Study of $K^0_S$ pair production in single-tag two-photon collisions

TL;DR

This paper measures the production cross section of $K^0_S$ pairs in single-tag two-photon collisions over a range of energies and momentum transfers, providing new insights into meson transition form factors and decay widths.

Contribution

It presents the first measurement of the $f_2'(1525)$ meson transition form factor for different helicity states and explores the $Q^2$ dependence of $ ext{chi}_{c0}$ and $ ext{chi}_{c2}$ meson decay widths.

Findings

Transition form factor of $f_2'(1525)$ measured for helicity components.

Partial decay widths of $ ext{chi}_{c0}$ and $ ext{chi}_{c2}$ as functions of $Q^2$.

Cross section results covering $W$ from 1.0 to 2.6 GeV.

Abstract

We report a measurement of the cross section for $K^0_S$ pair production in single-tag two-photon collisions, $\gamma^* \gamma \to K^0_S K^0_S$, for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon. The measurement covers the kinematic range 1.0 GeV < W < 2.6 GeV and $|\cos \theta^*| < 1.0$ for the total energy and kaon scattering angle, respectively, in the $\gamma^* \gamma$ center-of-mass system. These results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. For the first time, the transition form factor of the $f_2'(1525)$ meson is measured separately for the helicity-0, -1, and -2 components and also compared with theoretical calculations. Finally, the partial decay widths of the $\chi_{c0}$ and $\chi_{c2}$ mesons are measured as a function of $Q^2$.