The Cosmic Frontier
SDSS image of Galaxy n4753
In the universe's vast web of galaxies, black
holes grab matter at the speed of light into
cataclysmic space-time vortices and fling off
particles at energies millions of times greater
than any laboratory accelerator. Particles of
invisible dark matter are a critical element in
the formation of galaxies. A mysterious dark
energy accelerates the expansion of space
between galaxies. Such extraordinary things
never happen in a laboratory, but they can
reveal deeply hidden details of fundamental
physics beyond the Standard Model.
At the Cosmic Frontier, scientists investigate the relationship of matter with gravity
and spacetime and search for new physics beyond the reach of particle accelerators.
Fermilab pioneered particle physics at the Cosmic Frontier and has continued to
develop the connection between the very large and the very small for almost 30 years.
Cosmic Frontier experiments make use of Fermilab's world-leading technical capabilities,
such as high-precision, low-noise silicon detector technology, large and ultra-clean vacuum
and cryogenic systems, fast electronics, and large-scale data management, analysis and
simulation tools. Fermilab serves as the host institution for global Cosmic Frontier experiments,
providing scientific, technical and administrative support for widely distributed
international scientific collaborations.
Over the next two decades, Fermilab will lead the Dark Energy Survey and participate
in the Large Synoptic Survey Telescope as they explore the nature of dark energy; support
the search to directly detect dark matter particles by playing a major role in four experiments
using different technologies; study the highest-energy cosmic rays with the Pierre Auger
Observatory; and take experimental physics to the Planck scale with the Fermilab Holometer.
Theoretical Physics at the Cosmic Frontier
Fermilab theorists explore the connections between new ideas in fundamental physics and
experiments at the Cosmic Frontier. They compute the interactions of particle dark matter
in accelerators and experiments; estimate the measurable effects of various possible forms
of dark energy in Dark Energy Survey data; and calculate how the properties of the modern
universe, such as cosmic background radiation, depend on theories of the inflationary beginnings
of the Big Bang. Close collaboration with theorists is important in all stages of
experiments, from first conceptualization to the final analysis and interpretation of data.
The synergy between Cosmic Frontier and the Energy and Intensity Frontiers, and the
various theorists who work in these areas, has never been stronger at Fermilab than it is today.
Dark Energy Camera telescope simulator
Fermilab leads the international Dark Energy
Survey collaboration, which is deploying
the 570-megapixel Dark Energy Camera on the
4-meter telescope at the Cerro Tololo Interamerican
Observatory in Chile.
Measurements of the distant cosmos reveal a new force that appears to accelerate the expansion
of the universe and makes up most of its total energy content. This mysterious dark
energy can be studied through large-scale precision measurements of the expansion and
structure of the universe using massive surveys—maps of the cosmos extending far into
space and back in time.
Fermilab's connection to dark-energy research began with its role as the anchor laboratory
for the Sloan Digital Sky Survey. The SDSS, the highest-impact astronomy facility of the
2000s, was the world's first large, deep digital survey of the universe. The SDSS pioneered
precision cosmology and made many important contributions to dark energy measurements.
Fermilab now leads a survey with SDSS that is setting new standards for precision and error
calibration in the use of supernovae to measure very large cosmic distances.
In this decade, Fermilab's dark-energy research program is focused on the Dark Energy
Survey, a deeper, more precise successor to the SDSS. Fermilab leads the international
DES collaboration, which is deploying a powerful new instrument called the Dark Energy
Camera on the 4-meter telescope at the Cerro Tololo Interamerican Observatory in the
Chilean Andes. Starting in 2012, and over the course of 525 nights through 2017, the DES
will map about 5,000 square degrees of the sky. The final petabyte-scale survey database
will comprise approximately 300 million galaxies and will look back in time over more than
half of the age of the universe.
Measurement uncertainties in dark energy behavior
Sensitivity of the Dark Energy Survey to
equation-of-state parameters of dark energy:
w denotes the ratio of mean dark energy
pressure to density of the cosmic vaccuum state
and wa is the derivative of w with respect to
cosmic scale factor. DES will use a variety of
complementary techniques to study dark
energy, including baryon acoustic oscillations
(BAO), galaxy clustering, weak gravitational
lensing (WL) and supernovae (SN).
The DES will probe dark energy using a variety of complementary techniques: galaxy
clustering, weak gravitational lensing, baryon acoustic oscillations and supernovae. Together
they will provide unprecedented probes of the dark-energy equation of state and its effects on
the expansion of the universe and on the growth of cosmic structure. These probes will
allow scientists to distinguish the effects of various possible forms of dark energy from each
other. For example, they will test whether cosmic acceleration is due to the energy of the
vacuum or a more exotic form of dark energy, or if it is due to a new theory of gravity.
The deep DES sky survey will be even more powerful if it obtains spectra of many of its
galaxies, providing velocity and 3D position information. Fermilab and its collaborators
are developing the technology to create a catalog of 10 to 100 million spectra that will provide
an exquisitely sensitive probe of dark energy's effects on structure growth over time.
The next step in cosmic surveys after the DES is the Large Synoptic Survey Telescope,
which should start its survey in the early 2020s. Now in the final stages of planning and
design, this project proposes to create a dedicated telescope and camera system that will
survey the universe significantly wider, deeper and faster than the DES. LSST will combine
a larger mirror (8 meters), a bigger field of view (3 gigapixels over 10 square degrees) and
a faster cadence to make a dedicated survey of the universe. Fermilab brings its decades
of experience in digital surveys to the large consortium of institutions developing this project.
Cryogenic Dark Matter Search
Assembly of the CDMS detector in its cryostat
in Minnesota's Soudan Mine. The next-generation
SuperCDMS experiment will be
deployed in Canada's SNOLAB.
