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Director of Research Communications, Duke University

The Dukies Cited Most Highly

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The Web of Science ranking of the world’s most highly-cited scientists was released this morning, telling us who makes up the top 1 percent of the world’s scientists. These are the authors of influential papers that other scientists point to when making their arguments.

EDITOR’S NOTE! — Web of Science shared last year’s data! We apologize. List below is now corrected, changes to copy in bold. We’re so sorry.

Twenty-three of the citation laureates are Duke scholars or had a Duke affiliation when the landmark works were created over the last decade.

A couple of these Duke people disappeared from this year’s list, but we’re still proud of them.

Two names on the list belong to Duke’s international powerhouse of developmental psychology, the Genes, Environment, Health and Behavior Lab, led by Terrie Moffitt and Avshalom Caspi.

Dan Scolnic of Physics returns as our lone entry in Space Science, which just makes Duke sound cooler all around, don’t you think?

This is a big deal for the named faculty and an impressive line on their CVs. But the selection process weeds out “hyper-authorship, excessive self-citation and anomalous citation patterns,” so don’t even think about gaming it.

Fifty-nine nations are represented by the 6,636 individual researchers on this year’s list. About half of the citation champions are in specific fields and half in ‘cross-field’ — where interdisciplinary Duke typically dominates. The U.S. is still the most-cited nation with 36 percent of the world’s share, but shrinking slightly. Mainland China continues to rise, claiming second place with 20 percent of the cohort, up 2.5 percent from just last year. Then, in order, the UK, Germany and Australia round out the top five.

Tiny Singapore, home of the Duke NUS Graduate Medical School, is the tenth-most-cited with 1.6 percent of the global share.

In fact, five Duke NUS faculty made this year’s list: Antonio Bertoletti, Derek Hausenloy and Jenny Guek-Hong Low for cross-field; Carolyn S. P. Lam for clinical medicine, and the world famous “Bat Man,” Lin-Fa Wang, for microbiology.

Okay, you scrolled this far, let’s go!

Biology and Biochemistry

Charles A. Gersbach

Clinical Medicine

Christopher Bull Granger

Adrian F. Hernandez

Gary Lyman

Cross-Field

Priyamvada Acharya

Chris Beyrer

Stefano Curtarolo

Vance G. Fowler Jr.

Po-Chun Hsu (adjunct, now U. Chicago)

Ru-Rong Ji

William E. Kraus

David B. Mitzi

Christopher B. Newgard

Pratiksha I. Thakore (now with Genentech)

Xiaofei Wang

Mark R. Wiesner

Environment and Ecology

Robert B. Jackson (adjunct, now Stanford U.)

Microbiology

Barton F. Haynes

Neuroscience and Behavior

Quinn T. Ostrom

Plant and Animal Science

Sheng-Yang He

Psychiatry and Psychology

Avshalom Caspi

William E. Copeland

Terrie E. Moffitt

Space Science

Dan Scolnic

Most Highly Cited: 30 for ’23

It’s that most wonderful time of the year: The official list of Clarivate’s Most Highly Cited Scientists came out this morning.  Scientists all over the world came racing down the stairs in their PJs to see if Clarivate had left a treat under the tree for them.

L-R: Odgers, Scolnic, Dong, Hernandez, Harrington, Smith, Ostrom and Lopes.

Good news – there are 30 Duke names on the list!

Being highly cited is a point of pride for researchers. To make the cut, a paper has to be ranked in the top 1 percent for its field for the last decade. Clarivate’s “Institute for Scientific Information” crunches all the numbers.

Mostly, the names on this year’s list of Duke authors are the usual titans. Oddly, some returning names have changed categories since last year — but that’s okay, they’re still important.

And there are three fresh faces: Cardiologist Renato Delascio Lopes, MD Ph.D., who studies atrial fibrillation; David R. Smith Ph.D. of physics and electrical engineering, who’s a leading light in the field of metamaterials; and Dan Scolnic Ph.D. of physics, who’s measuring the expansion of the universe and trying to figure out the dark energy that apparently drives it.

