Symmetry factor

Today, at the conference NO-VE (IV International Workshop on neutrino oscillations) in Venice, collaboration DAMA/LIBRA claimed to see Dark Matter (DM) interactions in their detector. The effect is at the 8.2 sigma level (which means that the chance that it is a background that mimics their signal is WAY smaller than 1%). See their talk here. Here is their website.

Their search technique is based on DM interacting with their detector material (which happens to be well-known NaI), so they can trigger on detector’s “matter recoil” when DM particle hits the detector. In principle, it is a hard way to search for DM, as many non-DM backgrounds can also interact with NaI! For example, neutrons… Well, the deal with DAMA is that they look for the modulations in their signal that can appear due to Earth’s motion around the Sun (see Drukier, Freese and Spergel’s paper in Phys Rev D48). So one looks for a cosine-type signal over some years of data collecting. This cosine-type signal is very difficult to emulate by any (known) background. Nevertheless, (known) background studies are very important — and about half of the above talk is about them

This result is interesting, but still controversial… See, that XENON experiment has something to say about it — they used liquid xenon as their detecting media, which is very similar in properties to iodine in NaI that DAMA used. The thing is, they didn’t see anything…

I finally got around to update my blog. There are many things to talk about. But first, I have to finish blogging about that conference that happened more than a month ago. So here it is.

In the days 2-5 of the conference there were many interesting talks, so I can not talk about them all. One nice feature was that they introduced two special sessions for young scientists — each talk in a session was only 5 min long! You might be surprised how much info one can put into 5 min talk… Anyway, Lisa Randall gave a nice talk about warped geometries at the LHC,  where she indicated some potentially new ways of looking for extra dimensions.  Kellogg Stelle (who, among other five languages, speaks absolutely fluent Russian)  gave an excellent (but maybe a bit misplaced) talk about finite supergravity. Adam Falkowski gave a talk about Kaluza-Klein parity in Randall-Sundrum models (ways of creating stable Dark Matter candidates). Gustavo Burdman gave a talk about model building with extra dimensions… Thomas Humbye gave a nice talk about implications of see-saw mechanism in neutrinos. On experimental side, I want to emphasize final result from KTeV: Re e’/e=(19.2 +- 2.1)*10^(-4), which is a bit larger than corresponding NA48 result… but the error bars touch… Jean-Francois Glicenstein from HESS collaboration gave a talk about their Dark Matter (DM) search from dwarf galaxies with gamma-rays. They claim to put a strong exclusion bound on higgsino-type DM (one of the SUSY candidates), pretty much excluding masses of the order 80-200 GeV! This depends, of course, on the model of DM distribution, but it is a pretty strong claim! I tried to understand their result going to the original paper, but it’s not very clear. In particular, they claim exclusions of that mass range with technical gamma-ray threshold for their search of about 120 GeV (what also confuses me is that they talk about gamma rays with E > 250 GeV in their paper)… Of course, if gamma rays are produced in DM annihilations, their energies cannot exceed masses of those DM particles. That is to say, you cannot exclude 80 GeV DM particle by looking for gamma rays with energies greater than 120 GeV… N. Parua gave an experimental update on heavy meson and baryon lifetimes from FNAL without referencing any recent theoretical papers on this subject, including this seminal paper. I also learned about a cool experiment called COUPP — they managed to eat up part of available parameter space for DM. Their experiment is located in one of the FNAL neutrino tunnels - I wonder if high-energy neutrinos pose an irreducible background for them..

If you want to see the complete schedule of talks, you can find it here.