Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for Nonlinear Gluon Effects in QCD and their $A$ Dependence at
  STAR   The STAR Collaboration reports measurements of back-to-back azimuthal
correlations of di-$\pi^0$s produced at forward pseudorapidities
($2.6<\eta<4.0$) in $p$+$p$, $p+$Al, and $p+$Au collisions at a center-of-mass
energy of 200 GeV. We observe a clear suppression of the correlated yields of
back-to-back $\pi^0$ pairs in $p+$Al and $p+$Au collisions compared to the
$p$+$p$ data. The observed suppression of back-to-back pairs as a function of
event activity and transverse momentum suggests nonlinear gluon dynamics
arising at high parton densities. The larger suppression found in $p+$Au
relative to $p+$Al collisions exhibits a dependence of the saturation scale,
$Q_s^2$, on the mass number, $A$. The suppression in high-activity $p+$Au
collisions is consistent with theoretical predictions including gluon
saturation effects.

16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
18
The categories of this paper are: econ
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org