NATIONAL / SCIENCE & HEALTH| NATURAL SELECTIONS
Japan’s Super-K to resume seeking why anything exists
BY ROWAN HOOPER
To start the year, here’s an appreciation of a site in Japan that would have left even the Zen-imbued architects of Kyoto’s sublime Kinkaku-ji (Temple of the Golden Pavilion) open-mouthed with awe.
Not only that, but it’s a site where basic questions about the nature of reality are being probed — questions that go beyond even the most mind-bending conundrums posed by Zen masters at the Enkaku-ji Temple in Kamakura, Kanagawa Prefecture. (And I know they are mind-bending because I went on a Zen course there once, and we had to wake at 4 a.m. every day to meditate upon them.)
The site I speak of is the Super-Kamiokande detector located under Mount Kamioka in the Japanese Alps near Hida City, Gifu Prefecture.
There is certainly no shortage of UNESCO World Heritage Sites in Japan, but to my mind the detector of the Super-Kamiokande — the Super-Kamioka Nucleon Decay Experiment to give it its full name, though it’s normally abbreviated to Super-K — deserves at least as much attention. I only wish it was as easy to visit as those on the World Heritage tourist trail.
However, this Super-K story starts not in Gifu but some 120 km north of Tokyo in a village called Tokai on the Pacific coast of Ibaraki Prefecture. Until now, Tokai has perhaps been best known as the site of a nuclear accident in 1999 which killed two people — but this may soon change.
That’s because Tokai is home to one of the world’s most advanced particle accelerators — J-PARC (the Japan Proton Accelerator Research Complex) — which this year is being geared up to answer one of the greatest questions in the universe: Why does matter exist?
To do that, J-PARC generates mysterious subatomic particles called neutrinos, which it then beams through the solid bedrock of Japan to the Super-K detector sited deep under Mount Kamioka some 300 km away.
And while J-PARC is set to take aim at some of the universe’s biggest questions, in 2011 it was peripherally involved in two of the biggest stories of the year.
Although it is only 200 km south of Sendai in Myagi Prefecture, the facilities at J-PARC escaped largely unscathed after the Great East Japan Earthquake of March 11, whose undersea epicenter was some 130 km off that city. Despite just a few buildings and roads being damaged, however, the sensitivity of the J-PARC equipment is such that experiments were shut down.
The aftermath of the earthquake and tsunami — and the ongoing disasters at the Fukushima No. 1 nuclear power plant — have understandably dominated the news agenda ever since. But there was another story, in September 2011, that was for a while the biggest in the world — and it was all to do with those same mysterious neutrinos.
An experiment based in Gran Sasso, under the mountains of central Italy, had fired neutrinos to a detector at CERN (the European Organization for Nuclear Research) in Geneva, Switzerland. Precise measurements seemed to show that the neutrinos traveled faster than the speed of light — and the result shook the world of physics to its core.
Since Einstein’s special theory of relativity states that nothing can exceed the speed of light, if neutrinos have broken the speed limit then it would be necessary to construct a new physical reality to describe the world. It’s a big deal.
Once J-PARC is back online in March and firing its neutrino beam from Tokai to Kamioka — in what’s called, for that reason, its T2K experiment — it will be able to independently test the Gran Sasso result, and determine whether neutrinos really can break the cosmic speed limit.
Even on the scale of the giant physics experiments we have become familiar with in recent years, T2K is still something special.
Almost a kilometer down inside Mount Kamioka is the Mozumi mine, which used to supply zinc, silver and lead. Now it is home to the Super-K detector, a vast stainless-steel tank holding 50,000 tons of ultra-pure water. Surrounding the tank are more than 10,000 photo-detectors. The whole setup is exquisitely designed to detect the interaction of a neutrino with the atoms of water in the tank.
It has to be housed deep underground so the rock shields it from the cosmic rays that are constantly bombarding the surface of the Earth. When a neutrino interacts with matter, a tiny flash of light is generated, and this is what the photo-detectors are set up to catch.
So why does it all matter?
Well, neutrinos are elementary particles that come in three types (also known as flavors): electron neutrinos; muon neutrinos; and tau neutrinos. They are incredibly slippery and hardly ever interact with other forms of matter, so it has been very hard to learn about them. But we do know something.
Before the T2K experiment went offline following the March 11 earthquake, neutrinos had been detected changing from one flavor to another. Specifically, muon neutrinos had been generated at J-PARC, but when they were picked up at Super-K they had turned into electron neutrinos.
That might seem like the ultimate “so what” result, but the way these particles change into different flavors could shed light on the question of why there is more matter than antimatter in the universe.
In a way, it is all as otherly as the zazen meditation course I did at the Enkaku-ji Temple. There, we tried to find samadhi — the “one-pointedness” of mind where you try to tune in to the reality of nature beyond thought.
Physicists think that matter and antimatter were created in equal amounts at the start of the universe, but — luckily for us — matter came to dominate over antimatter. We don’t know why that happened, but Super-K is trying to find out.
Kinkaku-ji apparently houses relics of the Buddha, who lived about 2,500 years ago. Super-K, though, may be able to detect clues about what happened at the beginning of the universe, more than 13 billion years ago.
There should be a haiku composed to celebrate the endeavor taking place under Mount Kamioka.
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