Vector mesons and electromagnetic form factor of the $\mathrm{\Lambda }$ hyperon

The measured electromagnetic form factors of $\mathrm{\Lambda }$ hyperon in the timelike region are significantly deviated from pQCD prediction. We attribute the nonvanishing cross section near threshold to be the contribution of below-threshold $\varphi (2170)$ state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\overline{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.

Figure 1

Our fit to the world data of the cross section of $e^{+}{e}^{-}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}$. The green open circle, black dot, red triangle and blue rectangle represent the data from the DM2 [11], BABAR [12] and BESIII [13, 14] collaborations, respectively. The blue dash-dotted curve describes the pQCD contribution. The red dotted and green dashed curves denote the contributions from pQCD involved with $\varphi (2170)$ and $X(2340)$ resonances, respectively. The blue solid line is the total coherent contribution from pQCD, $\varphi (2170)$, and $X(2340)$ resonances.