From Symmetry: “Dark matter decoys”

04/07/20
Evelyn Lamb

Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

The ADMX experiment trains scientists to deal with real signals—by creating fake ones.

The Axion Dark Matter Experiment searches for dark matter the way you might search for a radio station in an unfamiliar location. In a process that takes quite a bit longer than simply turning the dial, it scans across frequency bands that correspond to the possible masses of the particle they’re looking for. If they get a hint on their first pass—metaphorically, a few notes that sound like the kind of music they’d like to hear—they conduct a more thorough analysis of that frequency.

They usually do get a few hints on each pass, says University of Washington physicist Gray Rybka, co-spokesperson of ADMX. Some of this is due to random signal fluctuation. Some of it is due to leaky radio signals. (At one point it was a local religious broadcaster. “We received a message from God,” Rybka jokes.)

And some of it is actually a test: A small subset of ADMX scientists are responsible for injecting synthetic signals into the data.

A tricky signal

Dark matter, so called because it does not interact with light or other electromagnetic radiation, explains many observations about the distribution and movements of stars and galaxies. Astrophysicists estimate that it makes up 85% of the total matter of the universe, but they don’t know what it is. “Everything in our zoo of particle physics—every particle we know of—does not fit the bill,” Rybka says

The axion is one of several dark matter candidates. The particle was originally proposed in the 1970s as a potential solution to the strong CP problem in particle physics. Later, researchers saw that the particle could also explain dark matter.

“This is two for one,” says ADMX analysis team member Leanne Duffy of the US Department of Energy’s Los Alamos National Laboratory. “Not only do you solve this existing problem with the Standard Model, but you also get an excellent dark matter candidate out of it.”

Assuming dark matter axions exist, the Earth and everyone on it is traveling through a “galactic halo” that is thick with them. To touch an axion, we don’t need to do anything.

ADMX is the only one of DOE’s flagship dark matter searches looking for axions. The question is how to detect them. ADMX scientists hope to do it by converting them into particles that are much easier to detect: photons, quanta of light.

In the presence of a strong magnetic field, axions should convert into photons. ADMX creates a magnetic field and isolates waves of specific frequencies in a microwave cavity where they can record any axions-turned-photons they come across.

Passing the test

Keeping the experiment cold (less than 100 millikelvins above absolute 0) helps separate the signal from the noise by decreasing the number of background photons coming from other sources. But some still do sneak in.

To make sure the scientists are up to the task of eliminating those background signals, ADMX scientists do something that other experiments do as well—they regularly inject false signals into their data.

“There is always a part of us that is excited to see a signal because you don’t know if it’s an axion signal or an injected signal.” says Rakshya Khatiwada, a physicist at Fermilab.

When they inject synthetic signals, the team members responsible for injecting them usually reveal them after the second pass. One time in late 2018, the test proceeded further than that. Only Noah Oblath, a researcher at the Pacific Northwest National Laboratory, and one other colleague knew. “It was a little bit strange,” Oblath says. “I like generally being honest with people.”

The team proceeded with the next steps of the analysis. When the signal persisted, they had a meeting to discuss how to proceed. “Fortunately this was a teleconference, and I didn’t have any video on, so I didn’t have to worry about covering my grin or anything,” Oblath says.

They kept up the ruse this time in order to test the scientists’ reactions.

Rybka says he was doubtful. “There was nothing strange about it,” he says.

And that was the problem. The signal had been perfectly clear, and its shape was exactly what they had predicted. “When I looked at it, I said, ‘This might be too good to be true.’”

Duffy had her suspicions as well. And unlike Rybka, she had the tools to test them.

The high-resolution analysis would have exposed the injections as false immediately. But going to the high-resolution channel wasn’t part of the analysis protocol. Still, she admits, “If I hadn’t been so busy, I probably would have gone and looked at it and just not told anyone.”

On the call, the doubtful scientists couldn’t let their suspicions guide their actions. If it was a test, it was a test of their process. They began to discuss the next step: Turning the detector’s magnet off to see whether changing the magnetic field affected the signal, as they would expect if it came from a real axion.

“At that point, Gray paused and gave me a chance to reveal whether it was an injection or not,” Oblath says.

Powering the magnet down would delay the rest of the experiment, so it was time for Oblath to confess. The test had gone according to plan.

“It was a great way to test that our axion detection procedure works,” Duffy says. “But it would be nice to actually detect a real axion at some point.”

See the full article here .

Dark Matter Research

Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

LBNL LZ Dark Matter project at SURF, Lead, SD, USA

Dark Matter Background

Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

Fritz Zwicky from http:// palomarskies.blogspot.com

In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

The Vera C. Rubin Observatory currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

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Symmetry is a joint Fermilab/SLAC publication.

From Science News: “Dark matter particles won’t kill you. If they could, they would have already”

From Science News

July 25, 2019
Lisa Grossman

A lack of mysterious deaths from hypothetical ‘macros’ suggests dark matter is small and light.

STRIKETHROUGH Hypothetical dark matter particles called “macros” could stream through space and constantly bombard Earth. Some could seriously injure any unlucky humans they pass through, but a lack of mysterious deaths suggests the biggest potential macros don’t exist. NASA JPL-Caltech

The fact that no one seems to have been killed by speeding blobs of dark matter puts limits on how large and deadly these particles can be, a study posted July 18 at arXiv.org suggests.

“In the last 30 years, if someone had died of this, we would have heard of it,” says physicist Glenn Starkman of Case Western Reserve University in Cleveland.

Physicists think the invisible dark matter must exist because they can see its gravitational effects on visible matter throughout the cosmos. But no one knows what it’s actually made of. Among the leading candidates are weakly interacting massive particles, or WIMPs, but scientists have hunted for them for decades with no success (SN: 6/23/18, p. 13).

WIMPING OUT The XENON1T experiment (contained inside the large tank above, at left) reports no hint of any interactions from particles of dark matter within, despite a yearlong search.

So physicists are turning to other theoretical candidates (SN Online: 4/9/18).

EVERY AXION HAS ITS DAY Physicist Gray Rybka of the University of Washington in Seattle and colleagues have created a detector sensitive enough to potentially find hypothetical dark matter particles called axions.

Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington

Starkman and colleagues focused on macroscopic dark matter, or macros, first proposed by physicist Edward Witten in the 1980s (SN Online: 10/7/13). If they exist, macros would be made up of subatomic particles called quarks, just like ordinary matter, but combined in a way never before observed.

Theoretically, macros could have almost any size and mass. And because dark matter doesn’t interact with regular matter, there would be nothing to stop these particles from zipping around unimpeded. So Starkman — along with Case Western physicist Jagjit Singh Sidhu and physicist Robert Scherrer of Vanderbilt University in Nashville — decided to do a gut check using human flesh as a dark matter detector.

If a macro as small as a square micrometer zipped through your body at hypersonic speed, it would deposit about as much energy in your body as a typical metal bullet, the team calculated. But the damage it caused would be different from that of a bullet: A macro would heat the cylinder of tissue in its wake to about 10,000,000° Celsius — vaporizing the tissue and leaving a path of plasma.

“It’s like if you were in Star Wars, and a Jedi hit you with their lightsaber, or someone shot you with their phaser [gun],” Starkman says.

There would be nothing you could do to shield yourself from such a macro strike. Still, there’s no reason to worry, Starkman says. Considering there have been no reports of anyone suddenly suffering a mysterious lightsaber wound, the researchers concluded that if macros exist, they have to be smaller than a micrometer and heavier than about 50 kilograms.

“The odds of dying from this are less than 1 in 100 million,” Starkman says.

As wacky as this might sound, physicist Katherine Freese thought these calculations were worth doing. “This study is fun,” says Freese of the University of Michigan in Ann Arbor. “Looking for macros in already existing detectors, such as the human body, is a good idea.” Though she wasn’t involved in the macro research, she and colleagues did a similar thought experiment with WIMPs in 2012 [Physics Letters B]. “But weak interactions are so weak as to be harmless” to human bodies.

Next, Starkman and Sidhu plan to look for macro tracks in slabs of granite, which would appear as cylinders of black obsidian running straight through the rock. They’re starting with a cemetery near the Case Western campus.

See the full article here .

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From Symmetry: “The building boom”

From Symmetry

10/23/18
By Diana Kwon

Illustration by Sandbox Studio, Chicago with Ana Kova

These international projects, selected during the process to plan the future of US particle physics, are all set to come online within the next 10 years.

A mile below the surface at Sanford Underground Research Facility in South Dakota, crews are preparing to excavate more than 800,000 tons of rock. Once the massive caverns they’re creating are complete, they will install four modules that make up a giant particle detector for the Deep Underground Neutrino Experiment. DUNE, hosted by the US Department of Energy’s Fermi National Accelerator Laboratory, is an ambitious, international effort to study neutrinos—the tiny, elusive and yet most abundant matter particles in the universe.

DUNE is one of several particle physics and astrophysics projects with US participation currently under some stage of construction. These include large-scale projects, such as the construction of Mu2e, the muon-to-electron conversion experiment at Fermilab, and upgrades to the Large Hadron Collider at CERN. And they include smaller ones, such as the assembly of the LZ and SuperCDMS dark matter experiments. Together, these scientific endeavors will investigate a wide range of important concepts, including neutrino mass, the nature of dark matter and cosmic acceleration.

“In the last 10 years, there have been many facilities in the US that wound down,” says Saul Gonzalez, a program director at the National Science Foundation. “But right now we’re definitely going through a boom—it’s a very exciting time.”

A community effort

Members of the US particle physics community identified these projects through a regularly occurring study of the field called the Snowmass planning process, named after the Colorado village where some of the first such dialogs took place in the early 1980s.

After the most recent Snowmass meeting in Minneapolis in 2013, the 25-member Particle Physics Project Prioritization Panel, or P5, gathered to pinpoint the most important scientific problems in particle physics and propose a 10-year plan to take them on. “Snowmass enabled us to get the questions out there as a field,” says Steven Ritz, the University of California, Santa Cruz physicist who led the P5 panel. “But we’re also aware that budgets are constrained—so P5’s job was to prioritize them.”

P5’s report, which was published in May 2014 [PDF], outlined five key areas of study: the Higgs boson; neutrinos; dark matter; dark energy and cosmic inflation; and undiscovered particles, interactions and physical principles.

Shorter-term efforts to address questions in these areas, such as the Mu2e experiment and the Large Synoptic Survey Telescope in Chile, both already under construction, have projected start-up dates around 2020. Longer-term plans, such as DUNE and the high-luminosity upgrade to the LHC, are expected be ready for physics in the mid to latter part of the 2020s.

“If you look at the timeline, we don’t build everything at once, because of budget and resource constraints,” says Young-Kee Kim, a physicist at the University of Chicago and a former member of the High Energy Physics Advisory Panel, the advisory group that P5 reports to.

Another consideration was the importance of maintaining a continual stream of data, Ritz says. “We didn’t want to have a building boom where there was no new data for 5 or 10 years.”

Having multiple experiments at various stages of completion is important for junior scientists. “If you’re a grad student or a postdoc and you’re working on something that’s not going to have physics data until 2024, that’s kind of a problem,” says Kate Scholberg, a physicist at Duke University who was on the P5 panel.

A staggered timeline gives junior scientists the option of working on a project like DUNE, where they can contribute to research and development, then switch to another experiment where data is available for analysis.

“Being in a construction phase does have some short-term challenges, but it’s really important as an investment for the future,” Scholberg says. “Because if you stop constructing, then eventually you’re not going to have any more data.”

Global contributions

The United States is not undertaking these experiments alone. “Every experiment is really an international collaboration,” Gonzalez says.

The DUNE collaboration, for example, already includes more than 1100 scientists from 32 countries and counting. And although the Long-Baseline Neutrino Facility, the future home of DUNE, will be in the US, researchers are currently building prototype detectors for the project at the CERN research center in Europe.

More than 1700 US scientists participate in research at the LHC at CERN; many of them are currently working on future upgrades to the accelerator and its experiments. Although LSST will operate on a mountaintop in Chile, its gigantic digital camera is being assembled at SLAC National Accelerator Laboratory using parts from institutions elsewhere in the United States and in France, Germany and the UK.

Smaller experiments also have a global presence. Dark matter experiment SuperCDMS, a 23-institution collaboration led by SLAC, will be located at SNOLAB underground laboratory in Ontario and has members in Canada, France and India.

People with specialized expertise are needed to build the apparatus for these experiments. For example, Fermilab’s Proton Improvement Plan-II, a project to upgrade the lab’s particle accelerator complex to provide protons beams for DUNE, requires individuals with expertise in superconducting radio-frequency technology. “We’re tapping into the SRF expertise around the world to build this,” says Michael Procario, the Director of the Facilities Division in the Office of High Energy Physics within DOE’s Office of Science.

These DOE-supported endeavors—and the theory and data analysis that go along with them—will likely keep scientists busy until 2035 and beyond. “All the experiments are going to give us definitive answers. Even a null result will give us important information,” Ritz says. “I think it’s a great time for physics.”

The experiments:

Muon g-2

This experiment will measure the magnetic moment of a muon, a subatomic particle 200 times more massive than an electron, in an attempt to identify physics beyond the Standard Model.

Location: Fermilab, Illinois, United States
Lead institution: Fermilab
Currently running

Axion Dark Matter Experiment (ADMX-Gen 2)

Physicists are probing for signs of axions, hypothetical low-mass dark matter particles at the University of Washington-based ADMX detector.

Location: University of Washington, United States
Lead institution: University of Washington
Currently running

Physicists will use Mu2e to search for the never-observed direct conversion of a muon into an electron, a process predicted by theories beyond the Standard Model.

Location: Fermilab, Illinois, United States
Lead institution: Fermilab
Scheduled start-up: 2020

LUX-ZEPLIN (LZ)

A liquified xenon detector surrounded by 70,000 gallons of water will be located more than 4000 feet underground at the Sanford Underground Research Facility, where researchers will hunt for interactions between matter and dark matter.

Location: Sanford Lab, South Dakota, United States
Lead institution: Berkeley Lab
Scheduled start-up: 2020

Dark Energy Spectroscopic Instrument (DESI)

LBNL/DESI Dark Energy Spectroscopic Instrument for the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, Ariz, USA

NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

Scientists will measure the effect of dark energy on cosmic expansion at the 4-meter Mayall Telescope at Kitt Peak National Observatory in Arizona.

Location: Kitt Peak National Observatory, Arizona, United States
Lead institution: Berkeley Lab
Scheduled start-up: 2021

Super Cyogenic Dark Matter Search (SuperCDMS)

SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

SLAC SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

Physicists will hunt for dark matter particles with a cryogenic germanium detector located deep underground at SNOLAB in Canada.

Location: SNOLAB, Ontario, Canada
Lead institution: SLAC
Scheduled start-up: Early 2020s

Large Synoptic Survey Telescope (LSST)

LSST

LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

The 8-meter Large Synoptic Survey Telescope, situated in northern Chile, will observe the whole accessible sky hundreds of times over 10 years to produce the deepest, widest image of the universe to date. This will allow physicists to probe questions about dark energy, dark matter, galaxy formation and more.

Location: Cerro Pachon, Chile
Lead institution: SLAC
Scheduled start-up: Early 2020s

Proton Improvement Pla-II (PIP-II)

Upgrades to the Fermilab accelerator complex, including the construction of a 175-meter-long superconducting linear particle accelerator, will create the high-intensity proton beam that will produce beams of neutrinos for DUNE.

Location: Fermilab, Illinois, United States
Lead institution: Fermilab
Scheduled start-up: mid-2020s

Deep Underground Neutrino Experiment (DUNE)

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

Scientists will send the world’s most powerful beam of neutrinos through two sets of detectors separated by 800 miles—one at the source of the beam at Fermilab in Illinois and the other at Sanford Underground Research Facility in South Dakota—to help scientists address fundamental concepts in particle physics, such as neutrino mass, matter-antimatter asymmetry, proton decay and black hole formation.

Location: Fermilab, Illinois and Sanford Lab, South Dakota, United States
Lead institution: Fermilab
Scheduled partial start-up (with two detector modules): 2026

High-Luminosity LHC (HL-LHC)

LHC

An upgrade to CERN’s Large Hadron Collider will increase its luminosity—the number of collisions it can achieve—by a factor of 10. More collisions means more data and a higher probability of spotting rare events. The LHC experiments will receive upgrades to manage the higher collision frequency.

Location: CERN, near Geneva, Switzerland
Lead institution: CERN
Scheduled start-up: 2026

See the full article here .

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Symmetry is a joint Fermilab/SLAC publication.

From Symmetry: “Looking for dark matter using quantum technology”

From Symmetry

10/16/18
Jim Daley

Photo by Reidar Hahn, Fermilab

For decades, physicists have been searching for dark matter, which doesn’t emit light but appears to make up the vast majority of matter in the universe. Several theoretical particles have been proposed as dark matter candidates, including weakly interacting massive particles—called WIMPs—and axions.

Fermilab’s Aaron Chou is leading a multi-institutional consortium to apply the techniques of quantum metrology to the problem of detecting axion dark matter. The project, which brings together scientists at Fermilab, the National Institute of Standards and Technology, the University of Chicago, University of Colorado and Yale University, was recently awarded $2.1 million over two years through the Department of Energy’s Quantum Information Science-Enabled Discovery (QuantISED) program, which seeks to advance science through quantum-based technologies.

If the scientists succeed, the discovery could solve several cosmological mysteries at once.

“It’d be the first time that anybody had found any direct evidence of the existence of dark matter,” says Fermilab’s Daniel Bowring, whose work on this effort is supported by a DOE Office of Science Early Career Research Award. “Right now, we’re inferring the existence of dark matter from the behavior of astrophysical bodies. There’s very good evidence for the existence of dark matter based on those observations, but nobody’s found a particle yet.”

The axion search

Finding an axion would also resolve a discrepancy in particle physics called the strong CP problem. Particles and antiparticles are “symmetrical” to one another: They exhibit mirror-image behavior in terms of electrical charge and other properties.

The strong force—one of the four fundamental forces of nature—obeys CP symmetry. But there’s no reason, at least in the Standard Model of physics, why it should. The axion was first proposed to explain why it does.

Finding an axion is a delicate endeavor, even compared to other searches for dark matter. An axion’s mass is vanishingly low—somewhere between a millionth and a thousandth of an electronvolt. By comparison, the mass of a WIMP is expected to be between a trillion and quadrillion times more massive—in the range of a billion electronvolts—which means they’re heavy enough that they could occasionally produce a signal by bumping into the nuclei of other atoms. To look for WIMPs, scientists fill detectors with liquid xenon (for example, in the LUX-ZEPLIN dark matter experiment at Sanford Underground Research Facility in South Dakota) or germanium crystals (in the SuperCDMS Soudan experiment in Minnesota [not current, now at SNOLAB a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario]) and look for indications of such a collision.

UC Santa Barbara postdoctoral scientist Sally Shaw stands with one of the four large acrylic tanks fabricated for the LZ dark matter experiment’s outer detector.

“You can’t do that with axions because they’re so light,” Bowring says. “So the way that we look for axions is fundamentally different from the way we look for more massive particles.”

When an axion encounters a strong magnetic field, it should—at least in theory—produce a single microwave-frequency photon, a particle of light. By detecting that photon, scientists should be able to confirm the existence of axions. The Axion Dark Matter eXperiment, ADMX, at the University of Washington and the HAYSTAC experiment at Yale are attempting to do just that.

ADMX Axion Dark Matter Experiment at the University of Washington

Yale HAYSTAC axion dark matter experiment

Yale Haloscope Sensitive To Axion CDM -HAYSTAC Experiment a microwave cavity search for cold dark matter (CDM)

Those experiments use a strong superconducting magnet to convert axions into photons in a microwave cavity. The cavity can be tuned to different resonant frequencies to boost the interaction between the photon field and the axions. A microwave receiver then detects the signal of photons resulting from the interaction. The signal is fed through an amplifier, and scientists look for that amplified signal.

“But there is a fundamental quantum limit to how good an amplifier can be,” Bowring says.

Photons are ubiquitous, which introduces a high degree of noise that must be filtered from the signal detected in the microwave cavity. And at higher resonant frequencies, the signal-to-noise ratio gets progressively worse.

Both Bowring and Chou are exploring how to use technology developed for quantum computing and information processing to get around this problem. Instead of amplifying the signal and sorting it from the noise, they aim to develop new kinds of axion detectors that will count photons very precisely—with qubits.

Aaron Chou works on an FNAL experiment that uses qubits to look for direct evidence of dark matter in the form of axions. Photo by Reidar Hahn, Fermilab

The qubit advantage

In a quantum computer, information is stored in qubits, or quantum bits.

A qubit can be constructed from a single subatomic particle, like an electron or a photon, or from engineered metamaterials such as superconducting artificial atoms. The computer’s design takes advantage of the particles’ two-state quantum systems, such as an electron’s spin (up or down) or a photon’s polarization (vertical or horizontal). And unlike classical computer bits, which have one of only two states (one or zero), qubits can also exist in a quantum superposition, a kind of addition of the particle’s two quantum states. This feature has myriad potential applications in quantum computing that physicists are just starting to explore.

In the search for axions, Bowring and Chou are using qubits. For a traditional antenna-based detector to notice a photon produced by an axion, it must absorb the photon, destroying it in the process. A qubit, on the other hand, can interact with the photon many times without annihilating it. Because of this, the qubit-based detector will give the scientists a much higher chance of spotting dark matter.

“The reason we want to use quantum technology is that the quantum computing community has already had to develop these devices that can manipulate a single microwave photon,” Chou says. “We’re kind of doing the same thing, except a single photon of information that’s stored inside this container is not something that somebody put in there as part of the computation. It’s something that the dark matter put in there.”

Light reflection

Using a qubit to detect an axion-produced photon brings its own set of challenges to the project. In many quantum computers, qubits are stored in cavities made of superconducting materials. The superconductor has highly reflective walls that effectively trap a photon long enough to perform computations with it. But you can’t use a superconductor around high-powered magnets like the ones used in Bowring and Chou’s experiments.

“The superconductor is just ruined by magnets,” Chou says. Currently, they’re using copper as an ersatz reflector.

“But the problem is, at these frequencies the copper will store a single photon for only 10,000 bounces instead of, say, a billion bounces off the mirrors,” he says. “So we don’t get to keep these photons around for quite as long before they get absorbed.”

And that means that they don’t stick around long enough to be picked up as a signal. So the researchers are developing another, better photon container.

“We’re trying to make a cavity out of very low-loss crystals,” Chou says.

Think of a windowpane. As light hits it, some photons will bounce off it, and others will pass through. Place another piece of glass behind the first. Some of the photons that passed through the first will bounce off the second, and others will pass through both pieces of glass. Add a third layer of glass, and a fourth, and so on.

“Even though each individual layer is not that reflective by itself, the sum of the reflections from all the layers gives you a pretty good reflection in the end,” Chou says. “We want to make a material that traps light for a long time.”

Bowring sees the use of quantum computing technology in the search for dark matter as an opportunity to reach across the boundaries that often keep different disciplines apart.

“You might ask why Fermilab would want to get involved in quantum technology if it’s a particle physics laboratory,” he says. “The answer is, at least in part, that quantum technology lets us do particle physics better. It makes sense to lower those barriers.”

See the full article here .

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Symmetry is a joint Fermilab/SLAC publication.

From Symmetry: “The origins of dark matter”

From Symmetry

11/08/16 [Just brought forward in social media]
Matthew R. Francis

Artwork by Sandbox Studio, Chicago with Corinne Mucha

[Because this article is well over a year old, I have updated it with Dark Matter experiments and also included a section on the origins of Dark Matter research by Vera Rubin and Fritz Zicky.]

Dark Matter Research

Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

Milky Way Dark Matter Halo Credit ESO L. Calçada

Dark matter halo. Image credit: Virgo consortium / A. Amblard / ESA

Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

Edelweiss Dark Matter Experiment, located at the Modane Underground Laboratory in France

Transitions are everywhere we look. Water freezes, melts, or boils; chemical bonds break and form to make new substances out of different arrangements of atoms. The universe itself went through major transitions in early times. New particles were created and destroyed continually until things cooled enough to let them survive. Those particles include ones we know about, such as the Higgs boson or the top quark. But they could also include dark matter, invisible particles which we presently know only because of their gravitational effects. In cosmic terms, dark matter particles could be a “thermal relic,” forged in the hot early universe and then left behind during the transitions to more moderate later eras. One of these transitions, known as “freeze-out,” changed the nature of the whole universe.

The hot cosmic freezer

On average, today’s universe is a pretty boring place. If you pick a random spot in the cosmos, it’s far more likely to be in intergalactic space than, say, the heart of a star or even inside an alien solar system. That spot is probably cold, dark and quiet. The same wasn’t true for a random spot shortly after the Big Bang. “The universe was so hot that particles were being produced from photons smashing into other photons, of photons hitting electrons, and electrons hitting positrons and producing these very heavy particles,” says Matthew Buckley of Rutgers University. The entire cosmos was a particle-smashing party, but parties aren’t meant to last. This one lasted only a trillionth of a second. After that came the cosmic freeze-out. During the freeze-out, the universe expanded and cooled enough for particles to collide far less frequently and catastrophically. “One of these massive particles floating through the universe is finding fewer and fewer antimatter versions of itself to collide with and annihilate,” Buckley says. “Eventually the universe would get large enough and cold enough that the rate of production and the rate of annihilation basically goes to zero, and you just a relic abundance, these few particles that are floating out there lonely in space.” Many physicists think dark matter is a thermal relic, created in huge numbers in before the cosmos was a half-second old and lingering today because it barely interacts with any other particle.

A WIMPy miracle

One reason to think of dark matter as a thermal relic is an interesting coincidence known as the “WIMP miracle.” WIMP stands for “weakly-interacting massive particle,” and WIMPs are the most widely accepted candidates for dark matter. Theory says WIMPs are likely heavier than protons and interact via the weak force, or at least interactions related to the weak force. The last bit is important, because freeze-out for a specific particle depends on what forces affect it and the mass of the particle. Thermal relics made by the weak force were born early in the universe’s history because particles need to be jammed in tight for the weak force, which only works across short distances, to be a factor.

“If dark matter is a thermal relic, you can calculate how big the interaction [between dark matter particles] needs to be,” Buckley says. Both the primordial light known as the cosmic microwave background [CMB] and the behavior of galaxies tell us that most dark matter must be slow-moving (“cold” in the language of physics).

That means interactions between dark matter particles must be low in strength. “Through what is perhaps a very deep fact about the universe,” Buckley says, “that interaction turns out to be the strength of what we know as the weak nuclear force.” That’s the WIMP miracle: The numbers are perfect to make just the right amount of WIMPy matter. The big catch, though, is that experiments haven’t found any WIMPs yet.

It’s too soon to say WIMPs don’t exist, but it does rule out some of the simpler theoretical predictions about them.

Ultimately, the WIMP miracle could just be a coincidence. Instead of the weak force, dark matter could involve a new force of nature that doesn’t affect ordinary matter strongly enough to detect. In that scenario, says Jessie Shelton of the University of Illinois at Urbana-Champaign, “you could have thermal freeze-out, but the freeze-out is of dark matter to some other dark field instead of [something in] the Standard Model.” In that scenario, dark matter would still be a thermal relic but not a WIMP. For Shelton, Buckley, and many other physicists, the dark matter search is still full of possibilities. “We have really compelling reasons to look for thermal WIMPs,” Shelton says. “It’s worth remembering that this is only one tiny corner of a much broader space of possibilities.”

Well, what about AXIONS?

Origins of Dark Matter Research

Vera Rubin measuring spectra (Emilio Segre Visual Archives AIP SPL)

Vera Florence Cooper Rubin was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted angular motion of galaxies and the observed motion, by studying galactic rotation curves. This phenomenon became known as the galaxy rotation problem, and was evidence of the existence of dark matter. Although initially met with skepticism, Rubin’s results were confirmed over subsequent decades. Her legacy was described by The New York Times as “ushering in a Copernican-scale change” in cosmological theory.

Fritz Zwicky, the Father of Dark Matter research.No image credit after long search

Fritz Zwicky, a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy. In 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter, describing it as “dunkle Materie”

There was no Nobel award for either Rubin or Zwicky.

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Symmetry is a joint Fermilab/SLAC publication.

From Symmetry: “ADMX brings new excitement to dark matter search”

Symmetry

04/09/18

Science contact
Andrew Sonnenschein
Fermilab
sonnenschein@fnal.gov
630-840-2883

Gray Rybka,
ADMX co-spokesperson
University of Washington
grybka@uw.edu
206-543-2797

Media contact
Andre Salles
Fermilab Office of Communication,
asalles@fnal.gov
630-840-6733

James Urton
University of Washington
jurton@uw.edu
206-543-2580

ADMX collaboration

Scientists on the Axion Dark Matter Experiment have demonstrated technology that could lead to the discovery of theoretical light dark matter particles called axions.

Forty years ago, scientists theorized a new kind of low-mass particle that could solve one of the enduring mysteries of nature: what dark matter is made of. Now a new chapter in the search for that particle, the axion, has begun.

This week, the Axion Dark Matter Experiment (ADMX) unveiled a new result (published in Physical Review Letters) that places it in a category of one: It is the world’s first and only experiment to have achieved the necessary sensitivity to “hear” the telltale signs of these theoretical particles. This technological breakthrough is the result of more than 30 years of research and development, with the latest piece of the puzzle coming in the form of a quantum-enabled device that allows ADMX to listen for axions more closely than any experiment ever built.

ADMX is managed by the US Department of Energy’s Fermi National Accelerator Laboratory [FNAL] and located at the University of Washington. This new result, the first from the second-generation run of ADMX, sets limits on a small range of frequencies where axions may be hiding, and sets the stage for a wider search in the coming years.

“This result signals the start of the true hunt for axions,” says Fermilab’s Andrew Sonnenschein, the operations manager for ADMX. “If dark matter axions exist within the frequency band we will be probing for the next few years, then it’s only a matter of time before we find them.”

One theory suggests that galaxies are held together by a vast number of axions, low-mass particles that are almost invisible to detection as they stream through the cosmos. Efforts in the 1980s to find these particles, named by theorist Frank Wilczek, currently of the Massachusetts Institute of Technology, were unsuccessful, showing that their detection would be extremely challenging.

ADMX is an axion haloscope—essentially a large, low-noise, radio receiver, which scientists tune to different frequencies and listen to find the axion signal frequency. Axions almost never interact with matter, but with the aid of a strong magnetic field and a cold, dark, properly tuned, reflective box, ADMX can “hear” photons created when axions convert into electromagnetic waves inside the detector.

“If you think of an AM radio, it’s exactly like that,” says Gray Rybka, co-spokesperson for ADMX and assistant professor at the University of Washington. “We’ve built a radio that looks for a radio station, but we don’t know its frequency. We turn the knob slowly while listening. Ideally we will hear a tone when the frequency is right.”

This detection method, which might make the “invisible axion” visible, was invented by Pierre Sikivie of the University of Florida in 1983. Pioneering experiments and analyses by a collaboration of Fermilab, the University of Rochester and Brookhaven National Laboratory, as well as scientists at the University of Florida, demonstrated the practicality of the experiment. This led to the construction in the late 1990s of a large-scale detector at Lawrence Livermore National Laboratory that is the basis of the current ADMX.

It was only recently, however, that the ADMX team has been able to deploy superconducting quantum amplifiers to their full potential, enabling the experiment to reach unprecedented sensitivity. Previous runs of ADMX were stymied by background noise generated by thermal radiation and the machine’s own electronics.

Fixing thermal radiation noise is easy: A refrigeration system cools the detector down to 0.1 Kelvin (roughly -460 degrees Fahrenheit). But eliminating the noise from electronics proved more difficult. The first runs of ADMX used standard transistor amplifiers, but then ADMX scientists connected with John Clarke, a professor at the University of California Berkeley, who developed a quantum-limited amplifier for the experiment. This much quieter technology, combined with the refrigeration unit, reduces the noise by a significant enough level that the signal, should ADMX discover one, will come through loud and clear.

“The initial versions of this experiment, with transistor-based amplifiers, would have taken hundreds of years to scan the most likely range of axion masses. With the new superconducting detectors, we can search the same range on timescales of only a few years,” says Gianpaolo Carosi, co-spokesperson for ADMX and scientist at Lawrence Livermore National Laboratory.

“This result plants a flag,” says Leslie Rosenberg, professor at the University of Washington and chief scientist for ADMX. “It tells the world that we have the sensitivity, and have a very good shot at finding the axion. No new technology is needed. We don’t need a miracle anymore, we just need the time.”

ADMX will now test millions of frequencies at this level of sensitivity. If axions were found, it would be a major discovery that could explain not only dark matter, but other lingering mysteries of the universe. If ADMX does not find axions, that may force theorists to devise new solutions to those riddles.

“A discovery could come at any time over the next few years,” says scientist Aaron Chou of Fermilab. “It’s been a long road getting to this point, but we’re about to begin the most exciting time in this ongoing search for axions.”

Editor’s note: This article is based on a Fermilab press release.

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From UC Berkeley: “MACHOs are Dead. WIMPs are a No-Show. Say Hello to SIMPs”

UC Berkeley

December 4, 2017
Robert Sanders
rlsanders@berkeley.edu

The intensive, worldwide search for dark matter, the missing mass in the universe, has so far failed to find an abundance of dark, massive stars or scads of strange new weakly interacting particles, but a new candidate is slowly gaining followers and observational support.

Fundamental structures of a pion (left) and a proposed SIMP (strongly interacting massive particle). Pions are composed of an up quark and a down antiquark, with a gluon (g) holding them together. A SIMP would be composed of a quark and an antiquark held together by an unknown type of gluon (G). (Kavli IPMU graphic)

Called SIMPs – strongly interacting massive particles – they were proposed three years ago by UC Berkeley theoretical physicist Hitoshi Murayama, a professor of physics and director of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, and former UC Berkeley postdoc Yonit Hochberg, now at Hebrew University in Israel.

Murayama says that recent observations of a nearby galactic pile-up [Nature] could be evidence for the existence of SIMPs, and he anticipates that future particle physics experiments will discover one of them.

Murayama discussed his latest theoretical ideas about SIMPs and how the colliding galaxies support the theory in an invited talk Dec. 4 at the 29th Texas Symposium on Relativistic Astrophysics in Cape Town, South Africa.

Astronomers have calculated that dark matter, while invisible, makes up about 85 percent of the mass of the universe. The solidest evidence for its existence is the motion of stars inside galaxies: Without an unseen blob of dark matter, galaxies would fly apart. In some galaxies, the visible stars are so rare that dark matter makes up 99.9 percent of the mass of the galaxy.

Theorists first thought that this invisible matter was just normal matter too dim to see: failed stars called brown dwarfs, burned-out stars or black holes. Yet so-called massive compact halo objects – MACHOs – eluded discovery, and earlier this year a survey of the Andromeda galaxy by the Subaru Telescope basically ruled out any significant undiscovered population of black holes.

NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

The researchers searched for black holes left over from the very early universe, so-called primordial black holes, by looking for sudden brightenings produced when they pass in front of background stars and act like a weak lens. They found exactly one – too few to contribute significantly to the mass of the galaxy.

This Hubble Space Telescope image of the galaxy cluster Abell 3827 shows the ongoing collision of four bright galaxies and one faint central galaxy, as well as foreground stars in our Milky Way galaxy and galaxies behind the cluster (Arc B and Lensed image A) that are distorted because of normal and dark matter within the cluster. SIMPs could explain why the dark matter, unseen but detectable because of the lensing, lags behind the normal matter in the collision.

“That study pretty much eliminated the possibility of MACHOs; I would say it is pretty much gone,” Murayama said.

WIMPs — weakly interacting massive particles — have fared no better, despite being the focus of researchers’ attention for several decades. They should be relatively large – about 100 times heavier than the proton – and interact so rarely with one another that they are termed “weakly” interacting. They were thought to interact more frequently with normal matter through gravity, helping to attract normal matter into clumps that grow into galaxies and eventually spawn stars.

SIMPs interact with themselves, but not others.

SIMPs, like WIMPs and MACHOs, theoretically would have been produced in large quantities early in the history of the universe and since have cooled to the average cosmic temperature. But unlike WIMPs, SIMPs are theorized to interact strongly with themselves via gravity but very weakly with normal matter. One possibility proposed by Murayama is that a SIMP is a new combination of quarks, which are the fundamental components of particles like the proton and neutron, called baryons. Whereas protons and neutrons are composed of three quarks, a SIMP would be more like a pion in containing only two: a quark and an antiquark.

Conventional WIMP theories predict that dark matter particles rarely interact. Murayama and Hochberg predict that dark matter SIMPs, comprised of a quark and an antiquark, would collide and interact, producing noticeable effects when the dark matter in galaxies collide. (Kavli IPMU graphic)

The SIMP would be smaller than a WIMP, with a size or cross section like that of an atomic nucleus, which implies there are more of them than there would be WIMPs. Larger numbers would mean that, despite their weak interaction with normal matter – primarily by scattering off of it, as opposed to merging with or decaying into normal matter – they would still leave a fingerprint on normal matter, Murayama said.

He sees such a fingerprint in four colliding galaxies within the Abell 3827 cluster, where, surprisingly, the dark matter appears to lag behind the visible matter. This could be explained, he said, by interactions between the dark matter in each galaxy that slows down the merger of dark matter but not that of normal matter, basically stars.

“One way to understand why the dark matter is lagging behind the luminous matter is that the dark matter particles actually have finite size, they scatter against each other, so when they want to move toward the rest of the system they get pushed back,” Murayama said. “This would explain the observation. That is the kind of thing predicted by my theory of dark matter being a bound state of new kind of quarks.”

SIMPs also overcome a major failing of WIMP theory: the ability to explain the distribution of dark matter in small galaxies.

Conventional WIMP theories predict a highly peaked distribution, or cusp, of dark matter in a small area in the center of every galaxy. SIMP theory predicts a spread of dark matter in the center, which is more typical of dwarf galaxies. (Kavli IPMU graphic based on NASA, STScI images)

“There has been this longstanding puzzle: If you look at dwarf galaxies, which are very small with rather few stars, they are really dominated by dark matter. And if you go through numerical simulations of how dark matter clumps together, they always predict that there is a huge concentration towards the center. A cusp,” Murayama said. “But observations seem to suggest that concentration is flatter: a core instead of a cusp. The core/cusp problem has been considered one of the major issues with dark matter that doesn’t interact other than by gravity. But if dark matter has a finite size, like a SIMP, the particles can go ‘clink’ and disperse themselves, and that would actually flatten out the mass profile toward the center. That is another piece of ‘evidence’ for this kind of theoretical idea.”

Ongoing searches for WIMPs and axions

Ground-based experiments to look for SIMPs are being planned, mostly at accelerators like the Large Hadron Collider at CERN in Geneva, where physicists are always looking for unknown particles that fit new predictions.

LHC

Another experiment at the planned International Linear Collider in Japan could also be used to look for SIMPs.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

As Murayama and his colleagues refine the theory of SIMPs and look for ways to find them, the search for WIMPs continues. The Large Underground Xenon (LUX) dark matter experiment in an underground mine in South Dakota has set stringent limits on what a WIMP can look like, and an upgraded experiment called LZ will push those limits further. Daniel McKinsey, a UC Berkeley professor of physics, is one of the co-spokespersons for this experiment, working closely with Lawrence Berkeley National Laboratory, where Murayama is a faculty senior scientist.

Lux Dark Matter 2 at SURF, Lead, SD, USA

Physicists are also seeking other dark matter candidates that are not WIMPs. UC Berkeley faculty are involved in two experiments looking for a hypothetical particle called an axion, which may fit the requirements for dark matter. The Cosmic Axion Spin-Precession Experiment (CASPEr), led by Dmitry Budker, a professor emeritus of physics who is now at the University of Mainz in Germany, and theoretician Surjeet Rajendran, a UC Berkeley professor of physics, is planning to look for perturbations in nuclear spin caused by an axion field. Karl van Bibber, a professor of nuclear engineering, plays a key role in the (ADMX-HF), which seeks to detect axions inside a microwave cavity within a strong magnetic field as they convert to photons.

“Of course we shouldn’t abandon looking for WIMPs,” Murayama said, “but the experimental limits are getting really, really important. Once you get to the level of measurement, where we will be in the near future, even neutrinos end up being the background to the experiment, which is unimaginable.”

Neutrinos interact so rarely with normal matter that an estimated 100 trillion fly through our bodies every second without our noticing, something that makes them extremely difficult to detect.

“The community consensus is kind of, we don’t know how far we need to go, but at least we need to get down to this level,” he added. “But because there are definitely no signs of WIMPs appearing, people are starting to think more broadly these days. Let’s stop and think about it again.”

Murayama’s research is supported by the U.S. Department of Energy, National Science Foundation and Japanese Ministry of Education, Culture, Sports, Science and Technology. Murayama is also collaborating with Eric Kuflik of Hebrew University, Tomer Volansky of Tel Aviv University and Jay Wacker of Quora Inc. in Mountain View, California, and Stanford University.

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Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.