Prof. Thomas Blum is one of two faculty to receive the Research Excellence award from the University of Connecticut in 2022. Tom came to UConn in 2004 and is a professor and associate department head for undergraduate education in the Physics Department. As a theoretical physicist, Blum specializes in making difficult, detailed mathematical calculations concerning how basic theories of physics, such as quantum mechanics, play out in setting the properties and behavior of matter, in his case the tiniest particles known. Notably, Blum is able to figure out how to perform calculations that others have found not possible. He has held visiting professorships at KEK in Japan, CERN in Switzerland, and the Helmholtz Institute in Germany. He has also won research awards including an Outstanding Junior Investigator award from the US Department of Energy, the Ken Wilson Award (top award in his subfield), is a Fellow of the American Physical Society, and was named a Fermilab Distinguished Scholar. At the same time, he is also a dedicated mentor, who supports the development of junior colleagues, and undergraduate and graduate students.
The following article appeared in UConn Today on May 20, 2021 under by-line Elaina Hancock– UConn Communications
Physicists are one step closer to describing an anomaly, called the Muon g-2, that could challenge the fundamental laws of physics. It seems the muon may be breaking what have been understood as the laws of physics, and the findings announced on April 7th were met with much excitement and speculation at what this might mean. UConn physics researchers Professor Thomas Blum and Assistant Professor Luchang Jin helped pioneer the theoretical physics behind the findings, and they recently met with UConn Today to help explain the excitement.
What is a muon, and how do you study them?
Blum: A muon is a “fundamental particle,” meaning it’s an elementary particle like an electron or a photon. Muons are unstable, so they don’t live very long. Unlike an electron, where we can focus on them as long as we want and do measurements, we only have a little bit of time to take measurements of muons.
The way researchers perform the experiment is by slamming particles into other particles to create the muons, and they eventually collect them into a beam. This beam of muons travels at almost the speed of light where they live a little bit longer than they would if they were at rest. That’s Einstein’s theory of relativity in action.
The researchers put the muons into what’s called a storage ring where, eventually, they decay into other particles, and it’s those other particles that are detected in the experiment.
Muons have a property called a magnetic moment, which is like a little compass that points in the direction of the magnetic field that it’s in. In the storage ring, there’s a uniform magnetic field, and as the muons are going around in the storage ring, their magnetic moment, which would be perfectly aligned with their direction of travel if there were no anomaly, actually precesses with respect to the direction of travel as it goes around the ring, because of the interaction with the magnetic field.
It’s that precession that they’re measuring, because the precession is proportional to the strength of the magnetic moment. We can measure this magnetic moment extremely precisely in experiments, and we can calculate its value theoretically very precisely, to less than one-half part per million. Then we can compare the two and see how well they agree.
Can you explain the excitement surrounding these results?
Blum: For a long time — almost 20 years — the best measurement had been done at Brookhaven National Lab on Long Island, where they measured this magnetic moment very precisely, and found that it didn’t agree with our best fundamental theory, which is called the Standard Model of particle physics. The discrepancy wasn’t big enough to say that there was definitely something wrong with the Standard Model or not.
The new results are from a new experiment done to measure the magnetic moment even more precisely. That effort has been going on at Fermilab outside of Chicago for a few years now, and they just announced these results in early April. Their measurement is completely compatible with the Brookhaven value, and if you take the two together, then the disagreement with the Standard Model gets even worse: it now stands at 4.2 standard deviations.
People are very excited, because this could possibly signal that there is new physics in the universe that that we don’t know about yet. The new physics could be new particles that we’ve never seen before, or new interactions beyond the ones we know about already and that could explain the difference between what’s measured and what’s calculated. So that’s what everybody’s excited about.
Can you tell us about the Standard Model?
Jin: The Standard Model describes electromagnetic interactions between charged particles. It also describes the so called weak interactions, which is responsible for nuclear decay. The weak interactions become more important in high energy collisions, and unifies with the electromagnetic interactions. Lastly, the Standard Model describes the strong interactions, which bind quarks into nucleons and nuclei.
