Carnegie Mellon University

News Snippets from CMU Physics

Fall/Winter 2017–18

Physics Honors Student research

December 2017 – Freshman Honors Physics Class presents research

On December 7, the students in the Freshman Honors Physics Class, Matter & Interactions I (33-151), presented their semester work in the Physics Department’s 7th Annual Poster Session. As part of the course, students team up for an independent research project which involves a scientific computing, a theoretical, and—optionally—an experimental component. The students develop their projects from both their specific interests in science and what they learned in the course, then present a poster at the annual poster event. Notable projects included simulating the flight of the spacecraft in the movie The Martian (the students confirmed: yes, Hollywood got it right!); what would happen to the solar system if the speed of light were much slower?; and interesting studies of the three-body problem.
This course is one of the very few CMU courses where students are able to carry out a research project in their first semester at CMU—and the only course where they can actively hone their scientific computing skills. In the Physics Department, we are excited to provide this opportunity to students at such an early stage in their academic careers.

Gaia 1 cluster

December 2017 – Hidden in plain sight: Space mission Gaia helps to uncover previously undiscovered star clusters

Star clusters are gravitationally bound groups of stars that likely formed at the same time and evolved together. A large number of these clusters is known in the Milky Way. Clusters that form and live in the Milky Way disk are categorized as open clusters, while the groups of stars that inhabit the spheroidal halo of our Galaxy are known as globular clusters and are believed to have been accreted onto the Milky Way after being formed in other galaxies. Studies of both cluster types are important to better understand the structure and formation history of our Galaxy; therefore, astronomers have been on the lookout for these objects since the times of Messier and Herschel, 18th century astronomers who identified clusters by finding areas of higher stellar density on the sky which collectively formed Messier's famous catalog of nebulous objects.

In his recent work, Carnegie Mellon professor Sergey Koposov and collaborators used data from an astrometric mission called Gaia to find star clusters and small galaxies orbiting the Milky Way. By identifying small stellar over-densities on the sky, their technique was surprisingly close to that of Herschel and Messier. However, this search was automated and processed more than a billion sources in the Gaia catalog. To their big surprise, along with already known clusters they also discovered a cluster that is so massive (tens of thousands of stars) and nearby (≈ 15,000 light years) that it should have been visible to 18th century astronomers. The reason it wasn't is that it hides behind Sirius – the brightest star on the sky. The high fidelity of the Gaia data, however, allowed to discover this elusive object, now named Gaia 1. First studies of Gaia 1 by researchers in Europe categorized it as an open cluster in the Milky Way disk. On the other hand, analysis of chemical abundances in stars and the orbit of the cluster around the Galaxy may still question this preliminary assessment and suggest that this object was accreted onto the Milky Way from another galaxy.

Alberto Nicolis at CMU Physics

November 2017 – Alberto Nicolis (Columbia University):
The Power of (Broken) Symmetries: From Particle Physics to the Cosmos"

MCS Theoretical Sciences Lecture Series, Tuesday, November 21, 4:30 pm, Gates-Hillman Center 4307

Symmetries arguably provide the most powerful organizing principle of theoretical physics. For particle physics, symmetries are the basis of effective field theory, an extremely successful theoretical framework for describing the dynamics and interactions of particles. Perhaps counter-intuitively, some of the most interesting consequences of symmetries arise when these are "broken" by the state of the system in question ("spontaneous symmetry breaking", or SSB).
After reviewing basic aspects of effective field theory and SSB, Nicolis will show how the same set of ideas can be fruitfully applied outside of particle physics. He will focus on fluids and superfluids, and on their excitations: sound waves, vortices, phonons, and rotons. In his lecture, Nicolis will show how the effective field theory language naturally invites new questions about these systems, and provides efficient tools to answer them. Finally, he will discuss how the dynamics of cosmological perturbations can also be understood in terms of SSB and effective field theory.

APS DNP meeting poster

October 2017 – APS Division of Nuclear Physics Comes to Pittsburgh for Annual Meeting

About 800 of the country’s leading nuclear and particle physics researchers and students will come to Pittsburgh Oct. 25-28 for the American Physical Society’s (APS) Division of Nuclear Physics (DNP) Fall Meeting, held in the Pittsburgh Marriott City Center, downtown.

