The Super Kamiokande (Kamioka Neutrino Detection Experiment) is a neutrino observatory located under Mount Kamioka in Japan. It is designed to observe solar and atmospheric neutrinos, neutrinos from supernovae, and aims to search for proton decay. It is a cylindrical structure measuring about 40 m tall and 40 m across, is covered in over 11,000 photomultiplier tubes (PMTs), and filled with 50,000 tons of pure water.
Neutrinos weakly interact with other particles, making it extremely difficult to detect them and observe their properties; in fact, they cannot be directed detected at all. Detectors are built underground to isolate it from other radiation. When a neutrino passes through the Super-K’s water tank, it will sometimes (hopefully) collide with a quark, causing it to change into a charged lepton (electron, muon, or tau). The very short version of what happens next is that the lepton will travel faster than the speed of light in water (not in vacuum), polarizing the water molecules; when they return to their ground state, Cherenkov radiation is emitted in a flash of light, which the PMTs detect. The last image is of Cherenkov ring by an electron created from a neutrino collision in the Super-K, in perspective view.
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How Many Neutrinos Does It Take to Screw Up Einstein?
Results from a second experiment uphold the observation that neutrinos are moving faster than the speed of light. The OPERA collaboration, which first reported the superluminal neutrinos in September, has rerun the experiment and detected 20 new neutrinos breaking Einstein’s theoretical limit.
The findings are heartening to anyone hoping to see a major physics revolution in their lifetime. But scientists, as ever, are being cautious, and it will take an independent replication of the results by another team to even begin convincing many of them.
“This eliminates one major class of systematic errors, and it’s impressive for the OPERA team to have mounted in a short period of time,” said physicist Robert Plunkett of Fermilab National Laboratory in Batavia, Illinois. “However, it doesn’t mean that there isn’t an error somewhere else in their system.”
Neutrinos are subatomic particles with hardly any mass that are able to fly through most matter as if it wasn’t there. Despite their negligible mass, if they were somehow able to exceed the speed of light limit set by Einstein’s theory of special relativity, it would present a major head-scratcher to modern physicists.
The OPERA team’s detector at Gran Sasso National Laboratory in Italy had previously detected neutrinos produced in bunches at CERN arriving 60 nanoseconds earlier than light speed would allow. The tricky part is that these bunches took a good length of time to produce — much longer than 60 nanoseconds — so the researchers had to be careful with their analysis. If they thought a neutrino was coming from the start of the bunch when it was actually coming from the end, then that neutrino would not actually be moving faster than light.
In their first experiment, the OPERA team used statistical analysis to show this situation was unlikely, but other scientists were not completely persuaded. The new experiment produced neutrinos in bunches over just three nanoseconds, far shorter than the faster-than-light anomaly. The results were the same: Neutrinos arrived 60 nanoseconds quicker than the speed of light. The findings were robust enough that members of the OPERA collaboration who had refused to sign on to the first paper were now willing to put their name on the new one.
But a great deal of scrutiny remains.
“I can now say that the probability of the result being correct has increased from 1 in a million to one in 100 thousand,” wrote physicist Philip Gibbs on the viXra log (though he stressed that those numbers were merely illustrative and not actual calculated values).
Rafting for Solar Neutrinos
Above, scientists check the equipment surrounding a huge tank of extremely pure water from the Super-Kamiokande experiment in Japan, designed to detect colliding neutrinos.
Credit: Super-Kamiokande Collaboration, Japan
Neutrinos: Everything You Need To Know
What exactly are they?
With a neutral charge and nearly zero mass, neutrinos are the shadiest of particles, rarely interacting with ordinary matter and slipping through our bodies, buildings and the Earth at a rate of trillions per second.
First predicted in 1930 by Wolfgang Pauli, who won a Nobel prize for this work in 1945, they are produced in various nuclear reactions: fusion, which powers the sun; fission, harnessed by humans to make weapons and energy; and during natural radioactive decay inside the Earth.
If they are so stealthy, how do we know they are there at all?
Wily neutrinos usually avoid contact with matter, but every so often, they crash into an atom to produce a signal that allows us to observe them. Fredrick Reines first detected them in 1956, garnering himself a Nobel prize in 1995.
Most commonly, experiments use large pools of water or oil. When neutrinos interact with electrons or nuclei of those water or oil molecules, they give off a flash of light that sensors can detect.
Where are these experiments found?
These days, a lot of expense and extreme engineering go into detectors that are sunk into the ground to shield them from extraneous particles that might interfere with them. For instance, OPERA, which detected the apparently faster-than-light neutrinos beamed from CERN, lies inside the Gran Sasso mountain in Italy. This works because neutrinos shoot straight through such shields.
Other detectors pick up naturally-produced neutrinos. One such detector – ANTARES – is miles under the Mediterranean Sea, while another, IceCube, is buried under Antarctic ice.
What’s cool about neutrinos?
Their stealth belies their potential importance. Take extra dimensions. Most particles come in two varieties: ones that spin clockwise and ones that spin anticlockwise. Neutrinos are the only particles that seem to just spin anticlockwise. Some theorists say this is evidence for extra dimensions, which could host the “missing”, right-handed neutrinos.
Anything else?
Unseen right-handed neutrinos may also account for mysterious dark matter. This is thought to make up 80 per cent of all matter in the universe and to stop galaxies from flying apart. The idea is that right-handed neutrinos might be much heavier than left-handed ones and so could provide the requisite gravity.
Without the sensationalism.
Particles Found to Travel Faster than The Speed of Light
An Italian experiment has unveiled evidence that fundamental particles known as neutrinos can travel faster than light. Other researchers are cautious about the result, but if it stands further scrutiny, the finding would overturn the most fundamental rule of modern physics—that nothing travels faster than 299,792,458 meters per second.
The experiment is called OPERA (Oscillation Project with Emulsion-tRacking Apparatus), and lies 1,400 meters underground in the Gran Sasso National Laboratory in Italy. It is designed to study a beam of neutrinos coming from CERN, Europe’s premier high-energy physics laboratory located 730 kilometers away near Geneva, Switzerland. Neutrinos are fundamental particles that are electrically neutral, rarely interact with other matter, and have a vanishingly small mass. But they are all around us—the sun produces so many neutrinos as a by-product of nuclear reactions that many billions pass through your eye every second.
The 1,800-tonne OPERA detector is a complex array of electronics and photographic emulsion plates, but the new result is simple—the neutrinos are arriving 60 nanoseconds faster than the speed of light allows. “We are shocked,” says Antonio Ereditato, a physicist at the University of Bern in Switzerland and OPERA’s spokesman.
Breaking the Law
The idea that nothing can travel faster than light in a vacuum is the cornerstone of Albert Einstein’s special theory of relativity, which itself forms the foundation of modern physics. If neutrinos are traveling faster than light speed, then one of the most fundamental assumptions of science—that the rules of physics are the same for all observers—would be invalidated. “If it’s true, then it’s truly extraordinary,” says John Ellis, a theoretical physicist at CERN.
