The First Measurements Of The Antihydrogen Spectrum

A New Result From ALPHA

Once you’ve trapped antihydrogen what do you do? You measure it! That’s just what we’ve done. Published in Nature, we report the first resonant quantum transitions in antihydrogen atoms. We’ve used microwave radiation to change the internal state of the atom, from one which can be kept in our trap, to one that is kicked out. This process depends on the frequency of the microwave radiation and the magnetic field in the trap, so by changing both of these, we demonstrated that we had enough control and sensitivity to sucessfully carry out the experiment. This is by no means easy, as antihydrogen is not found in nature, but must be prepared in our apparatus from antiprotons made in the Antiproton Decelerator, and positrons from a radioactive source, Even more, it must have low enough energy to remain trapped in the magnetic fields making up our trap. Here’s an animation describing how we do our measurement.

Eventually, we will use this technique to compare the structure of antihydrogen and hydrogen atoms, to search for difference between matter and antimatter, but In this first experiment, we do not yet have enough precision to test these fundamental symmetries. This is important, as the Universe has shown a preference for matter over antimatter as it has evolved, but so far, no measurements can explain why this came about. If matter and antimatter were truely identical, the Universe as we know it could not have come about. The next step at ALPHA is to construct an apparatus that will allow us to make these more precise measurements, using both microwave radiation, and laser light.
We’ve been waiting a long time for this result, so we’re really happy — the CERN People documentary has been following us through the process — check out the first video here.

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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