Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Testing CPT symmetry in ortho-positronium decays with positronium
  annihilation tomography   Charged lepton system symmetry under combined charge, parity, and
time-reversal transformation (CPT) remains scarcely tested. Despite stringent
quantum-electrodynamic limits, discrepancies in predictions for the
electron-positron bound state (positronium atom) motivate further
investigation, including fundamental symmetry tests. While CPT noninvariance
effects could be manifested in non-vanishing angular correlations between
final-state photons and spin of annihilating positronium, measurements were
previously limited by knowledge of the latter. Here, we demonstrate tomographic
reconstruction techniques applied to three-photon annihilations of
ortho-positronium atoms to estimate their spin polarisation without magnetic
field or polarised positronium source. We use a plastic-scintillator-based
positron-emission-tomography scanner to record ortho-positronium (o-Ps)
annihilations with single-event estimation of o-Ps spin and determine the
complete spectrum of an angular correlation operator sensitive to CPT-violating
effects. We find no violation at the precision level of 10^{-4}, with an over
threefold improvement on the previous measurement.

19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom