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Search for electroweak production of higgsinos in channels with two Higgs bosons decaying to b quarks in pp collisions at 8 TeV (SUS-13-022)

Contents

More Information

The analysis is documented in this Physics Analysis Summary.

Plots and tables from the PAS

(Pseudo) Feynman diagram

Figure Caption
Figure 1: Event diagram for the SUSY scenario considered in the analysis, with $\tilde{\chi}^0_1$ the lightest higgsino and $\tilde{G}$ a gravitino. Each Higgs boson H decays to a b-quark anti b-quark pair.

Signal (Sideband) region definitions

Figure Caption
Table 1: Intervals of $E^{miss}_T$-significance $S_{MET}$ used in the analysis.
Figure 6 (1): Illustration of the signal (SIG) and sideband (SB) regions in the |$\Delta m_{jj}$| versus <$m_{jj}$> plane.
Figure 6 (2): Distribution of simulated $t\bar{t}$ events in the 2b sample in the |$\Delta m_{jj}$| versus <$m_{jj}$> plane. The plot employs an arbitrary integrated luminosity.
Figure 6 (3): Distribution of simulated $t\bar{t}$ events in the 4b sample in the |$\Delta m_{jj}$| versus <$m_{jj}$> plane. The plot employs an arbitrary integrated luminosity.
Figure 6 (4): Distribution of simulated signal events in the 4b sample in the |$\Delta m_{jj}$| versus <$m_{jj}$> plane for a higgsino mass of 250 GeV. The plot employs an arbitrary integrated luminosity.
Figure 7: One-dimensional projections of (left) <$m_{jj}$> and (right) |$\Delta m_{jj}$| for simulated (top) $t\bar{t}$ and (bottom) signal events, with a higgsino mass of 250 GeV. For $t\bar{t}$ events (signal events), results are shown for the 2b and 4b samples (4b sample). The solid and dashed vertical lines indicate the boundaries of the signal (SIG) and sideband (SB) regions, respectively. The distributions are normalized to unit area.

Higgs mass variables

Figure Caption
Figure 2 (1): Distribution of reconstructed average mass <$m_{jj}$> for signal MC events in the 4b event sample for a 200 GeV higgsino. Separate distributions are shown for the cases where zero, one, or two of the generator-level Higgs bosons are reconstructed correctly. The distributions are shown after all signal-region requirements are applied except for that <$m_{jj}$>. The plot shows the results for all signal MC events.
Figure 2 (2): Distribution of reconstructed average mass <$m_{jj}$> for signal MC events in the 4b event sample for a 200 GeV higgsino. Separate distributions are shown for the cases where zero, one, or two of the generator-level Higgs bosons are reconstructed correctly. The distributions are shown after all signal-region requirements are applied except for that <$m_{jj}$>. The plot shows the results for events in which each of the four generator-level quarks from the Higgs boson decays is matched with a reconstructed jet with pT > 20 GeV (in other words, for events where a correct double-Higgs-boson reconstruction is possible in this analysis).
Figure 2 (3): Distribution of reconstructed average mass <$m_{jj}$> for signal MC events in the 4b event sample for a 400 GeV higgsino. Separate distributions are shown for the cases where zero, one, or two of the generator-level Higgs bosons are reconstructed correctly. The distributions are shown after all signal-region requirements are applied except for that <$m_{jj}$>. The plot shows the results for all signal MC events.
Figure 2 (4): Distribution of reconstructed average mass <$m_{jj}$> for signal MC events in the 4b event sample for a 400 GeV higgsino. Separate distributions are shown for the cases where zero, one, or two of the generator-level Higgs bosons are reconstructed correctly. The distributions are shown after all signal-region requirements are applied except for that <$m_{jj}$>. The plot shows the results for events in which each of the four generator-level quarks from the Higgs boson decays is matched with a reconstructed jet with pT > 20 GeV (in other words, for events where a correct double-Higgs-boson reconstruction is possible in this analysis).

Data and simulation comparisons

Figure Caption
Figure 3 (1): Distribution of |$\Delta m_{jj}$| in the 4b sample, after all signal-region requirements are applied except for that on the displayed variable, in comparison with simulations of background and signal events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] For the signal events, results are shown for higgsino masses of 200 and 400 GeV. The background distributions are stacked while the signal distributions are not. The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 3 (2): Distribution of $\Delta R_{max}$ in the 4b sample, after all signal-region requirements are applied except for that on the displayed variable, in comparison with simulations of background and signal events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] For the signal events, results are shown for higgsino masses of 200 and 400 GeV. The background distributions are stacked while the signal distributions are not. The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 3 (3): Distribution of <$m_{jj}$> in the 4b sample, after all signal-region requirements are applied except for that on the displayed variable, in comparison with simulations of background and signal events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] For the signal events, results are shown for higgsino masses of 200 and 400 GeV. The background distributions are stacked while the signal distributions are not. The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 3 (4): Distribution of $E^{miss}_T$-significance $S_{MET}$ in the 4b sample, after all signal-region requirements are applied except for that on the displayed variable, in comparison with simulations of background and signal events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] For the signal events, results are shown for higgsino masses of 200 and 400 GeV. The background distributions are stacked while the signal distributions are not. The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 4 (1): Distribution of $E^{miss}_T$-significance $S_{MET}$ in the $t\bar{t}$-BG event sample in comparison with simulations of background events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 4 (2): Distribution of $E^{miss}_T$-significance $S_{MET}$ in the QCD-BG background-enhanced event sample in comparison with simulations of background events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 5: Distribution of $E^{miss}_T$ in the QCD-BG background-enhanced event sample in comparison with simulations of background events. [$t\bar{t}$ (1l) and $t\bar{t}$ (2l) refer to $t\bar{t}$ events in which one or two top quarks decay semileptonically, respectively.] The hatched band indicates the statistical uncertainty of the total SM simulated prediction.

