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| CMS-PAS-B2G-19-005 | ||
| A search for bottom-type, vector-like quark pair production in a fully hadronic mode in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| July 2020 | ||
| Abstract: A search is described for the production of a pair of bottom-type vector-like quarks (VLQs), each decaying into a b quark and either a Higgs or a Z boson. The analysis is based on data from proton-proton collisions at a 13 TeV center-of-mass energy recorded by the CMS experiment, corresponding to a total integrated luminosity of 137 fb$^{-1}$. Since the predominant decay modes of the Higgs and Z bosons are to a pair of quarks, the analysis focuses on final states consisting of jets resulting from the six quarks produced in the events. Because the two jets produced in the decay of a highly boosted Higgs or Z boson might merge to form a single jet, three independent analyses are performed, categorized by the number of observed jets. No signal in excess of the expected background is observed. Lower limits are set on the VLQ mass at the 95% confidence level, at 1570 GeV in the case where the VLQ decays exclusively to a b quark and a Higgs boson, 1390 GeV for when it decays exclusively to a b quark and a Z boson, and 1450 GeV for when it decays equally in these two modes. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRD 102 (2020) 112004. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Diagrams of the pair production of bottom-type VLQ quarks (B) that subsequently decay to a $\mathrm{b}$ or $\mathrm{\bar{b}}$ quark and either a Higgs or Z boson. In events targeted by this analysis, the Z boson then decays to a pair of quarks, where q denotes any quark other than a t quark, while the Higgs predominantly decays to b quarks. Upper left: bHbH mode, upper right: bHbZ mode, lower: bZbZ mode. |
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Figure 2:
Reconstructed VLQ mass distributions for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. Mass distributions for 4-jet (left), 5-jet (center), and 6-jet (right) events are shown for the three decay modes: bHbH (upper row), bHbZ (middle row), and bZbZ (lower row). |
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Figure 2-a:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 4-jet events is shown for the bHbH decay mode. |
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Figure 2-b:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 5-jet events is shown for the bHbH decay mode. |
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Figure 2-c:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 6-jet events is shown for the bHbH decay mode. |
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Figure 2-d:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 4-jet events is shown for the bHbZ decay mode. |
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Figure 2-e:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 5-jet events is shown for the bHbZ decay mode. |
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Figure 2-f:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 6-jet events is shown for the bHbZ decay mode. |
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Figure 2-g:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 4-jet events is shown for the bZbZ decay mode. |
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Figure 2-h:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 5-jet events is shown for the bZbZ decay mode. |
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Figure 2-i:
Reconstructed VLQ mass distribution for simulated signal events with a generated VLQ mass $m_{\mathrm{B}} = $ 1200 GeV. A moderate requirement of $ {\chi ^2_\text {mod}/\text {ndf}} < $ 2 is applied to the events. The mass distribution for 6-jet events is shown for the bZbZ decay mode. |
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Figure 3:
Distribution of ${\chi ^2_\text {mod}}$ for the best jet combination for simulated 1200 GeV VLQ events (red histogram) and data (black points), for 4-jet events (left), 5-jet events (center), and 6-jet events (right). The simulated signal events and data events are normalized to the same value within the displayed ${\chi ^2_\text {mod}}$ range. |
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Figure 3-a:
Distribution of ${\chi ^2_\text {mod}}$ for the best jet combination for simulated 1200 GeV VLQ events (red histogram) and data (black points), for 4-jet events. The simulated signal events and data events are normalized to the same value within the displayed ${\chi ^2_\text {mod}}$ range. |
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Figure 3-b:
Distribution of ${\chi ^2_\text {mod}}$ for the best jet combination for simulated 1200 GeV VLQ events (red histogram) and data (black points), for 5-jet events. The simulated signal events and data events are normalized to the same value within the displayed ${\chi ^2_\text {mod}}$ range. |
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Figure 3-c:
Distribution of ${\chi ^2_\text {mod}}$ for the best jet combination for simulated 1200 GeV VLQ events (red histogram) and data (black points), for 6-jet events. The simulated signal events and data events are normalized to the same value within the displayed ${\chi ^2_\text {mod}}$ range. |
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Figure 4:
Distributions of the average reconstructed mass of VLQ candidates for the jet combination with the least $\chi ^2$ in 4-jet (left), 5-jet (center), and 6-jet (right) multiplicity events. The red lines show the exponential fit in the range 1000-2000 GeV. The lower panels show the fractional difference, (data-fit)/fit. |
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Figure 4-a:
Distributions of the average reconstructed mass of VLQ candidates for the jet combination with the least $\chi ^2$ in 4-jet multiplicity events. The red lines show the exponential fit in the range 1000-2000 GeV. The lower panels show the fractional difference, (data-fit)/fit. |
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Figure 4-b:
Distributions of the average reconstructed mass of VLQ candidates for the jet combination with the least $\chi ^2$ in 5-jet multiplicity events. The red lines show the exponential fit in the range 1000-2000 GeV. The lower panels show the fractional difference, (data-fit)/fit. |
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Figure 4-c:
Distributions of the average reconstructed mass of VLQ candidates for the jet combination with the least $\chi ^2$ in 6-jet multiplicity events. The red lines show the exponential fit in the range 1000-2000 GeV. The lower panels show the fractional difference, (data-fit)/fit. |