Five of the Duke names on the list this year are co-authors in the Terrie Moffit and Avshalom Caspi lab, a hugely influential group of psychologists and social scientists. Honnalee Harrington, Renate Houts, Caspi, Moffitt, and UC Irvine professor and Duke adjunct Candice Odgers are studying human development from cradle to grave using two cohorts of life-long study participants in New Zealand and England.

Two other longitudinal scientists, Jane Costello and William Copeland of the Great Smoky Mountains Study, are also on the list.

There are 6,938 highly cited scientists this year, from 69 countries and regions. Several appear in more than one division. The United States still dominates with 38 percent of the honorees, but Chinese scientists are on the rise at 16 percent.

The most highly cited Duke authors are:

Biology and Biochemistry

Charles A. Gersbach

Clinical Medicine

Christopher Bull Granger             

Adrian F. Hernandez      

Renato D. Lopes              

Cross-Field

Stefano Curtarolo

Xinnian Dong    

HonaLee Harrington

Renate Houts   

Tony Jun Huang               

Ru-Rong Ji

Robert Lefkowitz

Jason Locasale  

David B. Mitzi    

Christopher B. Newgard               

Michael J. Pencina    

Bryce B. Reeve                      

Pratiksha I. Thakore       

Mark R. Wiesner              

Microbiology    

Barton F. Haynes

Neuroscience and Behavior

Quinn T. Ostrom                              

Pharmacology and Toxicology

Evan D. Kharasch             

Physics

David R. Smith  

Plant and Animal Science

Sheng Yang He                 

Psychiatry and Psychology

Avshalom Caspi                

E. Jane Costello

Terrie E. Moffitt

Space Science  

Dan Scolnic        

Duke Affiliated:

Cross Field

Po-Chun Hsu – University of Chicago, Adjunct Assistant Professor in Mechanical Engineering and Materials Science at Pratt School of Engineering

Candice Odgers, UC Irvine, Adjunct at Duke

Environment and Ecology

Robert B. Jackson, Stanford University, Adjunct Professor of Earth and Ocean Science at Nicholas School of the Environment

William E. Copeland, University of Vermont, adjunct in psychiatry and behavioral sciences, School of Medicine.

New Rankings Place Duke Scholars on Top of the World

L-R: Tomasello, Moffitt, Caspi, Lefkowitz.

We didn’t know we needed another way to rank the importance of Duke’s scientists, but the folks at research.com have gone ahead and developed one anyway. And in its second year of data, several Duke people come out in the top ten nationally and globally. So, okay, maybe we did need a new ranking system!

Duke Psychology and Neuroscience swept the U.S. medals in psychology: Terrie E. Moffitt Ph.D., first, Michael Tomasello, Ph.D. second, and Avshalom Caspi, Ph.D. third. Duke University’s psychology is overall ninth in the world, according to this ranking.

Moffitt, the Nannerl O. Keohane University Distinguished Professor of P&N, and Caspi, the Edward M. Arnett Distinguished Professor of P&N, are frequent co-authors on a lifelong psychology and health study of 1,000 people born in Dunedin, New Zealand. Moffitt ranks fourth in the world in psychology, with 207,903 citations of her 582 works. Caspi’s 159,598 citations of 507 papers were good enough for 10th in the world.

Developmental psychologist Tomasello, the James F. Bonk Distinguished Professor of P&N, has focused his work on cognitive development, social cognition and language acquisition. He has 147,951 citations on an even 800 works, placing him second in the U.S. and ninth in the world.

Nobel laureate Robert Lefkowitz M.D., the chancellor’s distinguished professor of medicine, is ranked second in the nation and third in the world for Biology and Biochemistry with 198,000 citations of his 881 papers. The rankings reflect the importance of Lefkowitz’s discovery and characterization of the 7-transmembrane g-coupled protein receptor (GPCR), a fundamental signaling port on the surface of cells that is targeted by a third to a half of all prescription drugs.

Koenig

Psychiatry and Behavioral Sciences professor and Co-Director of Duke’s Center for Spirituality, Theology and Health, Harold G. Koenig M.D., was ranked seventh in the nation and 10th in the world for Social Sciences and Humanities for his work on spirituality and health. His 703 publications have earned 66,404 citations.

Many other Duke scholars finished in the top 100 worldwide in their respective fields, some even making a mark in multiple fields. Check it out.

Methodology: Research.com’s ranking of the best scholars by discipline relies on data consolidated from various sources including OpenAlex and CrossRef. The bibliometric data for estimating the citation-based metrics were collected on Dec. 21, 2022. Position in the ranking is based on a researcher’s D-index (Discipline H-index), which includes exclusively papers and citation metrics for an examined discipline.

And just to prevent some letters to the editor, we acknowledge that the H-index has its critics, including its inventor. We don’t make the rankings folks, we just share them.

Duke’s Most-Cited — The Scholars Other Scientists Look To

It’s not enough to just publish a great scientific paper.

Somebody else has to think it’s great too and include the work in the references at the end of their paper, the citations. The more citations a paper gets, presumably the more important and influential it is. That’s how science works — you know, the whole standing-on-the-shoulders-of-giants thing.

So it always comes as a chest swelling affirmation for Dukies when we read all those Duke names on the annual list of Most Cited Scientists, compiled by the folks at Clarivate.

This year is another great haul for our thought-leaders. Duke has 30 scientists among the nearly 7,000 authors on the global list, meaning their work is among the top 1 percent of citations by scientific field and year, according to Clarivate’s Web of Science citation index.

As befits Duke’s culture of mixing and matching the sciences in bold new ways, most of the highly cited are from “cross-field” work.

Duke’s Most Cited Are:

Biology and Biochemistry

Charles A. Gersbach       

Robert J. Lefkowitz         

Clinical Medicine

Scott Antonia

Christopher Bull Granger             

Pamela S. Douglas           

Adrian F. Hernandez      

Manesh R. Patel               

Eric D. Peterson

Cross-Field

Chris Beyrer

Stefano Curtarolo

Renate Houts 

Tony Jun Huang  

Ru-Rong Ji

Jie Liu

Jason Locasale  

Edward A. Miao

David B. Mitzi    

Christopher B. Newgard

John F. Rawls   

Drew T. Shindell

Pratiksha I. Thakore       

Mark R. Wiesner              

Microbiology

Barton F. Haynes             

Neuroscience and Behavior

Quinn T. Ostrom              

Pharmacology and Toxicology

Evan D. Kharasch

Plant and Animal Science

Xinnian Dong    

Sheng Yang He                 

Psychiatry and Psychology

Avshalom Caspi

William E. Copeland

E. Jane  Costello               

Terrie E. Moffitt

Social Sciences

Michael J. Pencina          

John W. Williams              

Congratulations, one and all! You’ve done us proud again.

A Fond Farewell for Our Three Senior Bloggers

It’s May! Time for our 2022 Duke graduates to endure Pomp and Circumstance on repeat, shed a tear, and then take wing. Always bittersweet for those of us who work with students.

This year, the Duke Research Blog celebrates the graduation of three outstanding student-bloggers. This class produced some real gems and we will be greatly diminished by their commencement.

This image has an empty alt attribute; its file name is IMG_1940.jpg
Anna Gotskind in the Galapagos, 2018

Anna Gotskind blogged for us all four years, after growing up in Chicago.

Most memorably, Anna took us along when she spent the summer of 2019 at an archaeology dig in Italy.

Her other topics were a liberal arts education in themselves: she wrote about invisible malaria, climate change, dance, drinking water standards, snow leopards, muscular dystrophy, cybercrime, autism and some fascinating classmates. This year, as she readied for her career, she wrote a three-part series about blockchain and bitcoins.

After graduating with a psychology major, an econ minor and an innovation and entrepreneurship certificate, Anna will be moving to Atlanta to work as an associate consultant at Bain and Company. She plans to continue learning about the web3 space in her “free time” and hopes to find an outlet to continue writing about cryptocurrency as well. 

Cydney Livingston, the pride of Anson County, NC, joined us as a sophomore and proceeded to shoot out the lights with 31 career posts.

