Search for vectorlike leptons in multilepton final states in proton-proton collisions at $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$

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Search for vectorlike leptons in multilepton final states in proton-proton collisions at $\sqrt{s} = 13 TeV$

A. M. Sirunyan et al. (CMS Collaboration)

Phys. Rev. D 100, 052003 – Published 6 September 2019

Abstract

A search for vectorlike leptons in multilepton final states is presented. The data sample corresponds to an integrated luminosity of $77.4 {fb}^{- 1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016 and 2017. Events are categorized by the multiplicity of electrons, muons, and hadronically decaying $τ$ leptons. The missing transverse momentum and the scalar sum of the lepton transverse momenta are used to distinguish the signal from background. The observed results are consistent with the expectations from the standard model hypothesis. The existence of a vectorlike lepton doublet, coupling to the third-generation standard model leptons in the mass range of 120–790 GeV, is excluded at 95% confidence level. These are the most stringent limits yet on the production of a vectorlike lepton doublet, coupling to the third-generation standard model leptons.

Received 26 May 2019

DOI:https://doi.org/10.1103/PhysRevD.100.052003

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.

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Hypothetical fermions

Hadron colliders

Particles & Fields

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Vol. 100, Iss. 5 — 1 September 2019

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Figure 1
Two illustrative leading-order Feynman diagrams for associated production of $τ^{'}$ with a $ν_{τ}^{'}$ (left) and for pair production of $τ^{'}$ (right) and possible subsequent decay chains that result in a multilepton final state.
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Figure 2
The upper row shows the $m_{T}$ (left) and the $L_{T}$ (right) distributions in the $W Z$ control region in data and simulation. The $W Z$ control region contains events with three leptons and an OSSF pair with mass on- $Z$ , and $50 < p_{T}^{miss} < 100 GeV$ . The lower row shows the $m_{4 ℓ}$ (left) and the $L_{T}$ (right) distributions in the $Z Z$ control region. The $Z Z$ control region contains events with two OSSF lepton pairs, both of which are on- $Z$ , and $p_{T}^{miss} < 50 GeV$ . The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events.
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Figure 3
The dilepton mass (left) and the $L_{T}$ (right) distributions in data and simulation in a misidentified $τ_{h}$ control region. This control region contains 2L1T (OS) events with $p_{T}^{miss} < 50 GeV$ . The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events.
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Figure 4
The $L_{T}$ distributions for the 3L signal regions with $p_{T}^{miss} < 150 GeV$ (upper left) and $p_{T}^{miss} > 150 GeV$ (upper right) and for the 4L signal regions with $p_{T}^{miss} < 50 GeV$ (lower left) and $p_{T}^{miss} > 50 GeV$ (lower right). The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (the sum of all production and decay modes) with $m_{τ^{'} / ν^{'}} = 200$ and 500 GeV are shown as dashed lines. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events.
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Figure 5
The $L_{T}$ distributions for the 2L1T OS signal regions with $p_{T}^{miss} < 150 GeV$ (upper left) and $p_{T}^{miss} > 150 GeV$ (upper right) and for the 2L1T SS signal regions with $p_{T}^{miss} < 150 GeV$ (lower left) and $p_{T}^{miss} > 150 GeV$ (lower right). The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (sum of all production and decay modes) with $m_{τ^{'} / ν^{'}} = 200$ and 500 GeV are also shown as dashed lines. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events.
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Figure 6
The 95% confidence level upper limits on the total cross section for associated ( $τ^{' \pm} ν_{τ}^{'}$ ) and pair ( $τ^{' +} τ^{' -} / ν_{τ}^{'} {\bar{ν}}_{τ}^{'}$ ) production of VLLs. Also shown is the theoretical prediction for the production cross section of a vectorlike lepton doublet coupling to the third-generation SM leptons. The observed (expected) exclusion limit on the masses of VLLs is in the range of 120–790 (120–680) GeV.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for vectorlike leptons in multilepton final states in proton-proton collisions at $\sqrt{s} = 13 TeV$

A. M. Sirunyan et al. (CMS Collaboration)

Phys. Rev. D 100, 052003 – Published 6 September 2019

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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for vectorlike leptons in multilepton final states in proton-proton collisions at s=13 TeV

A. M. Sirunyan et al. (CMS Collaboration)

Phys. Rev. D 100, 052003 – Published 6 September 2019

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Search for vectorlike leptons in multilepton final states in proton-proton collisions at $\sqrt{s} = 13 TeV$