MIT’s ABRACADABRA Instrument: Pulling the Secrets of Dark Matter Out of a Hat

Dark Matter Concept

ABRACADABRA, located in MIT’s Laboratory for Nuclear Science, aims to detect axions, hypothetical particles that could be a major component of dark matter, the mysterious substance that constitutes most of the universe.

MIT grad student Chiara Salemi and Professor Lindley Winslow use the ABRACADABRA instrument to reveal insights into dark matter.

On the first floor of MIT’s Laboratory for Nuclear Science hangs an instrument called “A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus,” or ABRACADABRA for short. As the name states, ABRACADABRA’s goal is to detect axions, a hypothetical particle that may be the primary constituent of dark matter, the unseen and as-of-yet unexplained material that makes up the bulk of the universe.

Chiara Salemi

Chiara Salemi, with ABRACADABRA open, shows the magnet inside. Credit: Jon Ouellet

For Chiara Salemi, a fourth-year physics graduate student in the group of Lindley Winslow, the Jerrold R. Zacharias Career Development Associate Professor of Physics, ABRACADABRA is the perfect instrument to work on during her PhD. “I wanted a small experiment so I could do all the different pieces of the experiment,” Salemi says. ABRACADABRA, which consists of an extremely well-shielded magnet, is the size of a basketball.

Salemi’s willingness to work on all aspects is unique. “Experimental physics roughly has three components: hardware, computation, and phenomenology,” Winslow explains, with students leaning toward one of the three. “Chiara’s affinity and strengths are evenly distributed across the three areas,” Winslow says. “It makes her a particularly strong student.”

Since beginning her PhD, Salemi has worked on everything from updating ABRACADABRA’s circuitry for its second run to analyzing the instrument’s data to look for the first sign of a dark matter particle.

A happy accident

When Salemi started college, she wasn’t planning on pursuing physics. “I was leaning towards science, but I wasn’t totally sure of that or what field within science I would like.” During her first semester at the University of North Carolina at Chapel Hill, she took physics with the aim of determining whether this might be a field she might be interested in. “And then, I just totally fell in love with it, because I started doing research, and research is fun.”

Throughout her undergraduate career, Salemi collected research experiences. She operated radio telescopes in West Virginia. She spent a semester in Geneva, Switzerland, looking for Higgs boson decays at the European Organization for Nuclear Research, better known as CERN. At the Lawrence Berkeley National Laboratory, she tinkered with the design of semiconductors for the detection of neutrinos. It was at one of these research experiences, a summer program at Fermilab in Illinois, that she began working with axions. “Like many things in life, it was an accident.”


MIT team members Jonathan Ouellet, Lindley Winslow, Chiara Salemi, and Reyco Henning (from UNC – Chapel Hill) with ABRACADABRA, the instrument used to detect axions, a hypothetical particle. Credit: Lindley Winslow

Salemi had applied for the summer program because she wanted to continue working on neutrinos and “Fermilab is the hub of all things neutrino.” But when she got there, Salemi found out that she was assigned to work on axions. “I was extremely disappointed, but I ended up falling in love with axions, because they’re really interesting and different from other particle physics experiments.”

Elementary particles in the universe and the forces that regulate their interactions are explained by the Standard Model of particle physics. The name belies the importance of this theory; the Standard Model, which was developed in the early 1970s, describes almost everything in the subatomic world. “But there are some huge gaping holes,” Salemi says. “And one of these huge gaping holes is dark matter.”

Dark matter is matter we cannot see. Unlike normal matter, which interacts with light — absorbing it, reflecting it, emitting it — dark matter does not or only barely interacts with light, making it invisible to both the naked eye and current instruments. Its existence is deduced by its impact on visible matter. Despite its invisibility, dark matter is vastly more abundant, Salemi says. “There’s five times more dark matter in the universe than normal matter.”

Like its visible counterpart, which is made up of particles such as neutrons, protons, and electrons, dark matter is also made up of particles, but physicists still don’t know exactly what types. One candidate is the axion, and ABRACADABRA was designed to find it.

Small but mighty

Compared to CERN’s Large Hadron Collider, which is an instrument tasked with detecting proposed particles and has a circumference of 16.6 miles, ABRACADABRA is tiny. For Salemi, the instrument is representative of a new era of tabletop physics. Creating ever-larger instruments to quest after increasingly elusive particles had been the go-to strategy, but these have become increasingly expensive. “Because of that, people are coming up with all sorts of really interesting ideas on how to still make discoveries, but on a smaller budget,” Salemi says.

