“From the Korean standpoint, naming a non-Korean as director of a research center at the Institute for Basic Science can be risky. But it means that Korea has truly arrived on the global stage. As the director of the center, I feel a huge sense of responsibility.” IBS Research met Prof. Yannis Semertzidis, the first non-Korean to lead the IBS and who recently started doing research there, on the campus of KAIST on October 18, with fall semester in full swing. He has entered the spotlight as the first overseas researcher to be appointed a director of an IBS Center.

Prof. Semertzidis, a fellow of the american Physics Society and a tenured, senior physicist at Brookhaven national Laboratory in new York, was appointed as director of the IBS research center last October in recognition of his experiments in precision particle physics and his plan to research the dark-matter axion. After around a year of contract talks, the IBS center was set up at KAIST and his position was established.

Prof. Semertzidis will take the helm of the IBS’s Center for Axion and Precision Physics Research, which conducts research in elementary particle physics. His lab is on the KAIST campus; IBS Research met him in the Department of Physics building, where we talked about the center’s goals in probing the secrets of the universe.

“Dark matter is a fundamental issue of the universe”Prof. Semertzidis was born in Greece. When asked why he chose to study particle physics, his thoughts turned to the science classrooms of his youth. He recalled something one of his elementary school teachers had said: “Think of breaking a rock into smaller and smaller pieces. What would happen if you repeated this process over and over? Would there be a moment where breaking was not possible anymore without altering the nature of the rock?” Though the teacher wanted to show that “things” are made of finite elementary particles the question aroused the boy’s interest and he became curious about what really makes up the universe.

So how do his childhood dreams relate to his current job? “What is the biggest, most fundamental question in the universe?”
Prof. Semertzidis asked. “Where did the asymmetry of matter and anti-matter come from?” His research concerns the cosmological mystery of dark matter as well as the asymmetry of matter and anti-matter. Naturally, these two subjects are substantive issues in connection with how the universe is constructed.

For Prof. Semertzidis, it was a long road to Korea as director of the IBS. Until recently, he focused mainly on two experimental projects: one exploring the dark-matter axion, and another to confirm the electric dipole moment (EDM) of protons. In the world of particle physics, the prevailing theory is that the existence of the EDM of protons is linked to the matter-anti-matter asymmetry problem. “In the U.S., the government is not spending enough on dark-matter (axion) experiments, but Korea’s choice will help reverse this trend,” he said. “Though we’re looking to do proton EDM experiments in collaboration with the Fermi National Accelerator Lab, in the United States, I think we can do international research based out of Korea.”

Encounter with Prof. Jihn-eui Kim’s axion at RochesterIBS Research asked about dark matter. “Have you ever seen the Milky Way?” he responded. Though the Milky Way looks like a river of milk, it is actually our galaxy projected onto the sky. The solar system, of which the Earth is a part, revolves around our galaxy. He went on to explain that “the solar system has revolved around our galaxy about 18 times so far,” then added: “If there were no more pull than we can infer from our star observations, the solar system would break away from the galaxy.” His explanations sought to associate our galaxy with dark matter; many scientists believe clumps of dark matter occupy the halo of our galaxy.

Dark matter was discovered in the 1930's by the Swiss astrophysicist Fritz Zwicky while he was investigating a cluster of galaxies in the constellation Coma Berenices. Zwicky noticed that the velocities of the individual galaxies in this cluster were so high that they would have broken off from the cluster if the only thing holding them together was the gravitational force of visible matter.

The astrophysicist suggested that invisible matter exerting gravitational force, namely dark matter, is needed to hold these galaxies in the cluster. In the 1970's, the American astronomer Vera Rubin provided further evidence of the presence of dark matter by observing the movement of stars (or hydrogen gas clouds) in a galaxy. She discovered that, contrary to expectations, the stars did not revolve more slowly the farther they were from the center of the galaxy. This meant that dark matter must be holding the stars together in the galaxy. Nowadays, dark matter is known to comprise about 27% of the universe. “It is hard to detect dark matter because, unlike other types of matter, it does not interact with light strongly enough to be seen,” said Prof. Semertzidis, adding that “dark matter can be divided into two general categories: particles such as axions, and super-symmetric particles.” The latter are hypothetical particles predicted by the super-symmetry theory. CERN (the European Organization for Nuclear Research) is searching for them with its Large Hadron Collider (LHC). A case in point is the WIMP, the weakly interacting massive particle.
Read on to learn more about the dark-matter axion that the IBS Center for Axion and Precision Physics Research will explore.

Axions are hypothetical particles postulated in 1977 to explain the CP symmetry in strong interactions (strong force). C symmetry means that physical laws would remain the same if a particle charge is reversed (or a particle is transformed into its antiparticle), while P symmetry means that the physical laws would also remain the same if a particle is mirrored. CP symmetry means that the laws of physics are the same for a particle and its antiparticle when viewed through a mirror. According to the theory of Quantum Chromodynamics (QCD), which uses quarks and gluons to help understand the binding of nuclei, CP symmetry is expected to be violated in strong interactions. However, it is preserved with extraordinary accuracy in QCD experiments, and the introduction of the axion offers a simple solution to this problem. Moreover, if the axions have a small mass, their interactions would be so weak as to be hard to detect, making them a candidate for dark matter.

Jihn-eui Kim, an endowed chair professor at Kyung Hee University, suggested a very light, ultra-long-life axion in 1979. In the early days, axions were seen as difficult to verify, lending them the moniker “invisible axions.” But in the 1980's, Prof. Pierre Sikivie of the Department of Physics at the University of Florida invented a device ― dubbed Sikivie’s cavity detector ― that can detect axions.