Cydney Livingston

Cydney’s biggest hit, by far, was her first-person account of trying to continue with college after the pandemic shut down Spring Term, 2020. “Wednesdays, My New Favorite Day,” appealed to Duke alumni, family and friends everywhere who were wondering what the heck was going on in Durham. Short answer: It was weird.

She was integral to our (mostly virtual) coverage of the COVID crisis, and helped the campus keep up with some of the larger questions the emerging virus presented, including social inequity and vaccine hesitancy. She also profiled some grad students, sharing a look inside their worlds from a student’s perspective. And in between, Cydney saw paleontologist Richard Leakey in one of his last public appearances and wrote about space junk, cervixes, lead poisoning, dog smarts, visual perception and North Carolina’s pungent pork industry.

Cydney is graduating with a BS in Biology and an AB II in History and is moving to Boston in the fall to begin work as an analyst with ClearView Healthcare Partners. But she is leaving open the possibility of a return to academia in history of science, technology and medicine, or science and technology studies. “I’m excited to spend a few years working and reflecting on my time at Duke and what lies ahead in my life journey.”

Rebecca Williamson

Rebecca Williamson, a first-year economics, but maybe arts major, signed up four years ago just for the experience and horizon- broadening. Mission accomplished! She’s graduating with distinction as an English major with minors in Econ and Music. Her blogging career covered The Muppets, grad student standup comedy, and the exhausting Datathon hackfest.

She will be staying in Durham to take part in the Analyst Program for DUMAC, the nonprofit corporation that manages the university’s investments.

Godspeed, young bloggers. We miss you already.

Written with fondness and gratitude by Karl Leif Bates, editor

Duke has 38 of the World’s Most Highly-Cited Scientists

Peak achievement in the sciences isn’t measured by stopwatches or goals scored, it goes by citations – the number of times other scientists have referenced your findings in their own academic papers. A high number of citations is an indication that a particular work was influential in moving the field forward.

Nobel laureate Bob Lefkowitz made the list in two categories this year.

And the peak of this peak is the annual “Highly Cited Researchers” list produced each year by the folks at Clarivate, who run the Institute for Scientific Information. The names on this list are drawn from publications that rank in the top 1% by citations for field and publication year in the Web of Science™ citation index – the most-cited of the cited.

Duke has 38 names on the highly cited list this year — including Bob Lefkowitz twice because he’s just that good — and two colleagues at the Duke NUS Medical School in Singapore. In all, the 2021 list includes 6,602 researchers from more than 70 countries.

The ISI says that US scientists are a little less than 40 percent of the highly cited list this year – and dropping. Chinese researchers are gaining, having nearly doubled their presence on the roster in the last four years.

“The headline story is one of sizeable gains for Mainland China and a decline for the United States, particularly when you look at the trends over the last four years,” said a statement from David Pendlebury, Senior Citation Analyst at the Institute for Scientific Information. “(This reflects) a transformational rebalancing of scientific and scholarly contributions at the top level through the globalization of the research enterprise.”

Without further ado, let’s see who our champions are!

Biology and Biochemistry

Charles A. Gersbach

Robert J. Lefkowitz

Clinical Medicine

Pamela S. Douglas

Christopher Bull Granger

Adrian F. Hernandez

Manesh R.Patel

Eric D. Peterson

Cross-Field

Richard Becker

Antonio Bertoletti (NUS)

Yiran Chen

Stefano Curtarolo

Derek J. Hausenloy (NUS)

Ru-Rong Ji

Jie Liu

Jason W. Locasale

David B. Mitzi

Christopher B. Newgard

Ram Oren

David R. Smith

Heather M. Stapleton

Avner Vengosh

Mark R. Wiesner

Environment and Ecology

Emily S. Bernhardt

Geosciences

Drew T. Shindell

Immunology

Edward A. Miao

Microbiology

Barton F. Haynes

Neuroscience and Behavior

Quinn T. Ostrom

Pharmacology and Toxicology

Robert J. Lefkowitz

Plant and Animal Science

Xinnian Dong

Sheng Yang He

Philip N. Benfey

Psychiatry and Psychology

Avshalom Caspi

E. Jane Costello

Honalee Harrington

Renate M. Houts

Terrie E. Moffitt

Social Sciences

Michael J. Pencina

Bryce B. Reeve

John W. Williams

Post by Karl Bates

Learning Something Surprising About “SuperLearners”

The discovery of a signaling pathway in the brain that could make mice into ‘superlearners’ understandably touched off a lot of excitement a few years back.

