Dib Venturelli, Claudio Omar

Abstract We consider light neutralinos of mass about 1 GeV, produced from τ lepton rare decays at Belle II, in the context of R-parity-violating (RPV) supersymmetry. With large and clean samples of τ leptons produced at the Belle II experiment, excellent sensitivity to such light neutralinos with the exotic signatures of displaced vertices is expected. We focus on two benchmark scenarios of single RPV operators, $$ {\lambda}_{311}^{\prime }{L}_3{Q}_1{\overline{D}}_1 $$ λ 311 ′ L 3 Q 1 D ¯ 1 and $$ {\lambda}_{312}^{\prime }{L}_3{Q}_1{\overline{D}}_2 $$ λ 312 ′ L 3 Q 1 D ¯ 2 , which induce both the production and decay of the lightest neutralino. For the reconstruction of a displaced vertex, we require at least two charged pions in the final states. We perform Monte-Carlo simulations for both signal and background events, and find that Belle II can explore regions in the parameter space competitive with other probes. In particular, for the $$ {\lambda}_{311}^{\prime } $$ λ 311 ′ scenario, it can put limits up to two orders of magnitude stronger than the current bounds.

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.