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CMS-PAS-FTR-18-035
Projection of searches for exotic Higgs boson decays to light pseudoscalars for the High-Luminosity LHC
Abstract: This Physics Analysis Summary details the projections of two searches for exotic decays of the Higgs boson from LHC Run 2 to the High-Luminosity LHC. Decays to a pair of light pseudoscalar bosons are explored, in the final states of two $\tau$ leptons and two muons, or two $\tau$ leptons and two b quarks. The projections are based on analyses that use 35.9 fb$^{-1}$ proton-proton collision data recorded at a center-of-mass energy of 13 TeV in 2016. Integrated luminosities of up to 3000 fb$^{-1}$ are considered in the projections, with different scenarios for the extrapolation of the systematic uncertainties.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Left: Projected expected limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})$ times the branching fraction for $ {\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}} \to 2 {\mathrm {b}}2 {\tau}$, for 36, 300, and 3000 fb$^{-1}$. Right: Projected expected limits $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({{{\mathrm {h}}}\to {{\mathrm {a}} {\mathrm {a}}}\to 2 {\tau}2{{\mathrm {b}}}})$, comparing different scenarios for systematic uncertainties for an integrated luminosity of 3000 fb$^{-1}$.

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Figure 1-a:
Projected expected limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})$ times the branching fraction for $ {\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}} \to 2 {\mathrm {b}}2 {\tau}$, for 36, 300, and 3000 fb$^{-1}$.

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Figure 1-b:
Projected expected limits $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({{{\mathrm {h}}}\to {{\mathrm {a}} {\mathrm {a}}}\to 2 {\tau}2{{\mathrm {b}}}})$, comparing different scenarios for systematic uncertainties for an integrated luminosity of 3000 fb$^{-1}$.

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Figure 2:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {\mathrm {b}}2 {\tau}$ final state in 2HDM+S type-1 (top left), type-2 (top right), type-3 (bottom left), and type-4 (bottom right).

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Figure 2-a:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {\mathrm {b}}2 {\tau}$ final state in 2HDM+S type-1.

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Figure 2-b:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {\mathrm {b}}2 {\tau}$ final state in 2HDM+S type-2.

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Figure 2-c:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {\mathrm {b}}2 {\tau}$ final state in 2HDM+S type-3.

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Figure 2-d:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {\mathrm {b}}2 {\tau}$ final state in 2HDM+S type-4.

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Figure 3:
Left: Projected expected limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({{{\mathrm {h}}}\to {{\mathrm {a}} {\mathrm {a}}}\to 2 {{\mu}}2{{\tau}}})$, for 36, 300, and 3000 fb$^{-1}$. Right: Projected expected limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({{{\mathrm {h}}}\to {{\mathrm {a}} {\mathrm {a}}}\to 2 {{\mu}}2{{\tau}}})$, comparing different scenarios for systematic uncertainties for an integrated luminosity of 3000 fb$^{-1}$.

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Figure 3-a:
Projected expected limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({{{\mathrm {h}}}\to {{\mathrm {a}} {\mathrm {a}}}\to 2 {{\mu}}2{{\tau}}})$, for 36, 300, and 3000 fb$^{-1}$.

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Figure 3-b:
Projected expected limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}}) \mathcal {B}({{{\mathrm {h}}}\to {{\mathrm {a}} {\mathrm {a}}}\to 2 {{\mu}}2{{\tau}}})$, comparing different scenarios for systematic uncertainties for an integrated luminosity of 3000 fb$^{-1}$.

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Figure 4:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})\mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {{\mu}}2 {\tau}$ final state in 2HDM+S type-1 (top left), type-2 (top right), type-3 (bottom left), and type-4 (bottom right).

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Figure 4-a:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})\mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {{\mu}}2 {\tau}$ final state in 2HDM+S type-1.

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Figure 4-b:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})\mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {{\mu}}2 {\tau}$ final state in 2HDM+S type-2.

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Figure 4-c:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})\mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {{\mu}}2 {\tau}$ final state in 2HDM+S type-3.

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Figure 4-d:
Expected upper limits on $(\sigma ({\mathrm {h}})/\sigma _{\textrm {SM}})\mathcal {B}({\mathrm {h}} \to {\mathrm {a}} {\mathrm {a}})$ for 3000 fb$^{-1}$ of data with YR18 systematic uncertainties for the $2 {{\mu}}2 {\tau}$ final state in 2HDM+S type-4.
Tables

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Table 1:
The sources of systematic uncertainty for which limiting values are applied in the ''YR18 systematics uncertainties'' scenario. Systematic uncertainties of the reference Run 2 analyses are described in Refs. [1,2].
Summary
Recent searches for exotic decays of the Higgs boson performed with 35.9 fb$^{-1}$ of data collected at 13 TeV [1,2] have been projected to integrated luminosities of up to 3000 fb$^{-1}$, achievable at the High-Luminosity LHC. They target decays of the Higgs boson to a pair of light pseudoscalars in the final states with two $\tau$ leptons and two muons, or two $\mathrm{b}$ quarks and two muons. The integrated luminosity of 3000 fb$^{-1}$ will improve the sensitivity by about an order of magnitude for the search in the $2\mathrm{b}2\tau$ final state. The improvement is larger in the $2{\mu}2\tau$ final state and scales almost linearly with the integrated luminosity for pseudoscalar masses close to 15 GeV.
References
1 CMS Collaboration Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state with two b quarks and two $ \tau $ leptons in proton-proton collisions at $ \sqrt{s}= $ 13 TeV PLB 785 (2018) 462 CMS-HIG-17-024
1805.10191
2 CMS Collaboration Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state of two muons and two $ \tau $ leptons in proton-proton collisions at $ \sqrt{s}= $ 13 TeV JHEP 11 (2018) 018 CMS-HIG-17-029
1805.04865
3 D. Curtin et al. Exotic decays of the 125 GeV Higgs boson PRD 90 (2014) 075004 1312.4992
4 CMS Collaboration The CMS Experiment at the CERN LHC JINST 3 (2008) S08004 CMS-00-001
5 G. Apollinari, B. O., T. Nakamoto, and L. Rossi High Luminosity Large Hadron Collider HL-LHC CERN Yellow Report (2015), no. 5, 1 1705.08830
6 D. Contardo et al. Technical Proposal for the Phase-II Upgrade of the CMS Detector CERN-LHCC-2015-010, LHCC-P-008, CMS-TDR-15-02
7 K. Klein The Phase-2 Upgrade of the CMS Tracker CERN-LHCC-2017-009, CMS-TDR-014
8 CMS Collaboration The Phase-2 Upgrade of the CMS Barrel Calorimeters Technical Design Report CDS
9 CMS Collaboration The Phase-2 Upgrade of the CMS Endcap Calorimeter CDS
10 CMS Collaboration The Phase-2 Upgrade of the CMS Muon Detectors CDS
11 CMS Collaboration Expected performance of the physics objects with the upgraded CMS detector at the HL-LHC CDS
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