Dib Venturelli, Claudio Omar

We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neu- tral vector bosons V = ρ0, ω, φ, J/ψ, Υ, Z0, as well as pseudoscalar P = π0, η, η′, ηc and scalar S = f0(500), f0(980), a0(980), χc0(1P ) mesons, without referring to a specific mechanism of LFV realization. In particular, we relate the rates of the three-body LFV decays τ (μ) → 3`, where ` = μ or e, to the two-body LFV decays (V, P ) → τ μ(τ e, μe), where V and P play the role of intermediate resonances in the decay process τ (μ) → 3`. From the experimental upper bounds for the branching ratios of τ (μ) → 3` decays, we derive upper limits for the branching ratios of (V, P ) → τ μ(τ e, μe). We compare our results to the available experimental data and known theoretical upper limits from previous studies of LFV processes and find that some of our limits are several orders of magnitude more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton dimension-six LFV operators from data on lepton decays. Some of these limits are either new or stronger than those existing in the literature.

Abstract We propose a search for B meson decays to a baryon plus missing energy at the Belle II experiment to probe supersymmetry with a GeV-scale lightest neutralino $$ {\overset{\sim }{\chi}}_1^0 $$ χ ~ 1 0 and R-parity violation (RPV). We perform analytic computations of the signal branching fractions in the framework of effective field theory, with a single nonzero RPV operator $$ {\lambda}_{ij3}^{\prime \prime }{\overline{U}}_i^c{\overline{D}}_j^c{\overline{D}}_3^c $$ λ ij 3 ′ ′ U ¯ i c D ¯ j c D ¯ 3 c , where i, j = 1, 2. The hadronic form factors are calculated using an SU(3) phenomenological Lagrangian approach for the proton, as well as several hyperons and charmed baryons. Since the decay of the neutralino is kinematically and CKM suppressed in this theoretical scenario, it decays outside the detector and appears experimentally only as missing energy. We detail the analysis techniques at the experimental level and estimate the background in the $$ {B}^{+}\to p{\overset{\sim }{\chi}}_1^0 $$ B + → p χ ~ 1 0 search using published results for $$ {B}^{+}\to {K}^{+}\nu \overline{\nu} $$ B + → K + ν ν ¯ . Our final sensitivity plots are shown for both $$ {\lambda}_{113}^{\prime \prime } $$ λ 113 ′ ′ versus the squark mass $$ {m}_{\tilde{q}} $$ m q ~ and $$ {\lambda}_{113}^{\prime \prime }/{m}_{\tilde{q}}^2 $$ λ 113 ′ ′ / m q ~ 2 versus the neutralino mass $$ {m}_{{\overset{\sim }{\chi}}_1^0} $$ m χ ~ 1 0 . We find that the search at Belle II could probe $$ {\lambda}_{113}^{\prime \prime }/{m}_{\tilde{q}}^2 $$ λ 113 ′ ′ / m q ~ 2 down to the order of 10−8 GeV−2 in the kinematically allowed $$ {m}_{{\overset{\sim }{\chi}}_1^0} $$ m χ ~ 1 0 range. We also obtain current limits on $$ {\lambda}_{123}^{\prime \prime } $$ λ 123 ′ ′ by recasting an existing search interpreted as $$ {B}^0\to {\Lambda}^0{\overset{\sim }{\chi}}_1^0 $$ B 0 → Λ 0 χ ~ 1 0 , and comment about searches for $$ {B}^{+}\to {\Sigma}^{+}{\overset{\sim }{\chi}}_1^0 $$ B + → Σ + χ ~ 1 0 , $$ {B}^0\to {\Sigma}^0{\chi}_1^0 $$ B 0 → Σ 0 χ 1 0 , $$ {B}^{+}\to {\Lambda}_c^{+}{\overset{\sim }{\chi}}_1^0 $$ B + → Λ c + χ ~ 1 0 , and $$ {B}^{+}\to {\Xi}_c^{+}{\overset{\sim }{\chi}}_1^0 $$ B + → Ξ c + χ ~ 1 0 . In closing, we briefly discuss potential searches at the LHCb and BESIII experiments.