Study of $\pi^0$ pair production in single-tag two-photon collisions

TL;DR

This paper measures the differential cross section of neutral pion pair production in single-tag two-photon collisions at high energies, providing new insights into meson transition form factors and testing theoretical models.

Contribution

It presents the first measurement of the transition form factors of the $f_0(980)$ and $f_2(1270)$ mesons with different helicity components in a wide kinematic range.

Findings

Transition form factors are measured for the first time.

Results are compared with theoretical predictions.

Data covers a broad $Q^2$ range up to 30 GeV$^2$.

Abstract

We report a measurement of the differential cross section of $\pi^0$ pair production in single-tag two-photon collisions, $\gamma^* \gamma \to \pi^0 \pi^0$, in $e^+ e^-$ scattering. The cross section is measured for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and $|\cos \theta^*|$ < 1.0 for the total energy and pion scattering angle, respectively, in the $\gamma^* \gamma$ center-of-mass system. The results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The transition form factor of the $f_0(980)$ and that of the $f_2(1270)$ with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.