“We are delighted to host this annual meeting of experts and talented students of nuclear and particle physics in Pittsburgh,” said Reinhard Schumacher, professor of physics at Carnegie Mellon University and chair of the meeting’s local organizing committee.

Nobel Laureate David Gross will give the meeting’s first plenary talk. Gross won the Nobel Prize in Physics in 2004 for his contributions to the discovery of asymptotic freedom in the theory of the strong interaction. This discovery led to the theory of quantum chromodynamics, which is essential to the standard model of physics.

Grain boundary in nickel

October 2017 – Liquid bismuth weakens metals: Professor Michael Widom's research featured in Science magazine

Liquid bismuth penetrates into grain boundaries of metals such as nickel. The figure shows that bismuth atoms (large pink) arrange in a specific ordered pattern on each side of the nickel (small blue) grain boundary. Bonding charge densities (red, positive and green, negative) derived from quantum mechanics by Professor Widom and graduate student Qin Gao reveal strong bonding of bismuth to the nickel grains but lack of bonding across the boundary, causing the nickel to break at the grain boundary.

This work emerged from a collaboration with electron microscopists at Lehigh University and was published in Science, volume 358 (2017), pp. 97-101.

Michelle Ntampaka

October 2017 – Dr. Michelle Ntampaka moves on to Harvard after PhD work on galaxy clusters

Galaxy clusters are the most massive gravitationally bound objects in the Universe, comprising hundreds or thousands of galaxies embedded in a dark matter halo. Because cluster abundance is sensitive to the underlying cosmological model, they can be used to understand the parameters that describe the growth of large-scale structure in the Universe. But using clusters to test models and constrain parameters requires a way to accurately measure cluster mass—not a simple task when about 85% of the cluster is unseen dark matter.

For her thesis, Dr. Ntampaka developed a machine learning method that uses cluster dynamics to predict cluster mass, reducing errors by a factor of two over a more conventional approach. She also developed a forward modeling method that constrains cosmological parameters directly from measurements of cluster dynamics and applied this method to a catalog of observed clusters. Her work produced preliminary constraints on the matter density parameter Ωm and the amplitude of matter fluctuations σ8, two parameters that govern the evolution of structure in the Universe.

Dr. Ntampaka will be a postdoctoral fellow at the Harvard Data Science Initiative, where she will build on the research that she began at CMU.

Cloud chamber shows radiation traces

September 2017 – Undergrad Nuclear Physics

CMU physics professor Reinhard Schumacher highlights a dry-ice-free cloud chamber for visualizing ionizing radiation in an educational YouTube video. The work was performed with undergraduate Adrian Relic as a research project. The video shows how they constructed their chamber and how it responds to α, β and γ radiation. Along the way, the video presents the nature of these radiation types and the sources used to produce them. It also features a particularly nice example of an α particle undergoing Rutherford scattering in the chamber gas (picture; scale is in centimeters).

New graduate program requirements

September 2017 – New graduate program requirements in effect

New graduate program requirements are in place for incoming graduate students and current pre-candidate graduate students were able to choose to qualify for PhD candidacy under the old or new set of requirements. An UPDATED GRADUATE HANDBOOK provides details.

With this step, the department aims to provide students with more time for and greater flexibility in research and focuses their evaluation for candidacy more on research promise. A reduction in core courses will enable students to engage in more serious research projects during the first year of graduate studies and facilitates rotation between research groups. Other aspects of the program, such as academic performance, breadth courses, and teaching requirements, remain unchanged. These modifications bring our program requirements better in line with its desired goals and will enhance the learning experience of our graduate students. Read more

Spring/Summer 2017

Sukhdeep Singh

August 2017 – Dr. Sukhdeep Singh moves on to Berkeley after PhD work on gravitational lensing

Gravitational lensing is the deflection of light rays from distant objects by the matter—including dark matter—along their path to us. In the limit that these deflections cause only small changes to the distant galaxies, lensing is referred to as "weak". Weak lensing is one of the most promising tools to map the distribution of dark matter in the Universe, including the degree to which it has clumped together ("clustered") due to gravitational attraction. This in turn teaches us about the origin of the accelerated expansion rate of the Universe, which suppresses the clustering of matter driven by gravity and is typically attributed to the mysterious "dark energy". Dark matter and dark energy are the dominant components of our Universe, yet we do not know what we are, which is why many cosmologists are very excited about gravitational lensing studies.

