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/

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

Victor Brar awarded prestigious Sloan Fellowship

University of Wisconsin–Madison physics professor Victor Brar has been named a 2021 Sloan Research Fellow, a competitive award given to researchers in the early stages of their careers.

Victor Brar

“A Sloan Research Fellow is a rising star, plain and simple,” says Adam F. Falk, president of the Alfred P. Sloan Foundation. “To receive a Fellowship is to be told by the scientific community that your achievements as a young scholar are already driving the research frontier.”

Brar’s research focuses on developing new microscopy techniques to look at quantum systems in ways that current microscopes cannot. Applying these techniques to study defects in materials — where a perfect crystal lattice is disrupted by one or more anomalous atoms — could lead to improvements in quantum computer performance or the discovery of new Physics.

“Everyone in the world is trying to make a quantum computer, but we don’t really have good diagnostics for what all the quantum systems are inside of a material,” Brar says. “One goal with this microscope is to figure out what’s in a material that could interfere with a quantum computer.”

Additionally, Brar hopes that by applying this technique to complex materials, new particles may be identified and studied. For example, many particle physics discoveries, such as the Higgs boson and the positron, have been first theorized based on materials science research and repurposed into high energy physics experiments.

“At CERN, for example, they try to get to higher and higher energies to see particles, and at some point CERN just can’t get high enough,” Brar explains. “But in a material, you can get analogous particles for what CERN scientists are looking for but at much lower energies. There are particles that we’ve never seen outside of a material, but we can see them in a material, and those are the kinds of things that we’d ideally like to study.”

Images of quantum defects embedded in the atomic lattice of tungsten diselenide (credit: Victor Brar)

The technique that Brar is developing combines optical and electron microscopy, two methods he worked on as a graduate student and post-doc. By bringing them together now, he hopes that his unique method will bring significant advances to his field — and that the Sloan Fellowship indicates that other scientists agree.

“The Sloan award has a history behind it, and they have a track record of funding good science,” Brar says. “So, it means a lot to be recognized by Sloan and I hope it will help when we start to try to make our case for why this method is important.”

The Sloan Research Fellowship is open to early-career scientists in one of eight fields, including physics. More than 1000 researchers are nominated each year for 128 fellowship slots. Winners receive a two-year, $75,000 fellowship which can be spent to advance the fellow’s research.

“Prof. Victor Brar winning the Sloan Foundation Fellowship is a very welcome recognition,” says Sridhara Dasu, chair of the UW–Madison physics department. “For decades now, the Sloan Fellowship is a highly sought-after honor amongst young scientists, and it is wonderful to note that our enthusiasm and confidence in Prof. Brar’s research prowess is recognized by an international panel selecting the Sloan Fellows.”

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.

 

 

Welcome, Professor Lu Lu!

Lu Lu

New UW–Madison assistant professor of physics Lu Lu’s research program combines the past with the future. Her research looks for sources of ultrahigh energy particles, which is done by analyzing data that has already been collected. As she says, “Maybe data is already talking to us, we just haven’t looked.” But she is also working toward improving future data collection, which will require more technologically-advanced detectors. “My teachers, my great masters, have taught me that the current young generation has the responsibility to look into new techniques to go to the future for younger generations to proceed forward,” she says about her work in sensor R&D.

On January 1, Professor Lu joined the Department of Physics and IceCube. Most recently, she was a postdoctoral fellow at the International Center for Hadron Astrophysics at Chiba University in Japan. To welcome her, we sat down for a (virtual) interview.

What are your research interests?

My prime interest is astroparticle physics, and my ultimate goal is to find the sources of the highest energy particles in the universe. These particles carry energy of about 1020 electronvolts. This is higher energy than what we have from the Large Hadron Collider and human technologies. The real attractiveness here is we don’t know how nature accelerates these particles. And once we identify the sources, we can test new theories beyond the Standard Model using sources crated by nature.

What are one or two main projects you focus your research on? 

I’m involved in two experiments. One is IceCube, the other is Pierre Auger Observatory. I was doing cosmic ray analysis, but cosmic rays are usually charged particles and they are deflected in the magnetic field of the galaxy; they would not travel in a straight line. IceCube studies neutrinos which are neutral particles, they travel directly from the source. Pierre Auger detects ultrahigh energy photons, which are also neutral particles. One thing I want to do immediately after I join Madison is to combine these two experiments to do a joint analysis. We have photon candidates but we haven’t really tried to connect them in the multimessenger regime. By combining Pierre Auger photons with IceCube neutrinos, we could possibly find a transient source, a source that doesn’t constantly emit ultrahigh energy photons or neutrinos but all of a sudden there’s a flare. This type of analysis has never been done, but we have data on disks.

The second thing I’m interested in is using new sensor technologies. In IceCube, we have Gen2 being planned right now. Instead of using a single photon sensor, we’d use a more sensitive design and R&D. UW–Madison is taking the lead of designing this future detector. There’s also radio technology. So, to detect the highest energy neutrinos we need to build a large instrument volume. With optical array, it is really hard to scale up because one has to drill holes inside the South Pole, which is really expensive. But radio technology doesn’t have to go so deep, so they can bury their detectors on the surface areas, and the radiowaves can transmit further away than the optical photons in ice. For optical you have to make the detectors very dense, but for radio you can make the antennas further apart, so that means you can have a larger area and detect more events easily. I think radio is the way to go for the future.

You said you have a lot of data collected already and just need to analyze it. How do you analyze the data from these detectors?

We would have to search for photon candidates from the data from Auger, and identify where it comes from and what the time this event happened. Correspondingly, do we see neutrinos from IceCube coming from the same direction and at the same time? Because you can never be sure it’s a photon. It could be a proton. We then want to build a statistical framework to combine different multimessengers together in real time.

What does it mean if you find a photon in coincidence with a neutrino? 

Cosmic rays were first detected more than 100 years ago, and there’s a rich history of studying where they come from. The mystery of origins still remains today because our poor knowledge on the galactic/extragalactic magnetic fields and mass composition of cosmic rays. In my opinion, the most probable way to solve this puzzle is to use neutral particles. If we can identify ultrahigh energy photons in coincidence with neutrinos, that is a smoking gun that we are actually looking at a source and we can finally pin down where in the universe is accelerating high energy particles. And therefore, we can study particle physics maybe beyond Standard Model. It’s just like a lab created by the universe to test particle physics.

What is your favorite element and/or elementary particle? 

My favorite elementary particle is the electron anti-neutrino. I like muons, too. My favorite element is hydrogen.

What hobbies and interests do you have?

I’m afraid I’ll disappoint you because my hobby is related to my research: Augmented reality. When I heard about something called Microsoft Hololens, I thought, I could make IceCube a hologram. I bought these special glasses, and then made a program on it and used it for some outreach events. But the glasses are very expensive, so people said, “Okay we can’t buy hologram glasses.” So I moved it to mobile phones so that everyone could look at it for fun. It’s called IceCubeAR (note: download it for iPhones or Android phones). I made it with a group of friends in Tokyo.

 

 

NSF Physics Frontier Center for neutron star modeling to include UW–Madison

A group of universities, including the University of Wisconsin–Madison, has been named the newest Physics Frontier Center, the National Science Foundation announced Aug. 17. The center expands the reach and depth of existing capabilities in modeling some of the most violent events known in the universe: the mergers of neutron stars and their explosive aftermath.

The Network for Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) is already an established hub of eight institutions, including UW–Madison, that uses the most extreme environments found in astrophysics — the Big Bang, supernovae, and neutron star and black hole mergers — as laboratories for testing fundamental physics under conditions beyond the reach of Earth-based labs. The upgrade to a Physics Frontier Center adds five institutions, provides $10.9 million in funding for postdoctoral fellowships and allows members to cover an expanded scope of research.

“For 20 years, we’ve expected that the growing precision of astrophysical and cosmological measurements would make this field an increasingly important part of fundamental physics. Indeed, four monumental discoveries — neutrino masses, dark matter, the accelerating universe, and gravitational waves — have confirmed this prediction,” says A. Baha Balantekin, a professor of physics at UW–Madison and one of the principal investigators for N3AS.

Read the full story 

Particle collider experiment CMS — and UW physicists who contribute — celebrate 1000th publication

In June 2020, The Compact Muon Solenoid (CMS) collaboration announced the submission of its 1000th scientific publication since the experiment began a decade ago. With multiple University of Wisconsin–Madison physics faculty involved in CMS over the years, the physics department wanted to use this milestone to celebrate their achievements.

