An Interview with Manuel F. Varela and Ann F. Varela: Mary Gaillard and Theoretical Physics

Jun 27, 2021 by

Professor Gaillard

Courtesy of M. K. Gaillard, with permission.

After I recounted some of my worst experiences, especially during my first year as a graduate student in Paris, I was asked why I hadn’t given up. I answered in part that I had once been told by Leon Lederman, my friend of many years, that I had some kind of ‘survival mechanism.’”

—Mary K. Gaillard

I endured many subtle and less subtle small insults as a young aspiring scientist and even as a more established one.”

—Mary K. Gaillard

Michael F. Shaughnessy

1) Mary Gaillard was somewhat of an oddity during her time—a female in physics—When and where was she born, and where did she initially go to school?

Theoretical physicist Dr. Mary Gaillard is most famous for her involvement with the Standard Model of experimental particle physics, mass predictions of the charm quark and the b-quark, and her research contributions to supersymmetry, supergravity, and superstring theory.

Gaillard was born in New Brunswick, New Jersey, on April 1, 1939. Her parents, Philip and Marion, affectionately called her Mary Kay, which she later shortened to Mary K. Her older brother’s name was George and the two siblings got along quite well. In fact, they performed together in a play called Our Town in high school.

As an undergraduate at Hollins College, Gaillard was interested in fine arts such as playing the piano, painting, and creative writing as a means of recreation. Once she was a graduate student, her interests leaned mostly toward physics, except for joining the French Club. Who would have thought that her fluency in French would be instrumental in meeting her future husband, Jean-Marc Gaillard?

She received a bachelor’s degree in 1960 from Hollins College, located in Virginia, and a master’s degree from Columbia University in 1961. Following that, Gaillard moved to Paris with her husband, Jean Mark Gaillard. The couple had three children. Gaillard earned a doctorate at the University of Paris at Orsay, France, in 1968.

2) Gaillard apparently studied at the University of Paris (Sorbonne) in Orsay—what did she learn, and what did she accomplish there?

When Gaillard was a graduate student at Columbia, she had transferred to the University of Paris and continued her studies in France. She would later refer to her initial stay there as “the worst year.” Gaillard had been extraordinarily interested in studying theoretical physics. However, she had been quickly discouraged from doing so. She was told that theory was beyond her reach, as women were believed to have low self-esteem.

Thus, Galliard was instead told to pursue experimental physics. Unfortunately for her, Galliard was rejected from every single experimental physics laboratory at the University of Paris. The reasons for these rejections varied. For example, each lab head informed Gaillard that they accepted students only from two institutions, the École Polytechnique and École Normale, both of which were all-male schools.

Thus, women students were effectively shut out from the study of experimental physics and physics theory. So, she returned to the U.S. to briefly finish her coursework at Columbia before moving on to graduate school in France.

Relief from Gaillard’s immersion in the experimental versus theory quagmire, which prevented her entry into both areas of study, came in the form of a move to CERN (Organisation Européen pour la Recherche Nucléaire, which translates to European Organization for Nuclear Research). Housed in Geneva, Switzerland, Gaillard followed her husband Jean-Marc, who had taken on a new staff position at the CERN. In Geneva, Gaillard had encountered a change of fortune.

At CERN, she met up with Bernard d’Espagnat, a professor from the University of Paris who was on sabbatical leave from Orsay, France. Professor d’Espagnat readily agreed to sponsor Gaillard, who could now conduct her Ph.D. thesis work at CERN while also enrolled as a bona fide graduate student at the University of Paris. Before d’Espagnat had agreed to the sponsorship, Gaillard had been a visiting scientist sharing a basement office with five guest residents. She was under the tutelage of Antonio Stanghellini, who was teaching the physics of atomic particle decay and strongly interacting particles of protons, neutrons, and pions to generate lighter hadrons.

Unfortunately, Stanghellini had unexpectedly died shortly after Gaillard’s arrival to CERN. With Gaillard being left without a supervisor, d’Espagnat’s stepped in, and his graduate advising was warmly welcomed. Fortunately, d’Espagnat would lend his expertise in teaching Gaillard the physics of weak interactions between atomic particles. The study of weak interactions would propel Gaillard into world research on particle physics. Consequently, she would become an expert, leading her to complete her education and make her first significant discovery.

