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

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 $μμ$) 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 $Λ$ 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, $Λ/g_*$, 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.

Figures (15)

• Figure 1: Representative Feynman diagrams for the production of dileptons via the ${ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace$ operator at the LHC, in association with 0 (left), 1 (center), and 2 (right) final state $\mathup{{{b}}{} _{ {}} ^{ {}}}$ quarks.
• Figure 2: Representative Feynman diagrams for the production of dileptons via the ${ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace { \mathup{{{s}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace$ operator at the LHC, in association with 0 (left) and 1 (right) final state $\mathup{{{b}}{} _{ {}} ^{ {}}}$ quarks.
• Figure 3: Observed data and various SM backgrounds in bins of DNN score evaluated from per-year and per-pseudorapidity trained models in the ${ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace$ (left) and ${ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace$ (right) channels. The solid cyan line in the upper panels correspond to the ${ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace$ signal expectation for $\Lambda = 6\,\text{Te\spaceV}\xspace$ in the LL constructive interference model. The lower panel of each plot shows the ratio of data to predicted background yields.
• Figure 4: Comparison of data and various SM backgrounds in the $\mathup{{{t}}{} _{ {}} ^{ {}}}$$\mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}}$ CR as a function of $m_{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}$ for the 0 $\mathup{{{b}}{} _{ {}} ^{ {}}}$ (upper) and $\geq1$$\mathup{{{b}}{} _{ {}} ^{ {}}}$ (lower) channels in the BB (left) and BE (right) categories. The lower panel of each plot shows the ratio of data to predicted background yields before correction with $\text{SF}_{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace{}{ \mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace}\xspace}$ values. The hatched band in the lower panels indicates the statistical uncertainty in the simulated background prediction.
• Figure 5: Comparison of data and various SM backgrounds in the $\mathup{{{t}}{} _{ {}} ^{ {}}}$$\mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}}$ VR as a function of $m_{{ \mathup{{{e}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upmu}}{} _{ {}} ^{ {}}} }\xspace}$ for the BB (left) and BE (right) categories. The lower panel of each plot shows the ratio of data to predicted background yields. The hatched band in the lower panels indicates the statistical uncertainty in the simulated background prediction.