Signatures of light new particles in B→K(*)Emiss

The recent Belle II observation of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>B</a:mi><a:mo stretchy="false">→</a:mo><a:mi>K</a:mi><a:msub><a:mi>E</a:mi><a:mrow><a:mi>miss</a:mi></a:mrow></a:msub></a:math> challenges theoretical interpretations in terms of Standard Model neutrino final states. Instead, we consider new physics scenarios where up to two new light-invisible particles of spin 0 up to <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mrow><d:mn>3</d:mn><d:mo>/</d:mo><d:mn>2</d:mn></d:mrow></d:math> are present in the final state. We identify viable scenarios by reconstructing the (binned) likelihoods of the relevant <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:mi>B</f:mi><f:mo stretchy="false">→</f:mo><f:msup><f:mi>K</f:mi><f:mrow><f:mo stretchy="false">(</f:mo><f:mo>*</f:mo><f:mo stretchy="false">)</f:mo></f:mrow></f:msup><f:msub><f:mi>E</f:mi><f:mrow><f:mi>miss</f:mi></f:mrow></f:msub></f:math> and also <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msub><k:mi>B</k:mi><k:mi>s</k:mi></k:msub><k:mo stretchy="false">→</k:mo><k:msub><k:mi>E</k:mi><k:mrow><k:mi>miss</k:mi></k:mrow></k:msub></k:math> experimental analyses and present preferred regions of couplings and masses. In particular, we find that the current data prefer two-body decay kinematics involving the emission of a single massive scalar or a vector particle or, alternatively, three-body decays involving pairs of massive scalars or spin <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mrow><n:mn>1</n:mn><n:mo>/</n:mo><n:mn>2</n:mn></n:mrow></n:math> fermions. When applicable, we compare our findings with existing literature and briefly discuss some model-building implications. Published by the American Physical Society 2024