In May, 2017 UConn alumnus Alex Barnes was awarded a postdoctoral fellowship in Nuclear Physics at Carnegie Mellon University, working in the group of Prof. Curtis Meyer. Alex begins this appointment immediately after completing his PhD at the University of Connecticut in April 2017, under the guidance of Prof. Richard Jones.
In his new position, Alex joins a team of 5 other junior scientists working at Jefferson Lab on the analysis of data from the GlueX experiment. He also assumes shared responsibility for operation and calibration of the Central Drift Chamber, and other detector subsystems. In his PhD thesis, Alex showed that a clean sample of exclusive phi(1020) mesons could be reconstructed using the GlueX detector. With the addition of higher statistics data in 2018 and following, he plans to push his investigation into the higher mass region, in search of new exotic particles that are predicted to exist based on the Standard Model of strong interactions.
The U.S. Centers for Disease Control lists radon as a primary cause of lung cancer, second only to smoking. The Environmental Protection Agency estimates that 20,000 deaths each year from lung cancer in the U.S. are the result of exposure to radon in the living environment. It is believed that as many as 1 in 15 homes in the continental United States have radon levels that require some form of mitigation. In spite of this, very few homes are equipped with continuous radon monitoring devices and most radiation monitoring facilities only provide feedback on time scales of weeks or even months.
The technology used in standard residential radon monitoring has not changed significantly over the past 50 years. On the other hand, development of fast detectors for particle physics experiments at large international laboratories such as the Large Hadron Collider over the past two decades has opened up new technologies for radiation detection that may result in a significant improvement in the efficiency and response time for radon detection.
UConn undergraduate Mira Varma, pictured above, is holding a part of what she hopes to assemble into a hand-held radon detector capable of detecting changes in radon concentration on the time scale of an hour, close to the time scale of the natural variation in a residential environment, rather than days or weeks. Mira is carrying out this development under the direction of UConn Physics Prof. Richard Jones.
As a research assistant in the physics department at UCONN, I assisted in the alignment, maintenance, and principles of operation of the various apparatuses and measurement techniques used within cold atomic, molecular, and optical (AMO) experimental physics research. This included optical components, laser alignment, laser locking, saturation absorption spectroscopy, and electrodynamic ion trapping. Some specific experiments ran included measuring the fraction of a trapped, sodium atom-cloud (fe) pumped into an optically excited state using laser beams as well as measuring the temperature of a trapped, neutral atom-cloud via spatio-temporal fluorescence imaging.
Attached is our record for the Mw 6.9 earthquake associated with eruptions of the Kilauea volcano on the big island of Hawaii. The large waves arriving after 2300 GMT are surface waves (elastic energy that exponentially decays with depth away from the surface) traveling from the earthquake to us. The beating pattern is characteristic of surface waves interfering from slightly different multi paths as they are refracted by the sharp transition in elastic structure between the ocean and continent.
The amplitude of strain associated with the waves is on the order of 10**-12 (peak particle velocity divided by propagation velocity). For comparison, the strain associated with gravity waves recorded by LIGO is on the order of 10**-21.
Scientists have been rigorously commissioning the experimental equipment to prepare for a new era of nuclear physics experiments. This equipment is at the newly upgraded Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab in Newport News, Virginia. These activities have already led to the first scientific result. This research demonstrates the feasibility of detecting a potential new form of matter.
The Impact
The result demonstrates the feasibility of detecting hybrid mesons. These mesons are particles that are built of the same stuff as ordinary protons and neutrons: quarks bound together by the “glue” of the strong force. But unlike ordinary mesons, the glue in hybrid mesons behaves differently. The research provides a window into how mesons and other particles that are smaller than atoms are built by the strong force. The study also offers insights into “quark confinement” — why no quark has ever been found alone.
