Anti-matter atoms to address anti-gravity question

Anti-matter can be made in the lab - but keeping it apart from matter in order to study it has been difficult

The question of whether normal matter’s shadowy counterpart anti-matter exerts a kind of “anti-gravity” is set to be answered, according to a new report.

Normal matter attracts all other matter in the Universe, but it remains unclear if anti-matter attracts or repels it.

A team reporting in Physics Review Letters says it has prepared stable pairs of electrons and their anti-matter particles, positrons.

A beam of these pairs can be used to finally solve the anti-gravity puzzle.

Falling up

For every particle in physics, there is an associated anti-particle, identical in every respect that scientists have yet measured, except that it holds an opposite electric charge.

Current theory holds that, at the birth of the Universe, matter and anti-matter were created in equal amounts. When they meet, however, they destroy each other in energetic flashes of light.

The question has remained, then, why did any Universe come into being at all, and why is the one we see overwhelmingly made of normal matter?

One of the characteristics that may differentiate anti-matter is its gravitational behaviour. Most scientists believe that anti-matter will be attracted to normal matter.

Others are not so sure; anti-matter may repel – it may “fall up”.

That has implications for the question of why the Universe didn’t disappear into a grand flash of light just as soon as it formed. It also might help explain why the Universe is expanding ever more quickly.

It has simply been impossible to test the idea, but researchers at the University of California Riverside are getting closer to addressing the question once and for all.

They have created electron-positron pairs that are in stable orbits around one another – the result is called positronium.

The pairs are kept from bumping into and destroying each other by carefully dumping energy into them to create what are known as “Rydberg states”.

Like the lanes of an automotive test track, particles can move into different orbits around one another if they reach higher energies, and these Rydberg positronium atoms are spun up to high energies, lasting for a comparatively long three billionths of a second.

The team hopes to extend the method, up to a few thousandths of a second, preparing a beam of the artificial atoms and seeing just which way they fall.

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Fermi gamma-ray space telescope confirms puzzling preponderance of positrons

This illustration shows how the electron-positron sky appears to the Large Area Telescope. The purple region contains positrons while electrons are blocked by the Earth's bulk, the orange region contains electrons but is inaccessible to positrons, and the green region is completely out of the Earth's shadow for both positrons and electrons. Image courtesy Justin Vandenbroucke, Fermi-LAT collaboration

By finding a clever way to use the Earth itself as a scientific instrument, members of a SLAC-led research team turned the Fermi Gamma-ray Space Telescope into a positron detector – and confirmed a startling discovery from 2009 that found an excess of these antimatter particles in cosmic rays, a possible sign of dark matter…..
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Could Earth’s ring of antimatter power spacecraft?

A belt of antimatter has been discovered circling the Earth, which in future could be used to fuel voyages that race at breakneck speeds to other planets in the Solar System.

Antimatter has properties that are opposite those of normal matter – for example the positive charge on a proton is negative in an antiproton. When antimatter and normal matter come into contact, they annihilate spectacularly, releasing energy. The Italian-run PAMELA (Payload Antimatter Matter Exploration and Light Nuclei Astrophysics) satellite, launched in 2006, has found thousands of times more antiprotons than expected in a region of the innermost Van Allen radiation belt called the South Atlantic Anomaly. The anomaly appears to be a concentrated region of a much larger antimatter belt, and is the point at which the innermost radiation belt is nearest the Earth’s surface (an altitude of about 500 kilometres) and Earth’s magnetic field lines, which confine the belts, are at their weakest.

An artist’s impression of an antimatter powered spacecraft. Such craft would be capable of making the round trip to Jupiter in just one year. Image: NASA.

James Bickford, the senior member of the technical staff at Draper Laboratory in Cambridge, Massachusetts, USA, has calculated that Earth’s antimatter belt contains 160 nanograms of antiprotons. This in itself doesn’t sound much – pure annihilation of this antimatter would produce just ten kilowatts of energy per hour – but it dwarfs the amount of antimatter that we can create in particle accelerators on Earth. (As an example, the Fermi National Accelerator Laboratory in Illinois, USA, would take an entire year, running up costs of millions of dollars, to create just one nanogram of antiprotons if the lab was used exclusively for that purpose.)

The antiprotons are produced via Earth’s interaction with incoming cosmic rays from beyond the Solar System. Cosmic rays are charged particles moving at close to the speed of light ejected from phenomena such as supernovae and their remnants. When they encounter Earth’s atmosphere they decay via pair production into antineutrons. These antineutrons can escape back into space where they decay into antiprotons and become trapped in Earth’s magnetic field. This process makes up the majority of the antimatter above Earth, but PAMELA also found that antiprotons were also being directly produced through pair production above the Earth…… Continue reading Could Earth’s ring of antimatter power spacecraft?

Antiprotons pass latest symmetry test

The Antiprotonic Decelerator at CERN

By Hamish Johnston

For something that is rare in the universe, antimatter has certainly been in the news a lot lately.

The latest breakthrough involves antiprotonic helium and is published in Nature today. This exotic “atom” is formed when one electron in a helium atom is replaced with an antiproton, which is negatively charged.

For two decades physicists have known that antiprotonic helium is formed in a metastable state that sticks around for a few milliseconds before decaying. This should make it to possible to study its energy levels and measure the ratio of the antiproton mass to the electron mass. This could then be compared to the well-known proton-to-electron mass ratio to see if the proton and antiproton have different masses. Such an asymmetry goes against the Standard Model of particle physics and its discovery could help physicists understand why the universe is dominated by matter.

Now, physicists working on the Antiprotonic Decelerator at CERN have done just that. Masaki Hori of the Max Planck Institute of Quantum Optics in Garching, Germany, and an international team made laser-spectroscopy measurements and worked out the mass ratio to a remarkable degree of precision.

The experiment begins with pulses of antiprotons being injected into helium gas to create the exotic atoms. The team then fires laser pulses at the atoms to knock the antiproton from its metastable state to an unstable state, causing it to annihilate with the helium nucleus. This produces pions, which are easily detected. By varying the wavelength of the lasers to find the maximum rate of pion production, the team found the exact energy of the transition.

The big challenge for the researchers was that the atoms are moving about, which causes a Doppler broadening of the transition wavelength. Scientists get around this in normal atoms by firing two identical lasers in opposite directions at the target. The atom absorbs one photon from each beam – which is only likely to occur if the atom has no relative motion in the direction of the lasers, eliminating the Doppler broadening.

This is trickier to do with antiprotonic helium, and Hori and colleagues instead used lasers at two different frequencies to eliminate much of the Doppler broadening.

So after all that hard work, did they discover any new physics? I’m afraid not. The antiproton-to-electron mass ratio is the same as the proton-to-electron ratio to an impressive nine significant figures.

The work is described in Nature 475 484.

Galactic Spin Underlies Matter/Antimatter Decay Asymmetry

According to the conclusions of a new study, it would appear that the gigantic mass our galaxy has may contribute to underlying the asymmetry in decay rates between matter and antimatter. This phenomenon, called charge-parity (C-P) violation, has remained mysterious for years.

Galactic masses may explain baryonic matter/antimatter decay asymmetries

The Milky Way has a tremendously large mass, accounted for by both normal, baryonic matter and dark matter. The latter makes its existence known only by the gravitational interactions it has with normal matter.

This mass is spinning, and is therefore controlled by the rules explaining the physics of angular momentum. When placing such a heavy, spinning object inside spacetime, the end result is the emergence of distortions in the latter.

Astrophysicists know about two types of distortions – frame-dragging and time dilation. The former is a process in which spacetime is wrapped around a massive spinning body, as proposed in Albert Einstein’s Theory of General Relativity…… Continue reading Galactic Spin Underlies Matter/Antimatter Decay Asymmetry

Tevatron particles shed light on antimatter mystery

WHY the universe is filled with matter rather than antimatter is one of the great mysteries in physics. Now we are a step closer to understanding it, thanks to an experiment which creates more matter than antimatter, just like the early universe did.

Our best understanding of the building blocks of matter and the forces that glue them together is called the standard model of particle physics. But this does a poor job of explaining why matter triumphed over antimatter in the moments after the big bang.

The standard model has it that matter and antimatter were created in equal amounts in the early universe. But if that was the case they should have annihilated in a blaze of radiation, leaving nothing from which to make the stars and galaxies. Clearly that didn’t happen.

A quirk in the laws of physics, known as CP violation, favours matter and leaves the universe lopsided. The standard model allows for a small amount of CP violation but not nearly enough to explain how matter came to dominate. “It fails by a factor of 10 billion,” says Ulrich Nierste, a physicist at the Karlsruhe Institute of Technology in Germany…….. Continue reading Tevatron particles shed light on antimatter mystery

Antimatter Tevatron mystery gains ground

The Dzero team is also part of a mystery about a potential new particle

US particle physicists are inching closer to determining why the Universe exists in its current form, made overwhelmingly of matter.
Physics suggests equal amounts of matter and antimatter should have been made in the Big Bang.
In 2010, researchers at the Tevatron accelerator claimed preliminary results showing a small excess of matter over antimatter as particles decayed.
The team has submitted a paper showing those results are on a firmer footing.
Each of the fundamental particles known has an antimatter cousin, with identical properties but opposite electric charge.

When a particle encounters its antiparticle, they “annihilate” each other, disappearing in a high-energy flash of light.

The question remains: why did this not occur in the early Universe with the equal amounts of matter and antimatter, resulting in a Universe devoid of both?

New physics?
The Tevatron results come from a shower of particles produced at the facility when smashing protons into their antimatter counterparts, antiprotons….. Continue reading Antimatter Tevatron mystery gains ground

Why antimatter should matter to us

The news that scientists can capture and store antimatter could have a profound effect on our understanding of the universe, says Tom Chivers.

The birth of a star: the ability to capture antimatter means that we can begin to 'study the animal in captivity' rather than document its destruction

Sixteen minutes is not a particularly long time. It’s enough time for a cup of tea, or to run two miles, if you’re in good shape. But if you have a few atoms of antimatter, it may be enough time to learn about the birth of the universe.

On Sunday, scientists at the European Organization for Nuclear Research (Cern) generated excited headlines worldwide when it was announced that they had created and stored antimatter – the elusive “mirror image” of everything we see around us – in a stable state for the first time. They have managed to keep atoms of antihydrogen – the antimatter equivalent of hydrogen, the simplest element – trapped for 1,000 seconds, or 16 minutes and 40 seconds. Their previous record stood at just 172 milliseconds, or rather less than a fifth of a second. It’s an exciting breakthrough, but one that may have been hard to grasp for those of us without a physics degree.

To understand it, we first need to know what matter and antimatter really are. The universe is made of subatomic particles – electrons, protons and neutrons being the best known. In 1928, the English physicist Paul Dirac, a pioneer of quantum mechanics, created a detailed mathematical model of the subatomic world – but he realised that, for his equations to work, he required a particle with the same mass as an electron, but with the opposite, “positive” charge. In 1932, an American, Carl Anderson, observed such a particle, which became known as a positron. Later, it became clear to physicists that every particle of matter had an associated antiparticle. In 1955, researchers at the University of California at Berkeley identified an antineutron and antiproton.

But studying this antimatter was not easy. When an antiparticle of any kind meets its matter counterpart, the pair annihilate each other in a small but fierce burst of energy. An atom of antihydrogen, consisting of a positron and an antiproton, would instantly vanish upon contact with any matter. The only way to store antimatter, then, is to keep it in a magnetic field.

Until very recently, that meant that only subatomic antiparticles could be stored and studied because only charged antiparticles, antiprotons and positrons, can be manipulated by a magnetic field. Whole atoms do not have an electric charge and so magnets were of limited use.
Last December, however, the Antihydrogen Laser Physics Apparatus (Alpha) team at Cern managed a world first: to make and trap whole atoms of antihydrogen using magnetic fields. At very low temperatures, anti-atoms will behave like minuscule magnets. Only when they are close to absolute zero are anti-atoms sluggish enough to be guided, even with powerful superconducting magnets. It was a remarkable technical feat, but a short-lived one: the team only held the antihydrogen for a few microseconds, before turning off the fields and allowing the anti-atoms to annihilate with matter. They then observed the resulting bursts with their detectors.

Amazing as this was, there is only so much we can learn about antimatter from such experiments. We want to watch its existence, not just document its destruction. As Tom Whyntie, a physicist at Cern, said: “It’s the difference between observing an animal’s tracks or droppings, and studying it in captivity.” And it is the latest breakthrough that may make such observation possible. Professor Jeffrey Hangst, a spokesman for the Alpha team, explained: “1,000 seconds is long enough to begin to study [antihydrogen atoms] – even with the small number that we can catch so far.”

We need to look back to the start of the universe, 13.7 billion years ago, to explain why this is important. In the moments after the Big Bang, the universe – according to our understanding – consisted of equal parts matter and antimatter. If that is the case, we should expect that the two would annihilate each other, but they did not. Almost all the antimatter in the universe is long gone, but somehow, we were left with enough matter to create a working universe.

That would make sense if there were some difference between antimatter and matter which meant that antimatter disappeared more readily. But it is a fundamental feature of modern physics, stretching back to Dirac’s equations, that antimatter and matter are symmetrical. “Any hint of symmetry-breaking would require a serious rethink of our understanding of nature,” says Prof Hangst. “But half of the universe has gone missing, so some kind of rethink is on the agenda.” Indeed, the very fact of our existence is one of the greatest mysteries facing modern physics.

A key goal of antimatter physics, then, is to find out what the asymmetry – or difference between matter and antimatter – is. There are two obvious starting points: first, does antihydrogen react to light in the same way as ordinary hydrogen; and second, does it interact with gravity in the usual fashion. Later this year, experiments will begin to determine both.

The first involves spectroscopy and is similar to the methods used to determine the chemical make-up of distant stars. By bombarding an atom with lasers or microwaves, scientists can see what frequencies the atom absorbs, and so learn more about its nature. “If you hit the trapped antihydrogen atoms with the right microwave frequency, they will escape the trap, and we can detect the annihilation – even for just a single atom,” explains Prof Hangst. “This would provide the first ever look inside the structure of antihydrogen – element number one on the anti-periodic table.” The second experiment, known as Aegis (Antimatter Experiment: Gravity, Interferometry, Spectroscopy), will determine whether antimatter falls to Earth in the same way as matter.

Will scientists find any evidence of asymmetry? It’s not clear, just as it’s not clear what it will mean if they do or don’t. Prof Hangst says: “If we find no difference, that just means that in this system, to this degree of accuracy, we can’t find a difference. You get that a lot in this kind of physics. But finding a difference would be really interesting. There is no model for what it would mean, and nothing, a priori, to suggest what we might find. It’s not obvious that it would point you towards what happened in the first moments of the universe. But it would mean that we haven’t understood everything.”

For now, though, simply being able to produce and capture the exotic anti-stuff is achievement enough. It may lead to profound breakthroughs at the very edge of physics. Or it may not. But there is only one way to find out – as Prof Hangst says: “My philosophy is, if you get hold of some antimatter, you should take the chance to look long and hard at it.”

Catching atoms

British physicist Paul Dirac, winner of the Nobel Prize for physics in 1933, first predicted the existence of an antimatter particle

• What is antimatter?

The universe is made up of subatomic particles, most famously the electron, proton and neutron. Every kind of particle has an associated antiparticle with the opposite electrical charge – electron and positron; proton and antiproton etc.

• Who discovered it?

The English physicist Paul Dirac, one of the fathers of quantum mechanics, realised in 1928 that for his equations to work, an antiparticle must exist. In 1932, the American Carl Anderson confirmed Dirac’s prediction.

• Where did it come from?

At the birth of the universe, matter and antimatter were created in equal amounts. One of the great unsolved mysteries of modern physics is why antimatter was almost entirely destroyed.

Powering starships and planting bombs: antimatter has featured in (left to right) Star Trek, Star Wars and Avatar.

Star Trek (1969)

Annihilation of matter and antimatter fuels the Starship Enterprise’s warp engines

Star Wars (1977-2005) The Jedi Interceptor hyperdrive rings utilise antimatter to provide density for the starship to remain in hyperspace

Angels & Demons (2009)

Terrorists plant an antimatter bomb underneath the Vatican

Avatar 2009

Mile-long interstellar spaceships cruise at 670 million miles per hour courtesy of hybrid antimatter fusion engines
Read also “Future is bright for CERN antimatter physicists