Basically, the Standard Model describes everything around us, ranging from things happening in our daily lives to the high-energy proton collisions in the Large Hadron Collider, with the major exception being gravity, which is only sort of visible, but we can feel it because gravity forces always add up, and there are a lot of other massive objects around us. It also doesn’t include dark matter, if we actually do have that in the universe.
People believe, and I think this is really true, that the Standard Model cannot possibly describe everything to extremely high precision, especially when we accelerate subatomic particles to very high energies. However, it was not very clear how high the energy or the precision has to be before we can see some discrepancies. We know the upper bound — usually referred to as the Planck scale, where the Standard Model has to fail due to the omission of gravity. But the Planck scale is so high that there is little hope to be able to perform experiments at that high energy. It is very nice to find a concrete example that the Standard Model actually misses something, and the g-2 anomaly is a very good candidate.
What roles did you each have in this research?
Jin: Theoretically, we decomposed the g-2 into contributions from the different types of interactions. At present, most of the values are obtained by analytic calculations of the various contributions. Other experimentally measurable quantities that have little to do with the muon magnetic moment experiments in terms of what they measure can be related through the Standard Model to the Muon g-2 value. So, to a large extent, this can still be viewed as a theory prediction. Blum pioneered the first lattice calculation for a certain g-2 contribution called the hadronic vacuum polarization, which doesn’t use experimental data at all.
Blum: Jin came up with new methods to compute the Hadronic Light-by-Light contribution which allowed us – with colleagues at Brookhaven National Lab, Columbia University, and Nagoya University – to compute it completely for the first time without experimental input. What Jin and I are doing, along with a host of other theorists around the world, is trying to better calculate the value of this magnetic moment from the theory side, so that we can have an even better comparison with the experimental measurements.
Jin: The Standard Model itself has a few parameters, which for most, we know very, very precisely. This includes the masses of the fundamental particles. In principle, as one might imagine, the theory prediction of the Muon g-2 is a very complicated expression just in terms of these numbers. We are not able to do that yet, but maybe soon we can. We expect that if we continue to improve our calculations, and as computers continue to get faster, the last digit determination may become more accurate.
To dig deeper into the science behind the findings, read Blum and Jin’s feature article on the findings in CERN Courier.
I would like to share some thoughts on Munir Islam who recently passed away. Prof. Islam came to UConn in 1967 from a faculty position at Brown University. In the late 1970s there were two particle theorists at UConn, Profs. Kurt Haller and Munir Islam. They set about building an elementary-particle theory program here and garnered the support of then Physics Head Joe Budnick and CLAS Dean Julius Elias. They soon obtained funding for a new Department of Energy initiative to support particle theory in the Department. In 1979 they
were able to bring me in as an Associate Professor and Mark Swanson as an Assistant Professor. So eager were Kurt and Munir to bring us in, they chose to forego the summer salary that they had been awarded on the DOE grant. The impact of the DOE grant on the UConn administration was quite far reaching and led to further internal support. Within a few years I had been tenured and promoted to Full and Mark had been tenured and appointed to Associate at our Stamford branch, where he later became an administrator.
After that, Kurt and Munir were able to secure a bridge position with the DOE that would provide five years of support, provided the UConn administration would create a tenure track position for the recipient. This they agreed to do, and so we brought in Daniel Caldi at the Assistant level, who subsequently was appointed Associate with tenure. Dan eventually opted to leave us for SUNY Buffalo, but our particle group was then able to convince the UConn administration to let us keep the position, and we then hired Gerald Dunne. Gerald went up the ladder very quickly to tenured Full professor. The success of our program enabled us subsequently to bring in Alex
Kovner, followed by Tom Blum (both now tenured Full) and current Assistant Luchang Jin. The success and endurance of the particle group for more than forty years now is a testament to the foresight and the unwavering and unabating commitment of Kurt and Munir to it, and it serves as permanent memorial to both of them.