CMS is an international collaboration of over 4000 scientists at CERN’s Large Hadron Collider, which churns out data that have contributed immensely to our understanding of particle physics and pointing directions to moving beyond the Standard Model. Amongst its achievements, CMS announced in 2012 the discovery of the Higgs boson, along with ATLAS collaboration.

UW–Madison’s Professor Emeritus Don Reeder, Professor Emeritus Wesley H. Smith, Emeritus Distinguished Scientist Richard Loveless and Professor and current department chair Sridhara Dasu are amongst the founding members of CMS. The team later expanded to include Professor Matt Herndon and Senior Scientists Dr. Sascha Savin and Dr. Armando Lanaro. In 2018, Professor Kevin Black and Professor Tulika Bose joined the physics department.

1000 boxes laid out to make an image of the CMS detector at CERN, and spells "1000 papers"
Image from CERN. The original image can be found at https://cms.cern/news/cms-collaboration-celebrates-1000th-paper

“It’s a proud moment for CMS in general and for the UW CMS group to see our work over the years culminate in this historic milestone!” says Bose, who currently serves as the Deputy U.S. CMS Software and Computing Operations program manager. “We are looking forward to more with the upcoming run and with the High-Luminosity LHC upgrade.”

Of the current UW­–Madison physics faculty involved:

  • Sridhara Dasu currently leads the UW–Madison High Energy Physics group. On CMS, his focus is in better understanding the Higgs boson, searching for its partners, and possible new physics connections, especially to dark matter. He helped design the CMS calorimeter trigger system and continues to dabble in designing its upgrades.
  • Matthew Herndon is involved in the ongoing upgrade of the CSC (cathode strip chamber) forward muon system and well as detailed studies of the performance of the CSC system. He studies the physics of multiple gauge boson interactions and associated new physics phenomena involving multiple gauge bosons.
  • Tulika Bose previously served as the Physics Co-coordinator (PC) of the CMS Experiment during 2017-2019 and as the CMS Trigger Co-coordinator (2014-2016). In addition to her current program manager role, she is involved in physics studies that cover both precision measurements of Standard Model processes as well as direct searches for new physics including dark matter and top quark partners.
  • Kevin Black joined CMS when he joined the UW–Madison physics department in 2018, after 13 years on the CMS companion experiment ATLAS. Since then, he has been involved in the forward muon upgrade project — which will install GEM (Gas Electron Multiplier) detectors — as manager of the U.S. component of the electronic readout project and as deputy run coordinator of the GEM system. His group is focusing on the data-acquisition development for that system.

“I am especially proud of our eighteen PhD graduates who have contributed about two papers each to this set of thousand; one on a search for new physics channel and another on a carefully made measurement,” Dasu says.

Adds Herndon, “It’s an amazing milestone and a testament to the scientific productivity of the CMS experiment!  UW personnel, especially our students, have been a major part of that achievement contributing to nearly 100 of those papers.”

In collaboration with the Physical Sciences Laboratory, the UW Physics team helped design the steel structures and other mechanical systems of the CMS experiment, especially leading the installation, commissioning and operations of the endcap muon system. The UW Physics team has also helped design, build, install and operate the electronics and data acquisition systems, in particular the calorimeter trigger system, and began collecting data from day one of LHC operations. They also collaborated with the HT Condor group of the Department of Computer Science to design and build the Worldwide LHC Computing Grid (WLCG), hosting one of the productive Tier-2 computing centers in Chamberlin.

The UW–Madison group was a key player in the discovery of Higgs boson in 4-lepton decay mode and establishing its coupling to fermions. The group has also searched for new physics especially looking for evidence of beyond the standard model in the form of heavy Higgs bosons that decay to tau-pairs. The group also upgraded the calorimeter trigger system and completed the endcap muon chamber system for the second higher energy run of the LHC. Searches continue for new Higgs partners, rare decays of the SM-like Higgs boson, and searches for new particles. They have added to our repertoire a series of searches for anomalous production of single high energy objects that are indicative of dark matter production in the LHC collisions.

The abundant production of papers proclaiming discoveries or the best measurements to date were possible in large part because of numerous UW–Madison electronics and computing personnel.

“The publication of the 1000th paper of the CMS collaboration is a significant milestone capping the achievement of thousands of physicists worldwide on a wide range of topics that can only be made at this unique instrument and facility,” Black says.