Constraints on Vector-Like Top Dipole Interactions from Top-Associated Photon Measurements at the LHC
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| Format: | Preprint |
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2026
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| _version_ | 1866913032746041344 |
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| author | Sahraei, Mohammad Hosseini, Yasaman Najafabadi, Mojtaba Mohammadi |
| author_facet | Sahraei, Mohammad Hosseini, Yasaman Najafabadi, Mojtaba Mohammadi |
| contents | Vector-like top partners with electric charge $+2/3$ are predicted in many extensions of the Standard Model and are actively searched for at the LHC through their electroweak decays $T\to Wb$, $Zt$, and $Ht$. More general scenarios, however, allow dipole interactions that induce radiative decays $T\to tγ$ and $T\to tg$. We reinterpret precision measurements of top-associated photon production to constrain such dipole operators. This approach provides a complementary probe to traditional resonance searches, which rely on direct reconstruction of heavy states, by instead exploiting distortions in precision observables. Using unfolded differential cross sections for $t\bar{t}γ$ production measured by CMS and the fiducial $t\bar{t}γγ$ cross section reported by ATLAS, we derive constraints on the electromagnetic and chromomagnetic dipole couplings of a vector like $T$ quark within an effective field theory framework. We present limits in terms of the effective couplings $c_{tγ}$ and $c_{tg}$, as well as the corresponding branching fractions $BR(T \to tγ)$ and $BR(T \to tg)$, for masses in the range $500~GeV \le m_T \le 2.0~TeV$. For $m_T = 500~GeV$, the analysis reaches sensitivity to the electromagnetic dipole coupling as small as $c_{tγ} \simeq 0.005~TeV^{-1}$ in the gluon dominated scenario $B_γ = 0.1$, while the sensitivity degrades to $O(1)~TeV^{-1}$ at $m_T = 2.0~TeV$. We find that the $t\bar{t}γ$ and $t\bar{t}γγ$ measurements provide complementary sensitivity, probing different regions of parameter space and lifting degeneracies between electromagnetic and chromomagnetic dipole interactions. These results demonstrate that precision measurements of top-associated photon final states provide a powerful and complementary probe of vector-like quarks in scenarios where radiative decays dominate. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_13270 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Constraints on Vector-Like Top Dipole Interactions from Top-Associated Photon Measurements at the LHC Sahraei, Mohammad Hosseini, Yasaman Najafabadi, Mojtaba Mohammadi High Energy Physics - Phenomenology Vector-like top partners with electric charge $+2/3$ are predicted in many extensions of the Standard Model and are actively searched for at the LHC through their electroweak decays $T\to Wb$, $Zt$, and $Ht$. More general scenarios, however, allow dipole interactions that induce radiative decays $T\to tγ$ and $T\to tg$. We reinterpret precision measurements of top-associated photon production to constrain such dipole operators. This approach provides a complementary probe to traditional resonance searches, which rely on direct reconstruction of heavy states, by instead exploiting distortions in precision observables. Using unfolded differential cross sections for $t\bar{t}γ$ production measured by CMS and the fiducial $t\bar{t}γγ$ cross section reported by ATLAS, we derive constraints on the electromagnetic and chromomagnetic dipole couplings of a vector like $T$ quark within an effective field theory framework. We present limits in terms of the effective couplings $c_{tγ}$ and $c_{tg}$, as well as the corresponding branching fractions $BR(T \to tγ)$ and $BR(T \to tg)$, for masses in the range $500~GeV \le m_T \le 2.0~TeV$. For $m_T = 500~GeV$, the analysis reaches sensitivity to the electromagnetic dipole coupling as small as $c_{tγ} \simeq 0.005~TeV^{-1}$ in the gluon dominated scenario $B_γ = 0.1$, while the sensitivity degrades to $O(1)~TeV^{-1}$ at $m_T = 2.0~TeV$. We find that the $t\bar{t}γ$ and $t\bar{t}γγ$ measurements provide complementary sensitivity, probing different regions of parameter space and lifting degeneracies between electromagnetic and chromomagnetic dipole interactions. These results demonstrate that precision measurements of top-associated photon final states provide a powerful and complementary probe of vector-like quarks in scenarios where radiative decays dominate. |
| title | Constraints on Vector-Like Top Dipole Interactions from Top-Associated Photon Measurements at the LHC |
| topic | High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2604.13270 |