A search for pairs of light neutral pseudoscalar bosons (A) resulting from the decay of a Higgs boson is performed. The search is conducted using LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected with the CMS detector in 2016$-$2018 and corresponding to an integrated luminosity of 138 fb$^{-1}$. The A boson decays into a highly collimated electron-positron pair. A novel multivariate algorithm using tracks and calorimeter information is developed to identify these distinctive signatures, and events are selected with two such merged electron-positron pairs. No significant excess above the standard model background predictions is observed. Upper limits on the branching fraction for H $\to$ AA $\to$ 4e are set at 95% confidence level, for masses between 10 and 100 MeV and proper decay lengths below 100 $μ$m, reaching branching fraction sensitivities as low as 10$^{-5}$. This is the first search for Higgs boson decays to four electrons via light pseudoscalars at the LHC. It significantly improves the experimental sensitivity to axion-like particles with masses below 100 MeV.
Invariant mass distribution of the four-electron system ($m_{4 e}$) for selected events (points), compared to the background-only fit (red) with its $68\%$ and $95\%$~CL uncertainty bands (green and yellow). A non-stacked benchmark signal (blue) for a Higgs boson decaying to a pair of ALPs with $m_a=20MeV$ and $c \tau = 10\,\mu\mathrm{m}$ is overlaid and normalized to a branching ratio of $4.6 \times 10^{-5}$, which corresponds to the $95\%$~CL upper limit value set by this analysis. The lower panel shows the same data after subtracting the background fit.
Observed (solid points) and expected (dashed lines) $95\%$ CL upper limits on the Higgs boson branching fraction to a pair of ALPs decaying into electron-positron pairs ($ H \to A A \to e e$), shown as a function of the ALP mass for benchmark proper decay lengths of 1 $\,\mu\mathrm{m}$ (upper left), 10 $\,\mu\mathrm{m}$ (upper right), and 100 $\,\mu\mathrm{m}$ (lower left). The green and yellow bands represent the one and two standard deviation confidence intervals around the expected limits. The lower right panel shows a map of the observed $95\%$ CL upper limit, shown as a color scale, as a function of the ALP mass $m_ A$ and proper decay length $c \tau$.
A map of the observed $95\%$ CL upper limit on the Higgs boson branching fraction for $ H \to A A \to4 e$, as a function of the ALP mass and the ratio of the ALP coupling to electrons to the energy scale of the ALP effective interaction.
The discovery of the Higgs boson has led to new possible signatures for heavy resonance searches at the LHC. Since then, search channels including at least one Higgs boson plus another particle have formed an important part of the program of new physics searches. In this report, the status of these searches by the CMS Collaboration is reviewed. Searches are discussed for resonances decaying to two Higgs bosons, a Higgs and a vector boson, or a Higgs boson and another new resonance. All analyses use proton-proton collision data collected at $\sqrt{s}$ = 13 TeV in the years 2016-2018. A combination of the results of these searches is presented together with constraints on different beyond-the-standard model scenarios, including scenarios with extended Higgs sectors, heavy vector bosons and extra dimensions. Studies are shown for the first time by CMS on the validity of the narrow-width approximation in searches for the resonant production of a pair of Higgs bosons. The potential for a discovery at the High Luminosity LHC is also discussed.
Upper limits on σB for a spin-0 resonance X obtained from the combination of the individual channels. The 68 and 95% CL intervals on the expected upper limits are shown as colored bands.
Upper limits on σB for a spin-2 resonance G obtained from the combination of the individual channels. The 68 and 95% CL intervals on the expected upper limits are shown as colored bands.
Upper limits at 95% CL on $\sigma$B(pp→X→Y(bb)H) for combination as a function of m$_Y$.
The first search exploiting the vector boson fusion process to probe heavy Majorana neutrinos and the Weinberg operator at the LHC is presented. The search is performed in the same-sign dimuon final state using a proton-proton collision data set recorded at $\sqrt{s}$ = 13 TeV, collected with the CMS detector and corresponding to a total integrated luminosity of 138 fb$^{-1}$. The results are found to agree with the predictions of the standard model. For heavy Majorana neutrinos, constraints on the squared mixing element between the muon and the heavy neutrino are derived in the heavy neutrino mass range 50 GeV-25 TeV; for masses above 650 GeV these are the most stringent constraints from searches at the LHC to date. A first test of the Weinberg operator at colliders provides an observed upper limit at 95% confidence level on the effective $\mu\mu$ Majorana neutrino mass of 10.8 GeV.
Distribution of $H_T / p_{T}^{\mu_{1}}$ for signals, backgrounds and data. The bins are used in the simultaneous fit. The bins 1-4 show the events in the high-$\Delta\Phi_{ll}$ signal region (SR), the bins 5-7 show the events in the low-$\Delta\Phi_{ll}$ SR, the bins 8-11 show the events in the low-$p_T^{miss}$ SR, the bins 12-15 show the events in the high-$p_T^{miss}$ SR, the bins 16-19 show the events in the b-tagged control region (CR), the bins 20-23 show the events in the high-$\Delta\Phi_{ll}$ and $p_T^{miss}$ CR, and the bins 24-26 show the events in the WZ CR, and the bins 31-33 show the events in the WZb CR. The predicted background yields are shown with their best fit normalizations from the simultaneous fit for the signal+background hypothesis. The signal yields are their expected yields from simulation, which are scaled by the some fators as from the plots. Vertical bars on data points represent the statistical uncertainty in the data. Vertical bars on total backgrounds represent the statistical+systematic uncertainties. Vertical bars on the signals represent the statistical+systematic uncertainties. The histograms for TVX backgrounds include the contributions from ttV and tZq processes. The histograms for other backgrounds include the contributions from double parton scattering, VVV. The overflow is included in the last bin in each corresponding region.
Exclusion limits on the squared mixing element between the muon and the heavy Majorana neutrino, as a function of the mass of the heavy Majorana neutrino.
Distribution of $H_T / p_{T}^{\mu_{1}}$ for signals, backgrounds and data. The bins are used in the simultaneous fit. The bins 1-4 show the events in the high-$\Delta\Phi_{ll}$ signal region (SR), the bins 5-7 show the events in the low-$\Delta\Phi_{ll}$ SR, the bins 8-11 show the events in the low-$p_T^{miss}$ SR, the bins 12-15 show the events in the high-$p_T^{miss}$ SR, the bins 16-19 show the events in the b-tagged control region (CR), the bins 20-23 show the events in the high-$\Delta\Phi_{ll}$ and $p_T^{miss}$ CR, and the bins 24-26 show the events in the WZ CR, and the bins 31-33 show the events in the WZb CR. The predicted background yields are the expected yields. The signal yields are their expected yields from simulation, which are scaled by the some fators as from the plots. Vertical bars on data points represent the statistical uncertainty in the data. Vertical bars on total backgrounds represent the statistical+systematic uncertainties. Vertical bars on the signals represent the statistical+systematic uncertainties. The histograms for TVX backgrounds include the contributions from ttV and tZq processes. The histograms for other backgrounds include the contributions from double parton scattering, VVV. The overflow is included in the last bin in each corresponding region.
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