Borexino: Solar Neutrinos
2002
The summer after my freshman year of college, I was chosen by the Princeton Borexino collaboration to take part in their international
research collaboration. Borexino is, like the usual particle physics collaboration, a very large, multi-university research experiment involving
on the order of several hundred people. The collaboration involves the Unites States, Italy, and Germany primarily and is concerned with
performing the most accurate measurement of low energy solar neutrinos. Neutrinos (once thought to be massless) come in several mass groups, have no
net electric charge, are thought to be point particles (like electrons), and travel near the speed of light. These neutrinos are produced during
nuclear reactions in the sun and are ejected out into space all the time. Most of them pass right through matter, which makes them quite difficult
to detect. The Standard Model (the prevailing formulation of the different forces in nature) predicts that more of these neutrinos should be measured
than are actually detected - hence, the solar neutrino puzzle.
Because it is so unlikely that a given neutrino will interact with matter (and, thus, show up on a detector), the game is to produce a very large volume of detecting material which is especially sensitive to the slightest evidence of a neutrino interaction. This means that, in addition to building spheres of detecting liquid seveal meters in diameter surrounded by stainless steel spheres, everything must be kept ultraclean so that absolutely no impurities whatsoever exist which could contaminate the experiment. Thus, enter me and Julie. We spent half of our summer working in a class 10 clean room at Princeton working on building the inner nylon vessel which contained psuedocumen which, effectively, lights up when neutrinos interact with the material (this light is then recorded by PMTs and, voila - a measurement is made!).
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We spent the second half of the summer working in the Gran Sasso labs in Italy. Because other particles from space would create a lot of background noise for the sensitive measurements being made, the experiment itself was inside the base of a mountain whereby the mile of earth above us acted as shielding. We lived in the external, office portion of the labs and spent some evenings in nearby L'aquila and our weekends traveling throughout Italy. The majority of our time was spent on making a cleanroom, cleaning, pickling and passivating tank D-201, and doing water purification. See below for pictures.
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