Lepton Flavor Violation at muon-electron colliders

Abstract

Lepton Flavor Violating (LFV) processes are clear signals of physics beyond the Standard Model. We investigate the possibility of measuring this kind of processes at present and foreseeable future muon-electron colliders, taking into account present day bounds from existing experiments. As a model of new physics we consider a Z’ boson with a Ut(1) gauge symmetry and generic couplings. Processes that violate lepton flavor by two units seem to be particularly promising.

Two-to-Two Processes at an Electron-Muon Collider

“…In addition, the recent confirmation of a significant deviation from the Standard Model (SM) value of ðg − 2Þ μ at Fermilab [9] has also encouraged the proposal of new physics models [10][11][12][13][14][15][16][17] as well as the calculation of higher order QED contributions to the eμ ⟶ eμ scattering process [18,19]. The idea of electronmuon collisions has been analyzed in past decades [20][21][22][23][24][25], and recently, it has been brought up again in a study of an extra Z ′ boson with generic couplings that could be searched for through a Lepton Flavor Violating (LFV) process like e − μ + ⟶ e + μ − [26]. In a subsequent article, the construction of a high energy e − μ + collider has been proposed [27].…”

$Μ$tristan

“…In Refs. [10,11], good physics performances of µ + e − colliders have been demonstrated for the measurements of the Higgs boson couplings as well as searches for lepton flavor violating interactions by assuming integrated luminosities of the order of ab −1 . It is then an important question whether such a collider can be constructed in a timely manner.…”

The Physics Case for an Electron-Muon Collider

“…Recently, a new experiment, MUonE [22], has been proposed, through elastic scattering of high-energy muons at around 150 GeV on atomic electrons, to determine the leading hadronic contribution to the muon g-2. A head-on electron-muon collider was first proposed in the 1990s [23][24][25] mainly to probe charged lepton flavor violation (CLFV) [26], which, however, has not been followed up much by the community. Here, we propose for the first time an electron-muon collider with more detailed configurations to run at both low and high energy, with broader physics goals to cover both CLFV and Higgs studies.…”

“…An electron-muon collider could operate at multiple energies to search for CLFV in eμ ⟶ Z and H, or eμ ⟶ ee, etc. Here, we take Higgs CLFV as an example (some other examples are discussed in [26]), which is interesting because its observation may provide insight into some fundamental questions in nature, e.g., whether there is a secondary mech-anism for the electroweak symmetry breaking. H ⟶ eμ has already been studied at the LHC [27,28], and the most stringent limit so far, from ATLAS, is BrðH ⟶ eμÞ < 6:2 × 10 −5 [28].…”