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Mapping the cosmos: Dark Energy Survey creates detailed guide to spotting dark matter

Monday, April 13th, 2015

This Fermilab press release came out on April 13, 2015.

This is the first Dark Energy Survey map to trace the detailed distribution of dark matter across a large area of sky. The color scale represents projected mass density: red and yellow represent regions with more dense matter. The dark matter maps reflect the current picture of mass distribution in the universe where large filaments of matter align with galaxies and clusters of galaxies. Clusters of galaxies are represented by gray dots on the map - bigger dots represent larger clusters. This map covers three percent of the area of sky that DES will eventually document over its five-year mission. Image: Dark Energy Survey

This is the first Dark Energy Survey map to trace the detailed distribution of dark matter across a large area of sky. The color scale represents projected mass density: red and yellow represent regions with more dense matter. The dark matter maps reflect the current picture of mass distribution in the universe where large filaments of matter align with galaxies and clusters of galaxies. Clusters of galaxies are represented by gray dots on the map – bigger dots represent larger clusters. This map covers three percent of the area of sky that DES will eventually document over its five-year mission. Image: Dark Energy Survey

Scientists on the Dark Energy Survey have released the first in a series of dark matter maps of the cosmos. These maps, created with one of the world’s most powerful digital cameras, are the largest contiguous maps created at this level of detail and will improve our understanding of dark matter’s role in the formation of galaxies. Analysis of the clumpiness of the dark matter in the maps will also allow scientists to probe the nature of the mysterious dark energy, believed to be causing the expansion of the universe to speed up.

The new maps were released today at the April meeting of the American Physical Society in Baltimore, Maryland. They were created using data captured by the Dark Energy Camera, a 570-megapixel imaging device that is the primary instrument for the Dark Energy Survey (DES).

Dark matter, the mysterious substance that makes up roughly a quarter of the universe, is invisible to even the most sensitive astronomical instruments because it does not emit or block light. But its effects can be seen by studying a phenomenon called gravitational lensing – the distortion that occurs when the gravitational pull of dark matter bends light around distant galaxies. Understanding the role of dark matter is part of the research program to quantify the role of dark energy, which is the ultimate goal of the survey.

This analysis was led by Vinu Vikram of Argonne National Laboratory (then at the University of Pennsylvania) and Chihway Chang of ETH Zurich. Vikram, Chang and their collaborators at Penn, ETH Zurich, the University of Portsmouth, the University of Manchester and other DES institutions worked for more than a year to carefully validate the lensing maps.

“We measured the barely perceptible distortions in the shapes of about 2 million galaxies to construct these new maps,” Vikram said. “They are a testament not only to the sensitivity of the Dark Energy Camera, but also to the rigorous work by our lensing team to understand its sensitivity so well that we can get exacting results from it.”

The camera was constructed and tested at the U.S. Department of Energy’s Fermi National Accelerator Laboratory and is now mounted on the 4-meter Victor M. Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile. The data were processed at the National Center for Supercomputing Applications at the University of Illinois in Urbana-Champaign.

The dark matter map released today makes use of early DES observations and covers only about three percent of the area of sky DES will document over its five-year mission. The survey has just completed its second year. As scientists expand their search, they will be able to better test current cosmological theories by comparing the amounts of dark and visible matter.

Those theories suggest that, since there is much more dark matter in the universe than visible matter, galaxies will form where large concentrations of dark matter (and hence stronger gravity) are present. So far, the DES analysis backs this up: The maps show large filaments of matter along which visible galaxies and galaxy clusters lie and cosmic voids where very few galaxies reside. Follow-up studies of some of the enormous filaments and voids, and the enormous volume of data, collected throughout the survey will reveal more about this interplay of mass and light.

“Our analysis so far is in line with what the current picture of the universe predicts,” Chang said. “Zooming into the maps, we have measured how dark matter envelops galaxies of different types and how together they evolve over cosmic time. We are eager to use the new data coming in to make much stricter tests of theoretical models.”

View the Dark Energy Survey analysis.

The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries. Its primary instrument, the Dark Energy Camera, is mounted on the 4-meter Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile, and its data is processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, ETH Zurich for Switzerland, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia, the Deutsche Forschungsgemeinschaft and the collaborating institutions in the Dark Energy Survey. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2012-39559, ESP2013-48274, FPA2013-47986 and Centro de Excelencia Severo Ochoa SEV-2012-0234, some of which include ERDF funds from the European Union.

Fermilab is America’s premier national laboratory for particle physics and accelerator 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 website at www.fnal.gov and follow us on Twitter at @Fermilab.

The DOE 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 science.energy.gov.

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Absence of gravitational-wave signal extends limit on knowable universe

Thursday, April 9th, 2015

This article appeared in Fermilab Today on Thursday, April 9.

