Responsible: ChristianContreras

Search for Vector-Like b′ Pair Production with Multilepton Final States in pp collisions at $\sqrt{s}$ = 8 TeV (B2G-13-003)

Further information

This analysis is documented in CMS-PAS-B2G-13-003. The Table and Figure numbers in the Material in PAS section correspond to the table and figure numbers in the PAS.

Abstract

A search for pair-production of vector-like partners of the b quark, b', is carried out in events with at least three leptons using 19.5fb$^{-1}$ of of integrated luminosity in pp collisions at $\sqrt{s}$ =8 TeV collected by the CMS experiment at the LHC. The data are binned in multiple exclusive channels according to the amount of expected standard model background in order to increase the search sensitivity. The observations are consistent with the standard model expectations. The search is interpreted for different b' masses and for varying branching ratios to the bZ, tW, and bH states. We exclude b' quarks with masses less than values in the range of 520$-$785 GeV (depending on the values of the branching ratios) at the 95% confidence level.

Approved tables and plots (click on plot to get larger version)

Material in PAS

Figures

Figure	Caption
	Figure 1: Background breakdown vs $S_\text{T}$ require 4 Leptons, OSSF2, on-Z, Tau0, 1 b-jet. For b$^\prime$b$^\prime$ $\rightarrow \textrm{bZ}\textrm{bZ}$ as the signal with b$^\prime$ having a mass of 750 GeV.
	Figure 2: Background breakdown vs $S_\text{T}$ require 4 Leptons, OSSF2, on-Z, Tau0, 1 b-jet. For b$^\prime$b$^\prime$ $\rightarrow \textrm{tW}\textrm{tW}$ as the signal with b$^\prime$ having a mass of 750 GeV.
	Figure 3: Background breakdown vs $S_\text{T}$ require 3 Leptons, OSSF1, above-Z, Tau0, 1 b-jet. For b$^\prime$b$^\prime$ $\rightarrow \textrm{bZ}\textrm{bZ}$ as the signal with b$^\prime$ having a mass of 750 GeV.
	Figure 4: Background breakdown vs $S_\text{T}$ require 3 Leptons, OSSF1, above-Z, Tau0, 1 b-jet. For b$^\prime$b$^\prime$ $\rightarrow \textrm{tW}\textrm{tW}$ as the signal with b$^\prime$ having a mass of 750 GeV.
	Figure 5: Cross section times branching ratio exclusion curves for a b$^\prime$ as a function of its mass for the decay modes b$^\prime$b$^\prime$ $\rightarrow \textrm{bZ}\textrm{bZ}$. The figure show expected (dashed), observed (solid) exclusions; sigma bands correspond to the experimental uncertainties.
	Figure 6: Cross section times branching ratio exclusion curves for a b$^\prime$ as a function of its mass for the decay modes b$^\prime$b$^\prime$ $\rightarrow \textrm{tW}\textrm{tW}$. The figure show expected (dashed), observed (solid) exclusions; sigma bands correspond to the experimental uncertainties.
	Figure 7: Cross section times branching ratio exclusion curves for a b$^\prime$ as a function of its mass for the decay modes b$^\prime$b$^\prime$ $\rightarrow \textrm{bH}\textrm{bH}$. The figure show expected (dashed), observed (solid) exclusions; sigma bands correspond to the experimental uncertainties.
	Figure 8: Exclusion limits for pair-produced b$^\prime$ quarks going to multileptons in the two-dimensional plane of branching ratio of b$^\prime$ to $\textrm{bZ}$ vs. b$^\prime$ mass. Signal points to the left of the curve are excluded. The y = 0 axis corresponds to b$^\prime$b$^\prime$ $\rightarrow \textrm{tW}\textrm{tW}$ and the $y = 1$ axis to b$^\prime$b$^\prime$ $\rightarrow \textrm{bZ}\textrm{bZ}$. The branching ratio for b$^\prime$ $\rightarrow \textrm{bH}$ is set to zero. We apply a conservative 10% theory uncertainty.
	Figure 9: Observed and expected 95% confidence level upper limits for the b$^\prime$ quark production cross section for branching ratio into into $\textrm{tW}$, $\textrm{bH}$, and $\textrm{bZ}$ of 50%, 25%, and 25%, respectively.
	Figure 10: Expected exclusion curves as a function of branching ratios. The $\mathcal{B}(\textrm{b'}\rightarrow \textrm{bZ})$ is plotted as a function of the b$^\prime$ mass and the various curves represent fixed $\mathcal{B}(\textrm{b'}\rightarrow \textrm{bH})$ from 0.0 (the rightmost) to 1.0 ( the leftmost)
	Figure 11: Observed exclusion curves as a function of branching ratios. The $\mathcal{B}(\textrm{b'}\rightarrow \textrm{bZ})$ is plotted as a function of the b$^\prime$ mass and the various curves represent fixed $\mathcal{B}(\textrm{b'}\rightarrow \textrm{bH})$ from 0.0 (the rightmost) to 1.0 ( the leftmost)
	Figure 12: Expected limit results with varied branching ratio of $\textrm{tW}$, $\textrm{bH}$, and $\textrm{bZ}$ in steps of 0.1.
	Figure 13: Observed limit results with varied branching ratio of $\textrm{tW}$, $\textrm{bH}$, and $\textrm{bZ}$ in steps of 0.1.

Tables

Table	Caption
	Table 1: The systematic uncertainties associated with this analysis.
	Table 2: Observed yields for four lepton events from 19.5fb$^{-1}$ recorded in 2012. The channels are broken down by the number of and mass of any opposite-sign same-flavor pairs (whether on or off Z), whether the leptons include taus, whether there are any b jets present and the $S_{\rm T}$. Expected yields are the sum of simulation and data-driven estimates of backgrounds in each channel. The channels are exclusive. Channels marked with an asterisk are used as control regions and are excluded from the limit calculations. Also, those channels with a dagger mark are used in the limit setting procedure and are representative of the top most sensitive channels for the $\textrm{b}^\prime$ decay with mass of 500 GeV where $\mathcal{B}(\textrm{b'}\rightarrow \textrm{bH})=1.0$.
	Table 3: Observed yields for three lepton events. The channels are broken down by the number of and mass of any opposite-sign, same-flavor pairs (whether on or off $\textrm{Z}$), whether the leptons include taus, whether there are any b jets present and the $S_{\rm T}$. Expected yields are the sum of simulation and data-driven estimates of backgrounds in each channel. The channels are exclusive. Channels marked with an asterisk are used as control regions and are excluded from the limit calculations. Also, those channels marked with a dagger are a representative subset of the top most sensitive channels for the $\textrm{b}^\prime$ decay, with a mass of 500 GeV and $\mathcal{B}(\textrm{b'}\rightarrow \textrm{bH})=1.0$, which are used in the limit setting procedure.
	Table 4: Sets of branching ratio values and the observed and expected 95% CL upper limits for the combined electron and muon channels.

Additional Material for B2G-13-003

Figure	Caption
	Figure 1: Background breakdown vs $S_\text{T}$ require 3 Leptons, OSSF1, below-Z, Tau0, 1 b-jet. For b$^\prime$b$^\prime$ $\rightarrow \textrm{bHbH}$ as the signal with b$^\prime$ having a mass of 750 GeV.
	Figure 2: Background breakdown vs $S_\text{T}$ require 4 Leptons, OSSF1, on-Z, Tau1, no b-jet. For b$^\prime$b$^\prime$ $\rightarrow \textrm{bHbH}$ as the signal with b$^\prime$ having a mass of 750 GeV.
	Figure 3: The isolation distribution of muons with large impact parameter ($\textrm{d$_{xy}$} > 0.02$ cm, primarily from jets) in a data sample enriched in $\textrm{t}\bar{\textrm{t}}$ $\rightarrow l\nu \textrm{bbjj}$.
	Figure 4: The isolation distribution of electrons with large impact parameter ($\textrm{d$_{xy}$} > 0.02$ cm, primarily from jets) in a data sample enriched in $\textrm{t}\bar{\textrm{t}}$ $\rightarrow l\nu \textrm{bbjj}$.

Additional Material from SUS-13-002 and SUS-13-003 (Links to Public Results)

Figure	Caption
	Figure 1: The $S_\text{T}$ distribution in an opposite sign e$\textrm{$\mu$}$ $\textrm{t}\bar{\textrm{t}}$ control region. The uncertainties in the ratio plot below include both statistical and systematic uncertainties.
	Figure 2: Distribution for H$_{\text{T}}$ in the opposite sign e$\textrm{$\mu$}$ dilepton $\textrm{t}\bar{\textrm{t}}$ control region.
	Figure 3: Distributions for E$^{miss}_{\text{T}}$ in the opposite sign e$\textrm{$\mu$}$ dilepton $\textrm{t}\bar{\textrm{t}}$ control region.
	Figure 4: The transverse mass M$_\text{T}$ distribution of events in a data sample enriched in $\textrm{WZ}$ requiring an OSSF pair with $m(\ell\ell)$ in the Z-window and 50 GeV < E$^{miss}_{\text{T}}$ < 100 GeV.
	Figure 5: Distributions for E$^{miss}_{\text{T}}$ in the WZ control region.
	Figure 6: 4-lepton mass distribution for low-E$^{miss}_{\text{T}}$, low-H$_{\text{T}}$ ZZ control region.
	Figure 7: 3-muon invariant mass showing asymmetric internal photon conversion.
	Figure 8: Efficiency ratio vs Rd$_{\textrm{xy}}$ ("b-ness of events") for muons and electrons.
	Figure 9: f$_\textrm{t}$-f$_\textrm{sb}$ for taus with p$_{\textrm{T}}$ between 40 and 60 GeV (f$_\textrm{t}$ is the fake-rate for taus and f$_\textrm{sb}$ is inversely proportional to jet activity).
	Figure 10: f$_\textrm{t}$-f$_\textrm{sb}$ for taus with p$_{\textrm{T}}$ between 20 and 40 GeV (f$_\textrm{t}$ is the fake-rate for taus and f$_\textrm{sb}$ is inversely proportional to jet activity).