Elsevier B.V. : Multi-lepton probes of new physics and lepton-universality in top-quark interactions

Afik, Yoav; Pal, Kuntal; Bar-Shalom, Shaouly; Wudka, Jose; Soni, Amarjit

doi:10.1016/j.nuclphysb.2022.115849

Article
Report number	arXiv:2111.13711
Title	Multi-lepton probes of new physics and lepton-universality in top-quark interactions
Author(s)	Afik, Yoav (CERN) ; Bar-Shalom, Shaouly (Technion) ; Pal, Kuntal (UC, Riverside) ; Soni, Amarjit (Brookhaven) ; Wudka, Jose (UC, Riverside)
Publication	2022-07
Imprint	2021-11-26
Number of pages	27
Note	arXiv admin note: substantial text overlap with arXiv:2101.05286
In:	Nucl. Phys. B 980 (2022) 115849
DOI	10.1016/j.nuclphysb.2022.115849 (publication)
Subject category	hep-ex ; Particle Physics - Experiment ; hep-ph ; Particle Physics - Phenomenology
Abstract	We explore the sensitivity to new physics (NP) in the associated production of top-quarks with leptons $pp \to t \bar t \ell^+ \ell^-$, which leads to the multi-leptons signals $pp \to n \ell + {\tt jets} + \not\!\! E_T$, where $n = 2,3,4$. The NP is parameterized via 4-Fermi effective $t\bar{t} \ell^+ \ell^-$ contact interactions of various types, which are generated by multi-TeV heavy scalar, vector or tensor exchanges in $t \bar t \to \ell^+ \ell^-$; we focus on the case of $\ell=e,\mu$. We match the 4-Fermi $t t \ell \ell$ terms to the SMEFT operators and also give examples of specific underlying heavy physics that can generate such terms. Analysis of the SM signals and corresponding backgrounds shows that the di-lepton and tri-lepton channels are much better probes of the effective $t\bar{t} \ell^+ \ell^-$ 4-Fermi terms than the four-lepton one at the 13 TeV LHC. Therefore, the best sensitivity is obtained in the di- and tri-lepton channels, for which the dominant background $pp \to t \bar t$ and $pp \to WZ$, respectively, can be essentially eliminated after applying the $2\ell$ and $ 3 \ell$ selections and a sufficiently high invariant mass selection for the opposite sign same flavor (OSSF) lepton-pair. We explore two cases: lepton flavor universal (LFU) NP where the $t t e e$ and $t t \mu \mu$ contact interactions are of same size and LFU violating (LFUV) NP, where the scale of the $t t \mu \mu$ terms is assumed to be much lower. We show that in both cases it is possible to obtain new 95% CL bounds on the scale of the $t t \ell \ell$ contact interactions at the level $\Lambda \gtrsim 2-3$ TeV, which are considerably tighter than the current bounds on these 4-Fermi terms.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2022-2025 The Author(s) (License: CC BY 4.0), sponsored by SCOAP³

$Expected number of SM, NP and Background event yields for the di-, tri- and four-leptons signals at the HL-LHC with an integrated luminosity of ${\cal L}=3000$~fb$^{-1}$. The event yields are plotted as a function of the lower cut on the invariant mass of the none-top di-muon pair $m_{2\ell}^{\tt min}$ (upper plots) and as a function of the lower cut on the invariant mass of all leptons in the final state in the tri-lepton and four-leptons channels (lower plot), $m_{3\ell}^{\tt min}$ and $m_{4\ell}^{\tt min}$, respectively. The jet selections of Table \ref{tab:selections} for each channel are applied. See also text.$ $Expected number of SM, NP and Background event yields for the di-, tri- and four-leptons signals at the HL-LHC with an integrated luminosity of ${\cal L}=3000$~fb$^{-1}$. The event yields are plotted as a function of the lower cut on the invariant mass of the none-top di-muon pair $m_{2\ell}^{\tt min}$ (upper plots) and as a function of the lower cut on the invariant mass of all leptons in the final state in the tri-lepton and four-leptons channels (lower plot), $m_{3\ell}^{\tt min}$ and $m_{4\ell}^{\tt min}$, respectively. The jet selections of Table \ref{tab:selections} for each channel are applied. See also text.$ $Expected number of SM, NP and Background event yields for the di-, tri- and four-leptons signals at the HL-LHC with an integrated luminosity of ${\cal L}=3000$~fb$^{-1}$. The event yields are plotted as a function of the lower cut on the invariant mass of the none-top di-muon pair $m_{2\ell}^{\tt min}$ (upper plots) and as a function of the lower cut on the invariant mass of all leptons in the final state in the tri-lepton and four-leptons channels (lower plot), $m_{3\ell}^{\tt min}$ and $m_{4\ell}^{\tt min}$, respectively. The jet selections of Table \ref{tab:selections} for each channel are applied. See also text.$ Show more plots

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