Search for nonresonant new physics signals in high-mass dilepton events produced in association with b-tagged jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This study searches for nonresonant new physics signals in high-mass dilepton events with b-tagged jets at 13 TeV, setting limits on new physics energy scales and testing lepton flavor universality with no significant deviations found.

Contribution

It provides the first constraints on dimension-six four-fermion contact interactions involving leptons and b or s quarks in high-mass dilepton events at the LHC.

Findings

No significant excess over the standard model backgrounds.

Lower limits on the energy scale $\\Lambda$ range from 6.9 to 9.0 TeV.

Limits on the ratio $\\Lambda/g_*$ are between 2.0 and 2.6 TeV.

Abstract

A search for nonresonant new physics phenomena in high-mass dilepton events produced in association with b-tagged jets is performed using proton-proton collision data collected in 2016$-$2018 by the CMS experiment at the CERN LHC, at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis considers two effective field theory models with dimension-six operators; involving four-fermion contact interactions between two leptons ($\ell\ell$, electrons or muons) and b or s quarks (bb$\ell\ell$ and bs$\ell\ell$). Two lepton flavor combinations (ee and $\mu\mu$) are required and events are classified as having 0, 1, and $\geq$ 2 b-tagged jets in the final state. No significant excess is observed over the standard model backgrounds. Upper limits are set on the production cross section of the new physics signals. These translate into lower limits on the energy scale $\Lambda$ of 6.9 to 9.0 TeV in the bb$\ell\ell$ model, depending on model parameters, and on the ratio of energy scale and effective coupling, $\Lambda/g_*$, of 2.0 to 2.6 TeV in the bs$\ell\ell$ model. Lepton flavor universality is also tested by comparing the dielectron and dimuon mass spectra for different b-tagged jet multiplicities. No significant deviation from the standard model expectation of unity is observed.