Lepton Flavor Violation at muon-electron colliders
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Springer
Received: March 17, Revised: August 11, Accepted: August 31, Published: October 6,
2020 2020 2020 2020
Fabio Bossia and Paolo Ciafalonib a
INFN — Laboratori Nazionali di Frascati, Via Enrico Fermi 54, I-00044, Italy b INFN — Sezione di Lecce, Via per Arnesano, I-73100 Lecce, Italy
E-mail: [email protected], [email protected] 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 U 0 (1) gauge symmetry and generic couplings. Processes that violate lepton flavor by two units seem to be particularly promising. Keywords: Beyond Standard Model, Global Symmetries ArXiv ePrint: 2003.03997
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP10(2020)033
JHEP10(2020)033
Lepton Flavor Violation at muon-electron colliders
Contents 1
2 Physics case
2
3 Low energy bounds on Z’ couplings
3
4 e+ µ− → e− µ+ and e− µ+ → e+ µ+
5
5 Other processes
7
6 Conclusions
8
1
Electron-muon collisions
Electron-muon collisions have been so far studied using the interaction of a muon beam with a fixed target. Muon beams can have energies up to several hundreds GeV, fluxes of 107 -108 particles per second and transverse dimensions of order of a few centimeters [1–3]. Although with this technique one can in principle reach very high luminosities by the use of properly studied targets, the available center of mass energy (c.m.e.) is strongly suppressed because of the Lorenz boost. In recent years, however, a very intense R&D program has been put forward in many laboratories to develop techniques to obtain very high energy muon-muon interactions in collider mode, motivated by the possibility of producing collisions of point-like particles at very high energy without the limitation from synchrotron radiation typical of electronpositron machines. In these studies muons are produced either as decay products of pions from fixed-target proton-proton collisions, or as a result of pair production in electronpositron collisions. Typically, at c.m.e. of 6 TeV, two single bunches of 2×1012 muons, each of transverse dimensions of ∼1.5 µm, collide at a rate of ∼50 kHz, providing a peak luminosity largely exceeding 1034 cm−2 s−1 [4–7]. One of the main technical limitations to obtain high luminosity comes from the difficulty in producing highly collimated muon beams. A big step forward in this direction has been recently reported by the MICE collaboration which has been able to confirm the success of a ionization cooling experiment on a low momentum muon beam using properly designed absorbers [8]. This experiment has to be considered as an important advance in the development of high brightness muon beams. In this paper we want to call the attention to the fact that such beams could also be us
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