CMSTOP21013 ; CERNEP2023214  
Search for flavor changing neutral current interactions of the top quark in final states with a photon and additional jets in protonproton collisions at $ \sqrt{s}= $ 13 TeV  
CMS Collaboration  
11 December 2023  
Phys. Rev. D 109 (2024) 072004  
Abstract: A search for the production of a top quark in association with a photon and additional jets via flavor changing neutral current interactions is presented. The analysis uses protonproton collision data recorded by the CMS detector at a centerofmass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{1} $. The search is performed by looking for processes where a single top quark is produced in association with a photon, or a pair of top quarks where one of the top quarks decays into a photon and an up or charm quark. Events with an electron or a muon, a photon, one or more jets, and missing transverse momentum are selected. Multivariate analysis techniques are used to discriminate signal and standard model background processes. No significant deviation is observed over the predicted background. Observed (expected) upper limits are set on the branching fractions of top quark decays: $ \mathcal{B}(\mathrm{t}\to\mathrm{u}\gamma) < $ 0.95 $\times$ 10$^{5} $ (1.20 $ \times$ 10$^{5} $) and $ \mathcal{B}(\mathrm{t}\to\mathrm{c}\gamma) < $ 1.51 $\times$ 10$^{5} $ (1.54 $ \times$ 10$^{5} $) at 95% confidence level, assuming a single nonzero coupling at a time. The obtained limit for $ \mathcal{B}(\mathrm{t}\to\mathrm{u}\gamma) $ is similar to the current best limit, while the limit for $ \mathcal{B}(\mathrm{t}\to\mathrm{c}\gamma) $ is significantly tighter than previous results.  
Links: eprint arXiv:2312.08229 [hepex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; 
Figures  
png pdf 
Figure 1:
LO Feynman diagrams for the production of a single top quark in association with a photon (left), and the decay of a top antiquark to a photon and a light antiquark in top quark pair production (right) via a $ \mathcal{\mathrm{t}\mathrm{q}\gamma} $ FCNC, where $ \mathrm{q}=\mathrm{u} $, c. The leptonic decay of the W boson from the top quark decay is included. The charge conjugate diagrams are also included. The FCNC interaction vertex is marked as a filled red circle. 
png pdf 
Figure 2:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2a:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2b:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2c:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2d:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2e:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2f:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2g:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 2h:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, reconstructed top quark mass, and $ \Delta R(\ell,\,\mathrm{b}\ \text{jet}) $ for the electron (left) and muon (right) channels in SR1. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} = \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} = $ 0.2 and are superimposed on the background expectations. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3a:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3b:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3c:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3d:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3e:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3f:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3g:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 3h:
From upper to lower, expected and observed distributions of photon $ p_{\mathrm{T}} $, transverse mass of W boson candidate, invariant mass of jet and photon, and reconstructed top quark mass, for the electron (left) and muon (right) channels in SR2. For presentational purposes, the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal distributions are normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.2 and are superimposed on the background expectations. The $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ distributions are not shown as they are the same as the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ distributions. The last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 4:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 4a:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 4b:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 4c:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 4d:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 5:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 5a:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 5b:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 5c:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
png pdf 
Figure 5d:
The BDT output distributions for the data, the background predictions, and the expected $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ signal for electron (left) and muon (right) channels in SR1 (upper) and SR2 (lower). The signal distribution is normalized to a cross section corresponding to $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}}= $ 0.10 (0.01) for ST (TT) and is stacked on the background expectations. The first bins include underflows, and the last bins include overflows. The vertical bars on the points depict the data statistical uncertainties and the hatched bands show the combined statistical and systematic uncertainties in the estimated background processes. 
Tables  
png pdf 
Table 1:
Estimated background yields and observed event counts for the electron and muon channels in the signal regions SR1 and SR2. The uncertainties are the statistical and systematic contributions summed in quadrature. 
png pdf 
Table 2:
The expected and observed 95% CL upper limits using the $ \text{CL}_\text{s} $ criterion on the anomalous couplings $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} $, $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} $ and the corresponding branching fractions $ \mathcal{B}(\mathrm{t}\to\mathrm{u}\gamma) $ and $ \mathcal{B}(\mathrm{t}\to\mathrm{c}\gamma) $ from the combination of the electron and muon channels at NLO for SR1, SR2, and combined (SR1+SR2). 
Summary 
The results of a search for flavor changing neutral current (FCNC) interactions in the top quark sector associated with the $ \mathcal{\mathrm{t}\mathrm{u}\gamma} $ and $ \mathcal{\mathrm{t}\mathrm{c}\gamma} $ vertices have been presented. These vertices are probed by a simultaneous evaluation of single top quark production in association with a photon and top quark pair production with one of the top quarks decaying via FCNC. The search is performed using protonproton collisions at a centerofmass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{1} $, collected by the CMS detector at the LHC. The results are in agreement with the standard model prediction. Upper limits are set at 95% confidence level on the anomalous FCNC couplings of $ \kappa_{\mathcal{\mathrm{t}\mathrm{u}\gamma}} < 6.2\times10^{3} $ and $ \kappa_{\mathcal{\mathrm{t}\mathrm{c}\gamma}} < 7.7\times10^{3} $. The upper limits on the corresponding branching fractions are $ \mathcal{B}(\mathrm{t}\to\mathrm{u}\gamma) < 0.95\times10^{5} $ and $ \mathcal{B}(\mathrm{t}\to\mathrm{c}\gamma) < 1.51\times10^{5} $. The obtained limit for $ \mathcal{B}(\mathrm{t}\to\mathrm{u}\gamma) $ is similar to the current best limit from the ATLAS experiment [14], while the limit for $ \mathcal{B}(\mathrm{t}\to\mathrm{c}\gamma) $ is significantly tighter. 
References  
1  S. L. Glashow, J. Iliopoulos, and L. Maiani  Weak interactions with leptonhadron symmetry  PRD 2 (1970) 1285  
2  J. A. AguilarSaavedra  Top flavorchanging neutral interactions: Theoretical expectations and experimental detection  in Proc. Final Meeting of the European Union Network Particle Physics Phenomenology at High Energy Colliders: Montpellier, France, 2004 Acta Phys. Polon. B 35 (2004) 2695 
hepph/0409342 
3  J. A. AguilarSaavedra and B. M. Nobre  Rare top decays $ {\mathrm{t}\to\mathrm{c}\gamma} $, $ {\mathrm{t}\to\mathrm{c}\mathrm{g}} $  PLB 553 (2003) 251  hepph/0210360 
4  F. Larios, R. Martinez, and M. A. Perez  New physics effects in the flavorchanging neutral couplings of the top quark  Int. J. Mod. Phys. A 21 (2006) 3473  hepph/0605003 
5  G. Couture, M. Frank, and H. König  Supersymmetric QCD flavorchanging top quark decay  PRD 56 (1997) 4213  hepph/9704305 
6  R. A. Diaz, R. Martinez, and J. A. Rodriguez  The rare decay $ {\mathrm{t}\to\mathrm{c}\gamma} $ in the general 2HDM type III  hepph/0103307  
7  G. Lu, F. Yin, X. Wang, and L. Wan  Rare top quark decays $ {\mathrm{t}\to\mathrm{c}\mathrm{V}} $ in the topcolorassisted technicolor model  PRD 68 (2003) 015002  hepph/0303122 
8  J. A. AguilarSaavedra  A minimal set of top anomalous couplings  NPB 812 (2009) 181  0811.3842 
9  CDF Collaboration  Search for flavorchanging neutral current decays of the top quark in $ {\mathrm{p}\overline{\mathrm{p}}} $ collisions at $ \sqrt{s}= $ 1.8 TeV  PRL 80 (1998) 2525  
10  L3 Collaboration  Search for single top production at LEP  PLB 549 (2002) 290  hepex/0210041 
11  H1 Collaboration  Search for single top quark production at HERA  PLB 678 (2009) 450  0904.3876 
12  ZEUS Collaboration  Search for singletop production in $ {\mathrm{e}\mathrm{p}} $ collisions at HERA  PLB 708 (2012) 27  1111.3901 
13  CMS Collaboration  Search for anomalous single top quark production in association with a photon in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 8 TeV  JHEP 04 (2016) 035  CMSTOP14003 1511.03951 
14  ATLAS Collaboration  Search for flavourchanging neutralcurrent couplings between the top quark and the photon with the ATLAS detector at $ \sqrt{s}= $ 13 TeV  PLB 842 (2023) 137379  2205.02537 
15  CMS Collaboration  HEPData record for this analysis  link  
16  CMS Collaboration  Performance of photon reconstruction and identification with the CMS detector in protonproton collisions at $ \sqrt{s}= $ 8 TeV  JINST 10 (2015) P08010  CMSEGM14001 1502.02702 
17  CMS Collaboration  Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC  JINST 16 (2021) P05014  CMSEGM17001 2012.06888 
18  CMS Collaboration  Performance of the CMS muon detector and muon reconstruction with protonproton collisions at $ \sqrt{s}= $ 13 TeV  JINST 13 (2018) P06015  CMSMUO16001 1804.04528 
19  CMS Collaboration  Performance of the CMS Level1 trigger in protonproton collisions at $ \sqrt{s}= $ 13 TeV  JINST 15 (2020) P10017  CMSTRG17001 2006.10165 
20  CMS Collaboration  The CMS trigger system  JINST 12 (2017) P01020  CMSTRG12001 1609.02366 
21  CMS Collaboration  The CMS experiment at the CERN LHC  JINST 3 (2008) S08004  
22  J. Alwall et al.  The automated computation of treelevel and nexttoleading order differential cross sections, and their matching to parton shower simulations  JHEP 07 (2014) 079  1405.0301 
23  M. Czakon and A. Mitov  \textsctop++: a program for the calculation of the toppair crosssection at hadron colliders  Comput. Phys. Commun. 185 (2014) 2930  1112.5675 
24  Y. Zhang et al.  Nexttoleading order QCD predictions for $ {\mathrm{t}\gamma} $ associated production via modelindependent flavorchanging neutralcurrent couplings at hadron colliders  PRD 83 (2011) 094003  1101.5346 
25  P. Nason  A new method for combining NLO QCD with shower Monte Carlo algorithms  JHEP 11 (2004) 040  hepph/0409146 
26  S. Frixione, P. Nason, and C. Oleari  Matching NLO QCD computations with parton shower simulations: the POWHEG method  JHEP 11 (2007) 070  0709.2092 
27  S. Alioli, P. Nason, C. Oleari, and E. Re  A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG \textscbox  JHEP 06 (2010) 043  1002.2581 
28  T. Sjöstrand et al.  An introduction to PYTHIA8.2  Comput. Phys. Commun. 191 (2015) 159  1410.3012 
29  CMS Collaboration  Event generator tunes obtained from underlying event and multiparton scattering measurements  EPJC 76 (2016) 155  CMSGEN14001 1512.00815 
30  CMS Collaboration  Extraction and validation of a new set of CMS PYTHIA8 tunes from underlyingevent measurements  EPJC 80 (2020) 4  CMSGEN17001 1903.12179 
31  NNPDF Collaboration  Parton distributions for the LHC run II  JHEP 04 (2015) 040  1410.8849 
32  NNPDF Collaboration  Parton distributions from highprecision collider data  EPJC 77 (2017) 663  1706.00428 
33  GEANT4 Collaboration  GEANT 4a simulation toolkit  NIM A 506 (2003) 250  
34  CMS Collaboration  Measurement of the inelastic protonproton cross section at $ \sqrt{s}= $ 13 TeV  JHEP 07 (2018) 161  CMSFSQ15005 1802.02613 
35  CMS Collaboration  Particleflow reconstruction and global event description with the CMS detector  JINST 12 (2017) P10003  CMSPRF14001 1706.04965 
36  CMS Collaboration  Technical proposal for the PhaseII upgrade of the Compact Muon Solenoid  CMS Technical Proposal CERNLHCC2015010, CMSTDR1502, 2015 CDS 

37  CMS Collaboration  Performance of electron reconstruction and selection with the CMS detector in protonproton collisions at $ \sqrt{s}= $ 8 TeV  JINST 10 (2015) P06005  CMSEGM13001 1502.02701 
38  M. Cacciari, G. P. Salam, and G. Soyez  The anti$ k_{\mathrm{T}} $ jet clustering algorithm  JHEP 04 (2008) 063  0802.1189 
39  M. Cacciari, G. P. Salam, and G. Soyez  FASTJET user manual  EPJC 72 (2012) 1896  1111.6097 
40  CMS Collaboration  Jet energy scale and resolution in the CMS experiment in $ {\mathrm{p}\mathrm{p}} $ collisions at 8 TeV  JINST 12 (2017) P02014  CMSJME13004 1607.03663 
41  CMS Collaboration  Jet algorithms performance in 13 TeV data  CMS Physics Analysis Summary, 2017 CMSPASJME16003 
CMSPASJME16003 
42  CMS Collaboration  Performance of missing transverse momentum reconstruction in protonproton collisions at $ \sqrt{s}= $ 13 TeV using the CMS detector  JINST 14 (2019) P07004  CMSJME17001 1903.06078 
43  CMS Collaboration  Identification of heavyflavour jets with the CMS detector in $ {\mathrm{p}\mathrm{p}} $ collisions at 13 TeV  JINST 13 (2018) P05011  CMSBTV16002 1712.07158 
44  B. Vormwald on behalf of the CMS Collaboration  The CMS Phase1 pixel detectorexperience and lessons learned from two years of operation  in Proc. 9th International Workshop on Semiconductor Pixel Detectors for Particles and Imaging (PIXEL ): Taipei, Taiwan, 2019 JINST 14 (2019) C07008 

45  Particle Data Group, R. L. Workman et al.  Review of particle physics  Prog. Theor. Exp. Phys. 2022 (2022) 083C01  
46  \DZERO Collaboration  Observation of single topquark production  PRL 103 (2009) 092001  0903.0850 
47  CDF Collaboration  Observation of electroweak single topquark production  PRL 103 (2009) 092002  0903.0885 
48  CMS Collaboration  Measurement of the $ t $channel single top quark production cross section in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 TeV  PRL 107 (2011) 091802  CMSTOP10008 1106.3052 
49  CMS Collaboration  Search for new physics with samesign isolated dilepton events with jets and missing transverse energy at the LHC  JHEP 06 (2011) 077  CMSSUS10004 1104.3168 
50  A. Hoecker et al.  TMVA: Toolkit for multivariate data analysis  PoS ACAT (2007) 040  physics/0703039 
51  S. Khatibi and M. Mohammadi Najafabadi  Probing the anomalous FCNC interactions in tophiggs boson final state and the charge ratio approach  PRD 89 (2014) 054011  1402.3073 
52  CMS Collaboration  Precision luminosity measurement in protonproton collisions at $ \sqrt{s}= $ 13 TeV in 2015 and 2016 at CMS  EPJC 81 (2021) 800  CMSLUM17003 2104.01927 
53  CMS Collaboration  CMS luminosity measurement for the 2017 datataking period at $ \sqrt{s}= $ 13 TeV  CMS Physics Analysis Summary, 2018 CMSPASLUM17004 
CMSPASLUM17004 
54  CMS Collaboration  CMS luminosity measurement for the 2018 datataking period at $ \sqrt{s}= $ 13 TeV  CMS Physics Analysis Summary, 2019 CMSPASLUM18002 
CMSPASLUM18002 
55  CMS Collaboration  Pileup mitigation at CMS in 13 TeV data  JINST 15 (2020) P09018  CMSJME18001 2003.00503 
56  CMS Collaboration  Measurement of the Higgs boson production rate in association with top quarks in final states with electrons, muons, and hadronically decaying tau leptons at $ \sqrt{s}= $ 13 TeV  EPJC 81 (2021) 378  CMSHIG19008 2011.03652 
57  CMS Collaboration  $ {\mathrm{W^+}\mathrm{W^}} $ boson pair production in protonproton collisions at $ \sqrt{s}= $ 13 TeV  PRD 102 (2020) 092001  CMSSMP18004 2009.00119 
58  CMS Collaboration  Measurements of $ {\mathrm{p}\mathrm{p}\to\mathrm{Z}\mathrm{Z}} $ production cross sections and constraints on anomalous triple gauge couplings at $ \sqrt{s}= $ 13 TeV  EPJC 81 (2021) 200  CMSSMP19001 2009.01186 
59  CMS Collaboration  Measurements of production cross sections of $ {\mathrm{W}\mathrm{Z}} $ and samesign $ {\mathrm{W}\mathrm{W}} $ boson pairs in association with two jets in protonproton collisions at $ \sqrt{s}= $ 13 TeV  PLB 809 (2020) 135710  CMSSMP19012 2005.01173 
60  ATLAS Collaboration  Observation of singletopquark production in association with a photon using the ATLAS detector  PRL 131 (2023) 181901  2302.01283 
61  CMS Collaboration  Measurement of the production cross section for single top quarks in association with W bosons in protonproton collisions at $ \sqrt{s}= $ 13 TeV  JHEP 10 (2018) 117  CMSTOP17018 1805.07399 
62  N. Kidonakis  Theoretical results for electroweakboson and singletop production  in 23rd International Workshop on DeepInelastic Scattering and Related Subjects (DIS ): Dallas TX, USA, 2015 PoS (DIS2015) 170 
1506.04072 
63  J. Butterworth et al.  PDF4LHC recommendations for LHC Run II  JPG 43 (2016) 023001  1510.03865 
64  A. L. Read  Presentation of search results: The $ \text{CL}_\text{s} $ technique  JPG 28 (2002) 2693  
65  T. Junk  Confidence level computation for combining searches with small statistics  NIM A 434 (1999) 435  hepex/9902006 
66  G. Cowan, K. Cranmer, E. Gross, and O. Vitells  Asymptotic formulae for likelihoodbased tests of new physics  EPJC 71 (2011) 1554  1007.1727 
Compact Muon Solenoid LHC, CERN 