The design of ABRACADABRA was developed in 2016 by three theorists: Jesse Thaler, an associate professor of physics; Benjamin Safdi, then an MIT Pappalardo Fellow; and Yonatan Kahn PhD ’15, then a graduate student of Thaler’s. Winslow, an experimental particle physicist, took that design and figured out how to make it a reality.

ABRACADABRA is composed of a series of magnetic coils in the shape of a toroid — picture an elongated donut — wrapped in a superconducting metal and kept refrigerated at around absolute zero. The magnet, which Salemi says is about the size of a large grapefruit, generates a magnetic field around the toroid but not in the donut hole. She explains that, should axions exist and interact with the magnetic field, a second magnetic field will appear within the donut hole. “The idea is that that would be a zero-field region, unless there’s an axion.”

It can take 10 or more years to take a theoretical design for an experiment and make it operational. ABRACADABRA’s journey was much shorter. “We went from a theoretical paper published in September 2016 to a result in October 2018,” Winslow says. The geometry of the toroidal magnet, Winslow says, provides a naturally low background region, the donut hole, in which to search for axions. “Unfortunately, we have gotten through the easy part and now have to reduce those already-low backgrounds,” says Winslow. “Chiara led the effort to increase the sensitivity of the experiment by a factor of 10,” says Winslow.

To detect a second magnetic field generated by an axion, you need an instrument that is incredibly sensitive, but also shielded from external noise. For ABRACADABRA, that shielding comes from the superconducting material and its frigid temperature. Even with these shields, ABRACADABRA can detect people walking in the lab and even pick up radio stations from around Boston, Massachusetts. “We can actually listen to the station from our data,” Salemi says. “It’s like the most expensive radio.”

If an axion signal is detected, Salemi and colleagues will first try hard to disprove it, looking for all potential sources of noise and eliminating them one by one. According to Salemi, detecting dark matter means awards, even a Nobel Prize. “So you don’t publish that kind of result without spending a very long time to make sure it’s correct.”

Results from ABRACADABRA’s first run were published in March 2019 in Physical Review Letters by Salemi, Winslow, and others in MIT’s Department of Physics. No axions were detected, but the run pointed out tweaks the team could make to increase the instrument’s sensitivity prior to its second run that began in January 2020. “We have been working on setting up, running, and analyzing run 2 for about a year and a half,” says Salemi. Currently, all the data has been collected and the group is finishing up the analysis. The results of which will be published later this year.

As they prepare those results for publication, Salemi and her colleagues are already thinking of the next generation of axion detectors, called DM Radios, for Dark Matter Radios. Salemi says that this will be a much larger, multi-institute collaboration, and the design of the new instrument is still being conceived, including deciding the shape of the magnet. “We have two possible designs: One is the donut shape, and the other one is a cylinder shape.”

The search for axions began in 1977, when they were first theorized, and since the 1980s experimental physicists have been designing and improving instruments for detecting this elusive particle. For Salemi, it would be amazing to continue working on axions through to their discovery, although no one can predict when that may happen. “But, seeing experimental low-mass axion dark matter through from around the start to the finish? That I could do,” she says. “Fingers crossed.”

14 Comments on "MIT’s ABRACADABRA Instrument: Pulling the Secrets of Dark Matter Out of a Hat"

  1. … I really don’t want to express my self at this moment…

    • Similar to other articles of this type, the people assume that dark matter exists and we just haven’t found it yet. To me, that’s very premature. All we know is that IF dark matter existed, it would explain discrepancies in experimental measurements. There could be other explanations, some already proposed and some not yet imagined.

      • … an limitation of a scientific thought, too …

        … if one adds >

        Das schönste Glück des denkenden Menschen ist, das Erforschliche erforscht zu haben und das Unerforschliche zu verehren.

        – Johann Wolfgang von Goethe
        , to its répertoire of songs, one would know…

  2. I remember being a physics student working with the Tokamak at UT at the time. It was so exciting! I too loved physics starting at age 16 from a high tiered high school physics class. I got my degree and a degree in mathematics but chose not to make my living that way (international technology negotiations between large corporations), but I’ve continued to study physics on my own non-stop since then! I love the dark matter experiments involving very innovative ways to find the candidates, the axion being one. They would be everywhere so a detector anywhere sensitive enough should find them, I agree. I love your enthusiasm and your experimental design. It is totally novel (don’t quite understand how there is no magnetic field in the doughnut hole since of course the opposite is true for a Tokamak). Your view to always (ALWAYS) try to disprove your apparent discoveries is a very, very good one. Never just get excited and say you found it. That will kill you if you are wrong! Keep going no matter where this takes you. I’m convinced of dark matter now and there is an awfully lot of it so supply should not be a problem. Be very, very patient and never give up (unless you find for sure there isn’t any and thus something else must be a work). I wish you great exploration excitement, success, and luck. I’m enjoying your exploits kind of vicariously I guess.

  3. … a pseudo science that can explain some parts of the Universe we live in, but that 4.6% – 10% that can be explained, is divided into quantum world and Albert’s one…

  4. … PS, I don’t want to listen to “those Helvete songns”…

  5. I have a theory that can revolutionize your quest of understanding dark energy. Email me back if you have time.

  6. Dark matter, along with dark energy, were originally envisioned as placeholders acknowledging the divide between what we seem to observe in the universe and what our math says we should observe. Yet it took only about a single generation for those placeholders to take on a life of their own and become presumed reality by the majority of the scientific community, especially those freshly indoctrinated in college. A perfect example of a scientific “cultural shift” that ends up misleading and distracting us from reality.
    Yet the real embarrassment for devotees of such thinking is that both placeholders are no longer necessary when one simply takes into account the effects of interstellar molecular hydrogen (much harder to detect than atomic hydrogen). Its mass accounts for the supposedly unexplained galactic gravity we observe, and light passing through it undergoes redshift–the same redshift that so many in the scientific field have been so successfully induced to assume is the result of acceleration from nonexistent dark energy. It’s quite obvious, at least when one ignores the popular rhetoric in this case and simply pays attention to the facts we already have.

    • Sekar Vedaraman | December 11, 2020 at 7:23 pm | Reply

      Wonder why Mr. Reto Barun (Big Honcho in Unisys the Computing Company which creted Univac) took back a Statue of Lord Ganesha to his Pensylvania home , to install in his garden!

      In ancient “Hindu ‘Mythology’ ” Lord Ganesha is is also caleed Ganapathi. In Sanskrit Gana
      which has many meanings also means Mathematics ( Ganit in Hindi) and and Pati means Husbband. So Gana Pati means Married to Mathematics !. Ofcourse the Lord Ganesha had other Consorts, and Ganapati festival is celebrated with fervour in this and other parts of the globe by the decout. This I wont educate you about!

      Just like Data does not lie ,but can be misinterpreted to prove your point of view, so also, Mathematics (which is the queen of the Sciences) also rarely lies or misleads.

      Theoritical Hypothesis which precede experimental research in search of Evidence is normally good science! It is good to question and doubt findings 0f scientiists and try to disprove the finding . Scientific Research which doubts the finding and questions it long and hard and discounts all possibility before publishing is GOOD Research. Such self doubt which questions the Scientific findings disclosed in Scientific Journals as the theory and mathematics on which the findings are based and questions the same, to try and disprove the same , which may be based on incomplete theory and incorrect assumptions and mathematic, and is moulded to fit the hypothesis –Should legitamately be questioned.

      However, to dismiss such research in whatever field of Science, Arts or human knoledge without any basis,certainly needs to be challengedand set aside.

      Subjective and faulty assumptions and juddgment and opinions based on such shaky foundations certainly needs to be challenged. However not even attempting to test the theory and attempt to find the truth is faulty and a Cop-Out in my pesonal oinion.

      The second methodology used by Scientists globally is to try and explain a unexplained phenomenon in the known universe and try to create a hypothesis to explain the saame using matematics as the primary tool iand Physics and Chemistry BAnd Biological Sciences and other Sciences like Earth Science ETC. as best as they can. Peersonally I prefer Science over Sttistca as the basis for arriving at conclusions.This does not mean that the role of statistical sciences should be underestimated. Far from it. However, unexplained outliers are always a problem as it means although most of the data fits into a hyporthesis and theory , one or some don’t.

      I could go on but, my request is Do Not BE a “Doubting Thomas”.

      Trust but verify is a principle which needs to be adopted by all Researchers in whatever field of knowledge theories are postulated backed by Mathematics.

      However, do Conduct rigorous Research and do not beleive and label everything you do not beleive and do or agree with and dismiss the same and doees not fit in with your philosophy of existence –as “Mythology” and Pseudo Science!!

      I ask you as a novice, please tell me when life begins and I will respond with my views and logic for my views about the same —which can be vrified by SCientific research. No Emoticons!

