CMS-PAS-FTR-21-005

CMS-PAS-FTR-21-005
Sensitivity projections for a search for new phenomena at high dilepton mass for the LHC Run 3 and the HL-LHC
CMS Collaboration
March 2022

Abstract: A projection of the sensitivity for a search for new physics in proton-proton collisions with two energetic leptons, e or $\mu$ , in the final state is presented. Two datasets are considered: a combination of the Run 2 dataset with the expected Run 3 dataset, 140 fb $^{-1}$ at a center-of-mass energy $\sqrt{s} =$ 13 TeV and 160 fb $^{-1}$ at $\sqrt{s} =$ 13.6 TeV respectively, as well as the dataset expected from the high-luminosity LHC (HL-LHC) corresponding to 3000 fb $^{-1}$ at $\sqrt{s} =$ 14 TeV. With these datasets, significant improvement in the sensitivity of searches for new physics will be achieved. In the search for new heavy gauge bosons Z', the expected exclusion limit at 95% CL will be improved by about 300 GeV with the combination of the Run 2 and Run 3 datasets, and by about 1.7 TeV with the HL-LHC dataset. The 5 $\sigma$ discovery potential for these particles is also assessed. Additionally, the expected sensitivity for testing lepton flavor universality by measuring the dimuon-to-dielectron ratio at high mass with these two datasets is presented.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Expected limits along with their 68% and 95% envelopes for the full Run 2 + Run 3 dataset, compared to the expected limits for the Run 2 analysis (shown in lighter color).
png pdf	Figure 2: Expected limits along with their 68% and 95% envelopes for the full Phase-2 dataset, compared to the expected limits for the Run 2 analysis (shown in lighter color).
png pdf	Figure 3: Product of the signal cross section and branching fraction that can be discovered at 5 $\sigma$ local significance as a function of the resonance mass.
png pdf	Figure 4: 68% uncertainty interval of the flavor ratio measurement as a function of the lower mass threshold, comparing the Run 2 dataset with the Run 2 + Run 3 and Phase-2 scenario extrapolations.

Tables
png pdf	Table 1: Expected lower mass limits for the Run 2 [22] and the extrapolations to the Run 2 + Run 3 and Phase-2 datasets for the Z' $_{\text{SSM}}$ and Z' $_{\psi}$ models.

Summary

The expected sensitivity of a search for new physics in events with high-mass lepton pairs has been presented. Two scenarios have been considered: the dataset delivered by the LHC at the end of Run 3, combining the Run 2 and Run 3 datasets and corresponding to 300 fb

$^{-1}$ at center-of-mass energies of

$\sqrt{s} =$ 13 TeV and

$\sqrt{s} =$ 13.6 TeV, respectively, and the dataset delivered by the high-luminosity LHC (HL-LHC), corresponding to 3000 fb

$^{-1}$ at

$\sqrt{s} =$ 14 TeV.

The sensitivity is assessed in the context of a sequential SM (SSM) and a superstring-inspired model that predict spin-1 resonances. Previous lower mass limits, set with the LHC Run 2 dataset and correspond to 5.15 (4.56) TeV in the Z'

$_{\text{SSM}}$ (Z'

$_{\psi}$ ) model, are expected to increase by 300 GeV by the end of Run 3, and by 1.7 TeV with the HL-LHC dataset. The product of signal cross section and branch fraction that can be discovered with 5

$\sigma$ significance ranges from 9.0

$\times$ 10

$^{-5}$ pb at a resonance mass of 1 TeV to 1.8

$\times$ 10

$^{-6}$ pb at 7 TeV. Z'

$_{\text{SSM}}$ and Z'

$_{\psi}$ bosons with masses up to 6.27 TeV and 5.72 TeV, respectively, can be discovered at the HL-LHC. For a test of lepton flavor universality, the precision improves by a factor of 2 in the Run 2 + Run 3 scenario and a factor of 5 in the HL-LHC scenario. Considering reduced systematic uncertainties for the HL-LHC scenario has a negligible effect on the results.

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