Search for New Phenomena in Final States with Two Leptons and One or No $b$-Tagged Jets at $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$ Using the ATLAS Detector

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Search for New Phenomena in Final States with Two Leptons and One or No $b$ -Tagged Jets at $\sqrt{s} = 13 TeV$ Using the ATLAS Detector

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. Lett. 127, 141801 – Published 1 October 2021

Abstract

A search for new phenomena is presented in final states with two leptons and one or no $b$ -tagged jets. The event selection requires the two leptons to have opposite charge, the same flavor (electrons or muons), and a large invariant mass. The analysis is based on the full run-2 proton-proton collision dataset recorded at a center-of-mass energy of $\sqrt{s} = 13 TeV$ by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of $139 {fb}^{- 1}$ . No significant deviation from the expected background is observed in the data. Inspired by the $B$ -meson decay anomalies, a four-fermion contact interaction between two quarks ( $b$ , $s$ ) and two leptons ( $e e$ or $μ μ$ ) is used as a benchmark signal model, which is characterized by the energy scale and coupling, $Λ$ and $g_{*}$ , respectively. Contact interactions with $Λ / g_{*}$ lower than 2.0 (2.4) TeV are excluded for electrons (muons) at the 95% confidence level, still far below the value that is favored by the $B$ -meson decay anomalies. Model-independent limits are set as a function of the minimum dilepton invariant mass, which allow the results to be reinterpreted in various signal scenarios.

Received 1 June 2021
Accepted 30 July 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.141801

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Physics Subject Headings (PhySH)

Flavor changing neutral currents Quark & gluon jets

Leptons

Particle data analysis

Accelerators & Beams

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Vol. 127, Iss. 14 — 1 October 2021

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Figure 1
Representative Feynman diagrams for the decay of a $B^{+}$ meson to a $K^{+}$ meson in association with two leptons (a) in the SM and (b) in the EFT approach and for production of two leptons via a $b s ℓ ℓ$ contact interaction in $p p$ collisions (c) without and (d) with a $b$ jet in the final state.
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Figure 2
Data overlaid on SM background postfit $m_{ℓ ℓ}$ distributions in the SRs of the (a) electron $b$ -veto, (b) electron $b$ -tag, (c) muon $b$ -veto, and (d) muon $b$ -tag categories. “Others” refers to diboson and $W + jets$ events. MC statistical uncertainties and systematic uncertainties are considered (hatched band). The prefit signal distribution is presented as well for a hypothesis of $Λ / g_{*} = 1 TeV$ . The bottom panels show the ratio of the data to the background prediction, while the arrows correspond to bins where the ratio is beyond the limits of the figure. The last bin is an overflow bin, which contains the yields in the bins beyond it. The dashed and dotted lines mark the transition point where the extrapolation is used in the analysis for the top and multijet backgrounds, respectively.
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Figure 3
Data overlaid on SM background postfit yields in the regions of the (a) electron $b$ -veto, (b) electron $b$ -tag, (c) muon $b$ -veto, and (d) muon $b$ -tag categories. “Others” refers to diboson and $W + jets$ events. MC statistical uncertainties and systematic uncertainties are considered (hatched band). The left part of each figure presents the yields in the CRs and the VR of each category, while the right part presents the yields in the SRs of each category. The bottom panels show the ratio of the data to the background prediction, while the arrows correspond to bins where the ratio is beyond the limits of the figure. The range of the $y$ axis is different between the left and right parts of the bottom panels, and the latter is presented at logarithmic scale. For the SRs, as the distribution is cumulative, each bin is contained in and therefore correlated with the lower mass bins.
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Figure 4
Model-independent observed (solid line) and expected (dashed line) upper limit on the visible cross section ( $σ_{vis} = σ ε A$ ) for the (a) electron $b$ -veto, (b) electron $b$ -tag, (c) muon $b$ -veto, and (d) muon $b$ -tag categories. The uncertainty bands around the expected limit represent the 68% and 95% confidence intervals. The theory lines (dotted lines) correspond to particular $Λ / g_{*}$ values of the signal model, and the red marker presents the strongest expected lower limit on $Λ / g_{*}$ .
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Physical Review Letters

Search for New Phenomena in Final States with Two Leptons and One or No b-Tagged Jets at s=13 TeV Using the ATLAS Detector

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. Lett. 127, 141801 – Published 1 October 2021

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Search for New Phenomena in Final States with Two Leptons and One or No $b$ -Tagged Jets at $\sqrt{s} = 13 TeV$ Using the ATLAS Detector