Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct detection of the 229Th nuclear clock transition   Today's most precise time and frequency measurements are performed with
optical atomic clocks. However, it has been proposed that they could
potentially be outperformed by a nuclear clock, which employs a nuclear
transition instead of the atomic shell transitions used so far. By today there
is only one nuclear state known which could serve for a nuclear clock using
currently available technology, which is the isomeric first excited state in
$^{229}$Th. Here we report the direct detection of this nuclear state, which is
a further confirmation of the isomer's existence and lays the foundation for
precise studies of the isomer's decay parameters. Based on this direct
detection the isomeric energy is constrained to lie between 6.3 and 18.3 eV,
and the half-life is found to be longer than 60 s for
$^{229\mathrm{m}}$Th$^{2+}$. More precise determinations appear in reach and
will pave the way for the development of a nuclear frequency standard.

20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn