Faster Than Light? More Like Faulty Wiring.

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You can shelf your designs for a warp drive engine (for now) and put the DeLorean back in the garage; it turns out neutrinos may not have broken any cosmic speed limits after all.

Ever since the news came out on September 22 of last year that a team of researchers in Italy had clocked neutrinos traveling faster than the speed of light, the physics world has been resounding with the potential implications of such a discovery — that is, if it were true. The speed of light has been a key component of the standard model of physics for over a century, an Einstein-established limit that particles (even tricky neutrinos) weren’t supposed to be able to break, not even a little.

Now, according to a breaking news article by Edwin Cartlidge on AAAS’ ScienceInsider, the neutrinos may be cleared of any speed violations.

“According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer,” Cartlidge reported.

The original OPERA (Oscillation Project with Emulsion-tRacking Apparatus) experiment had a beam of neutrinos fired from CERN in Geneva, Switzerland, aimed at an underground detector array located 730 km away at the Gran Sasso facility, near L’Aquila, Italy. Researchers were surprised to discover the neutrinos arriving earlier than expected, by a difference of 60 nanoseconds. This would have meant the neutrinos had traveled faster than light speed to get there.

Repeated experiments at the facility revealed the same results. When the news was released, the findings seemed to be solid — from a methodological standpoint, anyway.

Shocked at their own results, the OPERA researchers were more than happy to have colleagues check their results, and welcomed other facilities to attempt the same experiment.

Repeated attempts may no longer be needed.

Once the aforementioned fiber optic cable was readjusted, it was found that the speed of data traveling through it matched the 60 nanosecond discrepancy initially attributed to the neutrinos. This could very well explain the subatomic particles’ apparent speed burst.

Case closed? Well… it is science, after all.

“New data,” Cartlidge added, “will be needed to confirm this hypothesis.”

See the original OPERA team paper here.

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UPDATE 2/22/12 11:48 pm EST: According to a more recent article on Nature’s newsblog, the Science Insider report erroneously attributed the 60 nanosecond discrepancy to loose fiber optic wiring from the GPS unit, based on inside “sources”. OPERA’s statement doesn’t specify as such, “saying instead that its two possible sources of error point in opposite directions and it is still working things out.”

OPERA’s official statement released today is as follows:

“The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.

These two issues can modify the neutrino time of flight in opposite directions. While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the Collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012. An extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies.” (via Nature newsblog.)

Journal Club – Neutrino Vision

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According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. And of course, the first rule of Journal Club is… don’t talk about Journal Club.

So, without further ado – today’s journal article is about the latest findings in neutrino astronomy.

Today’s article:
Gaisser Astrophysical neutrino results..

This paper presents some recent observations from the IceCube neutrino telescope at the South Pole – which acually observes neutrinos from the northern sky – using the Earth to filter out some of the background noise. Cool huh?

Firstly, a quick recap of neutrino physics. Neutrinos are sub-atomic particles of the lepton variety and are essentially neutrally charged versions of the other leptons – electrons, muons and taus – which all have a negative charge. So, we say that neutrinos come in three flavours – electron neutrinos, muon neutrinos and tau neutrinos.

Neutrinos were initially proposed by Pauli (a proposal later refined by Fermi) to explain how energy could be transported away from a system undergoing beta decay. When solar fusion began to be understood in the 1930s – the role of neutrinos was problematic since only a third or more of the neutrinos that were predicted to be produced by fusion were being detected – an issue which became known as the solar neutrino problem in the 1960’s.

The solar neutrino problem was only resolved in the late 1990s when the three neutrino flavours idea gained wide acceptance and each were finally detected in 2001 – confirming that solar neutrinos in transit actually oscillate between the three flavours (electron, muon and tau) – which means that if your detector is set up to detect only one flavour you will detect only about one third of all the neutrinos coming from the Sun.

Ten years later, the Ice Cube the neutrino observatory is using our improved understanding of neutrinos to try and detect high energy neutrinos of extragalactic origin. The first challenge is to distinguish atmospheric neutrinos (produced in abundance as cosmic rays strike the atmosphere) from astrophysical neutrinos.

Using what we have learnt from solving the solar neutrino problem, we can be confident that any neutrinos from distant sources have had time to oscillate – and hence should arrive at Earth in approximately equal ratios. Atmospheric neutrinos produced from close sources (also known as ‘prompt’ neutrinos) don’t have time to oscillate before being detected.

When looking for point sources of high energy astrophysical neutrinos, IceCube is most sensitive to muon neutrinos – which are detected when the neutrino weakly interacts with an ice molecule – emitting a muon. A high energy muon will then generate Cherenkov radiation – which is what IceCube actually detects. Unfortunately muon neutrinos are also the most common source of cosmic ray induced atmospheric neutrinos, but we are steadily getting better at determining what energy levels represent astrophysical rather than atmospheric neutrinos.

