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Neutrino evidence against “faster-than-light” claim
Neutrinos do not go faster than light, according to new measurements made by an experiment called ICARUS at the Gran Sasso Laboratory using a new measuring technique, called a liquid argon time projection chamber and working independently from the OPERA scientists who had made the tentative but extremely controversial claim about “faster-than-light” particles. Particles that travel faster than light would unravel Albert Einstein’s 1905 theory of special relativity, a cornerstone of modern physics.
Their findings “indicate the neutrinos do not exceed the speed of light,” the European Centre for Nuclear Research (CERN) said, ading that there may have been technical hitches that had skewed the initial measurements, something that skeptics of the findings said they had always suspected.The controversy began last September, when CERN’s so-called OPERA team cautiously announced that sub-atomic particles called neutrinos had travelled some six kilometres (nearly four ) per second faster than the velocity of light, described by Einstein as the maximum speed in the cosmos.
The neutrinos were timed at their departure from CERN’s giant underground lab near Geneva and again, after travelling 732 km (454 miles) through the Earth’s crust, at their arrival at the Gran Sasso Laboratory in Italy.
To complete the trip, the neutrinos should have taken 0.0024 seconds. Instead, the particles were recorded as hitting the detectors in Italy 0.00000006 seconds sooner than expected.Knowing their findings would create a global controversy, the OPERA team urged other physicists to carry out their own checks to corroborate or refute what had been seen.
“ICARUS measures the neutrino’s velocity to be no faster than the speed of light,” said Carlo Rubbia, a Nobel winner and spokesperson for the ICARUS project..”Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny and inviting independent measurements. This is how science works,” said CERN Research Director Sergio Bertolucci, who added that further verifications were being made, including new experiments with particle beams in May, “to give us the final verdict.”
In February, CERN said that the OPERA team were verifying a cable connection and a timing instrument called an oscillator that may have flawed measurements of the neutrinos’ flight time.Strengthening this scenario, Bertolucci said on Friday “the evidence is beginning to point towards the OPERA result being an artifact of the measurement.”
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Neutrino experiment repeat at Cern finds same result
The team which found that neutrinos may travel faster than light has carried out an improved version of their experiment - and confirmed the result.
If confirmed by other experiments, the find could undermine one of the basic principles of modern physics.
Critics of the first report in September had said that the long bunches of neutrinos (tiny particles) used could introduce an error into the test.
The new work used much shorter bunches.
It has been posted to the Arxiv repositoryand submitted to the Journal of High Energy Physics, but has not yet been reviewed by the scientific community.
The experiments have been carried out by the Opera collaboration - short for Oscillation Project with Emulsion (T)racking Apparatus.
It hinges on sending bunches of neutrinos created at the Cern facility (actually produced as decays within a long bunch of protons produced at Cern) through 730km (454 miles) of rock to a giant detector at the INFN-Gran Sasso laboratory in Italy.
The initial series of experiments, comprising 15,000 separate measurements spread out over three years, found that the neutrinos arrived 60 billionths of a second faster than light would have, travelling unimpeded over the same distance.
The idea that nothing can exceed the speed of light in a vacuum forms a cornerstone in physics - first laid out by James Clerk Maxwell and later incorporated into Albert Einstein’s theory of special relativity.
(via BBC News - Neutrino experiment repeat at Cern finds same result)
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'Light-speed' neutrinos point to new physical reality
[This New Scientist article is only available to subscribers so it has been presented in its entirety.]
SUBATOMIC particles have broken the universe’s fundamental speed limit, or so it was reported last week. The speed of light is the ultimate limit on travel in the universe, and the basis for Einstein’s special theory of relativity, so if the finding stands up to scrutiny, does it spell the end for physics as we know it? The reality is less simplistic and far more interesting.
“People were saying this means Einstein is wrong,” says physicist Heinrich Päs of the Technical University of Dortmund in Germany. “But that’s not really correct.”
Instead, the result could be the first evidence for a reality built out of extra dimensions. Future historians of science may regard it not as the moment we abandoned Einstein and broke physics, but rather as the point at which our view of space vastly expanded, from three dimensions to four, or more.
“This may be a physics revolution,” says Thomas Weiler at Vanderbilt University in Nashville, Tennessee, who has devised theories built on extra dimensions. “The famous words ‘paradigm shift’ are used too often and tritely, but they might be relevant.”
The subatomic particles - neutrinos - seem to have zipped faster than light from CERN, near Geneva, Switzerland, to the OPERA detector at the Gran Sasso lab near L’Aquila, Italy. It’s a conceptually simple result: neutrinos making the 730-kilometre journey arrived 60 nanoseconds earlier than they would have if they were travelling at light speed. And it relies on three seemingly simple measurements, says Dario Autiero of the Institute of Nuclear Physics in Lyon, France, a member of the OPERA collaboration: the distance between the labs, the time the neutrinos left CERN, and the time they arrived at Gran Sasso.
But actually measuring those times and distances to the accuracy needed to detect nanosecond differences is no easy task. The OPERA collaboration spent three years chasing down every source of error they could imagine (see illustration) before Autiero made the result public in a seminar at CERN on 23 September.
Physicists grilled Autiero for an hour after his talk to ensure the team had considered details like the curvature of the Earth, the tidal effects of the moon and the general relativistic effects of having two clocks at different heights (gravity slows time so a clock closer to Earth’s surface runs a tiny bit slower).
They were impressed. “I want to congratulate you on this extremely beautiful experiment,” said Nobel laureate Samuel Ting of the Massachusetts Institute of Technology after Autiero’s talk. “The experiment is very carefully done, and the systematic error carefully checked.”
Most physicists still expect some sort of experimental error to crop up and explain the anomaly, mainly because it contravenes the incredibly successful law of special relativity which holds that the speed of light is a constant that no object can exceed. The theory also leads to the famous equation E = mc2.
Hotly anticipated are results from other neutrino detectors, including T2K in Japan and MINOS at Fermilab in Illinois, which will run similar experiments and confirm the results or rule them out (see “Fermilab stops hunting Higgs, starts neutrino quest”).
In 2007, the MINOS experiment searched for faster-than-light neutrinos but didn’t see anything statistically significant. The team plans to reanalyse its data and upgrade the detector’s stopwatch. “These are the kind of things that we have to follow through, and make sure that our prejudices don’t get in the way of discovering something truly fantastic,” says Stephen Parke of Fermilab.
In the meantime, suggests Sandip Pakvasa of the University of Hawaii, let’s suppose the OPERA result is real. If the experiment is tested and replicated and the only explanation is faster-than-light neutrinos, is E = mc2 done for?
Not necessarily. In 2006, Pakvasa, Päs and Weiler came up with a model that allows certain particles to break the cosmic speed limit while leaving special relativity intact. “One can, if not rescue Einstein, at least leave him valid,” Weiler says.
The trick is to send neutrinos on a shortcut through a fourth, thus-far-unobserved dimension of space, reducing the distance they have to travel. Then the neutrinos wouldn’t have to outstrip light to reach their destination in the observed time.
In such a universe, the particles and forces we are familiar with are anchored to a four-dimensional membrane, or “brane”, with three dimensions of space and one of time. Crucially, the brane floats in a higher dimensional space-time called the bulk, which we are normally completely oblivious to.
The fantastic success of special relativity up to now, plus other cosmological observations, have led physicists to think that the brane might be flat, like a sheet of paper. Quantum fluctuations could make it ripple and roll like the surface of the ocean, Weiler says. Then, if neutrinos can break free of the brane, they might get from one point on it to another by dashing through the bulk, like a flying fish taking a shortcut between the waves (see illustration).
This model is attractive because it offers a way out of one of the biggest theoretical problems posed by the OPERA result: busting the apparent speed limit set by neutrinos detected pouring from a supernova in 1987.
As stars explode in a supernova, most of their energy streams out as neutrinos. These particles hardly ever interact with matter. That means they should escape the star almost immediately, while photons of light will take about 3 hours. In 1987, trillions of neutrinos arrived at Earth 3 hours before the dying star’s light caught up. If the neutrinos were travelling as fast as those going from CERN to OPERA, they should have arrived in 1982.
OPERA’s neutrinos were about 1000 times as energetic as the supernova’s neutrinos, though. And Pakvasa and colleagues’ model calls for neutrinos with a specific energy that makes them prefer tunnelling through the bulk to travelling along the brane. If that energy is around 20 gigaelectronvolts - and the team don’t yet know that it is - “then you expect large effects in the OPERA region, and small effects at the supernova energies,” Pakvasa says. He and Päs are meeting next week to work out the details.
