Spectrum of anti-hydrogen?

What does the spectrum of anti-hydrogen look like?

This question came up at our Maths/ Physics Seminar Series on Wednesday, during a presentation I gave on the forthcoming experiments at the LHC (slides here).  It’s a good question, I never thought to ask it before. Before I look it up, here is my guess at an answer – any comments welcome.

First a definition: as you know, antimatter is the name given to matter consisting of elementary particles in which the electric charge (or other quantum property) of each particle is the reverse of that in ordinary matter (see blog title). Just as a Hydrogen atom consists of an electron orbiting a proton, an anti-Hydrogen atom consists of a positron orbiting an anti-proton. However, although antiparticles are often found in cosmic rays or produced in accelerators,  anti-atoms are very rare: only a few atoms of anti-Hydrogen are made at accelerator facilities around the world.

My guess is that the sprectrum of anti-H looks exactly like that of Hydrogen. After all, the emission spectrum of Hydrogen is due to an excited electron jumping from the excited energy level down to a lower level(s): presumably the positron in anti-H has the same separation of energy levels, so I can’t see how there would be any difference in the light emitted.

Pictorial representation of H and anti-H


However, there is a problem with this answer: how do we detect anti-atoms if their spectrum is the same as normal atoms? By deflection in a magnetic field, you say – this is how the positron was first discovered. But anti-atoms are neutral and in any case antimatter is not always matter of opposite charge, sometimes it is another quantum property that is swapped (consider the anti-neutrino). Indeed, how do we distinguish anti-neutrinos from neutrinos? I’m not sure, but I know we can.

Also, I think I  read somewhere that we have detected clusters of antimatter in some places in the universe. Again, how do we know it’s antimatter? These sort of unexpected questions are what makes giving a seminar worthwhile..


Filed under Particle physics

10 responses to “Spectrum of anti-hydrogen?

  1. James

    Having lived in Australia for a couple of years, but being a Brit by birth, I was somewhat concerned to notice the opposite spin of vanishing bath water in the region of Melbourne, and wondered if this counted as detection of anti-matter?

    Cetainly this was a hot discussion point around the Barbi. (Yeah the Coriolis force is too small, blah-de blah-de blah…, but that’s just a cover up of Roswell-Elvis stuff)

  2. dvd

    just a quick distraction for you..please view only one minute long but most salient and very enjoyable..


  3. cormac

    ?! As you know, it arises ue to the rotation of the earth about its axis. Nothing to do with antimatter, unfortunately..

  4. James

    We seem to have temporal fluctuations in the space-time-blog continuum – now is THAT evidence of anti-matter?

  5. Van Hooydonk

    Dear Cormac,
    If you have problems with the spectrum of antihydrogen, please read my views in arxiv:0902.1096 and references therein. This ‘antihydrogen’ spectrum is hidden in(or intertwined with) that of natural hydrogen, which makes antiH only a natural state of H.
    This may solve some of the problems you mention, although it contradicts conventional views on “neutral” antimatter.
    G. Van Hooydonk

  6. The prevailing wisdom is that anti-neutrinos are ‘right-handed’ i.e. their spin vector and their velocity vector point the same way. However, there are some dudes under a mountain in Frejus (the NEMO experiment) who are hoping to observe a reaction that would demonstrate that neutrinos and antineutrinos are in fact the same thing (a la photons and antiphotons – no such thing..). If they do see this, then the standard model is screwed and it’s time for a flurry of funding and research.

  7. cormac

    Thanks Kate! That sounds right (must look it up) and I’m happy to go with the prevailing view until proven otherwise.
    I wonder how they measure the relative orientations of spin and velocity vector.. passing them through successive slits? Quite a challenge as neutrinos have no charge and almost no mass!

  8. Pingback: Antimatter at the Royal Irish Academy « Antimatter

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