CMS-HIG-21-012

CMS-HIG-21-012 ; CERN-EP-2022-233
Search for boosted Higgs boson decay to a charm quark-antiquark pair in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
CMS Collaboration
25 November 2022
Phys. Rev. Lett. 131 (2023) 041801
Abstract: A search for the standard model (SM) Higgs boson (H) produced with transverse momentum greater than 450 GeV and decaying to a charm quark-antiquark ($ \mathrm{c} \overline{\mathrm{c}} $) pair is presented. The search is performed using proton-proton collision data collected at $ \sqrt{s}= $ 13 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. Boosted $ \mathrm{H}\to\mathrm{c}\overline{\mathrm{c}} $ decay products are reconstructed as a single large-radius jet and identified using a deep neural network charm tagging technique. The method is validated by measurement of the $ \mathrm{Z}\to\mathrm{c}\overline{\mathrm{c}} $ decay process, which is observed with a signal strength of 1.00 $ _{-0.14}^{+0.17} $ (syst) $ \pm $ 0.08 (theo) $ \pm $ 0.06 (stat), defined as the ratio of the observed process rate to the standard model expectation. The observed (expected) upper limit on $\sigma (\mathrm{H}) \mathcal{B} (\mathrm{ H \to c\bar{c} })$ is set at 47 (39) times the SM prediction at 95% confidence level.
Links: e-print arXiv:2211.14181 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The DDCvL and DDCvB performance for $ \mathrm{H}\to\mathrm{c}\overline{\mathrm{c}} $ identification versus QCD and $ \mathrm{H}\to\mathrm{b}\overline{\mathrm{b}} $ processes respectively. No selection apart from the displayed $ m_{\mathrm{SD}} $ and $ p_{\mathrm{T}} $ requirements is applied. The working points used in this search are marked with a cross. The AUC is the area-under-curve metric.
png pdf	Figure 2: The observed and fitted $ m_{\mathrm{SD}} $ distributions for the passing (left) and failing (right) regions, combining all $ p_{\mathrm{T}} $ categories and the three data-taking years. The fit is performed under the signal-plus-background hypothesis with a single inclusive $ \mathrm{H}(\mathrm{c}\overline{\mathrm{c}}) $ signal strength parameter. The $ \mathrm{t} \overline{\mathrm{t}} $ background yields and the QCD background yields and shapes are estimated from data. The $ \mathrm{t} \overline{\mathrm{t}} $ process constitutes the majority of contributions labeled ``Other''. The dashed line represents the $ \mathrm{H}\to\mathrm{c}\overline{\mathrm{c}} $ expectation, multiplied by a factor of 200. The step-like features at 166 and 180 GeV are due to $ m_{\mathrm{SD}} $ bins excluded from the $ \rho $ acceptance region. The lower panel shows the residual difference between the data and the overall background (excluding $ \mathrm{Z}\to\mathrm{c}\overline{\mathrm{c}} $), divided by the statistical uncertainty in the data. The near perfect model agreement with data in the failing region (right) is by construction.
png pdf	Figure 2-a: The observed and fitted $ m_{\mathrm{SD}} $ distributions for the passing region, combining all $ p_{\mathrm{T}} $ categories and the three data-taking years. The fit is performed under the signal-plus-background hypothesis with a single inclusive $ \mathrm{H}(\mathrm{c}\overline{\mathrm{c}}) $ signal strength parameter. The $ \mathrm{t} \overline{\mathrm{t}} $ background yields and the QCD background yields and shapes are estimated from data. The $ \mathrm{t} \overline{\mathrm{t}} $ process constitutes the majority of contributions labeled ``Other''. The dashed line represents the $ \mathrm{H}\to\mathrm{c}\overline{\mathrm{c}} $ expectation, multiplied by a factor of 200. The step-like features at 166 and 180 GeV are due to $ m_{\mathrm{SD}} $ bins excluded from the $ \rho $ acceptance region. The lower panel shows the residual difference between the data and the overall background (excluding $ \mathrm{Z}\to\mathrm{c}\overline{\mathrm{c}} $), divided by the statistical uncertainty in the data.
png pdf	Figure 2-b: The observed and fitted $ m_{\mathrm{SD}} $ distributions for the passing failing region, combining all $ p_{\mathrm{T}} $ categories and the three data-taking years. The fit is performed under the signal-plus-background hypothesis with a single inclusive $ \mathrm{H}(\mathrm{c}\overline{\mathrm{c}}) $ signal strength parameter. The $ \mathrm{t} \overline{\mathrm{t}} $ background yields and the QCD background yields and shapes are estimated from data. The $ \mathrm{t} \overline{\mathrm{t}} $ process constitutes the majority of contributions labeled ``Other''. The dashed line represents the $ \mathrm{H}\to\mathrm{c}\overline{\mathrm{c}} $ expectation, multiplied by a factor of 200. The step-like features at 166 and 180 GeV are due to $ m_{\mathrm{SD}} $ bins excluded from the $ \rho $ acceptance region. The lower panel shows the residual difference between the data and the overall background (excluding $ \mathrm{Z}\to\mathrm{c}\overline{\mathrm{c}} $), divided by the statistical uncertainty in the data. The near perfect model agreement with data in this failing region is by construction.

Tables
png pdf	Table 1: Summary of the applied data-to-simulation scale factors for the jet mass, jet mass resolution, $ N_{2}^{1\mathrm{,DDT}} $ selection, and DEEPDOUBLEX selections for different data-taking periods. The jet mass correction is additive, in units of GeV.
png pdf	Table 2: Sources of uncertainty in the measurement of the signal strength $ \mu_{\mathrm{H}}=$ 9.4$_{-19.9}^{+20.3} $, and their observed impact ($ \Delta\mu_{\mathrm{H}} $) in the fit to the full data set. The impact of each uncertainty is evaluated by computing the uncertainty excluding that source and subtracting it in quadrature from the total uncertainty. The total uncertainty does not match the sum in quadrature of each source because of correlations among the components.

Summary

In conclusion, a search for standard model (SM) Z and Higgs bosons produced with transverse momenta greater than 450 GeV and decaying to charm quark-antiquark ($ \mathrm{c} \overline{\mathrm{c}} $) pairs has been performed in a data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ at $ \sqrt{s}= $ 13 TeV. New algorithms based on deep neural networks have been developed to identify jets originating from charm quark pairs. The $ \mathrm{Z}\to\mathrm{c}\overline{\mathrm{c}} $ process is observed in association with jets at a hadron collider for the first time, with a signal strength of 1.00 $ _{-0.17}^{+0.19} $ relative to the SM prediction. An observed (expected) upper limit on the product of the Higgs boson production cross section and branching fraction to $ \mathrm{c} \overline{\mathrm{c}} $ of 47 (39) times the SM expectation is set at 95% confidence level.

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