Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Nab Experiment: A Precision Measurement of Unpolarized Neutron Beta
  Decay   Neutron beta decay is one of the most fundamental processes in nuclear
physics and provides sensitive means to uncover the details of the weak
interaction. Neutron beta decay can evaluate the ratio of axial-vector to
vector coupling constants in the standard model, $\lambda = g_A / g_V$, through
multiple decay correlations. The Nab experiment will carry out measurements of
the electron-neutrino correlation parameter $a$ with a precision of $\delta a /
a = 10^{-3}$ and the Fierz interference term $b$ to $\delta b = 3\times10^{-3}$
in unpolarized free neutron beta decay. These results, along with a more
precise measurement of the neutron lifetime, aim to deliver an independent
determination of the ratio $\lambda$ with a precision of $\delta \lambda /
\lambda = 0.03\%$ that will allow an evaluation of $V_{ud}$ and sensitively
test CKM unitarity, independent of nuclear models. Nab utilizes a novel, long
asymmetric spectrometer that guides the decay electron and proton to two large
area silicon detectors in order to precisely determine the electron energy and
an estimation of the proton momentum from the proton time of flight. The Nab
spectrometer is being commissioned at the Fundamental Neutron Physics Beamline
at the Spallation Neutron Source at Oak Ridge National Lab. We present an
overview of the Nab experiment and recent updates on the spectrometer,
analysis, and systematic effects.

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The categories of this paper are: hep-ph
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: cs
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
19
The categories of this paper are: eess