Systematic uncertainties on signal

Figure Caption
Table 2: Typical values of the systematic uncertainty for signal efficiency, in percentage, for a higgsino mass of 200 or 400 GeV.

SM background estimate

Figure CaptionSorted ascending
Figure 8: The ratio of the number of events in the signal (SIG) region to that in the sideband (SB) region as a function of $S_{MET}$ bin (see Table 1), for the 2b, 3b, and 4b event samples. The results for the simulation account for the various SM processes.

Likelihood fit

Figure Caption
Table 3: Parameters with values determined by the likelihood fit.
Figure 9: Expected p values for the null hypothesis (no SUSY) should a higgsino signal be present with the predicted cross section. The green and yellow bands indicate the one- and two-standard deviation intervals, and the horizontal solid (red) lines the sensitivity to a SUSY signal in standard deviations.

Results and interpretation

Figure Caption
Figure 10 (1): Observed numbers of events in the 3b-SIG region, in bins of $E^{miss}_T$-significance $S_{MET}$, in comparison with the SM background estimates from the likelihood fit. The hatched bands show the total uncertainty of the background prediction, with statistical and systematic terms combined. The (unstacked) results for signal events, with a higgsino mass of either 250 or 400 GeV, are also shown.
Figure 10 (2): Observed numbers of events in the 4b-SIG region, in bins of $E^{miss}_T$-significance $S_{MET}$, in comparison with the SM background estimates from the likelihood fit. The hatched bands show the total uncertainty of the background prediction, with statistical and systematic terms combined. The (unstacked) results for signal events, with a higgsino mass of either 250 or 400 GeV, are also shown.
Table 4: Observed numbers of events and corresponding SM background estimates from the likelihood fit for the 3b-SIG and 4b-SIG regions. For the data, the first uncertainty is statistical and the second systematic.
Figure 11: Observed numbers of events in bins of $E^{miss}_T$-significance $S_{MET}$ and corresponding prediction from SM simulation for the sideband SB (left) and signal SIG (right) regions, for the 2b (top), 3b (middle), and 4b (bottom) event samples. The hatched bands indicate the statistical uncertainty of the total SM simulated prediction.
Figure 12 (1): Observed and expected upper limits on the signal strength as a function of higgsino mass. The uncertainty associated with the theory cross section is 5%. The green and yellow bands indicate the one- and two-standard deviation intervals, respectively, for the expected result. A simple text file with these results can be found here.
Figure 12 (2): Observed and expected upper limits on the cross section as a function of higgsino mass. The uncertainty associated with the theory cross section is 5%. The green and yellow bands indicate the one- and two-standard deviation intervals, respectively, for the expected result. A simple text file with these results can be found here.

Additional material

MET Significance QCD rejection

Figure Caption
Additional Figure 1: The number of events with genuine and spurious $E^{miss}_T$ as predicted by simulation, in each of the five $E^{miss}_T$ and $S_{MET}$ bins indicated. The genuine $E^{miss}_T$ category is comprised of the sum of $Z\rightarrow\nu\bar{\nu}$ events and of $t\bar{t}$ events in which one or both top quarks undergoes semileptonic decay. The spurious $E^{miss}_T$ category is comprised of the sum of $t\bar{t}$ events in which both top quarks decay hadronically and of QCD multihadronic events with a bottom quark-antiquark pair. All analysis cuts are applied in this plot except it is the $\geq$2b selection with no $\Delta\phi_{min}$ cut. The QCD multijet component has been rescaled by a factor of 1.3 to improve the normalization agreement with the data.

Signal Efficiency

Additional Figure 2: Signal efficiency as a function of Higgsino mass $m_{\tilde{\chi}^0_1}$ for the 4b Higgs-mass signal region for each of the bins of $S_{MET}$. A simple text file with these results can be found here.

Electronic Material

  • The xsec-limits is a text file which contains the absolute cross section limits.
  • The signal-strength is a text file which contains signal strength (sig/sig_ref) limits.
  • The 4b signal efficiency is a text file which contains signal efficiency (in percent) for each of the bins of $S_{MET}$ for the 4b Higgs-mass signal region.
  • The 3b signal efficiency is a text file which contains signal efficiency (in percent) for each of the bins of $S_{MET}$ for the 3b Higgs-mass signal region.

-- PawandeepJandir - 02 Feb 2014

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