Lepton flavor violation and dilepton tails at the LHC

Andrei Angelescu; Darius A. Faroughy; Olcyr Sumensari

doi:10.1140/epjc/s10052-020-8210-5

EPJ

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2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2020) 80: 641
https://doi.org/10.1140/epjc/s10052-020-8210-5

Regular Article - Theoretical Physics

Lepton flavor violation and dilepton tails at the LHC

Andrei Angelescu¹^*, Darius A. Faroughy² and Olcyr Sumensari³^,4

¹ Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
² Physik-Institut, Universität Zürich, 8057, Zürich, Switzerland
³ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Padua, Italy
⁴ Istituto Nazionale Fisica Nucleare, Sezione di Padova, 35131, Padua, Italy

^* e-mail: aangelescu2@unl.edu

Received: 16 March 2020
Accepted: 7 July 2020
Published online: 19 July 2020

Abstract

Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes $pp \rightarrow \ell _k \ell _l$ (with $k\ne l$ ). The current (projected) limits derived in this paper from LHC data with $36~\mathrm {fb}^{-1}$ ( $3~\mathrm {ab}^{-1}$ ) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic $b\rightarrow d$ transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays $K\rightarrow \pi \ell ^{\pm }_k \ell ^{{\mp }}_l$ , $B\rightarrow \pi \ell ^{\pm }_k \ell ^{{\mp }}_l$ and $B\rightarrow K^{(*)} \ell ^{\pm }_k \ell ^{{\mp }}_l$ .