Science Current Events | Science News |

Neutrinos: Ghostly particles with unstable egos

September 06, 2011
They were always mysterious. 26 years had to pass before the prediction of theoretical physics was confirmed and the existence of neutrinos was finally proven experimentally in 1956. The reason for this ordeal: Neutrinos only interact by the weak interaction with other particles of matter. When a cosmic neutrino approaches the earth, it has the best chance of passing through the whole globe unhindered. It is correspondingly difficult to find direct evidence of neutrinos with the help of a detector. Further decades passed in the discussion about their masses: None or small but finite mass? In the meantime it is considered certain that the ghostly particles are carrying mass, if only a virtually infinitesimal amount: According to today's knowledge, no neutrino should exist that is heavier than 1 eV (an electron "weighs" about 500,000 eV!). There are three types of neutrinos. This is also believed to be true today, so that neutrinos can each easily be classified in one of the three particle families in the framework of the standard model.

The knowledge of the neutrino mass is based on numerous experiments, in which so-called neutrino oscillations were observed. Neutrinos freely flying through the space of a particular family (i.e. the electron neutrino) can transform themselves spontaneously into a neutrino of another family affiliation (the muon neutrino or tau neutrino). One refers to an oscillation because the neutrino may change its family affiliation periodically during an extended journey. Such oscillations are only possible if the particles are carrying mass. The experimental evidence of neutrino oscillations (and thus a neutrino mass other than zero) is among the greatest breakthroughs of modern particle physics in the past 20 years.

The conversion process among different neutrino flavors depends on three so-called mixing angles Theta 12, Theta 23 and Theta 13. In interplay with the neutrino mass-squared differences they regulate the transition probabilities among different flavors. Of the three mixing angles only two are well known and have large values, while the third one Theta 13 is at the focus of current searches. So far, it was known that its value had to be small compared to the other two neutrino mixing angles. That is, Theta 13 = 0 could not be excluded. In the past, several independent projects have tried to measure this elusive parameter without success. The most important piece of information came in 1998 from the Chooz experiment in France, which established that the oscillation evoked by Theta 13 cannot be larger than approximately one tenth of those induced by the each of the other two neutrino mixing angles.

Three years ago a group of theoretical physicists of whom one, Antonio Palazzo, is now at the Excellence Cluster Universe, the others at the University and INFN of Bari, evidenced for the first time a weak hint of non-zero Theta 13 thanks to an accurate work of global analysis of all the existing neutrino oscillation data. In the meantime, two accelerator experiments (MINOS and T2K) were at work to nailing down Theta 13 and they have recently released their results. Notably, both experiments point towards a non-zero Theta 13, in agreement with the hint evidenced by the group of theorists. By combining their previous findings with the new accelerator data, in June 2011 the same group came for the first time to a statistically clear conclusion according to which sin² Theta 13 ≈ 0.02 with a confidence level of at least 3 Sigma. This means that the odds against Theta 13 > zero are 1:400.

However, physicists are very prudent and, before claiming a discovery, need to have a higher confidence level of 5 Sigma, diminishing the odds against Theta 13 > zero to 1:1 million. In order to provide secure evidence, the researchers are performing other experiments. Among these, the reactor experiment Double-Chooz, in which physicists of the Universe Clusters are strongly involved, will have a crucial role. For this purpose, it has been developed a particularly effective, terrestrial neutrino source: The particles (more precisely: anti-neutrinos) are generated and emitted during the fission processes in a nuclear power plant in particularly high flux. About 1020 antineutrinos leave a typical reactor every second. For this reason, a new experiment, the inheritor of the forerunning Chooz experiment, has started in the vicinity of the nuclear power plant in the French municipality Chooz. Thanks to this setup the value of Theta 13 will be measured with a precision that hitherto has not been achieved.

The principle behind the Double-Chooz experiment is very simple: Immediately after their generation in the reactor, several anti-neutrinos collide with a detector located 400 meters away. The spatial proximity ensures that no oscillations (or only extremely few) occur between emission and initial detection. The first detector thus measures the electron anti-neutrinos, which haven't transformed to muon and or tau neutrinos yet. A second detector of identical construction is located approximately 1,050 meters away from the reactor. If the value of the neutrino mixing angle Theta 13 is large enough, a part of the electron anti-neutrinos will become muon or tau anti-neutrinos as a result of the oscillations. The electron-anti-neutrino rate observed at the second detector therefore is much smaller than expected without oscillations.

Both detectors are filled with about 10 tons of scintillation fluid. If an electron-anti-neutrino interacts with a proton within the fluid, this will lead to inverse-beta decay: The proton captures the electron-anti-neutrino thereby transforming into one neutron by emitting one positron. Both particles generate one quick flash each in the liquid in a set time sequence. 390 photo sensors mounted on the walls of the vessel record the events. The Double Chooz experiment started physics data taking in April 2011 and will search for corresponding signals for five years. The detector performance and the status of data taking will be reported at the TAUP conference in Munich from 5 to 9 September 2011. First results are expected by the end of this year.

Establishing that Theta 13 is effectively different from zero would entail that all the three mixing angles are non-vanishing. This would provide the three neutrino flavors with maximal freedom of flipping one to each other. In turn, such a high degree of freedom is the necessary condition to generate CP-violation in the leptonic sector, i.e. to give rise to a different behavior of neutrinos and anti-neutrinos. The observation of CP-violation is now the next target of neutrino physicists as it would have significant consequences for several unanswered questions of modern physics. It could soon be clarified, in particular, whether neutrinos were responsible for the minimal surplus of matter compared to anti-matter in the early Universe. Without this asymmetry, all matter would have been transformed to radiation shortly after the birth of the Universe. There would be no galaxies, no stars or planets and no one who could measure Theta 13.

Technische Universitaet Muenchen

Related Neutrino Current Events and Neutrino News Articles

NuSTAR provides explosive evidence for supernova asymmetry
New results from the NASA NuSTAR telescope show that a supernova close to our galaxy experienced a single-sided explosion.

Zooming in
The microwave oven has been around for almost 80 years. When it heats food or liquid, the frequency of electrons increases but their energy slows down due to their own microwave emissions. Until now, scientists have only been able to observe this phenomenon in a group of electrons.

Electron chirp: Cyclotron radiation from single electrons measured directly for first time
A year before Albert Einstein came up with the special theory of relativity, or E=mc2, physicists predicted the existence of something else: cyclotron radiation.

New tabletop detector 'sees' single electrons
MIT physicists have developed a new tabletop particle detector that is able to identify single electrons in a radioactive gas.

Detector at the South Pole explores the mysterious neutrinos
Neutrinos are a type of particle that pass through just about everything in their path from even the most distant regions of the universe.

Cosmic debris: Study looks inside the universe's most powerful explosions
A new study provides an inside look at the most powerful explosions in the universe: gamma-ray bursts.

Decoding the gravitational evolution of dark matter halos
Researchers at Kavli IPMU and their collaborators have revealed that considering environmental effects such as a gravitational tidal force spread over a scale much larger than a galaxy cluster is indispensable to explain the distribution and evolution of dark matter halos around galaxies.

Researchers show neutrinos can deliver not only full-on hits but also 'glancing blows'
In what they call a "weird little corner" of the already weird world of neutrinos, physicists have found evidence that these tiny particles might be involved in a surprising reaction.

Researchers detect possible signal from dark matter
Could there finally be tangible evidence for the existence of dark matter in the Universe? After sifting through reams of X-ray data, scientists in EPFL's Laboratory of Particle Physics and Cosmology (LPPC) and Leiden University believe they could have identified the signal of a particle of dark matter.

They know the drill: UW leads the league in boring through ice sheets
Wisconsin is famous for its ice fishers - the stalwarts who drill holes through lake ice in the hope of catching a winter dinner.
More Neutrino Current Events and Neutrino News Articles


by Frank Close (Author)

Neutrinos are perhaps the most enigmatic particles in the universe. These tiny, ghostly particles are formed by the billions in stars and pass through us constantly, unseen, at almost the speed of light. Yet half a century after their discovery, we still know less about them than all the other varieties of matter that have ever been seen.

In this engaging, concise volume, renowned scientist and writer Frank Close gives a vivid account of the discovery of neutrinos and our growing understanding of their significance, touching on speculative ideas concerning the possible uses of neutrinos and their role in the early universe along the way. Close begins with the discovery of radioactivity by Henri Becquerel and Marie and Pierre Curie, the early model of the atom by Ernest...

Neutrino Hunters: The Thrilling Chase for a Ghostly Particle to Unlock the Secrets of the Universe

Neutrino Hunters: The Thrilling Chase for a Ghostly Particle to Unlock the Secrets of the Universe
by Ray Jayawardhana (Author)

Winner of the Canadian Science Writers Association 2014 Science in Society Book Award
A Publishers Weekly Top 10 Science Book of the Season
A Book to Watch Out For, The New Yorker's Page-Turner Blog
A Los Angeles Times Gift Guide Selection
One of the Best Physics Books of 2013, Cocktail Party Physics Blog, Scientific American

Detective thriller meets astrophysics in this adventure into neutrinos and the scientists who pursue them

The incredibly small bits of matter we call neutrinos may hold the secret to why antimatter is so rare, how mighty stars explode as supernovae, what the universe was like just seconds after the big bang, and even the inner workings of our own planet.For more than eighty years, adventurous minds from around the world have been chasing...

The Physics of Neutrinos

The Physics of Neutrinos
by Vernon Barger (Author), Danny Marfatia (Author), Kerry Whisnant (Author)

The physics of neutrinos--uncharged elementary particles that are key to helping us better understand the nature of our universe--is one of the most exciting frontiers of modern science. This book provides a comprehensive overview of neutrino physics today and explores promising new avenues of inquiry that could lead to future breakthroughs.

The Physics of Neutrinos begins with a concise history of the field and a tutorial on the fundamental properties of neutrinos, and goes on to discuss how the three neutrino types interchange identities as they propagate from their sources to detectors. The book shows how studies of neutrinos produced by such phenomena as cosmic rays in the atmosphere and nuclear reactions in the solar interior provide striking evidence...

The Perfect Wave: With Neutrinos at the Boundary of Space and Time

The Perfect Wave: With Neutrinos at the Boundary of Space and Time
by Heinrich Päs (Author)

Almost weightless and able to pass through the densest materials with ease, neutrinos seem to defy the laws of nature. But these mysterious particles may hold the key to our deepest questions about the universe, says physicist Heinrich Päs. In The Perfect Wave, Päs serves as our fluent, deeply knowledgeable guide to a particle world that tests the boundaries of space, time, and human knowledge. The existence of the neutrino was first proposed in 1930, but decades passed before one was detected. Päs animates the philosophical and scientific developments that led to and have followed from this seminal discovery, ranging from familiar topics of relativity and quantum mechanics to more speculative theories about dark energy and supersymmetry. Many cutting-edge topics in neutrino...

Fundamentals of Neutrino Physics and Astrophysics

Fundamentals of Neutrino Physics and Astrophysics
by Carlo Giunti (Author), Chung W. Kim (Author)

This book deals with neutrino physics and astrophysics- a field in which some of the most exciting recent developments in particle physics, astrophysics and cosmology took place. The book is the most up-to-date, comprehensive and self-contained treatment of key issues in neutrino physics. It discusses all the topics vital to the understanding of the nature of neutrinos such as what they are, how to describe them, how they behave in nature, and the roles of neutrinos play in shaping our Universe. The book provides comprehensive discussions, both experimental and theoretical, with relevant mathematical details, on neutrino oscillations, extra-terrestrial as well as terrestrial neutrinos and relic neutrinos. It also discusses many implications of current experimental data on rector,...