The Holometer is sensitive to high-frequency gravitational waves, allowing it to look for events such as cosmic strings. Photo: Reidar Hahn

The Holometer is sensitive to high-frequency gravitational waves, allowing it to look for events such as cosmic strings. Photo: Reidar Hahn

Imagine an instrument that can measure motions a billion times smaller than an atom that last a millionth of a second. Fermilab’s Holometer is currently the only machine with the ability to take these very precise measurements of space and time, and recently collected data has improved the limits on theories about exotic objects from the early universe.

Our universe is as mysterious as it is vast. According to Albert Einstein’s theory of general relativity, anything that accelerates creates gravitational waves, which are disturbances in the fabric of space and time that travel at the speed of light and continue infinitely into space. Scientists are trying to measure these possible sources all the way to the beginning of the universe.

The Holometer experiment, based at the Department of Energy’s Fermilab, is sensitive to gravitational waves at frequencies in the range of a million cycles per second. Thus it addresses a spectrum not covered by experiments such as the Laser Interferometer Gravitational-Wave Observatory, which searches for lower-frequency waves to detect massive cosmic events such as colliding black holes and merging neutron stars.

“It’s a huge advance in sensitivity compared to what anyone had done before,” said Craig Hogan, director of the Center for Particle Astrophysics at Fermilab.

This unique sensitivity allows the Holometer to look for exotic sources that could not otherwise be found. These include tiny black holes and cosmic strings, both possible phenomena from the early universe that scientists expect to produce high-frequency gravitational waves. Tiny black holes could be less than a meter across and orbit each other a million times per second; cosmic strings are loops in space-time that vibrate at the speed of light.

The Holometer is composed of two Michelson interferometers that each split a laser beam down two 40-meter arms. The beams reflect off the mirrors at the ends of the arms and travel back to reunite. Passing gravitational waves alter the lengths of the beams’ paths, causing fluctuations in the laser light’s brightness, which physicists can detect.

The Holometer team spent five years building the apparatus and minimizing noise sources to prepare for experimentation. Now the Holometer is taking data continuously, and with an hour’s worth of data, physicists were able to confirm that there are no high-frequency gravitational waves at the magnitude where they were searching.

The absence of a signal provides valuable information about our universe. Although this result does not prove whether the exotic objects exist, it has eliminated the region of the universe where they could be present.

“It means that if there are primordial cosmic string loops or tiny black hole binaries, they have to be far away,” Hogan said. “It puts a limit on how much of that stuff can be out there.”

Detecting these high-frequency gravitational waves is a secondary goal of the Holometer. Its main purpose is to determine whether our universe acts like a 2-D hologram, where information is coded into two-dimensional bits at the Planck scale, a length around ten trillion trillion times smaller than an atom. That investigation is still in progress.

“For me, it’s gratifying to be able to contribute something new to science,” said researcher Bobby Lanza, who recently earned his Ph.D. conducting research on the Holometer. He is the lead author on an upcoming paper about the result. “It’s part of chipping away at the whole picture of the universe.”

Diana Kwon

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New magnet at Fermilab achieves high-field milestone

Friday, April 3rd, 2015

This article appeared in Fermilab Today on April 3, 2015.

This magnet recently achieved an important milestone, reaching its design field of 11.5 Tesla. It is the first successful niobium-3-tin, twin-aperture accelerator magnet in the world. Photo: Sean Johnson

This magnet recently achieved an important milestone, reaching its design field of 11.5 Tesla. It is the first successful niobium-3-tin, twin-aperture accelerator magnet in the world. Photo: Sean Johnson

Last month, a new superconducting magnet developed and fabricated at Fermilab reached its design field of 11.5 Tesla at a temperature nearly as cold as outer space. It is the first successful twin-aperture accelerator magnet made of niobium-3-tin in the world.

The advancements in niobium-3-tin, or Nb3Sn, magnet technology and the ongoing U.S. collaboration with CERN on the development of these and other Nb3Sn magnets are enabling the use of this innovative technology for future upgrades of the Large Hadron Collider (LHC). They may also provide the cornerstone for future circular machines of interest to the worldwide high-energy physics community. Because of the exceptional challenges — Nb3Sn is brittle and requires high-temperature processing — this important milestone was achieved at Fermilab after decades of worldwide R&D efforts both in the Nb3Sn conductor itself and in associated magnet technologies.

Superconducting magnets are at the heart of most particle accelerators for fundamental science as well as other scientific and technological applications. Superconductivity is also being explored for use in biosensors and quantum computing.

Thanks to Nb3Sn’s stronger superconducting properties, it enables magnets of larger field than any in current particle accelerators. As a comparison, the niobium-titanium dipole magnets built in the early 1980s for the Tevatron particle collider produced about 4 Tesla to bend the proton and antiproton beams around the ring. The most powerful niobium-titanium magnets used in the LHC operate at roughly 8 Tesla. The new niobium-3-tin magnet creates a significantly stronger field.

Because the Tevatron accelerated positively charged protons and negatively charged antiprotons, its magnets had only one aperture. By contrast, the LHC uses two proton beams. This requires two-aperture magnets with fields in opposite directions. And because the LHC collides beams at higher energies, it requires larger magnetic fields.

In the process of upgrading the LHC and in conceiving future particle accelerators and detectors, the high-energy physics community is investing as never before in high-field magnet technologies. This creative process involves the United States, Europe, Japan and other Asian countries. The latest strategic plan for U.S. high-energy physics, the 2014 report by the Particle Physics Project Prioritization Panel, endorses continued U.S. leadership in superconducting magnet technology for future particle physics programs. The U.S. LHC Accelerator Research Program (LARP), which comprises four DOE national laboratories — Berkeley Lab, Brookhaven Lab, Fermilab and SLAC — plays a key role in this strategy.

The 15-year investment in Nb3Sn technology places the Fermilab team led by scientist Alexander Zlobin at the forefront of this effort. The Fermilab High-Field Magnet Group, in collaboration with U.S. LARP and CERN, built the first reproducible series in the world of single-aperture 10- to 12-Tesla accelerator-quality dipoles and quadrupoles made of Nb3Sn, establishing a strong foundation for the LHC luminosity upgrade at CERN.

The laboratory has consistently carried out in parallel an assertive superconductor R&D program as key to the magnet success. Coordination with industry and universities has been critical to improve the performance of the next generation of high-field accelerator magnets.

The next step is to develop 15-Tesla Nb3Sn accelerator magnets for a future very high-energy proton-proton collider. The use of high-temperature superconductors is also becoming a realistic prospect for generating even larger magnetic fields. An ultimate goal is to develop magnet technologies based on combining high- and low-temperature superconductors for accelerator magnets above 20 Tesla.

The robust and versatile infrastructure that was developed at Fermilab, together with the expertise acquired by the magnet scientists and engineers in design and analysis tools for superconducting materials and magnets, makes Fermilab an ideal setting to look to the future of high-field magnet research.

Emanuela Barzi

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Superconducting test accelerator achieves first electron beam

Monday, March 30th, 2015

This article appeared in Fermilab Today on March 30, 2015.

Last week the first SRF cavities of Fermilab's superconducting test accelerator propelled their first electrons. Photo: Reidar Hahn

Last week the first SRF cavities of Fermilab’s superconducting test accelerator propelled their first electrons. Photo: Reidar Hahn

The newest particle accelerators and those of the future will be built with superconducting radio-frequency (SRF) cavities, and institutions around the world are working hard to develop this technology. Fermilab’s advanced superconducting test accelerator was built to take advantage of SRF technology accelerator research and development.

On Friday, after more than seven years of planning and building by scientists and engineers, the accelerator has delivered its first beam.

The Fermilab superconducting test accelerator is a linear accelerator (linac) with three main components: a photoinjector that includes an RF gun coupled to an ultraviolet-laser system, several cryomodules and a beamline. Electron bunches are produced when an ultraviolet pulse generated by the laser hits a cathode located on the back plate of the gun. Acceleration continues through two SRF cavities inside the cryomodules. After exiting the cryomodules, the bunches travel down a beamline, where researchers can assess them.

Each meter-long cavity consists of nine cells made from high-purity niobium. In order to become superconductive, the cavities sit in a vessel filled with superfluid liquid helium at temperatures close to absolute zero.

As RF power pulses through these cavities, it creates an oscillating electric field that runs through the cells. If the charged particles meet the oscillating waves at the right phase, they are pushed forward and propelled down the accelerator.

The major advantage of using superconductors is that the lack of electrical resistance allows virtually all the energy passing through to be used for accelerating particle beams, ultimately creating more efficient accelerators.

The superconducting test accelerator team celebrates first beam in the operations center at NML. Vladimir Shiltsev, left, is pointing to an image of the beam. Photo: Pavel Juarez, AD

The superconducting test accelerator team celebrates first beam in the operations center at NML. Vladimir Shiltsev, left, is pointing to an image of the beam. Photo: Pavel Juarez, AD

“It’s more bang for the buck,” said Elvin Harms, one of the leaders of the commissioning effort.

The superconducting test accelerator’s photoinjector gun first produced electrons in June 2013. In the current run, electrons are being shot through one single-cavity cryomodule, with a second, upgraded model to be installed in the next few months. Future plans call for accelerating the electron beam through an eight-cavity cryomodule, CM2, which was the first to reach the specifications of the proposed International Linear Collider (ILC).

Fermilab is one of the few facilities that provides space for advanced accelerator research and development. These experiments will help set the stage for future superconducting accelerators such as SLAC’s Linac Coherent Light Source II, of which Fermilab is one of several partner laboratories.

“The linac is similar to other accelerators that exist, but the ability to use this type of setup to carry out accelerator science experiments and train students is unique,” said Philippe Piot, a physicist at Fermilab and professor at Northern Illinois University leading one of the first experiments at the test accelerator. A Fermilab team has designed and is beginning to construct the Integrable Optics Test Accelerator ring, a storage ring that will be attached to the superconducting test accelerator in the years to come.

