Abstract
We present a comprehensive analysis of the potential sensitivity of the Electron-Ion Collider (EIC) to charged lepton flavor violation (CLFV) in the channel ep→τX, within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). We compute the relevant cross sections to leading order in QCD and electroweak corrections and perform simulations of signal and SM background events in various τ decay channels, suggesting simple cuts to enhance the associated estimated efficiencies. To assess the discovery potential of the EIC in τ-e transitions, we study the sensitivity of other probes of this physics across a broad range of energy scales, from pp→eτX at the Large Hadron Collider to decays of B mesons and τ leptons, such as τ→eγ, τ→eℓ+ℓ−, and crucially the hadronic modes τ→eY with Y∈{π, K, ππ, Kπ, …}. We find that electroweak dipole and four-fermion semi-leptonic operators involving light quarks are already strongly constrained by τ decays, while operators involving the c and b quarks present more promising discovery potential for the EIC. An analysis of three models of leptoquarks confirms the expectations based on the SMEFT results. We also identify future directions needed to maximize the reach of the EIC in CLFV searches: these include an optimization of the τ tagger in hadronic channels, an exploration of background suppression through tagging b and c jets in the final state, and a global fit by turning on all SMEFT couplings, which will likely reveal new discovery windows for the EIC.
Highlights
Processes involving charged lepton flavor violation (CLFV) are very powerful tools to search for new physics beyond the Standard Model (BSM) for a number of reasons
We present a comprehensive analysis of the potential sensitivity of the Electron-Ion Collider (EIC) to charged lepton flavor violation (CLFV) in the channel ep → τ X, within the model-independent framework of the Standard Model Effective Field Theory (SMEFT)
The renormalization group equations (RGEs) in the SMEFT were derived in refs. [27,28,29] and we report them for convenience in appendix A, where we provide the numerical solutions of the RGEs at leading logarithmic accuracy
Summary
Processes involving charged lepton flavor violation (CLFV) are very powerful tools to search for new physics beyond the Standard Model (BSM) for a number of reasons. For EIC itself, we account for all leading (dimension-six) CLFV operators, including heavy quark operators, in computing EIC’s reach in inclusive and differential ep → τ X searches We compare this reach with all existing CLFV probes today, at both high and low energy, within the model-independent framework of SMEFT. These include searches for pp → eτ at the LHC and decays of the τ lepton (τ → eY ) and B meson. In the context of this rich literature, our work introduces several new elements: the use of the full set of SMEFT operators, the study of a larger set of probes (including LHC and B meson decays besides all CLFV τ decays) and the focus on the EIC sensitivity and reach.
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