Search for the lepton-flavour violating decays B0 → K*0τ±μ∓

Abstract

A first search for the lepton-flavour violating decays B0 → K*0τ±μ∓ is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018, corresponding to an integrated luminosity of 9 fb−1. No significant signal is observed, and upper limits on the branching fractions are determined to be $$ \mathcal{B}\left({B}^0\to {K}^{\ast 0}{\tau}^{+}{\mu}^{-}\right)<1.0(1.2)\times {10}^{-5} $$ B B 0 → K ∗ 0 τ + μ − < 1.0 1.2 × 10 − 5 and $$ \mathcal{B}\left({B}^0\to {K}^{\ast 0}{\tau}^{-}{\mu}^{+}\right)<8.2(9.8)\times {10}^{-6} $$ B B 0 → K ∗ 0 τ − μ + < 8.2 9.8 × 10 − 6 at the 90% (95%) confidence level.

Charged Lepton-Flavour Violation

“…These collaborations, however, have set the most stringent limits on the decay B 0 → τ ± e ∓ of B(B 0 → τ ± e ∓ ) < 2.8 × 10 −5 and B(B 0 → τ ± e ∓ ) < 1.6 × 10 −5 at 90% CL, respectively [77,78]. Semileptonic b → sτ ± µ ∓ transitions have been searched for by LHCb, resulting in limits of B(B 0 → K * 0 τ + µ − ) < 1.0 × 10 −5 and B(B 0 → K * 0 τ − µ + ) < 8.2 × 10 −6 at 90% CL [79]. Using B * 0 s2 → B + K − decays, LHCb furthermore has set an upper limit of B(B + → K + µ − τ + ) < 3.9 × 10 −5 , also at 90% CL [80].…”

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

“…The decay 𝐵 0 → 𝐷 − (→ 𝐾 + 𝜋 − 𝜋 − )𝐷 + 𝑠 (→ 𝐾 + 𝐾 − 𝜋 + ) is used as normalisation mode. No significant excess was found and the first upper limits were set at 90(95%) confidence level [12]:…”

“…These proceedings focus on the recent measurements of the LFU ratios 𝑅 𝐾 and 𝑅 𝐾 * [9, 10], and searches for the Lepton Flavour Violating Decays 𝐵 0 → 𝐾 * 0 𝜇 ± 𝑒 ∓ , 𝐵 0 𝑠 → 𝜙𝜇 ± 𝑒 ∓ [11] and 𝐵 0 → 𝐾 * 0 𝜏 ± 𝜇 ∓ [12], all of them using the full Run 1 and Run 2 dataset (2011-18, 9 fb −1 ) 1.…”

Rare decays at Belle and Belle II

“…According to theory, if there is LFU violation there should be lepton-flavor violation (LFV) [11]. The best upper limits (ULs) for LFV + → + ℓ and 0 → * 0 decays are from BaBar [12] and LHCb [13], respectively, which are O (10 −5 ). Only + → + decay channel has been searched by BaBar using 342 fb −1 data sample and the upper limit is 2.45 × 10 −5 , while the SM expectation is O (10 −7 ).…”