      I prefer that funding occurs to fund basic research in all areas of knowledge and the Scientific temper as well as rigorous research is undertaken, and is developed in the youth and the search for new knowledge is not impaired as a result of doubt and blind faith.

      However, every individual who has been granted free choice and has come into existence has the choice to choose what to beleive and what not to beleive and have his own opinions about everything , whether the Flat Earthers or others who refuse to respect the views of others.

      Knowledge it is not the domain of a single individuall, nor is it the domain of only humans. Science has progressed at a extremely slow pace , what I would call a snails pace in my current lifetime and certainly needs a majot boost. Again Personal Opinion!

      Economic considderations which appear to dominate the decisions of all members of society’s community’s, nations and even individuals and seems to be the only consideration is extremely strange to me. This Virus’s impact on humanity will only be benefiacl to humakind, if we all considered the impact of such decisions on the temple in which we all exist ( Body-mind -consciousness complex ) , the Planet on which we exist and the impact the human virus hason the furture generations!!

      The rest of the Uiverse needs to be explored with an open mind to create a better world for all life and creatures which exist.

      The views expressed are personal and not binding on anyone including you.

      Message for C

      Best of luck in your quest for Axion C.
      Do not get so caught up in this searh that you forget to lead a life of joy and happiness which is the birthright of all humans and all creatures of the almighty has created. Never forget that your mastery of a three areas of technologyband Science may be great , but unless you depend on the many other briliant minds and the innumerable Gaints on whose shoulders who we all stand and where we all have reached today, and tom-tom about our findings BUT always maintain humility and willingness to learn and trust the entire team and work as a seamless one-team for the project. community, state, nation, world , progress in scientific progress as well applied areas of knowledge will remaain tortoise-like.

      Once again we wish you the best of luck from the East.May theyounger generation and future generations emulate you example and success in Scientific Research in their chosen field of expertise whether it is arts, fine arts and or any area of knowledge. If you ever forget do see the paintings on the ceiling by a great Scientist, sculptor, artist !

  7. My idea of dark matter and dark energy is they are purely ways we describe positive and negative curvature. Not that they are particles inside spacetime (something that could be causally connected time-like event).

    They are only space-like connected (causally disconnected), if you want to think of that as outside the universe, imaginary/orthogonal matter, etc. So looking for how they may interact with electromagnetism (light) may be a fools errand.

    I think dark matter and dark energy are good though, as it forces us to think outside the box, and in some way prove our universe of matter is not all there is, only a small part of the whole.

    The more these experiments find nothing, the more it will force minds to think outside the box, like orthogonal versions of standard model.

    • Interesting thoughts.

      Interesting Hypothesis.

      Hope some brilliant minds in the Mathematical Sciences are working on proving this and other such thoughts.

      Not sure , whether our current thoughts and development of mathematics has reached a stage where such proof can be provided. Maybe across functional team of great mathematicians needs too be put together to explore and define the challenges faced by Scientific Thought and development of new mathematical tools and its applications in solving real life problems and prove / disprove such hypthesis!

  8. Michael A Pitzel | December 15, 2020 at 11:24 pm | Reply

    Question: Could DM be “dents” in 4-space, in the same way that regular matter is dents in 3-space?
    Imagine that 4-space preceded 3-space, and we inherited matter, light, gravity, etc.
    The basic building block is topologically a 3-slice of a 3-ball in 3-space…a “dent” from a small 4-ball impact on our 3-surface universe.
    Abandon Gauss’ theorem, & compactifications, and embrace contractible nonorientable manifolds… a “surface” containing a 3-dimensional geodesic, a singularity, and fixed handedness. Minimal triangularization. Maximal information at it’s singularity.
    Ask me if you want to know.

  9. Michael A Pitzel | December 15, 2020 at 11:38 pm | Reply

    It really is possible that you could find a clue in a magical hat, just male sure that it’s a non-orientable, multiply-connected, magical hat that you can turn inside-out 6 times, and looks like the classical pointed wizard’s hat. Careful. There’s a lot of difference between a right or left handed one.

  10. … that dark matter is bit in question, there is some, …
    Galaxy rotation curves,
    Velocity dispersions,
    Galaxy clusters,
    Gravitational lensing,
    Cosmic microwave background,
    Structure formation,
    Bullet Cluster,
    Type Ia supernova distance measurements,
    Sky surveys and baryon acoustic oscillations,
    Redshift-space distortions,
    Lyman-alpha forest…
    … thingis, that one might need to read about it, on Wikipedia …

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