A search for an unexpected asymmetry in the production of $e^+ \mu^-$ and $e^- \mu^+$ pairs in proton-proton collisions recorded by the ATLAS detector at $\sqrt s = 13$ TeV

The ATLAS collaboration
Phys.Lett.B 830 (2022) 137106, 2022.

Abstract
This search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for $e^+ \mu^-$ and $e^- \mu^+$ pairs to constrain physics processes beyond the Standard Model. It uses $139 \text{fb}^{-1}$ of proton$-$proton collision data recorded at $\sqrt{s} = 13$ TeV at the LHC. Targeting sources of new physics which prefer final states containing $e^{+}\mu^{-}$ to $e^{-}\mu^{+}$, the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the $R$-parity-violating coupling $\lambda'_{231}$ is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when $g_{\text{1R}}^{eu}=g_{\text{1R}}^{\mu c}=1$, at 95% confidence level. The limit on the coupling reduces to $g_{\text{1R}}^{eu}=g_{\text{1R}}^{\mu c}=0.46$ for a mass of 1420 GeV.

  • SR-RPV and SR-LQ yields

    Data from Table 1 (Also seen in Figure 5)

    10.17182/hepdata.115579.v1/t1

    Observed yields, and (post-fit) expected yields for the data-driven SM estimates. Yields are shown for the benchmark RPV-supersymmetry signal points...

  • Obs RPV-SUSY limit lambdap231 1p0

    Data from Figure 6 (Also seen in Figure 7)

    10.17182/hepdata.115579.v1/t2

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=1.0$.

  • Exp RPV-SUSY limit lambdap231 1p0

    Data from Figure 6 (Also seen in Figure 7)

    10.17182/hepdata.115579.v1/t3

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=1.0$.

  • Exp RPV-SUSY 1sigma_exp limit band lambdap231 1p0

    Data from Figure 6

    10.17182/hepdata.115579.v1/t4

    The $1\sigma_{\text{exp}}$ variation of the expected exclusion contour at 95% CL as a function of the smuon and neutralino masses,...

  • Obs RPV-SUSY limit lambdap231 0p1

    Data from Figure 7

    10.17182/hepdata.115579.v1/t5

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.1$.

  • Exp RPV-SUSY limit lambdap231 0p1

    Data from Figure 7

    10.17182/hepdata.115579.v1/t6

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.1$.

  • Obs RPV-SUSY limit lambdap231 0p15

    Data from Figure 7

    10.17182/hepdata.115579.v1/t7

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.15$.

  • Exp RPV-SUSY limit lambdap231 0p15

    Data from Figure 7

    10.17182/hepdata.115579.v1/t8

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.15$.

  • Obs RPV-SUSY limit lambdap231 0p2

    Data from Figure 7

    10.17182/hepdata.115579.v1/t9

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.2$.

  • Exp RPV-SUSY limit lambdap231 0p2

    Data from Figure 7

    10.17182/hepdata.115579.v1/t10

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.2$.

  • Obs RPV-SUSY limit lambdap231 0p4

    Data from Figure 7

    10.17182/hepdata.115579.v1/t11

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.4$.

  • Exp RPV-SUSY limit lambdap231 0p4

    Data from Figure 7

    10.17182/hepdata.115579.v1/t12

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.4$.

  • Obs RPV-SUSY limit lambdap231 0p6

    Data from Figure 7

    10.17182/hepdata.115579.v1/t13

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0.6$.

  • Exp RPV-SUSY limit lambdap231 0p6

    Data from Figure 7

    10.17182/hepdata.115579.v1/t14

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=0p6$.

  • Obs RPV-SUSY limit lambdap231 1p5

    Data from Figure 7

    10.17182/hepdata.115579.v1/t15

    The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=1.5$.

  • Exp RPV-SUSY limit lambdap231 1p5

    Data from Figure 7

    10.17182/hepdata.115579.v1/t16

    The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=1.5$.

  • Obs leptoquark limit

    Data from Figure 8

    10.17182/hepdata.115579.v1/t17

    The observed exclusion contour at 95% CL as a function of the leptoquark mass and coupling strength.

  • Exp leptoquark limit

    Data from Figure 8

    10.17182/hepdata.115579.v1/t18

    The expected exclusion contour at 95% CL as a function of the leptoquark mass and coupling strength.

  • Obs leptoquark -1sigma_theory limit

    Data from Figure 8

    10.17182/hepdata.115579.v1/t19

    The minus $1\sigma_{\text{theory}}$ variation of the observed exclusion contour at 95% CL as a function of the leptoquark mass and...

  • Obs leptoquark 1sigma_theory limit

    Data from Figure 8

    10.17182/hepdata.115579.v1/t20

    The plus $1\sigma_{\text{theory}}$ variation of the observed exclusion contour at 95% CL as a function of the leptoquark mass and...

  • Exp leptoquark 1sigma_exp limit band

    Data from Figure 8

    10.17182/hepdata.115579.v1/t21

    The $1\sigma_{\text{exp}}$ variation of the expected exclusion contour at 95% CL as a function of the leptoquark mass and coupling...

  • $\rho$ measurement results in SR-MET

    Data from Table 1 of the auxiliary material (Also seen in Figures 2 and 3)

    10.17182/hepdata.115579.v1/t22

    Observed yields, and fake lepton background yields in the $e^{+}\mu^{-}$ and $e^{-}\mu^{+}$ channels of SR-MET, along with the results of...

  • $\rho$ measurement results in SR-JET

    Data from Table 1 of the auxiliary material (Also seen in Figures 2 and 3)

    10.17182/hepdata.115579.v1/t23

    Observed yields, and fake lepton background yields in the $e^{+}\mu^{-}$ and $e^{-}\mu^{+}$ channels of SR-JET, along with the results of...

  • Upper Limits SR-MET, $M_{\text{T2}}$

    Data from Table 2 of the auxiliary material (Also shown in Figure 4)

    10.17182/hepdata.115579.v1/t24

    Observed and expected 95% CL upper limits on the total number of signal events entering the $e^{+}\mu^{-}$ and $e^{-}\mu^{+}$ channels...

  • Upper Limits SR-JET, $H_{\text{P}}$

    Data from Table 2 of the auxiliary material (Also shown in Figure 4)

    10.17182/hepdata.115579.v1/t25

    Observed and expected 95% CL upper limits on the total number of signal events entering the $e^{+}\mu^{-}$ and $e^{-}\mu^{+}$ channels...

  • Signal Cutflow

    Data from Table 3 of the auxiliary material

    10.17182/hepdata.115579.v1/t26

    Signal yields following each cut in the analysis, for representative $R$-parity-violating supersymmetry and leptoquark signals. All yields are MC generator-weighted...

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