Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First determination of the $\rho $ parameter at $\sqrt{s} = 13$ TeV --
  probing the existence of a colourless three-gluon bound state   The TOTEM experiment at the LHC has performed the first measurement at
$\sqrt{s} = 13$ TeV of the $\rho$ parameter, the real to imaginary ratio of the
nuclear elastic scattering amplitude at $t=0$, obtaining the following results:
$\rho = 0.09 \pm 0.01$ and $\rho = 0.10 \pm 0.01$, depending on different
physics assumptions and mathematical modelling. The unprecedented precision of
the $\rho$ measurement, combined with the TOTEM total cross-section
measurements in an energy range larger than 10 TeV (from 2.76 to 13 TeV), has
implied the exclusion of all the models classified and published by COMPETE.
The $\rho$ results obtained by TOTEM are compatible with the predictions, from
alternative theoretical models both in the Regge-like framework and in the QCD
framework, of a colourless 3-gluon bound state exchange in the $t$-channel of
the proton-proton elastic scattering. On the contrary, if shown that the
3-gluon bound state $t$-channel exchange is not of importance for the
description of elastic scattering, the $\rho$ value determined by TOTEM would
represent a first evidence of a slowing down of the total cross-section growth
at higher energies. The very low-$|t|$ reach allowed also to determine the
absolute normalisation using the Coulomb amplitude for the first time at the
LHC and obtain a new total proton-proton cross-section measurement
$\sigma_{tot} = 110.3 \pm 3.5$ mb, completely independent from the previous
TOTEM determination. Combining the two TOTEM results yields $\sigma_{tot} =
110.5 \pm 2.4$ mb.

1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
19
The categories of this paper are: eess