Improved measurement of η ′ → e + e − ω

This is the authors' abstract. We don't add key points for this paper.

Using a sample of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mo stretchy="false">(</a:mo> <a:mn>10087</a:mn> <a:mo>±</a:mo> <a:mn>44</a:mn> <a:mo stretchy="false">)</a:mo> <a:mo>×</a:mo> <a:msup> <a:mn>10</a:mn> <a:mn>6</a:mn> </a:msup> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>J</a:mi> <a:mo>/</a:mo> <a:mi>ψ</a:mi> </a:math> events collected with the BESIII detector, an improved measurement of the decay <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msup> <e:mi>η</e:mi> <e:mo>′</e:mo> </e:msup> <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:mi>ω</e:mi> </e:math> , with <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mi>ω</h:mi> <h:mo stretchy="false">→</h:mo> <h:msup> <h:mi>π</h:mi> <h:mo>+</h:mo> </h:msup> <h:msup> <h:mi>π</h:mi> <h:mo>−</h:mo> </h:msup> <h:msup> <h:mi>π</h:mi> <h:mn>0</h:mn> </h:msup> </h:math> and <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msup> <k:mi>π</k:mi> <k:mn>0</k:mn> </k:msup> <k:mo stretchy="false">→</k:mo> <k:mi>γ</k:mi> <k:mi>γ</k:mi> </k:math> is performed. The branching fraction is determined to be <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:mi mathvariant="script">B</n:mi> <n:mo stretchy="false">(</n:mo> <n:msup> <n:mi>η</n:mi> <n:mo>′</n:mo> </n:msup> <n:mo stretchy="false">→</n:mo> <n:msup> <n:mi>e</n:mi> <n:mo>+</n:mo> </n:msup> <n:msup> <n:mi>e</n:mi> <n:mo>−</n:mo> </n:msup> <n:mi>ω</n:mi> <n:mo stretchy="false">)</n:mo> <n:mo>=</n:mo> <n:mo stretchy="false">(</n:mo> <n:mn>1.79</n:mn> <n:mo>±</n:mo> <n:mn>0.09</n:mn> <n:mo>±</n:mo> <n:mn>0.12</n:mn> <n:mo stretchy="false">)</n:mo> <n:mo>×</n:mo> <n:msup> <n:mn>10</n:mn> <n:mrow> <n:mo>−</n:mo> <n:mn>4</n:mn> </n:mrow> </n:msup> </n:math> , where the first uncertainty is statistical and the second is systematic. This result is consistent with the previous measurement and is obtained with significantly improved precision. Furthermore, the first measurement of the transition form factor cutoff parameter for this decay is reported, with <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"> <v:mrow> <v:msup> <v:mrow> <v:mi mathvariant="normal">Λ</v:mi> </v:mrow> <v:mrow> <v:mo>−</v:mo> <v:mn>1</v:mn> </v:mrow> </v:msup> <v:mo>=</v:mo> <v:mo stretchy="false">(</v:mo> <v:mn>2.92</v:mn> <v:mo>±</v:mo> <v:mn>0.83</v:mn> <v:mo>±</v:mo> <v:mn>0.15</v:mn> <v:mo stretchy="false">)</v:mo> <v:mtext> </v:mtext> <v:mtext> </v:mtext> <v:msup> <v:mrow> <v:mi>GeV</v:mi> </v:mrow> <v:mrow> <v:mo>−</v:mo> <v:mn>1</v:mn> </v:mrow> </v:msup> </v:mrow> </v:math> . These measurements provide valuable input for understanding the internal structure of the <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"> <ab:msup> <ab:mi>η</ab:mi> <ab:mo>′</ab:mo> </ab:msup> </ab:math> meson and testing theoretical models.