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GAPS

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GAPS is an indirect dark matter experiment. It will search for the antideuterons produced as a by-product of WIMP-WIMP annihilation or decay in the galaxy (WIMP = weakly interacting massive particle). WIMPS are predicted in many Beyond Standard Model (BSM) theories such as supersymmetry and extra-dimension theories such as 5-dimensional Kaluza-Klein. As seen in the left figure, the antideuteron signal predicted in many BSM theories (green lines) can be orders of magnitude higher than the antideuteron signal predicted by their production in “conventional” proton-proton collisions in the interstellar medium. Thus antideuteron detection can represent a “smoking gun” signature of dark matter.

To detect anideuterons near the earth GAPS is flown on a balloon from Antarctica. The experiment consists of 10 planes of Lithium-drifted silicon (Si(Li)) detectors surrounded by a time-of-flight systems. The antideuterons slow down in the upper silicon planes and are captured in the lower ones. When an antideuteron is captured by a Silicon atom the atom deexcites producing X-rays, and ultimately annihilates with the nucleus producing pions. The X-rays and pions are detected by the Silicon tracker planes, which thus serve as both target and detector. A prototype experiment called pGAPS was flown from Taiki, Japan in 2012 (middle figure). GAPS is a vastly scaled up version of pGAPS.

Currently the GAPS experiment is under construction by an international collaboration of institutions in the US, Japan and Italy. The Si(Li) detectors are being produced in Japan, and they are shipped to the Columbia University Nevis Labs where they are inspected, undergo some initial testing, and are coated with a “passivator” to protect the detectors from environmental contaminants such as water vapor and organic chemicals. They are then assembled into 4-detector sub-arrays enclosed by a window (ultimately there will be 250 such sub-arrays comprising the Silicon tracker).

An REU student working on GAPS will be based at Nevis Labs in New York and will participate in the acceptance testing of the Si(Li) detectors, their passivation and assembly in the sub-arrays. There is also the possibility to engage with a small modeling project associated with the GAPS detector performance.