Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First 3D vector tracking of helium recoils for fast neutron measurements
  at SuperKEKB   We present results from the first deployment of novel, high definition,
compact gas Time Projection Chambers (TPCs) with pixel chip readout as part of
the BEAST II beam background measurement project at SuperKEKB. The TPCs provide
detailed 3D imaging of ionization from neutron-induced nuclear recoils in a
helium and carbon dioxide target gas mixture at standard temperature and
pressure. We find excellent electron background rejection, leading to
background-free nuclear recoil measurements above 50 keVee, despite the extreme
high-background environment. We measure an angular resolution better than
20{\deg} for recoil tracks longer than 1.7 mm, corresponding to an average
ionization energy of ~100 keVee. We also obtain the 3D vector direction of
helium recoils by utilizing charge profile measurements along the recoil axis,
with a correct head/tail assignment efficiency of approximately 80%. With this
performance, we present comparisons between measured and simulated event rates,
recoil energy spectra, and directional distributions originating from beam-gas
and Touschek beam losses at SuperKEKB. We utilize head/tail recognition to
distinguish neutron components travelling with positive radial velocity in the
Belle II coordinate system from those with opposite directionality. Finally, we
present a novel method of discriminating beam-gas interactions from Touschek
beam losses that can eliminate the need for dedicated accelerator runs for
background measurements. This method is still statistics-limited. However,
future studies should be able to verify this method, which in turn could lead
to neutron background analysis runs symbiotic with normal Belle II operation.
The capabilities demonstrated here also suggest that high definition recoil
imaging in gas TPCs is applicable to low energy, low-background experiments,
such as directional dark matter searches.

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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org