3398: Cientistas encontram “partículas fantasmas” vindas de dentro da Terra

CIÊNCIA

Chamam-se geoneutrinos e são misteriosas partículas que raramente interagem com a matéria e, por isso, podem ser quase impossíveis de detectar. No entanto, os cientistas encontraram novas “partículas fantasmas” de radioactividade vindas de dentro da Terra.

Este fenómeno, conseguido com o detector Borexino, do laboratório italiano de Gran Sasso, foi registado em 53 novos eventos.

Geoneutrinos, as partículas fantasmas misteriosas

Os cientistas que trabalham no maior laboratório subterrâneo do mundo encontraram 53 novos eventos, quase duas vezes mais do que antes. Nesse sentido, foi possível aos investigadores detectar os eventos recorrendo ao detector Borexino, que está enterrado a 1400 metros no subsolo e faz medições incrivelmente sensíveis de fenómenos geralmente imperceptíveis.

O Borexino é uma experiência de física de partículas para estudar neutrinos solares de baixa energia (sub-MeV). Assim, o detector é o calorímetro cintilador líquido mais puro do mundo. Este é colocado dentro de uma esfera de aço inoxidável que segura os detectores de sinal (tubos foto-multiplicadores ou PMTs) e é protegido por um tanque de água para o proteger da radiação externa e marcar os raios cósmicos que conseguem penetrar a sobrecarga da montanha.

Há muita actividade que acontece no centro da Terra e que não temos a noção. Assim, os cientistas esperam que as novas descobertas possam trazer informações para decifrar os eventos que acontecem debaixo dos nossos pés. Grande parte desses eventos são ainda um mistério.

Esta vista mostra a esfera de aço inoxidável Borexino. Uma experiência que fez as primeiras medições dos geoneutrinos.

Núcleo da Terra está em chamas e as partículas da actividade chegam até à superfície

Os geoneutrinos são produzidos durante a decadência radioactiva dentro da Terra. Eles significam que o nosso planeta está em chamas e certas partículas esquivam-se e fluem até a sua superfície. Contudo, estas são totalmente invisíveis aos nossos olhos. O detector Borexino, localizado no Laboratori Nazionali del Gran Sasso, em Itália, tem como objectivo ver esse fluxo invisível de partículas.

Os cientistas têm estado atentos aos neutrinos desde 2007, e têm vindo a recolher informações ao longo desse tempo.

Assim, os investigadores, no passado ano, detectaram o novo fluxo de partículas fantasmas, além de tornar as suas medições mais seguras.

Os geoneutrinos são os únicos vestígios directos das decadências radioactivas que ocorrem dentro da Terra, e que produzem uma porção ainda desconhecida da energia que impulsiona toda a dinâmica do nosso planeta.

Explicou Livia Ludhova, uma das duas coordenadoras científicas actuais de Borexino, em comunicado.

Processos radioactivos são responsáveis pelos vulcões e terramotos

Indo ao encontro dessa e de outras questões relacionadas, as novas descobertas podem ajudar a lançar luz sobre estes misteriosos processos, do calor inexplicável que vem do centro da Terra. O mundo sob os nossos pés dá origem a uma série de fenómenos estranhos – como os espectaculares vulcões e o campo magnético da Terra – que não são como nenhum outro visto no sistema solar.

Campo magnético da Terra nasceu do cataclismo que criou a Lua

O campo magnético da Terra é uma espécie de escudo protetor que envolve o planeta. Segundo as pesquisas nesta área, a colisão de um “planeta” contra uma Terra primitiva iniciou um processo que gerou … Continue a ler

25 Jan 2020

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3397: Why physicists are determined to prove Galileo and Einstein wrong

SCIENCE

Scientists tested Galileo and Einstein’s theories by dropping two objects inside this satellite named MICROSCOPE (artist’s impression).
(Image: © CNES)

In the 17th century, famed astronomer and physicist Galileo Galilei is said to have climbed to the top of the Tower of Pisa and dropped two different-sized cannonballs. He was trying to demonstrate his theory — which Albert Einstein later updated and added to his theory of relativity — that objects fall at the same rate regardless of their size.

Now, after spending two years dropping two objects of different mass into a free fall in a satellite, a group of scientists has concluded that Galileo and Einstein were right: The objects fell at a rate that was within two-trillionths of a percent of each other, according to a new study.

This effect has been confirmed time and time again, as has Einstein’s theory of relativity — yet scientists still aren’t convinced that there isn’t some kind of exception somewhere. “Scientists have always had a difficult time actually accepting that nature should behave that way,” said senior author Peter Wolf, research director at the French National Center for Scientific Research’s Paris Observatory.

That’s because there are still inconsistencies in scientists’ understanding of the universe.

“Quantum mechanics and general relativity, which are the two basic theories all of physics is built on today …are still not unified,” Wolf told Live Science. What’s more, although scientific theory says the universe is made up mostly of dark matter and dark energy, experiments have failed to detect these mysterious substances.

“So, if we live in a world where there’s dark matter around that we can’t see, that might have an influence on the motion of [objects],” Wolf said. That influence would be “a very tiny one,” but it would be there nonetheless. So, if scientists see test objects fall at different rates, that “might be an indication that we’re actually looking at the effect of dark matter,” he added.

Wolf and an international group of researchers — including scientists from France’s National Center for Space Studies and the European Space Agency — set out to test Einstein and Galileo’s foundational idea that no matter where you do an experiment, no matter how you orient it and what velocity you’re moving at through space, the objects will fall at the same rate.

The researchers put two cylindrical objects — one made of titanium and the other platinum — inside each other and loaded them onto a satellite. The orbiting satellite was naturally “falling” because there were no forces acting on it, Wolf said. They suspended the cylinders within an electromagnetic field and dropped the objects for 100 to 200 hours at a time.

From the forces the researchers needed to apply to keep the cylinders in place inside the satellite, the team deduced how the cylinders fell and the rate at which they fell, Wolf said.

And, sure enough, the team found that the two objects fell at almost exactly the same rate, within two-trillionths of a percent of each other. That suggested Galileo was correct. What’s more, they dropped the objects at different times during the two-year experiment and got the same result, suggesting Einstein’s theory of relativity was also correct.

Their test was an order of magnitude more sensitive than previous tests. Even so, the researchers have published only 10% of the data from the experiment, and they hope to do further analysis of the rest.

Not satisfied with this mind-boggling level of precision, scientists have put together several new proposals to do similar experiments with two orders of magnitude greater sensitivity, Wolf said. Also, some physicists want to conduct similar experiments at the tiniest scale, with individual atoms of different types, such as rubidium and potassium, he added.

The findings were published Dec. 2 in the journal Physical Review Letters.

Originally published on Live Science.
By Yasemin Saplakoglu – Staff Writer
24/01/2020

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3396: Mysterious particles spewing from Antarctica defy physics

SCIENCE

What’s making these things fly out of the frozen continent?

Researchers prepare to launch the Antarctic Impulsive Transient Antenna (ANITA) experiment, which picked up signals of impossible-seeming particles as it dangled from its balloon over Antarctica.
(Image: © NASA)

Our best model of particle physics is bursting at the seams as it struggles to contain all the weirdness in the universe. Now, it seems more likely than ever that it might pop, thanks to a series of strange events in Antarctica. .

The death of this reigning physics paradigm, the Standard Model, has been predicted for decades. There are hints of its problems in the physics we already have. Strange results from laboratory experiments suggest flickers of ghostly new species of neutrinos beyond the three described in the Standard Model. And the universe seems full of dark matter that no particle in the Standard Model can explain.

But recent tantalizing evidence might one day tie those vague strands of data together: Three times since 2016, ultra-high-energy particles have blasted up through the ice of Antarctica, setting off detectors in the Antarctic Impulsive Transient Antenna (ANITA) experiment, a machine dangling from a NASA balloon far above the frozen surface.

As Live Science reported in 2018, those events — along with several additional particles detected later at the buried Antarctic neutrino observatory IceCube — don’t match the expected behavior of any Standard Model particles. The particles look like ultra high-energy neutrinos. But ultra high-energy neutrinos shouldn’t be able to pass through the Earth. That suggests that some other kind of particle — one that’s never been seen before — is flinging itself into the cold southern sky.

Now, in a new paper, a team of physicists working on IceCube have cast heavy doubt on one of the last remaining Standard Model explanations for these particles: cosmic accelerators, giant neutrino guns hiding in space that would periodically fire intense neutrino bullets at Earth. A collection of hyperactive neutrino guns somewhere in our northern sky could have blasted enough neutrinos into Earth that we’d detect particles shooting out of the southern tip of our planet. But the IceCube researchers didn’t find any evidence of that collection out there, which suggests new physics must be needed to explain the mysterious particles.

To understand why, it’s important to know why these mystery particles are so unsettling for the Standard Model.

Neutrinos are the faintest particles we know about; they’re difficult to detect and nearly massless. They pass through our planet all the time — mostly coming from the sun and rarely, if ever, colliding with the protons, neutrons and electrons that make up our bodies and the dirt beneath our feet.

But ultra-high-energy neutrinos from deep space are different from their low-energy cousins. Much rarer than low-energy neutrinos, they have wider “cross sections,” meaning they’re more likely to collide with other particles as they pass through them. The odds of an ultra-high-energy neutrino making it all the way through Earth intact are so low that you’d never expect to detect it happening. That’s why the ANITA detections were so surprising: It was as if the instrument had won the lottery twice, and then IceCube had won it a couple more times as soon as it started buying tickets.

And physicists know how many lottery tickets they had to work with. Many ultra-high-energy cosmic neutrinos come from the interactions of cosmic rays with the cosmic microwave background (CMB), the faint afterglow of the Big Bang. Every once in a while, those cosmic rays interact with the CMB in just the right way to fire high-energy particles at Earth. This is called the “flux,” and it’s the same all over the sky. Both ANITA and IceCube have already measured what the cosmic neutrino flux looks like to each of their sensors, and it just doesn’t produce enough high-energy neutrinos that you’d expect to detect a neutrino flying out of Earth at either detector even once.

“If the events detected by ANITA belong to this diffuse neutrino component, ANITA should have measured many other events at other elevation angles,” said Anastasia Barbano, a University of Geneva physicist who works on IceCube.

But in theory, there could have been  ultra-high-energy neutrino sources beyond the sky-wide flux, Barbano told Live Science: those neutrino guns, or cosmic accelerators.

“If it is not a matter of neutrinos produced by the interaction of ultra-high-energy cosmic rays with the CMB, then the observed events can be either neutrinos produced by individual cosmic accelerators in a given time interval” or some unknown Earthly source, Barbano said.

Blazars, active galactic nuclei, gamma-ray bursts, starburst galaxies, galaxy mergers, and magnetized and fast-spinning neutron stars are all good candidates for those sorts of accelerators, she said. And we know that cosmic neutrino accelerators do exist in space;  in 2018, IceCube tracked a high-energy neutrino back to a blazar, an intense jet of particles coming from an active black hole at the center of a distant galaxy.

ANITA picks up only the most extreme high-energy neutrinos, Barbano said, and if the upward-flying particles were cosmic-accelerator-boosted neutrinos from the Standard Model — most likely tau neutrinos — then the beam should have come with a shower of lower-energy particles that would have tripped IceCube’s lower-energy detectors.

“We looked for events in seven years of IceCube data,” Barbano said — events that matched the angle and length of the ANITA detections, which you’d expect to find if there were a significant battery of cosmic neutrino guns out there firing at Earth to produce these up-going particles. But none turned up.

Their results don’t completely eliminate the possibility of an accelerator source out there. But they do “severely constrain” the range of possibilities, eliminating all of the most plausible scenarios involving cosmic accelerators and many less-plausible ones.

“The message we want to convey to the public is that a Standard Model astrophysical explanation does not work no matter how you slice it,” Barbano said.

Researchers don’t know what’s next. Neither ANITA nor IceCube is an ideal detector for the needed follow-up searches, Barbano said, leaving the researchers with very little data on which to base their assumptions about these mysterious particles. It’s a bit like trying to figure out the picture on a giant jigsaw puzzle from just a handful of pieces.

Right now, many possibilities seem to fit the limited data, including a fourth species of “sterile” neutrino outside the Standard Model and a range of theorized types of dark matter. Any of these explanations would be revolutionary.hjh But none is strongly favored yet.

“We have to wait for the next generation of neutrino detectors,” Barbano said.

The paper has not yet been peer reviewed and was published January 8 in the arXiv database.

Originally published on Live Science.
By Rafi Letzter – Staff Writer
24/01/2020

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