Track length measurement of $^{19}$F$^+$ ions with the MIMAC Dark Matter directional detector prototype
26 Mar 2020
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Tao Y.
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Beaufort C.
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Moric I.
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Tao C.
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Santos D.
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Sauzet N.
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Couturier C.
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Guillaudin O.
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Muraz J. F.
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Naraghi F.
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Zhou N.
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Busto J.
Weakly Interacting Massive Particles (WIMPs) are one of the most preferred
candidate for Dark Matter. WIMPs should interact with the nuclei of detectors...If a robust signal is eventually observed in direct detection experiments, the
best signature to confirm its Galactic origin would be the nuclear recoil track
direction. The MIMAC collaboration has developed a low pressure gas detector
providing both the kinetic energy and three-dimensional track reconstruction of
nuclear recoils. In this paper we report the first ever observations of
$^{19}$F nuclei tracks in a $5$ cm drift prototype MIMAC detector, in the low
kinetic energy range ($6$-$26$ keV), using specially developed ion beam
facilities. We have measured the recoil track lengths and found significant
differences between our measurements and standard simulations. In order to
understand these differences, we have performed a series of complementary
experiments and simulations to study the impact of the diffusion and eventual
systematics. We show an unexpected dependence of the number of read-out
corresponding to the track on the electric field applied to the $512\
\mathrm{\mu m}$ gap of the Micromegas detector. We have introduced, based on
the flash-ADC observable, corrections in order to reconstruct the physical 3D
track length of the primary electron clouds proposing the physics behind these
corrections. We show that diffusion and space charge effects need to be taken
into account to explain the differences between measurements and standard
simulations. These measurements and simulations may shed a new light on the
high-gain TPC ionization signals in general and particularly at low energy.(read more)