Posts Tagged ‘speed of light

Measurement of the neutrino velocity with the OPERA detector in the CNGS beam

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The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (60.7 \pm 6.9 (stat.) \pm 7.4 (sys.)) ns was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.48±0.28 (stat.)±0.30 (sys.)) x 10-5……..

…… Conclusions
The OPERA detector at LNGS, designed for the study of neutrino oscillations in appearance mode, has provided a precision measurement of the neutrino velocity over the 730 km baseline of the CNGS neutrino beam sent from CERN to LNGS through the Earth’s crust. A time of flight measurement with small systematic uncertainties was made possible by a series of accurate metrology techniques. The data analysis took also advantage of a large sample of about 16000 neutrino interaction events detected by OPERA.
The analysis of internal neutral current and charged current events, and external νµ CC interactions from the 2009, 2010 and 2011 CNGS data was carried out to measure the neutrino velocity. The sensitivity of the measurement of (v-c)/c is about one order of magnitude better than previous accelerator neutrino experiments.
The results of the study indicate for CNGS muon neutrinos with an average energy of 17 GeV an early neutrino arrival time with respect to the one computed by assuming the speed of light in vacuum:
δt = (60.7 ± 6.9 (stat.) ± 7.4 (sys.)) ns.
The corresponding relative difference of the muon neutrino velocity and the speed of light
(v-c)/c = δt /(TOF’c – δt) = (2.48 ± 0.28 (stat.) ± 0.30 (sys.)) ×10-5.
with an overall significance of 6.0 σ.
The dependence of δt on the neutrino energy was also investigated. For this analysis the
data set was limited to the 5489 νµ CC interactions occurring in the OPERA target. A measurement performed by considering all νµ CC internal events yielded δt = (60.3 ± 13.1 (stat.)± 7.4 (sys.)) ns, for an average neutrino energy of 28.1 GeV. The sample was then split into two bins of nearly equal statistics, taking events of energy higher or lower than 20 GeV. The results for the low- and high-energy samples are, respectively, δt = (53.1 ± 18.8 (stat.).) ± 7.4 (sys.)) ns and (67.1 ± 18.2 (stat.).) ± 7.4 (sys.)) ns. This provides no clues on a possible energy dependence of δt in the domain explored by OPERA within the accuracy of the measurement.
Despite the large significance of the measurement reported here and the stability of the
analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.
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September 23, 2011 at 7:39 am

Neutrinos Travel Faster Than Light, According to One Experiment

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Read also: A Six-Sigma Signal Of Superluminal Neutrinos From Opera!

Fat lady singing? The OPERA particle detector may have spotted neutrinos traveling faster than light, which would bring down the curtain on special relativity as an exact theory.

If it’s true, it will mark the biggest discovery in physics in the past half-century: Elusive, nearly massless subatomic particles called neutrinos appear to travel just faster than light, a team of physicists in Europe reports. If so, the observation would wreck Einstein’s theory of special relativity, which demands that nothing can travel faster than light.

In fact, the result would be so revolutionary that it’s sure to be met with skepticism all over the world. “I suspect that the bulk of the scientific community will not take this as a definitive result unless it can be reproduced by at least one and preferably several experiments,” says V. Alan Kostelecky, a theorist at Indiana University, Bloomington. He adds, however, “I’d be delighted if it were true.”

The data come from a 1300-metric-ton particle detector named Oscillation Project with Emulsion-tRacking Apparatus (OPERA). Lurking in Italy’s subterranean Gran Sasso National Laboratory, OPERA detects neutrinos that are fired through the earth from the European particle physics laboratory, CERN, near Geneva, Switzerland. As the particles hardly interact at all with other matter, they stream right through the ground, with only a very few striking the material in the detector and making a noticeable shower of particles.

Over 3 years, OPERA researchers timed the roughly 16,000 neutrinos that started at CERN and registered a hit in the detector. They found that, on average, the neutrinos made the 730-kilometer, 2.43-millisecond trip roughly 60 nanoseconds faster than expected if they were traveling at light speed. “It’s a straightforward time-of-flight measurement,” says Antonio Ereditato, a physicist at the University of Bern and spokesperson for the 160-member OPERA collaboration. “We measure the distance and we measure the time, and we take the ratio to get the velocity, just as you learned to do in high school.” Ereditato says the uncertainty in the measurement is 10 nanoseconds.

However, even Ereditato says it’s way too early to declare relativity wrong. “I would never say that,” he says. Rather, OPERA researchers are simply presenting a curious result that they cannot explain and asking the community to scrutinize it. “We are forced to say something,” he says. “We could not sweep it under the carpet because that would be dishonest.” The results will be presented at a seminar tomorrow at CERN.

The big question is whether OPERA researchers have discovered particles going faster than light, or whether they have been misled by an unidentified “systematic error” in their experiment that’s making the time look artificially short. Chang Kee Jung, a neutrino physicist at Stony Brook University in New York, says he’d wager that the result is the product of a systematic error. “I wouldn’t bet my wife and kids because they’d get mad,” he says. “But I’d bet my house.”

Jung, who is spokesperson for a similar experiment in Japan called T2K, says the tricky part is accurately measuring the time between when the neutrinos are born by slamming a burst of protons into a solid target and when they actually reach the detector. That timing relies on the global positioning system, and the GPS measurements can have uncertainties of tens of nanoseconds. “I would be very interested in how they got a 10-nanosecond uncertainty, because from the systematics of GPS and the electronics, I think that’s a very hard number to get.”

No previous measurements obviously rule out the result, says Kostelecky, who has spent 25 years developing a theory, called the standard model extension, that accounts for all possible types of violations of special relativity in the context of particle physics. “If you had told me that there was a claim of faster-than-light electrons, I would be a lot more skeptical,” he says. The possibilities for neutrinos are less constrained by previous measurements, he says.

Still, Kostelecky repeats the old adage: Extraordinary claims require extraordinary evidence. Even Ereditato says that one measurement does not extraordinary evidence make.

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September 22, 2011 at 8:30 pm

Can Anything Move Faster Than Light?

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Yes, the universe itself will eventually outpace the speed of light. Just how this will happen is a bit complicated, so let’s begin at the very beginning: the big bang. Around 14 billion years ago, all matter in the universe was thrown in every direction. That first explosion is still pushing galaxies outward. Scientists know this because of the Doppler effect, among other reasons. The wavelengths of light from other galaxies shift as they move away from us, just as the pitch of an ambulance siren changes as it moves past.

Take Hydra, a cluster of galaxies about three billion light years away. Astronomers have measured the distance from the Earth to Hydra by looking at the light coming from the cluster. Through a prism, Hydra’s hydrogen looks like four strips of red, blue-green, blue-violet and violet. But during the time it takes Hydra’s light to reach us, the bands of color have shifted down toward the red end—the low-energy end—of the spectrum. On their journey across the universe, the wavelengths of light have stretched. The farther the light travels, the more stretched it gets. The farther the bands shift toward the red end, the farther the light has traveled. The size of the shift is called the redshift, and it helps scientists figure out the movement of stars in space. Hydra isn’t the only distant cluster of galaxies that displays a redshift, though. Everything is shifting, because the universe is expanding. It’s just easier to see Hydra’s redshift because the farther a galaxy is from our own, the faster it is moving away.

There is no limit to how fast the universe can expand, says physicist Charles Bennett of Johns Hopkins University. Einstein’s theory that nothing can travel faster than the speed of light in a vacuum still holds true, because space itself is stretching, and space is nothing. Galaxies aren’t moving through space and away from each other but with space—like raisins in a rising loaf of bread. Some galaxies are already so far away from us, and moving away so quickly, that their light will never reach Earth. “It’s like running a 5K race, but the track expands while you’re running,” Bennett says. “If it expands faster than you can run, you’ll never get where you’re going.”

Written by physicsgg

September 21, 2011 at 1:55 pm


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Light propagates as if ‘space is missing’

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Schematics of the zero-index metamaterial contained within a Mach-Zehnder interferometer.

Researchers in the UK and the US have crafted an optical nanostructure that allows light to pass through without accumulating a phase change – as if the medium were completely missing in space. The device could find applications in optoelectronics, they say, for instance as a way of transporting signals without allowing information to become distorted.

Whenever light travels through a medium it experiences a phase-shift, as individual oscillations become out of phase with each other. In certain optics applications, including interferometers, these phase variations can introduce an unwanted dispersion of frequencies. This effect can lead to phase distortions, which ultimately reduce the quality of signals….. Read the rest of this entry »

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July 18, 2011 at 2:05 pm

Light Traveled Faster in the Early Universe

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A brilliant physicist João Magueijo asks the heretical question: What if the speed of light—now accepted as one of the unchanging foundations of modern physics—were not constant?“A number of surprising observations made at the threshold of the 21st century have left cosmologists confused and other physicists in doubt over the reliability of cosmology,” Magueijo says. “For instance it has been found that the cosmological expansion appears to be accelerating. This is contrary to common sense, as it implies that on large scales gravity is repulsive. Another upheaval resulted from the high redshift mapping of the fine structure constant. Evidence was found for a time dependence of this supposed constant of Nature. Yet another puzzle was the observation of rare very high energy cosmic rays. Standard kinematic calculations, based on special relativity, predict a cut off well below the observed energies, so this may perhaps represent the first experimental mishap of special relativity.

“These three surprises are not alone and prompt several questions. Is the Universe trying to tell us something radical about the foundations of physics?” he continues. “Or are astronomers merely trying to irritate the conservative physicist? It could well be that the strange observations emerging from the new cosmology are correct, and that they provide a unique window into dramatically novel physics. Is the Universe trying to give us a physics lesson?”

Magueijo, a 40-year old native of Portugal, puts forth the heretical idea that in the very early days of the universe light traveled faster—an idea that if proven could dethrone Einstein and forever change our understanding of the universe. He is a pioneer of the varying speed of light (VSL) theory of cosmology -an alternative to the more mainstream theory of cosmic inflation- which proposes that the speed of light in the early universe was of 60 orders of magnitude faster than its present value….. Read the rest of this entry »

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July 14, 2011 at 5:34 pm


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