X-ray scientist Tais Gorkhover and particle physicist Michael Kagan have been named 2016 Panofsky Fellows at the Department of Energy’s SLAC National Accelerator Laboratory. The fellowship honors Wolfgang K. H. Panofsky, the lab’s founding director, and is awarded to exceptional and promising young scientists who would most benefit from the unique opportunity to conduct their research at the lab.
Panofsky fellows are appointed for five years, receive generous research support that includes funding for a postdoctoral researcher, and are eligible for continuing appointment at SLAC.
“I’m extremely honored that I was selected for this prestigious award,” says Gorkhover, a postdoc at the Technical University of Berlin in Germany. “The list of past fellows consists of extraordinary people who all went on to have very successful careers in science.” She will be working in the Stanford PULSE Institute, making use of the lab’s Linac Coherent Light Source to develop new methods for recording X-ray images and movies of tiny particles.
SLAC postdoc Kagan says, “It’s a very important step beyond being a postdoc. Panofsky fellows play a large role in shaping the research direction at the lab, so this is a very exciting opportunity.” His broad research goal is to understand the properties of the Higgs boson.
A better way to image particles with X-ray lasers
Many processes ranging from combustion and catalysis to large-scale climate dynamics involve free nanosized particles that are difficult to study with conventional imaging methods. One of the great prospects of X-ray laser science is the ability to take high-resolution snapshots of such nanoparticles.
“With LCLS we can study these particles, which can be very fragile and short-lived, in their native environments,” Gorkhover says. “This is a big opportunity but also a great challenge, because the interpretation of the images is not straightforward.”
In these experiments, researchers record the intensity of X-rays that scatter off a sample’s atomic structure. But they need additional information about the relationships between X-rays coming from different parts of the sample, known as the X-ray phases, to reconstruct the sample’s shape.
“Retrieving phases from diffraction images recorded with X-ray lasers is a time-consuming procedure that involves many steps and often leads to ambiguous solutions for the image,” Gorkhover says. “I’m developing a method that could provide a unique solution within seconds.”
Using this technique, called X-ray Fourier holography, researchers can directly record the phases by superimposing the scattered light from the sample with scattered light from a reference object. Until now, samples had to be attached to a mask in order to record a holographic image. This type of preparation can severely damage particles.
“We’ve already shown in proof-of-principle experiments at LCLS that we can use clusters of xenon atoms to create holograms of free particles,” Gorkhover says. “The clusters serve as reference samples that are injected into intense X-ray laser pulses along samples. As a Panofsky fellow, I’ll further develop and improve this approach and apply it to a number of samples, including biological ones. I’m also planning on finding new holography applications. One big goal is to advance direct imaging of ultrafast processes as demonstrated in a study recently published in Nature Photonics.”
Gorkhover, who completed her master’s and PhD degrees at the Technical University of Berlin in Germany and came to SLAC in 2014 on a Peter Paul Ewald fellowship from the Volkswagen Foundation, also intends to push the limits of another imaging technique, known as super-resolution imaging, which uses optical lasers.
It was long believed that optical microscopes cannot reveal structures smaller than half of the wavelength of the light they employ. Yet, by labeling samples with fluorescent markers, researchers have surpassed this limitation – an achievement that was recognized with the 2014 Nobel Prize in Chemistry.
“I want to look into the possibility of doing this type of imaging based on holography, without the need for fluorescent markers,” Gorkhover says. “The outcome of these efforts is totally unclear, but that’s one of the great things about the Panofsky fellowship: It also allows me to explore a somewhat risky project.”
Searching for new physics beyond the Higgs boson
Kagan’s research focuses on the Higgs boson – a fundamental particle discovered in 2012 by the ATLAS and CMS experiments at CERN’s Large Hadron Collider (LHC). It was the last missing piece of the Standard Model of nature’s elementary matter particles and force carriers.
“We still know very little about the Higgs boson, so there is a lot to be discovered,” says Kagan, who is a member of SLAC’s ATLAS team. “It’s a quite unique particle – the only known fundamental particle with zero spin – and there might be completely new physics linked to it.” The spin of a particle is a quantum mechanical property that doesn’t have a classical analogue but is often compared to the rotation of a ball about its own axis.
At the LHC, many searches for new physics focus on hypothetical particles that are heavier than the ones known today. Produced in the collider’s proton-proton collisions, the heavy particles would decay into Higgs bosons and other fragments. The Higgs particle, in turn, would decay into even more fragments. By analyzing the fragments, particle physicists hope to discover new phenomena.
Kagan has already been searching for signs of new heavy force carriers in the ATLAS data. In the future, he will also look for traces left behind by new particles that behave similarly to fundamental quarks but are much heavier.
Because collisions at the LHC are extremely energetic, the fragments emerge from the collision point bundled in very narrow particle jets. Jets can be formed by the fragments of the Higgs particle decay but can also be formed by other particles. The identification of what particle created these jets poses a big challenge, and part of Kagan’s work involves developing tools to better analyze jets. One approach is through machine learning: “smart” computer programs, or algorithms, that are inspired by structures in the brain.
“These algorithms are used to look for certain patterns in data,” Kagan says. “In some cases, they have been shown to recognize objects better than humans can. I’m trying to find out if the ATLAS data are a good match for these algorithms or if there are even better algorithms that can help us with the data analysis.”
After receiving a bachelor’s degree from the University of Michigan, Ann Arbor, and master’s and PhD degrees from Harvard University, Kagan came to SLAC in 2012 as a postdoc. In that role he took part in the construction and testing of the Insertable B-Layer – a new detector layer for the ATLAS detector that sits only 1.3 inches away from LHC’s proton beams.
“SLAC will also play a role in a future replacement of the ATLAS inner detector,” Kagan says. “This is necessary because the LHC will be upgraded to a 10 times greater luminosity. This will produce many more particle collisions than now, and the current detector won’t be able to withstand the damage caused by the collisions any longer. I’m looking forward to using my experience from previous detector work to help build and test this detector upgrade.”
Kagan’s work in particle physics, which includes a fair amount of programming, has also allowed him to nurture his humanitarian side. He co-founded “THE Port,” a Geneva-based nonprofit organization that helps humanitarian organizations tackle technological challenges.
“Large organizations like the International Committee of the Red Cross and the United Nations face enormous humanitarian crises but they often don’t have modern technology to deal with them,” Kagan says. “They often don’t have big IT teams or engineering teams, either, that could develop technology and software solutions. That’s where THE Port comes in. We regularly organize three-day hackathons at CERN, where several teams try to build prototype solutions over the weekend.”
One example is a phone app that assists with mapping potential refugee sites in areas without satellite imaging. In some cases, these efforts have led to spin-off businesses that take prototypes to completion.
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