“This cements the fact that Fermilab has been building up the infrastructure for mastering SRF technology,” Harms said. “This is the crown jewel of that: saying that we can build the components, put them together, and now we can accelerate a beam.”

Diana Kwon

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The dawn of DUNE

Wednesday, March 25th, 2015

This article appeared in symmetry on March 25, 2015.

A powerful planned neutrino experiment gains new members, new leaders and a new name. Image: Fermilab

A powerful planned neutrino experiment gains new members, new leaders and a new name. Image: Fermilab

The neutrino experiment formerly known as LBNE has transformed. Since January, its collaboration has gained about 50 new member institutions, elected two new spokespersons and chosen a new name: Deep Underground Neutrino Experiment, or DUNE.

The proposed experiment will be the most powerful tool in the world for studying hard-to-catch particles called neutrinos. It will span 800 miles. It will start with a near detector and an intense beam of neutrinos produced at Fermi National Accelerator Laboratory in Illinois. It will end with a 10-kiloton far detector located underground in a laboratory at the Sanford Underground Research Facility in South Dakota. The distance between the two detectors will allow scientists to study how neutrinos change as they zip at close to the speed of light straight through the Earth.

“This will be the flagship experiment for particle physics hosted in the US,” says Jim Siegrist, associate director of high-energy physics for the US Department of Energy’s Office of Science. “It’s an exciting time for neutrino science and particle physics generally.”

In 2014, the Particle Physics Project Prioritization Panel identified the experiment as a top priority for US particle physics. At the same time, it recommended the collaboration take a few steps back and invite more international participation in the planning process.

Physicist Sergio Bertolucci, director of research and scientific computing at CERN, took the helm of an executive board put together to expand the collaboration and organize the election of new spokespersons.

DUNE now includes scientists from 148 institutions in 23 countries. It will be the first large international project hosted by the US to be jointly overseen by outside agencies.

This month, the collaboration elected two new spokespersons: André Rubbia, a professor of physics at ETH Zurich, and Mark Thomson, a professor of physics at the University of Cambridge. One will serve as spokesperson for two years and the other for three to provide continuity in leadership.

Rubbia got started with neutrino research as a member of the NOMAD experiment at CERN in the ’90s. More recently he was a part of LAGUNA-LBNO, a collaboration that was working toward a long-baseline experiment in Europe. Thomson has a long-term involvement in US-based underground and neutrino physics. He is the DUNE principle investigator for the UK.

Scientists are coming together to study neutrinos, rarely interacting particles that constantly stream through the Earth but are not well understood. They come in three types and oscillate, or change from type to type, as they travel long distances. They have tiny, unexplained masses. Neutrinos could hold clues about how the universe began and why matter greatly outnumbers antimatter, allowing us to exist.

“The science is what drives us,” Rubbia says. “We’re at the point where the next generation of experiments is going to address the mystery of neutrino oscillations. It’s a unique moment.”

Scientists hope to begin installation of the DUNE far detector by 2021. “Everybody involved is pushing hard to see this project happen as soon as possible,” Thomson says.

Jennifer Huber and Kathryn Jepsen

Image: Fermilab

Image: Fermilab

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Expanding the cosmic search

Friday, March 20th, 2015

This article appeared in Fermilab Today on March 20, 2015.

The South Pole Telescope scans the skies during a South Pole winter. Photo: Jason Gallicchio, University of Chicago

The South Pole Telescope scans the skies during a South Pole winter. Photo: Jason Gallicchio, University of Chicago

Down at the South Pole, where temperatures drop below negative 100 degrees Fahrenheit and darkness blankets the land for six months at a time, the South Pole Telescope (SPT) searches the skies for answers to the mysteries of our universe.

This mighty scavenger is about to get a major upgrade — a new camera that will help scientists further understand neutrinos, the ghost-like particles without electric charge that rarely interact with matter.

The 10-meter SPT is the largest telescope ever to make its way to the South Pole. It stands atop a two-mile thick plateau of ice, mapping the cosmic microwave background (CMB), the light left over from the big bang. Astrophysicists use these observations to understand the composition and evolution of the universe, all the way back to the first fraction of a second after the big bang, when scientists believe the universe quickly expanded during a period called inflation.

One of the goals of the SPT is to determine the masses of the neutrinos, which were produced in great abundance soon after the big bang. Though nearly massless, because neutrinos exist in huge numbers, they contribute to the total mass of the universe and affect its expansion. By mapping out the mass density of the universe through measurements of CMB lensing, the bending of light caused by immense objects such as large galaxies, astrophysicists are trying to determine the masses of these elusive particles.

A wafer of detectors for the SPT-3G camera undergoes inspection at Fermilab. Photo: Bradford Benson, University of Chicago

A wafer of detectors for the SPT-3G camera undergoes inspection at Fermilab. Photo: Bradford Benson, University of Chicago

To conduct these extremely precise measurements, scientists are installing a bigger, more sensitive camera on the telescope. This new camera, SPT-3G, will be four times heavier and have a factor of about 10 more detectors than the current camera. Its higher level of sensitivity will allow researchers to make extremely precise measurements of the CMB that will hopefully make it possible to cosmologically detect neutrino mass.

