Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Arrival time in quantum mechanics   A self-adjoint operator with dimensions of time is explicitly constructed,
and it is shown that its complete and orthonormal set of eigenstates can be
used to define consistently a probability distribution of the time of arrival
at a spatial point.

1
The categories of this paper are: cs
16
The categories of this paper are: stat
2
The categories of this paper are: math
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys