CMS-PAS-B2G-20-005

CMS-PAS-B2G-20-005
Search for a W' boson decaying to a top and a bottom quark at $\sqrt{s}= $ 13 TeV
CMS Collaboration
December 2020

Abstract: A search is performed for a W' boson decaying to a top and a bottom quark in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data have been collected by the CMS Collaboration between 2016 and 2018 and correspond to an integrated luminosity of 137 fb$^{-1}$. Deep neural network algorithms are used to identify the jets initiated by the b quark and also the jets containing the decay products of the top quark when the W boson from the top quark decays hadronically. No excess above the estimated standard model background is observed and upper limits on the production cross section of W' bosons are set. Both left- and right-handed W' bosons with masses below 3.4 TeV are excluded at 95% confidence level. These results are the best limits to date on W' bosons decaying to a top and a bottom quark in the all-handronic final state.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in SR (left) and VR (right) for the data-taking period of 2016. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 1-a: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in SR for the data-taking period of 2016. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 1-b: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in VR for the data-taking period of 2016. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 2: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in SR (left) and VR (right) for the data-taking period of 2017. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 2-a: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in SR for the data-taking period of 2017. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 2-b: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in VR for the data-taking period of 2017. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 3: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in SR (left) and VR (right) for the data-taking period of 2018. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 3-a: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in SR for the data-taking period of 2018. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 3-b: The reconstructed ${m_{\mathrm{t} \mathrm{b}}}$ distributions in data (black dots), and backgrounds in VR for the data-taking period of 2018. The yield in each bin is divided by the corresponding bin width. Distributions expected from right-handed W' bosons of mass 2 and 3 TeV and a left-handed W' boson of mass 2 TeV are shown normalized to the integrated luminosity of the data using a cross section of 1 pb. The total uncertainty in the estimated background, including both statistical and systematic components, is shown in the bottom panel.
png pdf	Figure 4: Upper limits at 95% CL on the cross section for the production of W'$_{\mathrm{R}}$ boson (top) and W'$_{\mathrm{L}}$ boson with SM interference (bottom) using data and backgrounds in three years combined. The observed (expected) limits are shown with the black solid (dashed) line. The uncertainty in the expected limit bands represent the 68% and 95% confidence intervals. The theory prediction and its uncertainty due to scale and PDF are shown with the red curve and red band, respectively.
png pdf	Figure 4-a: Upper limits at 95% CL on the cross section for the production of a W'$_{\mathrm{R}}$ boson using data and backgrounds in three years combined. The observed (expected) limits are shown with the black solid (dashed) line. The uncertainty in the expected limit bands represent the 68% and 95% confidence intervals. The theory prediction and its uncertainty due to scale and PDF are shown with the red curve and red band, respectively.
png pdf	Figure 4-b: Upper limits at 95% CL on the cross section for the production of a W'$_{\mathrm{L}}$ boson with SM interference using data and backgrounds in three years combined. The observed (expected) limits are shown with the black solid (dashed) line. The uncertainty in the expected limit bands represent the 68% and 95% confidence intervals. The theory prediction and its uncertainty due to scale and PDF are shown with the red curve and red band, respectively.

Tables
png pdf	Table 1: Regions of phase space used in the analysis. SR is the region where one expects the maximum signal sensitivity. VR is used for the validation of the technique used for the estimation of multijet background, and differs in the top quark tagging condition with respect to SR. SR' and VR' differ in the b tagging condition compared with SR and VR respectively. The control regions CR1 and CR1' (CR2 and CR2') are used to derive the b tagging pass-to-fail ratio to be applied to estimate the multijet background in SR (VR).
png pdf	Table 2: The assumed correlation of systematic uncertainties between different years of data taking. The impact of the systematic uncertainties for a 2 TeV right-handed W' boson signal for the data-taking condition in 2017 is mentioned in the right-most column.

Summary

A search is performed for heavy W' bosons decaying to a top and a b quark in the hadronic final state using data corresponding to an integrated luminosity of 137 fb$^{-1}$ collected by the CMS Collaboration during the data-taking period from 2016 to 2018. The analysis utilized top quark tagging and b quark tagging algorithms based on deep neural networks. Upper limits on the production cross section of W' boson are obtained at 95% confidence level (CL) for W' boson masses in the range 1-4 TeV. Both left- and right-handed W' bosons of mass below 3.4 TeV are excluded at 95% CL. These limits provided on W' bosons decaying to a top and a bottom quark are the most stringent published to date in the case of all-handronic final state.

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