Sukhdeep's thesis included observational studies aimed at using gravitational lensing and other types of observations with large sky studies to better understand the distribution of dark matter in the Universe and the nature of the accelerated expansion rate. In addition, he carried out several studies of physical effects that mimic the signatures of gravitational lensing, and hence need to be modeled in order to properly interpret observations. After getting his Ph.D., Sukhdeep moved to a postdoctoral research fellowship at the Berkeley Center for Cosmological Physics at the University of California, Berkeley.

COHERENT neutron experiment

August 2017 – Diana Parno's involvement in COHERENT

The COHERENT experiment at the Oak Ridge National Laboratory’s Spallation Neutron Source (SNS, shown left) has recently detected and measured the coherent elastic scattering of neutrinos off of nuclei – a process that is predicted by the Standard Model of physics, but has never been observed before. The new findings uncover a fingerprint of neutrino-nucleus reactions that will provide better understanding of neutrinos, the dynamics of neutron star formation and supernovae explosions. It could also provide parameter limits for future experimental dark matter searches.

Coherent in ScienceMore than 80 researchers from 19 institutions contributed to this study. Diana Parno, an assistant research professor in the Department of Physics, is a member of the COHERENT collaboration and contributed simulations that calculate the number of neutrinos that pass through the SNS detectors. She plans to continue working on the project while at Carnegie Mellon. The research was featured on the Sept.-15 cover of Science. Read more on this research at the AAAS website.

Eclipse News

August 2017 – The Solar Eclipse at Carnegie Mellon's Pittsburgh campus

On August 21, 2017, Sun and the moon aligned, causing a great lack of UV ray exposure in some parts of North America. In celebration of this joyous occasion, the Carnegie Mellon Astronomy Club held a viewing event on campus, where solar eclipse glasses were given out like candy. In addition, telescopes with the proper eye damage prevention equipment were set up  to get a closer look at the movement of these celestial bodies. This gathering of astronomical enormity took place from 12:00 noon till 4:30 PM. Over 4,000 people were in attendance. At about 1:11 PM, eclipsing started and around 2:30 PM, the peak of the eclipse was observed in Pittsburgh, PA. While totality was not observable in the immediate area, a partial eclipse of about 80% cover baffled the observers. In the dim lighting of the partially visible hot ball of plasma, the student body and the relevant community members of Carnegie Mellon all gathered together and experienced the wonders and marvels that the laws of physics have to offer. It was truly a memorable event, not only for new students at orientation, but for all people involved! For those who missed it: See you all on April 8, 2024!

(Eyewitness report by Joanne Hsueh)

Xin Wang

May 2017 – Xin Wang earns Ph.D. with thesis on “Elasticity of lipid membrane leaflets"

The biological functions of lipid membranes often depend on fascinating elastic properties which in turn arise from molecular structure: membranes assemble spontaneously from lipid molecules, forming a 5 nm thin fluid film that consists of two individual molecular sheets. This film is hard to stretch but bends easily to adjust its local curvature. And upon imposing curvature, each individual lipid leaflet bends around an internal surface called the “pivotal plane”.

Working with Prof. Deserno, Xin Wang developed precise methods for pinpointing the pivotal plane and in the process discovered a novel method for measuring the so-called "lipid tilt modulus"—a parameter that determines how easily the orientation of individual lipids an deviate from the direction perpendicular to the membrane’s surface. This modulus matters whenever local membrane phenomena are studied, such as membrane pores or inserted proteins. Xin’s work therefore contributes to the ongoing quest to better understand the molecular origin of the fundamental mechanical structures that protect our cells from the environment.

Stephanie O'Neil

May 2017 – Stephanie O’Neil receives the Physics Department’s RE Cutkosky Award and the JP Fugassi and LE Monteverde Award from MCS

With a double major in physics and creative writing, Stephanie O’Neil is now leaving CMU where she has been a dedicated student and researcher, as well as an active member of the campus community. With the Dr. J Paul Fugassi and Linda E Monteverde Award, MCS recognizes the graduating female senior with the greatest academic achievement and professional promise. The Richard E Cutkosky Award is presented each year to an outstanding graduating senior in the physics department.