But new work led by Duke neurologist and neuroscientist Nicole Calakos MD PhD suggests there’s more to the story of the superlearner chemical pathway than anybody realized.

A genetically-enhanced ‘smart mouse’ doing some important work. (Boston University)

In a study led by postdoctoral researchers Ashley Helseth and Ricardo Hernandez-Martinez,  the Calakos lab developed a new tool to visualize activity of this Integrated Stress Response (ISR) signaling pathway because it contributes to synaptic plasticity – the brain’s ability to rewire circuits – as well as to learning and memory.

What they didn’t expect to see is that a population of cells called cholinergic interneurons, which comprise only 1 or 2 percent of the whole basal ganglia structure, seem to have the ISR pathway working all the time. The basal ganglia, which is the focus of much of Calakos’ work, plays a role in Parkinson’s and Huntington’s diseases, Tourette’s syndrome, obsessive compulsive disorder and more.

Nicole Calakos, the Lincoln Financial Group distinguished professor of Neurobiology and Neurology. (Alex Boerner)

“This totally changes how you think about the pathway,” Calakos said. “Everybody thought this pathway used an on-demand response type of mechanism, but what if some cells needed it for their everyday activities?”

To answer this, they blocked the ISR in just those rare interneurons in mice and it actually reproduced the enhanced performance on learned tasks that the earlier studies had shown when the pathway was blocked universally throughout the brain. This finding focuses attention on this select subset of brain cells, the cholinergic interneurons that release the chemical signal acetylcholine, as being responsible for at least some of the ‘superlearner’ behavior.

Since the integrated stress response pathway and its potential to enhance learning and memory was identified, drugs for dementia and traumatic brain injury are being designed to manipulate it and help the brain recover. But there may be more to the story than anyone realized, Calakos said.

“Our results show that the ISR plays a major role in acetylcholine-releasing cells, and our current best dementia drugs boost acetylcholine,” she said.

With their new tool, SPOTlight, the team were able to highlight the presence of cholinergic interneurons (red) which are only 1 to 2 percent of the cell population in the ganglia. (Helseth et al)

Acetylcholine, the chemical that these rare cholinergic interneurons use to signal in the brain, is well known for its powerful effects on influencing brain states for attention and learning. This finding suggests that at least some of the ‘superlearner’ properties of inhibiting the ISR occur by influencing brain state, rather than acting directly in the cells that are being rewired during learning.

In addition to the full research article, Science published on April 23 an article summary by Helseth and Calakos and a perspective piece by a pair of University of Minnesota neuroscientists highlighting the finding’s importance.

More work is required to sort out what ISR is and is not doing, but it’s possible that these new findings can help to develop “more precise, more nuanced Alzheimer’s drugs,” Calakos said.

Post by Karl Leif Bates

Most Highly Cited List Includes 37 from Duke

Five of the ten Duke women included in the most highly-cited list this year. Their scholarly publications are viewed as important and influential by their peers. (Clockwise from upper left: Costello, Curtis, Dawson, Bernhardt, Moffitt)

Duke’s leading scholars are once again prominently featured on the annual list of “Most Highly Cited Researchers.”

Thirty-seven Duke faculty were named to the list this year, based on the number of highly cited papers they produced over an 11-year period from January 2009 to December 2019.  Citation rate, as tracked by Clarivate’s Web of Science, is an approximate measure of a study’s influence and importance.

Barton Haynes

Two Duke researchers appear in two categories: Human Vaccine Institute Director Barton Haynes, and Michael Pencina, vice dean of data science and information technology in the School of Medicine.

And two of the Duke names listed are new faculty, recruited as part of the Science & Technology initiative: Edward Miao in Immunology and Sheng Yang He in Biology.