In 1968, Dr. Mary K. Gaillard would successfully defend her Ph.D. thesis dealing with the physics of weak interactions involving atomic particles during their decay.

3) Supposedly, she received not one but two doctorates—what were they in, and how did this come about?

Mary Gaillard earned what is considered nowadays as two doctoral degrees from the University of Paris. The first in 1964 was called the doctorat de troisieme cycle, and the second, in 1968, was named the doctorat d’État. Under the French higher education system, in 1964, Gaillard completed three cycles, the first two consisting of an undergraduate degree and the third cycle completing a so-called third cycle thesis.

Gaillard considered the degree to be the equivalent of a thesis project on the level of somewhere between a master’s and a doctorate. Alas, the three-cycle thesis system for doctoral degree-granting does not exist in present times.

For the first doctoral thesis, Gaillard became an expert on the weak interactions and the physics of kaons, which are atomic particles known as K-mesons. See Figure 1. In addition, she had developed methods for measuring resonance properties, such as the rotating motions, called spin, of nuclear particles. The spins of sub-atomic particles typically occur in integer multiples of ½ h where h equals Planck’s constant 6.63 x 10-34 Joules・sec. These various spin behaviors would later become essential entities regarding Gaillard’s newer advances in particle physics.

Figure 1. The quark structure of the neutral kaon (K⁰). The neutral kaon is composed of a down quark and an anti-strange quark. The strong force is mediated by gluons (wavey line). The strong force has three types of charges, called red, green, and blue. Here, the down has blue, and the anti-strange or anti-blue has yellow.

File:Quark structure of the neutral kaon.png

Gaillard’s second thesis project continued with the kaons, and she expanded the work to consider weak decays of so-called strange hypothetical particles, baryons. Another part of Gaillard’s early work with the kaons dealt with their potential to violate the so-called CP, a quantum number. C is the charge conjugation where atomic particles turn into anti-particle counterparts, and P is the parity in two spatial dimensions, like a mirror reflection. According to physics lore, while the C or P can vary according to given conditions, the CP number remained constant and conserved.

Thus, any violation of C or P was thought possible as long as the value of CP itself was conserved. However, the nature of the kaon decay into pion particles was uncertain, as it appeared that no evidence had yet existed that CP violation could occur. Still a graduate student, Gaillard had brilliantly developed a novel method to test CP violation when kaons decayed. One of her first papers, published in 1965, described how a CP violation could be possible when a kaon particle decayed into a smaller particle called 3π.

During these times when Gaillard was conducting thesis projects for two doctoral degrees in tandem, she was also busy having and raising three children and working fewer hours in the laboratory than her male colleagues to arrange for childcare. Her first child was born in 1962, and her second child was born when Gaillard was writing up her first doctoral thesis project. Her third child was born when Gaillard was writing up the second thesis project.

Gaillard recalled that one time she had forgotten to pick up one of her children, Bruno, who was eight or nine years old, from his music lessons. Bruno had waited a long time in the cold and the dark. Finally, though freighted, Bruno got a car ride from an elderly couple who drove Bruno to the French border, where an au pair retrieved the child and brought him home that evening.

Gaillard commuted to Paris at her own expense for much of the duration after the first doctorate was granted. The periodic trips to Paris arose because her pay was dismal, even after earning the doctorate. Hence, she had to make extra money tutoring male students at the École Polytechnique. This institute had denied Gaillard admission because she was female.

Furthermore, Gaillard had to deal with less respect than her male colleagues did from specific individuals, like Leon Van Hove, group leader of the theoretical section of the lab at CERN. Van Hove was said to have delayed the publication of one of Gaillard’s first manuscripts because he had had several nitpicking remarks about it. While the manuscript was eventually published in the journal Nuovo Cimento, the incident with the group leader had troubled Gaillard. When she became pregnant a second time, Gaillard had feared Van Hove would find out and deny her access to the laboratory’s facilities, despite not being paid by CERN at the time. In later years, Gaillard and Van Hove would interact in an adversarial manner.

