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Sterile neutrinos
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Particle physics can be a bit like playing Whac-a-Mole: knock one mystery down, and another one pops right up. True to form, a study that last week ended controversy about the sterile neutrino - a particle that shouldn't exist - also stirred up new intrigue. The findings, if confirmed, could provide tantalising hints of extra dimensions.
Neutrinos are tiny particles that barely interact with matter. They come in three types or "flavours" - electron, muon and tau - that can, along with their antiparticle counterparts, flip from one flavour to another, or "oscillate", as they travel.
One of the experiments to show this, the Liquid Scintillator Neutrino Detector (LSND) at Los Alamos National Laboratory in New Mexico, ran from 1993 to 1998 and suggested that some muon anti-neutrinos had flipped into electron anti-neutrinos after travelling about 30 metres.

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MiniBooNE experiment
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Results of an international particle physics experiment announced last week have solved a long-standing question about the nature of neutrinos, one of the fundamental particles that make up the universe. The MiniBooNE experiment has taken significant steps towards refuting some unexpected results that occurred during a neutrino experiment in the 1990s, which suggested a new type of neutrino exists. The new MiniBooNE results also help to clarify the overall picture of how neutrinos behave.

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MiniBooNE project
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Tasked to check the finding, MiniBooNE researchers fired a beam of normal matter muon neutrinos at a 12-meter-wide spherical tank of mineral oil 500 meters away. When an electron neutrino strikes a carbon nucleus in the oil, it emits a flash of bluish light. The beam produces electron neutrinos directly at a certain rate; a higher frequency would signal something unanticipated.
The group reported no overall increase in the rate of electron neutrino events for muon neutrinos of different energies, which would have bolstered the LSND case for neutrinos switching flavours.

"We have quite conclusively ruled out that model for what might be going on" - Physicist Janet Conrad, Columbia University, spokesperson for the MiniBooNE team.

But there are other, more exotic models that still have to be checked, says co-spokesperson William Louis of LANL, who worked on LSND.

"That is the $64,000 question. Are the MiniBooNE results consistent with LSND, and is the LSND excess a real signal?''

The team has begun running the experiment with antineutrinos to rule out other possibilities, such as a slight asymmetry between matter and antimatter.
The group did spot an odd uptick in the number of electron neutrinos at lower energies369 events instead of 273. But Louis says the significance of that is unclear. It could mean that physicists have overlooked a subtle detail in the experiment or miscalculated the rate at which neutrinos collide with atomic nuclei.

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MiniBooNE
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Today at Fermilab, the MiniBooNE experiment announced to a packed auditorium their long-awaited results looking for neutrino oscillations. Below is a guest post from Dr. Heather Ray, a scientist at Los Alamos National Lab, who has been working on the experiment for several years. I have known Heather since she was a graduate student on the CDF experiment at Fermilab, when she was at the University of Michigan.

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MiniBooNE project
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An announcement by scientists at the Department of Energys Fermilab today significantly clarifies the overall picture of how neutrinos behave.
The results of the so-named MiniBooNE project resolve questions raised by observations an earlier DOE experiment Liquid Scintillator Neutrino Detector (LSND) - in the 1990s that appeared to contradict findings of other neutrino experiments worldwide. The announcement today significantly clarifies the overall picture of how neutrinos behave.
In addition, scientists at Virginia Tech have proposed a new experiment, known as LENS (Low Energy Neutrino Spectroscopy), which will push the search for sterile neutrinos well beyond the scope of the MiniBooNE project.

"The possibility of sterile-neutrino-induced oscillation observed by LSND now seems to be ruled out. But there may still be sterile neutrinos with somewhat different properties" - Jonathan Link, Virginia Tech College of Science physicist who, along with 77 scientists from 16 other universities around the world, was a member of the MiniBooNE collaboration.

Since the LSND result, theorists have used sterile neutrinos to solve many problems in physics from supernova explosions to the mysterious dark matter that binds galaxies together. Virginia Techs LENS (full name here) project will push the search for mysterious sterile neutrinos even further.
Currently, three types or "flavours" of neutrinos are known to exist: electron neutrinos, muon neutrinos and tau neutrinos. In the last 10 years, several experimentsincluding the LSND collaborationhave shown that neutrinos can oscillate from one flavour to another and back. However, reconciling the LSND observations with the oscillation results of other neutrino experiments would have required the presence of a fourth, or "sterile" type of neutrino, with properties different from the three standard neutrinos. The existence of sterile neutrinos would throw serious doubt on the current structure of particle physics, known as the Standard Model of Particles and Forces. Because of the far-reaching consequences of this interpretation, the LSND findings cried out for independent verification.
The MiniBooNE experiment, approved in 1998, took data for the current analysis from 2002 until the end of 2005 using neutrinos produced by the Booster accelerator at the Fermilab. The experiments goal was either to confirm or to refute the startling observations reported by the LSND collaboration, thus answering a long-standing question that has troubled the neutrino physics community for more than a decade.
The MiniBooNE collaboration used a blind-experiment technique to ensure the credibility of their analysis and results. While collecting their neutrino data, the MiniBooNE collaboration did not permit themselves access to data in the region, or "box," where they would expect to see the same signature of oscillations as LSND. When the MiniBooNE collaboration opened the box and "unblinded" its data less than three weeks ago, the telltale oscillation signature was absent.
Simply put, neutrinos are particles that originate from the centre of the sun. They are one of the fundamental particles of the universe but also one of the least understood. Neutrinos differ from electrons in that they do not carry an electric charge and can pass through great distances in matter without being affected by it.
Studying neutrinos helps scientists understand about the sun, stars, and even the deep core of the Earth. It also provides the capability to detect extremely small trace amounts of radioactivity contained in samples of material, resulting in applications for homeland security, microelectronics, and space science.
For its observations, MiniBooNE relied on a 250,000-gallon tank filled with ultra pure mineral oil, clearer than water from a faucet. A layer of 1280 light-sensitive photomultiplier tubes, mounted inside the tank, detects collisions between neutrinos made by the Booster accelerator and carbon nuclei of oil molecules. Since January 2006, the MiniBooNE experiment has been collecting data using beams of antineutrinos instead of neutrinos and expects further results from these new data.

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The initial data from the 10-year long "MiniBooNE" experiment at the Department of Energy's Fermilab significantly clarifies the overall picture of how the neutrino fundamental particles behave.

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RE: Neutrinos
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Title: Plasmaneutrino spectrum
Authors: A. Odrzywolek

Spectrum of the neutrinos produced in the massive photon and longitudal plasmon decay process has been computed with four levels of approximation for the dispersion relations. Some analytical formulae in limiting cases are derived. Interesting conclusions related to previous calculations of the energy loss in stars are presented. High energy tail of the neutrino spectrum is shown to be proportional to exp(-E/kT), where E is the neutrino energy and kT is the temperature of the plasma.

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Title: Are small neutrino masses unveiling the missing mass problem of the Universe?
Authors: C. Boehm, Y. Farzan, T. Hambye, S. Palomares-Ruiz, S. Pascoli

We present a scenario in which a remarkably simple relation linking dark matter properties and neutrino masses naturally emerges. This framework points towards a low energy theory where the neutrino mass originates from the existence of a light scalar dark matter particle in the MeV mass range. A very surprising aspect of this scenario is that the required MeV dark matter is one of the favoured candidates to explain the mysterious emission of 511 keV photons in the centre of our galaxy. A possible interpretation of these findings is that dark matter is the stepping stone of a theory beyond the standard model instead of being an embarrassing relic whose energy density must be accounted for in any successful model building.

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Violation of CPT
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Title: Violation of CPT and Lorentz Invariance, Neutrino Oscillation and the Early Universe
Authors: Paola Arias, Ashok Das, Jorge Gamboa, Justo Lopez-Sarrion, Fernando Mendez
UPDATE

We propose that a tiny violation of Lorentz and CPT symmetry can lead to very interesting physical phenomena in the neutrino sector. For example, it is already known that Lorentz and CPT violation can give rise to oscillations of even massless neutrinos. In this paper, we carry this investigation further quantitatively and taking a simple model derive bounds on such symmetry violating parameters from the known experimental results on neutrino oscillation. We argue that a violation of Lorentz and CPT invariance can also give a way of calculating the neutrino asymmetry in the universe.

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RE: Neutrinos
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Since 1983 researchers at the Fermi National Accelerator Laboratory in Batavia, Ill., have plumbed the subatomic realm by smashing high-energy protons and antiprotons together in the Tevatron, the world's most powerful particle collider. Next year, however, the high-energy frontier will move to Europe, where the even more powerful Large Hadron Collider will begin operations near Geneva. Fermilab intends to shut down the Tevatron by 2010. But rather than scrapping the device, lab officials have outlined an ambitious plan to use some of the collider's parts to enhance a promising research program: the study of the mysterious neutrino, whose strange properties may offer clues to new laws of physics.

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Physicists have confirmed that neutrinos, which are thought to have played a key role during the creation of the Universe, have mass.

This is the first major finding of the US-based Main Injector Neutrino Oscillation Search (Minos) experiment.
The findings suggest that the Standard Model, which describes how the building blocks of the Universe behave and interact, needs a revision.
Neutrinos are believed to be vital to our understanding of the Universe.
But scientists know frustratingly little about these fundamental particles.
The findings build on work carried out by Japanese physicists.

There are three kinds - or "flavours" - of neutrinos: muon, tau and electron.
To examine their properties, scientists created muon neutrinos in a particle accelerator at the Fermi National Accelerator Laboratory (Fermilab) in Illinois, US.
A high intensity beam of these particles was fired through a particle detector at Fermilab, and then to another particle detector 724km away in a disused mine in Soudan, US.
The scientists' set up established that fewer particles were being detected at the Soudan site than had been sent. They had effectively "disappeared".
Physicists call the process of transforming from one type of neutrino into another flavour oscillation. And to be able to perform this transformation, particle physics theory states that the particles need mass.

These are the first results from the Minos experiment, which has involved scientists from 32 institutions in six countries.

It confirms the earlier observations of neutrino "disappearance" found in 2002 by the Japanese K2K experiment, where scientists fired muon neutrinos at a detector situated 240km away.

The corroboration that the neutrino has mass has profound implications for particle physics.



"In particle physics there is the Standard Model which describes how the fundamental building blocks of matter behave and interact with each other. And this model tells us that neutrinos should have no mass. So the fact that we have now got independent measurements of neutrinos saying that they must have mass, means that this Standard Model is going to have be revised or superseded by something else" - Dr Lisa Falk Harris, a particle physicist at the University of Sussex.

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