Sand Hill, CA, United States
Sand Hill, CA, United States

Time filter

Source Type

Atomic model of the crystalline occlusion bodies, derived from the X-ray diffraction images recorded at the X-ray free-electron laser LCLS at SLAC National Accelerator Laboratory. The individual proteins (right) stick together to form the building blocks (left, seen from the side; center, seen from above) of the crystalline occlusion bodies. Credit: Dominik Oberthuer, CFEL/DESY An international team of scientists has used high-intensity X-ray pulses to determine the structure of the crystalline protein envelope of an insect virus. Their analysis reveals the fine details of the building blocks that make up the viral cocoon down to a scale of 0.2 nanometres (millionths of a millimetre) - approaching atom-scale resolution. The tiny viruses with their crystal casing are by far the smallest protein crystals ever analysed using X-ray crystallography. This opens up new opportunities in the study of protein structures, as the team headed by DESY's Leading Scientist Henry Chapman from the Center for Free-Electron Laser Science reports in the Proceedings of the National Academy of Sciences (PNAS). "The granulovirus attacks certain insects and kills them. This initially leaves it stranded inside the decaying host, so it has to protect itself, perhaps for years, against adverse environmental conditions such as heat, ultraviolet radiation and drought, until it is once again ingested by an insect. To achieve this, the virus wraps itself in a cocoon made of protein crystals, which only dissolve again once it reaches an insect's gut," explains Cornelius Gati from DESY, the main author of the paper. These viruses are a particular interest of Peter Metcalf from the University of Auckland in New Zealand and Johannes Jehle from the Julius Kühn Institute in Darmstadt, who teamed up with DESY for this research. The researchers examined the cocoon of the Cydia pomonella granulovirus (CpGV), which infects the caterpillars of the codling moth (Cydia pomonella) and is used in agriculture as a biological pesticide. The virus is harmless to humans. Scientists are interested in the spatial structure of proteins and other biomolecules because this sheds light on the precise way in which they work. This has led to a specialised science known as structural biology. "Over the past 50 years, scientists have determined the structures of more than 100,000 proteins," says Chapman, who is also a professor of physics at the University of Hamburg. "By far the most important tool for this is X-ray crystallography." In this method, a crystal of the protein under investigation is grown and irradiated with bright X-rays. This produces a characteristic diffraction pattern, from which the spatial structure of the crystal and its building blocks can be calculated. "One of the big challenges of this procedure is, however, growing the crystals," adds Chapman. Many proteins do not readily align to form crystals, because that is not their natural state. The smaller the crystals that can be used for the analysis, the easier it is to grow them, but the harder it is to measure them. "We are hoping that in future we will be able to dispense altogether with growing crystals and study individual molecules directly using X-rays," says Chapman, "so we would like to understand the limits". "These virus particles provided us with the smallest protein crystals ever used for X-ray structure analysis," explains Gati. The occlusion body (the virus "cocoon") has a volume of around 0.01 cubic micrometres, about one hundred times smaller than the smallest artificially grown protein crystals that have until now been analysed using crystallographic techniques. To break this limit in crystal size, an extremely bright X-ray beam was needed, which was obtained using a so-called free-electron laser (FEL), in which a beam of high-speed electrons is guided through a magnetic undulator causing them to emit laser-like X-ray pulses. The scientists used the free-electron laser LCLS at the SLAC National Accelerator Laboratory in the U.S., and employed optics to focus each X-ray pulse to a similar size as one of the virus particles. "Directing the entire power of the FEL onto one tiny virus exposed it to the tremendous radiation levels," reports Gati, who now works at SLAC. The dose was 1.3 billion Grays; for comparison: the lethal dose for humans is around 50 Grays. The FEL dose was certainly lethal for the viruses too - each was completely vaporised by a single X-ray pulse. But the femtosecond-duration pulse carries the information of the pristine structure to the detector and the destruction of the virus occurs only after the passage of the pulse. The analysis of the recorded diffraction showed that even tiny protein crystals which are bombarded with extremely high radiation doses can still reveal their structure on an atomic scale. "Simulations based on our measurements suggest that our method can probably be used to determine the structure of even smaller crystals consisting of only hundreds or thousands of molecules," reports Chapman, who is also a member of the Hamburg Center for Ultrafast Imaging (CUI). "This takes us a huge step further towards our goal of analysing individual molecules." More information: Atomic structure of granulin determined from native nanocrystalline granulovirus using an X-ray free-electron laser, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1609243114


