AT SOME point in our lives, most of us learn that atoms are comprised of three types of particle: neutrons, protons and electrons. Each has distinct properties. The electron and proton have opposite electrical charge from one another, while the neutron lacks an electrical charge entirely. The electron is also an elementary particle – not comprised of any other entities – while the proton and neutron are both composite particles, each made of three quarks (which are themselves elementary).
From a category standpoint, protons and neutrons are baryons, particles that contain an odd number of quarks. One major difference between elementary particles and composites like baryons is that baryons can fall apart into pieces. For example, a free neutron outside an atomic nucleus has a pretty quick decay time of just under 15 minutes. This is essentially real-life alchemy, as it transforms one element into another. This can occur as beta-minus decay, in which a neutron “crumbles” into a proton, an electron and the antimatter counterpart to neutrinos, an antineutrino. Since the neutron has no charge, the particles that are left over must collectively be chargeless. The electron and proton charges cancel, while the antineutrino is also chargeless.
This leads one to wonder what proton decay is like. Interestingly, it remains an open question. In the 1960s, Andrei Sakharov proposed a hypothetical mechanism for this in which the particle would give way to a positron and a pion, a composite particle made of a quark and an antiquark. But, to this day, proton decay has never been observed in the lab, making it the subject of an intense, global scientific search.
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One of the sites for this will be the Deep Underground Neutrino Experiment (DUNE), still under construction, but which will eventually fire neutrinos from Fermilab outside Chicago under Earth’s surface to the Sanford Underground Research Facility (SURF) in Lead, South Dakota. Its primary goal is to study the elusive neutrino elementary particles, which interact so little with other types of matter that they are fairly difficult to capture.
But it turns out that experimental conditions that are perfect for studying neutrinos in this way are also perfect for seeking out evidence of proton decay. DUNE’s detection facilities are both enormous and deep underground, allowing scientists to monitor large numbers of protons in extremely cold liquid argon. Since proton decay – if it occurs at all – must be extremely rare, observing a sizable number of protons (1034 to be specific) is the best way to have a chance of seeing anything unusual, and the argon vats contain a lot of protons.
Now you are intrigued by DUNE, you have to hear the hard part. It has had some bad press because of cost overruns and construction delays at SURF, which is in a gold mine that closed in 2002. The pit’s origins go back to the 1800s, when the first miners problematically colonised parts of the traditional homelands of the Oceti Sakowin (Sioux) tribal nations.
In this context, it is interesting to consider the ways in which, for all its complications, DUNE is also a significant international project, and not only because its users must contend with recognising the historical injustices faced by the land’s traditional knowledge holders. With the support of scientists like US-based particle physicists Kétévi Assamagan and Young-Kee Kim, a group of Malagasy students from Madagascar have trained as neutrino physicists and returned home to create the first African DUNE research team at the University of Antananarivo.
There, a growing group that includes Roland Raboanary is working on an important piece of equipment for the DUNE project, the “near” detector. According to former team member Laza Rakotondravohitra, this will help scientists explore neutrinos more accurately and in ways that have never been done before.
As part of the DUNE experiment, neutrinos will be produced at Fermilab and go through the near detector placed underground at that facility. Then, 1300 kilometres away in Lead, another deep detector will capture the neutrinos from Fermilab, looking for changes in them.
Neutrinos are non-trinary: they come in three flavours and randomly oscillate between them as they travel through space. One of DUNE’s goals is to study these oscillations by watching how the flavour population statistics change between the start of the journey and the end.
This is where the University of Antananarivo’s contribution to the near detector is key. That instrument will scan the particles as they leave Fermilab on their way to Lead, potentially providing insight into the non-trinary nature of neutrinos in the process.
Chanda’s week
What I’m reading
Julian Randall’s forthcoming memoir The Dead Don’t Need Reminding. It is brilliant.
What I’m watching
I recently marathoned every episode of The Real Housewives of Potomac, and it was terrible.
What I’m working on
I have been thinking a lot about how to convince people that knowing things is valuable.
Chanda Prescod-Weinstein is an associate professor of physics and astronomy, and a core faculty member in women’s studies at the University of New Hampshire. Her most recent book is The Disordered Cosmos: A journey into dark matter, spacetime, and dreams deferred