Michael Pencina

This year, 6,127 researchers from 60 countries are being recognized by the listing. The United States still dominates, with 41 percent of the names on the list, but China continues to grow its influence, with 12 percent of the names.

Clinical Medicine:

Robert M. Califf, Lesley H. Curtis, Pamela S. Douglas, Christopher Bull Granger, Adrian F. Hernandez, L. Kristen Newby, Erik Magnus Ohman, Manesh R. Patel, Michael J. Pencina, Eric D. Peterson.

Environment and Ecology:

Emily S. Bernhardt, Stuart L. Pimm, Mark R. Weisner.

Geosciences:

Drew T. Shindell

Immunology:

Barton F. Haynes, Edward A. Miao

Microbiology:

Barton F. Haynes

Plant and Animal Science:

Sheng Yang He

Psychiatry and Psychology:

Avshalom Caspi, E. Jane Costello, Renate M. Houts, Terrie E. Moffitt

Social Sciences:

Michael J. Pencina

Cross-Field:

Dan Ariely, Geraldine Dawson, Xinnian Dong, Charles A. Gersbach, Ru-Rong Ji, Robert J. Lefkowitz, Sarah H. Lisanby, Jie Liu, Jason W. Locasale, David B. Mitzi, Christopher B. Newgard, Ram Oren, David R. Smith, Avner Vengosh.

Hard-Won Answer Was Worth the Wait

Most of Physics Professor Haiyan Gao’s students see their doctoral dissertations posted on her lab’s web site very soon after they have been awarded their Ph.Ds.

But Yang Zhang, Ph.D. 2018, had to wait two years, because his thesis work had a very good chance of being accepted by a major journal. And this week, it has been published in the journal Science.

What Zhang did was to create the world’s most precise value for a subatomic nuclear particle called a neutral pion. It’s a quark and an antiquark comprising a meson. The neutral pion (also known as p0) is the lightest of the mesons, but a player in the strong attractive force that holds the atom’s nucleus together.

Haiyan Gao (left) with newly-minted physics Ph.D. Yang Zhang in 2018. (Photo courtesy of Min Huang, Ph.D. ’16)

And that, in turn, makes it a part of the puzzle Gao and her students have been trying to solve for many years. The prevailing theory about the strong force is called quantum chromodynamics (QCD), and it’s been probed for years by high-energy physics. But Gao, Zhang and their collaborators are trying to study QCD under more normal energy states, a notoriously difficult problem.

Yang Zhang spent six years analyzing and writing up the data from a Primakoff  (PrimEx-II) experiment in Hall B at Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, VA. His work was done on equipment supported by both the National Science Foundation and the Department of Energy.  


This is the quark structure of the positive pion – an up quark and an anti-down quark. The strong force is from gluons, represented as the wavy lines (Arpad Horvath via Wikimedia Commons)

In a Primakoff experiment, a photon beam is directed on a nuclear target, producing neutral pions. In both the PrimEx-I and PrimEx-II experiments at Jefferson Lab, the two photons from the decay of a neutral pionwere subsequently detected in an electromagnetic calorimeter. From that, Zhang extracted the pion’s ‘radiative decay width.’ That decay width is a handy thing to have, because it is directly related to the pion’s life expectancy, and QCD has a direct prediction for it.

Zhang’s hard-won answer: The neutral pion has a radiative decay width of 7.8 electron-volts, give or take. That makes it an important piece of the dauntingly huge puzzle about QCD. Gao and her colleagues will continue to ask the fundamental questions about nature, at the finest but perhaps most profound scale imaginable.

The PrimEx-I and PrimEx-II collaborations were led by Prof. Ashot Gasparian from North Carolina A&T State University. Gao and Zhang joined the collaboration in 2011.

“Precision Measurement of the Neutral Pion Lifetime,” appears in Science May 1. Dr. Yang Zhang is now a quantitative researcher at JPMorgan Chase & Co.

How Small is a Proton? Smaller Than Anyone Thought

The proton, that little positively-charged nugget inside an atom, is fractions of a quadrillionth of a meter smaller than anyone thought, according to new research appearing Nov. 7 in Nature.

