CMS-PAS-B2G-16-025

CMS-PAS-B2G-16-025
Search for pair production of excited top quarks in the lepton+jets final state
CMS Collaboration
July 2017

Abstract: A search is performed for pair production of spin-3/2 excited top quarks, each decaying to a top quark and a gluon. The search uses the data collected with the CMS detector from pp collisions at a center-of-mass energy of $\sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 36 fb$^{-1}$. The selected events require the presence of an isolated muon or electron, an imbalance in the transverse momentum, and at least six jets, out of which exactly two must be compatible with originating from the fragmentation of a b quark. The analysis shows no significant excess over the standard model predictions, and provides a lower limit of 1.2 TeV at 95% confidence level on the mass of the spin-3/2 excited top quark in an extension of the Randall-Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 778 (2018) 349. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Kinematic distributions of events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mu $($\mathrm{ e } $)+jet final state are shown on the left (right). From top to bottom, the kinematic variable displayed are the lepton ${p_{\mathrm {T}}}$ spectra, the jet ${p_{\mathrm {T}}}$ spectra and the $m_{ {{\mathrm{ t } }+\text {jet}}}$ spectra. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 1-a: Lepton ${p_{\mathrm {T}}}$ spectrum for events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mu $+jet final state are shown. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 1-b: Lepton ${p_{\mathrm {T}}}$ spectrum for events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mathrm{ e } $+jet final state are shown. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 1-c: Jet ${p_{\mathrm {T}}}$ spectrum for events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mu $+jet final state are shown. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 1-d: Jet ${p_{\mathrm {T}}}$ spectrum for events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mathrm{ e } $+jet final state are shown. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 1-e: $m_{ {{\mathrm{ t } }+\text {jet}}}$ spectrum for events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mu $+jet final state are shown. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 1-f: $m_{ {{\mathrm{ t } }+\text {jet}}}$ spectrum for events selected with a single lepton, $\geq $ 6 jets with exactly two b tagged jets in data (points), simulated background processes (stacked histograms), and simulated 800 GeV signal process (dashed line). Events selected in the $\mathrm{ e } $+jet final state are shown. The shaded region is the total uncertainty of the simulated background processes, which includes statistical and systematic uncertainties.
png pdf	Figure 2: The $m_{ {{\mathrm{ t } }+\text {jet}}}$ spectrum for data (points), the signal+background fit (green), the background component of the signal+background fit (blue), and the expected spectrum for 800 GeV signal process (red dashed) normalized to the integrated luminosity of data. The plot on the left (right) shows the distributions for the $ \mu $+jets (e+jets) data. The probability of the Kolmogorov-Smirnov test between the data versus the signal+background model, and data versus the background component is notated $K_\text {all}$ and $K_\text {bkg}$ respectively.
png pdf	Figure 2-a: The $m_{ {{\mathrm{ t } }+\text {jet}}}$ spectrum for data (points), the signal+background fit (green), the background component of the signal+background fit (blue), and the expected spectrum for 800 GeV signal process (red dashed) normalized to the integrated luminosity of data. The plot on the left (right) shows the distributions for the $ \mu $+jets (e+jets) data. The probability of the Kolmogorov-Smirnov test between the data versus the signal+background model, and data versus the background component is notated $K_\text {all}$ and $K_\text {bkg}$ respectively.
png pdf	Figure 2-b: The $m_{ {{\mathrm{ t } }+\text {jet}}}$ spectrum for data (points), the signal+background fit (green), the background component of the signal+background fit (blue), and the expected spectrum for 800 GeV signal process (red dashed) normalized to the integrated luminosity of data. The plot on the left (right) shows the distributions for the $ \mu $+jets (e+jets) data. The probability of the Kolmogorov-Smirnov test between the data versus the signal+background model, and data versus the background component is notated $K_\text {all}$ and $K_\text {bkg}$ respectively.
png pdf	Figure 3: The expected (red dotted, and green-yellow double band region) and observed (black, solid) upper limit for the production cross section of ${{\mathrm{ t } ^{}}} {{\mathrm{ \bar{t} } {}^{}}}$ versus ${{\mathrm{ t } ^{*}}}$ mass at 95% confidence level is presented for the combined lepton+jets analysis. The theoretical production cross section (blue hashed) is shown along with the uncertainties (blue hashed) on the signal acceptance as described in Section 7.

Summary

A search for spin-3/2 $ \mathrm{ t^{*} \bar{t}^{*} } $ production in pp interactions, with each $ \mathrm{ t^{*}} $ decaying exclusively to a standard model t quark and a gluon, has been conducted. Events that have a single muon or electron and at least six jets, exactly two of which must be identified as originating from a b quark, are selected for the analysis. Assuming $ \mathrm{ t^{*} \bar{t}^{*} } $ production, an attempt is made to reconstruct the final state objects to a $ \mathrm{ t^{*}} $ candidate in each event. The observed mass spectrum of the t+jet system shows no significant deviation from standard model predictions, and is used to set an upper limit on the production of $ \mathrm{ t^{*} \bar{t}^{*} } $ as a function of $ \mathrm{ t^{*}} $ mass. By comparing the results with the expectations for a spin-3/2 excited top quark model, $ \mathrm{ t^{*}} $ masses below 1.2 TeV at 95% confidence level are excluded.

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