Summary
The first experimental result has been published from the newly upgraded Continuous Electron Beam Accelerator Facility (CEBAF). The 12-GeV CEBAF Upgrade is a $338 million, multi-year project to triple CEBAF’s original operational energy for investigating the quark structure of the atom’s nucleus. The upgrade is scheduled for completion in the fall of 2017. This first result demonstrates the feasibility of detecting a potential new form of matter. It comes from the Gluonic Excitations Experiment, which is staged in the new Experimental Hall D that was built as part of the upgrade. GlueX collaborators are working to produce new particles, called hybrid mesons, which are particles in which both the quarks and the strong-force gluons have a role in the structure. Producing and studying the spectrum of these particles will provide nuclear physicists a window to “quark confinement” — why no quark has ever been found alone. Data were collected over a two-week period following equipment commissioning in the spring of 2016. The experiment produced two ordinary mesons called the neutral pion and the eta, and the production mechanisms of these two particles were carefully studied. The data provided powerful new information on meson production mechanisms, ruling out several, and the data also showed that the GlueX experiment can produce timely results.
Daniel Hoying on April 13, 2017. (Peter Morenus/UConn Photo)
As a theoretical physicist studying the fundamental elements of matter, UConn graduate student Daniel Hoying creates calculations so large and complex they require supercomputers to perform them.
So Hoying is obviously excited that he will soon have regular access to one of the world’s most powerful supercomputers at the U.S. Department of Energy’s Brookhaven National Laboratory in Long Island, N.Y. The system is outfitted with Intel’s powerful new Knights Landing Xeon Phi chip. The chip’s 8 billion transistors and other cutting-edge technologies can carry the heavy processing loads that scientists like Hoying need to do their work.
“This represents an enormous opportunity for me,” says Hoying, who is headed to Brookhaven as a recipient of a U.S. Department of Energy (DOE) Office of Science Graduate Student Research (SCGSR) Award. “The level of precision offered by these processors allows us to make calculations that we would never have conceived of a few years ago. The on-site expertise can’t be discounted either. There are a lot of people there who know a lot of things I don’t know. It’s very exciting to have an opportunity to learn from them.”
Starting in July, Hoying will spend 12 consecutive months conducting part of his dissertation research at Brookhaven. Only 53 graduate students around the country received SCGSR awards this year. Other winners included students from Yale, Princeton, MIT, Duke, Cornell, CalTech, and Michigan State.
“The SCGSR program prepares graduate students for science, technology, engineering, or mathematics (STEM) careers critically important to the DOE Office of Science’s mission,” says Steve Binkley, acting director of DOE’s Office of Science. “We are proud of the accomplishments these outstanding students already have made, and look forward to following their achievements in years to come.”
Hoying’s research focuses on the Standard Model of particle physics. The Standard Model explains how the basic building blocks of matter interact and are governed by fundamental forces such as gravity and electromagnetism. It is the most fundamental theory of nature.
Hoying specifically studies the strong force in the Standard Model, otherwise known as Quantum Chromodynamics or QCD. The strong force binds fundamental particles of matter together to form larger particles. For example, the strong force helps quarks and gluons combine to make protons and neutrons, which in turn combine to make atoms, which in turn combine to make molecules and so on.
He is currently looking at the decaying cycle of particles known as kaons, which decay into two other particles called pions. These extremely small particles, first discovered in cosmic rays, only exist for fractions of a second and have been identified in experiments run in large particle accelerators. They are an essential part of the Standard Model of particle physics.
Previous calculations have shown that theory and experiments involving the decay of kaons have differed by small amounts. Hoying’s research aims to reduce those uncertainties, to help scientists learn more about what these particles are and how they behave.
Besides increasing understanding and advancing basic science, ultimately the information gathered through Hoying’s research could have a variety of applications in advanced computing and various energy fields.
“Dan is a talented young physicist who works hard,” says Professor Thomas Blum, Hoying’s advisor in the Department of Physics. “I’m fortunate to have him working for me.”
This article by Colin Poitras (UConn Communications) appeared in UConn Today on April 17, 2016.
For the first time, scientists have directly detected gravitational waves — ripples in space-time — in addition to light from the spectacular collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light.
The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector; and some 70 ground- and space-based observatories.
Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas. As these neutron stars spiraled together, they emitted gravitational waves that were detectable for about 100 seconds; when they collided, a flash of light in the form of gamma rays was emitted and seen on Earth about two seconds after the gravitational waves. In the days and weeks following the smashup, other forms of light, or electromagnetic radiation — including X-ray, ultraviolet, optical, infrared, and radio waves — were detected.
