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Observation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:math> decays to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>−</mml:mo></mml:msup></mml:math> and <mml:math xmlns:…
Using a data sample of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>4.481</a:mn><a:mo>×</a:mo><a:msup><a:mn>10</a:mn><a:mn>8</a:mn></a:msup><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>ψ</a:mi><a:mo stretchy="false">(</a:mo><a:mn>3686</a:mn><a:mo stretchy="false">)</a:mo></a:math> events collected with the BESIII detector, we report the first observation of the four-lepton-decays <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>J</e:mi><e:mo>/</e:mo><e:mi>ψ</e:mi><e:mo stretchy="false">→</e:mo><e:msup><e:mi>e</e:mi><e:mo>+</e:mo></e:msup><e:msup><e:mi>e</e:mi><e:mo>−</e:mo></e:msup><e:msup><e:mi>e</e:mi><e:mo>+</e:mo></e:msup><e:msup><e:mi>e</e:mi><e:mo>−</e:mo></e:msup></e:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mi>J</h:mi><h:mo>/</h:mo><h:mi>ψ</h:mi><h:mo stretchy="false">→</h:mo><h:msup><h:mi>e</h:mi><h:mo>+</h:mo></h:msup><h:msup><h:mi>e</h:mi><h:mo>−</h:mo></h:msup><h:msup><h:mi>μ</h:mi><h:mo>+</h:mo></h:msup><h:msup><h:mi>μ</h:mi><h:mo>−</h:mo></h:msup></h:math> utilizing the process <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>ψ</k:mi><k:mo stretchy="false">(</k:mo><k:mn>3686</k:mn><k:mo stretchy="false">)</k:mo><k:mo stretchy="false">→</k:mo><k:msup><k:mi>π</k:mi><k:mo>+</k:mo></k:msup><k:msup><k:mi>π</k:mi><k:mo>−</k:mo></k:msup><k:mi>J</k:mi><k:mo>/</k:mo><k:mi>ψ</k:mi></k:math>. The branching fractions are determined to …