Determination of the Σ+ Timelike Electromagnetic Form Factors

Based on data samples collected with the BESIII detector at the BEPCII collider, the process <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msup><a:mrow><a:mi>e</a:mi></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup><a:msup><a:mrow><a:mi>e</a:mi></a:mrow><a:mrow><a:mo>−</a:mo></a:mrow></a:msup><a:mo stretchy="false">→</a:mo><a:msup><a:mrow><a:mi mathvariant="normal">Σ</a:mi></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup><a:msup><a:mrow><a:mover accent="true"><a:mrow><a:mi mathvariant="normal">Σ</a:mi></a:mrow><a:mrow><a:mo stretchy="false">¯</a:mo></a:mrow></a:mover></a:mrow><a:mrow><a:mo>−</a:mo></a:mrow></a:msup></a:mrow></a:math> is studied at center-of-mass energies <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mrow><h:msqrt><h:mrow><h:mi>s</h:mi></h:mrow></h:msqrt><h:mo>=</h:mo><h:mn>2.3960</h:mn></h:mrow></h:math>, 2.6454, and 2.9000 GeV. Using a fully differential angular description of the final state particles, both the relative magnitude and phase information of the <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:msup><j:mi mathvariant="normal">Σ</j:mi><j:mo>+</j:mo></j:msup></j:math> electromagnetic form factors in the timelike region are extracted. The relative phase between the electric and magnetic form factors is determined to be <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:mi>sin</m:mi><m:mi mathvariant="normal">Δ</m:mi><m:mi mathvariant="normal">Φ</m:mi><m:mo>=</m:mo><m:mo>−</m:mo><m:mn>0.67</m:mn><m:mo>±</m:mo><m:mn>0.29</m:mn><m:mo stretchy="false">(</m:mo><m:mi>stat</m:mi><m:mo stretchy="false">)</m:mo><m:mo>±</m:mo><m:mn>0.18</m:mn><m:mo stretchy="false">(</m:mo><m:mi>syst</m:mi><m:mo stretchy="false">)</m:mo></m:mrow></m:math> at <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mrow><u:msqrt><u:mrow><u:mi>s</u:mi></u:mrow></u:msqrt><u:mo>=</u:mo><u:mn>2.3960</u:mn><u:mtext> </u:mtext><u:mtext> </u:mtext><u:mi>GeV</u:mi></u:mrow></u:math>, <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mrow><w:mi mathvariant="normal">Δ</w:mi><w:mi mathvariant="normal">Φ</w:mi><w:mo>=</w:mo><w:mn>55</w:mn><w:mo>°</w:mo><w:mo>±</w:mo><w:mn>19</w:mn><w:mo>°</w:mo><w:mo stretchy="false">(</w:mo><w:mi>stat</w:mi><w:mo stretchy="false">)</w:mo><w:mo>±</w:mo><w:mn>14</w:mn><w:mo>°</w:mo><w:mo stretchy="false">(</w:mo><w:mi>syst</w:mi><w:mo stretchy="false">)</w:mo></w:mrow></w:math> at <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"><eb:msqrt><eb:mi>s</eb:mi></eb:msqrt><eb:mo>=</eb:mo><eb:mn>2.6454</eb:mn><eb:mtext> </eb:mtext><eb:mtext> </eb:mtext><eb:mi>GeV</eb:mi></eb:math>, and <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:mrow><gb:mn>78</gb:mn><gb:mo>°</gb:mo><gb:mo>±</gb:mo><gb:mn>22</gb:mn><gb:mo>°</gb:mo><gb:mo stretchy="false">(</gb:mo><gb:mi>stat</gb:mi><gb:mo stretchy="false">)</gb:mo><gb:mo>±</gb:mo><gb:mn>9</gb:mn><gb:mo>°</gb:mo><gb:mo stretchy="false">(</gb:mo><gb:mi>syst</gb:mi><gb:mo stretchy="false">)</gb:mo></gb:mrow></gb:math> at <mb:math xmlns:mb="http://www.w3.org/1998/Math/MathML" display="inline"><mb:msqrt><mb:mi>s</mb:mi></mb:msqrt><mb:mo>=</mb:mo><mb:mn>2.9000</mb:mn><mb:mtext> </mb:mtext><mb:mtext> </mb:mtext><mb:mi>GeV</mb:mi></mb:math>. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons. Published by the American Physical Society 2024