Related papers: Displaced Searches for Light Vector Bosons at Bell…

The surprising excess of missing-energy events far beyond all standard-model expectations in the weak decays of the charged ground-state $B^+$ meson into some charged strange meson, rather recently observed by the Belle-II experiment, may…

The Belle II experiment at the SuperKEKB electron-positron collider aims to collect an unprecedented data set of $\rm 50~{\rm ab}^{-1}$ to study $CP$-violation in the $B$-meson system and to search for Physics beyond the Standard Model…

We consider light neutralinos of mass about 1 GeV, produced from $\tau$ lepton rare decays at Belle II, in the context of R-parity-violating (RPV) supersymmetry. With large and clean samples of $\tau$ leptons produced at the Belle II…

The upcoming MUonE experiment aims to precisely measure the running of the fine structure constant via elastic muon-electron scattering, to shed light on the current tension in the muon's anomalous magnetic moment. In addition to its…

We study the possibilities on the search of the light and weakly interacting gauge boson in the gauged $L_\mu - L_\tau$ model. Introducing the kinetic mixing at the tree-level, the allowed parameter regions for the gauge coupling and…

The Belle II Collaboration reported the first measurement on ${\rm Br}(B^+\rightarrow K^+\nu\bar{\nu})$, which lies 2.7$\sigma$ away from the Standard Model expectation. This result may be manifestation of new physics beyond the Standard…

The Belle II experiment is an upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The accelerator has already successfully completed the first phase of commissioning and first electron…

We utilize a sample of 34.6 fb$^{-1}$, collected by the Belle II experiment at the SuperKEKB asymmetric energy $e^+e^-$ collider, to search for the $B^+ \to \phi K^+$, $B^+ \to \phi K^{*+}$, $B^0 \to \phi K^0_S$, and $B^0 \to \phi K^{*0}$…

Belle II has recently reported the new measurement ${\cal B}(B^+\to K^+\nu\bar\nu)=(2.3\pm0.7)\times 10^{-5}$ \cite{Belle-II:2023esi} which is two times larger than their previous result (although consistent within errors) and about…

Belle II is an upcoming experiment at the next generation SuperKEKB e+e- collider. It will record about 50 ab-1 of data mostly at the Y(4S) resonance. The high statistics will allow precision measurements for rare decays, which can be then…

Spin-1/2 inelastic dark matter (DM) models are popular among sub-GeV to GeV thermal DM scenarios due to the dominant role of co-annihilation in determining the DM relic abundance. In these models, the dark Higgs boson plays a crucial role…

The dark photon $A^\prime$ and the dark Higgs boson $h^\prime$ are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of $A^\prime$ and $h^\prime$ in the dark Higgsstrahlung process…

Axionlike particles (ALPs) can be produced in meson decays via tree-level quark-flavor-violating couplings, and decay to a pair of sterile neutrinos if also coupled to them. Such light sterile neutrinos are necessarily long-lived and may…

The QCD axion is a well-motivated addition to the standard model to solve the strong $C\!P$ problem. If the axion acquires mass dominantly from a hidden sector, it can be as heavy as $O(1)$ GeV, and the decay constant can be as low as…

Dark photons in the MeV to GeV range with kinetic mixing of the order of $\lesssim 10^{-4}-10^{-3}$ can be produced in significant numbers at low energy colliders such as Belle II. Their decay length can be macroscopic raising the hope for…

Inelastic dark matter models that have two dark matter particles and a massive dark photon can reproduce the observed relic dark matter density without violating cosmological limits. The mass splitting between the two dark matter particles…

Rare and flavour-changing neutral current decays of the B meson are an important probe in the search for physics beyond the Standard Model. There have recently been several anomalies in rare B decays, and lepton-universality measurements,…

Inelastic dark matter is an interesting scenario for light thermal dark matter which is fully consistent with all cosmological probes as well as direct and indirect dark matter detection. The required mass splitting between dark matter…

The Belle II experiment operates at the SuperKEKB asymmetric-energy $e^+e^-$ collider. During the Run 1 data taking, we have collected an integrated luminosity of $424\text{ fb}^{-1}$ of collision data at the energy near the $\Upsilon (4S)$…

The Belle II experiment's ability to identify particles critically affects the sensitivity of its measurements. We describe Belle II's algorithms for identifying charged particles and evaluate their performance in separating pions, kaons,…