Munir Islam always retained an enthusiasm for research, an enthusiasm which did not diminish at all after he retired. He focused on fundamental problems in particle physics, with particular emphasis on the theory of the structure of the proton as revealed by high-energy proton-proton scattering. This is perhaps best evidenced in what essentially became a lifelong collaboration with his former graduate student Richard Luddy (at the right, with Prof Islam at the left in the above photograph) as the two of them grappled with Munir’s deep ideas on proton scattering during many of Munir’s later years as a Professor and then as an Emeritus. Munir had a gift for simple pictorial explanations of his research, which he was able to explain lucidly in a lecture for visiting high-school teachers and students during an open house. Munir was urbane, worldly, and wise, and it was a great joy to have him not just as a colleague but also as a friend. He will be sorely missed by all of those that knew him and especially by me as my career owes so much to him. In appreciation, Philip Mannheim.In appreciation,
UConn astrophysicist Chiara Mingarelli is part of a team of researchers who recently published data on a hint of a signal that sent ripples of excitement through the physics community. These monumental findings are the culmination of twelve and a half years of data gathered from NANOGrav — a network of pulsars across the galaxy — all in the hopes of detecting gravitational waves.
Gravitational waves are generated when galaxies merge and supermassive black holes at their centers collide and send low-frequency gravitational waves out into the universe. The team thinks the source of the signal could be gravitational waves, but it will take about 2 more years of data to be sure.
The findings sparked the interest of other physicists with their own speculations about the signal, such as cosmic strings or primordial black holes. Though still a couple of years away, Mingarelli says the final results could also help test General Relativity or even open the door to entirely new physics.
This article first appeared on UConn Today, February 15, 2021
Jonathan Trump, Assistant Professor of Physics, will receive $738,090 over five years to compile a census of supermassive black holes in the universe. This will give insights into how supermassive black holes and galaxies evolve across cosmic time. Trump will also develop a bridge program for underrepresented undergraduate physics majors at UConn to increase their participation in STEM fields.
The NSF Faculty Early Career Development (CAREER) Program supports 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. Activities pursued by early-career faculty build a firm foundation for a lifetime of leadership in integrating education and research.
Medical imaging techniques such as MRIs use heavy metals from the bottom of the periodic table as “dyes” to make certain tissues easier to see. But these metals, called lanthanides, are toxic. To protect the person getting the MRI, some chemists wrap the lanthanide inside a cage of carbon atoms.
Molecular physicist Razib Obaid and his mentor, Prof. Nora Berrah in the physics department, wanted to know more about how the lanthanides interact with the carbon cages they’re wrapped in. The cages, 80 carbon atoms strong, are called fullerenes and are shaped like soccer balls. They don’t actually bond to the lanthanide; the metal floats inside the cage. There are many similar situations in nature. Proteins, for example, often have a metal hanging out close to a giant organic (that is, mostly made of carbon) molecule.
So Obaid and his team of collaborators from Kansas State University, Pulse Institute at Stanford, Max Planck Institute at Heidelberg, and the University of Heidelberg studied how three atoms of the lanthanide element holmium inside of an 80-carbon fullerene reacted to x-rays. Their initial guess was that when an x-ray first hit one of the holmium atoms, it would get absorbed by an electron. But that electron would be so energized by the absorbed x-ray thatit would fly right out of the atom, leaving a vacant spot. That spot would than get taken by another of the holmium’s electrons, which would have to jump down from the outer edge of the atom to fill it. That electron had formerly been partnered with another electron on the outskirts of the atom. When it jumped down, its lonely ex, called an Auger electron, would zoom away from the whole molecule and get detected by the scientists. Its distinctive energy would give it away.
It sounds complicated, but that would have been the simplest (and thus most likely) scenario, the physicists thought. But it’s not what they saw.