Haiyan Gao of Duke Physics

In work they hope solves the contentious “proton radius puzzle” that has been roiling some corners of physics in the last decade, a team of scientists including Duke physicist Haiyan Gao have addressed the question of the proton’s radius in a new way and discovered that it is 0.831 femtometers across, which is about 4 percent smaller than the best previous measurement using electrons from accelerators. (Read the paper!)

A single femtometer is 0.000000000000039370 inches imperial, if that helps, or think of it as a millionth part of a billionth part of a meter. And the new radius is just 80 percent of that.

But this is a big — and very small — deal for physicists, because any precise calculation of energy levels in an atom will be affected by this measure of the proton’s size, said Gao, who is the Henry Newson professor of physics in Trinity College of Arts & Sciences.

Bohr model of Hydrogen. One proton, one electron, as simple as they come.

What the physicists actually measured is the radius of the proton’s charge distribution, but that’s never a smooth, spherical point, Gao explained. The proton is made of still smaller bits, called quarks, that have their own charges and those aren’t evenly distributed. Nor does anything sit still. So it’s kind of a moving target.

One way to measure a proton’s charge radius is to scatter an electron beam from the nucleus of an atom of hydrogen, which is made of just one proton and one electron. But the electron must only perturb the proton very gently to enable researchers to infer the size of the charge involved in the interaction. Another approach measures the difference between two atomic hydrogen energy levels. Past results from these two methods have generally agreed.

Artist’s conception of a very happy muon by Particle Zoo

But in 2010, an experiment at the Paul Scherrer Institute replaced the electron in a hydrogen atom with a muon, a much heavier and shorter-lived member of the electron’s particle family. The muon is still negatively charged like an electron, but it’s about 200 times heavier, so it can orbit much closer to the proton. Measuring the difference between muonic hydrogen energy levels, these physicists obtained a proton charge radius that is highly precise, but much smaller than the previously accepted value. And this started the dispute they’ve dubbed the “proton charge radius puzzle.”

To resolve the puzzle, Gao and her collaborators set out to do a completely new type of electron scattering experiment with a number of innovations. And they looked at electron scattering from both the proton and the electron of the hydrogen atom at the same time. They also managed to get the beam of electrons scattered at near zero degrees, meaning it came almost straight forward, which enabled the electron beam to “feel” the proton’s charge response more precisely.

Voila, a 4-percent-smaller proton. “But actually, it’s much more complicated,” Gao said, in a major understatement.

The work was done at the Department of Energy’s Thomas Jefferson National Accelerator Facility in Newport News, Virginia, using new equipment supported by both the National Science Foundation and the Department of Energy, and some parts that were purpose-built for this experiment. “To solve the argument, we needed a new approach,” Gao said.

Gao said she has been interested in this question for nearly 20 years, ever since she became aware of two different values for the proton’s charge radius, both from electron scattering experiments.  “Each one claimed about 1 percent uncertainty, but they disagreed by several percent,” she said.

And as always in modern physics, had the answer not worked out so neatly, it might have called into question parts of the Standard Model of particle physics. But alas, not this time.

“This is particularly important for a number of reasons,” Gao said. The proton is a fundamental building block of visible matter, and the energy level of hydrogen is a basic unit of measure that all physicists rely on.

The new measure may also help advance new insights into quantum chromodynamics (QCD), the theory of strong interaction in quarks and gluons, Gao said. “We really don’t understand how QCD works.”

“This is a very, very big deal,” she said. “The field is very excited about it. And I should add that this experiment would not have been so successful without the heroic contributions from our highly talented and hardworking graduate students and postdocs from Duke.”

This work was funded in part by the U. S. National Science Foundation (NSF MRI PHY-1229153) and by the U.S. Department of Energy (Contract No. DE-FG02-03ER41231), including contract No. DE-AC05-06OR23177 under which Jefferson Science Associates, LLC operates Thomas Jefferson National Accelerator Facility.

CITATION: “A Small Proton Charge Radius from An Electron-Proton Scattering Experiment,”  W. Xiong, A. Gasparian, H. Gao, et al. Nature, Nov. 7, 2019. DOI: 10.1038/s41586-019-1721-2 (ONLINE)

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