Session T04: DNP Prize Session

"Wherever they may lead": Effective field theories in nuclear physics (Feshbach 2020 Prize Talk)

Effective field theory (EFT) provides a paradigm to describe nature through the controlled expansion of observables in a small ratio of distance scales. I will relate our progress in deploying EFTs to make sense of striking features in the emergence of nuclear structure from the Standard Model of particle physics: pseudo-Goldstone bosons (pions) provide the long-range components of the interaction among nucleons, which are singular but renormalizable; few-nucleon systems are close to the unitarity limit where discrete scale invariance holds; nuclei heavier than the alpha particle often have cluster substructures; nuclear matter saturates at finite binding energy per nucleon and density; and nuclei offer a unique arena to test fundamental symmetries such as lepton number and time reversal.   

Tom W. Bonner Prize in Nuclear Physics: Precision Muon Physics: Capturing a Moment in a Lifetime

Low-energy precision measurements can both establish key parameters of the Standard Model (SM) and test predictions in the quest for new physics. I will describe the suite of experiments our group has been involved in, all having impactful results, and all involving muons.  In the early 2000s, the Brookhaven muon g-2 experiment measured a value for the muon magnetic anomaly that has been in persistent tension since then with an ever improving SM prediction.  A group of us from that era began studying how to design a "discovery’" experiment capable of reaching a much higher precision.  We also had figure out where it might be located.  The effort resulted in the Fermilab Muon g-2 experiment that is now in its 5^th year of data taking. The recently published results from the year 1 data have already confirmed the BNL finding and, when averged,  exceeds the SM theory prediction with a significance of 4.2 standard deviations.  Of course, this is but the tip of the iceberg as greater than 10 times more data are already acquired and running continues.  In parallel, a world-wide theory initiative is ongoing with breakthrough improvements. Both experimental and theoretical uncertainties are thus expected to improve significantly.  Sandwiched between the the completion of the BNL and start of the Fermilab campaigns, our group developed two precision experiments at the Paul Scherrer Institute (PSI) using low-energy beams of stopped muons.  MuLan measured the positive muon lifetime and determined the Fermi Constant to 0.5 ppm.  MuCap measured the negative muon lifetime in a hydrogen TPC. The difference is the muon capture rate, which is used to determine the nucleon weak pseudoscalar coupling constant g_P in an unambiguous manner.   

Herman Feshbach Prize in Theoretical Nuclear Physics (2022): The curious physics behind the breakdown of an effective field theory.

Understanding better the radius of convergence of effective field theory expansions for nuclear physics is important for estimating errors at each order, and for finding ways to extend the range of its applicability. Here I discuss some very curious physics that controls the convergence of the KSW expansion in the triplet channel. High order calculations in a simplified system can reveal the problem in detail and corroborate the semi-analytic theory of Michael Birse for how the expansion breaks down.  It is hoped that this result will eventually lead to a method for extending the validity of the expansion to higher energy physics.