CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-HIG-18-012 ; CERN-EP-2019-254
Search for new neutral Higgs bosons through the $\mathrm{H} \to Z \mathrm{A} \to \ell^{+}\ell^{-} \mathrm{b\bar{b}}$ process in pp collisions at $\sqrt{s} = $ 13 TeV
JHEP 03 (2020) 055
Abstract: This paper reports on a search for an extended scalar sector of the standard model, where a new CP-even (odd) boson decays to a Z boson and a lighter CP-odd (even) boson, and the latter further decays to a b quark pair. The Z boson is reconstructed via its decays to electron or muon pairs. The analysed data were recorded in proton-proton collisions at a center-of-mass energy $\sqrt{s} = $ 13 TeV, collected by the CMS experiment at the LHC during 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Data and predictions from the standard model are in agreement within the uncertainties. Upper limits at 95% confidence level are set on the production cross section times branching fraction, with masses of the new bosons up to 1000 GeV. The results are interpreted in the context of the two-Higgs-doublet model.
Figures & Tables Summary References CMS Publications
Figures

png pdf
Figure 1:
Possible 2HDM mass hierarchies: conventional, where A is degenerate in mass with the charged scalars; and twisted [9], where H is degenerate in mass with the charged scalars. In both scenarios, the lighter boson between A and H can be either heavier or lighter than the observed Higgs boson H(125).

png pdf
Figure 2:
The H and A branching fractions as a function of $\cos(\beta - \alpha)$ in Type-II 2HDM for the following set of parameters: $\tan\beta = $ 1.5, $ {{m}_{\mathrm{H}}} = $ 300 GeV, $ {{m}_{\mathrm{A} }} = $ 200 GeV (left). The H and A branching fractions as a function of $\tan\beta $ in Type-II 2HDM for the following set of parameters: $\cos(\beta - \alpha) = $ 0.01, $ {{m}_{\mathrm{H}}} = $ 300 GeV and $ {{m}_{\mathrm{A} }} = $ 200 GeV (right).

png pdf
Figure 3:
The $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ (left) and $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ (right) distributions in data and background events after requiring all the analysis selections, for $\mu \mu $+ee events. The background shapes and normalisations are obtained from simulation. The various signal hypotheses displayed have been scaled to a cross section of 1 pb for illustrative purposes. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties prior to the fit (introduced in Section 6).

png pdf
Figure 3-a:
The $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ distribution in data and background events after requiring all the analysis selections, for $\mu \mu $+ee events. The background shapes and normalisations are obtained from simulation. The various signal hypotheses displayed have been scaled to a cross section of 1 pb for illustrative purposes. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties prior to the fit (introduced in Section 6).

png pdf
Figure 3-b:
The $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ distribution in data and background events after requiring all the analysis selections, for $\mu \mu $+ee events. The background shapes and normalisations are obtained from simulation. The various signal hypotheses displayed have been scaled to a cross section of 1 pb for illustrative purposes. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties prior to the fit (introduced in Section 6).

png pdf
Figure 4:
The $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane for signal samples under three different mass hypotheses, on which the parametrised ellipses are shown (left). A signal hypothesis with ${{m}_{\mathrm{H}}} =$ 500 GeV and ${{m}_{\mathrm{A} }} =$ 300GeV is shown in the $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane (right). The different ellipses show the variation of the $\rho $ parameter in steps of 0.5, from 0 to 3. The intensity of the color in each hexagonal bin is proportional to the number of events in it.

png pdf
Figure 4-a:
The $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane for signal samples under three different mass hypotheses, on which the parametrised ellipses are shown. The intensity of the color in each hexagonal bin is proportional to the number of events in it.

png pdf
Figure 4-b:
A signal hypothesis with ${{m}_{\mathrm{H}}} =$ 500 GeV and ${{m}_{\mathrm{A} }} =$ 300GeV is shown in the $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane. The different ellipses show the variation of the $\rho $ parameter in steps of 0.5, from 0 to 3. The intensity of the color in each hexagonal bin is proportional to the number of events in it.

png pdf
Figure 5:
Post-fit $\rho $ distributions from a background-only fit for the same-flavour lepton (left) and mixed-flavour lepton (right) events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} = $ 261 GeV and ${{m}_{\mathrm{A} }} =$ 150 GeV (upper) and ${{m}_{\mathrm{H}}} =$ 442 GeV and ${{m}_{\mathrm{A} }} =$ 193 GeV (lower). The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit.

png pdf
Figure 5-a:
Post-fit $\rho $ distribution from a background-only fit for the same-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} = $ 261 GeV and ${{m}_{\mathrm{A} }} =$ 150 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit.

