Measurement of the gamma gamma -> pi+ pi- and gamma gamma -> K+ K- processes at energies of 2.4 - 4.1 GeV

TL;DR

This study precisely measures the cross sections of gamma gamma to pi+ pi- and K+ K- processes at energies 2.4-4.1 GeV, revealing a consistent cross section ratio and angular distribution, and observes chi_c meson production.

Contribution

First high-precision measurement of these processes in this energy range with detailed cross section ratios and angular behavior, including observation of chi_c mesons.

Findings

Cross section ratio sigma(K+K-)/sigma(pi+pi-) is 0.89 ± 0.04 (stat) ± 0.15 (syst).

Cross section exhibits sin^{-4} theta^{*} dependence.

Production of chi_c0 and chi_c2 mesons observed in both modes.

Abstract

We have measured pi+pi- and K+K- production in two-photon collisions using 87.7 /fb of data collected with the Belle detector at the asymmetric energy e+e- collider KEKB. The cross sections are measured to high precision in the two-photon center-of-mass energy (W) range between 2.4 GeV < W < 4.1 GeV and angular region |cos theta^{*}| < 0.6. The cross section ratio sigma(gammagamma->K+K-)/sigma(gammagamma->pi+pi-) is measured to be 0.89 +- 0.04(stat) +- 0.15(syst) in the range of 3.0 GeV < W < 4.1 GeV, where the ratio is energy independent. We observe a sin^{-4} theta^{*} behavior of the cross section in the same W range. Production of chi_{c0} and chi_{c2} mesons is observed in both gammagamma -> pi+pi- and gammagamma -> K+K- modes.