So, it’s still early days with this technology – with much of the effort going in to learning how to observe, rather than just observing. But maybe one day we will be observing the cosmic neutrino background – and hence the first second of the Big Bang. One day…

So… comments? Are neutrinos the fundamentally weirdest fundamental particle out there? Could IceCube be used to test the faster-than-light neutrino hypothesis? Want to suggest an article for the next edition of Journal Club?

Neutrinos Still Breaking Speed Limits

Particle Collider

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New test results are in from OPERA and it seems those darn neutrinos, they just can’t keep their speed down… to within the speed of light, that is!

report released in September by scientists working on the OPERA project (Oscillation Project with Emulsion-tracking Apparatus) at Italy’s Gran Sasso research lab claimed that neutrinos emitted from CERN 500 miles away in Geneva arrived at their detectors 60 nanoseconds earlier than expected, thus traveling faster than light. This caused no small amount of contention in the scientific community and made news headlines worldwide – and rightfully so, as it basically slaps one of the main tenets of modern physics across the face.

Of course the scientists at OPERA were well aware of this, and didn’t make such a proclamation lightly; over two years of repeated research was undergone to make sure that the numbers were accurate… as well as could be determined, at least. And they were more than open to having their tests replicated and the results reviewed by their peers. In all regards their methods were scientific yet skepticism was widespread… even within OPERA’s own ranks.

One of the concerns that arose regarding the discovery was in regards to the length of the neutrino beam itself, emitted from CERN and received by special detector plates at Gran Sasso. Researchers couldn’t say for sure that any neutrinos detected were closer to the beginning of the beam versus the end, a disparity (on a neutrino-sized scale anyway) of 10.5 microseconds… that’s 10.5 millionths of a second! And so in October, OPERA requested that proton pulses be resent – this time lasting only 3 nanoseconds each.

The OPERA Neutrino Detector

The results were the same. The neutrinos arrived at Gran Sasso 60 nanoseconds earlier than anticipated: faster than light.

The test was repeated – by different teams, no less – and so far 20 such events have been recorded. Each time, the same.

Faster. Than light.

What does this mean? Do we start tearing pages out of physics textbooks? Should we draw up plans for those neutrino-powered warp engines? Does Einstein’s theory of relativity become a quaint memento of what we used to believe?

Hardly. Or, at least, not anytime soon.

OPERA’s latest tests have managed to allay one uncertainty regarding the results, but plenty more remain. One in particular is the use of GPS to align the clocks at the beginning and end of the neutrino beam. Since the same clock alignment system was used in all the experiments, it stands that there may be some as-of-yet unknown factor concerning the GPS – especially since it hasn’t been extensively used in the field of high-energy particle physics.

In addition, some scientists would like to see more results using other parts of the neutrino detector array.

Of course, like any good science, replication of results is a key factor for peer acceptance. And thus Fermilab in Batavia, Illinois will attempt to perform the same experiment with its MINOS (Main Injector Neutrino Oscillation Search) facility, using a precision matching OPERA’s.

MINOS hopes to have its independent results as early as next year.

No tearing up any textbooks just yet…

 

Read more in the Nature.com news article by Eugenie Samuel Reich. The new result was released on the arXiv preprint server on November 17. (The original September 2011 OPERA team paper can be found here.)

Borexino Collaboration Detects pep Neutrinos

View from inside the Borexino neutrino detector. Image Credit: Borexino Collaboration

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Solar neutrino physics has quieted down over the past decade. In the past, it had been a source of major excitement and puzzlement for scientists as they struggled to detect these elusive particles emitted from the fusion reactions in the center of the Sun. Although difficult to detect, they provide the most direct probe of the Solar core. Once astronomers learned to detect them and solved the Solar neutrino problem, they were able to confirm their understanding of the main nuclear reaction that powers the sun, the proton-proton (pp) reaction. But now, astronomers have for the first time, detected the neutrinos of another, far rarer nuclear reaction, the proton-electron-proton (pep) reaction.

At any given time, several separate fusion processes are converting the Sun’s hydrogen into helium, creating energy as a byproduct. The main reaction requires the formation of deuterium (hydrogen with an extra neutron in the nucleus) as the first step in a series of events that leads to the creation of stable helium. This typically takes place by the fusion of two protons which ejects a positron, a neutrino, and a photon. However, nuclear physicists predicted an alternative method of creating the necessary deuterium. In it, a proton and electron fuse first, forming a neutron and a neutrino, and then they join with a second proton. Based on solar models, they predicted that only 0.23% of all Deuterium would be created by this process. Given the already elusive nature of neutrinos, the diminished production rate has made these pep neutrinos even more difficult to detect.