The flying fish shortcut isn’t available to all particles. In the language of string theory, a mathematical model some physicists hope will lead to a comprehensive “theory of everything”, most particles are represented by tiny vibrating strings whose ends are permanently stuck to the brane. One of the only exceptions is the theoretical “sterile neutrino”, represented by a closed loop of string. These are also the only type of neutrino thought capable of escaping the brane.
Neutrinos are known to switch back and forth between their three observed types (electron, muon and tau neutrinos), and OPERA was originally designed to detect these shifts. In Pakvasa’s model, the muon neutrinos produced at CERN could have transformed to sterile neutrinos mid-flight, made a short hop through the bulk, and then switched back to muon before reappearing on the brane.
So if OPERA’s results hold up, they could provide support for the existence of sterile neutrinos, extra dimensions and perhaps string theory. Such theories could also explain why gravity is so weak compared with the other fundamental forces. The theoretical particles that mediate gravity, known as gravitons, may also be closed loops of string that leak off into the bulk. “If, in the end, nobody sees anything wrong and other people reproduce OPERA’s results, then I think it’s evidence for string theory, in that string theory is what makes extra dimensions credible in the first place,” Weiler says.
Meanwhile, alternative theories are likely to abound. Weiler expects papers to appear in a matter of days or weeks.
Even if relativity is pushed aside, Einstein has worked so well for so long that he will never really go away. At worst, relativity will turn out to work for most of the universe but not all, just as Newton’s mechanics work until things get extremely large or small. “The fact that Einstein has worked for 106 years means he’ll always be there, either as the right answer or a low-energy effective theory,” Weiler says.
(via New Scientist)
Related reading » Neutrinos: Everything you need to know
(via section5)
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Neutrinos: Delta force
EVEN by the elevated standards of particle physics neutrinos are weird beasts. They travel within a whisker of the speed of light, have no electric charge, practically no mass and precious little will to interact with anything else. Billions penetrate every square centimetre of the Earth’s surface every second without so much as a quiver. This makes them rather hard to detect. So hard that Wolfgang Pauli, the Austrian physicist who postulated their existence in 1930, wagered a case of champagne that no one would ever do so. He lost the bet in 1956. Since then, neutrinos (of which there are now known to be three fundamentally different sorts) have allowed researchers to glimpse inside the sun, study exploding stars and examine the universe’s distant past.
The latest example of neutrinos’ weirdness comes from Japan. Researchers using a detector called Super-Kamiokande think they have observed the beasts changing their fundamental nature in a way not seen before. They are not yet quite sure. Their result has a 0.7% chance of being a fluke. But if it is confirmed, it will have implications for one of the deepest mysteries of the universe—why it is made of matter.
EDIT/UPDATE: On June 24th it emerged that an American neutrino experiment produced results consistent with T2K’s.
(via The Economist)
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Neutrino Transformation Could Help Explain Mystery of Matter
Two research teams have found new evidence of transformations in elusive elementary particles called neutrinos. The findings may finally help explain why the universe didn’t vanish shortly after its birth.
“These results are just the beginning of the story for neutrinos,” said physicist Robert Plunkett of Fermilab in Chicago. “They could lead to clues … and tell us why there’s now far more matter than antimatter.”
Most neutrinos are emitted by the sun, and are so small and ghostly that billions pass through our bodies every second. Most go right through Earth without hitting anything. But some human-built devices — slabs of iron and plastic, big chambers of oil or water lined with photon detectors, or detector arrays plunged into seawater or Antarctic ice — can record the blip of light when a neutrino occasionally slams into an atom.
Using these detection events, physicists have identified three types of neutrino, called muon, tau and electron neutrinos. Further discoveries suggested that each type can transform into another, with muon-to-tau neutrino transformations being dominant, at least in particle-accelerator-powered experiments.
Researchers proposed a third and weaker change, that of muon-to-electron neutrinos, but until now lacked evidence for its existence.
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Check out the awesome audio clip on the first page of the article.
(via Ars photo essay: standing in the beam line of a neutrino detector)
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CERN Press Release: Particle Chameleon Caught in the act of Changing
“Researchers on the OPERA experiment at the INFN1’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 CERN2, 730km 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.”
