Search for B^ + →K^ + νν over ¯ Decays Using an Inclusive Tagging Method at Belle II.
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| Abstract | 
   :  
              A search for the flavor-changing neutral-current decay B^{+}→K^{+}νν[over ¯] is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb^{-1} collected at the ϒ(4S) resonance and a sample of 9 fb^{-1} collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B^{+}→K^{+}νν[over ¯] decay, but also the inclusive properties of the other B meson in the ϒ(4S)→BB[over ¯] event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B^{+}→K^{+}νν[over ¯] of 4.1×10^{-5} is set at the 90% confidence level.  | 
        
| Year of Publication | 
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              2021 
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| Journal | 
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              Physical review letters 
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| Volume | 
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              127 
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| Issue | 
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              18 
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| Number of Pages | 
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              181802 
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| Date Published | 
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              2021 
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| ISSN Number | 
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              0031-9007 
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| URL | 
   :  
              https://link.aps.org/abstract/PRL/v127/p181802 
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| DOI | 
   :  
              10.1103/PhysRevLett.127.181802 
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| Short Title | 
   :  
              Phys Rev Lett 
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