4) Gaillard taught at the University of California-Berkeley—what did she teach, and how long was she there?

Turning down a job offer from the prestigious Fermilab in Chicago, Gaillard arrived in Berkeley, California, in 1982 to accept a full professorship position with tenure in physics at the University of California system. She also took on a joint appointment at the famous Lawrence Berkeley Laboratory (LBL), which later became known as Lawrence Berkeley National Laboratory (LBNL). In Berkeley at the time, Gaillard became the physics department’s first female professor and the first woman to be granted tenure.

One of the first subjects that Professor Gaillard taught at Berkeley was a graduate-level course in quantum mechanics, and she later taught upper-division physics courses.

In an interview, Gaillard would remark that she had found it much easier to provide lectures to her fellow scientists in seminars at physics conferences or even public speeches to the community than lecture to university students. Prof. Gaillard would teach physics at Berkeley, see Figure 2, until her retirement in 2009, when she became professor emeritus. In retirement, Gaillard has been on the graduate faculty at Berkeley and a visiting scientist at LBNL.

Because of her involvement with mentoring female Berkley students, who were very interested in knowing her experiences, Gaillard wrote an autobiography called A Singularly Unfeminine Profession: One Woman’s Journey in Physics, published in 2015. During an interview, Gaillard said that the two main themes of her published memoir dealt with her career in physics in a male-dominated profession and the joy of discovery that she experienced when investigating atomic particle physics.

File:LeConte Hall west entrance.jpg

Figure 2. A western view of Le Conte Hall at Berkeley which houses the physics department.

5) Gaillard theoretically predicted the mass of the charm quark. Now, what exactly is a “charm quark,” and why was this important?

Many physicists believe that one of Gaillard’s most significant discoveries involved her prediction for the mass of the charm quark before the experimental evidence in favor of its presence was collected. See Figure 3. Gaillard’s work on the charm quark began when she was a visiting scientist at the famous Fermilab in Batavia, Illinois, where she collaborated with Benjamin W. Lee.

File:Charm quark.svg

Figure 3. Charm quark.

In general, atoms consist of protons, electrons, and neutrons. The protons are positively charged, and electrons carry a negative charge. While the neutrons have no charged behavior, they can be divided into smaller particles called quarks. One of these quarks was predicted to be the charmed quark.

Shelly Glashow and James Bjorken coined the term “charm” as they needed to invent a quark, c, with an electric charge, μ (mu), called the “charm quark” to explain a new confusing theory and experimental data of alternating neutral currents. The presence of a new theoretical quark was required to clarify the prediction that a neutral kaon called K0 decayed into smaller particles called muons, denoted as μ+ and μ. The charm quark would conveniently cancel the enormous contribution of the kaon decay into the muons, a condition predicted by theory but not seen consistently in the experimental world.

Gaillard and Lee considered two predictive models based on the scheme of Shelly Glashow, Steven Weinberg, and Abdus Salam (GWS) and a variation proposed by Glashow, John Iliopoulos, and Luciano Maiani (GIM). Considering the various parameters of GWS and GIM theories, such as the conditions of the so-called up and down quarks and their associated hadronic bound states, Gaillard and Lee came up with an accurate charmed quark mass calculation of 1.5 billion electron volts.

It was a giant breakthrough amidst the reams of confusing experimental data, which kept seeing hints of the so-called “neutral currents” that were not explained by the masses and charges of the then known existing atomic particles. What was worse was that the neutral currents sometimes disappeared, which Gaillard and others referred to as alternating. Therefore, when Gaillard and Lee calculated an accurate value for the mass of the charmed quark, it generated intense excitement amongst the physicists because their charmed quark mass amount fit nicely with the GWS/GIM model of atomic particle physics. Gaillard and Lee published the significant discovery in the prestigious Physical Review D journal in 1974.

6) As I understand it, there are six different quarks. What is a “quark,” and why are they important?

The quarks are members of a group of so-called elementary or fundamental particles (i.e., sub-atomic particles with no other pieces) that make up atoms.

The elementary particles constitute an essential component of matter. In general, quarks can combine to generate so-called composite particles like hadrons, of which the proton and the neutron are considered the most highly stable. The proton is made up of a down quark, two up quarks, and gluons, which harbor the forces that hold the combination together. On the other hand, the neutron is built with one up quark and two down quarks held together by gluon forces. See Figure 4.


