French physicist Léon Foucault celebrated in Google doodle
Category: AQA Physics Spec A 1451/2451
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Aug 07 2013
‘Critical phase’ for fusion dream https://www.bbc.co.uk/news/science-environment-23408073
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Jul 21 2013
Neutrino ‘flavour’ flip confirmed https://www.bbc.co.uk/news/science-environment-23366318
An important new discovery has been made in Japan about neutrinos. These are the ghostly particles that flood the cosmos but which are extremely hard to detect and study. Experiments have now established that one particular type, known as the muon “flavour”, can flip to the electron type during flight. The observation is noteworthy because it allows for the possibility that neutrinos and their anti-particle versions might behave differently. If that is the case, it could be an explanation for why there is so much more matter than antimatter in the Universe. Theorists say the counterparts would have been created in equal amounts at the Big Bang, and should have annihilated each other unless there was some significant element of asymmetry in play.
“The fact that we have matter in the Universe means there have to be laws of physics that aren’t in our Standard Model, and neutrinos are one place they might be,” Prof Dave Wark, of the UK’s Science and Technology Facilities Council (STFC) and Oxford University, told BBC News. The confirmation that muon flavour neutrinos can flip, or oscillate, to the electron variety comes from T2K, an international collaboration involving some 500 scientists. The team works on a huge experimental set-up that is split across two sites separated by almost 300km. At one end is the Japan Proton Accelerator Research Centre (J-Parc) located on the country’s east coast.
The ‘ghostly’ neutrino particle
- Second most abundant particle in the Universe, after photons of light
- Means ‘small neutral one’ in Italian; was first proposed by Wolfgang Pauli in 1930
- Uncharged, and created in nuclear reactions and some radioactive decay chains
- Shown to have a tiny mass, but hardly interacts with other particles of matter
- Comes in three flavours, or types, referred to as muon, tau and electron
- These flavours are able to oscillate – flip from one type to another – during flight
- Could be a Majorana particle – that is a particle that is equal to its anti-particle
It generates a beam of muon neutrinos that it fires under the ground towards the Super-Kamiokande facility on the west coast. The Super-K, as it is sometimes called, is a tank of 50,000 tonnes of ultra-pure water surrounded by sensitive optical detectors. These photomultiplier tubes pick up the very rare, very faint flashes of light emitted when passing neutrinos interact with the water.
In experiments in early 2011, the team saw an excess of electron neutrinos turning up at Super-K, suggesting the muon types had indeed changed flavour en route. But just as the collaboration was about to verify its findings, the Great Tohoku Earthquake damaged key pieces of equipment and took T2K offline. Months of repairs followed before the project was able then to gather more statistics and show the muon-electron oscillation to be a formal discovery. Details are being reported on Friday at the European Physical Society Conference on High Energy Physics in Stockholm, Sweden.
“Up until now the oscillations have always been measured by watching the types disappear and then deducing that they had turned into another type. But in this instance, we observe muon neutrinos disappearing and we observe electron neutrinos arriving – and that’s a first,” said Prof Alfons Weber, another British collaborator on T2K from the STFC and Oxford.
Neutrino oscillations are governed by a matrix of three angles that can be thought of as the three axes of rotation in an aeroplane – roll, pitch and yaw. Other research has already shown two of the matrix angles to have non-zero values. T2K’s work confirms that the third angle – referred to as theta-one-three – also has to have a non-zero value.
This is critical because it allows for the oscillations of normal neutrinos and their anti-particles, anti-neutrinos, to be different – that they can have enough degrees of freedom to display an asymmetrical behaviour called charge parity (CP) violation. CP-violation has already been observed in quarks, the elementary building blocks of the protons and neutrons that make up atoms, but it is a very small effect – too small to have driven the preference for matter over anti-matter after the Big Bang. However, if neutrinos can also display the asymmetry – and especially if it was evident in the very massive neutrinos thought to have existed in the early Universe – this might help explain the matter-antimatter conundrum. The scientists must now go and look for it. It is likely, though, that much more powerful neutrino laboratories than even T2K will be needed to investigate the issue.
“We have the idea for a Hyper-Kamiokande which will require an upgrade of the accelerator complex,” Prof Weber told BBC News.
“And in America there’s something called the LBNE, which again would have bigger detectors, more sensitive detectors and more intense beams, as well as a longer baseline to allow the neutrinos to travel further.”
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Jul 18 2013
Neutron starbursts can forge gold https://www.bbc.co.uk/news/science-environment-23361153
New evidence has been uncovered of a rare cosmic event that is proposed as a source of heavy elements such as gold. Observations from the Hubble Space Telescope appear to show a distant collision between two neutron stars – the remnants of massive supernovae. Astronomers suggest that such collisions are responsible for ultra-short bursts of gamma rays occasionally seen across the Universe. The work is described in a paper on the pre-print server Arxiv.org.
Although rare, neutron star collisions would generate the enormous fluxes of neutrons needed to make elements heavier than iron, like platinum, lead and gold, by rapid neutron capture. Prof Edo Berger and colleagues from Harvard University analysed Hubble observations of a short burst of gamma rays, lasting only one fifth of a second, seen from a galaxy 3.9 billion light years away. The infrared afterglow of this burst of gamma-ray light appears to show the characteristics expected during radioactive decay of atomic nuclei generated in a neutron star collision.
This sort of event emits light with an intensity that lies between normal star light and that of a supernova, and the term “kilonova” has been coined to describe it. They appear to be around 1,000 times rarer than supernova explosions, and occur when the remnants of two supernovae collide.
If confirmed, the result represents the first observation of a neutron star collision, and provides an explanation for the rapid “R-process” of atom-building that must generate the heavy elements on the periodic table, such as gold and platinum. Neutron stars are incredibly dense and massive. As well as bursts of light, when they collide they are also expected to send gravity “shock waves” through the Universe. Experiments in America and Europe are now focussed on measuring such waves, and combined with the type of events seen by Hubble in the last month this will provide a further confirmation of neutron star collision. Astronomers are now testing the conclusions of the Harvard group with further detailed analysis of the Hubble data.
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Apr 04 2013
LHC to enter ‘new realm of physics’ https://www.bbc.co.uk/news/science-environment-21941666
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Feb 28 2013
LHC wraps up antimatter ‘flip’ story https://www.bbc.co.uk/news/science-environment-21594357
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