e+e−→Λc+Λ¯c− Cross Sections and the Λc+ Electromagnetic Form Factors within the Extended Vector Meson Dominance Model
Cheng 诚 Chen 陈, Bing 冰 Yan 闫, Ju-Jun Xie
Abstract
Within the extended vector meson dominance model, we investigate the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <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:mo>→</mml:mo> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:msubsup> <mml:mover accent="true"> <mml:mi>Λ</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>c</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> reaction and the electromagnetic form factors of the charmed baryon <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> . The model parameters are determined by fitting them to the cross sections of the process <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <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:mo>→</mml:mo> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:msubsup> <mml:mover accent="true"> <mml:mi>Λ</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>c</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> and the magnetic form factor | G M | of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> . By considering four charmonium-like states, called ψ (4500), ψ (4660), ψ (4790), and ψ (4900), we can well describe the current data on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <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:mo>→</mml:mo> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> <mml:msubsup> <mml:mover accent="true"> <mml:mi>Λ</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>c</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> reaction from the reaction threshold up to 4.96 GeV. In addition to the total cross sections and | G M |, the ratio | G E / G M | and the effective form factor | G eff | for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> are also calculated, and found that these calculations are consistent with the experimental data. Within the fitted model parameters, we have also estimated the charge radius of the charmed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> baryon.