GW170817: A Global Astronomy Event
The observations have given astronomers an unprecedented opportunity to probe a collision of two neutron stars. For example, observations made by the U.S. Gemini Observatory, the European Very Large Telescope, and the Hubble Space Telescope reveal signatures of recently synthesized material, including gold and platinum, solving a decades-long mystery of where about half of all elements heavier than iron are produced.
The LIGO-Virgo results are published today in the journal Physical Review Letters; additional papers from the LIGO and Virgo collaborations and the astronomical community have been either submitted or accepted for publication in various journals.
“It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the universe,” says France A. Córdova, director of the National Science Foundation (NSF), which funds LIGO. “This discovery realizes a long-standing goal many of us have had, that is, to simultaneously observe rare cosmic events using both traditional as well as gravitational-wave observatories. Only through NSF’s four-decade investment in gravitational-wave observatories, coupled with telescopes that observe from radio to gamma-ray wavelengths, are we able to expand our opportunities to detect new cosmic phenomena and piece together a fresh narrative of the physics of stars in their death throes.”
Written by Jennifer Chu, MIT News Office, full text of original article available here on the LIGO web site.
Instead of directly searching for new particles as the LHC experiments are doing in Geneva, the muon g-2 experiment at Fermilab measures a well-known physical property of the muon to ever greater precision, looking for deviations from the value it should have based on the Standard Model of particle physics, assuming that no new forces or particles are in play. UConn theorists Tom Blum and Luchang Jin are contributing to this effort by reducing the theoretical uncertainty on the Standard Model prediction to match the anticipated experimental precision.
The Muon g-2 experiment has begun its search for phantom particles with its world-famous and well-traveled electromagnet.
June 1, 2017
The Muon g-2 ring with instrumentation, awaiting muons at Fermi National Accelerator Laboratory. Credit: Fermilab
What do you get when you revive a beautiful 20-year-old physics machine, carefully transport it 3,200 miles over land and sea to its new home, and then use it to probe strange happenings in a magnetic field? Hopefully you get new insights into the elementary particles that make up everything. The Muon g-2 experiment, located at the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory, has begun its quest for those insights. On May 31, the 50-foot-wide superconducting electromagnet at the center of the experiment saw its first beam of muon particles from Fermilab’s accelerators, kicking off a three-year effort to measure just what happens to those particles when placed in a stunningly precise magnetic field. The answer could rewrite scientists’ picture of the universe and how it works.
“The Muon g-2 experiment’s first beam truly signals the start of an important new research program at Fermilab, one that uses muon particles to look for rare and fascinating anomalies in nature,” said Fermilab Director Nigel Lockyer. “After years of preparation, I’m excited to see this experiment begin its search in earnest.”
Getting to this point was a long road for Muon g-2, both figuratively and literally. The first generation of this experiment took place at the U.S. DOE’s Brookhaven National Laboratory in New York State in the late 1990s and early 2000s. The goal of the experiment was to precisely measure one property of the muon – the particles’ precession, or wobble, in a magnetic field. The final results were surprising, hinting at the presence of previously unknown phantom particles or forces affecting the muon’s properties.
Video depicting the first leg of the g-2 electromagnet’s 3,200-mile journey from Brookhaven to Fermilab
The new experiment at Fermilab will make use of the laboratory’s intense beam of muons to definitively answer the questions the Brookhaven experiment raised. And since it would have cost 10 times more to build a completely new machine at Brookhaven rather than move the magnet to Fermilab, the Muon g-2 team transported that large, fragile superconducting magnet in one piece from Long Island to the suburbs of Chicago in the summer of 2013.
The magnet took a barge south around Florida, up the Tennessee-Tombigbee waterway and the Illinois River, and was then driven on a specially designed truck over three nights to Fermilab. And thanks to a GPS-powered map online, it collected thousands of fans over its journey, making it one of the most well-known electromagnets in the world.
“Getting the magnet here was only half the battle,” said Chris Polly, project manager of the Muon g-2 experiment. “Since it arrived, the team here at Fermilab has been working around the clock installing detectors, building a control room and, for the past year, adjusting the uniformity of the magnetic field, which must be precisely known to an unprecedented level to obtain any new physics. It’s been a lot of work, but we’re ready now to really get started.”