When Obaid and his colleagues zapped the holmium-fullerene molecule with a soft x-ray (about 160 electron-volts), the number of the Auger electrons detected was too low. And too many of the electrons had energies much less than the Auger electrons should have.
After some calculating, the team figured out there was more going on than they’d guessed.
First, the x-ray would hit the holmium, which would lose an electron. The vacant spot would then be filled by the outer edge electron from the holmium atom. That much was correct. But the energy released by the jumping electron (when it jumps ‘down’ from the outskirts of the atom to the interior, it also jumps ‘down’ in energy) would then be absorbed by the carbon fullerene cage or another of the neighboring holmium atoms. In either case, the energy would cause an additional electron to zoom away from whatever absorbed it, the fullerene cage or the holmium atom.
Losing these multiple electrons destabilized the whole molecule, which would then fall apart entirely.
The end result?
“You can induce radiation damage just by striking one atom out of 84,” says Obaid. That is, a single x-ray strike isenough to destroy the entire molecule complex through this energy transfer process involving neighboring atoms. It gives some insight into how radiation damage occurs in living systems, Obaid says. It was always thought that radiation damaged tissue by stripping away electrons directly. This experiment shows that interactions between an ionized atom or molecule and its neighbors can cause even more damage and decay than the original irradiation.
The work also gives medical physicists an idea of how to limit patient’s exposure to heavy metals used as dyes in medical imaging. Shielding all parts of the body from the radiation except for those to be imaged with heavy metal dyes can potentially restrict the heavy metal exposure as well as the radiation damage, the researchers say. The next step of this work would be to understand exactly how fast this interaction with the neighbors occurs. The researchers expect it to take place in just a few femtoseconds (10-15s).
The work was funded by Department of Energy, Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences, and Biosciences, under Grant No. DE-SC0012376.
The Geophysics research group (Prof. Vernon Cormier and students) operate a seismic wave station that continuously monitors vibrations in the earth’s crust, many of which arise from seismic events that happen far away. These waves travel through the deep earth, and eventually make their way to the surface where they are detected. The above figures show high frequency and low frequency filtered seismograms recorded at UConn’s seismic station for the vertical component of ground motion from the earthquakes in Puerto Rico on January 7, 2020. The 3 bursts of energy are P and S elastic waves, followed by a T wave, which propagates as an acoustic wave in the ocean. In the high frequency seismogram (first figure), the large red trace is the main shock and the black trace below it is an aftershock. In the low frequency filtered seismogram (second figure), the largest energy propagates as a surface wave trapped in Earth’s crust and upper most mantle, with energy exponentially decaying into the mantle. Amplitude scale for ground particle velocity is shown by a bar in the upper left corner.
What is a Bachelors of Science degree in Physics good for? What kinds of jobs are available to graduates who complete a 4-year degree in physics, but decide not to pursue an advanced degree? How does a physics degree stack up against other STEM fields in terms of employment options in today's highly competitive job market? Each year the American Physical Society gathers data to help answer questions like these, which they post on their physics careers web site and summarize in their Insight Slideshow. Scroll inside the window below to browse the latest edition of Insight.
Could traveling into the past be part of our future? Quite possibly, says Ron Mallett, a UConn emeritus professor of physics who has studied the concept of time travel for decades. Earlier this month, he spoke with NBC Connecticut reporter Kevin Nathan about his life and work as a theoretical physicist, and discussed how time travel may be possible someday.
UConn Astrophysicist and observational astronomer Jonathan Trump was a recent guest on UConn 360, a podcast from the Storrs campus of the University of Connecticut. In this conversation, Jonathan tells about how attending a lecture as an undergraduate at Penn State captured his interest and changed the course of his professional career. Now Jonathan offers similar career-changing opportunities to UConn students, who just this year have applied for and obtained dedicated time for observations by the Hubble space telescope.