Figure 4. Quarks.

The quarks include bosons, fermions, plus hypothetical particles and so-called ghost fields. Quarks and leptons constitute most of the sub-atomic composition of fermions. Presently, all quarks are subsets of fermions and, together with the leptons, can form fermions. Fermions have so-called half-integer spins, while bosons have integer spins. The six quark types that you mentioned, also known as flavors, include the bottom quark, the charmed quark, the down quark, the strange quark, the top quark, and the up quark. The entirety of the universe’s observable matter appears to be made up of the electrons, the up quarks, and the down quarks.

The bottom quark is also referred to as the beauty quark or the b quark. The name “bottom” was coined by Haim Harari to distinguish it from the top quark, discussed below. Working with Mike Chanowitz and John Ellis, Gaillard had predicted a mass for the b quark to about five billion electron volts. Toshihide Maskawa and Makoto Kobayashi had expected the presence of the bottom quark theoretically in 1973.

They took the 2008 Nobel Prize in physics because they had explained a reasonable possibility of violating the CP quantum number. Leon Lederman at the famous Fermilab experimentally confirmed the bottom quark in 1977. When top quarks decay, bottom quarks form. When the famous Higgs boson decays, bottom quarks are produced as well.

The charm or charmed quark, also denoted as the c quark, can combine to generate hadrons. Gaillard would become noted for her clever calculation of its mass charge while a visiting scientist at Fermilab in 1974. See Figure 5. One consequence of this discovery was the so-called November revolution, in which new insights were emerging in quick succession.

One of these was the formulation of the so-called psion, which is a meson composed of a charm quark and a charm antiquark. The psion is also called the J/ψ particle. The Greek letter ψ (psi) was given because it resembled the shape of the new event. The letter J was assigned to the particle name because its shape resembled the Chinese character for “Ting” of Samuel Ting, who in 1974 was the group leader at MIT where the particle was discovered and who would share the 1976 Nobel Prize in physics with Burton Richter.

File:High Rise at Fermilab.jpg

Figure 5. Fermilab’s High Rise.

The down quark, or d quark, was proposed to exist theoretically in 1964 by the famous Murray Gell-Mann, with whom Gaillard had once collaborated and who would get the 1969 physics Nobel award. Two down quarks are known to combine with one up quark to form a neutron. Similarly, one down quark and two up quarks form a proton.

Working with Kazuhiko Nishijima, Gell-Mann also postulated the so-called strange quark, which is described as such to account for its excited state but with an elementary electric charge of -1/3 e and an isospin value of zero, in contrast to the up and down quarks, which have isospin values of +1/2 and -1/2, respectively. The strange quarks have been found in specific hadrons, such as the kaons.

The top quark, also called the t or truth quark, is a massive elementary particle because it combines with the Higgs Boson. The top quark is known to decay into a bottom quark, a strange quark, and a down quark, among other particles. In 1973, Toshihide Maskawa and Makoto Kobayashi had hypothesized its presence to account for kaon decay products and their violation of CP.

Finally, the up quark, which is the lightest of the known quarks, forms neutrons if one up quark is combined with two down quarks. Likewise, as mentioned above, the proton is formed by two of the up quarks and one down quark. Gell-Mann had predicted the up quark in 1964, and experimental evidence for it was obtained in 1968.

7) What is the Higgs particle, and what does this have to do with mass?

Gaillard made significant contributions to the so-called Standard Model of the universe’s composition of its matter. According to this working model, material substances are altogether made up of elementary particles. All matter in the known universe is composed up of these fundamental particles, making more prominent objects. The Model seemed to explain the material’s behavior in the universe most elegantly and satisfyingly—for a while. However, a significant flaw with the Standard Model was glaring.

It predicted that virtually none of the elementary particles had mass. Physicists had traditionally accepted that the photon was a “massless” entity, and the Standard Model fits nicely with this property. Still, a much more significant component, i.e., the mass itself, seemed to be missing from the material in the rest of the universe. It was a substantial shortcoming of the Standard Model. See Figure 6.

