Page 16 - EUREKA! Fall 2017

In addition to the scientific legacy we’re building on, there’s

a technical one. All the lessons we learned in making a deep
underground experiment, in making very pure materials and

keeping the whole system very clean, not only did we learn how to
do this, but we also convinced the world that it’s possible to do.

as neutrinoless double beta decay, a type of radioactive “In addition to the scientific legacy we’re building on,
decay in which two protons are simultaneously transformed there’s a technical one. All the lessons we learned in making
into two neutrons, or vice versa, inside an atomic nucleus. a deep underground experiment, in making very pure mate-
Observing any signs of this process, says the Institute of rials and keeping the whole system very clean, not only did
Physics magazine Physics World, would show that neutrinos we learn how to do this, but we also convinced the world
are their own antiparticles (a particle with the same mass that it’s possible to do.”
but opposite charge). “This would constitute discovering a In the echo of the empty Cryopit, Sinclair explains the
new class of particles that lies beyond the Standard Model significance of nEXO, which can trace its lineage directly to
of particle physics,” says Physics World, “and would be a SNO. The breakthrough Higgs boson, which gives mass to
major breakthrough in modern physics.” Measurements of all particles, might not work for neutrinos, which are much
this decay process could also be used to determine the ab- lighter than any other fundamental particle. It appears that
solute mass of a neutrino. a different mechanism may provide mass to the neutrino. If
Sinclair, who chairs the international nEXO collaboration’s the neutrino is its own antiparticle, that theory makes sense,
board and is its spokesperson in Canada, is concentrating and double beta decay can only occur if the neutrino is its
on the conceptual design for the full-scale detector that own antiparticle. “The physics would allow a different way to
could be installed in SNOLAB’s Cryopit. The push for fund- provide mass to such a particle,” says Sinclair. “It would go a
Mil mossus. Ro elliquis qui volessitaes doluptaquas expernatum si destrum sit omnimuscia iusdae. Am nos aut ma voloribus et optatia ing — “at the couple hundred million dollar level,” he says long way toward understanding the structure of the funda-
denderro berit facimag niminci liquae nonsequ atemperspit exerruntenis quid quam qui abor minctor eperfero eseniaesti
— is under way. The project, which involves scientists from mental particles of the universe.
the U.S., Russia, China and Germany, is looking for financial “But there’s another motivation, a cosmological mystery
support from U.S. Dept. of Energy, among other potential that we’ve been struggling with for a long time,” he adds.
Bellerive, who chairs the university’s physics department. him. He only sees what needs to be done.” backers interested in this type of physics. The experiment is “Why is the universe here? Or, at least, why are we in it? We
Bellerive came to Carleton as a Canada Research Chair in Sinclair and several others, including the late Carleton so expensive in part because it will need five tonnes of iso- understand the big bang, that the universe started in a state
2001, recruited from a postdoctoral position at CERN (the physicist Cliff Hargrove, were the true builders of SNOLAB, topically enriched xenon, which alone is worth about $100 of enormous energy. This energy can produce particles and
European Organization for Nuclear Research) to head SNO’s says Bellerive. They put so many hours and so much heart million. To get that amount, 50 tonnes of normal xenon must antiparticles, and particles and antiparticles can annihilate
data analysis effort. “What attracted me was the expertise into making it a reality. “At the end of the day, it comes be put through an isotope separator — and global produc- back into energy, and this happened over and over and over
of the Carleton physics group as a whole,” says Bellerive. down to passion,” says Bellerive. “It comes down to physi- tion of xenon, a byproduct of liquid oxygen used in the steel again as the universe cooled and expanded. But at the end
“But I quickly realized the intellect of David and his vision cists who really want to understand how things work. Deep making industry, is only about 40 tonnes per year, much of of that process, we were left with just particles. So there
for SNO. We built the thing, and it would have been a shame inside, that’s what they want. They build on the generation it ending up in car headlights, plasma televisions and space- must be a symmetry between matter and antimatter, par-
if we weren’t the leader for the data analysis. that came before, and create opportunities for the next one craft ion drives. ticles and their antiparticles, and we don’t know what that is.
“For me, SNO was a new thing,” he continues, “because to follow.” If the funding for nEXO was secured tomorrow, it still “One of the really surprising outcomes of SNO — maybe
I had worked on a collider experiment at CERN. I helped would take about six years to build the experiment, and the most significant outcome of SNO — is that maybe the
bring in some cross-pollination, and a new technique for Even though he is officially retired — a move he made three another six years to take data. But to Sinclair, the wait — and answer lies in the properties of neutrinos. The arguments
data analysis — a novel, more modern, multi-variable analy- years ago to allow Carleton to hire new physics faculty — effort — is worth it. “People have been looking for double are somewhat indirect, but one of the criteria is that we
sis technique. It’s like an orange, and if you want to extract Sinclair is in the line at a campus Tim Hortons at 8 a.m. after beta decay for decades, and the discovery that neutrinos have to understand the question as to whether neutrinos
all the juice, you have to really work hard to get everything a late-night flight back to Ottawa from Sudbury. He’s still have mass means that we now know where to look,” he says. are their own their antiparticles. Other aspects of the theory
out of it.” working full-time, going to his lab every day and supervising “It’s a very challenging experiment still, but we know it’s not are going to be very challenging to test, but this is one of
Bellerive, whose responsibility as a departmental chair grad students, with the nEXO experiment occupying most infinitely challenging, so it has new scientific impetus. the windows that we can look at and see if we’re on the
is to ensure that teaching and research proceed, and that of his research attention. Sinclair has been involved with the “We set up this lab to do experiments that are abso- right track to understanding this very important fundamen-
funding for grad students is in place, is a data analysis project since its start a dozen years ago, when EXO-200 — a lutely fundamental to our understanding of the universe,” tal property of the universe — that we’re here. Because if
expert. Scientists usually like to do what they’re good at, he prototype detector using 200 kilograms of liquid argon in- he continues. “It’s a very competitive and challenging field, we didn’t have the asymmetry, by the time the annihilation
says. “But David Sinclair is one of those rare scientists,” says side a vessel made from thin, ultra-pure copper — was built to come up with experiments that can distinguish the very was over, we would be left with a scattering of particles and
Bellerive, “who is not only a physicist, he’s also a chemist, at Stanford. In 2007, the detector was moved to the Waste feeble signals we’re looking for from the backgrounds that antiparticles at such low density that they never interacted.
and he can do both nuclear and particle physics, and even Isolation Pilot Plant, a geological repository for nuclear normally surround us with radioactivity and cosmic rays and So, we’d never get matter. We’d never get material forming.
civil engineering. He has an ability to see the broader pic- waste 650 metres below ground near Carlsbad, New Mexico. all kinds of other surface noise that we’ve avoided by com- We’d never form. It’s absolutely critical to understanding the
ture. He doesn’t have any confinement. Science is science to The detector is looking for evidence of a process known ing deep underground. universe — that, to me, is the main reason we’re here.”

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