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Fermilab | Batavia, IL | USA

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CDMS: The uncertainty principle for dark matter searches

 
As an undergraduate physics major, I was introduced to the Heisenberg uncertainty principle, which states that it is impossible to measure the exact momentum and position of an object at the same time.  This is not caused by inadequacies in our experiments.  Instead, it implies a fundamental limit to our ability to predict the future of a system because we cannot precisely determine its present state.  Such a conclusion is shocking to any physicist. Even Einstein himself refused to accept it.  

Visible matter accounts for only 5 percent of the universe. CDMS hopes to identify the dark matter contained in the remainder of the universe. Courtesy: SLAC/Nicolle Rager

Shocking as the principle is, my university education at least prepared me for the uncertainty of the subatomic world.  What I wasn’t taught was how much uncertainty is embedded in the day-to-day life of a physicist.   A little over a week ago, the mine where my experiment is housed experienced a fire.  The name of my experiment is the Cryogenic Dark Matter Search, or CDMS.  

Before I tell you about the fire, let me explain the purpose of CDMS. Scientists have gathered a large body of evidence that tells us most of the matter in the universe is not in a form that we can see.   Matter that we can see takes on the form of stars, planets, moons, comets, interstellar dust etc..  Dark matter is instead composed of a form of matter that we have never observed on Earth.  My experiment is attempting to probe this dark matter component of the universe and will help us understand what  dark matter is really made of.  CDMS is located approximately 1 km, or a little more than half a mile, underground inside the Soudan Underground Laboratory – up near the Boundary Waters of northern Minnesota.  This unusual location allows us to use the earth as a barrier to cosmic rays.  These can produce signals that  will confuse our attempts to observe dark matter.

The CDMS with sheilding surrounding the silver cryostat where the detectors are housed. Credit: Fermilab

So while housing the experiment deep underground is necessary for its function, it can make for some unexpected challenges. The day of the fire, I and my colleagues waited anxiously, hour-by-hour for the latest news on the attempts to extinguish it.  Luckily, the fire was not in the lab, but was instead in the mine shaft.  Since this shaft serves as the entry and exit to the laboratory, it was still quite a serious situation.  In the end, the fire was put out after heroic efforts on the part of the Minnesota Department of Natural Resources, which operates the laboratory, and the various emergency responders.  Thankfully no one was injured and the damage to the mine shaft and infrastructure were minimal compared to our initial fears.  Since last week, the laboratory staff has been busy restoring power to the underground lab and assessing damage to the mine infrastructure.   As of this Monday, a few scientists have finally been allowed restricted access to the lab.  They are  beginning to assess the status of CDMS.

Before the fire broke out, we were in the midst of an engineering run.  The purpose of this run was to commission a new design for our detectors.   We were very excited about the results of this run because they would demonstrate the power of the new detector design.  This is a necessary step towards convincing our funding agencies that we are ready for the next step of building a much bigger experiment.   Now everything has come to a screeching halt as we continue to wait to find out when we will be able to resume our work. 

 Even without the drama of the mine fire, these past few weeks are a very tense time for a postdoc, such as myself, who is in the process of applying for faculty positions.   I was one of the lucky few this year who was able to land several interviews at top universities.   These interviews are grueling sessions where one must meet and talk to many people over the course of a few days.  During a packed series of 30-45 minute interviews, where one often doesn’t even get a few minutes break in between sessions, you must simultaneously explain your research and try to find out as much about the university as possible. 

The interview rounds are largely finished for this year.  Now it is the time when the schools begin making offers to their first-choice candidates.  Some of these decisions will make or break the dreams of young physicists.  On the part of the universities, its a very large investment, especially because the recent downturn in the economy has prohibited many schools from making hires in the past few years.

 Anxiety runs high on all sides as I continue to wait for news of my future and that of CDMS…

–Lauren Hsu

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