(Possibly) Breaking the Standard Model, One Lepton-universality-violating Decay at a Time

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Category: Research News

Published: Thursday, February 09 2023 02:53

Physicists in general, and high energy physicists in particular, like to "break" things. It can be useful to prove again that a well established theory is true, especially if you are probing a yet-untested prediction of the venerable theory. But proving that the theory is wrong--or at least not completely true--that is where the fun is. This is why a series of measurements of b hadron decays that seemingly break the Standard Model (SM) of particle physics is garnering so much excitement.

You see, the SM is the most well established theory of them all, the only one with predictions corroborated to the 11th digit (see the anomalous magnetic moment of the electron). It was fully fleshed out in the 70's, and since then it has racked up success after success. Its crowning achievement came in 2012 when the long-predicted Higgs boson was finally confirmed to be alive and well. Despite this resiliency, the SM is not the end of it all. It can't explain why the mass of the Higgs is so low, what the nature of dark matter is, or why there is so much more matter than antimatter in the universe. Finding answers to these questions will thus require breaking, or extending, the SM.

Enter Lepton Flavor Universality (LFU) violation. LFU is a fundamental assumption within the SM involving the three lepton flavors: electron, muon, and tau. All SM interactions other than the Higgs are assumed to be flavor universal, and this has been shown to be true in numerous measurements. Since 2012, however, an intriguing pattern has emerged in decays of b hadrons (particles with a b quark inside) to final states with a c quark, a tau lepton τ, and a neutrino ν. When results involving a tau lepton and a neutrino are compared to decays involving a muon or an electron and a neutrino, they tend to be higher than we'd expect from SM calculations. This is shown in the nearby figure by all the measurements keeping their distance from the theoretical predictions in blue. Measurements that measured the two LFU quantities RD and RD* are shown as Artistic representation of a proton-proton collision resulting in a B meson that subsequently decays to a charmed D0 or D* meson, a tau lepton, as well as a smaller antineutrino. Credit: Greg Stewart, SLAC National Accelerator Laboratory/BaBar and Manuel Franco Sevilla.ellipses while measurements of RD* alone are shown as markers with uncertainties.

And the first of these new results was just submitted to Physical Review Letters  Professor Hassan Jawahery and Dr. Phoebe Hamilton, together with Dr. Greg Ciezarek from CERN, measured for the first time RD and RD* simultaneously at LHCb. The uncertainties are still large, so it is hard to say whether the discrepancy will be proven true. But this result sets the stage for another meaThe results reflect analysis of two years of data by Phoebe Hamilton and Hassan Jawahery and their CERN collaborator, Greg Ciezarek.surement based on the same techniques that uses a data sample more than 6 times larger. This work, carried out by the all-UMD team Professor Manuel Franco Sevilla, Dr. Hamilton, Dr. Christos Hadjivasiliou, Yipeng Sun, and Alex Fernez, is now fairly advanced. So stay tuned, there's potential for SM-breaking ahead!

 --Manuel Franco Sevilla

James J. Griffin, 1930-2022

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Category: Department News

Published: Sunday, February 05 2023 10:37

Professor Emeritus James J. Griffin died on December 13, 2022.

Griffin earned his Ph.D. in theoretical physics at Princeton University in 1956 and then accepted a Fulbright Scholarship to the Institute for Theoretical Physics in Copenhagen. Following a National Science Foundation Fellowship at the University of Birmingham and an appointment as a Visiting Lecturer at the University of Wisconsin, he joined UMD as an assistant professor in 1966. He was promoted to associate professor and full professor in 1968 and 1973, respectively. In the 1968-69 academic year, Griffin served as Associate Chair of the UMD Department of Physics and Astronomy.

Griffin studied nuclear structure and heavy ions, and was perhaps best known for his publication, “The statistical model of intermediate structure,” which appeared in Physical Review Letters.  He received a John Simon Guggenheim Foundation Fellowship to work at the Lawrence Berkeley Laboratory in 1972-73. In 1975, he received an Alexander von Humboldt Foundation Senior Scientist Fellowship and worked at the Justus Liebig University in Giessen and the Hahn Meitner Institute for Nuclear Research in Berlin.   

During his career, Griffin also enjoyed visiting positions at Los Alamos National Laboratory, Oak Ridge National Laboratory, the University of California in Berkeley, and several institutions in France and Germany. He was an invited guest lecturer in Germany, Canada, Poland, China, Israel, Japan, France and Romania. 

A memorial is planned for the spring. If you'd like to be notified when it is scheduled, please contact This email address is being protected from spambots. You need JavaScript enabled to view it..

Jim Griffin and John Toll.

Jean-Paul Richard, Jim Griffin and Steve Wallace

Jim Griffin, Hans Griem and Doug Currie

Wolfgang Losert Elected AAAS Fellow

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Category: Department News

Published: Tuesday, January 31 2023 10:37

Wolfgang Losert  has been elected a Fellow of the American Association for the Advancement of Science. Wolfgang Losert. Credit: UMD/Lisa Helfert.

