the UW–Madison CMS group, including Herndon, moved on to Higgs hunting and the discoveries. The group, now bolstered by the addition of Black and Tulika Bose to the physics department faculty, continues the work of understanding the Higgs Boson thoroughly.
The UW–Madison ATLAS group, founded and led by Wu, is an important leader of Higgs physics. The group is fortunate to attract another important leader of ATLAS, Higgs physicist Kyle Cranmer, who recently joined UW–Madison as physics department faculty and the director of the American Family Data Science Institute.
Both CMS and ATLAS announced the discovery, made separately but concurrently, in 2012. When it was first discovered, it conformed to expected energies and momentum of the Higgs, but finding it in this rare decay mode was unexpected, so LHC scientists called it the Higgs-like particle for a while.
The UW–Madison ATLAS group at CERN at the time of the Higgs discovery all celebrated with printouts of the data confirming 5sigma. | Provided by Sau Lan Wu
At 3:00pm [on June 25, 2012], there was a commotion in the Wisconsin corridor on the ground floor of CERN Building 32. My graduate student Haichen Wang was saying loudly, ‘Haoshuang is going to announce the Higgs discovery!’ Our first reaction was that it was a joke; thus when we entered Haoshuang’s office, we all had smiles on our faces. Those smiles suddenly became much bigger when we got to look at the result of Haoshuang’s combination: It showed the 5.08s close to the Higgs mass of 125GeV/c2. Pretty soon, cheers were ringing down the Wisconsin corridor.
ATLAS had a discovery!”
The Higgs-like announcement from ten years ago has since been confirmed to be the Higgs particle. Several years later, Dasu’s group’s work saw the Higgs decay into the tau, and provided the first evidence of the particle coupling to matter particles, not just to bosons.
Sau Lan Wu and other Higgs scientists were featured on the cover of the New York Times for a story about the chase for the Higgs boson.
On the ten-year anniversary, both ATLAS and CMS collaborations published summaries of their findings to date and future directions. Experimental questions still being addressed include continuing to measure higher-precision interactions between the Higgs and particles it has already been observed to interact with, and detecting previously-unobserved interactions between the Higgs and other particles.
“One big question that immediately comes to my mind is the mass problem. The breakthrough generated by the Higgs discovery was that elementary particles acquire their masses through the Higgs particle,” Wu writes in her Physics Today essay. “A deeper question that needs to be answered is how to explain the values of the individual masses of the elementary particles. In my mind, this mass problem remains a big topic to be explored in the years to come.”
“Another one of the big things that we’re looking for in future data is to understand Higgs potential,” Black says. “Right now, by measuring the mass, we’ve only measured right around its ground state, and that has great implications for the stability of our universe.”
Also on the ten-year anniversary, CERN announced that the LHC — which had been shut down for three years to work on upgrades — was ready to again start delivering proton collisions at an unprecedented energy of 13.6 TeV in its third round of runs. It is expected that the ATLAS and CMS detectors will record more collisions in this upcoming run than in the previous two combined.
The LHC program is scheduled to run through 2040, and the UW–Madison scientists who are part of the CMS and ATLAS collaborations will almost certainly continue to play key roles in future discoveries.
UW–Madison’s current CMS collaboration members include Kevin Black, Tulika Bose, Sridhara Dasu, and Matthew Herndon, and their research groups. Current ATLAS collaboration members include Kyle Cranmer and Sau Lan Wu and their research groups.
Brian Rebel promoted to full professor
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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!