Figure 6. Standard Model.

Particle Fever: Particles of the Standard Model of Physics

To reconcile the defective nature of the “massless particles” predicted by the Standard Model, Sir Peter Higgs and François Englert proposed the existence of a new particle, now called the Higgs boson particle. The novel particle could account for the masses within the fermions and, thus, for all matter. The proposed Higgs that the boson particle, in theory, would harbor most of the needed mass. Further, to help explain the properties of the new theoretical particle, professors Higgs and Englert proposed that the fabric of space where the elementary particles behaved was filled with a kind of “viscosity” that provided the particles with a mass. This viscosity came to be known as the Higgs Field. In the Higgs field, the theoretical Higgs boson was instilled with mass! Thus, the Higgs boson had the mass as it occupied the Higgs field, and in theory, it would account for the mass of the matter in the entire universe. Hence, the Higgs particle frequently has been called the “God particle.” Without the Higgs boson, there would be no galaxies in the universe or life on Earth.

Unfortunately, however, the new clarification of the Standard Model with the proposed new Higgs boson particle, which explained the particle mass as it occupied the Higgs field, introduced another problem. The Higgs boson and the Higgs field needed experimental evidence for their existence. The new challenge was monumental in its scope. The theorists had calculated that the Higgs boson was an extremely massive particle with zero charges and zero spins. For the Higgs boson to be verified experimentally, it would take decades. At the time, no linear particle accelerators or colliders yet existed that had enough power or energy to run or generate such hypothetical Higgs particles.

Likewise, no detector was yet invented with which to find it. Without experimental proof, no one would ever know whether the Higgs boson and its field were fundamentally true.

Meanwhile, Gaillard worked with John Ellis to study the theoretical properties of the Higgs boson, its production, and its decays. In the mid-1970s, they had considered production and decay rates assuming a mass somewhere between one million and 100 billion electron volts (100 Giga electron volts, i.e., 100 GeV). Thus, publication of their theoretical analysis for the Higgs particle and field would significantly impact the nature of what to expect when and if a proton collider would be built and put in operation.

A breakthrough came when the newly built Large Hadron Collider, housed at CERN in Geneva, Switzerland. See Figure 7. The “machine” was the most complicated human-made device ever made. The Collider had new superconducting magnets cooled with liquid helium to guide the high-energy elementary particles around an accelerator of 17-miles in circumference. Completion of the Collider’s construction occurred in 2008. The device had smashed protons into each other at extremely high speeds to break off new pieces of neutrons, and the machine ran for 24 hours a day for years to disrupt the Higgs field and “see” statistically the rare Higgs boson particle. Finally, in July of 2012, the discovery of a candidate particle was announced, and in 2013, the Higgs boson was confirmed by experimental analysis.

File:Views of the LHC tunnel sector 3-4, tirage 2.jpg

Figure 7. A view of the Large Hadron Collider tunnel sector 3-4.,_tirage_2.jpg

Today, we know that the Standard Model has fermions of matter with quarks and leptons, plus bosons with force carriers such as gauge bosons and the Higgs boson.

The Higgs boson particle in the Higgs field, which fills all space, gives the elementary particles their mass. The Higgs boson has a mass of over 130 times that of the proton and an energy of 126.5 GeV.

8) Supersymmetry, supergravity, and string theory—what were her contributions here? And who did Gaillard work with at this time?

Gaillard collaborated with her second husband, Bruno Zumino, John Ellis, and Luciano Maiani. They published scientific articles together on supersymmetry, supergravity, and string theory.

The Standard Model considers the various known elementary particles of atoms into a more extensive structural system called supersymmetry. See Figure 8. In the supersymmetric theory, each elementary particle, like a boson or a fermion, is given a so-called “superpartner” with their alternative spins. In supersymmetry, there were interchanges of particles that differed in their spins by one-half units. For instance, for each quark with a spin 1/2, there is a companion “superquark,” colloquially called a “squark,” with a zero spin. Likewise, for each lepton, there is a corresponding “slepton.” For every electron, there was a “selectron.” Every photon of spin one had a corresponding spin-1/2 “photino.” If one continues the logic, then the gauge boson g with spin 1 had a “gaugino” with spin 1/2.