In his research, Losert aims to discover emergent dynamic properties of complex systems at the interface of physics and biology. He currently leads a Multidisciplinary University Research Initiative program funded by the Air Force Office of Scientific Research that transformed our understanding of how cells sense their physical environment. He also serves as co-principal investigator on a Brain Research through Advancing Innovative Neurotechnologies (BRAIN) initiative center grant from the National Institutes of Health focused on information processing in sensory brain circuits.

Losert actively fosters cross-disciplinary interactions and new research and educational opportunities on campus and beyond. He helped launch and currently co-leads the American Physical Society Group on Data Science. He was part of a trans-university initiative of the Howard Hughes Medical Institute (called NEXUS) that developed new science and math courses for biology majors and pre-health care students that are being widely adopted. He led the development of and co-directs the NCI-UMD Partnership for Integrative Cancer Research, which provides UMD faculty members and graduate students the opportunity to tackle pressing problems in cancer research in collaboration with National Cancer Institute experts. 

A Fellow of the American Physical Society, Losert joined UMD in 2000 as an assistant professor and served as an associate dean in CMNS (2014-22) and as interim IPST director (2019-20). He earned his Ph.D. in physics from the City College of the City University of New York in 1998 and his diplom in applied physics from the Technical University of Munich in Germany in 1995.

Also elected from the College of Computer, Mathematical, and Natural Sciences (CMNS) were  mathematician Abba Gumel and computer scientists Mohammad Hajiaghayi  and Dana Nau.

“I join the CMNS community in congratulating Professors Gumel, Hajiaghayi, Losert and Nau on their well-deserved election as AAAS Fellows,” said CMNS Dean Amitabh Varshney. “This is an affirmation of what we already know—that they are each pushing the boundaries in their respective fields and making a significant impact on the grand challenges our society faces today.”

UMD’s 2022 Fellows, seven in total, join a class of 506 new Fellows who have moved their fields forward, paving the way for scientific advances that benefit society. They bring diverse and novelty thinking, innovative approaches and passion that will help solve the world’s most complex problems, according to AAAS’s announcement.

“AAAS is proud to elevate these standout individuals and recognize the many ways in which they’ve advanced scientific excellence, tackled complex societal challenges and pushed boundaries that will reap benefits for years to come,” Sudip S. Parikh, AAAS chief executive officer and executive publisher of the Science family of journals, said in an announcement. 

Distinguished University Professor Ed Ott Retires

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Category: Department News

Published: Tuesday, January 31 2023 01:53

Distinguished University Professor Ed Ott retired in December, having served on the UMD faculty for a remarkable and stellar 43 years. Ott is globally known for his pioneering contributions in nonlinear dynamics and chaos theory. 

"Ed has had a magnificient career, exploring and explaining chaos and helping researchers to understand its impact across disciplines," said Physics chair Steve Rolston. 

In recent years, Ott was instrumental in sparking intense activity in applying machine learning to nonlinear dynamics, giving keynote lectures and invited talks in several countries. For the AIP journal Chaos he was asked to co-edit a special 2020 issue: When machine learning meets complex systems: Networks, chaos, and nonlinear dynamics.

Ott, a member of the National Academy of Sciences, is a University of Maryland Distinguished University Professor and holder of the Yuen Sang and Yu Yuen Kit So Endowed Professorship in nonlinear dynamics. He received the 2014 Julius Edgar Lilienfeld Prize of the American Physical Society, and in 2016, with  Celso Grebogi and James A. Yorke, was named a Thomson Reuters Citation Laureate in physics for "...development of a control theory of chaotic systems."

In 2017,  Ott received the Lewis Fry Richardson Medal of the European Geosciences Union for pioneering contributions in the theory of chaos.  Also in 2017, he was selected for the Jürgen Moser Lecture and Award, of the Society for Industrial and Applied Mathematics "... for his extensive and influential contributions to nonlinear dynamics, including seminal work on chaos theory and on the dynamics of physical systems." He was elected a foreign member of the Academia Europaea for his outstanding achievements and international scholarship as a researcher.  

Ott is a Fellow of the Society for Industrial and Applied Mathematics, the American Physical Society and the Institute of Electrical and Electronics Engineers.  He has served as an editor or editorial board member for most renowned journals in his field, including Physica D, Physical Review Letters, Physics of Fluids, Physical Review, Chaos and Dynamics and Stability of Systems.  

Ott received his B.S. in Electrical Engineering at The Cooper Union and his M.S. and Ph.D. in Electrophysics from the Brooklyn Polytechnic Institute, then enjoyed a postdoctoral fellowship at the Department of Applied Mathematics and Theoretical Physics of Cambridge University. Upon his return to the U.S., he joined the Electrical Engineering faculty at Cornell. He left Ithaca in 1979 to join the Department of Physics and Department of Electrical Engineering on this campus. He is a member of the Institute for Research in Electronics and Applied Physics (IREAP), and has held appointments at the Naval Research Lab and what is now the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. 

In addition to more than 500 papers, Ott has written the book "Chaos in Dynamical Systems", and edited "Coping with Chaos,"  a collection of reprints that focuses on how scientists observe, quantify, and control chaos.   He has advised more than 50 doctoral students, starting with Distinguished University Professor Tom Antonsen at Cornell University (1977) and most recently including Amitava Banerjee (2022).