High-statistics study of K^0_S pair production in two-photon collisions

TL;DR

This study provides a detailed high-statistics measurement of K^0_S pair production in two-photon collisions, identifying resonances, extracting parameters, and comparing results with QCD predictions using extensive data from the Belle detector.

Contribution

It offers the first high-statistics differential cross section measurement for gamma gamma --> K^0_S K^0_S, identifying multiple resonances and updating charmonium parameters.

Findings

Identification of f_2(1270), a_2(1320), and f_2'(1525) as dominant in D_2 wave

Observation of f_2(2200), f_0(1710), and possibly f_0(2500) resonances

Updated parameters for chi_c0 and chi_c2 states

Abstract

We report a high-statistics measurement of the differential cross section of the process gamma gamma --> K^0_S K^0_S in the range 1.05 GeV <= W <= 4.00 GeV, where W is the center-of-mass energy of the colliding photons, using 972 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider operated at and near the Upsilon-resonance region. The differential cross section is fitted by parameterized S-, D_0-, D_2-, G_0- and G_2-wave amplitudes. In the D_2 wave, the f_2(1270), a_2(1320) and f_2'(1525) are dominant and a resonance, the f_2(2200), is also present. The f_0(1710) and possibly the f_0(2500) are seen in the S wave. The mass, total width and product of the two-photon partial decay width and decay branching fraction to the K bar{K} state Gamma_{gamma gamma}B(K bar{K}) are extracted for the f_2'(1525), f_0(1710), f_2(2200) and f_0(2500). The destructive interference between the f_2(1270) and a_2(1320) is confirmed by measuring their relative phase. The parameters of the charmonium states chi_{c0} and chi_{c2} are updated. Possible contributions from the chi_{c0}(2P) and chi_{c2}(2P) states are discussed. A new upper limit for the branching fraction of the P- and CP-violating decay channel eta_c --> K^0_S K^0_S is reported. The detailed behavior of the cross section is updated and compared with QCD-based calculations.