Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Search for production of vector-like quark pairs and of four top quarks
  in the lepton-plus-jets final state in $pp$ collisions at $\sqrt{s}=8$ TeV
  with the ATLAS detector   A search for pair production of vector-like quarks, both up-type ($T$) and
down-type ($B$), as well as for four-top-quark production, is presented. The
search is based on $pp$ collisions at $\sqrt{s}=8$ TeV recorded in 2012 with
the ATLAS detector at the CERN Large Hadron Collider and corresponding to an
integrated luminosity of 20.3 fb$^{-1}$. Data are analysed in the
lepton-plus-jets final state, characterised by an isolated electron or muon
with high transverse momentum, large missing transverse momentum and multiple
jets. Dedicated analyses are performed targeting three cases: a $T$ quark with
significant branching ratio to a $W$ boson and a $b$-quark ($T\bar{T} \to
Wb$+X), and both a $T$ quark and a $B$ quark with significant branching ratio
to a Higgs boson and a third-generation quark ($T\bar{T} \to Ht$+X and
$B\bar{B} \to Hb$+X respectively). No significant excess of events above the
Standard Model expectation is observed, and 95% CL lower limits are derived on
the masses of the vector-like $T$ and $B$ quarks under several branching ratio
hypotheses assuming contributions from $T \to Wb$, $Zt$, $Ht$ and $B \to Wt$,
$Zb$, $Hb$ decays. The 95% CL observed lower limits on the $T$ quark mass range
between 715 GeV and 950 GeV for all possible values of the branching ratios
into the three decay modes, and are the most stringent constraints to date.
Additionally, the most restrictive upper bounds on four-top-quark production
are set in a number of new physics scenarios.

7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys