Revisiting models that enhance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>B</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mi>K</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:mi>ν</mml:mi><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover></mml:math> in light of the new Belle II measurement

Abstract

Belle II recently reported the new measurement <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi mathvariant="script">B</a:mi><a:mo stretchy="false">(</a:mo><a:msup><a:mi>B</a:mi><a:mo>+</a:mo></a:msup><a:mo stretchy="false">→</a:mo><a:msup><a:mi>K</a:mi><a:mo>+</a:mo></a:msup><a:mi>ν</a:mi><a:mover accent="true"><a:mi>ν</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:mo stretchy="false">)</a:mo><a:mo>=</a:mo><a:mo stretchy="false">(</a:mo><a:mn>2.3</a:mn><a:mo>±</a:mo><a:mn>0.7</a:mn><a:mo stretchy="false">)</a:mo><a:mo>×</a:mo><a:msup><a:mn>10</a:mn><a:mrow><a:mo>−</a:mo><a:mn>5</a:mn></a:mrow></a:msup></a:math> [I. Adachi (Belle-II Collaboration), ] which is two times larger than their previous result (although consistent within errors) and about <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mn>2.7</k:mn><k:mi>σ</k:mi></k:math> higher than the SM prediction. We reexamine new physics scenarios we discussed previously, which can enhance this rate to determine if they can accommodate the higher value reported in the new measurement. We use consistency with existing bounds on <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>B</m:mi><m:mo stretchy="false">→</m:mo><m:msup><m:mi>K</m:mi><m:mo>*</m:mo></m:msup><m:mi>ν</m:mi><m:mover accent="true"><m:mi>ν</m:mi><m:mo stretchy="false">¯</m:mo></m:mover></m:math>, <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mi>b</r:mi><r:mo stretchy="false">→</r:mo><r:mi>s</r:mi><r:msup><r:mo>ℓ</r:mo><r:mo>+</r:mo></r:msup><r:msup><r:mo>ℓ</r:mo><r:mo>−</r:mo></r:msup></r:math>, <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mi>B</u:mi><u:mo stretchy="false">→</u:mo><u:msup><u:mi>D</u:mi><u:mrow><u:mo stretchy="false">(</u:mo><u:mo>*</u:mo><u:mo stretchy="false">)</u:mo></u:mrow></u:msup><u:mo>ℓ</u:mo><u:mover accent="true"><u:mi>ν</u:mi><u:mo stretchy="false">¯</u:mo></u:mover></u:math>, and <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"><bb:msub><bb:mi>B</bb:mi><bb:mi>s</bb:mi></bb:msub></bb:math> mixing to limit possible explanations for the excess. For the case of lepton flavor violating neutrino couplings, we find that only two leptoquarks remain viable requiring a large <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msubsup><db:mi>C</db:mi><db:msup><db:mn>9</db:mn><db:mo>′</db:mo></db:msup><db:mrow><db:mi>τ</db:mi><db:mi>τ</db:mi></db:mrow></db:msubsup><db:mo>=</db:mo><db:mo>−</db:mo><db:msubsup><db:mi>C</db:mi><db:mrow><db:msup><db:mn>10</db:mn><db:mo>′</db:mo></db:msup></db:mrow><db:mrow><db:mi>τ</db:mi><db:mi>τ</db:mi></db:mrow></db:msubsup></db:math>. For models with different types of light dark matter particle pairs (scalar, fermion, or vector), the preliminary <fb:math xmlns:fb="http://www.w3.org/1998/Math/MathML" display="inline"><fb:msup><fb:mi>q</fb:mi><fb:mn>2</fb:mn></fb:msup></fb:math> distribution from Belle II, which shows that the excess appears mostly for bins with <hb:math xmlns:hb="http://www.w3.org/1998/Math/MathML" display="inline"><hb:mn>3</hb:mn><hb:mo>≤</hb:mo><hb:msup><hb:mi>q</hb:mi><hb:mn>2</hb:mn></hb:msup><hb:mo>≤</hb:mo><hb:mn>7</hb:mn><hb:mtext> </hb:mtext><hb:mtext> </hb:mtext><hb:msup><hb:mrow><hb:mi>GeV</hb:mi></hb:mrow><hb:mrow><hb:mn>2</hb:mn></hb:mrow></hb:msup></hb:math> [I. Adachi (Belle-II Collaboration), ], implies only the vector current operators with scalar or vector dark matter particles with masses in the hundreds of MeV can match the anomaly. Published by the American Physical Society 2024

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