Abstract
We investigate the sensitivity of electron-proton (ep) colliders for charged lepton flavor violation (cLFV) in an effective theory approach, considering a general effective Lagrangian for the conversion of an electron into a muon or a tau via the effective coupling to a neutral gauge boson or a neutral scalar field. For the photon, the Z boson and the Higgs particle of the Standard Model, we present the sensitivities of the LHeC for the coefficients of the effective operators, calculated from an analysis at the reconstructed level. As an example model where such flavor changing neutral current (FCNC) operators are generated at loop level, we consider the extension of the Standard Model by sterile neutrinos. We show that the LHeC could already probe the LFV conversion of an electron into a muon beyond the current experimental bounds, and could reach more than an order of magnitude higher sensitivity than the present limits for LFV conversion of an electron into a tau. We discuss that the high sensitivities are possible because the converted charged lepton is dominantly emitted in the backward direction, enabling an efficient separation of the signal from the background.
Highlights
In this paper, we show that future electron-proton colliders such as the Large Hadron electron Collider (LHeC) would be excellent facilities for probing the charged lepton flavor violation (cLFV) conversion of an electron into a muon or a tau via the effective coupling to a neutral gauge boson or a neutral scalar
As an example model where such flavor changing neutral current (FCNC) operators are generated at loop level, we consider the extension of the Standard Model by sterile neutrinos
In this work we have investigated the sensitivity of electron-proton colliders, in particular of the LHeC, for charged lepton flavor violation
Summary
Compared to electron-positron colliders, the high center-of-mass energy at ep colliders can provide an environment to test the SM at high energies with comparably low rates of background. The proposed electronproton experiment at the FCC (FCC-eh) is designed with the same energy level of the electron beam from the LHeC electron linac, but with the upgraded proton beam with energy of 50 TeV from the FCC-hh This will achieve a center of mass energy of 3.5 TeV. Charged lepton flavor violating processes can occur at the LHeC through an effective vertex that couples the incoming electron to a muon or a tau and a neutral scalar or vector boson. The effective FCNC Lagrangian for charged leptons contains effective operators coupling the charged leptons to neutral scalars and neutral vector bosons. The part of the effective Lagrangian for the coupling to vector bosons can be expressed in terms of monopole and dipole operators. DL,R denoting the left and right form factors of the dipole operator
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