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Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS experiment

The collaboration
Phys.Lett. B800 (2020) 135082, 2020

Abstract (data abstract)
CERN-LHC, ATLAS. A search for flavour-changing neutral current events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81$fb^{−1}$ of proton-proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a $b$-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the $tq\gamma$ coupling in an effective field theory. These are also interpreted as 95 % CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tu\gamma$ coupling of 36 fb (78 fb) and on the branching ratio for $t \rightarrow \gamma u$ of $2.8 \times 10^{−5}$ ($6.1 \times 10^{−5}$). In addition, they are interpreted as 95 % CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tc\gamma$ coupling of 40 fb (33 fb) and on the branching ratio for $t \rightarrow \gamma c$ of $22 \times 10^{−5}$ ($18 \times 10^{−5}$).

• #### Figure 2(a)

Data from Figure 2(a)

10.17182/hepdata.91241.v1/t1

Post-fit distributions of a background-only fit to the signal region (SR) and the control regions (CRs) of the NN output...

• #### Table 1

Data from Table 1

10.17182/hepdata.91241.v1/t2

Observed (expected) 95 % CL limits on the effective coupling strengths for different vertices and couplings, the production cross section,...

• #### Auxiliary Figure 2(a)

Data from Figure 2(a) of auxiliary material

10.17182/hepdata.91241.v1/t3

Post-fit distributions of a background-only fit to the SR and the CRs of the NN output in the SR for...

• #### Auxiliary Figure 2(b)

Data from Figure 2(b) of auxiliary material

10.17182/hepdata.91241.v1/t4

Post-fit distributions of a background-only fit to the SR and the CRs of the NN output in the SR for...

• #### Auxiliary Figure 2(c)

Data from Figure 2(c) of auxiliary material

10.17182/hepdata.91241.v1/t5

Post-fit distributions of a background-only fit to the SR and the CRs of the NN output in the SR for...