CMS-PAS-FTR-18-030

CMS-PAS-FTR-18-030
Sensitivity study for a heavy gauge boson W' in the decay channel with a tau lepton and a neutrino at the High-Luminosity LHC
CMS Collaboration
February 2019

Abstract: A sensitivity study for the discovery or exclusion of a heavy vector boson W' in the final state with a tau lepton and a neutrino is presented. Event samples are simulated for the Phase-2 CMS detector at the High-Luminosity LHC (corresponding to an integrated luminosity of 3 ab$^{-1}$), using the parameterized detector simulation program DELPHES. A signal would appear as an excess of events with high transverse mass of the hadronic tau and missing transverse momentum, compared to the standard model background. With the high integrated luminosity during Phase-2, a W' boson with SM-like couplings could be observed with a significance exceeding five standard deviations with a mass up to 6.0 TeV. In case of no observation, the results are interpreted as lower limits on the mass of the W' boson in the context of the sequential standard model. In addition, variations in the coupling strength are studied, and a model-independent cross section limit is provided.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Illustration of the production and decay of the W' boson with the subsequent hadronic decay of tau ($\tau _h$).
png pdf	Figure 2: Distribution of ${m_\mathrm {T}}$, after all selections for HL-LHC conditions of 3000 fb$^{-1}$ and 200 PU. The relevant SM backgrounds are shown according to the labels in the legend. Signal examples for values of the W' boson mass of $m_{{\mathrm {W}'}}=$ 4 TeV and 6 TeV are scaled to their SSM LO cross section and 3000 fb$^{-1}$ integrated luminosity.
png pdf	Figure 3: Sensitivity for a SSM W' boson for 300 fb$^{-1}$ and 3000 fb$^{-1}$. Discovery significance (left) and expected exclusion limit on the SSM W' boson mass at 95% CL (right).
png pdf	Figure 3-a: Discovery significance for a SSM W' boson for 300 fb$^{-1}$ and 3000 fb$^{-1}$.
png pdf	Figure 3-b: Expected exclusion limit on the SSM W' boson mass at 95% CL for 300 fb$^{-1}$ and 3000 fb$^{-1}$.
png pdf	Figure 4: Sensitivity to the coupling ratio $g_{{\mathrm {W}'}}/g_{{\mathrm {W}}}$ of a W' boson using 3000 fb$^{-1}$ of integrated luminosity at the HL-LHC. On the left, the coupling ratio $g_{{\mathrm {W}'}}/g_{{\mathrm {W}}}$ is shown as a function of the W' boson mass. The theory line of the SSM W' boson is shown in blue. The 2D graph on the right includes additionally the limit on the cross section represented by the color code.
png pdf	Figure 4-a: Expected limit on the coupling ratio $g_{{\mathrm {W}'}}/g_{{\mathrm {W}}}$ as a function of the W' boson mass, using 3000 fb$^{-1}$ of integrated luminosity at the HL-LHC. The theory line of the SSM W' boson is shown in blue.
png pdf	Figure 4-b: Expected limit on the coupling ratio $g_{{\mathrm {W}'}}/g_{{\mathrm {W}}}$ as a function of the W' boson mass, using 3000 fb$^{-1}$ of integrated luminosity at the HL-LHC. The 2D limit on the cross section is represented by the color code.
png pdf	Figure 5: Model-independent cross section limit scaled to 3000 fb$^{-1}$. For this, a single-bin limit is calculated considering events above a lower threshold ${m_\mathrm {T}^\mathrm {min}}$ while keeping the signal yield constant in order to avoid including any signal shape information on this limit calculation.

Summary

Taking guidance from the published Run 2 analysis based on proton-proton collisions corresponding to an integrated luminosity of 35.9 fb$^{-1}$ at $\sqrt{s} = $ 13 TeV [4], the physics reach at the High-Luminosity LHC with 3000 fb$^{-1}$ at $\sqrt{s} = $ 14 TeV with the upgraded CMS detector was studied. The final state consists of a hadronically decaying tau lepton and ${p_{\mathrm{T}}}^{\text{miss}}$ caused by neutrinos. The interpretation was performed in the benchmark sequential standard model (SSM) with an additional charged gauge boson W'. With the high luminosity, the sensitivity can be substantially improved. The discovery at a significance level of 3(5) standard deviations is possible for W' boson masses of 6.9(6.4) TeV, respectively. In case of no observation, SSM W' boson masses up to 7.0 TeV can be excluded.

While the SSM assumes standard-model-like couplings, weaker couplings are possible. Depending on the value of the W' boson mass, the high-luminosity data will allow to study couplings down to nearly 10$^{-2}$. To allow interpretations in other models, a model-independent limit on the cross section was provided.

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