【分享】探索中微子的奥秘

太阳雨落

MINOS experiment sheds light on mystery of neutrinos

---

News

31 March 2006

Scientists have announced the first results of an experiment to send mysterious particles called neutrinos on a 450-mile journey through the earth. Oxford University is one of five UK institutions involved in a new five-year international research programme studying the properties of neutrinos, which it is thought may have had a key role in the evolution of the universe.

Dr Alfons Weber, leader of the MINOS research group in the University's Department of Physics, said: 'Neutrinos are one of the most abundant particles in the universe and if they do have some mass they change the way that the universe evolves. They influence how galaxies are created and large neutrino masses could be responsible for making the universe implode at the end of all time.'

Neutrinos are hard to catch and change form as they travel through space. Although they are one of the most abundant types of particles in the Universe, very little is known about these 'ghost particles'. They interact so weakly with matter that millions pass unnoticed through the air, earth and even people. The huge number of neutrinos in the universe, produced by stars and nuclear processes, may explain the origin of the neutrons, protons, and electrons that make up all the matter in the world around us.

The Main Injector Neutrino Oscillation Search (MINOS) fired a beam of neutrinos through the earth, from the lab's site (Fermilab) in Illinois to a particle detector in Soudan, Minnesota - a distance of 450 miles. One 1,000- ton neutrino 'near' detector sampled the beam as it left Fermilab and provided the control measurements. The 5,500-ton 'far' detector (pictured) half a mile underground in Soudan measured the neutrinos when they arrived just 2.5 milliseconds later. To compare neutrinos at the start with those at the finish, the scientists measured the difference in mass. This told them how many neutrinos had changed from one type to another - an effect known as 'neutrino oscillation'. A muon neutrino can transform into electron neutrinos or tau neutrinos, but alternative models - such as neutrino decay and extra dimensions - are not yet excluded.

Dr Weber said: 'The MINOS experiment shows that neutrinos do have mass and that at least one neutrino is heavier than 0.05 eV. This is 10 million times lighter than an electron. We previously thought that neutrinos are massless and this is quite an important measurement.'

It will take the recording of much more data by the MINOS collaboration to test more precisely the exact nature of the disappearance process.

Picture: The 100-foot-long MINOS far detector is located in a cavern half a mile underground in the Soudan Underground Laboratory, Minnesota. Credit: Fermilab.

［ 本帖最后由 太阳雨落 于 2006-04-06 21:41:47 编辑 ］