Micro-physics simulations of columnar recombination along nuclear recoil tracks in high-pressure Xe gas for directional dark matter searches
14 May 2015
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Nakajima Y.
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Goldschmidt A.
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Long M.
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Nygren D.
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Oliveira C.
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Renner J.
Directional sensitivity is one of the most important aspects of WIMP dark
matter searches. Yet, making the direction of nuclear recoil visible with large
target masses is a challenge...To achieve this, we are exploring a new method of
detecting directions of short nuclear recoil tracks in high-pressure Xe gas,
down to a few micron long, by utilizing columnar recombination. Columnar
recombination changes the scintillation and ionization yields depending on the
angle between a track and the electric field direction. In order to realize
this, efficient cooling of electrons is essential. Trimethylamine(TMA) is one
of the candidate additives to gaseous Xe in order to enhance the effect, not
only by efficiently cooling the electrons, but also by increasing the amount of
columnar recombination by Penning transfer. We performed a detailed simulation
of ionization electrons transport created by nuclear recoils in a Xe + TMA gas
mixture, and evaluated the size of the columnar recombination signal. The
results show that the directionality signal can be obtained for a track longer
than a few micrometers in some ideal cases. Although more studies with
realistic assumptions are still needed in order to assess feasibility of this
technique, this potentially opens a new possibility for dark matter searches.(read more)