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CMS-B2G-24-006 ; CERN-EP-2026-005
Search for pair production of heavy resonances in final states with a photon and large-radius jets in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
Submitted to Physical Review D
Abstract: A search for the pair production of heavy spin-1$/$2 or spin-3$/$2 resonances ($\mathrm{t}$*) in proton-proton collisions at $ \sqrt{s}= $ 13 TeV is presented. Data collected with the CMS detector at the CERN LHC from 2016 to 2018 corresponding to an integrated luminosity of 138 fb$ ^{-1} $ are used. The analysis targets benchmark signal scenarios where one $\mathrm{t}$* decays into a top quark (t) and a photon ($ \gamma $), and the other into a t quark and a gluon ($ \mathrm{g} $), i.e., $\mathrm{p}\mathrm{p}\to\mathrm{t}{*} \bar{\mathrm{t}}{*} \to\mathrm{t}\mathrm{t}\gamma\mathrm{g} $. All-hadronic final states from the t pair decay chain are selected using jet substructure techniques. The signal is probed as a function of the $\mathrm{t}$* candidate mass, which is reconstructed using the photon and a top quark candidate jet. No significant deviation from the background-only hypothesis is found. Observed (expected) upper limits on the signal cross section at 95% confidence level are set, excluding masses of spin-1$/$2 $\mathrm{t}$* particles below 930 (930) GeV and spin-3$/$2 $\mathrm{t}$* particles below 1330 (1390) GeV. This analysis marks the first search for heavy resonances in the $ {\mathrm{t}\overline{\mathrm{t}}} \gamma\mathrm{g} $ channel. Exploiting the high-energy photon to reduce the backgrounds, this search achieves sensitivity competitive with $ \mathrm{p}\mathrm{p}\to\mathrm{t}{*} \bar{\mathrm{t}}{*} \to{\mathrm{t}\overline{\mathrm{t}}} \mathrm{g}\mathrm{g}$ searches for spin-1$/$2 $\mathrm{t}$* despite the small expected ${\mathrm{t}}{*} \to\mathrm{t}\gamma $ branching fraction.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Representative LO Feynman diagram for pair production of \tstar in the $ \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g} $ channel.

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Figure 2:
Shape comparison of the $ m_{\gamma\text{j}_{1}} $ distribution for $ \mathrm{t}{*} \bar{\mathrm{t}}{*} $ signal events generated at different $ m_{\mathrm{t}{*}} $, for the spin-1$/$ 2 (solid) and spin-3$/$2 (dashed) cases.

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Figure 3:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

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Figure 3-a:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

png pdf
Figure 3-b:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

png pdf
Figure 3-c:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

png pdf
Figure 3-d:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

png pdf
Figure 3-e:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

png pdf
Figure 3-f:
The photon (left) and j$ _1 $ (right) $ p_{\mathrm{T}} $ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-1$/$2 and spin-3$/$2 $\mathrm{t}{*}$ with a mass of 900 GeV are overlaid for comparison, with both samples normalized to a cross section of 10fb. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.

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Figure 4:
The background-only postfit $m_{\gamma\text{j}_{1}}$ distributions for the SR (left) and VR1 (right) are shown. Notations are as in Fig. 3.

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Figure 4-a:
The background-only postfit $m_{\gamma\text{j}_{1}}$ distributions for the SR (left) and VR1 (right) are shown. Notations are as in Fig. 3.

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Figure 4-b:
The background-only postfit $m_{\gamma\text{j}_{1}}$ distributions for the SR (left) and VR1 (right) are shown. Notations are as in Fig. 3.

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Figure 5:
The expected (red solid lines) and the observed (black solid lines) 95% CL upper limits on the cross section of the $ \mathrm{p} \mathrm{p} \to {\mathrm{t}}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g} $ process as functions of the $ m_{\mathrm{t}{*}} $ for a spin-1$/$2 (left) and spin-3$/$2 (right) ${\mathrm{t}}{*}$. The blue (inner) and yellow (outer) bands indicate the 68% and 95% coverage of the expected upper limits. The black dashed lines indicate the theoretical expectations [22].

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Figure 5-a:
The expected (red solid lines) and the observed (black solid lines) 95% CL upper limits on the cross section of the $ \mathrm{p} \mathrm{p} \to {\mathrm{t}}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g} $ process as functions of the $ m_{\mathrm{t}{*}} $ for a spin-1$/$2 (left) and spin-3$/$2 (right) ${\mathrm{t}}{*}$. The blue (inner) and yellow (outer) bands indicate the 68% and 95% coverage of the expected upper limits. The black dashed lines indicate the theoretical expectations [22].

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Figure 5-b:
The expected (red solid lines) and the observed (black solid lines) 95% CL upper limits on the cross section of the $ \mathrm{p} \mathrm{p} \to {\mathrm{t}}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g} $ process as functions of the $ m_{\mathrm{t}{*}} $ for a spin-1$/$2 (left) and spin-3$/$2 (right) ${\mathrm{t}}{*}$. The blue (inner) and yellow (outer) bands indicate the 68% and 95% coverage of the expected upper limits. The black dashed lines indicate the theoretical expectations [22].
Tables

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Table 1:
Observed and expected 95% CL lower mass limits for ${\mathrm{t}}{*}$ searches comparing this analysis to previous results in the $ \mathrm{t}\overline{\mathrm{t}}\mathrm{g}\mathrm{g} $ channel [21].
Summary
A search has been presented for spin-1$/$2 and spin-3$/$2 heavy particles in a final state with a photon and large-radius jets. The data correspond to an integrated luminosity of 138 fb$ ^{-1} $ collected between 2016 and 2018 with the CMS detector at the LHC in proton-proton collisions at $ \sqrt{s}= $ 13 TeV. The pair production of excited top quarks is searched for, considering the decay to (top quark and antiquark, photon and gluon) signature $ {\mathrm{t}}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g} $. Lorentz-boosted top quark identification techniques are used to select events containing large-radius jets originating from top quarks and to suppress standard model (SM) backgrounds. A small deviation from the SM expectations with a local significance of 2.5 standard deviations is seen in the data. Upper limits are placed on the product of the ${\mathrm{t}}{*} \bar{\mathrm{t}}{*} $ cross section and $ \mathcal{B}({\mathrm{t}}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g}) $, as a function of the ${\mathrm{t}}{*}$ mass. A spin-1$/$2 (spin-3$/$2) ${\mathrm{t}}{*}$ with a mass below 930 (1330) GeV is excluded at 95% confidence level. These are the first limits obtained from the ${\mathrm{t}}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\gamma\mathrm{g} $ channel. They are competitive to the limits obtained from the $ \mathrm{t}{*} \bar{\mathrm{t}}{*} \to \mathrm{t}\overline{\mathrm{t}}\mathrm{g}\mathrm{g} $ channel for a spin-1$/$2 ${\mathrm{t}}{*}$ using complementary techniques.
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