Category: Science and Physics

I’ve been attending the TAUP 2009 conference (Topics in Astroparticle and Underground Physics) in Rome this past week.  Yesterday, the DAMA/LIBRA collaboration presented their results on an observation of a seasonal variation of events in their detector.  They interpret this as dark matter.  There is good reason to believe that dark matter rates through the earth vary over the course of the year.  Sometimes the earth is moving “with the wind” from our dark matter halo and sometimes we are moving “against the wind”.  When we are with the wind, fewer dark matter particles travel through us, when we are against more dark matter particles travel through us.  The controversy is that no other dark matter detector has verified this discovery.  As a matter of fact, using convential hypotheses of how dark matter particles behaves, several experiments independently have “ruled out” their discovery.  This leads to one of two conclusions, either DAMA/LIBRA is observing some unaccounted for background that also varies by season or the dark matter interacts in a way that is not expected.

I always walk away with a few questions. 

1.  Is DAMA a poorly designed experiment?   By this what I mean is without independent confirmation, will anyone ever believe that they have found dark matter.  I think not.  However, the same question would be asked of any experiment that claimed a discovery of dark matter.

2.  What do we learn by continuing to run the experiment in the same mode, same location?
    – Wouldn’t it be better if we could learn more details about the interactions of these events.  For example, it would be great if DAMA/LIBRA could do a pulse-shape analysis that would tell us if the events are interacting with the atom’s nucleus or the electrons surrounding the nucleus.  However, I have been told by DAMA collaborators that they have no discrimination power between these types of interactions in there pulses.
   –  What if the experiment were moved to the southern hemisphere?  If the modulation were observed out of phase, this would certianly point to a seasonal effect.  Dark matter particles don’t care which hemisphere your experiment is in.  This question was asked at the conference.  The speaker responded that there were not plans to move the experiment.  It was too much work.  True enough, it does take years to build and commission these experiments. 

In the end, it leaves me asking:  exactly what is it that we are learning by continuing to run DAMA/LIBRA int he same location, without changing anything?  They already have an 8.2 sigma result – certianly enough to claim discovery.  No one doubts that they are seeing a modulation.  The question is a modulation of what.  In order to answer that, I think it is time for a new approach.

Yesterday I gave a Journal Club Seminar at Cornell University in Ithaca, New York.  Giving talks is one of the things I both enjoy and fear most as a physicist.  Ironically, what I enjoy is what I fear.  I enjoy explaining what I do to others.  I find that it helps me think more clearly about my research and my motivation for doing that research.  However, opening yourself up to a room full of brilliant, insightful people often means that your knowledge of any particular subject will be brought to it’s limits.  This can be quite humbling, but also what I need to become a more knowledge scientist. 

By the time I reached the end of my seminar at Cornell yesterday, I remembered why the CDMS (Cryogenic Dark Matter Search) was so appealing to me when I was starting my postdoc career.  The breadth of science  — from astrophysics to particle physics to superconductivity — required to master how it is we go about trying to detect the elusive dark matter with our experiment is quite impressive.  The same can be said about many experiments.  But for me, it was the unique collaborative effort that brought together not only particle- and astro-phyicists, a combination we often see now-a-days, but also low temperature physicists that sold me.  At the time my experience in low temperature physics was a couple of trips to the South Pole and phonons where kind of like photons with a slightly different spelling. 🙂  So, joining CDMS presented me a challenge to really expand my knowledge.

So as I sit here in the very comfortable Ithaca airport, waiting for my delayed flight back home, I realize that over the four years I have been working in the Cabrera group at Stanford University I have learned much and that I really enjoy spreading that knowledge and understanding to others.

Over the last few weeks I have been spending alot of time working on final edits for a paper and a proposal my collaboration has been trying to finish.  It brings me to inevitable grammar question which google and basic grammar books seem not to be able to answer.  Below I list some of my dilemmas.  Many concerns are related to fractional or decimal numbers.

1.)  Do we see no event (or events)?

2.)  Is our expected background 0.6 +- 0.5 event (or events)?

3.)  Do we expect 0.2 misidentified photons (or photon)?

4.)  Are our detectors one-inch thick, 1-inch thick, or maybe even one-inch-thick or 1-inch-thick.

5.)  Is it ever okay to use numerical representation for whole numbers less than 10?

6.)  Are three semicolons and one colon too many for a sentence that makes up an entire paragraph?  Just how many are to many?