CMS-PAS-EXO-16-020

CMS-PAS-EXO-16-020
Search for high-mass resonances in $\mathrm{Z}(\mathrm{q}\bar{\mathrm{q}})\gamma$ final state in pp collisions at $ \sqrt{s} = $ 13 TeV with 2.7 fb$^{-1}$
CMS Collaboration
June 2016

Abstract: A search for massive resonances decaying to a Z boson and a photon is performed in events with a hadronically decaying Z boson candidate, using jet substructure and advanced b tagging techniques. Results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC corresponding to an integrated luminosity of 2.7 fb$^{-1}$ collected with the CMS detector in 2015. Spin-0 resonances with various widths and with masses in a range between 650 GeV and 3 TeV are searched for. The results are presented in terms of an upper limit on the production cross section of such resonances.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1-a: Full acceptance times efficiency (including $\mathcal {BR}(\mathrm{ Z } \to {\mathrm{ q } \mathrm{ \bar{q} } } )$) of the two signal categories for resonances with (a) $\Gamma /m =$ 0.014% and (b) $\Gamma /m =$ 5.6%. Points show the numbers extracted from the Monte Carlo simulation, lines show the fit of the values with a polynomial.
png pdf	Figure 1-b: Full acceptance times efficiency (including $\mathcal {BR}(\mathrm{ Z } \to {\mathrm{ q } \mathrm{ \bar{q} } } )$) of the two signal categories for resonances with (a) $\Gamma /m =$ 0.014% and (b) $\Gamma /m =$ 5.6%. Points show the numbers extracted from the Monte Carlo simulation, lines show the fit of the values with a polynomial.
png pdf	Figure 2-a: Observed $ {M_{\text {Z}\gamma }} $ invariant mass spectra for (a) anti-b-tagged and (b) b-tagged SRs. The results of the fits to the two categories with the parametric background shape are shown. The difference between the yields measured in data and the estimates from the fit is divided by the statistical uncertainty of the measurement and reported in the lower panel.
png pdf	Figure 2-b: Observed $ {M_{\text {Z}\gamma }} $ invariant mass spectra for (a) anti-b-tagged and (b) b-tagged SRs. The results of the fits to the two categories with the parametric background shape are shown. The difference between the yields measured in data and the estimates from the fit is divided by the statistical uncertainty of the measurement and reported in the lower panel.
png pdf	Figure 3-a: Expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained in the (a) anti-b-tagged and (b) b-tagged categories.
png pdf	Figure 3-b: Expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained in the (a) anti-b-tagged and (b) b-tagged categories.
png pdf	Figure 4-a: Expected and observed limits on the broad spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained in the (a) anti-b-tagged and (b) b-tagged categories.
png pdf	Figure 4-b: Expected and observed limits on the broad spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained in the (a) anti-b-tagged and (b) b-tagged categories.
png pdf	Figure 5-a: Expected and observed limits on the production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained with the combination of the two categories for (a) narrow and (b) broad spin-0 resonance.
png pdf	Figure 5-b: Expected and observed limits on the production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained with the combination of the two categories for (a) narrow and (b) broad spin-0 resonance.

Tables
png pdf	Table 1: Summary of the sources of uncertainties, their magnitude, and affected quantities. The second column indicates the magnitude of the yield variation. The third column indicates if the source of the uncertainty affects the total signal yield or introduces a category migration.

Summary

We have presented a search for narrow and broad resonances in the mass range from 650 GeV to 3 TeV, decaying to a Z boson and a photon, where Z boson further decays hadronically. The search is carried out with two exclusive categories of events, with or without a $\mathrm{ Z }\to\mathrm{ b \bar{b} }$ candidate, and the final result is obtained by combining the two categories. Information from jet substructure variables is used in order to enhance the sensitivity of the analysis to heavy-particle production. The result is presented in a form of upper limit at a 95% confidence level on the production cross section of a new resonance. For a narrow resonance with a mass of 750 GeV an observed (expected) cross section limit is 73 (92) fb. At higher masses the sensitivity improves and reaches 26 (9) fb in the observed (expected) limits for a narrow resonance with a mass of 2 TeV, and 3.7 (4.5) fb at 3 TeV. Corresponding upper limits on the cross sections in the searches with leptonic Z decays are 44 (36) fb for a mass of 750 GeV, and 23 (22) fb for a mass of 2 TeV [7]. For a broad resonance, the observed (expected) upper limits on the resonance production cross section are 109 (131) fb at 750 GeV, and 27 (37) fb at 3 TeV. This analysis improves on the sensitivity achieved in the similar ATLAS $\mathrm{ Z }\to\mathrm{ q\bar{q} } $ analysis [6].

Additional Figures
png pdf	Additional Figure 1-a: Expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained (a) with the leptonic $\mathrm {Z}({\rm e}^+{\rm e}^-,\mu ^+\mu ^-)\gamma $ analysis in CMS-PAS-EXO-16-019 and (b) with the hadronic $\mathrm {Z}({\rm q} {\rm \bar{q}})\gamma $ search.
png pdf	Additional Figure 1-b: Expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained (a) with the leptonic $\mathrm {Z}({\rm e}^+{\rm e}^-,\mu ^+\mu ^-)\gamma $ analysis in CMS-PAS-EXO-16-019 and (b) with the hadronic $\mathrm {Z}({\rm q} {\rm \bar{q}})\gamma $ search.
png pdf	Additional Figure 2-a: Overlaid expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained with the leptonic $\mathrm {Z}({\rm e}^+{\rm e}^-,\mu ^+\mu ^-)\gamma $ analysis in CMS-PAS-EXO-16-019 and with the hadronic $\mathrm {Z}(\mathrm{ q \bar{q} })\gamma $ search. Plots are with (a) log-scale and (b) double-log scale.
png pdf	Additional Figure 2-b: Overlaid expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained with the leptonic $\mathrm {Z}({\rm e}^+{\rm e}^-,\mu ^+\mu ^-)\gamma $ analysis in CMS-PAS-EXO-16-019 and with the hadronic $\mathrm {Z}(\mathrm{ q \bar{q} })\gamma $ search. Plots are with (a) log-scale and (b) double-log scale.
png pdf	Additional Figure 3-a: Overlaid expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained with the leptonic $\mathrm {Z}({\rm e}^+{\rm e}^-,\mu ^+\mu ^-)\gamma $ analysis in CMS-PAS-EXO-16-019 and with the hadronic $\mathrm {Z}(\mathrm{ q \bar{q} })\gamma $ search. Plots are with (a) log-scale and (b) double-log scale.
png pdf	Additional Figure 3-b: Overlaid expected and observed limits on the narrow spin-0 resonance production cross section times branching fraction $\mathrm {X} \rightarrow \mathrm {Z}\gamma $ obtained with the leptonic $\mathrm {Z}({\rm e}^+{\rm e}^-,\mu ^+\mu ^-)\gamma $ analysis in CMS-PAS-EXO-16-019 and with the hadronic $\mathrm {Z}(\mathrm{ q \bar{q} })\gamma $ search. Plots are with (a) log-scale and (b) double-log scale.
png pdf	Additional Figure 4-a: The reconstructed mass spectrum in the anti-b-tagged category of the hadronic analysis for (a) narrow and (b) wide spin-0 resonance. The acceptance includes $\mathcal {BR}({\rm Z}\to \mathrm{ q \bar{q} })$.
png pdf	Additional Figure 4-b: The reconstructed mass spectrum in the anti-b-tagged category of the hadronic analysis for (a) narrow and (b) wide spin-0 resonance. The acceptance includes $\mathcal {BR}({\rm Z}\to \mathrm{ q \bar{q} })$.

References
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