Search for the lepton-flavour violating decays B0 → K*0μ±e∓ and $$ {B}_s^0 $$ → ϕμ±e∓

Abstract

A search for the lepton-flavour violating decays B0 → K*0μ±e∓ and $$ {B}_s^0 $$ B s 0 → ϕμ±e∓ is presented, using proton-proton collision data collected by the LHCb detector at the LHC, corresponding to an integrated luminosity of 9 fb−1. No significant signals are observed and upper limits of$$ {\displaystyle \begin{array}{c}\mathcal{B}\left({B}^0\to {K}^{\ast 0}{\mu}^{+}{e}^{-}\right)<5.7\times {10}^{-9}\left(6.9\times {10}^{-9}\right),\\ {}\mathcal{B}\left({B}^0\to {K}^{\ast 0}{\mu}^{-}{e}^{+}\right)<6.8\times {10}^{-9}\left(7.9\times {10}^{-9}\right),\\ {}\mathcal{B}\left({B}^0\to {K}^{\ast 0}{\mu}^{\pm }{e}^{\mp}\right)<10.1\times {10}^{-9}\left(11.7\times {10}^{-9}\right),\\ {}\mathcal{B}\left({B}_s^0\to \phi {\mu}^{\pm }{e}^{\mp}\right)<16.0\times {10}^{-9}\left(19.8\times {10}^{-9}\right)\end{array}} $$ B B 0 → K ∗ 0 μ + e − < 5.7 × 10 − 9 6.9 × 10 − 9 , B B 0 → K ∗ 0 μ − e + < 6.8 × 10 − 9 7.9 × 10 − 9 , B B 0 → K ∗ 0 μ ± e ∓ < 10.1 × 10 − 9 11.7 × 10 − 9 , B B s 0 → ϕ μ ± e ∓ < 16.0 × 10 − 9 19.8 × 10 − 9 are set at 90% (95%) confidence level. These results constitute the world’s most stringent limits to date, with the limit on the decay $$ {B}_s^0 $$ B s 0 → ϕμ±e∓ the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios.

Tests of Lepton Flavour Universality and searches for Lepton Flavour Violation at LHCb

“…In addition to testing LFU, LHCb also explores transitions of the form 𝑏 → 𝑠ℓ ′ ℓ, that would indicate lepton flavour violation. Thus far, no evidence for such decays has been observed, leading to stringent limits on their existence [11].…”

“…Recent results on these searches are published in Ref. [11], where no significant signal for any of the signatures is found and hence a limit of B (𝐵 0 → 𝐾 * 0 𝜇 ± 𝑒 ∓ ) < 9.9 × 10 −9 (90 % CL), B (𝐵 0 𝑠 → 𝜙𝜇 ± 𝑒 ∓ ) < 16 × 10 −9 (90 % CL) is set at 90 % confidence level. These limits are the most stringent limits for these decays to date and place strong constraints on New Physics scenarios involving lepton flavour violation.…”

Charged Lepton-Flavour Violation

“…Figure 12 shows signal candidates for the lepton-flavour violating decays B 0 → K * 0 µ + e − and B 0 → K * 0 µ − e + using LHCb data corresponding to an integrated luminosity of 9 fb −1 . No significant signal is observed and LHCb sets limits of B(B 0 → K * 0 µ + e − ) < 5.7 × 10 −9 , B(B 0 → K * 0 µ − e + ) < 6.8 × 10 −9 , and B(B 0 s → ϕµ ± e ∓ ) < 16.0 × 10 −9 at 90% CL [71]. For the decay B + → K + µ ± e ∓ , LHCb sets the limits of B(B + → K + µ + e − ) < 6.4 × 10 −9 and B(B + → K + µ − e + ) < 7.0 × 10 −9 at 90% CL using 3 fb −1 of data [72].…”

The LHCb Upgrade I

“…The most widely adopted fast-simulation option (see for example refs. [231][232][233][234]) is implemented in the ReDecay package [235]. Once a signal process is identified, for example the production of a heavy hadron, multiple random instances of its decay products are propagated through the detector while the detector response to the rest of the event is computed only once and superposed to the decay products of the signal particle.…”