WEI-SHU HOU2021-07-282021-07-28201717426588https://www.scopus.com/inward/record.uri?eid=2-s2.0-85017246101&doi=10.1088%2f1742-6596%2f800%2f1%2f012024&partnerID=40&md5=877d3c44de8c9bf8f1c420b07f7bc7aehttps://scholars.lib.ntu.edu.tw/handle/123456789/574922The Grossman-Nir bound concept is robust, but the common perception of KL → π0v v < 1:4 × 10-9 may be circumvented. Because of the blinding Kπ2(3) decay, K+ decay experiments such as E787/E949 and the currently running NA62 kinematically exclude the "blinding zone". This offers an opportunity for the currently running KOTO experiment. With no kinematic control, if the KOTO experiment is able to veto all true background, it may discover KL → π0 + X0, where X0 is an invisible " dark " boson with mass mX0? mπ0 . This could happen with 2015 data at hand, which supposedly should allow KOTO to reach nominal GN bound sensitivity. An explicit model of gauged Lμ -LT , linked with muon g-2 hence with very light Z' , is given. Adding vector-like quarks that mix with usual quarks, W-boson loops induce s → dZ' and b → sZ' transitions. Besides realizing the scenario, the model provides further illustration of potential impact. Given that usual dark bosons linked with the photon are tightly constrained, KOTO has a unique opportunity to probe the muon-related dark sector. ? Published under licence by IOP Publishing Ltd.Charged particles; Elementary particles; Hadrons; High energy physics; Explicit modeling; Kinematic control; Potential impacts; W bosons; Bosonsconference paper10.1088/1742-6596/800/1/0120242-s2.0-85017246101