This photo shows an up-close look at a single SPT-3G detector. Photo: Volodymyr Yefremenko, Argonne National Laboratory

This photo shows an up-close look at a single SPT-3G detector. Photo: Volodymyr Yefremenko, Argonne National Laboratory


“In the next several years, we should be able to get to the sensitivity level where we can measure the number of neutrinos and derive their mass, which will tell us how they contribute to the overall density of the universe,” explained Bradford Benson, the head of the CMB Group at Fermilab. “This measurement will also enable even more sensitive constraints on inflation and has the potential to measure the energy scale of the associated physics that caused it.”

SPT-3G is being completed by a collaboration of scientists spanning the DOE national laboratories, including Fermilab and Argonne, and universities including the University of Chicago and University of California, Berkeley. The national laboratories provide the resources needed for the bigger camera and larger detector array while the universities bring years of expertise in CMB research.

“The national labs are getting involved because we need to scale up our infrastructure to support the big experiments the field needs for the next generation of science goals,” Benson said. Fermilab’s main role is the initial construction and assembly of the camera, as well as its integration with the detectors. This upgrade is being supported mainly by the Department of Energy and the National Science Foundation, which also supports the operations of the experiment at the South Pole.

Once the camera is complete, scientists will bring it to the South Pole, where conditions are optimal for these experiments. The extreme cold prevents the air from holding much water vapor, which can absorb microwave signals, and the sun, another source of microwaves, does not rise between March and September.

The South Pole is accessible only for about three months during the year, starting in November. This fall, about 20 to 30 scientists will head down to the South Pole to assemble the camera on the telescope and make sure everything works before leaving in mid-February. Once installed, scientists will use it to observe the sky over four years.

“For every project I’ve worked on, it’s that beginning — when everyone is so excited not knowing what we’re going to find, then seeing things you’ve been dreaming about start to show up on the computer screen in front of you — that I find really exciting,” said University of Chicago’s John Carlstrom, the principal investigator for the SPT-3G project.

Diana Kwon

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Einstein’s most famous equation

Friday, March 13th, 2015

This article appeared in symmetry on March 12, 2015.

You’ve heard of Einstein’s E=mc2, but what does it mean?

You’ve heard of Einstein’s E=mc2, but what does it mean?

With Einstein’s birthday just around the corner on March 14 (which also happens to be Pi Day), it seems appropriate to take a fresh look at one of his biggest accomplishments with a short video.

In 1905, Einstein published four papers that radically changed how we look at the world around us. Dubbed Einstein’s “Annus Mirabilis,” or “Year of Wonders,” it gave us revolutionary new ideas about light, atoms and how your frame of reference makes a big difference in your perception.

It was Einstein’s final paper that year that really took the (birthday) cake. In it, he gave us a deceptively simple idea—that mass and energy were equivalent. He even summed it up for us with the tiny equation E=mc2*.

However, while appearing simple, the implications of E=mc2 are huge and far-reaching. To find out why, sit back, enjoy some birthday cake (or pie, depending on how you’re celebrating), and watch the video!

*Although we are most familiar with E=mc2, Einstein didn’t quite say it that way in the original paper. It was actually in the form of a sentence in German: “If a body gives off the energy L in the form of radiation, its mass diminishes by L/V2.”

Chris Smith

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Scientists find rare dwarf satellite galaxy candidates in Dark Energy Survey data

Tuesday, March 10th, 2015

This Fermilab press release came out on March 10, 2015.

 

 

Scientists on two continents have independently discovered a set of celestial objects that seem to belong to the rare category of dwarf satellite galaxies orbiting our home galaxy, the Milky Way.

Dwarf galaxies are the smallest known galaxies, and they could hold the key to understanding dark matter and the process by which larger galaxies form.

A team of researchers with the Dark Energy Survey, headquartered at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, and an independent group from the University of Cambridge jointly announced their findings today. Both teams used data taken during the first year of the Dark Energy Survey, all of which is publicly available, to carry out their analysis.

“The large dark matter content of Milky Way satellite galaxies makes this a significant result for both astronomy and physics,” said Alex Drlica-Wagner of Fermilab, one of the leaders of the Dark Energy Survey analysis.

Satellite galaxies are small celestial objects that orbit larger galaxies, such as our own Milky Way. Dwarf galaxies can be found with fewer than 100 stars and are remarkably faint and difficult to spot. (By contrast, the Milky Way, an average-sized galaxy, contains billions of stars.)

These newly discovered objects are a billion times dimmer than the Milky Way and a million times less massive. The closest of them is about 100,000 light-years away.

“The discovery of so many satellites in such a small area of the sky was completely unexpected,” said Cambridge’s Institute of Astronomy’s Sergey Koposov, the Cambridge study’s lead author. “I could not believe my eyes.”

Scientists have previously found more than two dozen of these satellite galaxies around our Milky Way. About half of them were discovered in 2005 and 2006 by the Sloan Digital Sky Survey, the precursor to the Dark Energy Survey. After that initial explosion of discoveries, the rate fell to a trickle and dropped off entirely over the past five years.

The Dark Energy Survey is looking at a new portion of the southern hemisphere, covering a different area of sky than the Sloan Digital Sky Survey. The galaxies announced today were discovered in a search of only the first of the planned five years of Dark Energy Survey data, covering roughly one-third of the portion of sky that DES will study. Scientists expect that the full Dark Energy Survey will find up to 30 of these satellite galaxies within its area of study.

graphic

Download: Med-res | Low-res

This illustration maps out the previously discovered dwarf satellite galaxies (in blue) and the newly discovered candidates (in red) as they sit outside the Milky Way. Image: Yao-Yuan Mao, Ralf Kaehler, Risa Wechsler (KIPAC/SLAC).

 

 

Atlas image obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

While more analysis is required to confirm any of the observed celestial objects as satellite galaxies, researchers note their size, low surface brightness and significant distance from the center of the Milky Way as evidence that they are excellent candidates. Further tests are ongoing, and data collected during the second year of the Dark Energy Survey could yield more of these potential dwarf galaxies to study.

Newly discovered galaxies would also present scientists with more opportunities to search for signatures of dark matter. Dwarf satellite galaxies are dark matter-dominated, meaning they have much more mass in unseen matter than in stars. The nature of this dark matter remains unknown but might consist of particles that annihilate each other and release gamma rays. Because dwarf galaxies do not host other gamma ray sources, they make ideal laboratories to search for signs of dark matter annihilation. Scientists are confident that further study of these objects will lead to even more sensitive searches for dark matter.

In a separate result also announced today, the Large Area Telescope Collaboration for NASA’s Fermi Gamma-Ray Telescope mission reported that they did not see any significant excess of gamma ray emission associated with the new Dark Energy Survey objects. This result demonstrates that new discoveries from optical telescopes can be quickly translated into tests of fundamental physics.

“We did not detect significant emission with the LAT, but the dwarf galaxies that DES has and will discover are extremely important targets for the dark matter search,” said Peter Michelson, spokesperson for the LAT collaboration. “If not leading to an identification of particle dark matter, they will certainly be useful to constrain its properties.”

The Dark Energy Survey is a five-year effort to photograph a large portion of the southern sky in unprecedented detail. Its primary instrument is the Dark Energy Camera, which – at 570 megapixels – is the most powerful digital camera in the world, able to see galaxies up to 8 billion light-years from Earth. Built and tested at Fermilab, the camera is now mounted on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory in the Andes Mountains in Chile.

The survey’s five-year mission is to discover clues about the nature of dark energy, the mysterious force that makes up about 70 percent of all matter and energy in the universe. Scientists believe that dark energy may be the key to understanding why the expansion of the universe is accelerating.

“The Dark Energy Camera is a perfect instrument for discovering small satellite galaxies,” said Keith Bechtol of the Kavli Institute for Cosmological Physics at the University of Chicago, who helped lead the Dark Energy Survey analysis. “It has a very large field of view to quickly map the sky and great sensitivity, enabling us to look at very faint stars. These results show just how powerful the camera is and how significant the data it collects will be for many years to come.”

The Dark Energy Survey analysis is available here. The University of Cambridge analysis is available here.

The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries. For more information about the survey, please visit the experiment’s website.

Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia, the Deutsche Forschungsgemeinschaft and the collaborating institutions in the Dark Energy Survey. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2012-39559, ESP2013-48274, FPA2013-47986 and Centro de Excelencia Severo Ochoa SEV-2012-0234, some of which include ERDF funds from the European Union.

Fermilab is America’s premier national laboratory for particle physics and accelerator 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 website at www.fnal.gov and follow us on Twitter at @Fermilab.

The DOE 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 science.energy.gov .

The mission of the University of Cambridge is to contribute to society through the pursuit of education, learning and research at the highest international levels of excellence. To date, 90 affiliates of the university have won the Nobel Prize. Founded in 1209, the university comprises 31 autonomous colleges, which admit undergraduates and provide small-group tuition, and 150 departments, faculties and institutions. Cambridge is a global university. Its 19,000 student body includes 3,700 international students from 120 countries. Cambridge researchers collaborate with colleagues worldwide, and the university has established larger-scale partnerships in Asia, Africa and America. The university sits at the heart of one of the world’s largest technology clusters. The ‘Cambridge Phenomenon’ has created 1,500 hi-tech companies, 14 of them valued at over US$1 billion and two at over US$10 billion. Cambridge promotes the interface between academia and business and has a global reputation for innovation. www.cam.ac.uk .

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Detecting something with nothing

Tuesday, March 3rd, 2015

This article appeared in Fermilab Today on March 3, 2015.

From left: Jason Bono (Rice University), Dan Ambrose (University of Minnesota) and Richie Bonventre (Lawrence Berkeley National Laboratory) work on the Mu2e straw chamber tracker unit at Lab 3. Photo: Reidar Hahn

From left: Jason Bono (Rice University), Dan Ambrose (University of Minnesota) and Richie Bonventre (Lawrence Berkeley National Laboratory) work on the Mu2e straw chamber tracker unit at Lab 3. Photo: Reidar Hahn

Researchers are one step closer to finding new physics with the completion of a harp-shaped prototype detector element for the Mu2e experiment.

Mu2e will look for the conversion of a muon to only an electron (with no other particles emitted) — something predicted but never before seen. This experiment will help scientists better understand how these heavy cousins of the electron decay. A successful sighting would bring us nearer to a unifying theory of the four forces of nature.

The experiment will be 10,000 times as sensitive as other experiments looking for this conversion, and a crucial part is the detector that will track the whizzing electrons. Researchers want to find one whose sole signature is its energy of 105 MeV, indicating that it is the product of the elusive muon decay.

In order to measure the electron, scientists track the helical path it takes through the detector. But there’s a catch. Every interaction with detector material skews the path of the electron slightly, disturbing the measurement. The challenge for Mu2e designers is thus to make a detector with as little material as possible, says Mu2e scientist Vadim Rusu.

“You want to detect the electron with nothing — and this is as close to nothing as we can get,” he said.

So how to detect the invisible using as little as possible? That’s where the Mu2e tracker design comes in. Panels made of thin straws of metalized Mylar, each only 15 microns thick, will sit inside a cylindrical magnet. Rusu says that these are the thinnest straws that people have ever used in a particle physics experiment.

These straws, filled with a combination of argon and carbon dioxide gas and threaded with a thin wire, will wait in vacuum for the electrons. Circuit boards placed on both ends of the straws will gather the electrical signal produced when electrons hit the gas inside the straw. Scientists will measure the arrival times at each end of the wire to help accurately plot the electron’s overall trajectory.

“This is another tricky thing that very few have attempted in the past,” Rusu said.

The group working on the Mu2e tracker electronics have also created the tiny, low-power circuit boards that will sit at the end of each straw. With limited space to run cooling lines, necessary features that whisk away heat that would otherwise sit in the vacuum, the electronics needed to be as cool and small as possible.

“We actually spent a lot of time designing very low-power electronics,” Rusu said.

This first prototype, which researchers began putting together in October, gives scientists a chance to work out kinks, improve design and assembly procedures, and develop the necessary components.

One lesson already learned? Machining curved metal with elongated holes that can properly hold the straws is difficult and expensive. The solution? Using 3-D printing to make a high-tech, transparent plastic version instead.

Researchers also came up with a system to properly stretch the straws into place. While running a current through the straw, they use a magnet to pluck the straw — just like strumming a guitar string — and measure the vibration. This lets them set the proper tension that will keep the straw straight throughout the lifetime of the experiment.

Although the first prototype of the tracker is complete, scientists are already hard at work on a second version (using the 3D-printed plastic), which should be ready in June or July. The prototype will then be tested for leaks and to see if the electronics pick up and transmit signals properly.

A recent review of Mu2e went well, and Rusu expects work on the tracker construction to begin in 2016.

Lauren Biron

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Ten unusual detector materials

Tuesday, February 17th, 2015

This article appeared in symmetry on Feb. 17, 2015.

The past century has generated some creative ideas for tracking particles. Image: Sandbox Studio

The past century has generated some creative ideas for tracking particles. Image: Sandbox Studio

Hans had been waiting in the darkened room for 45 minutes. It was a dull part of his day, but acclimating his eyes was a necessary part of his experiment—counting faint sparkles of light caused by alpha particles deflecting off a thin metal foil.

The experiment was part of a series organized by Ernest Rutherford in 1908, and it led to the discovery of the atomic nucleus. Rutherford’s assistant, physicist Hans Geiger, would share credit for the discovery.

Their experiment was particle physics in its infancy.

Studying particle physics requires revealing the smallest bits of matter. This work might involve hurling billions of accelerated particles at a target and watching for the flash of energy that results from the crash. It might involve setting up a detector to wait for particles created in nature to pass through.

Over the years, electronics and mainframe computers have taken over Rutherford and Geiger’s painstaking particle-counting duties. And physicists have used a host of materials other than foil to lure those particles—including hard-to-catch neutrinos—into view.

1. Dry cleaning fluid.

Physicist Ray Davis had either a terrific idea for a particle detector or a tremendous load of laundry. In a few years leading up to 1966, he obtained 600 tons of a common dry cleaning solvent, perchloroethylene, and deposited it nearly a mile beneath the Black Hills of South Dakota in a detector stationed in the Homestake gold mine. He hoped to count solar neutrinos, which trigger a detectable chemical reaction when they pass through this fluid. Davis’ perchloroethylene-filled particle detector was a success, even though he tallied only a third of the neutrinos he was expecting. Revelations that neutrinos change form as they travel were soon to follow.

