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.

 

 

Welcome, Assistant Professor Jeff Parker!

profile photo of Jeff Parker

Have you heard the joke about the lawyer who became a physics professor? Jeff Parker has, but rather than be the punchline, he was always in on the joke. After earning his Ph.D. in plasma physics from Princeton in 2014, Parker enrolled at Stanford Law School to pursue a career in energy and climate policy. “I lasted one year in law school, decided I really didn’t like it and just loved physics, and I wanted to get back to physics research,” Parker says.

After that one year, Parker accepted a postdoctoral fellowship at Lawrence Livermore National Lab, and two years later became a staff scientist there. On July 1, 2020, Parker joined the UW–Madison Physics Department as its newest assistant professor. Here, he will focus his research interests in theoretical plasma astrophysics. To welcome Professor Parker, we sat down for a (virtual) Q+A with him.

What are the main topics or projects that you will focus your research on?

My immediate research program has two main directions.

One area of research is going to be in plasma astrophysics and astrophysical fluid dynamics. This concerns plasmas in space or in the universe, like in the sun, or the origin of magnetic fields in the cosmos and how they shape what we see in the universe.  I will be investigating angular momentum transport by magnetic fields, which can occur in stars, accretion disks around black holes, and planetary interiors.

Another area is topological phases of matter in plasma physics, related to the 2016 Nobel prize on topological insulators, which came out of condensed matter physics. I am applying these ideas for the first time to plasma physics and plasma waves. This is a brand-new field in plasmas and I’m just getting into it, but I think it’s really, really interesting.

You’re in Madison now, and you’re getting started with your research. What is the first thing you’re doing?

One particular project I’m very interested in is the astrophysical fluid dynamics involving angular momentum transport due to magnetic fields. I have developed theory on something that I call magnetic eddy viscosity, which could be important where there are magnetic fields and rotation. This can occur in astrophysical objects like stars or accretion discs or planets. And so where I studied this was in a pretty idealized system, and I’d really like to extend this into more realistic models that are closer to reality that would help us say something more about real object like stars or accretion discs, or potentially could be measured in the laboratory. So, there are these experiments, Prof. Forest has one, and there are other experiments throughout the country or the world that have rotating plasmas or liquid metals. This effect could potentially be seen in those experiments as well, and that is something I’d love to do right away.

Your work is primarily theory and computation. Do you see your work as predicting ideas that would be tested with collaborators in the department?

That is one thing I do hope to do. But I do also enjoy developing theory to better understand plasmas, even if those theories cannot be tested immediately in an experiment. I’m a theoretical physicist at heart, but there are so many great plasma physics experiments at Madison, which enable a close collaboration of theory and experiment. Progress is truly made when you can measure, observe, analyze, and use theory to understand what you see.

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

I want students to take away how plasma physics is everywhere, how most of the universe is plasma, and so if we want to understand the universe, we need to understand plasma physics.

What is your favorite element and/or elementary particle?

For elementary particle, I’ll say the neutrino because it’s so mysterious, and mysterious is good for physics. For favorite element, hydrogen and its isotopes because they’re what’s important for fusion.

What hobbies/other interests do you have?

I like to hike, run, and travel.