https://doi.org/10.1140/epjc/s10052-017-5488-z
Regular Article - Theoretical Physics
CP violation in leptonic rare 
decays as a probe of new physics
1
Nikhef, Science Park 105, 1098 XG, Amsterdam, The Netherlands
2
Department of Physics and Astronomy, Vrije Universiteit Amsterdam, 1081 HV, Amsterdam, The Netherlands
3
Physics Department, Université Paris-Sud, 91405, Orsay, France
* e-mail: robert.fleischer@nikhef.nl
Received:
20
November
2017
Accepted:
19
December
2017
Published online:
29
December
2017
The decay 
is a key probe for the search of physics beyond the Standard Model. While the current measurements of the corresponding branching ratio agree with the Standard Model within the uncertainties, significant New-Physics effects may still be hiding in . In order to reveal them, the observable 
, which is provided by the decay width difference 
of the -meson system, plays a central role. We point out that a measurement of a CP-violating observable 
, which is induced through interference between –
mixing and 
decay processes, is essential to obtain the full picture, in particular to establish new scalar contributions and CP-violating phases. We illustrate these findings with future scenarios for the upgrade(s) of the LHC, exploiting also relations which emerge within an effective field theory description of the Standard Model, complemented with New Physics entering significantly beyond the electroweak scale.
© The Author(s), 2017
