Search for heavy neutral leptons in final states with electrons, muons, and hadronically decaying tau leptons in proton-proton collisions at $\sqrt{s}$ =13 TeV

The CMS collaboration
JHEP 06 (2024) 123, 2024.

Abstract
A search for heavy neutral leptons (HNLs) of Majorana or Dirac type using proton-proton collision data at $\sqrt{s}$ = 13 TeV is presented. The data were collected by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. Events with three charged leptons (electrons, muons, and hadronically decaying tau leptons) are selected, corresponding to HNL production in association with a charged lepton and decay of the HNL to two charged leptons and a standard model (SM) neutrino. The search is performed for HNL masses between 10 GeV and 1.5 TeV. No evidence for an HNL signal is observed in data. Upper limits at 95% confidence level are found for the squared coupling strength of the HNL to SM neutrinos, considering exclusive coupling of the HNL to a single SM neutrino generation, for both Majorana and Dirac HNLs. The limits exceed previously achieved experimental constraints for a wide range of HNL masses, and the limits on tau neutrino coupling scenarios with HNL masses above the W boson mass are presented for the first time.

  • Limits on Majorana HNL with electron coupling

    Figure 12 (top left)

    10.17182/hepdata.146676.v1/t1

    The 95% CL limits on $|V_{eN}|^2$ as a function of the HNL mass for a Majorana HNL.

  • Limits on Majorana HNL with muon coupling

    Figure 12 (middle left)

    10.17182/hepdata.146676.v1/t2

    The 95% CL limits on $|V_{\mu N}|^2$ as a function of the HNL mass for a Majorana HNL.

  • Limits on Majorana HNL with tau coupling

    Figure 12 (bottom left)

    10.17182/hepdata.146676.v1/t3

    The 95% CL limits on $|V_{\tau N}|^2$ as a function of the HNL mass for a Majorana HNL.

  • Limits on Dirac HNL with electron coupling

    Figure 12 (top right)

    10.17182/hepdata.146676.v1/t4

    The 95% CL limits on $|V_{eN}|^2$ as a function of the HNL mass for a Dirac HNL.

  • Limits on Dirac HNL with muon coupling

    Figure 12 (middle right)

    10.17182/hepdata.146676.v1/t5

    The 95% CL limits on $|V_{\mu N}|^2$ as a function of the HNL mass for a Dirac HNL.

  • Limits on Dirac HNL with tau coupling

    Figure 12 (bottom right)

    10.17182/hepdata.146676.v1/t6

    The 95% CL limits on $|V_{\tau N}|^2$ as a function of the HNL mass for a Dirac HNL.

  • Data and background yields (Low Mass Region La)

    Figure 8

    10.17182/hepdata.146676.v1/t7

    Comparison of the number of predicted background events and the observed events in search regions La. The predicted background yields...

  • Predicted signal yields (Low Mass Region La, $e$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t8

    Signal yields predicted in search regions La as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (Low Mass Region La, $\mu$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t9

    Signal yields predicted in search regions La as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (Low Mass Region La, $\tau$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t10

    Signal yields predicted in search regions La as function of HNL mass and coupling strength for a scenario with exclusive...

  • Data and background yields (Low Mass Region Lb)

    Figure 8

    10.17182/hepdata.146676.v1/t11

    Comparison of the number of predicted background events and the observed events in search regions Lb. The predicted background yields...

  • Predicted signal yields (Low Mass Region Lb, $e$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t12

    Signal yields predicted in search regions Lb as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (Low Mass Region Lb, $\mu$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t13

    Signal yields predicted in search regions Lb as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (Low Mass Region Lb, $\tau$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t14

    Signal yields predicted in search regions Lb as function of HNL mass and coupling strength for a scenario with exclusive...

  • Data and background yields (High Mass Region Ha)

    Figure 8

    10.17182/hepdata.146676.v1/t15

    Comparison of the number of predicted background events and the observed events in search regions Ha. The predicted background yields...

  • Predicted signal yields (High Mass Region Ha, $e$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t16

    Signal yields predicted in search regions Ha as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (High Mass Region Ha, $\mu$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t17

    Signal yields predicted in search regions Ha as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (High Mass Region Ha, $\tau$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t18

    Signal yields predicted in search regions Ha as function of HNL mass and coupling strength for a scenario with exclusive...

  • Data and background yields (High Mass Region Hb)

    Figure 8

    10.17182/hepdata.146676.v1/t19

    Comparison of the number of predicted background events and the observed events in search regions Hb. The predicted background yields...

  • Predicted signal yields (High Mass Region Hb, $e$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t20

    Signal yields predicted in search regions Hb as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (High Mass Region Hb, $\mu$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t21

    Signal yields predicted in search regions Hb as function of HNL mass and coupling strength for a scenario with exclusive...

  • Predicted signal yields (High Mass Region Hb, $\tau$-coupling)

    Figure 8

    10.17182/hepdata.146676.v1/t22

    Signal yields predicted in search regions Hb as function of HNL mass and coupling strength for a scenario with exclusive...

  • Covariance Matrix (Low Mass SR La)

    10.17182/hepdata.146676.v1/t23

    Covariance matrix for the postfit background prediction in signal region bins La.

  • Covariance Matrix (Low Mass SR Lb)

    10.17182/hepdata.146676.v1/t24

    Covariance matrix for the postfit background prediction in signal region bins Lb.

  • Covariance Matrix (High Mass SR Ha)

    10.17182/hepdata.146676.v1/t25

    Covariance matrix for the postfit background prediction in signal region bins Ha.

  • Covariance Matrix (High Mass SR Hb)

    10.17182/hepdata.146676.v1/t26

    Covariance matrix for the postfit background prediction in signal region bins Hb.

  • Cut flow: e-coupling, low mass region

    10.17182/hepdata.146676.v1/t27

    Simulated signal yields passing each stage of the low mass region selection as function of HNL mass and signal strength....

  • Cut flow: mu-coupling, low mass region

    10.17182/hepdata.146676.v1/t28

    Simulated signal yields passing each stage of the low mass region selection as function of HNL mass and signal strength....

  • Cut flow: tau-coupling, low mass region

    10.17182/hepdata.146676.v1/t29

    Simulated signal yields passing each stage of the low mass region selection as function of HNL mass and signal strength....

  • Cut flow: e-coupling, high mass region

    10.17182/hepdata.146676.v1/t30

    Simulated signal yields passing each stage of the high mass region selection as function of HNL mass and signal strength....

  • Cut flow: mu-coupling, high mass region

    10.17182/hepdata.146676.v1/t31

    Simulated signal yields passing each stage of the high mass region selection as function of HNL mass and signal strength....

  • Cut flow: tau-coupling, high mass region

    10.17182/hepdata.146676.v1/t32

    Simulated signal yields passing each stage of the high mass region selection as function of HNL mass and signal strength....

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