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This week's guest blogger is Ben Still. He's a postdoctoral researcher at the Particle Physics Research Centre Queen Mary, University of London. He can be found on twitter @benstill.
Last week around 150 scientists travelled to Japan to not only discuss exciting new physics but also how to re-build one of the biggest experiments on the planet. The Tokai to Kamioka (T2K) experiment is an international collaboration of around 500 scientists and engineers in total, from 12 different countries. We are using neutrinos, the smallest and most ghostly building blocks of nature, in an attempt to understand a major chapter in the creation story of the Universe.
Many of the participants of the meeting were retracing steps they took just months earlier when evacuating Japan after the March 11th earthquake. The quake devastated much of the north-eastern Japanese seaboard and with it the Japan Proton Accelerator Research Complex (J-PARC), the base of the T2K experiment. J-PARC itself was too damaged in the quake to host a meeting and so the venue was changed to the sister particle physics site KEK in Tsukuba, Japan.
Apart from a different location, and the background of aftershocks still resonating through the country, the meeting went as usual. Three days of pre-meetings where every aspect of the experiment was discussed in detail. Following this, three days of plenary in which all progress since the last meeting in December 2010 and plans for the future were discussed.
Neutrinos interact extremely rarely with anything around them, so rarely that on the T2K experiment we fire an intense beam of them 295km directly through the Earth from the East to West of Japan. Why do this? Neutrinos display a crisis of character. They are born as a certain type in conjunction with a charged particle, E.g. an electron-neutrino and electron, but sometime later may be seen to have changed their type. This change of character is known as neutrino oscillation. It is a well known and explained effect that happens in the very small ‘quantum’ world.
The T2K experiment hopes for the first time to directly see a change of muon-neutrino to electron-neutrino (the muon is the heavier cousin of the electron, same in almost every way just heavier). Once measured then scientists can start to understand the interplay between neutrinos and their anti-matter versions, anti-neutrinos.
The Science Bit
When experiments are conducted in the lab new particles can be created from pure energy, thanks to Einstein’s E=mc2 equation. The new mass (m) created is however always seen to be a 1:1 mix of matter and anti-matter. This is a problem. Matter and anti-matter inevitably meet again, because opposites attract, and annihilate each other when they do to form pure energy once more. If the 1:1 ratio were perfectly true then the Universe, thought to have started in a pure energy Big Bang, would today be nothing but a warm bath of energy – microwaves in fact. But we are not – us, the Earth and the entire visible Universe out there is made from matter.
So where has the excess matter come from? At some level this 1:1 ratio (symmetry) is flawed (asymmetric). The flaw has been well measured when using just quark particles. Due to the ghostly nature of the neutrino the same flaw has not been measured yet using the other six particles that make up Natures Lego set – the Leptons. By measuring the character crisis of the neutrino T2K hopes to allow us to measure the imbalance between Leptons and anti-Leptons.
After the March quake the particle accelerator, detector and other essential systems were heavily damaged. A plan was discussed during last weeks meeting and people are optimistic that given the right support the experiment may be back and taking data in early 2012.
In the meantime the experiment hopes to present new results in the upcoming summer conferences. Once back on track the T2K experiment will rapidly improve the precision to which we understand the neutrino, and may yield the answer to the creation of the visible Universe.
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