Andy’s Los Alamos Blog

Another exciting day at the lab, as always. I can’t believe that I’m only here for about another 2.5 weeks. Tempus fugit indeed.
Today, I finished up my symposium presentation, worked a little on testing our power meters, and received the part I was waiting for for the angular PMT testing. So, I should be getting that started tomorrow, at last. Perhaps if I’m very lucky my new part for the cryogenic testing setup will be done as well…

After work I went climbing at the YMCA. It’s always a good time, but I’m really looking forward to getting back outside this weekend.

It seems I have received another question! This, fresh from the comments: “Are the neutrinos something that is found in dark matter? Or are they an altogether different ‘animal’???” In retrospect, I guess I hadn’t been too clear on this. So, here’s a bit about elementary particle physics. I’m sorry if this gets techincal… if you have any questions post a comment and I’ll try to clear things up.

Currently, everything we know about particle physics (arguably everything we know) is summed up in the Standard Model. There are hundreds of different types of particles that we’ve observed so far, and every observed particle can be explained by the Standard Model as of today. The Model is really pretty neat and tidy; it’s simple and does its job well. Fermilab sums it up in this little table (a nicer, more copywritten table can be found here):

You’ll notice in the third row down and first three columns the three neutrinos, one associated with each of electrons, muons, and taus. Most people have heard of electrons; muons and taus are just heavy, electron-like particles that we see in various interactions. The neutrinos (meaning “little neutral one”) are very light particles (thought to be completely massless until the 1990s), and are created in a lot of interactions, and so tell us a great deal about certain particle processes. SNO (the Sudbury Neutrino Observatory) was looking for neutrinos from the sun, for example, and has yielded a wealth of information about the sun’s core. Note that for each neutrino, there is a corresponding antineutrino (this is antimatter) not listed on the chart.

The Standard Model neutrinos, however, are just “plain old matter.” Part of what makes the dark matter search so exciting is that the dark matter particle can’t be anything currently described in the Standard Model. So, if projects like the one I’m working on are successful, it will rewrite textbooks and herald the first real development in particle physics since 1973 (when the Standard Model was formulated. String theory doesn’t count as an acheivement). If found, WIMP dark matter will be a new and revolutionary particle. For those so interested, WIMP dark matter is predicted in the MSSM, the Minimal Supersymmetic Standard Model, a theoretical extension to the current Model. In this model, WIMPs would be the lightest superparticle (LSP).

Curiously, there is another dark matter theory which posits that the dark matter is in fact a new and different (also non-Standard Model) kind of neutrino. The hypothetical “sterile neutrino” is a (right-handed) neutrino that interacts only gravitationally. The MiniBooNE experiment at Fermilab that I talked about yesterday is, I think, looking for them in the lab. Sterile neutrinos are, like WIMPs, a frontrunner among dark matter particle candidates. We, of course, like WIMPs better.

So, long story short, dark matter and regular neutrinos are fundamentally different creatures. Neutrinos, though very interesting, are normal Standard Model physics, whereas dark matter is something new entirely.

There’s another question I get a lot that also deserves attention, and that is whether dark matter and antimatter are the same. They aren’t, but that’s another story, so I think I’ll tackle that one tomorrow.

Thanks for reading, and as I said, if any of this is unclear, please ask in a comment and I’ll clarify.