Joint explanation of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>π</mml:mi><mml:mi>K</mml:mi></mml:math> puzzle and the <mml:math xmlns:mml="http://www.w3.

In light of the recent branching fraction measurement of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><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:math> decay by Belle II and its poor agreement with the Standard Model expectation, we analyze the effects of an axionlike particle (ALP) in <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:mi>B</f:mi></f:math> meson decays. We assume a long-lived ALP with a mass of the order of the pion mass that decays to two photons. We focus on a scenario where the ALP decay length is of the order of meters such that the ALP has a non-negligible probability to decay outside the detector volume of Belle II, mimicking the <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:msup><h:mi>B</h:mi><h:mo>+</h:mo></h:msup><h:mo stretchy="false">→</h:mo><h:msup><h:mi>K</h:mi><h:mo>+</h:mo></h:msup><h:mi>ν</h:mi><h:mover accent="true"><h:mi>ν</h:mi><h:mo stretchy="false">¯</h:mo></h:mover></h:math> signal. Remarkably, such an arrangement is also relevant for the long-standing <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:mi>π</m:mi><m:mi>K</m:mi></m:math> puzzle by noting that the measured <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:msup><p:mi>B</p:mi><p:mn>0</p:mn></p:msup><p:mo stretchy="false">→</p:mo><p:msup><p:mi>π</p:mi><p:mn>0</p:mn></p:msup><p:msup><p:mi>K</p:mi><p:mn>0</p:mn></p:msup></p:math> and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:msup><s:mi>B</s:mi><s:mo>+</s:mo></s:msup><s:mo stretchy="false">→</s:mo><s:msup><s:mi>π</s:mi><s:mn>0</s:mn></s:msup><s:msup><s:mi>K</s:mi><s:mo>+</s:mo></s:msup></s:math> decays could have a <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:msup><v:mi>B</v:mi><v:mn>0</v:mn></v:msup><v:mo stretchy="false">→</v:mo><v:mi>a</v:mi><v:msup><v:mi>K</v:mi><v:mn>0</v:mn></v:msup></v:math> and <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:msup><y:mi>B</y:mi><y:mo>+</y:mo></y:msup><y:mo stretchy="false">→</y:mo><y:mi>a</y:mi><y:msup><y:mi>K</y:mi><y:mo>+</y:mo></y:msup></y:math> component, respectively. We also argue based on our results that the required ALP-photon effective coupling belongs to a region of parameter space that can be extensively probed in future beam dump experiments like SHiP.