Speaker
Prof.
Martin Schumacher
(Zweites Physikalisches Institut der Universität Göttingen)
Description
The scalar mesons sigma(600), kappa(800), f0(980) and a0(980) together with the pseudo Goldstone bosons pi, K and eta may be considered as the Higgs sector of strong interaction. After a long time of uncertainty about the internal structure of the scalar mesons there now seems to be consistency which is in line with the major parts of experimental observations. Great progress has been made by introducing the unified model of Close and Törnqvist [1]. This model states that scalar mesons below 1 GeV may be understood as tetraquarks in S-wave with some qbarq in P-wave. Further out they rearrange as meson-meson states. We show that the P-wave component inherent in the structure of neutral scalar mesons can be understood as doorway state for the formation of the scalar meson via two-photon fusion, whereas in nucleon Compton scattering these P-wave components serve as intermediate states of the scattering process [2]. Explicit expressions for the flavour structure of the qbarq states are derived and it is shown that these flavour structures are consistent with the two-photon widths of the scalar mesons. The masses of the scalar mesons are predicted in terms of spontaneous and explicit symmetry breaking. Spontaneous symmetry breaking leads to the same mass for all scalar mesons being 652 MeV. Explicit symmetry breaking increases the masses of the scalar mesons by an amount which depends on the fraction of strange and/or anti-strange quarks in the scalar meson. The Goldstone bosons showing up as part of the spontaneous symmetry-breaking process as mass-less particles acquire mass due to explicit symmetry breaking. This mass is absorbed into the mass of the scalar meson and in this way contributes to explicit symmetry breaking. Good agreement is obtained between the experimental and predicted masses of the scalar mesons. A comparison between spontaneous symmetry breaking in strong and EW interaction is given.
[1] F.E. Close and N.A. Törnqvist, J. Phys. G: Nucl. Part. Phys. 28 R249 (2002), arXiv:hep-ph/0204205.
[2] M. Schumacher, Eur. Phys. J. C 67, 283 (2010), arXiv:1001.0500 [hep-ph].
Primary author
Prof.
Martin Schumacher
(Zweites Physikalisches Institut der Universität Göttingen)
