Physicists awarded Panofsky Prize in Experimental Particle Physics for Muon g-2 experiment

William M. Morse of the U.S. Department of Energy’s Brookhaven National Laboratory and Bradley Lee Roberts of Boston University will receive the American Physical Society’s 2023 WKH Panofsky Prize in Experimental Particle Physics for their leadership of the experiment muon g-2 at the Brookhaven laboratory and its role in triggering a worldwide search for new physics. Physicists will receive the award, consisting of $10,000 (shared equally) and a certificate citing their outstanding achievement in experimental particle physics at the April 2023 APS meeting to be held in Minneapolis, Minnesota.

The pair’s official quote reads:

“For his leadership and technical ingenuity in achieving a measurement of the anomalous magnetic moment of the muon with an accuracy suitable for probing Standard Model-mediated loop diagrams and possible manifestations of new physics, which inspired a synergy dynamics between experimental and theoretical particle physics to determine comparable accuracy. Predicting the Standard Model and interpreting the implications of any discrepancy.”

Morse and Roberts, along with Vernon Hughes of Yale University (d. 2003), led the “E821 g-2” experiment at Brookhaven Laboratory from construction (beginning in 1990) to first data collection in 1997 until the publication of the first results in 2001 and the final analysis in 2004.

This experiment made precision measurements of how muons spin; heavy subatomic cousins ​​of electrons; precessions, or “oscillations”, as particles move through the magnetic field of a large muon storage ring (see diagram). The results revealed a discrepancy with predictions of muon spin precession that take into account muon interactions with all known particles and forces in the Standard Model of particle physics. Although the level of significance was below that required to claim a major discovery, the discrepancy was intriguing enough to suggest that some factor”beyond the standard model”-;a particle or interaction yet to be discovered-;could explain the aberrant behavior of the muon.

Morse, Brookhaven’s resident spokesperson for the g-2 experience, explained the beauty of the approach as follows:

One can search for new massive particles by going to high energy, by E = mc2, or by making a precise measurement of the rate of muon spin precession in our storage ring magnet. Classically, the vacuum has zero energy. However, the quantum vacuum in our storage ring knows all particles and forces, and this virtual foam affects spin precession. Often the precision measurement is more sensitive to new physics than the high energy path.

This great experience was made possible thanks to all the dedicated engineers, technicians and physicists who worked there. This prize rewards all our efforts,” he said.

Roberts, who served as co-spokesperson for the Brookhaven muon g-2 experiment, led the program of experiments and led the formation of the collaboration, said: “I am honored to share this award with Bill Morse, who played a crucial role in the design and construction of the storage ring at Brookhaven, and in understanding the data during its analysis.” He also noted that “Brookhaven engineering and technical staff have built an incredible storage ring magnet by realizing the brilliant magnetic design of Brookhaven Laboratory physicist Gordon Danby.”

Brookhaven’s g-2 muon experiment launched a worldwide effort to improve the accuracy of theoretical predictions and experimental measurements to see if the difference would widen. Both Morse and Roberts played a role in this ongoing quest.

In 2013, under the direction of physicists and a large international team, Brookhaven Laboratory’s g-2 muon storage magnet embarked on an epic land and sea journey from Long Island, New York, to Fermi National Accelerator Laboratory outside of Chicago. There it was set up to repeat the experiment using Fermilab’s higher intensity muon beam and other advanced technologies.

Roberts noted that the original magnet design, “enabled significant improvements in magnetic field uniformity that were achieved after the ring was moved to Fermilab.And Morse recalled how, after the “Big Move” and the reassembly of the experiment, “our beautiful magnet was once again storing muons.”

In 2021, Fermilab’s Muon g-2 experiment reported its first results, which confirmed Brookhaven’s original result. Fermilab now has nearly twenty times the data set of the original Brookhaven experiment, of which only a small fraction has ever been analyzed. New results from their more precise g-2 measurement are expected to be published in spring 2023.

The two physicists are impatiently awaiting the rest of the story.

The tension between the Brookhaven laboratory experimental result and the Standard Model theoretical value motivated both the Fermilab experiment and the formation of the International Muon g-2 Theory Initiative to further refine the Standard Model value used to comparison with experimental results,” Roberts said.

Morse acknowledged that “For me, the most important outcome of the Brookhaven Lab g-2 experiment was all the young people who became physicists doing this beautiful physics.”

Roberts co-led the development of Brookhaven Lab’s experimental g-2 muon science program. He recruited collaborators, worked with Vernon Hughes to obtain funding for the experiment, and orchestrated the analysis of the data and the publication of the results. His critical contributions included the design and construction of the fast pulsing magnet needed to inject muons, generated by protons from Brookhaven’s Alternating Gradient Synchrotron (AGS), directly into the g-2 storage magnet. During the design and construction of the experiment, Roberts traveled to Brookhaven from Boston every two weeks. In early 1996, he spent a three-semester sabbatical in residence with his family on-site at Brookhaven to help ensure his success. His clear communication of the science behind g-2 was instrumental in recruiting collaborators, sharing results, and laying the groundwork for the Fermilab version of the experiment.

A professor in the Department of Physics at Boston University, Roberts received his doctorate. in Physics from the College of William and Mary (1974). After his role as co-spokesperson for the Brookhaven Lab g-2 experiment, he served as co-spokesperson for the Fermilab E989 Muon g-2 experiment. Previously, he developed prototype hardware for a neutron electric dipole moment search at the Spallation Neutron Source at Oak Ridge National Laboratory and for the CPLEAR experiment’s tests for violation of charge parity (CP ) in kaons at the European Center for Nuclear Research (CERN). He has served on the SNOLAB Experimental Advisory Board, as well as the AGS Program Advisory Board at Brookhaven Laboratory. He was made a Fellow of the American Physical Society in 1994 for his work at Brookhaven on hyperon physics and is a Fellow of the American Association for the Advancement of Science.

Morse, a physicist at Brookhaven and leader of the experimental muon program at the laboratory for more than twenty-five years, was the resident spokesperson for Brookhaven’s g-2 muon experiment. For the Fermilab experiment, he coordinated the movement of the 15-meter-diameter storage ring magnet off the Brookhaven site on the journey to Fermilab. He also led the drafting of the beam/spin dynamics systematic error section of the Fermilab Conceptual Design Report and was the original beam/spin dynamics systematic error coordinator for Fermilab.

With a doctorate. in physics from Purdue University (1976), Morse was also a leader in the study of rare kaon decays, notably as a spokesperson for the Brookhaven Lab experiment E845 in search of the violation charge/parity (CP), and has written several papers on the rare decay of kaons. He was made a Fellow of the American Physical Society in 2006 and received Brookhaven Lab’s highest honor, a science and technology award, in 2012.

The Brookhaven Lab and Fermilab muon g-2 experiments were funded primarily by the DOE Office of Science (HEP).


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