München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 48: Elektromagnetische und Hadronische Sonden

HK 48.1: Gruppenbericht

Donnerstag, 23. März 2006, 17:00–17:30, F

Sum-rule for the $∖sigma$-meson — •Martin Schumacher¹, M.I. Levchuk², A.I. L vov³, and A.I. Milstein⁴ — ¹Zweites Physikalisches Institut der Universität, D-37077 Göttingen — ²B.I. Stepanov Institute of Physics, BY-220072 Minsk, Belarus — ³P.N. Lebedev Physical Institute, RU-117924 Moscow, Russia — ⁴Budker Institute of Nuclear Physics, RU-630090 Novosibirsk, Russia

Arguments are found that the $∖sigma$ meson couples to two photons via its non-strange $q∖bar{q}$ structure component. This ansatz leads to a quantitative explanation of the $t$-channel component of the difference of electromagnetic polarizabilities, $(∖alpha-∖beta)^t$, of the nucleon. The prediction is $(∖alpha-∖beta)^t_{p,n}=(5 ∖alpha_e g_{∖pi NN})/(6∖pi^2 m^2_∖sigma f_∖pi) =15.3$ in units of $10^{-4}{∖rm fm}^3$ to be compared with the experimental values $(∖alpha-∖beta)^t_{p}=15.1∖pm 1.3$ for the proton and $(∖alpha-∖beta)^t_{n}=14.8∖pm 2.7$ for the neutron. The equivalent approach to exploit the $∖pi∖pi$ structure component of the $∖sigma$ meson via the BEFT sum rule leads to $(∖alpha-∖beta)^t_{p,n}=15.3∖pm 1.3$, what also is in agreement with the experimental results. We show that the observed agreement of the two different predictions for $(∖alpha-∖beta)^t_{p,n}$ may be understood as a sum rule for the $∖sigma$ meson where the chiral partner of the $∖pi$ meson is linked together with the $f_0(600)$ particle observed in particle reactions where a resonant $∖pi∖pi$ intermediate state is involved.