Search for the semileptonic decays Ξc0→Ξ0ℓ+ℓ− at Belle

Using the full data sample of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>980</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:msup><a:mi>fb</a:mi><a:mrow><a:mo>−</a:mo><a:mn>1</a:mn></a:mrow></a:msup></a:math> collected with the Belle detector at the KEKB asymmetric energy electron-positron collider, we report the results of the first search for the rare semileptonic decays <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msubsup><c:mi mathvariant="normal">Ξ</c:mi><c:mi>c</c:mi><c:mn>0</c:mn></c:msubsup><c:mo stretchy="false">→</c:mo><c:msup><c:mi mathvariant="normal">Ξ</c:mi><c:mn>0</c:mn></c:msup><c:msup><c:mo>ℓ</c:mo><c:mo>+</c:mo></c:msup><c:msup><c:mo>ℓ</c:mo><c:mo>−</c:mo></c:msup></c:math> (<h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mo>ℓ</h:mo><h:mo>=</h:mo><h:mi>e</h:mi></h:math> or <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mi>μ</j:mi></j:math>). No significant signals are observed in the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:msup><l:mi mathvariant="normal">Ξ</l:mi><l:mn>0</l:mn></l:msup><l:msup><l:mo>ℓ</l:mo><l:mo>+</l:mo></l:msup><l:msup><l:mo>ℓ</l:mo><l:mo>−</l:mo></l:msup></l:math> invariant-mass distributions. Taking the decay <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:msubsup><o:mi mathvariant="normal">Ξ</o:mi><o:mi>c</o:mi><o:mn>0</o:mn></o:msubsup><o:mo stretchy="false">→</o:mo><o:msup><o:mi mathvariant="normal">Ξ</o:mi><o:mo>−</o:mo></o:msup><o:msup><o:mi>π</o:mi><o:mo>+</o:mo></o:msup></o:math> as the normalization mode, we report 90% credibility upper limits on the branching fraction ratios <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mi mathvariant="script">B</t:mi><t:mo stretchy="false">(</t:mo><t:msubsup><t:mi mathvariant="normal">Ξ</t:mi><t:mi>c</t:mi><t:mn>0</t:mn></t:msubsup><t:mo stretchy="false">→</t:mo><t:msup><t:mi mathvariant="normal">Ξ</t:mi><t:mn>0</t:mn></t:msup><t:msup><t:mi>e</t:mi><t:mo>+</t:mo></t:msup><t:msup><t:mi>e</t:mi><t:mo>−</t:mo></t:msup><t:mo stretchy="false">)</t:mo><t:mo>/</t:mo><t:mi mathvariant="script">B</t:mi><t:mo stretchy="false">(</t:mo><t:msubsup><t:mi mathvariant="normal">Ξ</t:mi><t:mi>c</t:mi><t:mn>0</t:mn></t:msubsup><t:mo stretchy="false">→</t:mo><t:msup><t:mi mathvariant="normal">Ξ</t:mi><t:mo>−</t:mo></t:msup><t:msup><t:mi>π</t:mi><t:mo>+</t:mo></t:msup><t:mo stretchy="false">)</t:mo><t:mo><</t:mo><t:mn>6.7</t:mn><t:mo>×</t:mo><t:msup><t:mn>10</t:mn><t:mrow><t:mo>−</t:mo><t:mn>3</t:mn></t:mrow></t:msup></t:math> and <hb:math xmlns:hb="http://www.w3.org/1998/Math/MathML" display="inline"><hb:mi mathvariant="script">B</hb:mi><hb:mo stretchy="false">(</hb:mo><hb:msubsup><hb:mi mathvariant="normal">Ξ</hb:mi><hb:mi>c</hb:mi><hb:mn>0</hb:mn></hb:msubsup><hb:mo stretchy="false">→</hb:mo><hb:msup><hb:mi mathvariant="normal">Ξ</hb:mi><hb:mn>0</hb:mn></hb:msup><hb:msup><hb:mi>μ</hb:mi><hb:mo>+</hb:mo></hb:msup><hb:msup><hb:mi>μ</hb:mi><hb:mo>−</hb:mo></hb:msup><hb:mo stretchy="false">)</hb:mo><hb:mo>/</hb:mo><hb:mi mathvariant="script">B</hb:mi><hb:mo stretchy="false">(</hb:mo><hb:msubsup><hb:mi mathvariant="normal">Ξ</hb:mi><hb:mi>c</hb:mi><hb:mn>0</hb:mn></hb:msubsup><hb:mo stretchy="false">→</hb:mo><hb:msup><hb:mi mathvariant="normal">Ξ</hb:mi><hb:mo>−</hb:mo></hb:msup><hb:msup><hb:mi>π</hb:mi><hb:mo>+</hb:mo></hb:msup><hb:mo stretchy="false">)</hb:mo><hb:mo><</hb:mo><hb:mn>4.3</hb:mn><hb:mo>×</hb:mo><hb:msup><hb:mn>10</hb:mn><hb:mrow><hb:mo>−</hb:mo><hb:mn>3</hb:mn></hb:mrow></hb:msup></hb:math> based on the phase-space assumption for signal decays. The 90% credibility upper limits on the absolute branching fractions of <vb:math xmlns:vb="http://www.w3.org/1998/Math/MathML" display="inline"><vb:mi mathvariant="script">B</vb:mi><vb:mo stretchy="false">(</vb:mo><vb:msubsup><vb:mi mathvariant="normal">Ξ</vb:mi><vb:mi>c</vb:mi><vb:mn>0</vb:mn></vb:msubsup><vb:mo stretchy="false">→</vb:mo><vb:msup><vb:mi mathvariant="normal">Ξ</vb:mi><vb:mn>0</vb:mn></vb:msup><vb:msup><vb:mi>e</vb:mi><vb:mo>+</vb:mo></vb:msup><vb:msup><vb:mi>e</vb:mi><vb:mo>−</vb:mo></vb:msup><vb:mo stretchy="false">)</vb:mo></vb:math> and <dc:math xmlns:dc="http://www.w3.org/1998/Math/MathML" display="inline"><dc:mi mathvariant="script">B</dc:mi><dc:mo stretchy="false">(</dc:mo><dc:msubsup><dc:mi mathvariant="normal">Ξ</dc:mi><dc:mi>c</dc:mi><dc:mn>0</dc:mn></dc:msubsup><dc:mo stretchy="false">→</dc:mo><dc:msup><dc:mi mathvariant="normal">Ξ</dc:mi><dc:mn>0</dc:mn></dc:msup><dc:msup><dc:mi>μ</dc:mi><dc:mo>+</dc:mo></dc:msup><dc:msup><dc:mi>μ</dc:mi><dc:mo>−</dc:mo></dc:msup><dc:mo stretchy="false">)</dc:mo></dc:math> are found to be <lc:math xmlns:lc="http://www.w3.org/1998/Math/MathML" display="inline"><lc:mn>9.9</lc:mn><lc:mo>×</lc:mo><lc:msup><lc:mn>10</lc:mn><lc:mrow><lc:mo>−</lc:mo><lc:mn>5</lc:mn></lc:mrow></lc:msup></lc:math> and <nc:math xmlns:nc="http://www.w3.org/1998/Math/MathML" display="inline"><nc:mn>6.5</nc:mn><nc:mo>×</nc:mo><nc:msup><nc:mn>10</nc:mn><nc:mrow><nc:mo>−</nc:mo><nc:mn>5</nc:mn></nc:mrow></nc:msup></nc:math>, respectively. Published by the American Physical Society 2024