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| CMS-PAS-HIG-20-018 | ||
| A search for light Higgs bosons from supersymmetric cascade decays in proton-proton collisions at 13 TeV | ||
| CMS Collaboration | ||
| September 2021 | ||
| Abstract: A search for pairs of boosted light Higgs bosons ($\mathrm{H}_1$) produced in supersymmetric cascade decays is performed in final states with small missing transverse momentum. The complete LHC Run II proton-proton collision data set is used, recorded with the CMS detector at a centre-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 137 fb$^{-1}$. The search targets events where both $\mathrm{H}_1$ bosons decay into $\mathrm{b}\bar{\mathrm{b}}$ pairs that are reconstructed as large-radius jets using substructure techniques. No evidence is found for any excess of events beyond the background expectations of the standard model (SM). Results from the search are interpreted in the next-to-minimal supersymmetric extension of the SM, where a low-mass singlino leads to multi-step squark and gluino decays that can predominantly end with a boosted singlet-like $\mathrm{H}_1$ boson and a low-momentum singlino-like neutralino. Upper limits are set on the product of the squark or gluino pair-production cross section and the $\mathrm{b}\bar{\mathrm{b}}$ branching ratio of the $\mathrm{H}_1$ for a benchmark model with almost mass-degenerate light flavour squarks and gluinos. Under the assumption of an SM-like $\mathrm{H}_1\to\mathrm{b}\bar{\mathrm{b}}$ branching ratio, $\mathrm{H}_1$ bosons with masses in the range 40-120 GeV, arising from the decays of squarks or gluinos with a mass from 1200-2500 GeV, are excluded at the 95% confidence level. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to EPJC. |
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| Figures | |
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Figure 1:
Diagram of squark pair production and subsequent cascade decay in the benchmark signal model. The particle $\tilde{\chi}^{0}_{2}$ is the NLSP, ${\tilde{\chi} _{\text {S}}^0}$ is the singlino-like LSP, and ${\mathrm{H} _1}$ is the CP-even singlet-like Higgs boson. |
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Figure 2:
The normalised ${H_{\mathrm {T}}}$ distribution in signal events with different values of ${M_{\text {SUSY}}}$, and for the simulated SM background processes, as labelled in the legend. The numbers specified in the legend have unit GeV. All events satisfy the pre-selection and have $ {H_{\mathrm {T}}} \ge $ 1200 GeV. |
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Figure 3:
The normalised distributions of simulated signal and multijet events in the 2D double-b-tag discriminator plane, where the event densities in each bin are represented by the areas of red and blue squares, respectively. The signal parameters are $ {M_{\mathrm{H} _1}} = $ 70 GeV and $ {M_{\text {SUSY}}} = $ 2000 GeV. The kinematic event selection is applied, and the masses of the two AK8 jets are required to be within the set of signal and sideband mass regions defined in Figure 4. The green, brown, and grey shaded areas represent the tag region (TR), control region (CR), and validation region (VR), respectively. |
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Figure 4:
The mass regions used in the 2D soft-drop mass plane. The regions labelled $S_i$ are the signal mass regions, and the disconnected regions ${U_{i}}$ form the corresponding sidebands. |
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Figure 5:
The normalised distribution of events in the 2D soft-drop mass plane with the mass regions overlaid. The first three sub-figures correspond to signal events with $ {M_{\text {SUSY}}} = $ 2000 GeV and ${M_{\mathrm{H} _1}}$ values of 40, 70, and 125 GeV respectively. The final sub-figure corresponds to simulated multijet events. All events satisfy the TR requirement and the kinematic event selection. |
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Figure 5-a:
The normalised distribution of events in the 2D soft-drop mass plane with the mass regions overlaid. The first three sub-figures correspond to signal events with $ {M_{\text {SUSY}}} = $ 2000 GeV and ${M_{\mathrm{H} _1}}$ values of 40, 70, and 125 GeV respectively. The final sub-figure corresponds to simulated multijet events. All events satisfy the TR requirement and the kinematic event selection. |
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Figure 5-b:
The normalised distribution of events in the 2D soft-drop mass plane with the mass regions overlaid. The first three sub-figures correspond to signal events with $ {M_{\text {SUSY}}} = $ 2000 GeV and ${M_{\mathrm{H} _1}}$ values of 40, 70, and 125 GeV respectively. The final sub-figure corresponds to simulated multijet events. All events satisfy the TR requirement and the kinematic event selection. |
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Figure 5-c:
The normalised distribution of events in the 2D soft-drop mass plane with the mass regions overlaid. The first three sub-figures correspond to signal events with $ {M_{\text {SUSY}}} = $ 2000 GeV and ${M_{\mathrm{H} _1}}$ values of 40, 70, and 125 GeV respectively. The final sub-figure corresponds to simulated multijet events. All events satisfy the TR requirement and the kinematic event selection. |
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Figure 5-d:
The normalised distribution of events in the 2D soft-drop mass plane with the mass regions overlaid. The first three sub-figures correspond to signal events with $ {M_{\text {SUSY}}} = $ 2000 GeV and ${M_{\mathrm{H} _1}}$ values of 40, 70, and 125 GeV respectively. The final sub-figure corresponds to simulated multijet events. All events satisfy the TR requirement and the kinematic event selection. |
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Figure 6:
Observed and predicted yields in the search regions, summed over the three data-taking years. The multijet background is from the data-driven prediction of Section 5, while the other backgrounds are from simulation. Example signal distributions are shown for $ {M_{\mathrm{H} _1}} = $ 70 GeV and ${M_{\text {SUSY}}} = $ 1200, 2000 and 2800 GeV. The numbers specified in the legend have unit GeV. The error bars represent the statistical uncertainties, and the hatched bands the systematic uncertainties. |
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Figure 7:
A comparison of the predicted and observed multijet yields in the validation region (VR), after subtraction of the other simulated backgrounds. The prediction is made separately for the three data-taking years, and the results are summed. The error bars on the data points represent their statistical uncertainties. The uncertainty in the predicted yields (statistical and systematic) is shown by the hatched bands. |
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Figure 8:
Search region yields after the background-only fit, summed over the three data-taking years. Example signal contributions used in the signal-plus-background fits are shown for ${M_{\text {SUSY}}} = $ 2200 GeV and ${M_{\mathrm{H} _1}} = $ 50, 90, and 125 GeV. The numbers specified in the legend have unit GeV. |
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Figure 9:
The observed and expected 95% CL upper limit of $\sigma \times \text {BR}$ as a function of ${M_{\mathrm{H} _1}}$. The value of ${M_{\text {SUSY}}}$ is held constant at 1200 GeV (top), 2000 GeV (middle), and 2800 GeV (bottom). The solid (dashed) black line indicates the observed (median expected) limit. The yellow (green) bands indicate the expected limits with $ \pm 1 \sigma $ ($ \pm 2 \sigma $) in experimental uncertainty. The solid and dashed red lines show the theoretical prediction and its uncertainty [16,17,18,19,20,21,22,23,24,25]. The theoretical prediction is not shown in the upper plot, since its value (0.58 pb $\times$ BR) is beyond the upper extent of the vertical axis. |
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Figure 9-a:
The observed and expected 95% CL upper limit of $\sigma \times \text {BR}$ as a function of ${M_{\mathrm{H} _1}}$. The value of ${M_{\text {SUSY}}}$ is held constant at 1200 GeV (top), 2000 GeV (middle), and 2800 GeV (bottom). The solid (dashed) black line indicates the observed (median expected) limit. The yellow (green) bands indicate the expected limits with $ \pm 1 \sigma $ ($ \pm 2 \sigma $) in experimental uncertainty. The solid and dashed red lines show the theoretical prediction and its uncertainty [16,17,18,19,20,21,22,23,24,25]. The theoretical prediction is not shown in the upper plot, since its value (0.58 pb $\times$ BR) is beyond the upper extent of the vertical axis. |
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Figure 9-b:
The observed and expected 95% CL upper limit of $\sigma \times \text {BR}$ as a function of ${M_{\mathrm{H} _1}}$. The value of ${M_{\text {SUSY}}}$ is held constant at 1200 GeV (top), 2000 GeV (middle), and 2800 GeV (bottom). The solid (dashed) black line indicates the observed (median expected) limit. The yellow (green) bands indicate the expected limits with $ \pm 1 \sigma $ ($ \pm 2 \sigma $) in experimental uncertainty. The solid and dashed red lines show the theoretical prediction and its uncertainty [16,17,18,19,20,21,22,23,24,25]. The theoretical prediction is not shown in the upper plot, since its value (0.58 pb $\times$ BR) is beyond the upper extent of the vertical axis. |
png pdf |
Figure 9-c:
The observed and expected 95% CL upper limit of $\sigma \times \text {BR}$ as a function of ${M_{\mathrm{H} _1}}$. The value of ${M_{\text {SUSY}}}$ is held constant at 1200 GeV (top), 2000 GeV (middle), and 2800 GeV (bottom). The solid (dashed) black line indicates the observed (median expected) limit. The yellow (green) bands indicate the expected limits with $ \pm 1 \sigma $ ($ \pm 2 \sigma $) in experimental uncertainty. The solid and dashed red lines show the theoretical prediction and its uncertainty [16,17,18,19,20,21,22,23,24,25]. The theoretical prediction is not shown in the upper plot, since its value (0.58 pb $\times$ BR) is beyond the upper extent of the vertical axis. |
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Figure 10:
The observed 95% CL upper limit of $(\sigma \times \text {BR}) / (\sigma \times \text {BR})_{\textrm {theory}}$ (indicated by the colour scale) as a function of ${M_{\mathrm{H} _1}}$ and ${M_{\text {SUSY}}}$. The solid red (black) line delineates the observed (median expected) excluded region. The dashed red (black) line delineates the observed (expected) excluded regions with $ \pm 1 \sigma $ in theoretical (experimental) uncertainty. |
| Tables | |
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Table 1:
The ${M_{\text {SUSY}}}$ values considered in this search and corresponding production cross sections (the sum of $\mathrm{\tilde{q}} \mathrm{\tilde{q}} $, $\mathrm{\tilde{q}} {\mathrm{\tilde{g}}} $, and ${\mathrm{\tilde{g}}} {\mathrm{\tilde{g}}} $), calculated at approximately NNLO+NNLL in ${\alpha _\mathrm {S}}$ [16,17,18,19,20,21,22,23,24] for a squark mass of ${M_{\text {SUSY}}}$ and a gluino mass 1% larger. The quoted uncertainty is from variations in the choice of scale, parton distribution functions, and ${\alpha _\mathrm {S}}$. |
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Table 2:
The ${M_{\mathrm{H} _1}}$ values considered in this search and corresponding $ {\mathrm{H} _1} \rightarrow \mathrm{b} {}\mathrm{\bar{b}} $ branching ratios, calculated for a SM-like Higgs boson using the hdecay package [25]. |
| Summary |
|
This note presents a search for pairs of light Higgs bosons (${\mathrm{H}_1} $) produced in supersymmetric cascade decays. The targeted final states have small missing transverse momentum and two ${\mathrm{H}_1} \rightarrow\mathrm{b\bar{b}}$ decays that are reconstructed as large-radius jets using substructure techniques. The search uses a data sample of proton-proton collision events collected by the CMS experiment at centre-of-mass energy $\sqrt s = $ 13 TeV during LHC Run II, corresponding to an integrated luminosity of 137 fb$^{-1}$. No evidence is found for any excess of events beyond the background expectations of the standard model (SM). The results are interpreted in the next-to-minimal supersymmetric extension of the SM, where a low-mass singlino leads to multi-step squark and gluino decays that can predominantly end with a boosted singlet-like ${\mathrm{H}_1}$ boson and a low-momentum singlino-like neutralino. Upper limits are set on the product of the production cross section and the $\mathrm{b\bar{b}}$ branching ratio of the ${\mathrm{H}_1}$ boson for a benchmark model with almost mass-degenerate light flavour squarks and gluinos. Under the assumption of a SM-like ${\mathrm{H}_1} \to\mathrm{b\bar{b}}$ branching ratio, ${\mathrm{H}_1}$ bosons with masses in the range 40-120 GeV, arising from the decays of squarks or gluinos with a mass from 1200-2500 GeV, are excluded at the 95% confidence level. |
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