Since the 1930s astronomers have accumulated evidence that the mass that holds galaxies
and clusters together with its gravity far exceeds the amount of mass in normal atoms in
any detectable form. Scientists suspect that this gravity comes from an invisible "dark matter"
made of some new kind of elementary particle left over from the early universe. A leading
postulate, based on Big Bang cosmology and natural extensions of Standard Model physics,
is that the dark matter is made of Weakly Interacting Massive Particles. WIMPs would
weigh more than atomic nuclei but would interact only by the weak force and gravity.
There is hope that some of them might one day be produced in accelerators, but they
have never been directly detected.
Fermilab is a leader in the worldwide hunt for dark matter particles. In collaboration
with international partners, the laboratory plays a major role in four kinds of experimental
searches. These experiments, which are based on a variety of technologies, all seek to detect
the very rare interactions of dark-matter particles from the Galaxy's halo with nuclei of
ordinary matter using very low-background detectors placed deep underground.
Fermilab is a lead laboratory in the Cryogenic Dark Matter Search, which uses ultra-cold
silicon and germanium crystals to achieve a high level of control over unwanted backgrounds.
The experiment is entering a new phase with the deployment of 10 kilograms of advanced
detectors in its existing facility at the Soudan Underground Laboratory in Minnesota.
The 10-kg SuperCDMS experiment will take data until about 2013. A next-generation
100-kg experiment is planned for Canada's SNOLAB, with the goal of improving sensitivity
to dark-matter particles by a factor of 100 without any backgrounds generated
by normal-matter particles.
The Chicagoland Observatory for Underground Particle Physics uses bubble-chamber
technology, allowing for relatively inexpensive scaling to larger volumes and flexibility in
target material. A 4-kg COUPP chamber is operating at SNOLAB, and a 60-kg chamber
being tested underground at Fermilab will be deployed in Canada in 2012. Designs for a
500-kg system are underway.
Pierre Auger Observatory
Seventeen countries contributed to the
construction of Auger, which uses 1,600
water tanks and 24 fluorescence telescopes
to study the highest-energy cosmic rays.
Fermilab contributes key technology for the DarkSide project that is based on a liquid-argon
detector similar to that being developed for Fermilab's long-baseline neutrino experiments.
A 50-kg chamber is now under construction that will start operations in 2013 at
the Gran Sasso National Laboratory in Italy. Larger follow-up experiments are planned.
A new Fermilab project called DAMIC is based on the same CCD detectors used to build
the Dark Energy Camera. In the DAMIC technology, very fine-grain imaging of particle tracks
allows eYcient diagnosis of unwanted particle backgrounds and an extended
sensitivity to low WIMP masses. An experimental system is currently under development
underground at Fermilab, and will be deployed to the much deeper SNOLAB site in 2012.
Over the next few years, the next generation of experiments will be able to either detect
these particles for the first time—revealing a new kind of matter and opening a new way
to study the universe—or to exclude many of the theoretical ideas that lead to the WIMP
hypothesis. In the next decade, based on the results of those experiments, some of these
technologies will be deployed with a ton or more of detector mass, leading to a conclusive test.
High-Energy Cosmic Particles
The universe accelerates particles to energies far greater than human-made accelerators
can, reaching collision energies nearly 100 times greater than those achieved at the Large
Hadron Collider. Although the highest-energy particles are extremely rare, they can be studied
by large arrays of ground-based detectors. Their composition, interactions and natural
history provide a unique window into high-energy particle interactions and the extreme
sources in the universe that accelerate them.
Fermilab is the lead laboratory supporting the Pierre Auger Observatory in Argentina,
the world's premier facility for studying the highest-energy cosmic rays. Auger's international
collaboration has published many groundbreaking results on the composition,
interactions, anisotropy and spectrum of ultra-high-energy cosmic rays. The highest-energy
events can be statistically traced back to their sources in the sky, the nuclei of distant galaxies.
The Planck scale
Experiments beyond the Planck scale probe a
deeper level of quantum spacetime. In this
diagram, log of length is plotted against log of
mass-energy. At upper left, the equation
relating wavelength and energy for a quantum
particle, Einstein's photoelectric formula. At
upper right, the equation relating the radius and
mass of a black hole, predicted by Einstein's
theory of spacetime. These two realms cross at
the Planck scale.
A new experiment called the Fermilab Holometer will study physics at the Planck scale,
the deepest layer of reality we can explore with the tools of conventional physics. The
Planck scale defines the intersection of two realms of physics: the quantum world, which
describes the fundamental particle/wave behavior of all forms of mass and energy; and
spacetime physics or relativity, which describes the large-scale space and time within which
the mass and energy move and transform.
Planck-energy particles are impossible to study at particle accelerators because they
have such high energies—about 1016 TeV. The Fermilab Holometer will study Planck-scale
physics indirectly by detecting directionally coherent quantum noise in spacetime position.
With collaborators from the gravitational-wave community, Fermilab is developing this
new experimental capability using intense, ultra-stable laser cavities and interferometers.
The Holometer will start taking data in late 2012 and will run for several years.
The target precision of the Holometer is set by the Planckian amplitude of predicted
"holographic noise" in spacetime. If holographic noise exists, it causes the difference of
position compared in two different directions to wander randomly, by about a Planck length
every Planck time. Although the Planck length itself is far too small to see directly, the
effect of the accumulated wandering over the light crossing time of the 40-meter apparatus—a few attometers in a fraction of a microsecond—can be detected. The holometer will
find out whether or not such noise exists in nature. If it does, it will be our first experimental
glimpse beyond spacetime as we know it.