Testing lepton flavour universality with (semi)-leptonic decays

Robert Fleischer; Ruben Jaarsma; Gabriël Koole

doi:10.1140/epjc/s10052-020-7702-7

2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2020) 80: 153
https://doi.org/10.1140/epjc/s10052-020-7702-7

Regular Article - Theoretical Physics

Testing lepton flavour universality with (semi)-leptonic $D_{(s)}$ $\varvec{D_{(s)}}$ decays

Robert Fleischer¹^,2, Ruben Jaarsma¹ and Gabriël Koole¹^,3^c

¹ Nikhef, Science Park 105, 1098 XG, Amsterdam, The Netherlands
² Faculty of Science, Vrije Universiteit Amsterdam, 1081 HV, Amsterdam, The Netherlands
³ Max Planck Institute for Physics, Föhringer Ring 6, 80805, Munich, Germany

^c koole@mpp.mpg.de

Received: 2 January 2020
Accepted: 30 January 2020
Published online: 20 February 2020

Abstract

Data in B-meson decays indicate violations of lepton flavour universality, thereby raising the question about such phenomena in the charm sector. We perform a model-independent analysis of NP contributions in (semi)-leptonic decays of $D_{(s)}$ $D_{(s)}$ mesons which originate from $c \to d \bar{ℓ} ν_{l}$ $c \rightarrow d \bar{{\ell }} \nu _l$ and $c \to s \bar{ℓ} ν_{ℓ}$ $c \rightarrow s \bar{{\ell }} \nu _{\ell }$ charged-current interactions. Starting from the most general low-energy effective Hamiltonian containing four-fermion operators and the corresponding short-distance coefficients, we explore the impact of new (pseudo)-scalar, vector and tensor operators and constrain their effects through the interplay with current data. We pay special attention to the elements $| V_{cd} |$ $|V_{cd}|$ and $| V_{cs} |$ $|V_{cs}|$ of the Cabibbo–Kobayashi–Maskawa matrix and extract them from the $D_{(s)}$ $D_{(s)}$ decays in the presence of possible NP decay contributions, comparing them with determinations utilizing unitarity. We find a picture in agreement with the Standard Model within the current uncertainties. Using the results from our analysis, we make also predictions for leptonic $D_{(s)}^{+} \to e^{+} ν_{e}$ $D_{(s)}^+ \rightarrow e^+ \nu _e$ modes which could be hugely enhanced with respect to their tiny Standard Model branching ratios. It will be interesting to apply our strategy at the future high-precision frontier.

© The Author(s) 2020

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