A search for the flavor-changing neutral-current decay B+ → K+νν ̄ 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 Y(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 ̄ decay, but also the inclusive properties of the other B meson in the Y(4S) → BB 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 ̄ of 4.1 × 10−5 is set at the 90% confidence level.
Search for B⁺→K⁺νν¯ Decays Using an Inclusive Tagging Method at Belle II
Bettarini, S.;Casarosa, G.;Forti, F.;Lueck, T.;Paladino, A.;Paoloni, E.;Rizzo, G.;Tenchini, F.;
2021-01-01
Abstract
A search for the flavor-changing neutral-current decay B+ → K+νν ̄ 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 Y(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 ̄ decay, but also the inclusive properties of the other B meson in the Y(4S) → BB 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 ̄ of 4.1 × 10−5 is set at the 90% confidence level.File | Dimensione | Formato | |
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PhysRevLett.127.181802.pdf
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