New antimatter method to provide 'a major experimental advantage'

Jan 06, 2013

(Phys.org)—Researchers have proposed a method for cooling trapped antihydrogen which they believe could provide 'a major experimental advantage' and help to map the mysterious properties of antimatter that have to date remained elusive.

The new method, developed by a group of researchers from the USA and Canada, could potentially cool trapped antihydrogen to temperatures 25 times colder than already achieved, making them much more stable and a lot easier to experiment on.

The suggested method, which has been published today in IOP Publishing's Journal of Physics B: Atomic, Molecular and , involves a laser which is directed at antihydrogen atoms to give them a 'kick', causing them to lose energy and cool down.

Antihydrogen atoms are formed in an ultra-high vacuum trap by injecting into positron . An atomic process causes the antiproton to capture a positron which gives an electronically excited antihydrogen atom.

Typically, the antihydrogen atoms have a lot of energy compared to the trapping depth which can distort the measurements of their properties. As it is only possible to trap very few antihydrogen atoms, the main method for reducing the high energies is to laser cool the atoms to extremely low temperatures.

Co-author of the study, Professor Francis Robicheaux of Auburn University in the USA, said: "By reducing the antihydrogen energy, it should be possible to perform more of all of its parameters. Our proposed method could reduce the average energy of trapped antihydrogen by a factor of more than 10.

The ultimate goal of antihydrogen experiments is to compare its properties to those of . Colder antihydrogen will be an important step for achieving this."

This process, known as Doppler cooling, is an established method for cooling atoms; however, because of the restricted parameters that are needed to trap , the researchers need to be absolutely sure that it is possible.

"It is not trivial to make the necessary amount of laser light at a specific wavelength of 121 nm. Even after making the light, it will be difficult to mesh it with an antihydrogen trapping experiment. By doing the calculations, we've shown that this effort is worthwhile," continued Professor Robicheaux.

Through a series of computer simulations, they showed that antihydrogen atoms could be cooled to around 20 millikelvin; trapped antihydrogen atoms so far have energies up to 500 millikelvin.

In 2011, researchers from CERN reported that they had trapped antimatter for over 1000 seconds – a record. A year later, the first experiments were performed on antihydrogen whilst it was trapped between a series of magnets.

Even though the processes that control the are largely unknown, the researchers believe that the laser cooling should increase the amount of time antihydrogen can be trapped for.

"Whatever the processes are, having slower moving, and more deeply trapped, antihydrogen should decrease the loss rate," said Professor Robicheaux.

Colder antihydrogen atoms could also be used to measure the gravitational property of antimatter. "No one has ever seen antimatter actually fall in the field of gravity," said co-author Dr Makoto Fujiwara of TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics. "Laser cooling would be a very significant step towards such an observation."

Antimatter fast facts:

  • Every particle has an antiparticle. For example, an electron's antiparticle is the positron and a proton's antiparticle is an antiproton.
  • An antiparticle is exactly the same as its corresponding particle but carries an opposite charge.
  • If a particle and its corresponding antiparticle meet, they destroy each other. This is known as annihilation.
  • The combination of one positron and one antiproton creates antihydrogen.
  • Theories suggest that after the Big Bang, equal amounts of matter and antimatter should have formed. As the Universe today is composed almost entirely of matter, it remains a great mystery why we don't have this symmetry.
  • Scientists such as the ALPHA collaboration at CERN have been trying to measure the properties of antihydrogen to find clues as to why this asymmetry exists.

Explore further: X-ray powder diffraction beamline at NSLS-II takes first beam and first data

More information: "A proposal for laser cooling antihydrogen atoms" 2013 J. Phys. B: At. Mol. Opt. Phys. 46 025302. iopscience.iop.org/0953-4075/46/2/025302

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User comments : 19

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Ben D
not rated yet Jan 06, 2013
Ok, a positron has an opposite charge to an electron, is that brought about by an opposite direction of spin?
Parsec
4.5 / 5 (4) Jan 07, 2013
Ok, a positron has an opposite charge to an electron, is that brought about by an opposite direction of spin?

No. It has a different charge, in the same manner that a proton and an electron have an opposite charge.
Ben D
1 / 5 (2) Jan 07, 2013
Ok in what way different, I thought a positron had the same electric charge as a proton?

And how about spin difference?
thermodynamics
5 / 5 (2) Jan 07, 2013
They have both opposite charge and spin. Good question.

The positron does have the same electric charge as the proton, but it has the mass of an electron.
Ben D
1 / 5 (2) Jan 07, 2013
They have both opposite charge and spin. Good question.

The positron does have the same electric charge as the proton, but it has the mass of an electron.


So the question remains, does the opposite spin of a positron bring about the opposite charge?

antialias_physorg
4.2 / 5 (6) Jan 07, 2013
Ok, a positron has an opposite charge to an electron, is that brought about by an opposite direction of spin?


Positrons have positive charge. They have spin 1/2 (same as the electron...so no 'anti' property there)

The charge of the positron is a the same as a proton, however it seems to be brought about differently.
Whereas a proton is composed of three quarks (two up an one down, with the up having charge 2/3 and the down having charge -1/3). The positron (and the electron) aren't divisible into quarks.

Summary: positrons are different critters. The spin isn't the cause of the charge difference.
Ben D
1 / 5 (2) Jan 07, 2013
Ok, a positron has an opposite charge to an electron, is that brought about by an opposite direction of spin?


Positrons have positive charge. They have spin 1/2 (same as the electron...so no 'anti' property there)

The charge of the positron is a the same as a proton, however it seems to be brought about differently.
Whereas a proton is composed of three quarks (two up an one down, with the up having charge 2/3 and the down having charge -1/3). The positron (and the electron) aren't divisible into quarks.

Summary: positrons are different critters. The spin isn't the cause of the charge difference.


So if positrons and electrons have the same mass and the same spin, what is the unique difference responsible for their opposite charge?
ian_j_allen
5 / 5 (2) Jan 07, 2013
Ben D, you simply aren't getting it. Spin is not responsible for charge. Charge is its own innate physical parameter. Just like mass is, and just like spin is. If you could answer WHY a given particle has its specific parameters set as such, you would be above the realm of modern science. All we do right now, for the most part, is describe the interactions these parameters cause between particles.
antialias_physorg
4 / 5 (4) Jan 07, 2013
what is the unique difference responsible for their opposite charge?

They are antiparticles.

It's like the proton and the antiproton. The proton is two up and one down quark, while the antiproton consists of two anti-up and one anti-down quark (with charges of -2/3 and 1/3 respectively, giving the anti-proton a total charge of -1).
Protons and anti-protons (and neutrons and anti-neutrons) are Hadrons. I.e. they are compose of quarks.

Electrons and positrons (seem to be) funamdental/indivisible particles (so no further subdivision here). These are called a Leptons.
Leptons are *probably* not quarks (the jury is still out on that one).
ian_j_allen
5 / 5 (3) Jan 07, 2013
I'll add that the "unique physical difference" is rather abstract, and that anti-particles are predicted by symmetry arguments within the Standard Model. That they do in fact exist, is simply evidence for the validity so far of the Standard Model. It is not so much a physical explanation as limited mathematical description for a process that humans otherwise cannot entirely observe or describe.
Ben D
1 / 5 (1) Jan 07, 2013
Ben D, you simply aren't getting it. Spin is not responsible for charge. Charge is its own innate physical parameter. Just like mass is, and just like spin is. If you could answer WHY a given particle has its specific parameters set as such, you would be above the realm of modern science. All we do right now, for the most part, is describe the interactions these parameters cause between particles.


Ok ok, i get it. Thank you (and others) for your patience.

But if I may test your patience a little more with some what to you may be ridiculous questions,...is it theoretically possible for the spin of an electron to be made to rotate in the opposite direction?
And if so, would this be the equivalent of inverting the electron on its axis?

I think then I'm just about done..

TheKnowItAll
5 / 5 (3) Jan 07, 2013
I think you need to read this.... http://en.wikiped...physics)
Torbjorn_Larsson_OM
4.2 / 5 (5) Jan 07, 2013
Anti-matter is the particle that annihilates a matter particle. In some cases it is itself. (Say. photons.)

Classically it is the mirror of the particle in all ways. (Say, light wave of opposite phase.)

But as in everything else, quantum relativistic Standard Model particles are surprisingly complex.

Spin can't be understood classically on the particle level. Spin is handed, it has helicity (left and right spin of a classical particle). These particles have mass, therefore they need to have chirality instead - how helicity looks for an observer, including the universal speed limit (left and right chirality - shifts of a quantum wavefunction).

['ctd]
Torbjorn_Larsson_OM
4 / 5 (4) Jan 07, 2013
[ctd] This means instead of 2 classical spin particles, we have 4 chiral quantum field particles: electron (left-chiral), anti-electron (right-spiral), positron (right-chiral), anti-positron (left-chiral). The Higgs field (gives the mass for massed chirality) superpositions the field particles into 2 physical particles by mixing (flipping between the particles): "electron" = electron & anti-positron, "positron" = positron & anti-electron.

So the physical anti-particles are composites of SM anti-particles.

The two other possible mixings disappear, as per your question and perhaps intuition, because SM interacts only with left-chiral particles through the weak force. Why is unknown, I think. [ http://www.quantu...e-higgs/ ]

The Wikipedia article isn't wrong, but I think Quantum Diaries is better - those are LHC physicists - and simpler: "Flip" Tanedo is really pedagogical! I didn't get chirality before I read his article.
Torbjorn_Larsson_OM
4 / 5 (4) Jan 07, 2013
I meant to say: "So the physical anti-particles are composites of SM particles." Too much symmetries to keep track of!

Also, the symmetry breaking that leaves the Standard Model and the observable universe slightly left-handed and "simpler" than it could be, is one of these questions related to "why do matter dominate".

If there wasn't a difference, we would have more possible physical particles, but ironically all that leaves us is radiation and no structure (annihilation of attempts to make atoms).
Torbjorn_Larsson_OM
4 / 5 (4) Jan 07, 2013
Well, true, but actually my point there was to sum up all of that part: the physical particles are composites of SM particles.
Ojorf
4 / 5 (4) Jan 07, 2013
Don't be confused by the word 'spin', it has nothing to do with either spin or rotation. It is just an unfortunate, confusing label chosen for an otherwise apparently fundamental property of particles.
Ben D
5 / 5 (2) Jan 07, 2013
I thank you all for your kind and informative responses, it has cleared up some misconceptions of mine and I can now move on.
thermodynamics
5 / 5 (1) Jan 07, 2013
Torbjorn_Larsson_OM: You gave us the link to the Quantum Diaries and I just want to say that is a great link. It will keep me busy for quite a while. I was not interpreting spin correctly at all (still not comfortable with it) but the QD link is helping.

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