Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photon pair distributions and event-mixing at low invariant mass   Neutral meson cross-section and direct photon HBT measurements in high energy
pp, pA, and AA collisions rely on either subtracting or dividing out the
background underlying the $M_\mathrm{inv}$ or $Q_\mathrm{inv}$ distributions.
In this paper we investigate the photon pair distributions for simulated
proton-proton collisions at $\sqrt{s}=13~$TeV, and study why the background in
$M_\mathrm{inv}$ gets poorly described by the conventional event-mixing method
implemented in experimental analyses. We show that it fails to describe the
background as it gives a qualitatively different shape especially at invariant
masses around the $\pi^{0}$ and $\eta$ meson mass, which is mainly caused by
the correlations originating from parton fragmentation.

29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys