UC Irvine Center for Cosmology

Can something the size of a few washing machines find the biggest thing in the Universe?

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UCI physicists have designed and built a new particle detector called FASER that could lift the veil on one of the Universe’s most enduring mysteries.

The FASER particle detector, built in large part out of spare parts from other experiments at CERN like ATLAS, could fit comfortably inside a laundromat.  Picture Credit: CERN

When Savannah Shively awoke on the morning of October 5th — it was a Monday — she knew that that day was going to be a bit different than the day before. Chains of days can pass without anything memorable happening, particularly when a pandemic makes “last month” and “last Wednesday” have almost the same meaning. But for Shively, October 5th stands out, because on that day she traveled almost 300 feet underground to a place where scientists try to find out, among other things, how the Universe was made.

When she awoke on that Monday, Shively, who’s a Ph.D. student in the UCI Department of Physics & Astronomy, awoke in an apartment in France. She’d just moved to the apartment from an old one; she moved not because she wanted to, but because her landlord at her old place told her they needed the home again because of a pandemic-related job loss. That first apartment, when she moved into it back in February after flying from the United States to France, didn’t have a washing machine, and for months Shively washed her clothes in the sink. She then got a washing machine, but then found out that she had to vacate, and, again, in her new place, she was without a washing machine.

Shively lost her washing machine, but she gained something else: Blancblanc. French for “Whitewhite,” Blancblanc‘s the name of a cat who would visit every day so Shively could pet him. Blancblanc would crawl onto Shively’s lap, lay on his back, look at Shively and wait for her to pet his white fur. “He’s helped with not making it feel so lonesome,” said Shively, who moved to France by herself on the eve of the pandemic. “At first I didn’t know his name, so I just called him the Snuggle Lord, because he always wants to be pet.”

The descent

But Blancblanc wasn’t with Shively on October 5th, the day she went underground. On that day, she walked for half an hour to a bus stop, and after a ten-minute ride she stood on the grounds of the Center for European Nuclear Research, which straddles the French-Swiss border, and which is where Shively’s been working all this year. She faced a non-descript building, and went inside and got into an elevator big enough to fit five people with those people staying about six feet away from one another. There were pandemic stickers on the ground that helped her and her group keep apart from one another.

Standing in formation, she began her descent.

“It shows you the meters on this little screen instead of floors because there’s really only the top floor and the bottom floor,” Shively said. “I was really quite excited, and I was trying very hard not to think about being 80 meters underground, which makes me considerably more nervous than being the same amount of space above ground.” It didn’t help that she had to wear a waist belt that held a gas mask, which would give her about 30 minutes of oxygen if something happened to the air supply.

The elevator stopped, and Shively and her group stepped into a concrete tube, one that looks like it could hold a subway train. But it holds something that moves a little faster: the Large Hadron Collider (LHC), which, as the largest machine in the world, smashes two beams of subatomic particles together after those beams zip around a nearly-17-mile-long tunnel at close to the speed of light. If you’d been there, you’d have seen a cylindrical machine sitting in front of you in the middle of the tube. Looking left and then right, you’d see that machine stretching away on either side, and then slowly disappearing around the bends of the tube.

But Shively wasn’t there for the LHC, at least not directly. Her stop was a short walk through the tube to a side-tunnel that, like a minor subway line, sits tangential to the main LHC tube. Back in 2017, that side-tunnel caught the eye of UCI theoretical particle physicist Jonathan Feng, who’s one of Shively’s doctoral advisors. It caught his eye because Feng is one of many physicists who want to find evidence for the existence of what’s become the grand prix of his field: dark matter. Nobody’s ever detected dark matter in a lab before, but physicists suspect that it comprises most of the mass of the cosmos. They suspect this because, without something like dark matter, there isn’t enough mass in the visible Universe — and, thus, not enough gravity — to explain the spin of things like entire galaxies.

Feng and his team think they might be able to detect dark matter with a machine that’s only a little longer than a row of washing machines. It’s a machine they’re calling FASER (it’s short for ForwArd Search ExpeRiment — but, really, the team just wanted to name it after the ray gun from “Star Trek”).

“We have three magnets, two of them are a meter long,” said Dave Casper, an experimental particle physicist in Physics & Astronomy who helped lead the effort to design FASER after Feng and his team proposed the idea, and who also advises Shively. “And the third is a meter-and-a-half, and they more or less line up in a row with small gaps between them. So, if you take three-and-a-half meters worth of magnets and a meter or two of detectors that go in between and at either end, it’s about roughly five meters long.”

So, about five washing machines.

By building FASER in the side-tunnel, Feng and his team hope to detect new particles that emerge when LHC collisions happen, but which, until now, passed unnoticed through other detectors’ blind spots. FASER, like an extra pair of eyes, will sit and watch those blind spots for renegade particles, some of which might come from dark matter.

“We might have been missing some integral sign all along,” said Hitoshi Murayama, a particle physicist at UC Berkeley who’s not involved with Feng’s work. “I think FASER’s a brilliant idea.”

A bird’s-eye view of the LHC tube where it intersects with the FASER tube. Credit: CERN Geographical Information System

New particles

As far as physicists know, there’re four forces that, like a washing machine’s buttons, make the Universe work the way it does. The worn labels on the buttons might read like this: The Strong Force, The Electroweak Force, The Electromagnetic Force and Gravity. If you put in four coins, you can select all four buttons, and you get the Super Wash cycle that spins the Universe we have into life, where gravity keeps you stuck on Earth without jettisoning you into space, and where the electromagnetic force makes light and gives us the colors of the world — and Blancblanc his name. Each of the forces is carried by a particle — like light’s photon, which carries the electromagnetic force — that interacts with the Universe in some way.

The strong force keeps the neutrons and protons that make the nuclei of atoms stick together, and “it’s important because otherwise the positive charges of the protons would push each other apart — but this is a force that sticks them together that’s even stronger,” said Tim Tait, who’s a theoretical particle physicist and who’s the chair of Physics & Astronomy. “That’s why we call it the strong force, and it’s necessary really for us to have any kind of element that’s heavier than hydrogen.” And the electroweak force, Tait explained, is responsible for radioactivity, “like when uranium decays, the process that powers nuclear reactors is through the weak force,” he said. Tait explained that without the electroweak force, there wouldn’t even be atomic nuclei. “In some ways it would be a dull Universe,” he said. “Instead of having all this structure, like us and the Earth and the trees and everything, we would actually just have this sort of cloud of protons and neutrons that wouldn’t do very much with each other.”

Definitely worth the extra coins for a Super Wash.

One day in 2017, Tait walked into Feng’s office and found him and three postdocs — Iftah Galon, Felix King and Sebastian Trojanowski — looking at LHC blueprints, trying to see if there was a place far enough away from its collisions, and where they could put FASER. What they spotted was the tunnel that Shively ventured to on October 5th, five meters from LHC — and, most importantly, in sight of LHC’s colliding beams.

Back then, Feng’s team didn’t yet have the money to build FASER, but in just over a year, he was able to secure enough funding from the Heising-Simons Foundation and the Simons Foundation — about 2 million dollars — along with support from CERN to make FASER a reality. That, and a donation of $25,000 from two UCI alumni, Nancy and Corwin Evans, gave Feng the funding he needed to send Shively to CERN to work on FASER for her doctoral research, where she’s helping to build the detector and run tests to make sure the data readings from FASER are accurate.

“It went from being an idea on the whiteboard in Jonathan’s office to being an approved and designed experiment in less than two years,” said Casper. “It took 20 years to build ATLAS — we’re really in a lot of ways breaking the mold.”

ATLAS is another particle detector at CERN — but, unlike FASER, it’s about six stories tall and cost many millions more to build. “I think it’s really cool, because FASER’s a really low-cost extension of the LHC,” said Rouven Essig, a particle physicist at Stony Brook University who’s not involved in FASER’s development.

It’s breaking molds, and FASER may also lift the veil on dark matter. FASER won’t detect dark matter itself, Casper explained, but it could detect something called a dark photon, a particle that, like the particles associated with the four fundamental forces of physics, would be how dark matter interacts with the rest of the stuff in the Universe.

“Nothing from standard physics should be able to produce the signal we’re looking for,” said Casper. “It would be an extremely, extremely important discovery. We’re gambling on something where, if we do win, it’ll be a big, big win.”

It’ll be big because, as Tait explained, the discovery of dark photons might herald the discovery of a new “fifth force,” one that, like the other four, could be a key part of the Universe’s machinery.

Fred Reines and the neutrino

FASER will also be on the lookout for a different kind of particle, one that, like dark matter, rarely interacts with anything: the neutrino, which, co-discovered by UCI physicist Fred Reines in 1956, is the most abundant particle in the Universe, and which is part of the process that make stars burn. FASER won’t be the first detector to spot a neutrino, but, Casper explained, neutrino observations are rare, and FASER stands to drastically increase the number of high energy neutrino observations, widening understanding of how the particle helps make the Universe spin the way it does.

“No neutrino has ever been detected at the LHC,” said Feng. “But FASER will detect about 10,000 in the coming three years, opening up a whole new area of research at the LHC.”

When Shively stood in the FASER tunnel on October 5th, it was empty. But just seeing the place where years of her and her team’s work have gone was, she said, “pretty dang cool.” In the next couple months, she and the rest of the UCI-led team will start installing FASER in the tunnel, and, come 2021 or 2022, once LHC starts running again, it’ll be ready for her and the team to insert an extra coin and see, when they punch the “Fifth Force” button, if something exists beyond the Super Wash cycle.

“There’s always some luck involved, and fortune,” said Essig of what the team might find. But when it comes to the first-of-its-kind detector, Essig added: “Some people make their luck.”

UCI Cosmology Center led study rules out dark matter destruction as origin of extra radiation in galaxy center

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An artist’s interpretation of the Milky Way shows the “boxy” distribution of stars in the Galactic Center. A UCI-led team of physicists said in a newly published study that this shape leaves very little room for excess radiation from the destruction of dark matter particles. Dr. Oscar Macias for UCI.

Irvine, Calif., Aug. 26, 2020 – The detection more than a decade ago by the Fermi Gamma Ray Space Telescope of an excess of high-energy radiation in the center of the Milky Way convinced some physicists that they were seeing evidence of the annihilation of dark matter particles, but a team led by researchers at the University of California, Irvine has ruled out that interpretation.

In a paper published recently in the journal Physical Review D, the UCI scientists and colleagues at Virginia Polytechnic Institute and State University and other institutions report that – through an analysis of the Fermi data and an exhaustive series of modeling exercises – they were able to determine that the observed gamma rays could not have been produced by what are called weakly interacting massive particles, most popularly theorized as the stuff of dark matter.

By eliminating these particles, the destruction of which could generate energies of up to 300 giga-electron volts, the paper’s authors say, they have put the strongest constraints yet on dark matter properties.

“For 40 years or so, the leading candidate for dark matter among particle physicists was a thermal, weakly interacting and weak-scale particle, and this result for the first time rules out that candidate up to very high-mass particles,” said co-author Kevork Abazajian, UCI professor of physics & astronomy.

“In many models, this particle ranges from 10 to 1,000 times the mass of a proton, with more massive particles being less attractive theoretically as a dark matter particle,” added co-author Manoj Kaplinghat, also a UCI professor of physics & astronomy. “In this paper, we’re eliminating dark matter candidates over the favored range, which is a huge improvement in the constraints we put on the possibilities that these are representative of dark matter.”

Abazajian said that dark matter signals could be crowded out by other astrophysical phenomena in the Galactic Center – such as star formation, cosmic ray deflection off molecular gas and, most notably, neutron stars and millisecond pulsars – as sources of excess gamma rays detected by the Fermi space telescope.

This representation of data from the Fermi Gamma Ray Space Telescope after its launch in 2008 shows an excess of high-energy radiation in the Milky Way’s Galactic Center. Many physicists attributed this to the annihilation of weakly interacting dark matter particles, but a UCI-led study has excluded this possibility through a range of particle masses. Oscar Macias for UCI

“We looked at all of the different modeling that goes on in the Galactic Center, including molecular gas, stellar emissions and high-energy electrons that scatter low-energy photons,” said co-author Oscar Macias, a postdoctoral scholar in physics and astronomy at the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo whose visit to UCI in 2017 initiated this project. “We took over three years to pull all of these new, better models together and examine the emissions, finding that there is little room left for dark matter.”

Macias, who is also a postdoctoral researcher with the GRAPPA Centre at the University of Amsterdam, added that this result would not have been possible without data and software provided by the Fermi Large Area Telescope collaboration.

The group tested all classes of models used in the Galactic Center region for excess emission analyses, and its conclusions remained unchanged. “One would have to craft a diffuse emission model that leaves a big ‘hole’ in them to relax our constraints, and science doesn’t work that way,” Macias said.

Kaplinghat noted that physicists have predicted that radiation from dark matter annihilation would be represented in a neat spherical or elliptical shape emanating from the Galactic Center, but the gamma ray excess detected by the Fermi space telescope after its June 2008 deployment shows up as a triaxial, bar-like structure.

“If you peer at the Galactic Center, you see that the stars are distributed in a boxy way,” he said. “There’s a disk of stars, and right in the center, there’s a bulge that’s about 10 degrees on the sky, and it’s actually a very specific shape – sort of an asymmetric box – and this shape leaves very little room for additional dark matter.”

Does this research rule out the existence of dark matter in the galaxy? “No,” Kaplinghat said. “Our study constrains the kind of particle that dark matter could be. The multiple lines of evidence for dark matter in the galaxy are robust and unaffected by our work.”

Far from considering the team’s findings to be discouraging, Abazajian said they should encourage physicists to focus on concepts other than the most popular ones.

“There are a lot of alternative dark matter candidates out there,” he said. “The search is going to be more like a fishing expedition where you don’t already know where the fish are.”

Also contributing to this research project – which was supported by the National Science Foundation, the U.S. Department of Energy Office of Science and Japan’s World Premier International Research Center Initiative – were Ryan Keeley, who earned a Ph.D. in physics & astronomy at UCI in 2018 and is now at the Korea Astronomy and Space Science Institute, and Shunsaku Horiuchi, a former UCI postdoctoral scholar in physics & astronomy who is now an assistant professor of physics at Virginia Tech.

Dark Matter Day at UC Irvine Center for Cosmology! October 31!

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The UC Irvine Center for Cosmology is celebrating International Dark Matter Day, October 31, at the Physical Sciences Plaza in front of Reines Hall. Dark matter is 85% of the matter in the Universe, but we do not know what it is. After its initial detection 86 years ago in clusters of galaxies by astronomer Fritz Zwicky, dark matter remains one of the biggest questions in science.

Dark matter is a major focus of research of many members of the UCI Center for Cosmology. So much so that it could be thought of as a “Center for Dark Matter.” Learn about a wide cross-section of it at our Dark Matter Day event!

When: Thursday, October 31: 12 noon – 1 pm

Where: Physical Sciences Plaza in front of F. Reines Hall

Hosts: Prof. Kev Abazajian and Michael Sean Wright, with Space Chunks Live!

Guests:

Bonuses:

  • We will have a solar telescope so that you can see the surface of the Sun—safely!
  • And you’ll get to enjoy some spooky dark matter particle themed ghost cookies, all while hearing about this wonderfully mysterious substance that permeates the Universe!

See you all there! Please share the event so no one misses out on enjoying this worldwide event at UC Irvine!

UC Irvine Cosmologists Turn On First Light for Dark Energy Spectroscopic Instrument

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DESI’s 5,000 spectroscopic “eyes” can cover an area of sky about 38 times larger than can the full moon, as seen in this overlay of DESI’s focal plane on the night sky (top). Each robotically controlled eye can fix a fiber-optic cable on a single object to gather its light. (The red circle marks the location of a single positioner.) The gathered light collected from a small region in the Triangulum galaxy (bottom) by a single fiber-optic cable is split into a spectrum that reveals the fingerprints of the elements present in the galaxy and aids in gauging their distance. The test spectrum shown here was collected by DESI on Oct. 22. Dustin Lang, Aaron Meisner, DESI Collaboration / Imagine Sky Viewer; NASA/JPL-Caltech / UCLA; Legacy Surveys project

The Dark Energy Spectroscopic Instrument aimed its robotic array of 5,000 fiber-optic eyes at the night sky for the first time recently to capture images showing its unique view of galaxy light. Mounted on a telescope at Kitt Peak National Observatory near Tucson, Arizona, DESI was designed to explore the mystery of dark energy, which is responsible for the accelerating expansion of the universe. Implementation of the tool was long anticipated by five UCI astronomers, members of a 500-person international team responsible for the development and activation of DESI. The UCI players designed a subcomponent to monitor the varying brightness of the night sky to ensure that each image captured by the instrument is properly exposed. “This is the culmination of six years of design, research and development efforts at UCI to be ready for this moment,” said David Kirkby, UCI Professor of Physics & Astronomy. “We are all excited to start building and analyzing an unprecedented 3D map of the universe.” His UCI collaborators are graduate students Bela Abolfathi, Abby Bault, Dylan Green and Noble Kennamer. DESI’s components are designed to automatically target preselected sets of galaxies, gather their light, and then split it into narrow bands of color to precisely map galaxies’ distance from Earth and gauge how much the universe expanded as this light traveled to our planet. In ideal conditions, DESI can cycle through a new set of 5,000 galaxies every 20 minutes. The operation was the latest milestone toward the final testing of DESI and planned formal start of observations in early 2020. [UCI News]

 

Philosophy of Dark Energy Workshop March 8-10 – UC Irvine Logic & Philosophy of Science and Center for Cosmology

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Please mark your calendar for an upcoming workshop, Philosophy of Dark Energy, to be held in at UC Irvine. If you are interested in attending, please contact Deborah Fox. A workshop schedule will be available soon.

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Philosophy of Dark Energy Workshop
March 8 – 10, 2019
University of California, Irvine

In the late 1990s, scientists working on the High-Z Supernovae Search Team and the Supernova Cosmology Project provided the first evidence that the expansion of the universe is accelerating. To explain this acceleration, cosmologists have posited “dark energy”, a previously unknown kind of energy now believed to permeate all of space and to make up approximately 70% of the total energy of the universe. But what is dark energy? Is it the vacuum energy associated with known particle species? Or is it a manifestation of an entirely new entity? Or is it simply a reflection of a non-zero value for Einstein’s “cosmological constant”? This workshop will bring together physicists and philosophers to explore the epistemological and methodological issues raised by dark energy, with a focus on understanding the theoretical motivations and empirical evidence for different proposals concerning its nature.

Invited Speakers:

Luca Amendola (Institute of Theoretical Physics in Heidelberg), The ever-changing dark energy

Robert Brandenberger (McGill University), Dynamical Relaxation of the Cosmological Constant and Dark Energy

Robert Caldwell (Dartmouth College), Dark Energy Needs Dark Radiation

Sean Carroll (Caltech University), Holography, Hilbert Space, and the Cosmological Constant

Anne-Christine Davis (University of Cambridge), Recent developments in Modified Gravity and Chameleons

Paul Hamilton, University of California, Los Angeles

Lavinia Heisenberg, Institute for Theoretical Physics, ETH Zurich

Dragan Huterer (University of Michigan), Dark Energy Two Decades After: Cosmological Probes and Consistency Tests

Jim Peebles (Princeton University), Finding LambdaCDM

Thomas Ryckman, Stanford University

Daniela Saadeh (University of Nottingham), Dark energy: can the fifth force be screened?

Chris Smeenk, University of Western Ontario

Shinji Tsujikawa, Tokyo University of Science

David Wallace, University of Southern California

This event is made possible by a grant from the John Templeton Foundation, to Chris Smeenk and Jim Weatherall.