Figure 8. Supersymmetry model.


By considering the influence of gravity within their supersymmetric operations, then supergravity became an issue. Here, Einstein’s theory of general relativity was combined with principles of supersymmetry. One consequence of this new combination was the emergence of the superpartner of the graviton, called the “gravitino,” and its influence on a value called N, the number of distinct supersymmetric operations. Notably, the Higgs boson’s supersymmetric partner was the “Higgsino.” In effect, the application of supersymmetric principles interchanged the Higgs bosons with the fermions.

Thus, the boson behaves like it’s a fermion such that a product of different operators manifests themselves only during antisymmetric combinations. For example, Gaillard and collaborators considered operators with two components, one in which the spin is raised a half unit and the other that is decreased by a half spin unit.

Gaillard and her collaborators began theoretical studies on supersymmetry in the 1980s before experimental evidence was provided. They had considered going beyond the so-called Grand Unification Theory (GUT) parameters to include additional forces as supported by new accelerator data. See Figure 9. The latest data pointed to a so-called “Super GUT” when gravity was considered one of the new forces. Their newly extended supersymmetric considerations examined the number of different operations N based on the particle spin components. They briefly considered a so-called “N = 8 supergravity” idea as a sort of “super-unification” to produce a new version of the “Theory of Everything.” The new Theory of Everything was supposed to satisfy Einstien’s longing for a simple unifying set of equations that described the universe’s physics. Unfortunately, theoretical studies plus emerging experimental data did not support the N = 8 supergravity idea, and it collapsed in the mid-1990s. Theory and empirical data instead favored superstring theory.

Figure 9. Conceptual drawing of The Grand Unification Theory.

The Theory Of Everything On A Prim 09

Regarding superstrings, Gaillard and collaborators addressed the so-called color quantum numbers and the nature of their conservation. In string theory, the sub-atomic particles are now considered as tiny oscillating strings. The distinctive particles are thought to be on different modes of string oscillations. The mathematics seemed to fit nicely if supersymmetric principles were applied to classic string theory. According to superstring theory, the elementary particles are now thought of as extremely short strings, which vibrate, oscillate, or wiggle. Each wiggle mode represents a vibration frequency that can be applied to a particular particle. These vibrational modes of the tiny strings permit one to determine their energies and, therefore, their particle masses!

Furthermore, some strings are open while others are closed, sort of like loops. Open strings can combine to form new linear strings or closed ones. Superstring theory holds the latest promise of unifying all of physics and is an active area of research. Gaillard conducted a considerable amount of her latest work dealing with the implications of vibrational modes on superstring theory. She and collaborators examined the so-called lowest vibrational modes of the tiniest of the known strings. Her work had implications for extending superstring theory regarding multiple dimensions, like 11-dimensional space-time called M-theory. Even today, particle physicists are still grappling with superstring theory.

9) What have I forgotten to ask, and is she still alive and working?

As of this writing, Gaillard is 82 years old and is active with her work on superstring theory. See Figure 10. In her 2015 memoir, she recalls having to deal with being a woman in a largely male-dominated field, physics. Many of her dealings with male physicists primarily consisted of being mistaken for a wife of a physicist or a secretary and with inappropriate, disparaging comments made by male physicists in faculty meetings and scientific conferences throughout the years.

Figure 10. Mary K. Gaillard.

Courtesy of M. K. Gaillard, with permission.

One of her most serious concerns, however, had to do with a disparity of salary. While at CERN, she realized only 10 percent of women physicists received a total compensation as scientists, while 86 percent of the female scientists were not paid while working at CERN. Gaillard noted that the reasons for the disparity given by CERN varied widely. For example, because the husband was an employee of CERN, the wife did not require any remuneration as the male husband could support her. Another reason for the unfair salary difference or lack of pay to females was that priority was given to unemployed males.

Later in life, she recalls having realized that positive opportunities for women were still left wanting, and women still have to deal with the same sorts of issues that Gaillard did in the 1960s well into the 21st century. The precarious situation for female scientists compelled Gaillard to pen the autobiography. In her book, Gaillard was frank and, rightly so, named names.

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