“I became familiar with Prof. Kim’s axion theory when I was studying for my PhD at the University of Rochester,” said Prof. Semertzidis. “This theory, which proposes that axions can explain dark matter, got me interested in axion research.” He stressed that “the IBS Center will launch experiments to find the axions that Prof. Kim explained with his theory. Because axions interact very weakly, they are hard to detect; detecting them will call for much research and perseverance.”

The dark matter theory revolves around the two pillars of axions and super-symmetric particles. The Large Hadron Collider (LHC) at CERN (the European Organization for Nuclear Research) is playing a pivotal role in the search for supersymmetric particles. The photo shows a data analysis image using LHC.

Great competition and collaboration efforts around the world on axionsAround the world, there is fierce competition to discover axions. In Europe, such efforts are led by CERN, which seeks to measure axions from the sun with a solar telescope. In the U.S., efforts include the University of Washington-led Axion Dark Matter Experiment (ADMX), which is a microwave cavity search for axions as part of the halo of our galaxy.

“Currently, a microwave cavity search is one of the most constructive ways to discover axions,” said Prof. Semertzidis. ADMX seeks to discover the dark-matter axion coming from the halo of the Milky Way. ADMX uses an apparatus consisting of an 8-tesla magnet and cryogenically cooled microwave cavity to detect the microwave photons that would result from the very weak conversion of axions. When the cavity’s resonant frequency is tuned to the mass of an axion, the axions are more likely to interact with the ADMX’s magnetic field. The interaction results in the deposit of the faintest amount of power into the microwave cavity. The relatively weak axion signal is amplified by a Superconducting Quantum Interference Device (SQUID).

“We do not know the accurate mass of an axion,” said Prof. Semertzidis. “An axion is very light and its mass window is as wide as 10-6eV to 10-3eV, making it hard to discover.That’s why they create a magnetic field in a low-temperature environment and use a superconductor to detect the axion signal.” He elaborated that “it would better to cooperate with the ADMX research team in the U.S., in order not to duplicate the research efforts and maximize the discovery potential.”

The center plans to develop an axion detector using a SQUID. “The plan can be dubbed the Korean Axion Experiment, or KAE,” he said. And if axions are indeed discovered, is a Nobel Prize within reach? To which he answered, “Though it’s hard to draw a comparison with the discovery of the Higgs particle, which won the Nobel Prize in Physics in 2013, if we succeed in discovering axions, it would be an achievement extraordinary enough to boost Korea’ s global standing in the science world.”

Why is there more matter than antimatter?
Presumably, when matter and antimatter were created after the Big Bang of our universe, they were created in equal amounts. Today, however, the universe is dominated by matter. But for some reason, matter became much more abundant than antimatter, leaving behind only matter. Much more than our physics laws, as we currently understand them, allow. The discrepancy is a factor of 100 million, i.e., there is more matter by a factor of 100 million than one calculates, assuming the current physics laws. This surviving matter has enabled galaxies, stars, the Earth, and human beings to be born.

But why was there so much more matter than antimatter? That problem is associated with the Proton EDM Search Project, which the IBS Center is leading. The question of whether fundamental particles like protons have EDM is important to solving the mysteries relating to the asymmetry of matter and antimatter. The electric dipole moment of fundamental particles can be characteristics of the “interactions that break CP symmetry.” Such a CP violation is known to be an essential element in the creation of asymmetry between matter and antimatter in the earliest universe and the survival of only matter. So finding the presence of EDM in fundamental particles will offer clues in the mystery of matter-antimatter asymmetry. The EDM, which Prof. Semertzidis is trying to measure, is a measure of the separation of positive and negative electric charges within a particle along the direction of its spin. The proton EDM has yet to be measured.

In 2011, Prof. Semertzidis submitted the proton EDM (pEDM) proposal to the U.S. Department of Energy on behalf of an international research team comprising 28 institutions and 89 researchers from around the world with Prof. Semertzidis at its helm. The project is going to be seriously considered by the Fermi National Accelerator Laboratory near Chicago in the US. If it is approved by the Department of Energy it would require of order $80 million to be constructed, with the main funding source coming from the US.

The international research team he leads aims to measure the proton EDM in a strikingly innovative manner: (i) whirl the protons in circles in a storage ring with a radial electric field and a certain momentum; (ii) minimize change in the angle of the spin vector relative to the momentum vector; and (iii) accurately measure the EDM by measuring the change of the vertical spin component of the proton spin as a function of storage time.

Experts expect the experiment to enable measurement of a very small moment. To be specific, they expect the value of proton EDM to be measured in a unit where the positive and negative electric charges, the unit electric charges of proton EDM, are separated by a length smaller than one trillionth of a trillionth of the thickness of a human hair. It is expected to be the most sensitive search for an EDM of a hadronic particle as is the proton. The existence of proton EDM and its value can be used to verify the standard model of particle physics as well as theories beyond the standard model. “By measuring the proton EDM, and comparing it with the neutron EDM and other particles one can tell whether supersymmetry is the source of it,” said Prof. Semertzidis. Experiments in the proton EDM project will take place in the U.S., and the IBS Center will research related theories and develop related experimental equipment and software.

“Researching with tireless passion, do not let mistakes or failure get in the way of research.Do not doubt,” the physicist stressed. “The center’s chief task is searching for the dark-matter axion. The existence of axions is necessary to explain the problems of the standard model. To perform dark matter experiments, it takes several years to build the testing facilities. If such experiments yield results within 3 to 5 years, I will consider it a success.” As he outlined his ambitions, he expressed the expectation that testing facilities would be built at KAIST as soon as possible.