Beyond her flawless academic record, Stephanie was a whirlwind of activities as a member of the Kiltie Band, the Flute Choir, the All University Orchestra, as well as the Physics Steering Committee, the secretary of the Astronomy Club and a tutor in the Physics Upper Class Course Center. Last year, she was the undergraduate representative for the MCS college council. In undergraduate research, she has been studying dwarf galaxies with Assistant Professor of Physics Matthew Walker. In this work, she focused on inferring dark matter contents of dwarf spheroidal galaxies that orbit our milky way. Stephanie was also greatly appraised by her faculty mentors as REU (Research Experience for Undergrad program of the NSF) scholar at William & Mary and at MIT in the summers of 2015 and 2016. After graduation, she will join MIT’s Kavli Institute for Astrophysics and Space Research to pursue a Ph.D. in astrophysics.

Freeman PhD thesis defense

May 2017 – Krista Freeman earns Ph.D. with thesis on “Viral DNA Retention and Ejection controlled by Capsid Stability

Viruses are submicroscopic pathogens that infect every branch, twig and sprig of the tree of life. They consist of little more than a genome stored inside a protein shell, called the capsid, and exploit the cellular machinery of the organisms they infect for their own replication. Many bacterial viruses, and also some human ones, store their genome under enormous pressure in the capsid—more than 10 times that of an inflated car tire. Because such genomes consist of DNA that is several hundred times longer than the size of the capsid, the highly charged DNA strand must be very tightly squeezed to fit in. Upon infection, the capsid opens up and the DNA gets ejected into the host cell much like a jack-in-the-box.

In her thesis, Krista investigated the time course of this dynamic process and the physical principles underlying the construction of capsids that can withstand such enormous pressures. Besides gaining fascinating insights into these genome-loaded nano-machines, such studies also touch upon basic medical concerns: understanding the physical mechanisms that viruses rely on may open new avenues to combat them. And since this invokes general physical principles, the virus may not easily be able to respond with adaptive mutations.

Satpathy Hugh Grant teaching award

May 2017 – Sidd Satpathy receives Hugh Young Teaching Award

As a teaching assistant (TA), Siddharth Satpathy, a Ph.D. candidate in the Department of Physics, is described as conscientious, compassionate, dedicated, nurturing, and helpful – in short, “one of the best TA’s ever” by students and faculty alike. During the last three years, Satpathy – better known as Sidd – has taught five different sections of the introductory course Physics for Science Students and Calculus in Three Dimensions, the latter for the Department of Mathematical Sciences. Sidd also served for two years as an instructor in Carnegie Mellon University’s Summer Academy for Math and Science for high school students.

In recognition of his enthusiasm for teaching and his unyielding dedication to going above and beyond for his mentee students, Siddharth Satpathy has been awarded the 2017 Hugh Young Graduate Student Teaching Award. Congratulations, Sidd!

Belle II detector roll-in

April 2017 – Belle II Project at KEK in Tsukuba/Japan

The Belle experiments study collisions of electrons and positrons at a total energy of ~10 GeV. This energy is chosen to produce B mesons: particles composed of a heavy "bottom" quark and a light anti-quark. These are of special interest since they violate "CP symmetry", that is, they differ in the behavior of matter and anti-matter. This asymmetry poses one of the deepest mysteries of particle physics, and solving it may shed light on the unexplained observation that the Universe is dominantly made of matter, rather than anti-matter. Belle II is an improved version of the very successful first Belle experiment and aims to collect a larger data samples with an improved detector.

CMU is involved in a variety of activities at Belle II: Prof. Roy Briere is co-chair of the charm physics analysis group, exploring the physics reach and planning analyses on these topics. Postdoc Jake Bennett is data production coordinator, overseeing production and processing of simulated Monte-Carlo samples and preparing for real data-taking in the near future. Together, Jake and Roy are also responsible for calibrating dE/dx measurements from the CDC wire chamber, one of several methods employed to distinguish the identities of the various particles measured in the Belle II detector.