That work has included the creation of a new beamline to deliver a pure beam of muons to the ring, the installation of a host of instrumentation to measure both the magnetic field and the muons as they circulate within it, and a year-long process of “shimming” the magnet, inserting tiny pieces of metal by hand to shape the magnetic field. The field created by the magnet is now three times more uniform than the one it created at Brookhaven.
The Muon g-2 electromagnet arriving at Fermilab in July 2013 after a 3,200-mile journey from Brookhaven National Laboratory. Credit: Fermilab
Over the next few weeks the Muon g-2 team will test the equipment installed around the magnet, which will be storing and measuring muons for the first time in 16 years. Later this year, they will start taking science-quality data, and if their results confirm the anomaly first seen at Brookhaven, it will mean that the elegant picture of the universe that scientists have been working on for decades is incomplete, and that new particles or forces may be out there, waiting to be discovered.
“It’s an exciting time for the whole team, and for physics,” said David Hertzog of the University of Washington, co-spokesperson of the Muon g-2 collaboration. “The magnet has been working, and working fantastically well. It won’t be long until we have our first results, and a better view through the window that the Brookhaven experiment opened for us.”
The Muon g-2 collaboration includes more than 150 scientists and engineers from more than 30 institutions in nine countries.
The Muon g-2 experiment is supported by DOE’s Office of Science and the National Science Foundation.
Fermilab Media Contact
Andre Salles, Fermilab Office of Communication, 630-840-6733, media@fnal.gov
Science contacts
David Hertzog, Muon g-2 collaboration co-spokesperson, University of Washington, 206-543-0839, hertzog@uw.edu
Chris Polly, Muon g-2 project manager, Fermilab, 630-840-2552, polly@fnal.gov
B. Lee Roberts, Muon g-2 collaboration co-spokesperson, Boston University, 791-799-7483, roberts@bu.edu
Fermilab is America’s premier national laboratory for particle physics research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC. Visit Fermilab’s websiteand follow us on Twitter@Fermilab.
Brookhaven National Laboratory and Fermilab are supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science of the U.S. Department of Energy’s website.
Leon Cooper, 1972 Nobel Laureat delivered the Distinguished Katzenstein lecture at UConn in October, 2016
The Katzenstein Distinguished Lectures series continued in Fall 2016 for its 19th year, with an October 28, 2016 lecture by Professor Leon N. Cooper of Brown University, entitled “On the Interpretation of the Quantum Theory: Can Free Will And Locality Exist Together In The Quantum Theory?” Professor Cooper shared the 1972 Nobel Prize in Physics with Professors J. Bardeen and J. R. Schrieffer. The Nobel Prize was awarded for the first microscopic theory of superconductivity, now known as the BCS Theory. Superconductivity as evidenced by the disappearance of electrical resistivity was first observed in Mercury by Kamerlingh Onnes in 1911. Immediately, many theorists including Albert Einstein, set out to explain this newly observed phenomena. However it was not until 1933 that the essential property of magnetic flux exclusion was observed by Meissner and Ochsenfeld. No successful microscopic theory was developed until the 1957 Physical Review Paper that developed the BCS theory. A crucial element for the theory was published in a short letter to the Physical Review in 1956 by Leon Cooper, entitled ‘Bound Electron Pairs, in a degenerate Fermi Gas’. These pairs are now commonly referred to as ‘Cooper Pairs’.
The 2016 lecture took place in Physics Building Lecture Room P-36, and an excellent attendance included physics undergraduates, graduate students, faculty from Physics and other departments, and a number of UConn Physics alumni. Prior to the lecture, Professor Cooper met informally with Physics students in the Physics Library, and then met people at a reception that preceded the lecture. Following the lecture, Professor Cooper joined with Henry Katzenstein’s son David, a Professor at Stanford Medical School, along with faculty, staff, alumni and guests for a gala dinner at the University of Connecticut’s Foundation Building. The Katzenstein Lectures are made possible by an endowment established by the late Dr. Henry S. Katzenstein and his wife Dr. Constance A. Katzenstein. Cornell Professor David Lee (1996 Nobel Laureate in Physics and 1956 M. S. alumnus of UConn) gave the first lecture of the current series of annual lectures by Nobel Laureates, in 1997. Henry Katzenstein received the very first Ph.D. in physics from our Department in 1954 after only three years as a graduate student here.
UConn Physics lecture hall PB-36 filled for 2016 Katzenstein Distinguished Lecture
This story was published in the University of Connecticut 2017 Annual Newsletter.
August 9, 2017 – Kim Krieger – UConn Communications
(Yesenia Carrero/UConn Image)
Whoever said rules were made to be broken wasn’t a physicist. When something doesn’t act the way you think it should, either the rules are wrong, or there’s new physics to be discovered. Which is exactly what UConn’s Connor Occhialini ’18 (CLAS), an honors student majoring in physics and math, found when he began researching scandium fluoride.
Scandium fluoride is a transparent crystal with a cubic shape, a byproduct of mining. It’s not used commercially and it wouldn’t be particularly interesting to anyone except for one odd thing: it shrinks as it warms.
Most materials swell as they heat up. Really simple materials like hydrogen gas swell because the heat makes their atoms zoom around faster, bumping into each other more, so the same number of hydrogen atoms need more space. More complicated materials also swell, which is why your wooden front door tends to stick in the summertime. But solids like wood can’t swell as much as a gas because their atoms are tightly linked together into long, interlocked molecules, so they just jiggle around, swelling the door a little bit.
Scandium fluoride must be doing something else, reasoned Occhialini. His advisor for his honors physics project, Jason Hancock, had been working with scandium fluoride, and asked Occhialini to study a model of the crystal’s dynamics. Scandium fluoride has a pretty simple structure: it’s a solid crystal, with each scandium atom surrounded by six fluorines to make stacks of octahedra (eight-sided diamonds). The researchers hoped the simple structure might be easy to understand. Understanding scandium fluoride’s strange ‘negative thermal expansion’, as physicists call the heat-related shrinkage, might yield more general insight into other, more complex materials that do the same thing.
Occhialini’s first step was to simplify the problem. So instead of a three-dimensional crystal, he decided to think about it as a two-dimensional sheet that looks like this:
Figure 1. Help, I’m shrinking! The black diamonds represent scandium fluoride molecules. As they warm, they rotate, and the crystal contracts. Notice how the molecules near the center of mass (central dot) move less than the molecules closer to the crystal’s edge. (Yesenia Carrero/UConn Image)
Each black diamond represents a molecule of scandium fluoride. The scandium atoms (blue dots) are at the center of each diamond, and a fluorine atom is at each corner.
Most of the time, bonds between atoms are flexible. So in a normal crystalline solid – calcium fluoride, for example – the fluorines and calcium atoms would all be able to wiggle around independently when the material warmed up. As they wiggled, they’d take up a little more space, and the solid would swell. Normal solid behavior.
But Occhialini wondered if maybe that wasn’t what was happening in scandium fluoride. Maybe in this model, he should assume the bonds connecting each fluorine to its scandium were stiff? So stiff the fluorine-scandium bonds don’t move at all, so the diamonds are like solid blocks. The only places the structure would be able to flex when it warmed up would be at the fluorine atoms, which would act like tiny little joints. As the crystal heated up, the little scandium fluoride blocks would tilt around the fluorines at the corners. That’s what you see happening in the picture. You’ll notice that when the diamonds tilt, the whole structure gets smaller. It actually tightens up. The blue outline shows the structure at its coldest, perfectly ordered state, with no molecular motion. When the diamonds tilt, they take up a smaller total volume than the blue outline delineates. This is negative thermal expansion.
Figure 2. How much a scandium fluoride crystal shrinks depends on how far the molecules rotate. Here, the blue diamond in the upper right corner is rotating clockwise, sweeping out an angle theta. The dotted lines show its position when the angle was zero. (Yesenia Carrero/UConn Image)
Occhialini figured out that you can describe this shrinkage mathematically, using just the angle of the molecules’ tilt. He called the angle Θ (theta). When the scandium fluoride blocks tilt by an angle Θ, the distance between the center of each block shortens by a factor of cosine Θ, and the crystal’s total volume shrinks.
To calculate that shrinkage (or, in a normal material, expansion) in detail, Occhialini added a third term to the classic equation that describes the energy of a vibrating crystal. The first two terms in the standard equation describe the potential energy a crystal has from the bending at each molecular junction, plus the kinetic energy of rotation of each molecule. Occhialini’s equation also describes the translational kinetic energy of the molecules–not just from rotating around, but also moving toward and away from their original positions as they rotate. The further they are from the center of mass of the crystal, the more they move. Look back at Figure 1 and notice the dot in the middle; that’s the center of mass. The diamonds in the middle barely move in relation to it, while the diamonds at the edges move a lot. Now imagine how much of a difference there would be if the crystal had millions of molecules instead of just 25. And now you understand how important that third term could be to the energy of the crystal.
Now, molecules being molecules, they don’t just shrink and stay there. They’re moving constantly, and the warmer they get, the more they move. Part of Occhialini’s insight is that, on average, the molecular structure gets bendier the warmer it gets. So the molecules tilt more and spend more time at bigger values of Θ, closer to 45 degrees. After Occhialini thought it over for a while together with Hancock and physics Ph.D. students Sahan Handunkanda and Erin Curry, they realized there was a geometric shape that had the same mathematical description. It’s Archimedes’ spiral pendulum, and it looks like this:
Figure 3. Twist and shrink. The equation describing the rotation of the scandium fluoride molecules is the same as the equation describing the movement of a ball on an Archimedes’ spiral pendulum. Notice how it spends more time at larger angles. (Yesenia Carrero/UConn Image)
Each turning of the spiral is exactly the same distance from the last. That spacing – the distance between turns – is controlled by Θ. Imagine a line that stretches from the center of the sphere to a point on the spiral. The angle between that line and the pole of the sphere is Θ. You see the little ball traveling along the spiral? That’s the end of the imaginary line. As Θ gets bigger, the ball moves towards the equator.Imagine that the ball represents the instantaneous state of the scandium fluoride crystal – the physicists calculated the statistical average of what every molecule in the crystal is doing. You’ll notice the ball spends more time near the equator of the spiral sphere, that is, it tends to hang out where Θ is large. If the temperature of the crystal drops and the molecules wiggle less, Θ gets smaller, the more time the ball spends near the pole of the sphere and the less the crystal shrinks.
So not only can a really weird phenomenon of a crystal that shrinks as it warms be explained by just assuming the molecules are rigid, but it can be illustrated with a classical geometric shape!
Occhialini was just a freshman when Hancock introduced him to the scandium fluoride puzzle. He had to learn the math as he went, but after about two semesters of working on it he’d figured out the equation that described what was going on. Now in his senior year, he says his research experiences in Hancock’s lab have been integral to his experience as an undergraduate.
The equation works beautifully and explains certain aspects of Hancock’s experimental x-ray measurements as well.
“I learned a lot more doing research than any course could have given me,” Occhialini says.
And now you, dear reader, have learned a little bit, too.
Occhialini’s research has been funded through his advisor’s NSF grant no. DMR-1506825 and a SURF fellowship from the Office of Undergraduate Research. He was also named a Treibick Scholar.
This article was first published by UConn Today article here
The U.S. Centers for Disease Control lists 
As a research assistant in the physics department at UCONN, I assisted in the alignment, maintenance, and principles of operation of the various apparatuses and measurement techniques used within cold atomic, molecular, and optical (AMO) experimental physics research. This included optical components, laser alignment, laser locking, saturation absorption spectroscopy, and electrodynamic ion trapping. Some specific experiments ran included measuring the fraction of a trapped, sodium atom-cloud (fe) pumped into an optically excited state using laser beams as well as measuring the temperature of a trapped, neutral atom-cloud via spatio-temporal fluorescence imaging.
Attached is our record for the Mw 6.9 earthquake associated with eruptions of the Kilauea volcano on the big island of Hawaii. The large waves arriving after 2300 GMT are surface waves (elastic energy that exponentially decays with depth away from the surface) traveling from the earthquake to us. The beating pattern is characteristic of surface waves interfering from slightly different multi paths as they are refracted by the sharp transition in elastic structure between the ocean and continent.
