Quark spin effects in <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:math> annihilation: A Monte Carlo

Quark spin effects in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msup><a:mi>e</a:mi><a:mo>+</a:mo></a:msup><a:msup><a:mi>e</a:mi><a:mo>−</a:mo></a:msup></a:math> annihilation to pseudoscalar and vector mesons are implemented for the first time in the Monte Carlo event generator. The spin-dependent fragmentation of the string stretched between the produced quark-antiquark pair with correlated spin states is described by the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>string</c:mi><c:mo>+</c:mo><c:mrow><c:msub><c:mrow><c:mmultiscripts><c:mrow><c:mi>P</c:mi></c:mrow><c:mprescripts/><c:none/><c:mrow><c:mn>3</c:mn></c:mrow></c:mmultiscripts></c:mrow><c:mrow><c:mn>0</c:mn></c:mrow></c:msub></c:mrow></c:math> model implemented in the string fragmentation routine of by using the package. The simulated events are used to study the model predictions for the Collins asymmetries of mesons produced back-to-back in the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><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> center of mass system by using both the thrust axis method and the hadronic plane method. The obtained asymmetries are compared to the available data from the BELLE and experiments and the underlying Collins analyzing power from the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mi>string</g:mi><g:mo>+</g:mo><g:mrow><g:msub><g:mrow><g:mmultiscripts><g:mrow><g:mi>P</g:mi></g:mrow><g:mprescripts/><g:none/><g:mrow><g:mn>3</g:mn></g:mrow></g:mmultiscripts></g:mrow><g:mrow><g:mn>0</g:mn></g:mrow></g:msub></g:mrow></g:mrow></g:math> model is compared with phenomenological extractions. Published by the American Physical Society 2024