Search for type-III seesaw heavy leptons in leptonic final states in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

The ATLAS collaboration
Eur.Phys.J.C 82 (2022) 988, 2022.

Abstract
A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139 fb$^{-1}$ of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on final states with three or four electrons or muons from the possible decays of new heavy leptons via intermediate electroweak bosons. No significant deviations above the Standard Model expectation are observed; upper and lower limits on the heavy lepton production cross-section and masses are derived respectively. These results are then combined for the first time with the ones already published by ATLAS using the channel with two leptons in the final state. The observed lower limit on the mass of the type-III seesaw heavy leptons combining two, three and four lepton channels together is 910 GeV at the 95% confidence level.

  • Table 1

    Data from Table 4

    10.17182/hepdata.114228.v1/t1

    Expected background yields and observed data after the background-only fit in the SRs.

  • Table 2

    Data from Figure 3a

    10.17182/hepdata.114228.v1/t2

    Distribution of $m_{\mathrm{T},3l}$ in the ZL SR after the background-only fit. The uncertainty on the expected number of background events...

  • Table 3

    Data from Figure 3b

    10.17182/hepdata.114228.v1/t3

    Distribution of $m_{\mathrm{T},3l}$ in the ZL Veto SR after the background-only fit. The uncertainty on the expected number of background...

  • Table 4

    Data from Figure 3c

    10.17182/hepdata.114228.v1/t4

    Distribution of $m_{\mathrm{T},3l}$ in the JNLow SR after the background-only fit. The uncertainty on the expected number of background events...

  • Table 5

    Data from Figure 4a

    10.17182/hepdata.114228.v1/t5

    Distribution of $H_\text{T} + E_\text{T}^\text{miss}$ in the Q0 SR after the background-only fit. The uncertainty on the expected number of...

  • Table 6

    Data from Figure 4b

    10.17182/hepdata.114228.v1/t6

    Distribution of $H_\text{T} + E_\text{T}^\text{miss}$ in the Q2 SR after the background-only fit. The uncertainty on the expected number of...

  • Table 7

    Data from Figure 5a

    10.17182/hepdata.114228.v1/t7

    Distribution of $m_{\mathrm{T},3l}$ in the ZL-CR after the background-only fit.

  • Table 8

    Data from Figure 5b

    10.17182/hepdata.114228.v1/t8

    Distribution of $m_{\mathrm{T},3l}$ in the Fake-CR after the background-only fit.

  • Table 9

    Data from Figure 5c

    10.17182/hepdata.114228.v1/t9

    Distribution of $H_\text{T} + E_\text{T}^\text{miss}$ in the Q0 DB-CR after the background-only fit.

  • Table 10

    Data from Figure 5d

    10.17182/hepdata.114228.v1/t10

    Distribution of $H_\text{T} + E_\text{T}^\text{miss}$ in the Q0 RT-CR after the background-only fit.

  • Table 11

    Data from Figure 7

    10.17182/hepdata.114228.v1/t11

    Expected and observed exclusion limit for the combination of the two- (from Ref. EXOT-2018-33), three- and four-lepton channels, for the...

  • Table 12

    Data from Figure 8

    10.17182/hepdata.114228.v1/t12

    Expected and observed 95% ( $CL_s$ ) exclusion limits in the three lepton channel for the type-III seesaw process with...

  • Table 13

    Data from Figure 9

    10.17182/hepdata.114228.v1/t13

    Expected and observed 95% ( $CL_s$ ) exclusion limits in the four lepton channel for the type-III seesaw process with...

  • Table 14

    Data from Table 1 in auxiliary material

    10.17182/hepdata.114228.v1/t14

    Cross-sections of signal Monte Carlo samples for each mass point considered in this analysis. Leading order cross-sections ( $\sigma_{LO}$ )...

  • Table 15

    Data from Table 2 in auxiliary material

    10.17182/hepdata.114228.v1/t15

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 16

    Data from Table 3 in auxiliary material

    10.17182/hepdata.114228.v1/t16

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 17

    Data from Table 4 in auxiliary material

    10.17182/hepdata.114228.v1/t17

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 18

    Data from Table 5 in auxiliary material

    10.17182/hepdata.114228.v1/t18

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 19

    Data from Table 6 in auxiliary material

    10.17182/hepdata.114228.v1/t19

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 20

    Data from Table 7 in auxiliary material

    10.17182/hepdata.114228.v1/t20

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 21

    Data from Table 8 in auxiliary material

    10.17182/hepdata.114228.v1/t21

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 22

    Data from Table 9 in auxiliary material

    10.17182/hepdata.114228.v1/t22

    Expected signal and background yields after each of the analysis selection cuts for the 800 GeV mass hypothesis in the...

  • Table 23

    Data from Table 10 in auxiliary material

    10.17182/hepdata.114228.v1/t23

    Expected background yields and observed data after the background-only fit, in the three-lepton CRs and VRs.

  • Table 24

    Data from Table 11 in auxiliary material

    10.17182/hepdata.114228.v1/t24

    Expected background yields and observed data after the background-only fit, in the four-lepton CRs and VRs.

  • Table 25

    Data from Figure 1 in auxiliary material

    10.17182/hepdata.114228.v1/t25

    Expected and observed 95% ( $CL_s$ ) exclusion limits in the three and four lepton channels for the type-III seesaw...

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