PhysOrg: Neutrino oscillation: OPERA sees first tau-neutrino

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PhysOrg: Neutrino oscillation: OPERA sees first tau-neutrino

Post by bystander » Tue Jun 01, 2010 9:21 am

'Neutrino oscillation': The OPERA experiment likely seen the first tau-neutrino
PhysOrg - General Physics - 31 May 2010
After seven years since the start of construction of the OPERA experiment and three years of operation in the underground Gran Sasso Laboratory of the Italian National Institute of Nuclear Physics (INFN), one of the many billions of muon-neutrinos produced at the CERN accelerator complex (CNGS) has likely "transformed" into a tau-neutrino that has been observed by the OPERA apparatus.

This is an extremely important result. The observation of a few more of these tau-neutrino events over a large number of conventional muon-neutrino interactions will represent the long awaited proof of the direct conversion of one type of neutrino into another: the so called "neutrino oscillation" mechanism.

The disappearance of the initial neutrino flavour has already been observed by several experiments in the last 15 years, but the "direct appearance" is still the outstanding missing tile of the puzzle, and the OPERA experiment is unique worldwide for this purpose. Neutrino oscillation is today the only indication of new, fascinating physics beyond the so-called Standard Model of particles and interactions, opening the possibility of unexpected implications in cosmology, astrophysics and particle physics.

The experiment was inaugurated in 2006, when the first "normal" muonneutrinos were detected after a trip of 730 km from CERN, covered in about 2.4 milliseconds, at the speed of light. After then, a careful and tireless search started to find the tiny and very special signal induced by a tau-neutrino.
More information: The OPERA experiment

Particle Chameleon Caught in the Act of Changing
Science Daily - 31 May 2010
Researchers on the OPERA experiment at the INFN's Gran Sasso laboratory in Italy today announced the first direct observation of a tau particle in a muon neutrino beam sent through the Earth from CERN, 730 km away. This is a significant result, providing the final missing piece of a puzzle that has been challenging science since the 1960s, and giving tantalizing hints of new physics to come.

The neutrino puzzle began with a pioneering and ultimately Nobel Prize winning experiment conducted by US scientist Ray Davis beginning in the 1960s. He observed far fewer neutrinos arriving at the Earth from the Sun than solar models predicted: either solar models were wrong, or something was happening to the neutrinos on their way. A possible solution to the puzzle was provided in 1969 by the theorists Bruno Pontecorvo and Vladimir Gribov, who first suggested that chameleon-like oscillatory changes between different types of neutrinos could be responsible for the apparent neutrino deficit.

Several experiments since have observed the disappearance of muon-neutrinos, confirming the oscillation hypothesis, but until now no observations of the appearance of a tau-neutrino in a pure muon-neutrino beam have been observed: this is the first time that the neutrino chameleon has been caught in the act of changing from muon-type to tau-type.

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Re: PhysOrg: Neutrino oscillation: OPERA sees first tau-neut

Post by wonderboy » Tue Jun 01, 2010 10:53 am

I'm just an ignorant soul, but what does this mean in terms of significance? I know its a significant event, but I don't know why it is significant?


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Re: PhysOrg: Neutrino oscillation: OPERA sees first tau-neut

Post by neufer » Tue Jun 01, 2010 11:38 am

wonderboy wrote:I'm just an ignorant soul, but what does this mean in terms of significance? I know its a significant event, but I don't know why it is significant?
http://en.wikipedia.org/wiki/Neutrino#Mass wrote:
<<The Standard Model of particle physics assumed that neutrinos are massless [and thus travel at exactly the speed of light], although adding massive neutrinos to the basic framework is not difficult. Indeed, the experimentally established phenomenon of neutrino oscillation requires neutrinos to have nonzero masses. In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos do indeed flavor oscillate, and therefore have mass. While this shows that neutrinos have mass, the absolute neutrino mass scale is still not known. This is due to the fact that neutrino oscillations are sensitive only to the difference in the squares of the masses. All neutrino masses are nearly equal [and probably on the order of 10 to 100 milli-eV] , with mass differences between the 3 flavors on the order milli-eV.

The strongest upper limit on the masses of neutrinos comes from cosmology: the Big Bang model predicts that there is a fixed ratio between the number of neutrinos and the number of photons in the cosmic microwave background. If the total energy of all three types of neutrinos exceeded an average of 50 electronvolts per neutrino, there would be so much mass in the universe that it would collapse. This limit can be circumvented by assuming that the neutrino is unstable; however, there are limits within the Standard Model that make this difficult. A much more stringent constraint comes from a careful analysis of cosmological data, such as the cosmic microwave background radiation, galaxy surveys, and the Lyman-alpha forest. These indicate that the sum of the neutrino masses must be less than 0.3 electronvolt. However, in 2009 lensing data of a galaxy cluster were analyzed to predict a neutrino mass of about 1.5 eV. If it is found around 1.5 eV, the Cold Dark Matter particle likely does not exist.

Currently a number of efforts are under way to directly determine the absolute neutrino mass scale in laboratory experiments. The methods applied involve nuclear beta decay (KATRIN and MARE) or neutrinoless double beta decay (e.g. GERDA, CUORE/Cuoricino, NEMO-3 and others).>>
Art Neuendorffer

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FNAL: Key property of neutrinos and antineutrinos different?

Post by bystander » Mon Jun 14, 2010 9:04 pm

New measurements suggest a difference in a key property of neutrinos and antineutrinos
Fermilab | MINOS experiment | 14 June 2010
Scientists of the MINOS experiment at the Department of Energy’s Fermi National Accelerator laboratory today (June 14) announced the world’s most precise measurement to date of the parameters that govern antineutrino oscillations, the back-and-forth transformations of antineutrinos from one type to another. This result provides information about the difference in mass between different antineutrino types. The measurement showed an unexpected variance in the values for neutrinos and antineutrinos.

This mass difference parameter, called Δm2 (“delta m squared”), is smaller by approximately 40 percent for neutrinos than for antineutrinos. However, there is a still a five percent probability that Δm2 is actually the same for neutrinos and antineutrinos. With such a level of uncertainty, MINOS physicists need more data and analysis to know for certain if the variance is real.

Neutrinos and antineutrinos behave differently in many respects, but the MINOS results, presented today at the Neutrino 2010 conference in Athens, Greece, and in a seminar at Fermilab, are the first observation of a potential fundamental difference that established physical theory could not explain.
Neutrino oscillations depend on two parameters: the square of the neutrino
mass difference, Δm2, and the mixing angle, sin22θ. MINOS results (shown in
black), accumulated since 2005, yield the most precise known value of Δm2,
namely Δm2 = 0.0024 ± 0.0001 eV2.

The oscillations of antineutrinos also depend on two parameters: the square
of the antineutrino mass difference, Δm2, and the antineutrino mixing angle,
sin22θ (shown in red). MINOS has found Δm2 = 0.0034 ± 0.0004 eV2. The MINOS
neutrino results are show in blue for comparison. Theorists expected the values
for neutrinos and antineutrinos to be the same.

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ars: Unexpected antineutrino masses: Standard Model puzzler

Post by bystander » Mon Jun 14, 2010 9:14 pm

Unexpected antineutrino masses a puzzler for Standard Model
ars technica | 14 June 2010
Two weeks ago, experimental results seemed to indicate that we're getting a handle on the low-mass particles called neutrinos. Today, Fermilab announced results generated using antineutrinos that suggests we may need to make major revisions to the Standard Model of physics. The textbook description of antimatter is that it's like a mirror image of more familiar particles. But new work from Fermilab indicates that the mass differences among antineutrinos aren't the same as those for regular neutrinos. If the findings hold up, they would call for some new physics to explain the discrepancy.

Like the earlier results, the new data relies on observations of neutrino flavor changes. Neutrinos and antineutrinos, unlike other particles, appear not to have a fixed nature. They exist as a mixture of three identities—electron, muon, and tau—and a given particle oscillates among these identities in a probabilistic manner that depends in part on the mass differences among the three classes. So, if we can observe these oscillations, we can get some indication of the relative masses of these extremely light particles.

Observing the oscillations is a serious challenge, since it requires a large distance between the source of the neutrinos and the detector. In this case, the work was done by Fermilab's MINOS team, which produces neutrinos and antineutrinos using the Tevatron's injector ring. The resulting beam is sent to a detector in a mine in Minnesota, over 700km away, a trip that takes about 2.5 milliseconds.

Scientists from the MINOS team presented some preliminary results of their work at a meeting being held in Athens (the catchy meeting name: Neutrino 2010). The release announcing them cautions that the data is only just approaching statistical significance, and will require extensive confirmation work, not to mention a trip through peer review before publication. Those cautions aside, the results are pretty intriguing, since they suggest something very strange is up with the neutrinos' masses.