While they may be hard to detect, pep neutrinos are readily distinguishable from ones created by the pp reaction. The key difference is the energy they carry. Neutrinos from the pp reaction have a range of energy up to a maximum of 0.42 MeV, while pep neutrinos carry a very select 1.44 MeV.

However, to pick out these neutrinos, the team had to carefully clean the data of signals from cosmic ray strikes which create muons that could then interact with carbon inside the detector to generate a neutrino with similar energy that might create a false positive. In addition, this process would also create a free neutron. To eliminate these, the team rejected all signals of neutrinos that occurred within a short amount of time from a detection of a free neutron. Overall, this indicated that the detector received 4,300 muons passing through it per day, which would generate 27 neutrons per 100tons of detector liquid, and similarly, 27 false positives.

Removing these detections, the team still found a signal of neutrinos with the appropriate energy and used this to estimate the total amount of pep neutrinos flowing through every square centimeter to be about 1.6 billion, per second, which they note is in agreement with predictions made by the standard model used to describe the interior workings of the Sun.

Aside from further confirming astronomers understanding of the processes that power the Sun, this finding also places constraints on another fusion process, the CNO Cycle. While this process is expected to be minor in the Sun (making only ~2% of all helium produced), it is expected to be more efficient in hotter, more massive stars and dominate in stars with 50% more mass than the Sun. Better understanding the limits of this process would help astronomers to clarify how those stars work as well.

Particle Physics and Faster-Than-Light Neutrinos…Discuss.

On September 22, an international team of researchers working on the OPERA project at the Gran Sasso research facility released a paper on some potentially physics-shattering findings: beams of neutrinos that had traveled from the CERN facility near Geneva to their detector array outside of Rome at a speed faster than light. (Read more about this here and here.) Not a great deal faster, to be sure – only 60 nanoseconds faster than expected – but still faster. There’s been a lot of recoil from the scientific community about this announcement, and rightly so, since if it does end up being a legitimate finding then it would force us to rework much of what we have come to know about physics ever since Einstein’s theory of relativity.

Of course, to those of us not so well-versed in particle physics *raises hand* a lot of this information can quickly become overwhelming, to say the least. Thankfully the folks at Sixty Symbols have recorded this interview with two astrophysicists at the UK’s University of Nottingham. It helps explain some of the finer points of the discovery, what it means and what the science community in general thinks about it. Check it out!

Thanks to Dan Satterfield for posting this at his Wild Wild Science blog.

Faster Than The Speed Of Light… OPERA Update

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A few days ago, the physics world was turned upside down at the announcement of “faster than the speed of light”. The mighty neutrino has struck again by breaking the cosmic speed limit and traveling at a velocity 20 parts per million above light speed. To absolutely verify this occurrence, collaboration is needed from different sources and we’re here to give you the latest update.

“This result comes as a complete surprise,” said OPERA spokesperson, Antonio Ereditato of the University of Bern. “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.”

Since the OPERA measurements go against everything we think we know, it’s more important than ever to verify its findings through independent research.

“When an experiment finds an apparently unbelievable result and can find no artifact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice,” said CERN Research Director Sergio Bertolucci. “If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane, explanations. That will require independent measurements.”

To get the job done, the OPERA Collaboration joined forces with CERN metrology experts and other facilities to establish absolute calibrations. There cannot be any error margin in parameters between the source and detector distances – and the neutrino’s flight time. In this circumstance, the measurements of the initial source of the neutrino beam and OPERA has an uncertainty value of 20 cm over the 730 km. The neutrino flight time has an accuracy of less than 10 nanoseconds, and was confirmed through the use of highly regarded GPS equipment and an atomic clock. Every care was given to ensure precision.

“We have established synchronization between CERN and Gran Sasso that gives us nanosecond accuracy, and we’ve measured the distance between the two sites to 20 centimetres,” said Dario Autiero, the CNRS researcher who will give this afternoon’s seminar. “Although our measurements have low systematic uncertainty and high statistical accuracy, and we place great confidence in our results, we’re looking forward to comparing them with those from other experiments.”

“The potential impact on science is too large to draw immediate conclusions or attempt physics interpretations. My first reaction is that the neutrino is still surprising us with its mysteries.” said Ereditato. “Today’s seminar is intended to invite scrutiny from the broader particle physics community.”

Original Story Source: CERN Press Release. For Further Reading: Measurement of the neutrino velocity with the OPERA detector in the CNGS beam.

Read our previous article on this paper.