Archivi tag: neutrino oscillations

Massive or massless neutrinos?

Gli scienziati avrebbero risolto uno dei problemi aperti dell’attuale modello cosmologico standard combinando i dati del satellite Planck e quelli ottenuti grazie al fenomeno della lente gravitazionale allo scopo di determinare la massa dei neutrini.

The team, from the universities of Nottingham and Manchester, used observations of the Big Bang and the curvature of spacetime to accurately measure the mass of these elementary particles for the first time. The recent Planck spacecraft observations of the Cosmic Microwave Background (CMB), the fading glow of the Big Bang, highlighted a discrepancy between these cosmological results and the predictions from other types of observations. The CMB is the oldest light in the Universe, and its study has allowed scientists to accurately measure cosmological parameters, such as the amount of matter in the Universe and its age. But an inconsistency arises when large-scale structures of the Universe, such as the distribution of galaxies, are observed. Dr Adam Moss, from The University of Nottingham’s School of Physics and Astronomy said: “We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest. A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies.” Neutrinos interact very weakly with matter and so are extremely hard to study. They were originally thought to be massless but particle physics experiments have shown that neutrinos do indeed have mass and that there are several types, known as flavours by particle physicists. The sum of the masses of these different types has previously been suggested to lie above 0.06 eV (much less than a billionth of the mass of a proton). Dr Moss and Professor Richard Battye from The University of Manchester have combined the data from Planck with gravitational lensing observations in which images of galaxies are warped by the curvature of spacetime.

They conclude that the current discrepancies can be resolved if massive neutrinos are included in the standard cosmological model.

They estimate that the sum of masses of neutrinos is 0.320 +/- 0.081 eV (assuming active neutrinos with three flavours). Professor Battye added: “If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade”.

Nottingham University: Massive neutrinos solve a cosmological conundrum

arXiv: Evidence for massive neutrinos from CMB and lensing observations

Discovered a new type of neutrino oscillation

Grazie ad uno studio recente guidato da un gruppo di fisici inglesi e giapponesi è stato possibile confermare che le particelle subatomiche, denominate neutrini, possiedono una nuova identità. Questi risultati, che danno inoltre credito agli esperimenti realizzati in Giappone presso il rivelatore T2K che ha lo scopo di studiare l’oscillazione dei neutrini, potrebbero un giorno aiutare gli scienziati a capire come mai l’Universo contiene in gran parte materia e solo ‘poche tracce’ di antimateria (vedasi Enigmi Astrofisici).

Alfons Weber, a professor of Physics at STFC and the University of Oxford is one of many scientists in the UK working on T2K. He explains: “The UK particle physics community was one of the driving forces behind this experiment. We not only provided part of the detector that characterises the beam, but also designed the target that produces the neutrinos in the first place. The long years of hard work have now come to fruition. Our findings now open the possibility to study this process for neutrinos and their antimatter partners, the anti-neutrinos. A difference in the rate of electron or anti-electron neutrino being produced may lead us to understand why there is so much more matter than antimatter in the Universe. The neutrino may be the very reason we are here“.

In 2011, the T2K collaboration announced the first indication of this process. Now with 3.5 times more data and a significance of 7.5 sigma, this behaviour is firmly established and can now be called a discovery.

There are three types, or ‘flavours,’ of neutrinos, one paired with the electron (called the electron neutrino), and two more paired with the electron’s heavier cousins, the muon and tau leptons. These different flavours of neutrinos can spontaneously change into each other, a phenomenon called neutrino oscillations. Observations have previously been made of a number of different types of oscillations, however the T2K results are the first discovery of the appearance of electron neutrinos in a beam of muon neutrinos, and it is this kind of oscillation which is the key to making measurements to distinguish the oscillations of neutrinos and anti-neutrinos. To explore the neutrinos’ oscillations, the T2K experiment fired a beam of neutrinos from the J-PARC laboratory at Tokai Village on the eastern coast of Japan, and detected them at the Super-Kamiokande neutrino detector, 295 km away in the mountains of the north-western part of the country. Here, the scientists looked to see if the neutrinos at the end of the beam matched those emitted at the start.

They found 22.5 neutrinos appearing in the beam of muon neutrinos, where if there were no oscillations they only expected to see an average of 6.4. This indicates the discovery of the new type of oscillation.

Now the team must make more accurate measurements of this new oscillation, and then run their experiment with an anti-neutrino beam to see if the results change. Professor Dave Wark of the Science and Technology Facilities Council (STFC) and Oxford University, leads the UK’s involvement in the international experiment. He said: “It’s a joy to see T2K deliver the science we designed it for. I have been working on this for more than a decade, and what these results tell us is that we have more than another decade of work ahead of us. We have seen a new way for neutrinos to change, and now we have to find out if neutrinos and anti-neutrinos do it the same way. If they don’t, it may be a clue to help solve the mystery of where the matter in the Universe came from in the first place. Surely answering that is worth a couple of decades of work!“.

STFC: UK researchers make new discovery about neutrinos, bringing us one step closer to perhaps solving one of the biggest mysteries in fundamental physics