Neutrino Physics, Second Edition (Series in High Energy Physics, Cosmology and Gravitation)

Neutrino Physics, Second Edition (Series in High Energy Physics, Cosmology and Gravitation)
by Kai Zuber (Author)

When Kai Zuber’s pioneering text on neutrinos was published in 2003, the author correctly predicted that the field would see tremendous growth in the immediate future. In that book, Professor Zuber provided a comprehensive self-contained examination of neutrinos, covering their research history and theory, as well as their application to particle physics, astrophysics, nuclear physics, and the broad reach of cosmology; but now to be truly comprehensive and accurate, the field’s seminal reference needs to be revised and expanded to include the latest research, conclusions, and implications. Revised as needed to be equal to the research of today, Neutrino Physics, Second Edition delves into neutrino cross sections, mass measurements, double beta decay, solar neutrinos, neutrinos from...

Neutrinos in High Energy and Astroparticle Physics

Neutrinos in High Energy and Astroparticle Physics
by José Wagner Furtado Valle (Author), Jorge Romao (Author)

This self-contained modern textbook provides a modern description of the Standard Model and its main extensions from the perspective of neutrino physics. In particular it includes a thorough discussion of the varieties of seesaw mechanism, with or without supersymmetry. It also discusses schemes where neutrino mass arises from lighter messengers, which might lie within reach of the world's largest particle accelerator, the Large Hadron Collider. Throughout the text, the book stresses the role of neutrinos due to the fact that neutrino properties may serve as a guide to the correct model of unification, hence for a deeper understanding of high energy physics, and because neutrinos play an important role in astroparticle physics and cosmology. Each chapter includes summaries and set of...

Neutrino Cosmology

Neutrino Cosmology
by Dr Julien Lesgourgues (Author), Dr Gianpiero Mangano (Author), Professor Gennaro Miele (Author), Dr Sergio Pastor (Author)

The role that neutrinos have played in the evolution of the Universe is the focus of one of the most fascinating research areas that has stemmed from the interplay between cosmology, astrophysics and particle physics. In this self-contained book, the authors bring together all aspects of the role of neutrinos in cosmology, spanning from leptogenesis to primordial nucleosynthesis, their role in CMB and structure formation, to the problem of their direct detection. The book starts by guiding the reader through aspects of fundamental neutrino physics, such as the standard cosmological model and the statistical mechanics in the expanding Universe, before discussing the history of neutrinos in chronological order from the very early stages until today. This timely book will interest graduate...

Introduction to the Physics of Massive and Mixed Neutrinos (Lecture Notes in Physics)

Introduction to the Physics of Massive and Mixed Neutrinos (Lecture Notes in Physics)
by Samoil Bilenky (Author)

For many years neutrino was considered a massless particle. The theory of a two-componentneutrino,whichplayedacrucialroleinthecreationofthetheoryof theweakinteraction,isbasedontheassumptionthattheneutrinomassisequalto zero. We now know that neutrinos have nonzero, small masses. In numerous exp- iments with solar, atmospheric, reactor and accelerator neutrinos a new p- nomenon, neutrino oscillations, was observed. Neutrino oscillations (periodic transitionsbetweendifferent?avorneutrinos? ,? ,? )arepossibleonlyifneutrino e ? ? mass-squareddifferencesaredifferentfromzeroandsmalland?avorneutrinosare “mixed”. The discovery of neutrino oscillations opened a new era in neutrino physics: an era of investigation of neutrino masses, mixing, magnetic moments and other neutrino properties. After...

The Neutrino: Ghost Particle of the Atom

The Neutrino: Ghost Particle of the Atom
by Isaac Asimov (Author)


© 2015