Flavorful Lepton Number Violation at the EIC

Abstract

We explore the prospects of detecting flavorful lepton number violation at the Electron-Ion Collider (EIC) through resonant production of heavy neutral leptons (HNLs), resulting in $e^- p \to \ell^+_α+ k\, j+X$, where $α\in \{e, μ, τ\}$ and $k$ denotes the number of jets. We work in the $ν$SMEFT framework of the Standard Model Effective Field Theory augmented with $n$ singlet HNLs, one of which is in the mass range $10-100$~GeV, within kinematic reach of the EIC. To explore the EIC sensitivity, we focus on the HNL production mechanism induced by mixing with light neutrinos. We study kinematic distributions for signal and backgrounds, including hadronization and detector effects, and suggest a set of cuts to minimize backgrounds. In the mass range considered, we find that the EIC with muon detection capabilities and an integrated luminosity of $100~\mathrm{fb}^{-1}$ can reach sensitivities comparable to the strongest direct (LHC) and indirect constraints, and is especially relevant in the $ν$SMEFT framework beyond dimension four. Our study motivates further assessment of muon detection capabilities at the EIC and $τ$ hadronic reconstruction, as well as a more general theoretical analysis involving production mechanisms mediated by higher-dimensional operators in the effective theory.

Figures (11)

• Figure 1: Parton-level diagrams for the process $e^-p\to \ell_\alpha^++k\,j+X$ ($\alpha\in\{e,\mu,\tau\}$), where $k$ denotes the number of jets.
• Figure 2: Kinematic distributions for the electron channel $e^-p\to e^+jj(j)$ after imposing the signal selection cuts (Cut-SS) in Box \ref{['box:signal_selection']}. Background contributions are shown as filled histograms, while representative HNL mass benchmarks are displayed as solid lines.
• Figure 3: Kinematic distributions for the muon channel $e^-p\to\mu^+jj(j)$, with the same conventions as in Fig. \ref{['fig:distributions_electron_bkg']}.
• Figure 4: Kinematic distributions for the $\tau$ channel $e^-p\to\tau^+jj(j)$, with the same conventions as in Fig. \ref{['fig:distributions_electron_bkg']}.
• Figure 5: Expected 95% C.L. exclusion limits from the electron channel $e^-p\to e^+jj(j)$ at the EIC with $\sqrt{s}=141\,\mathrm{GeV}$ ($E_e\times E_p=18\,\mathrm{GeV}\times275\,\mathrm{GeV}$), integrated luminosity $\mathcal{L}=100\,\mathrm{fb}^{-1}$, and electron polarization $P_e=70\%$. A charge-misidentification probability $P_{\rm misID}=10^{-3}$ is assumed. The solid red curve shows the limits obtained after applying the kinematic cuts (Cut-$e$) of Box \ref{['box:cut_e']}, while the red dot-dashed curve corresponds to a maximally optimistic scenario with complete background rejection and perfect signal reconstruction (see text for details). The dashed green curve corresponds to a CMS analysis at the LHC probing the same coupling combination through resonant production in $\ell$ + jets final states, using a comparable analysis strategy CMS:2018jxx.