Monday, January 01, 2007


What are these people staring at?

Here is what they see out of their window:

What is this?! No, it's not the preparation for the New Year's firework. This is the main spectrometer of the KATRIN experiment as it is transported through the small German city Eggenstein-Leopoldshafen. If you have a high bandwidth, you can look at the full video here (~35 MB).

KATRIN stands for KArlsruhe TRItium Neutrino experiment, and is designed to detect the spectrum of the tritium beta decay with very high precision to directly measure the absolute mass of the electron neutrino. Keep in mind that neutrino-oscillations only measure mass-differences (for an elementary introduction, see here). In the beta decay, an electron is emitted together with the electron neutrino. The neutrino is hard to detect, therefore the measurement of the absolute mass with KATRIN is done by detecting the electron that is emitted, and measuring its energy, from which the neutrino mass can be extracted.

(Figure 6b, page 29)

The figure above shows the signature in the electron's spectrum for an electron neutrino with a mass of 1 eV in comparison to the spectrum in case the neutrino was massless. The distortion is statistically significant only in a region close to the endpoint of the spectrum of E0 = 18.6keV. Since we already know that the electron neutrino's mass is very tiny, it requires such a huge spectrometer to resolve the spectrum of the electron's energy fine enough. The Design Report of the experiment says that they anticipate a sensitivity on the neutrino mass of 0.2 eV (90% C.L.) corresponding to a 5 sigma discovery potential for a mass of 0.35 eV.

The detector was manufactured by MAN DWE in Deggendorf, but then had to be brought to Karlsruhe, which is about 400 km away from Deggendorf. However, since the tank is too big for motorways, the spectrometer had to make a detour of almost 9000 km as shown on this map. You find much more information about the detector at this website.

See also: KATRIN moved

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  1. I had had a vague impression that there is a Rhine-Danube canal, and this reinforces that. (Do visit the link for some nice photos!). So??????? I suppose Katrin wanted a Mediterranean vacation?

  2. Hi Arun,

    I had the same thought. There is half-a-sentence on this website that says 'and the canal between the rivers Rhine and Danube has to be ruled out, too', but no further explanation. Maybe these are just the mysterious ways of DHL... (if you look at the movie, last minute, you'll see a huge DHL tag prominently displayed on the spectrometer ;-)



  3. I have posted a number of pictures I took of KATRINs transport inside the FZK on my blog:

    Most in this post and the one before and after that!

  4. btw, nice photos indeed, thanks for the link! I'll send it to my Mum, she'll love it :-)

  5. Hey Joer?,

    thanks for the link, this is nice, I'll add it to the post



  6. Poor Mitb├╝rgerinnen and Mitb├╝rger. I hope that they will at least measure the mass or at least determine whether it is of the same order as the differences or much smaller. Or greater? Happy New Year!

  7. I now remember that the story of the arrival of the KATRIN detector in Karlsruhe made it even into the evening news on German television - I somehow didn't take care of it, shame on me ;-).

    Anyhow, the news then did make a major point of the long journey around Europe instead of a shipping on the direct way, and they said that some bridges along the Danube and Main rivers and the channel are not high enough for a transport of the detector, see e.g. here, or here.

    Let's hope the experiment will work and do better than just establishing some new upper bound on the neutrino mass!

    BTW, am I the only one who is reminded by the foto of the detector in the small town of a certain scence in a Woody Allen movie ;-) ?

    Best, stefan

  8. First, the electron neutrino doesn't have a mass, at least in the sense that the eletron, muon and tau have masses. The electron neutrino is a flavor eigenstate, not a mass eigenstate, so it can only be assigned an equivalent mass.

    Second, I don't think that there are very many people out there expecting a neutrino mass anywhere near 0.35 eV. Of the people who predicted the masses of the three mass eigenstate neutrinos, the highest I found was 0.0530 eV (see page 8, with references).

    Now I didn't look exhaustively, I simply searched the literature until my slide ran out of room (7+1 papers), so the experiment will likely limit somebody's conjecture out there, but it could hardly be considered mainstream.

  9. I had to give it some ancient thoughts, while symbolically linking it to what scientists do today:)

    I like Susskinds and Greene's quotes as well today. Evolve to what? :)

  10. Can they also detect the neutrino background e.g. from the sun or the relic neutrinos by using the fact that beta decay is very slightly suppressed by these external sources because of Fermi statistics?

    You would expect a very small directional effect, but I guess that this is too small.

  11. Stupid mistake, the Sun emits
    neutrinos not antineutrinos :(

    But in principle, one could contemplate detecting the relic neutrino background this way...

  12. Hi Plato,

    Evolve to what? Good question. I'm not sure I exactly want to know what Susskind had in mind. I also admit I apparently have one of these brains that are wired in the old fashioned way, and trouble visualizing 4 or more dimensions.

    However, it is true that as the first and only species on this planet we potentially have the power to change our own genome, and direct evolution on purpose. It can also very easily go wrong though. I don't think we should mess around carelessly with well balanced processes that took millions of years to optimize. We're just not smart enough for this. But I am optimistic that if we mess it up, nature will find it's balance back by erasing us from the surface of the planet.



  13. B:I'm not sure I exactly want to know what Susskind had in mind.

    An "image" in mind?

    There is a "sense of accomplishment" in mathematical deduction, similar to a simple experiment transcending the "abstractness of logic?"

    Maybe this is what we are evolving too? :)

  14. Bee (#2): I believe that the Rhine-Main-Danube canal doesn't have very high overhead clearance. I have a photo of the spectrometer clearing a bridge on the Danube at the Austrian border with about 2" to spare. And that was after adding tons of gravel ballast to the barge.

    Count Iblis: Actually, several early tritium beta-decay experiments reported a "negative mass" as the result of their best fit to the spectrum. Nowadays, we realize that this is because they hadn't included all of the tritium *atomic* corrections: when you're writing the decay "T -> e nu 3He", you have to take into account that it's really "T2* -> e nu 3He* T*", where the initial tritium molecule may be excited/rotating, either the 3He or the T atom in the final state may be excited or ionized, and so on. It's all calculable, but it has to be included. Anyway, my point is, before people realized that these corrections were causing the "negative mass" fits, someone actually calculated the effects of the relic neutrino background. It turns out to be totally negligible. However, if you somehow enhanced the antineutrino density by some huge factor, you would indeed see a little "peak" just past the expected endpoint, thus explaining the early fits ...


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