Tag Archives: neutrino

The Anomaly

Is the smallest, lightest, most ghostly particle about to upend our understanding of the universe? Recently, the ephemeral neutrino has begun to give up some of its secrets. Beginning in 1998 the neutrino experiments at Super-Kamiokande and Sudbury Neutrino Observatory showed for the first time that neutrinos oscillate with one of three flavors. In 2015, two physicists were awarded the Nobel prize for this discovery, which also proved that neutrinos must have mass. More recently, a small anomaly at the Super-Kamiokande detector has surfaced, which, is hoped, could shed light on why the universe is constructed primarily from matter and not anti-matter.

From Quanta:

The anomaly, detected by the T2K experiment, is not yet pronounced enough to be sure of, but it and the findings of two related experiments “are all pointing in the same direction,” said Hirohisa Tanaka of the University of Toronto, a member of the T2K team who presented the result to a packed audience in London earlier this month.

“A full proof will take more time,” said Werner Rodejohann, a neutrino specialist at the Max Planck Institute for Nuclear Physics in Heidelberg who was not involved in the experiments, “but my and many others’ feeling is that there is something real here.”

The long-standing puzzle to be solved is why we and everything we see is matter-made. More to the point, why does anything — matter or antimatter — exist at all? The reigning laws of particle physics, known as the Standard Model, treat matter and antimatter nearly equivalently, respecting (with one known exception) so-called charge-parity, or “CP,” symmetry: For every particle decay that produces, say, a negatively charged electron, the mirror-image decay yielding a positively charged antielectron occurs at the same rate. But this cannot be the whole story. If equal amounts of matter and antimatter were produced during the Big Bang, equal amounts should have existed shortly thereafter. And since matter and antimatter annihilate upon contact, such a situation would have led to the wholesale destruction of both, resulting in an empty cosmos.

Somehow, significantly more matter than antimatter must have been created, such that a matter surplus survived the annihilation and now holds sway. The question is, what CP-violating process beyond the Standard Model favored the production of matter over antimatter?

Many physicists suspect that the answer lies with neutrinos — ultra-elusive, omnipresent particles that pass unfelt through your body by the trillions each second.

Read the entire article here.

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Neutrinos in the News

Something’s up. Perhaps there’s some degree of hope that we may be reversing the tide of “dumbeddownness” in the stories that the media pumps through its many tubes to reach us. So, it comes as a welcome surprise to see articles about the very, very small making big news in publications like the New Yorker. Stories about neutrinos no less. Thank you New Yorker for dumbing us up. And, kudos to the latest Nobel laureates — Takaaki Kajita and Arthur B. McDonald — for helping us understand just a little bit more about our world.

From the New Yorker:

This week the 2015 Nobel Prize in Physics was awarded jointly to Takaaki Kajita and Arthur B. McDonald for their discovery that elementary particles called neutrinos have mass. This is, remarkably, the fourth Nobel Prize associated with the experimental measurement of neutrinos. One might wonder why we should care so much about these ghostly particles, which barely interact with normal matter.

Even though the existence of neutrinos was predicted in 1930, by Wolfgang Pauli, none were experimentally observed until 1956. That’s because neutrinos almost always pass through matter without stopping. Every second of every day, more than six trillion neutrinos stream through your body, coming directly from the fiery core of the sun—but most of them go right through our bodies, and the Earth, without interacting with the particles out of which those objects are made. In fact, on average, those neutrinos would be able to traverse more than one thousand light-years of lead before interacting with it even once.

The very fact that we can detect these ephemeral particles is a testament to human ingenuity. Because the rules of quantum mechanics are probabilistic, we know that, even though almost all neutrinos will pass right through the Earth, a few will interact with it. A big enough detector can observe such an interaction. The first detector of neutrinos from the sun was built in the nineteen-sixties, deep within a mine in South Dakota. An area of the mine was filled with a hundred thousand gallons of cleaning fluid. On average, one neutrino each day would interact with an atom of chlorine in the fluid, turning it into an atom of argon. Almost unfathomably, the physicist in charge of the detector, Raymond Davis, Jr., figured out how to detect these few atoms of argon, and, four decades later, in 2002, he was awarded the Nobel Prize in Physics for this amazing technical feat.

Because neutrinos interact so weakly, they can travel immense distances. They provide us with a window into places we would never otherwise be able to see. The neutrinos that Davis detected were emitted by nuclear reactions at the very center of the sun, escaping this incredibly dense, hot place only because they so rarely interact with other matter. We have been able to detect neutrinos emerging from the center of an exploding star more than a hundred thousand light-years away.

But neutrinos also allow us to observe the universe at its very smallest scales—far smaller than those that can be probed even at the Large Hadron Collider, in Geneva, which, three years ago, discovered the Higgs boson. It is for this reason that the Nobel Committee decided to award this year’s Nobel Prize for yet another neutrino discovery.

Read the entire story here.

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Wolfgang Pauli’s Champagne

PauliAustrian theoretical physicist dreamed up neutrinos in 1930, and famously bet a case of fine champagne that these ghostly elementary particles would never be found. Pauli lost the bet in 1956. Since then researchers have made great progress both theoretically and experimentally in trying to delve into the neutrino’s secrets. Two new books describe the ongoing quest.

From the Economist:

Neutrinoa are weird. The wispy particles are far more abundant than the protons and electrons that make up atoms. Billions of them stream through every square centimetre of Earth’s surface each second, but they leave no trace and rarely interact with anything. Yet scientists increasingly agree that they could help unravel one of the biggest mysteries in physics: why the cosmos is made of matter.

Neutrinos’ scientific history is also odd, as two new books explain. The first is “Neutrino Hunters” by Ray Jayawardhana, a professor of astrophysics at the University of Toronto (and a former contributor to The Economist). The second, “The Perfect Wave”, is by Heinrich Päs, a neutrino theorist from Technical University in the German city of Dortmund.

The particles were dreamed up in 1930 by Wolfgang Pauli, an Austrian, to account for energy that appeared to go missing in a type of radioactivity known as beta decay. Pauli apologised for what was a bold idea at a time when physicists knew of just two subatomic particles (protons and electrons), explaining that the missing energy was carried away by a new, electrically neutral and, he believed, undetectable subatomic species. He bet a case of champagne that it would never be found.

Pauli lost the wager in 1956 to two Americans, Frederick Reines and Clyde Cowan. The original experiment they came up with to test the hypothesis was unorthodox. It involved dropping a detector down a shaft within 40 metres of an exploding nuclear bomb, which would act as a source of neutrinos. Though Los Alamos National Laboratory approved the experiment, the pair eventually chose a more practical approach and buried a detector near a powerful nuclear reactor at Savannah River, South Carolina, instead. (Most neutrino detectors are deep underground to shield them from cosmic rays, which can cause similar signals.)

However, as other experiments, in particular those looking for neutrinos in the physical reactions which power the sun, strove to replicate Reines’s and Cowan’s result, they hit a snag. The number of solar neutrinos they recorded was persistently just one third of what theory said the sun ought to produce. Either the theorists had made a mistake, the thinking went, or the experiments had gone awry.

In fact, both were right all along. It was the neutrinos that, true to form, behaved oddly. As early as 1957 Bruno Pontecorvo, an Italian physicist who had defected to the Soviet Union seven years earlier, suggested that neutrinos could come in different types, known to physicists as “flavours”, and that they morph from one type to another on their way from the sun to Earth. Other scientists were sceptical. Their blueprint for how nature works at the subatomic level, called the Standard Model, assumed that neutrinos have no mass. This, as Albert Einstein showed, is the same as saying they travel at the speed of light. On reaching that speed time stops. If neutrinos switch flavours they would have to experience change, and thus time. That means they would have to be slower than light. In other words, they would have mass. (A claim in 2011 by Italian physicists working with CERN, Europe’s main physics laboratory, that neutrinos broke Einstein’s speed limit turned out to be the result of a loose cable.)

Pontecorvo’s hypothesis was proved only in 1998, in Japan. Others have since confirmed the phenomenon known as “oscillation”. The Standard Model had to be tweaked to make room for neutrino mass. But scientists still have little idea about how much any of the neutrinos actually weigh, besides being at least 1m times lighter than an electron.

The answer to the weight question, as well as a better understanding of neutrino oscillations, may help solve the puzzle of why the universe is full of matter. One explanation boffins like a lot because of its elegant maths invokes a whole new category of “heavy” neutrino decaying more readily into matter than antimatter. If that happened a lot when the universe began, then there would have been more matter around than antimatter, and when the matter and antimatter annihilated each other, as they are wont to do, some matter (ie, everything now visible) would be left over. The lighter the known neutrinos, according to this “seesaw” theory, the heftier the heavy sort would have to be. A heavy neutrino has yet to be observed, and may well, as Pauli described it, be unobservable. But a better handle on the light variety, Messrs Jayawardhana and Päs both agree, may offer important clues.

These two books complement each other. Mr Jayawardhana’s is stronger on the history (though his accounts of the neutrino hunters’ personal lives can read a little too much like a professional CV). It is also more comprehensive on the potential use of neutrinos in examining the innards of the sun, of distant exploding stars or of Earth, as well as more practical uses such as fingering illicit nuclear-enrichment programmes (since they spew out a telltale pattern of the particles).

Read the entire article here.

Image: Wolfgang Pauli, c1945. Courtesy of Wikipedia.

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Time for the Neutrino

Enough of the Higgs boson, already! It’s time to shine the light on its smaller, swifter cousin, the neutrino.

From the NYT:

HAVE you noticed how the Higgs boson has been hogging the limelight lately? For a measly little invisible item, whose significance cannot be explained without appealing to thorny concepts of quantum field theory, it has done pretty well for itself. The struggling starlets of Hollywood could learn a thing or two about the dark art of self-promotion from this boson.

First, its elusiveness “sparked the greatest hunt in science,” as the subtitle of one popular book put it. Then came all the hoopla over its actual discovery. Or should I say discoveries? Because those clever, well-meaning folks at the CERN laboratory outside Geneva proclaimed their finding of the particle not once but twice. First in 2012, on the Fourth of July no less, they told the world that their supergigantic — and awesomely expensive — atom smasher had found tentative evidence of the Higgs. Eight months later, they made a second announcement, this time with more data in hand, to confirm that they had nabbed the beast for real. Just recently, there was yet more fanfare when two of the grandees who had predicted the particle’s existence back in 1964 shared a Nobel Prize for their insight.

In fact, ever since another Nobel-winning genius, Leon Lederman, branded it the “God particle” some 20 years ago, the Higgs boson has captured the public imagination and dominated the media coverage of physics. Some consider Professor Lederman’s moniker a brilliant P.R. move for physics, while others denounce it as a terrible gaffe that confuses people and cheapens a solemn scientific enterprise. Either way, it has been effective. Nobody ever talks about the fascinating lives of other subatomic particles on “Fox and Friends.”

Sure, the story of Higgs is a compelling one. The jaw-dropping $9 billion price tag of the machine built to chase it is enough to command our attention. Plus, there is the serene, wise man at the center of this epic saga: the octogenarian Peter Higgs, finally vindicated after waiting patiently for decades. Professor Higgs was seen to shed a tear of joy at a news conference announcing the discovery, adding tenderness to the triumphant moment and tugging ever so gently at our heartstrings. For reporters looking for a human-interest angle to this complicated scientific brouhaha, that was pure gold.

But I say enough is enough. It is time to give another particle a chance.

And have I got a terrific candidate for you! It moves in mysterious ways, passing right through wood, walls and even our bodies, with nary a bump. It morphs among three forms, like a cosmic chameleon evading capture. It brings us news from the sun’s scorching heart and from the spectacular death throes of monstrous stars. It could tell us why antimatter is so rare in the universe and illuminate the inner workings of our own planet. Someday, it may even help expose rogue nuclear reactors and secret bomb tests, thus promoting world peace. Most important, we might not be here without it.

WHAT is this magical particle, you ask? It is none other than the ghostly neutrino.

O.K., I admit that I am biased, having just written a book about it. But believe me, no other particle comes close to matching the incredibly colorful and quirky personality of the neutrino, or promises to reveal as much about a mind-boggling array of natural phenomena, both subatomic and cosmic. As one researcher told me, “Whenever anything cool happens in the universe, neutrinos are usually involved.” Besides, John Updike considered it worthy of celebrating in a delightful poem in The New Yorker, and on “The Big Bang Theory,” Sheldon Cooper’s idol Professor Proton chose Gino the Neutrino as his beloved puppet sidekick.

Granted, the neutrino does come with some baggage. Remember how it made headlines two years ago for possibly traveling faster than light? Back then, the prospects of time travel and breaking Einstein’s speed limit provided plenty of fodder for rampant speculation and a few bad jokes. In the end, the whole affair turned out to be much ado about a faulty cable. I maintain it is unfair to hold the poor little neutrino responsible for that commotion.

Generally speaking, the neutrino tends to shun the limelight. Actually, it is pathologically shy and hardly ever interacts with other particles. That makes it tough to pin down.

Thankfully, today’s neutrino hunters have a formidable arsenal at their disposal, including newfangled observatories buried deep underground or in the Antarctic ice. Neutrino chasing, once an esoteric sideline, has turned into one of the hottest occupations for the discerning nerd. More eager young ones will surely clamor for entry into the Promised Land now that the magazine Physics World has declared the recent detection of cosmic neutrinos to be the No. 1 physics breakthrough of the year.

Drum roll, please. The neutrino is ready to take center stage. But don’t blink: It zips by at nearly the speed of light.

Read the entire story here.

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Everything Comes in Threes

From the Guardian:

Last week’s results from the Daya Bay neutrino experiment were the first real measurement of the third neutrino mixing angle, ?13 (theta one-three). There have been previous experiments which set limits on the angle, but this is the first time it has been shown to be significantly different from zero.

Since ?13 is a fundamental parameter in the Standard Model of particle physics1, this would be an important measurement anyway. But there’s a bit more to it than that.

Neutrinos – whatever else they might be doing – mix up amongst themselves as they travel through space. This is a quantum mechanical effect, and comes from the fact that there are two ways of defining the three types of neutrino.

You can define them by the way they are produced. So a neutrino which is produced (or destroyed) in conjunction with an electron is an “electron neutrino”. If a muon is involved, it’s a “muon neutrino”. The third one is a “tau neutrino”. We call this the “flavour”.

Or you can define them by their masses. Usually we just call this definition neutrinos 1, 2 and 3.

The two definitions don’t line up, and there is a matrix which tells you how much of each “flavour” neutrino overlaps with each “mass” one. This is the neutrino mixing matrix. Inside this matrix in the standard model there are potentially four parameters describing how the neutrinos mix.

You could just have two-way mixing. For example, the flavour states might just mix up neutrino 1 and 2, and neutrino 2 and 3. This would be the case if the angle ?13 were zero. If it is bigger than zero (as Daya Bay have now shown) then neutrino 1 also mixes with neutrino 3. In this case, and only in this case, a fourth parameter is also allowed in the matrix. This fourth parameter (?) is one we haven’t measured yet, but now we know it is there. And the really important thing is, if it is there, and also not zero, then it introduces an asymmetry between matter and antimatter.

This is important because currently we don’t know why there is more matter than antimatter around. We also don’t know why there are three copies of neutrinos (and indeed of each class of fundamental particle). But we know that three copies is minimum number which allows some difference in the way matter and antimatter experience the weak nuclear force. This is the kind of clue which sets off big klaxons in the minds of physicists: New physics hiding somewhere here! It strongly suggests that these two not-understood facts are connected by some bigger, better theory than the one we have.

We’ve already measured a matter-antimatter difference for quarks; a non-zero ?13 means there can be a difference for neutrinos too. More clues.

Read the entire article here.

Image: The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph. Courtesy of Wikipedia.

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Faster Than Light Travel

The world of particle physics is agog with recent news of an experiment that shows a very unexpected result – sub-atomic particles traveling faster than the speed of light. If verified and independently replicated the results would violate one of the universe’s fundamental properties described by Einstein in the Special Theory of Relativity. The speed of light — 186,282 miles per second (299,792 kilometers per second) — has long been considered an absolute cosmic speed limit.

Stranger still, over the last couple of days news of this anomalous result has even been broadcast on many cable news shows.

The experiment known as OPERA is a collaboration between France’s National Institute for Nuclear and Particle Physics Research and Italy’s Gran Sasso National Laboratory. Over the course of three years scientists fired a neutrino beam 454 miles (730 kilometers) underground from Geneva to a receiver in Italy. Their measurements show that neutrinos arrived an average of 60 nanoseconds sooner than light would have done. This doesn’t seem like a great amount, after all is only 60 billionths of a second, however the small difference could nonetheless undermine a hundred years of physics.

Understandably most physicists remain skeptical of the result, until further independent experiments are used to confirm the measurements or not. However, all seem to agree that if the result is confirmed this would be a monumental finding and would likely reshape modern physics and our understanding of the universe.

More on this intriguing story here courtesy of ARs Technica, which also offers a detailed explanation of several possible sources of error that may have contributed to the faster-than-light measurements.

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More subatomic spot changing

From the Economist:

IN THIS week’s print edition we report a recent result from the T2K collaboration in Japan which has found strong hints that neutrinos, the elusive particles theorists believe to be as abundant in the universe as photons, but which almost never interact with anything, are as fickle as they are coy.

It has been known for some time that neutrinos switch between three types, or flavours, as they zip through space at a smidgen below the speed of light. The flavours are distinguished by the particles which emerge on the rare occasion a neutrino does bump into something. And so, an electron-neutrino conjures up an electron, a muon-neutrino, a muon, and a tau-neutrino, a tau particle (muons and tau are a lot like electrons, but heavier and less stable). Researchers at T2K observed, for the first time, muon-neutrinos transmuting into the electron variety—the one sort of spot-changing that had not been seen before. But their results, with a 0.7% chance of being a fluke, was, by the elevated standards of particle physics, tenuous.

Now, T2K’s rival across the Pacific has made it less so. MINOS beams muon-neutrinos from Fermilab, America’s biggest particle-physics lab located near Chicago, to a 5,000-tonne detector sitting in the Soudan mine in Minnesota, 735km (450 miles) to the north-west. On June 24th its researchers annouced that they, too, had witnessed some of muon-neutrinos change to the electron variety along the way. To be precise, the experiment recorded 62 events which could have been caused by electron-neutrinos. If the proposed transmutation does not occur in nature, it ought to have seen no more than 49 (the result of electron-neutrinos streaming in from space or radioactive rocks on Earth). Were the T2K figures spot on, as it were, it should have seen 71.

As such, the result from MINOS, which uses different methods to study the same phenomenon, puts the transmutation hypothesis on a firmer footing. This advances the search for a number known as delta (?). This is one of the parameters of the formula which physicists think describes neutrinos spot-changing antics. Physicists are keen to pin it down, since it also governs the description of the putative asymmetry between matter and antimatter that left matter as the dominant feature of the universe after the Big Bang.

In light of the latest result, it remains unclear whether either the American or the Japanese experiment is precise enough to measure delta. In 2013, however, MINOS will be supplanted by NOvA, a fancier device located in another Minnesota mine 810km from Fermilab’s muon-neutrino cannon. That ought to do the trick. Then again, nature has the habit of springing surprises.

And in more ways than one. Days after T2K’s run was cut short by the earthquake that shook Japan in March, devastating the muon-neutrino source at J-PARC, the country’s main particle-accelerator complex, MINOS had its own share of woe when the Soudan mine sustained significant flooding. Fortunately, the experiment itself escaped relatively unscathed. But the eerie coincidence spurred some boffins, not a particularly superstitious bunch, to speak of a neutrino curse. Fingers crossed that isn’t the case.

More from theSource here.

Image courtesy of Fermilab.

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