https://doi.org/10.1140/epjc/s10052-017-4864-z
Regular Article - Theoretical Physics
In-flight cLFV conversion: 
, 
and 
in minimal extensions of the standard model with sterile fermions
1
Laboratoire de Physique Théorique, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405, Orsay, France
2
Departamento de Física Teórica and Instituto de Física Teórica, IFT-UAM/CSIC, Universidad Autónoma de Madrid, Cantoblanco, 28049, Madrid, Spain
3
Laboratoire de Physique Corpusculaire, CNRS/IN2P3-UMR 6533, Campus des Cézeaux, 4 Av. Blaise Pascal, 63178, Aubière Cedex, France
* e-mail: deromeri@ific.uv.es
Received:
17
January
2017
Accepted:
26
April
2017
Published online:
12
May
2017
We revisit charged lepton flavour in-flight conversions, in which a beam of electrons or muons is directed onto a fixed target, 
, 
and 
, focusing on elastic interactions with a nucleus N. After a general discussion of this observable, we carry a full phenomenological analysis in the framework of minimal Standard Model extensions via sterile neutrinos, with a strong emphasis on the rôle of the increasingly more stringent constraints arising from other (low-energy) charged lepton flavour-violation observables. Despite the potential interest of this observable, in particular in the light of certain upcoming facilities with the capability of very intense lepton beams, our study suggests that due to current bounds on three-body decays (
) and 
conversion in nuclei, the expected number of conversions in such a minimal framework is dramatically reduced. An experimental observation of such a conversion would thus signal the presence of another source of flavour violation, possibly at tree level.
© The Author(s), 2017