png pdf
Figure 5-b:
Post-fit $\rho $ distribution from a background-only fit for the mixed-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} = $ 261 GeV and ${{m}_{\mathrm{A} }} =$ 150 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit.

png pdf
Figure 5-c:
Post-fit $\rho $ distribution from a background-only fit for the same-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} =$ 442 GeV and ${{m}_{\mathrm{A} }} =$ 193 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit.

png pdf
Figure 5-d:
Post-fit $\rho $ distribution from a background-only fit for the mixed-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} =$ 442 GeV and ${{m}_{\mathrm{A} }} =$ 193 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit.

png pdf
Figure 6:
Distribution of the local p-value in the $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane.

png pdf
Figure 7:
Observed 95% CL upper limits on the product of the production cross section and branching fraction $\sigma \mathcal {B}$ for $\mathrm{H} (\mathrm{A} ) \to Z \mathrm{A} (\mathrm{H}) \to \ell \ell \mathrm{b} \mathrm{\bar{b}} $ as a function of ${{m}_{\mathrm{A} }}$ and ${{m}_{\mathrm{H}}}$. The limits are computed using the asymptotic CLs method, combining the ee and $\mu\mu$ channels.

png pdf
Figure 8:
Expected and observed 95% CL exclusion contours for the Type-II 2HDM benchmark $\tan\beta =$ 1.5 and $\cos(\beta -\alpha)=$ 0.01 as a function of ${{m}_{\mathrm{A} }}$ and ${{m}_{\mathrm{H}}}$. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of the exclusion contours expected under the background-only hypothesis. The limits are computed using the asymptotic CLs method, combining the ee and $\mu\mu$ channels.

png pdf
Figure 9:
Expected and observed 95% CL exclusion contours for ${{m}_{\mathrm{H}}} =$ 379 GeV and ${{m}_{\mathrm{A} }} =$ 172 GeV as a function of $\tan\beta $ and ${\cos(\beta - \alpha)}$. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of the exclusion contours expected under the background-only hypothesis. The limits are computed using the asymptotic CLs method, combining the ee and $\mu\mu$ channels.
Tables

png pdf
Table 1:
Expected and observed event yields prior to the fit in the signal region with ${{m}_{\mathrm{H}}} =$ 500 GeV and ${{m}_{\mathrm{A} }} =$ 200 GeV for each elliptical bin. The signal is normalised to its theoretical cross section for the Type-II 2HDM benchmark $\tan\beta =$ 1.5 and $\cos(\beta - \alpha)=$ 0.01. The ee and $\mu\mu$ categories are summed.

png pdf
Table 2:
Summary of the systematic uncertainties prior to the fit and the variation, in percentages, that they induce on the total event yields for the dominant background and signal processes, under a particular signal hypothesis with ${{m}_{\mathrm{H}}} = $ 379 GeV and ${{m}_{\mathrm{A} }} = $ 172 GeV.
Summary
This paper reports on a search for a new CP-even (odd) neutral Higgs boson, decaying into a Z boson and a lighter CP-odd (even) neutral Higgs boson, where the Z decays into an electron or muon pair, and the light Higgs boson into a b quark pair. The search is based on LHC proton-proton collision data at a center-of-mass energy $\sqrt{s}=$ 13 TeV collected by the CMS experiment during 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. We consider decays such as $\mathrm{H} \to \mathrm{Z}\mathrm{A} \to \ell\ell\mathrm{b\bar{b}}$, where H and A are the additional CP-even and -odd Higgs bosons above-mentioned, respectively, in the context of the two-Higgs-doublet model (2HDM). They are searched for in the mass range from 120 to 1000 GeV for H and 30 to 1000 GeV for A. The search is subsequently extended to the $\mathrm{A} \to \mathrm{Z}\mathrm{H} \to \ell\ell\mathrm{b\bar{b}}$ process via interchanging the two mass parameters.

No significant deviations from the standard model expectations are observed. Model independent upper limits on the product of cross section and branching fraction are set. Limits are also set on the parameters of the 2HDM, assuming the Type-II formulation. Under the specific benchmark scenario corresponding to $\tan\beta=$ 1.5 and $\cos (\beta - \alpha)=$ 0.01, regions with ${{m}_{\mathrm{H}}}$ in the range 150-700 GeV and ${{m}_{\mathrm{A} }}$ in the range 30-295 GeV with ${{m}_{\mathrm{H}}} > {{m}_{\mathrm{A} }} $, or alternatively for ${{m}_{\mathrm{H}}}$ in the range 30-280 GeV and ${{m}_{\mathrm{A} }}$ in the range 150-700 GeV with ${{m}_{\mathrm{H}}} < {{m}_{\mathrm{A} }} $ are excluded at 95% confidence level. Results are also interpreted in the scenario where ${{m}_{\mathrm{H}}} =$ 379 GeV and ${{m}_{\mathrm{A} }} =$ 172 GeV. In this context, the region with $\cos (\beta - \alpha)$ in the range $-$0.9-0.3 and $\tan\beta$ in the range 0.5-7.0 is excluded at 95% confidence level. With respect to previous searches, a larger region of the Type-II 2HDM parameter space is excluded.
Additional Material: Signal Efficiencies

JASON files of signal efficiencies :
MuMu channel,
ElEl channel.

In each file:
First column: mA; Second column: mH; Third column: signal efficiency.

References
1 ATLAS Collaboration Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC PLB 716 (2012) 1 1207.7214
2 CMS Collaboration Observation of a new boson at a mass of 125~GeV with the CMS experiment at the LHC PLB 716 (2012) 30 CMS-HIG-12-028
1207.7235
3 CMS Collaboration Observation of a new boson with mass near 125~GeV in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s} = $ 7 and 8 TeV JHEP 06 (2013) 081 CMS-HIG-12-036
1303.4571
4 ATLAS and CMS Collaborations Combined measurement of the Higgs boson mass in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 and 8 tev with the ATLAS and CMS experiments PRL 114 (2015) 191803 1503.07589
5 CMS Collaboration Measurements of properties of the Higgs boson decaying into the four-lepton final state in pp collisions at $ \sqrt{s}= $ 13 TeV JHEP 11 (2017) 047 CMS-HIG-16-041
1706.09936
6 ATLAS Collaboration Measurement of the Higgs boson mass in the $ \mathrm{H}\rightarrow \mathrm{ZZ}^* \rightarrow 4\ell $ and $ \mathrm{H} \rightarrow \gamma\gamma $ channels with $ \sqrt{s}= $ 13 TeV pp collisions using the ATLAS detector PLB 784 (2018) 345 1806.00242
7 G. C. Branco et al. Theory and phenomenology of two-Higgs-doublet models PR 516 (2012) 1 1106.0034
8 C. Cs\'aki The minimal supersymmetric standard model MPLA 11 (1996) 599 hep-ph/9606414
9 J. M. G\'erard and M. Herquet A twisted custodial symmetry in the two-Higgs-doublet model PRL 98 (2007) 251802 hep-ph/0703051
10 ATLAS Collaboration Search for a heavy Higgs boson decaying into a $ Z $ boson and another heavy Higgs boson in the $ \ell\ell $bb final state in pp collisions at $ \sqrt{s}= $ 13 TeV with the ATLAS detector PLB 783 (2018) 392 1804.01126
11 CMS Collaboration Search for neutral resonances decaying into a Z boson and a pair of b jets or $ \tau $ leptons PLB 759 (2016) 369 CMS-HIG-15-001
1603.02991
12 ATLAS Collaboration Search for a CP-odd Higgs boson decaying to Zh in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector PLB 744 (2015) 163 1502.04478
13 CMS Collaboration Search for a pseudoscalar boson decaying into a Z boson and the 125 GeV Higgs boson in $ \ell^{+}\ell^{-} \mathrm{b}\overline{\mathrm{b}} $ final states PLB 748 (2015) 221 CMS-HIG-14-011
1504.04710
14 CMS Collaboration Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at $ \sqrt{s} = $ 13 TeV EPJC 79 (2019) 564 CMS-HIG-18-005
1903.00941
15 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
16 CMS Collaboration The CMS experiment at the CERN LHC JINST 03 (2008) S08004 CMS-00-001
17 J. Alwall et al. The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations JHEP 07 (2014) 079 1405.0301
18 R. Frederix and S. Frixione Merging meets matching in MC@NLO JHEP 12 (2012) 061 1209.6215
19 P. Artoisenet, R. Frederix, O. Mattelaer, and R. Rietkerk Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations JHEP 03 (2013) 015 1212.3460
20 P. Nason A new method for combining NLO QCD with shower Monte Carlo algorithms JHEP 11 (2004) 040 hep-ph/0409146
21 S. Frixione, P. Nason, and C. Oleari Matching NLO QCD computations with parton shower simulations: the POWHEG method JHEP 11 (2007) 070 0709.2092
22 S. Alioli, P. Nason, C. Oleari, and E. Re A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX JHEP 06 (2010) 043 1002.2581
23 S. Alioli, S.-O. Moch, and P. Uwer Hadronic top-quark pair-production with one jet and parton showering JHEP 01 (2012) 137 1110.5251
24 S. Alioli, P. Nason, C. Oleari, and E. Re NLO single-top production matched with shower in POWHEG: $ s $- and $ t $-channel contributions JHEP 09 (2009) 111 0907.4076
25 T. Sjostrand et al. An introduction to PYTHIA 8.2 CPC 191 (2015) 159 1410.3012
26 NNPDF Collaboration Parton distributions for the LHC Run II JHEP 04 (2015) 040 1410.8849
27 CMS Collaboration Event generator tunes obtained from underlying event and multiparton scattering measurements EPJC 76 (2015) 155 CMS-GEN-14-001
1512.00815
28 P. Skands, S. Carrazza, and J. Rojo Tuning PYTHIA 8.1: the Monash 2013 tune EPJC 74 (2014) 3024 1404.5630
29 GEANT4 Collaboration GEANT4--a simulation toolkit NIMA 506 (2003) 250
30 M. Czakon and A. Mitov Top++: A program for the calculation of the top-pair cross-section at hadron colliders CPC 185 (2014) 2930 1112.5675
31 Y. Li and F. Petriello Combining QCD and electroweak corrections to dilepton production in the framework of the FEWZ simulation code PRD 86 (2012) 094034 1208.5967
32 J. Butterworth et al. PDF4LHC recommendations for LHC Run II JPG 43 (2016) 023001 1510.03865
33 T. Gehrmann et al. $ \mathrm{W}^+\mathrm{W}^- $ production at hadron colliders in next-to-next-to-leading order QCD PRL 113 (2014) 212001 1408.5243
34 J. M. Campbell, R. K. Ellis, and C. Williams Vector boson pair production at the LHC JHEP 07 (2011) 018 1105.0020
35 LHC Higgs Cross Section Working Group Handbook of LHC Higgs cross sections: 4. Deciphering the nature of the Higgs sector CERN (2016) 1610.07922
36 CMS Collaboration Measurement of the inclusive W and Z production cross sections in pp collisions at $ \sqrt{s} = $ 7 TeV with the CMS experiment JHEP 10 (2011) 132 CMS-EWK-10-005
1107.4789
37 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector JINST 12 (2017) P10003 CMS-PRF-14-001
1706.04965
38 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm JHEP 04 (2008) 063 0802.1189
39 M. Cacciari, G. P. Salam, and G. Soyez FastJet user manual EPJC 72 (2012) 1896 1111.6097
40 CMS Collaboration Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV JINST 10 (2015) P06005 CMS-EGM-13-001
1502.02701
41 CMS Collaboration Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s}= $ 13 TeV JINST 13 (2018) P06015 CMS-MUO-16-001
1804.04528
42 CMS Collaboration Jet energy scale and resolution in the CMS experiment in $ {\mathrm{p}}{\mathrm{p}} $ collisions at 8 TeV JINST 12 (2017) P02014 CMS-JME-13-004
1607.03663
43 CMS Collaboration Performance of the CMS missing transverse momentum reconstruction in $ {\mathrm{p}}{\mathrm{p}} $ data at $ \sqrt{s} = $ 8 TeV JINST 10 (2015) P02006 CMS-JME-13-003
1411.0511
44 CMS Collaboration Performance of missing transverse momentum reconstruction in proton-proton collisions at $ \sqrt{s} = $ 13 TeV using the CMS detector JINST 14 (2019) P07004 CMS-JME-17-001
1903.06078
45 CMS Collaboration Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV JINST 13 (2018) P05011 CMS-BTV-16-002
1712.07158
46 CMS Collaboration CMS luminosity measurements for the 2016 data taking period CMS-PAS-LUM-17-001 CMS-PAS-LUM-17-001
47 CMS Collaboration Measurement of the inelastic proton-proton cross section at $ \sqrt{s}= $ 13 TeV JHEP 07 (2018) 161 CMS-FSQ-15-005
1802.02613
48 E. Gross and O. Vitells Trial factors for the look elsewhere effect in high energy physics EPJC 70 (2010) 525 1005.1891
49 O. Vitells and E. Gross Estimating the significance of a signal in a multi-dimensional search Astropart. Phys. 35 (2011) 230 1105.4355
50 T. Junk Confidence level computation for combining searches with small statistics NIMA 434 (1999) 435 hep-ex/9902006
51 A. L. Read Presentation of search results: the $ \mathrm{CL_s} $ technique JPG 28 (2002) 2693
52 G. Cowan, K. Cranmer, E. Gross, and O. Vitells Asymptotic formulae for likelihood-based tests of new physics EPJC 71 (2011) 1554 1007.1727
Compact Muon Solenoid
LHC, CERN