Right now, we can't directly measure the masses of the neutrinos very precisely, but we can get a sense of how the masses differ among the three flavors. The MINOS experiment only produces muon neutrinos and their antimatter counterparts, but on their way to Minnesota some of these will change flavor. This oscillation is governed in part by the relative masses of the different flavors, providing researchers with a glimpse into the particles' masses.

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NS: Sterile neutrino back from the dead

Post by bystander » Tue Jun 22, 2010 5:22 pm

Sterile neutrino back from the dead
New Scientist | Physics & Math | 22 June 2010
A ghostly particle given up for dead is showing signs of life.

Not only could this "sterile" neutrino be the stuff of dark matter, thought to make up the bulk of our universe, it might also help to explain how an excess of matter over antimatter arose in our universe.

Neutrinos are subatomic particles that rarely interact with ordinary matter. They are known to come in three flavours – electron, muon and tau – with each able to spontaneously transform into another.

In the 1990s, results from the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos National Laboratory in New Mexico suggested there might be a fourth flavour: a "sterile" neutrino that is even less inclined to interact with ordinary matter than the others.

Sterile neutrinos would be big news because the only way to detect them would be by their gravitational influence – just the sort of feature needed to explain dark matter.

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UCL: "Ghost particle" sized up by cosmologists

Post by bystander » Wed Jun 23, 2010 1:41 am

"Ghost particle" sized up by cosmologists
University College London | 22 June 2010
Cosmologists at UCL are a step closer to determining the mass of the elusive neutrino particle, not by using a giant particle detector, but by gazing up into space.

Although it has been shown that a neutrino has a mass, it is vanishingly small and extremely hard to measure – a neutrino is capable of passing through a light year (about six trillion miles) of lead without hitting a single atom.

New results using the largest ever survey of galaxies in the universe puts total neutrino mass at no larger than 0.28 electron volts – less than a billionth of the mass of a single hydrogen atom. This is one of the most accurate measurements of the mass of a neutrino to date.
Upper bound of 0.28 eV on neutrino masses from the largest photometric redshift survey
  • Physical Review Letters > Gravitation and Astrophysics > 17 May 2010 (accepted)

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IU: rules of particle physics may need a rewrite

Post by bystander » Fri Jun 25, 2010 7:19 pm

IU scientists in two collaborations see evidence that rules of particle physics may need a rewrite
Indiana University | 24 June 2010
Two separate collaborations involving Indiana University scientists have reported new results suggesting unexpected differences between neutrinos and their antiparticle brethren. These results could set the stage for what one IU physicist calls a "radical modification of our understanding of particle physics."
...
The Standard Model of particle physics holds that particle and antiparticle masses should be equal, with no discrepancy in masses inferred from the energy scale at which the conversion process from muon to tau occurs separately for neutrinos and antineutrinos. But MINOS scientists found that not to be the case: the new results indicate that neutrino and antineutrino masses differ by about 40 percent.
...
At the same time the new differences in neutrino and antineutrino behavior were being announced last week by the MINOS team, the group of MiniBooNE (Mini Booster Neutrino Experiment) scientists that includes IU associate professor of physics Rex Tayloe found muon antineutrinos turning into electron antineutrinos at a higher rate than expected. With a second discrepancy in neutrino oscillation (flavor change) uncovered, IU scientists realized the momentum building toward a reworking of the long-held Standard Model of particle physics.
Neutrino experiments sow seeds of possible revolution
Science News - 25 June 2010
Nearly massless particles could turn physics on its ear

Neutrinos are the big nothings of subatomic physics. Nearly massless and lacking an electric charge, these ghostly particles interact so weakly with other types of matter that more than 50 trillion of them pass unimpeded through a person’s body each second.

Yet recent preliminary findings from two experiments hint that neutrinos may be opening a window on a hidden world of subatomic particles and forces.

The findings from both experiments have relatively large margins of error, so they could end up being statistical flukes. But so far the results, announced June 14 at the Neutrinos 2010 conference in Athens, indicate that neutrinos and their antiparticle counterparts, antineutrinos, are not the nearly exact mirror images of each other that current physics supposes them to be.

If confirmed, those conclusions “indicate a fundamentally new direction in our thinking” about subatomic particles and the origin of matter in the universe, says theorist Rabindra Mohapatra of the University of Maryland in College Park.

The new results may help explain a long-standing puzzle — how the universe, believed to have begun with such a perfect balance of matter and antimatter that the two would have destroyed each other upon contact, became dominated by matter. That imbalance has led to the evolution of galaxies, planets and life

The new findings “could even signal a tiny breakdown of Einstein’s theory of special relativity,” Mohapatra adds. “This could completely alter the way we are doing physics now.”