Search for Flavor-Changing Neutral Current Interactions of the Top Quark and Higgs Boson in Final States with Two Photons in Proton-Proton Collisions at $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$

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Search for Flavor-Changing Neutral Current Interactions of the Top Quark and Higgs Boson in Final States with Two Photons in Proton-Proton Collisions at $\sqrt{s} = 13 TeV$

A. Tumasyan et al. (CMS Collaboration)

Phys. Rev. Lett. 129, 032001 – Published 13 July 2022

Abstract

Proton-proton interactions resulting in final states with two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks ( $t$ ) and Higgs bosons ( $H$ ). The analysis is based on data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of $137 {fb}^{- 1}$ . No significant excess above the background prediction is observed. Upper limits on the branching fractions ( $B$ ) of the top quark decaying to a Higgs boson and an up ( $u$ ) or charm ( $c$ ) quark are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 0.019% (0.031%) for $B (t \to H u)$ and 0.073% (0.051%) for $B (t \to H c)$ . These are the strictest upper limits yet determined.

Received 3 November 2021
Accepted 13 June 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.032001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Physics Subject Headings (PhySH)

Higgs bosons Top quark

Hadron colliders

Particles & Fields

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Vol. 129, Iss. 3 — 15 July 2022

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Figure 1
Representative Feynman diagrams for the production modes considered: FCNC associated production of a single top quark with a Higgs boson (ST, left), and $t \bar{t}$ production with the FCNC decay of the top quark to a Higgs boson and an up or charm quark (TT, right). The Higgs boson decay to two photons is considered. The FCNC vertex in each process is denoted with a red circle.
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Figure 2
Left: distribution of the BDT-nonres scores used for the hadronic event categorization targeting $t \to H u$ FCNC interactions from data (points) and predictions from simulation (colored histograms). The “Other” category includes contributions from $t \bar{t} Z$ , $t \bar{t} W$ , $W W$ , $W Z$ , $Z Z$ , and $t + γ + jets$ . The “ $top + H$ ” category includes $t \bar{t} H$ , $t H q$ , and $t H W$ , while the “Other H” category includes $g g H$ , VBF, $W H$ , and $Z H$ . The nonresonant background histograms are stacked, while the two signal, “Other H”, and “ $top + H$ ” distributions are shown separately. Boundaries defining event categories are indicated with dotted lines in the upper panel. Events in the gray shaded region are not considered in the analysis. The lower panel shows the ratio of the data to the sum of the nonresonant background predictions. The simulated signal and background distributions are normalized to the integrated luminosity of the data, assuming a coupling of unity for the signal. Statistical and total (statistical $\oplus$ systematic) background uncertainties are represented by the gray- and red-shaded bands, respectively. The $(γ) + jets$ sample of multijet and $γ + jets$ events from data is not assigned a systematic uncertainty, as described in the text. Right: hadronic event categorization targeting $t \to H u$ FCNC interactions from requirements placed on BDT-nonres (horizontal dotted lines) and BDT-res (vertical dotted lines). The color denotes the $s / \sqrt{b}$ of each category.
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Figure 3
The diphoton invariant mass distribution for the selected events from data (black points), and the results of the fits to the signal plus background models (solid red curve), and the background model alone (dotted blue curve), for the categories targeting $t \to H u$ FCNC interactions (left) and $t \to H c$ FCNC interactions (right). The signal model is normalized to the best-fit value. The green and yellow bands give the $\pm 1$ and $\pm 2$ standard deviation uncertainties in the background model (dotted blue curve). The background model includes $H \to γ γ$ events from SM processes. Events are weighted by the $S / (S + B)$ of their respective categories. The lower panels show the same information, but with the background component subtracted.
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Figure 4
The observed (solid line) and expected (dotted line) 95% CL upper limits on $B (t \to H u)$ (left) and $B (t \to H c)$ (right) for each of the hadronic and leptonic categories, defined as described in the text. The last bin gives the overall combined upper limit. The $\pm 1$ and $\pm 2$ standard deviation variations on the expected limit are given by the green and yellow bands, respectively.
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Physical Review Letters

Search for Flavor-Changing Neutral Current Interactions of the Top Quark and Higgs Boson in Final States with Two Photons in Proton-Proton Collisions at s=13 TeV

A. Tumasyan et al. (CMS Collaboration)

Phys. Rev. Lett. 129, 032001 – Published 13 July 2022

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Search for Flavor-Changing Neutral Current Interactions of the Top Quark and Higgs Boson in Final States with Two Photons in Proton-Proton Collisions at $\sqrt{s} = 13 TeV$