News Article | February 15, 2017
Site: www.newscientist.com

A hint of matter and antimatter behaving differently to each other has been spotted in a new particle for the first time. If the find bears out, it could help explain the existence of all the matter in the universe, and why it was not snuffed out by antimatter long ago. Physicists think that the big bang should have produced equal amounts of matter and antimatter. But these contrasting particles annihilate each other in a puff of energy whenever they meet, so they should have destroyed each other long ago. The fact that there is enough matter in the universe today for us to exist and wonder why, means that some mechanism must have favoured matter over antimatter. “Today we have this complete imbalance between matter and antimatter. We have no evidence of antimatter in the universe,” says Nicola Neri of the National Institute for Nuclear Physics in Milan, Italy. “This is one of the main questions we’d like to answer.” One way the two could differ is by violating a rule about the way the laws of physics affect particles and antiparticles known as CP symmetry. Previously, experiments showed that CP symmetry is in fact violated in particles called mesons, which are made up of a quark and an antiquark. Those results garnered two Nobel prizes, one in 1980 and one in 2008. But it wasn’t enough. “The sources we’ve found so far are not sufficient to explain this huge imbalance,” Neri says. Now, Neri and his colleagues have checked another kind of particle: baryons, which are made of three quarks and no antiquarks. Neutrons and protons, the building blocks of matter, are baryons. They watched for differences in the decay of baryons and their antimatter counterparts made of three antiquarks, and they were lucky. The particles decayed in a way that seems to violate CP symmetry. “This is the first hint, a sign that something is going on there,” Neri says. During the first run of the Large Hadron Collider at CERN near Geneva, between 2011 and 2012, the large international team used the LHCb experiment to watch the decay of heavy baryons called lambda-b particles, which are about six times heavier than a neutron. They observed about 6500 instances of lambda-b particles decaying into a proton and three particles called pions, and about 1000 instances of a different decay that included particles called kaons as well. Theory suggested that there should be a lot of CP violation in these events, but because they needed the extreme energies of the LHC to be produced, they had never been seen before. “It was not anticipated that we could have such a large signal yield,” Neri says. “That was a nice surprise.” The kaon decay looked normal. But the pion version showed a deviation from the standard predictions to a statistical significance of 3.3 sigma, meaning random fluctuations would produce a similar signal less than once every 1000 times. Particle physicists consider that level of significance evidence that something strange is happening, but it’s not quite enough to declare discovery. That will have to wait for 5-sigma, when the odds of random fluctuations producing a similar signal are less than one in a million. But the LHC has been upgraded and collected more data since these measurements, and is still ramping up to its full potential. Neri expects to increase their data set by at least a factor of 10. And even if the signal goes away with more data, it’s still useful to be able to compare CP violation in baryons and mesons, Neri says. “We can do studies for the first time in baryon decays and make good comparisons with decays with similar quark transitions, and in that way get information on the underlying physics,” he says. “We are entering an era with LHCb where we can make precision measurements in CP violation in heavy baryons. You open a new series of measurements with this kind of result. That’s the excitement.” “It’s an important observation,” says David MacFarlane at the SLAC National Accelerator Laboratory in Menlo Park, California, who was on the team that measured CP violation in mesons. “The more systems we see CP violations in, the more chance we have to understand whether the standard model is correct, or whether there are other sources.”


News Article | February 15, 2017
Site: cerncourier.com

Tom Dombeck, an innovative and versatile physicist and project manager, passed away in Kāneʻohe, Hawaii, on 4 November 2016. His legacy includes many measurements in particle physics, the development of new techniques for the production of ultra-cold neutrons and substantial contributions to the management of several major scientific projects. Tom received a BA in physics from Columbia University in 1967 and a PhD in particle physics from Northwestern University in 1972, and his career saw him hold prominent roles at numerous institutes. He was a research associate at Imperial College London from 1972 to 1974 and visiting scientist at Dubna in the former USSR in 1975. Following six years at the University of Maryland, from 1981 to 1988 Tom held various roles at Los Alamos National Laboratory (LANL) after which he spent a year working in the US Department of Energy in the office of the Superconducting Supercollider (SSC). Afterwards he became a staff physicist and ultimately deputy project manager for operations at the SSC laboratory in Texas, where he led the successful “string test”. In 1994 he moved to a role as project manager for the Sloan Digital Sky Survey at the University of Chicago. Tom was deputy head for the technical division at Fermilab from 1997 to 1999, and project manager for the Next Linear Collider project at Fermilab between 2000 and 2002. From 2003 to 2006 he was project manager for the Pan-STARRS telescope at the University of Hawaii and an affiliated graduate faculty member there until 2016. Tom began his scientific research with bubble chambers and was a key participant in the experiment that observed the first neutrino interaction in a hydrogen filled bubble chamber in 1970 at the ZGS at Argonne National Laboratory. For many years he pursued measurements of the electric dipole moment (EDM) of the neutron and was also involved in the development of ultra-cold neutrons by Doppler shifting at pulsed sources. He proposed a new method for a neutron EDM measurement that involved Bragg scattering polarised neutrons from a silicon crystal and led an initial effort at the Missouri University Research Reactor, after which he initiated an experiment using the reactor at the NIST Center for Neutron Research. While at LANL, Tom led a neutrino-oscillation search that involved constructing a new beamline and neutrino source at LAMPF and provided improved limits on muon-neutrino to electron-neutrino oscillations. He carried these fundamental physics interests and abilities to his later work as a highly effective scientific programme manager. Tom was able to see the connections between disparate scientific areas and bring together new ideas and approaches that moved the field forwards. He could inspire people around him with his enthusiasm and kindness, and his wry sense of humour and wicked smile were trademarks that will long be remembered by his friends and colleagues. Tom was a devoted family man and is missed greatly by his wife Bonnie, his two children, Daniel and Heidi, and his four grandchildren. Sidney David Drell, professor emeritus of theoretical physics at SLAC National Accelerator Laboratory, senior fellow at Stanford’s Hoover Institution and a giant in the worlds of both academia and policy, died on 21 December 2016 at his home in Palo Alto, California. He was 90 years old. Drell made immense contributions to his field, including uncovering a process that bears his name and working on national and international security. His legacy as a humanitarian includes his friendship and support of Soviet physicist and dissident Andrei Sakharov, who won the Nobel Peace Prize in 1975 for his opposition of the abuse of power in the Soviet Union. Drell was also known for his welcoming nature and genuine, albeit perhaps unwarranted, humility. Drell’s commitment to arms control spanned more than 50 years. He served on numerous panels advising US Congress, the intelligence community and military. He was an original member of JASON, a group of academic scientists created to advise the government on national security and defence issues, and from 1992 to 2001 he was a member of the President’s Foreign Intelligence Advisory Board. He was also the co-founder of the Center for International Security and Cooperation at Stanford, and in 2006 he and former Secretary of State George Shultz began a programme at the Hoover Institution dedicated to developing practical steps towards ridding the world of nuclear weapons. In 1974, Drell met Sakharov at a conference hosted by the Soviet Academy of Sciences and they quickly became friends. When Sakharov was internally exiled to Gorky from 1980 to 1986 following his criticism of the Soviet invasion of Afghanistan, Drell exchanged letters with him and called on Soviet leader Mikhail Gorbachev for his release. He also organised a petition to allow another Soviet physicist and dissident, Nohim Meiman, to emigrate to Israel, and obtained the signatures of 118 members of the US National Academy of Sciences. Having graduated with a bachelor’s degree from Princeton University in 1946, Drell earned a master’s degree in 1947 and a PhD in physics in 1949 from the University of Illinois, Urbana-Champaign. He began at Stanford in 1950 as an instructor in physics, leaving to work as a researcher and assistant professor at the Massachusetts Institute of Technology and then returning to Stanford in 1956 as a professor of physics. He served as deputy director of SLAC from 1969 until his retirement from the lab in 1998. Drell’s research was in the fields of quantum electrodynamics and quantum chromodynamics. While at SLAC, he and research associate Tung-Mow Yan formulated the famous Drell–Yan Process, which has become an invaluable tool in particle physics. His theoretical work was critical in setting SLAC on the course that it took. As head of the SLAC theory group, Drell brought in a host of younger theoretical physicists who began creating the current picture of the structure of matter. He played an important role in developing the justification for experiments and turning the results into what became the foundation of the Standard Model of particle physics. For his research and lifetime of service to his country, Drell received many prestigious awards, including: the National Medal of Science; the Enrico Fermi Award; a fellowship from the MacArthur Foundation; the Heinz Award for contributions in public policy; the Rumford Medal from the American Academy of Arts and Sciences; and the National Intelligence Distinguished Service Medal. Drell was one of 10 scientists honoured as the founders of satellite reconnaissance as a space discipline by the US National Reconnaissance Office. He was elected to the National Academy of Sciences, the American Academy of Arts and Sciences and the American Philosophical Society, and was president of the American Physical Society in 1986. Drell was also an accomplished violinist who played chamber music throughout his life. He is survived by his wife, Harriet, and his children, Daniel, Virginia, Persis and Joanna. Persis Drell, a former director of SLAC who is also a physicist at Stanford and dean of the School of Engineering, will be the university’s next provost. • Based, with permission, on the obituary published on the Stanford University website on 22 December 2016. Mambillikalathil Govind Kumar Menon, a pioneer in particle physics and a distinguished statesman of science, passed away peacefully on 22 November at his home in New Delhi, India. He graduated with a bachelor of science from Jaswant College, Jodhpur, in 1946, and inspired by Chandrasekhara Venkata Raman, studied under the tutelage of spectroscopist Nanasaheb R Tawde before joining Cecil Powell’s group at the University of Bristol, UK, in 1949. Menon’s first important contribution was to establish the bosonic character of the pion through a study of fragments emerging from π-capture by light nuclei. He then focused his attention on the emerging field of K-meson physics. Along with his colleagues at Bristol, notably Peter Fowler, Cecil Powell and Cormac O’Ceallaigh, Menon discovered K+ → π+ π0 and K+ → π+ π– π+ events in nuclear emulsion indicating parity non-conservation, (the τ – θ puzzle). He also identified a sizeable collection of events showing the associated production of kaons and hyperons. In 1955 Menon joined the Tata Institute of Fundamental Research (TIFR), where he worked on cosmic-ray research programmes initiated by Homi Bhabha. Following Bhabha’s death in an air crash over Mont Blanc in 1966, the responsibility of the directorship of TIFR fell squarely on his shoulders, along with the wide-ranging initiatives for national development that Bhabha had started. Notwithstanding these additional demands on his time, his focus on particle physics never wavered. He continued with his research, establishing a collaboration with Arnold W Wolfendale at the University of Durham, UK, and Saburo Miyake of Osaka City University, Japan, for the study of particle physics with detectors deployed deep underground; he detected events induced by cosmic-ray neutrino interactions; and he also launched a dedicated effort to test the early predictions of violation of baryon-number conservation leading to proton decay. During his Bristol years, Menon established a close friendship with William O Lock, who had moved to CERN in 1959. This facilitated collaboration between TIFR and CERN, leading to the development of bubble-chamber techniques to study mesons produced in proton–antiproton collisions. These initial studies eventually led to highly successful collaborations between Indian researchers and the L3 experiment at LEP, and the CMS, ALICE and ATLAS experiments at the LHC. Menon won several awards including the Cecil F Powell and C V Raman medals, and was elected to the three scientific academies in India. He was elected as a fellow of the Royal Society in 1970, and subsequently to the Pontifical Academy of Sciences, American Academy of Arts and Sciences, the Russian Academy of Sciences and as an honorary fellow of the Institute of Physics and the Institution of Electrical & Electronics Engineers. He also served two terms as president of the International Council of Scientific Unions, and stimulated its participation in policy issues, including climate change. Menon held a firm conviction that science can bring about technological development and societal progress, which motivated him to work with Abdus Salam in founding the Third World Academy of Sciences. He held several high positions in the Indian government, and thus contributed to the growth of science and technology in India. Alongside his scientific achievements, M G K Menon was also very close to his wife Indumati and their two children Preeti and Anant Kumar. Our warmest thoughts go out to them and to innumerable others whose lives he touched in so many important ways. Helmut Oeschler, an active member of the ALICE collaboration, passed away from heart failure on 3 January while working at his desk. Born in Southern Germany, he received his PhD from the University of Heidelberg in 1972 and held postdoc positions at the Niels Bohr Institute in Copenhagen, and in Strasbourg, Saclay and Orsay in France. From 1981 he was at the Institute for Nuclear Physics of TU Darmstadt. He held a Doctorate Honoris Causa from Dubna University, Russia, and in 2006 he received the Gay-Lussac-Humboldt prize. Oeschler’s physics interests concerned the dynamics of nuclear reactions over a broad energy range, from the Coulomb barrier to ultra-relativistic collisions. He was a driving force for building the kaon spectrometer at the GSI in Darmstadt, which made it possible to measure strange particles in collisions of heavy nuclei. From the late 1990s he was actively involved in addressing new aspects of equilibration in relativistic nuclear reactions. Oeschler became a member of the ALICE collaboration at CERN in 2000 and made important contributions to the construction of the experiment. Together with his students, he was involved in developing track reconstruction software for measuring the production of charged particles in lead–lead collisions at the LHC. He also led the analysis efforts for the measurements of identified charged hadrons in the LHC’s first proton–proton collisions. From 2010 to 2014 he led the ALICE editorial board, overseeing the publication of key results relating to quark-gluon matter at the highest energy densities. His deep involvement in the data analysis and interpretation continued unabated and he made important contributions to several research topics. Advising and working in close collaboration with students was a much loved component of Helmut’s activity and was highly appreciated among the ALICE collaboration. Helmut Oeschler was a frequent visitor of South Africa and served there on numerous international advisory committees. He was instrumental in helping the South African community develop the physics of heavy-ion collisions and collaboration with CERN. With Helmut Oeschler we have lost an internationally renowned scientist and particular friend and colleague. His scientific contributions, especially on the production of strange particles in high-energy collisions, are important achievements.


News Article | February 15, 2017
Site: phys.org

A recent study led by scientists at the Department of Energy's SLAC National Accelerator Laboratory helps describe how the contaminant cycles through the environment at former uranium mining sites and why it can be difficult to remove. Contrary to assumptions that have been used for modeling uranium behavior, researchers found the contaminant binds to organic matter in sediments. The findings provide more accurate information for monitoring and remediation at the sites. The results were published in the Proceedings of the National Academy of Sciences. In 2014, researchers at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL) began collaborating with the DOE Office of Legacy Management, which handles contaminated sites associated with the legacy of DOE's nuclear energy and weapons production activities. Through projects associated with the Uranium Mill Tailings Radiation Control Act, the DOE remediated 22 sites in Colorado, Wyoming and New Mexico where uranium had been extracted and processed during the 1940s to 1970s. Uranium was removed from the sites as part of the cleanup process, and the former mines and waste piles were capped more than two decades ago. Remaining uranium deep in the subsurface under the capped waste piles was expected to leave these sites due to natural groundwater flow. However, uranium has persisted at elevated levels in nearby groundwater much longer than predicted by scientific modeling. In an earlier study, the SLAC team discovered that uranium accumulates in the low-oxygen sediments near one of the waste sites in the upper Colorado River basin. These deposits contain high levels of organic matter—such as plant debris and bacterial communities. During this latest study, the researchers found the dominant form of uranium in the sediments, known as tetravalent uranium, binds to organic matter and clays in the sediments. This makes it more likely to persist at the sites. The result conflicted with current models used to predict movement and longevity of uranium in sediments, which assumed that it formed an insoluble mineral called uraninite. Different chemical forms of the element vary widely in how mobile they are—how readily they move around—in water, says Sharon Bone, lead author on the paper and a postdoctoral researcher at SSRL, a DOE Office of Science User Facility. Since the uranium is bound to organic matter in sediments, it is immobile under certain conditions. Tetravalent uranium may become mobile when the water table drops and oxygen from the air enters spaces in the sediment that were formerly filled with water, particularly if the uranium is bound to organic matter in sediments rather than being stored in insoluble minerals. "Either you want the uranium to be soluble and completely flushed out by the groundwater, or you just want the uranium to remain in the sediments and stay out of the groundwater," Bone says. "But under fluctuating seasonal conditions, neither happens completely." This cycling in the aquifer may result in the persistent plumes of uranium contamination found in groundwater, something that wasn't captured by earlier modeling efforts. "For the most part, uranium contamination has only been looked at in very simple model systems in laboratories," Bone says. "One big advancement is that we are now looking at uranium in its native environmental form in sediments. These dynamics are complicated, and this research will allow us to make field-relevant modeling predictions." More information: Sharon E. Bone et al. Uranium(IV) adsorption by natural organic matter in anoxic sediments, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1611918114


News Article | February 15, 2017
Site: www.eurekalert.org

The race is on to build the most sensitive U.S.-based experiment designed to directly detect dark matter particles. Department of Energy officials have formally approved a key construction milestone that will propel the project toward its April 2020 goal for completion. The LUX-ZEPLIN (LZ) experiment, which will be built nearly a mile underground at the Sanford Underground Research Facility (SURF) in Lead, S.D., is considered one of the best bets yet to determine whether theorized dark matter particles known as WIMPs (weakly interacting massive particles) actually exist. There are other dark matter candidates, too, such as "axions" or "sterile neutrinos," which other experiments are better suited to root out or rule out. The fast-moving schedule for LZ will help the U.S. stay competitive with similar next-gen dark matter direct-detection experiments planned in Italy and China. On Feb. 9, the project passed a DOE review and approval stage known as Critical Decision 3 (CD-3), which accepts the final design and formally launches construction. "We will try to go as fast as we can to have everything completed by April 2020," said Murdock "Gil" Gilchriese, LZ project director and a physicist at the DOE's Lawrence Berkeley National Laboratory (Berkeley Lab), the lead lab for the project. "We got a very strong endorsement to go fast and to be first." The LZ collaboration now has about 220 participating scientists and engineers who represent 38 institutions around the globe. The nature of dark matter--which physicists describe as the invisible component or so-called "missing mass" in the universe that would explain the faster-than-expected spins of galaxies, and their motion in clusters observed across the universe--has eluded scientists since its existence was deduced through calculations by Swiss astronomer Fritz Zwicky in 1933. The quest to find out what dark matter is made of, or to learn whether it can be explained by tweaking the known laws of physics in new ways, is considered one of the most pressing questions in particle physics. Successive generations of experiments have evolved to provide extreme sensitivity in the search that will at least rule out some of the likely candidates and hiding spots for dark matter, or may lead to a discovery. LZ will be at least 50 times more sensitive to finding signals from dark matter particles than its predecessor, the Large Underground Xenon experiment (LUX), which was removed from SURF last year to make way for LZ. The new experiment will use 10 metric tons of ultra-purified liquid xenon, to tease out possible dark matter signals. Xenon, in its gas form, is one of the rarest elements in Earth's atmosphere. "The science is highly compelling, so it's being pursued by physicists all over the world," said Carter Hall, the spokesperson for the LZ collaboration and an associate professor of physics at the University of Maryland. "It's a friendly and healthy competition, with a major discovery possibly at stake." A planned upgrade to the current XENON1T experiment at National Institute for Nuclear Physics' Gran Sasso Laboratory (the XENONnT experiment) in Italy, and China's plans to advance the work on PandaX-II, are also slated to be leading-edge underground experiments that will use liquid xenon as the medium to seek out a dark matter signal. Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders. Hall noted that while WIMPs are a primary target for LZ and its competitors, LZ's explorations into uncharted territory could lead to a variety of surprising discoveries. "People are developing all sorts of models to explain dark matter," he said. "LZ is optimized to observe a heavy WIMP, but it's sensitive to some less-conventional scenarios as well. It can also search for other exotic particles and rare processes." LZ is designed so that if a dark matter particle collides with a xenon atom, it will produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank--over four times more than were installed in LUX--will carry the telltale fingerprint of the particles that created them. Daniel Akerib, Thomas Shutt, and Maria Elena Monzani are leading the LZ team at SLAC National Accelerator Laboratory. The SLAC effort includes a program to purify xenon for LZ by removing krypton, an element that is typically found in trace amounts with xenon after standard refinement processes. "We have already demonstrated the purification required for LZ and are now working on ways to further purify the xenon to extend the science reach of LZ," Akerib said. SLAC and Berkeley Lab collaborators are also developing and testing hand-woven wire grids that draw out electrical signals produced by particle interactions in the liquid xenon tank. Full-size prototypes will be operated later this year at a SLAC test platform. "These tests are important to ensure that the grids don't produce low-level electrical discharge when operated at high voltage, since the discharge could swamp a faint signal from dark matter," said Shutt. Hugh Lippincott, a Wilson Fellow at Fermi National Accelerator Laboratory (Fermilab) and the physics coordinator for the LZ collaboration, said, "Alongside the effort to get the detector built and taking data as fast as we can, we're also building up our simulation and data analysis tools so that we can understand what we'll see when the detector turns on. We want to be ready for physics as soon as the first flash of light appears in the xenon." Fermilab is responsible for implementing key parts of the critical system that handles, purifies, and cools the xenon. All of the components for LZ are painstakingly measured for naturally occurring radiation levels to account for possible false signals coming from the components themselves. A dust-filtering cleanroom is being prepared for LZ's assembly and a radon-reduction building is under construction at the South Dakota site--radon is a naturally occurring radioactive gas that could interfere with dark matter detection. These steps are necessary to remove background signals as much as possible. The vessels that will surround the liquid xenon, which are the responsibility of the U.K. participants of the collaboration, are now being assembled in Italy. They will be built with the world's most ultra-pure titanium to further reduce background noise. To ensure unwanted particles are not misread as dark matter signals, LZ's liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals. Brookhaven National Laboratory is handling the production of another very pure liquid, known as a scintillator fluid, that will go into this tank. The cleanrooms will be in place by June, Gilchriese said, and preparation of the cavern where LZ will be housed is underway at SURF. Onsite assembly and installation will begin in 2018, he added, and all of the xenon needed for the project has either already been delivered or is under contract. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry. "South Dakota is proud to host the LZ experiment at SURF and to contribute 80 percent of the xenon for LZ," said Mike Headley, executive director of the South Dakota Science and Technology Authority (SDSTA) that oversees SURF. "Our facility work is underway and we're on track to support LZ's timeline." UK scientists, who make up about one-quarter of the LZ collaboration, are contributing hardware for most subsystems. Henrique Araújo, from Imperial College London, said, "We are looking forward to seeing everything come together after a long period of design and planning." Kelly Hanzel, LZ project manager and a Berkeley Lab mechanical engineer, added, "We have an excellent collaboration and team of engineers who are dedicated to the science and success of the project." The latest approval milestone, she said, "is probably the most significant step so far," as it provides for the purchase of most of the major components in LZ's supporting systems. For more information about LZ and the LZ collaboration, visit: http://lz. . Major support for LZ comes from the DOE Office of Science's Office of High Energy Physics, South Dakota Science and Technology Authority, the UK's Science & Technology Facilities Council, and by collaboration members in South Korea and Portugal. Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www. . DOE's 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 website at http://science. . The Sanford Underground Research Facility's mission is to enable compelling underground, interdisciplinary research in a safe work environment and to inspire our next generation through science, technology, engineering, and math education. For more information, please visit the Sanford Lab website at http://www. .


News Article | February 28, 2017
Site: phys.org

Acoustic droplet ejection allows scientists to deposit nanoliters of sample directly into the X-ray beam, considerably increasing the efficiency of sample consumption. A femtosecond pulse from an X-ray free-electron laser then intersects with a droplet that contains protein crystals. Credit: SLAC National Accelerator Laboratory Biological samples studied with intense X-rays at free-electron lasers are destroyed within nanoseconds after they are exposed. Because of this, the samples need to be continually refreshed to allow the many images needed for an experiment to be obtained. Conventional methods use jets that supply a continuous stream of samples, but this can be very wasteful as the X-rays only interact with a tiny fraction of the injected material. To help address this issue, scientists at the Department of Energy's Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory, Brookhaven National Laboratory, and other institutes designed a new assembly-line system that rapidly replaces exposed samples by moving droplets along a miniature conveyor belt, timed to coincide with the arrival of the X-ray pulses. The droplet-on-tape system now allows the team to study the biochemical reactions in real-time from microseconds to seconds, revealing the stages of these complex reactions. In their approach, protein solution or crystals are precisely deposited in tiny liquid drops, made as ultrasound waves push the liquid onto a moving tape. As the drops move forward, they are hit with pulses of visible light or treated with oxygen gas, which triggers different chemical reactions depending on the sample studied. This allows the study of processes such as photosynthesis, which determines how plants absorb light from the sun and convert it into useable energy. Finally, powerful X-ray pulses from SLAC's X-ray laser, the Linac Coherent Light Source (LCLS), probe the drops. In this study published in Nature Methods, the X-ray light scattered from the sample onto two different detectors simultaneously, one for X-ray crystallography and the other for X-ray emission spectroscopy. These are two complementary methods that provide information about the geometric and electronic structure of the catalytic sites of the proteins and allowed them to watch with atomic precision how the protein structures changed during the reaction. Explore further: New, detailed snapshots capture photosynthesis at room temperature More information: Drop-on-demand sample delivery for studying biocatalysts in action at X-ray free-electron lasers. Nature Methods (2017) DOI: 10.1038/nmeth.4195


News Article | February 15, 2017
Site: phys.org

The LUX-ZEPLIN (LZ) experiment, which will be built nearly a mile underground at the Sanford Underground Research Facility (SURF) in Lead, S.D., is considered one of the best bets yet to determine whether theorized dark matter particles known as WIMPs (weakly interacting massive particles) actually exist. There are other dark matter candidates, too, such as "axions" or "sterile neutrinos," which other experiments are better suited to root out or rule out. The fast-moving schedule for LZ will help the U.S. stay competitive with similar next-gen dark matter direct-detection experiments planned in Italy and China. On Feb. 9, the project passed a DOE review and approval stage known as Critical Decision 3 (CD-3), which accepts the final design and formally launches construction. "We will try to go as fast as we can to have everything completed by April 2020," said Murdock "Gil" Gilchriese, LZ project director and a physicist at the DOE's Lawrence Berkeley National Laboratory (Berkeley Lab), the lead lab for the project. "We got a very strong endorsement to go fast and to be first." The LZ collaboration now has about 220 participating scientists and engineers who represent 38 institutions around the globe. The nature of dark matter—which physicists describe as the invisible component or so-called "missing mass" in the universe that would explain the faster-than-expected spins of galaxies, and their motion in clusters observed across the universe—has eluded scientists since its existence was deduced through calculations by Swiss astronomer Fritz Zwicky in 1933. The quest to find out what dark matter is made of, or to learn whether it can be explained by tweaking the known laws of physics in new ways, is considered one of the most pressing questions in particle physics. Successive generations of experiments have evolved to provide extreme sensitivity in the search that will at least rule out some of the likely candidates and hiding spots for dark matter, or may lead to a discovery. LZ will be at least 50 times more sensitive to finding signals from dark matter particles than its predecessor, the Large Underground Xenon experiment (LUX), which was removed from SURF last year to make way for LZ. The new experiment will use 10 metric tons of ultra-purified liquid xenon, to tease out possible dark matter signals. Xenon, in its gas form, is one of the rarest elements in Earth's atmosphere. "The science is highly compelling, so it's being pursued by physicists all over the world," said Carter Hall, the spokesperson for the LZ collaboration and an associate professor of physics at the University of Maryland. "It's a friendly and healthy competition, with a major discovery possibly at stake." A planned upgrade to the current XENON1T experiment at National Institute for Nuclear Physics' Gran Sasso Laboratory (the XENONnT experiment) in Italy, and China's plans to advance the work on PandaX-II, are also slated to be leading-edge underground experiments that will use liquid xenon as the medium to seek out a dark matter signal. Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders. Hall noted that while WIMPs are a primary target for LZ and its competitors, LZ's explorations into uncharted territory could lead to a variety of surprising discoveries. "People are developing all sorts of models to explain dark matter," he said. "LZ is optimized to observe a heavy WIMP, but it's sensitive to some less-conventional scenarios as well. It can also search for other exotic particles and rare processes." LZ is designed so that if a dark matter particle collides with a xenon atom, it will produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank—over four times more than were installed in LUX—will carry the telltale fingerprint of the particles that created them. Daniel Akerib, Thomas Shutt, and Maria Elena Monzani are leading the LZ team at SLAC National Accelerator Laboratory. The SLAC effort includes a program to purify xenon for LZ by removing krypton, an element that is typically found in trace amounts with xenon after standard refinement processes. "We have already demonstrated the purification required for LZ and are now working on ways to further purify the xenon to extend the science reach of LZ," Akerib said. SLAC and Berkeley Lab collaborators are also developing and testing hand-woven wire grids that draw out electrical signals produced by particle interactions in the liquid xenon tank. Full-size prototypes will be operated later this year at a SLAC test platform. "These tests are important to ensure that the grids don't produce low-level electrical discharge when operated at high voltage, since the discharge could swamp a faint signal from dark matter," said Shutt. Hugh Lippincott, a Wilson Fellow at Fermi National Accelerator Laboratory (Fermilab) and the physics coordinator for the LZ collaboration, said, "Alongside the effort to get the detector built and taking data as fast as we can, we're also building up our simulation and data analysis tools so that we can understand what we'll see when the detector turns on. We want to be ready for physics as soon as the first flash of light appears in the xenon." Fermilab is responsible for implementing key parts of the critical system that handles, purifies, and cools the xenon. All of the components for LZ are painstakingly measured for naturally occurring radiation levels to account for possible false signals coming from the components themselves. A dust-filtering cleanroom is being prepared for LZ's assembly and a radon-reduction building is under construction at the South Dakota site—radon is a naturally occurring radioactive gas that could interfere with dark matter detection. These steps are necessary to remove background signals as much as possible. The vessels that will surround the liquid xenon, which are the responsibility of the U.K. participants of the collaboration, are now being assembled in Italy. They will be built with the world's most ultra-pure titanium to further reduce background noise. To ensure unwanted particles are not misread as dark matter signals, LZ's liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals. Brookhaven National Laboratory is handling the production of another very pure liquid, known as a scintillator fluid, that will go into this tank. The cleanrooms will be in place by June, Gilchriese said, and preparation of the cavern where LZ will be housed is underway at SURF. Onsite assembly and installation will begin in 2018, he added, and all of the xenon needed for the project has either already been delivered or is under contract. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry. "South Dakota is proud to host the LZ experiment at SURF and to contribute 80 percent of the xenon for LZ," said Mike Headley, executive director of the South Dakota Science and Technology Authority (SDSTA) that oversees SURF. "Our facility work is underway and we're on track to support LZ's timeline." UK scientists, who make up about one-quarter of the LZ collaboration, are contributing hardware for most subsystems. Henrique Araújo, from Imperial College London, said, "We are looking forward to seeing everything come together after a long period of design and planning." Kelly Hanzel, LZ project manager and a Berkeley Lab mechanical engineer, added, "We have an excellent collaboration and team of engineers who are dedicated to the science and success of the project." The latest approval milestone, she said, "is probably the most significant step so far," as it provides for the purchase of most of the major components in LZ's supporting systems. Explore further: Construction of world's most sensitive dark matter detector moves forward


News Article | March 1, 2017
Site: phys.org

A profile of the focused X-ray beam, without (top) and with (bottom) the corrective lens. Credit: Frank Seiboth, DESY An international team of scientists has tailored special X-ray glasses to concentrate the beam of an X-ray laser stronger than ever before. The individually produced corrective lens eliminates the inevitable defects of an X-ray optics stack almost completely and concentrates three quarters of the X-ray beam to a spot with 250 nanometres (millionths of a millimetre) diameter, closely approaching the theoretical limit. The concentrated X-ray beam can not only improve the quality of certain measurements, but also opens up entirely new research avenues, as the team surrounding DESY lead scientist Christian Schroer writes in the journal Nature Communications. Although X-rays obey the same optical laws as visible light, they are difficult to focus or deflect: "Only a few materials are available for making suitable X-ray lenses and mirrors," explains co-author Andreas Schropp from DESY. "Also, since the wavelength of X-rays is very much smaller than that of visible light, manufacturing X-ray lenses of this type calls for a far higher degree of precision than is required in the realm of optical wavelengths—even the slightest defect in the shape of the lens can have a detrimental effect." The production of suitable lenses and mirrors has already reached a very high level of precision, but the standard lenses, made of the element beryllium, are usually slightly too strongly curved near the centre, as Schropp notes. "Beryllium lenses are compression-moulded using precision dies. Shape errors of the order of a few hundred nanometres are practically inevitable in the process." This results in more light scattered out of the focus than unavoidable due to the laws of physics. What's more, this light is distributed quite evenly over a rather large area. Such defects are irrelevant in many applications. "However, if you want to heat up small samples using the X-ray laser, you want the radiation to be focussed on an area as small as possible," says Schropp. "The same is true in certain imaging techniques, where you want to obtain an image of tiny samples with as much details as possible." In order to optimise the focussing, the scientists first meticulously measured the defects in their portable beryllium X-ray lens stack. They then used these data to machine a customised corrective lens out of quartz glass, using a precision laser at the University of Jena. The scientists then tested the effect of these glasses using the LCLS X-ray laser at SLAC National Accelerator Laboratory in the U.S. "Without the corrective glasses, our lens focused about 75 per cent of the X-ray light onto an area with a diameter of about 1600 nanometres. That is about ten times as large as theoretically achievable," reports principal author Frank Seiboth from the Technical University of Dresden, who now works at DESY. "When the glasses were used, 75 per cent of the X-rays could be focused into an area of about 250 nanometres in diameter, bringing it close to the theoretical optimum." With the corrective lens, about three times as much X-ray light was focused into the central speckle than without it. In contrast, the full width at half maximum (FWHM), the generic scientific measure of focus sharpness in optics, did not change much and remained at about 150 nanometres, with or without the glasses. The same combination of mobile standard optics and tailor-made glasses has also been studied by the team at DESY's synchrotron X-ray source PETRA III and the British Diamond Light Source. In both cases, the corrective lens led to a comparable improvement to that seen at the X-ray laser. "In principle, our method allows an individual corrective lens to be made for every X-ray optics," explains lead scientist Schroer, who is also a professor of physics at the University of Hamburg. "These so-called phase plates can not only benefit existing X-ray sources, but in particular they could become a key component of next-generation X-ray lasers and synchrotron light sources," emphasises Schroer. "Focusing X-rays to the theoretical limits is not only a prerequisite for a substantial improvement in a range of different experimental techniques; it can also pave the way for completely new methods of investigation. Examples include the non-linear scattering of particles of light by particles of matter, or creating particles of matter from the interaction of two particles of light. For these methods, the X-rays need to be concentrated in a tiny space which means efficient focusing is essential." Explore further: New type of X-ray lens: Lamellar lens prototype has been successfully tested More information: Perfect X-ray focusing via fitting corrective glasses to aberrated optics; Frank Seiboth et al.; Nature Communications, 2017; DOI: 10.1038/ncomms14623


News Article | March 1, 2017
Site: www.rdmag.com

Scientists will soon be able to concentrate on the beam of an X-ray laser stronger than ever before thanks to a new pair of special X-ray glasses. An international team of scientists have created corrective lenses that eliminate the inevitable defects of an X-ray optics stack almost completely and concentrate three quarters of the X-ray beam to a spot with 250 nanometers diameter, closely approaching the theoretical limit. By improving the concentrated X-ray beam, scientists can not only improve the quality of certain measurements but also open up entirely new research avenues. With the corrective lenses, about three times as much X-ray light was focused into the central speckle than without it. In contrast, the full width at half maximum—the generic scientific measure of focus sharpness in optics—did not change much and remained at about 150 nanometers, with or without the glasses. While X-rays obey the same optical laws as visible light, they are difficult to focus or deflect. “Only a few materials are available for making suitable X-ray lenses and mirrors,” co-author Andreas Schropp from Deutsches Elektronen-Synchrotron (DESY) in Germany, said in a statement. “Also, since the wavelength of X-rays is very much smaller than that of visible light, manufacturing X-ray lenses of this type calls for a far higher degree of precision than is required in the realm of optical wavelengths—even the slightest defect in the shape of the lens can have a detrimental effect.” The suitable lenses and mirrors have already reached a high level or precision but the standard lenses—made of beryllium—are usually slightly too strongly curved near the center, according to Schropp. “Beryllium lenses are compression-molded using precision dies,” he said. “Shape errors of the order of a few hundred nanometers are practically inevitable in the process.” This process results in more light scattered out of the focus than unavoidable due to the laws of physics. This light is also distributed fairly evenly over a rather large area. While these defects are irrelevant in many applications, Schropp said they are necessary in certain imaging techniques. “However, if you want to heat up small samples using the X-ray laser, you want the radiation to be focused on an area as small as possible,” he said. “The same is true in certain imaging techniques, where you want to obtain an image of tiny samples with as much details as possible.” To optimize the focusing, the scientists first measured the defects in the portable beryllium X-ray stack. They then used the data to produce a customized corrective lens out of quartz glass with a precisions laser at the University of Jena in Germany. The scientists then tested the effect of the glasses using the LCLS X-ray laser at SLAC National Accelerator Laboratory in California. “Without the corrective glasses, our lens focused about 75 percent of the X-ray light onto an area with a diameter of about 1,600 nanometers,” principal author Frank Seiboth, from the Technical University of Dresden and DESY, said in a statement. “That is about ten times as large as theoretically achievable. “When the glasses were used, 75 percent of the X-rays could be focused into an area of about 250 nanometers in diameter, bringing it close to the theoretical optimum,” he added. DESY lead scientist Christian Schroer explained what the glasses can be used for. “These so-called phase plates can not only benefit existing X-ray sources, but in particular they could become a key component of next-generation X-ray lasers and synchrotron light sources,” Schroer said in a statement. “Focusing X-rays to the theoretical limits is not only a prerequisite for a substantial improvement in a range of different experimental techniques; it can also pave the way for completely new methods of investigation. “Examples include the non-linear scattering of particles of light by particles of matter or creating particles of matter from the interaction of two particles of light,” he added. “For these methods, the X-rays need to be concentrated in a tiny space which means efficient focusing is essential.”


News Article | March 1, 2017
Site: www.eurekalert.org

An international team of scientists has tailored special X-ray glasses to concentrate the beam of an X-ray laser stronger than ever before. The individually produced corrective lens eliminates the inevitable defects of an X-ray optics stack almost completely and concentrates three quarters of the X-ray beam to a spot with 250 nanometres (millionths of a millimetre) diameter, closely approaching the theoretical limit. The concentrated X-ray beam can not only improve the quality of certain measurements, but also opens up entirely new research avenues, as the team surrounding DESY lead scientist Christian Schroer writes in the journal Nature Communications. Although X-rays obey the same optical laws as visible light, they are difficult to focus or deflect: "Only a few materials are available for making suitable X-ray lenses and mirrors," explains co-author Andreas Schropp from DESY. "Also, since the wavelength of X-rays is very much smaller than that of visible light, manufacturing X-ray lenses of this type calls for a far higher degree of precision than is required in the realm of optical wavelengths -- even the slightest defect in the shape of the lens can have a detrimental effect." The production of suitable lenses and mirrors has already reached a very high level of precision, but the standard lenses, made of the element beryllium, are usually slightly too strongly curved near the centre, as Schropp notes. "Beryllium lenses are compression-moulded using precision dies. Shape errors of the order of a few hundred nanometres are practically inevitable in the process." This results in more light scattered out of the focus than unavoidable due to the laws of physics. What's more, this light is distributed quite evenly over a rather large area. Such defects are irrelevant in many applications. "However, if you want to heat up small samples using the X-ray laser, you want the radiation to be focussed on an area as small as possible," says Schropp. "The same is true in certain imaging techniques, where you want to obtain an image of tiny samples with as much details as possible." In order to optimise the focussing, the scientists first meticulously measured the defects in their portable beryllium X-ray lens stack. They then used these data to machine a customised corrective lens out of quartz glass, using a precision laser at the University of Jena. The scientists then tested the effect of these glasses using the LCLS X-ray laser at SLAC National Accelerator Laboratory in the U.S. "Without the corrective glasses, our lens focused about 75 per cent of the X-ray light onto an area with a diameter of about 1600 nanometres. That is about ten times as large as theoretically achievable," reports principal author Frank Seiboth from the Technical University of Dresden, who now works at DESY. "When the glasses were used, 75 per cent of the X-rays could be focused into an area of about 250 nanometres in diameter, bringing it close to the theoretical optimum." With the corrective lens, about three times as much X-ray light was focused into the central speckle than without it. In contrast, the full width at half maximum (FWHM), the generic scientific measure of focus sharpness in optics, did not change much and remained at about 150 nanometres, with or without the glasses. The same combination of mobile standard optics and tailor-made glasses has also been studied by the team at DESY's synchrotron X-ray source PETRA III and the British Diamond Light Source. In both cases, the corrective lens led to a comparable improvement to that seen at the X-ray laser. "In principle, our method allows an individual corrective lens to be made for every X-ray optics," explains lead scientist Schroer, who is also a professor of physics at the University of Hamburg. "These so-called phase plates can not only benefit existing X-ray sources, but in particular they could become a key component of next-generation X-ray lasers and synchrotron light sources," emphasises Schroer. "Focusing X-rays to the theoretical limits is not only a prerequisite for a substantial improvement in a range of different experimental techniques; it can also pave the way for completely new methods of investigation. Examples include the non-linear scattering of particles of light by particles of matter, or creating particles of matter from the interaction of two particles of light. For these methods, the X-rays need to be concentrated in a tiny space which means efficient focusing is essential." Involved in this research project were the Technical University of Dresden, the Universities of Jena and Hamburg, the Royal Technical University of Stockholm (KTH), Diamond Light Source, SLAC National Accelerator Laboratory and DESY. Deutsches Elektronen-Synchrotron DESY is the leading German accelerator centre and one of the leading in the world. DESY is a member of the Helmholtz Association and receives its funding from the German Federal Ministry of Education and Research (BMBF) (90 per cent) and the German federal states of Hamburg and Brandenburg (10 per cent). At its locations in Hamburg and Zeuthen near Berlin, DESY develops, builds and operates large particle accelerators, and uses them to investigate the structure of matter. DESY's combination of photon science and particle physics is unique in Europe. Perfect X-ray focusing via fitting corrective glasses to aberrated optics; Frank Seiboth et al.; Nature Communications, 2017; DOI: 10.1038/ncomms14623

Loading National Accelerator Laboratory collaborators
Loading National Accelerator Laboratory collaborators