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Figure 5:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 4-jet (left column), 5-jet (center column), and 6-jet (right column) multiplicities, and for the bHbH (upper row), bHbZ (middle row), and bZbZ (lower row) event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-a:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 4-jet multiplicities, and for the bHbH event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-b:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 5-jet multiplicities, and for the bHbH event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-c:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 6-jet multiplicities, and for the bHbH event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-d:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 4-jet multiplicities, and for the bHbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-e:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 5-jet multiplicities, and for the bHbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-f:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 6-jet multiplicities, and for the bHbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-g:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 4-jet multiplicities, and for the bZbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-h:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 5-jet multiplicities, and for the bZbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 5-i:
Dependence of the BJTF on the average reconstructed VLQ mass in the control region 12 $ < {\chi ^2_\text {mod}/\text {ndf}} < $ 48, for 6-jet multiplicities, and for the bZbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 4-jet (left column), 5-jet (center column), and 6-jet (right column) multiplicities, and for the bHbH (upper row), bHbZ (middle row), and bZbZ (lower row) event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-a:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 4-jet ultiplicities, and for the bHbH event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-b:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 5-jet multiplicities, and for the bHbH event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-c:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 6-jet multiplicities, and for the bHbH event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-d:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 4-jet multiplicities, and for the bHbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-e:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 5-jet multiplicities, and for the bHbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-f:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 6-jet multiplicities, and for the bHbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-g:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 4-jet multiplicities, and for the bZbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-h:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 5-jet multiplicities, and for the bZbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 6-i:
Dependence of the BJTF on ${\chi ^2_\text {mod}/\text {ndf}}$ in the low-mass VLQ region, for 6-jet multiplicities, and for the bZbZ event modes. The data is shown in black points, and the linear fit and its uncertainty are shown as the red line and the pale red band. |
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Figure 7:
The reduction factor in data events, for 4-jet (left column), 5-jet (center column), and 6-jet (right column) multiplicities, and for the bHbH (upper row), bHbZ (middle row), and bZbZ (lower row) event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-a:
The reduction factor in data events, for 4-jet multiplicities, and for the bHbH event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-b:
The reduction factor in data events, for 5-jet multiplicities, and for the bHbH event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-c:
The reduction factor in data events, for 6-jet multiplicities, and for the bHbH event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-d:
The reduction factor in data events, for 4-jet multiplicities, and for the bHbZ event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-e:
The reduction factor in data events, for 5-jet multiplicities, and for the bHbZ event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-f:
The reduction factor in data events, for 6-jet multiplicities, and for the bHbZ event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-g:
The reduction factor in data events, for 4-jet multiplicities, and for the bZbZ event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-h:
The reduction factor in data events, for 5-jet multiplicities, and for the bZbZ event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 7-i:
The reduction factor in data events, for 6-jet multiplicities, and for the bZbZ event modes. The red box indicates the signal region, which is excluded from these plots. |
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Figure 8:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 4-jet (left column), 5-jet (center column), and 6-jet (right column) multiplicities, and for the bHbH (upper row), bHbZ (middle row), and bZbZ (lower row) event modes. The red box indicates the signal region. |
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Figure 8-a:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 4-jet multiplicities, and for the bHbH event modes. The red box indicates the signal region. |
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Figure 8-b:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 5-jet multiplicities, and for the bHbH event modes. The red box indicates the signal region. |
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Figure 8-c:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 6-jet multiplicities, and for the bHbH event modes. The red box indicates the signal region. |
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Figure 8-d:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 4-jet multiplicities, and for the bHbZ event modes. The red box indicates the signal region. |
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Figure 8-e:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 5-jet multiplicities, and for the bHbZ event modes. The red box indicates the signal region. |
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Figure 8-f:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 6-jet multiplicities, and for the bHbZ event modes. The red box indicates the signal region. |
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Figure 8-g:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 4-jet multiplicities, and for the bZbZ event modes. The red box indicates the signal region. |
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Figure 8-h:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 5-jet multiplicities, and for the bZbZ event modes. The red box indicates the signal region. |
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Figure 8-i:
The reduction factor in simulated VLQ signal events with $m_{\mathrm{B}} = $ 1200 GeV, for 6-jet multiplicities, and for the bZbZ event modes. The red box indicates the signal region. |
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Figure 9:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines). Left column: 4-jet events, center column: 5-jet events, right column: 6-jet events; upper row: bHbH, middle row: bHbZ, lower row: bZbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-a:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 4-jet events; bHbH. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-b:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 5-jet events; bHbH. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-c:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 6-jet events; bHbH. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-d:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 4-jet events; bHbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-e:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 5-jet events; bHbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-f:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 6-jet events; bHbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-g:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 4-jet events; bZbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-h:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 5-jet events; bZbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 9-i:
Data (black points), expected background (solid blue histogram), and expected background plus a VLQ signal for different VLQ masses (colored lines); 6-jet events; bZbZ. For the signal, a 100% ${\mathrm{B} \to \mathrm{b} \mathrm{H}}$ branching fraction is assumed. The hatched regions for the background and background plus signal distributions indicate the systematic uncertainties. All three data-taking years are combined. |
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Figure 10:
Expected limits on the VLQ mass at 95% CL as a function of the branching fractions $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{H}})$ and $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{Z}} $). |
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Figure 11:
Observed limits on the VLQ mass at 95% CL as a function of the branching fractions $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{H}})$ and $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{Z}} $). |
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Figure 12-a:
The 95% confidence limit on the cross section for VLQ pair production as a function of VLQ mass for the $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{H}}) = $ 100% branching fraction hypothesis. The solid black line indicates the observed limit and the dashed line indicates the expected limit with 1 sigma (green band) and 2 sigma (yellow band) uncertainties. The theoretical cross section and its uncertainty are shown as the red line and pale red band. |
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Figure 12-b:
The 95% confidence limit on the cross section for VLQ pair production as a function of VLQ mass for the $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{Z}}) = $ 100% branching fraction hypothesis. The solid black line indicates the observed limit and the dashed line indicates the expected limit with 1 sigma (green band) and 2 sigma (yellow band) uncertainties. The theoretical cross section and its uncertainty are shown as the red line and pale red band. |
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Figure 12-c:
The 95% confidence limit on the cross section for VLQ pair production as a function of VLQ mass for the $\mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{H}}) = \mathcal {B}({\mathrm{B} \to \mathrm{b} \mathrm{Z}}) = $ 50% branching fraction hypothesis. The solid black line indicates the observed limit and the dashed line indicates the expected limit with 1 sigma (green band) and 2 sigma (yellow band) uncertainties. The theoretical cross section and its uncertainty are shown as the red line and pale red band. |
| Tables | |
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Table 1:
Measured values of the trigger efficiencies for events with $ {H_{\mathrm {T}}} > $ 1350 GeV. The uncertainties are statistical only. |
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Table 2:
Efficiency of the offline ${H_{\mathrm {T}}}$ selection for each of the jet multiplicity channels, for three VLQ masses (1000, 1200, and 1400 GeV). The efficiency is the fraction of events in each jet multiplicity category meeting the $ {H_{\mathrm {T}}} > $ 1350 GeV cut. |
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Table 3:
Values of the BJTF for data events with VLQ mass candidates in the range of 500 to 800 GeV for each of the three event modes and three jet multiplicities. |
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Table 4:
Systematic uncertainties common to all three event modes and all three jet multiplicities. |
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Table 5:
Systematic uncertainties for each event mode and jet multiplicity. The reported values indicate the uncertainty in the event yield in a $\pm $75 GeV window about the signal peak for a generated signal mass $m_{\mathrm{B}} = $ 1600 GeV. |
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Table 6:
Optimized values of the ${\chi ^2_\text {mod}/\text {ndf}}$ selection as a function of jet multiplicity and event mode. |
| Summary |
| This note describes a search for bottom-type, vector-like quark (VLQ) pair production based on data collected by the CMS detector in 2016--2018 at $\sqrt{s} = $ 13 TeV, where the VLQ B decays into a b quark and either a Higgs boson H or a Z boson. The analysis targets the fully hadronic $\mathrm{ B \to b H}$ and $\mathrm{ B \to b Z}$ decays by tagging each jet and using a modified $\chi^2$ metric to reconstruct the event. Different jet multiplicity categories were used to account for the fact that Higgs or Z boson decays can produce either two distinct jets or, if boosted, a single merged jet. Backgrounds were estimated using data from a low VLQ mass region and extrapolated into the signal region using a modified $\chi^2$ control region. Limits were set on the VLQ mass at 95% confidence level as a function of the branching fractions for $\mathrm{ B \to b H}$ and $\mathrm{ B \to b Z}$. Previous limits [15,16] on the B mass have been increased from 1010 GeV to 1570 GeV in the 100% $\mathrm{ B \to b H}$ case, from 1070 GeV to 1390 GeV in the 100% $\mathrm{ B \to b Z}$ case, and from 1025 GeV to 1450 GeV in the 50% $\mathrm{ B \to b H}$ and 50% $\mathrm{ B \to b Z}$ case. |
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