Two-photon width and gluonic component of

Abstract

We analyse data on ππ and γγ scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: π + π − ) and their subsequent annihilation or through a "direct" transition into photons. Our analysis confirms the rather large total radiative width of the σ resonance which we find as (3.9 ± 0.6) keV but suggests its dominance by the ππ rescattering process. This process is not sensitive to the internal structure of the resonance contrary to the direct component which we find small, (0.13 ± 0.05) keV, and well consistent with the expectations for an unmixed glueball according to the QCD sum rule calculations.

Yang-Mills Propagators and QCD

“…This means that Yang-Mills theory has a higher ground state than full QCD as quarks lower it to the pion mass. Indeed, f 0 (600) or σ seems to have a large gluonic content due to the very small width for γγ decay that can be due to ππ rescattering [29,30] and as also seen through χPT [31,32]. We have shown that our computed mass is very near the one obtained from experiments [33].…”

“…A more conservative choice of 410 MeV can take both σ and σ * , the latter eventually being f 0 (980), to agree with measured data giving m σ ≈ 491 M eV and m σ * ≈ 982 M eV . This view is shared in recent analysis [29,30]. But while these resonances are seen both experimentally and theoretically and, in indirect way through lattice computations for the propagator, a direct evidence on lattice computations for spectra appears difficult to achieve presently [34].…”

Chiral perturbation theory, the1/Ncexpansion and Regge behavior determine the structure of the lightest scalar meson

“…Eqs. (11,12). Indeed, there is probably no closer link between amplitudes with definite t-channel quantum numbers and their low energy behaviour in the schannel physics region than that shown here.…”

The σ and f0(980) from Ke4⊕ππ, γγ scatterings, J/ψ, Mennessier1, Narison2, Wang3 2010Nuclear Physics B - Proceedings SupplementsSelf Cite

“…We introduce a real analytic form factor shape function [2]: It allows for an Alder zero s = s AP and a pole at σ DP < 0 to simulate left hand singularities. The unitary I = 0 S wave ππ scattering amplitude is then written as:…”

“…-This model is improved by introducing a form factor shape function in a single channel [2], which is generalized [3][4][5] to the coupled channels case in order to extract the pole postions and the previous couplings of the σ and f 0 (980). In this talk, we review these recent results.…”