2. Soviet-era artillery shells.

In the 1940s, the Russian navy armed its vessels with a grade of brass specifically designed to hold its shape under extreme stress and for long periods of time. More than 50 years later, the CMS particle detector under construction at the Large Hadron Collider at CERN required brass with the same high standards. It needed to be able to withstand a bombardment of particles with unflinching consistency over its lifetime. The lab struck a deal with Russian officials to melt down old, unused shells for the CMS hadron calorimeter, a part of the detector that measures the energy of particles produced in collisions in the LHC.

3. 2.5 million gallons of mineral oil.

Fermilab’s 14,000-ton NOvA neutrino detector in northern Minnesota, possibly the largest freestanding plastic structure in the world, is filled with a liquid substance that is 95 percent mineral oil. That single raw material took up 108 rail cars and a barge as it left a refinery in southwest Louisiana for a facility 1000 miles away near Chicago, where it was blended with the remaining ingredients 110,000 gallons at time. The result was a liquid scintillator, which releases measurable light as a result of collisions between neutrinos and particles in the liquid.

4. Lead bricks wrapped in foil by robots.

The OPERA detector at Gran Sasso National Laboratory catches neutrinos with something a bit more, as they say in Italy, duro—a wall of 150,000 18-pound bricks. The bricks themselves are stacks of lead sheets and radiation-sensitive film, wrapped in reflective aluminum tape and sealed in an airtight container. When neutrinos collide with the lead, they create other particles that streak across the film and leave tracks that can be analyzed after the film is developed. The 11 robots of Gran Sasso’s brick-assembly machine, otherwise known as BAM, cranked out 750 bricks per day, faster and with much less complaining than an army of graduate students.

5. Smartphones. Yep, there’s an app for that.

Actually, there are at least two. A physicist at the University of Wisconsin, Madison, and a director of citizen science at the LA Makerspace are working on one called DECO, an educational app that records speedy cosmic-ray particles that your phone’s camera accidentally detects. Two more physicists, one from University of California, Irvine, and the other from University of California, Davis, are at work on a similar app called CRAYFIS. Their objective: gather enough users to create a functional cosmic ray detector from a massive network of devices.

6. A crystal ball.

No, SLAC National Accelerator Laboratory did not enlist a psychic medium to locate subatomic particles when they built the Crystal Ball detector in the late ’70s. They did, however, arrange more than 600 sodium iodide crystals into a sphere 13 ½ feet around to detect neutral particles at the SPEAR particle collider. The crystals work in similar fashion to the liquid inside the NOvA detector (see No. 2 in this list), converting energy from particle collisions to measurable light. The detector is still in use, currently at Johannes Gutenberg University in Mainz, Germany. Its future, ironically, is uncertain.

7. Antarctica, from below.

When penguins look down, there’s a chance they might discover one of 86 holes drilled more than a mile deep into the Antarctic ice for the IceCube experiment. When turbocharged cosmic neutrinos collide with ice, the resulting particle shrapnel creates a blue flash of light otherwise known as Cherenkov light. Scientists survey the ice sheet for that light with an array of more than 5000 separate, bauble-like detectors strung on wires running down each hole.

8. Antarctica, from above.

Should penguins look up instead, they may spot the Antarctic Impulsive Transient Antenna, or ANITA, floating above them, suspended from a massive scientific balloon. ANITA listens for radio waves emanating from the ice below. The pure, polar ice makes an unbelievably clear medium for the Askaryan effect, discovered only in 2000, in which cosmic neutrinos similar to the ones that produce light for the IceCube experiment generate a signature radio signal. The floating antenna is so sensitive that it can detect a handheld radio up to 400 miles away.

9. A breath of fresh Martian air.

Our descendants may well enjoy a beautiful sunset on Mars—if we can engineer its atmosphere to warm the planet from its current average temperature of about minus 60 degrees Celsius to something more friendly to vacationing humans. For such a project, some researchers have singled out the compound octofluoropropane as the greenhouse gas of choice. In the meantime, researchers on the PICO experiment at underground Canadian laboratory SNOLAB are using octofluoropropane in its liquid state to detect dark matter. If a particle of dark matter can knock one fluorine nucleus hard enough, it will cause the superheated liquid to boil and form a telltale bubble in the chamber.

10. Dry ice, alcohol and a fish tank.

This one you can build yourself. The cloud chamber earned its inventor the 1927 Nobel Prize in physics, and variations of it—including No. 9 on this list— have a long history of use in particle physics labs. But many DIY varieties exist online, too. The gist is usually to create a thick vapor (of alcohol) that is cooled (by dry ice). Be patient, and you’ll catch a passing particle such as a cosmic muon as it bumps into vapor molecules and triggers a cloudy streak of condensation through the chamber (a.k.a. fish tank).

 

Troy Rummler

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