Naslov
Two-photon processes of pi^0, eta, eta", eta_c and eta_b
(Two-photon proceses of pi^0, eta, eta", eta_c and eta_b)

Autori
Klabučar, Dubravko ; Kekez, Dalibor

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
Proceedings of 32nd rencontres de moriond: QCD and High-energy hadronic interactions / J. Tran Thanh Van - Pariz : Editions Frontieres, 1997, 607-608

Skup
32nd rencontres de Moriond: QCD and high-energy hadronic interactions

Mjesto i datum
Les Arcs, Francuska, 22.03.1997. - 29.03.1997

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
non-perturbative QCD; hadronic structure; axial anomaly; two--photon processes; pseudoscalar mesons; chiral symmetry breaking; quark models

Sažetak
We study two-photon processes of $pi^0, eta, eta^prime, eta_c$ and $eta_b$ in the consistently coupled Schwinger-Dyson (SD) and Bethe-Salpeter (BS) approach, where dynamical chiral symmetry breaking (D$chi$SB) is obtained through the SD equation for the quark propagator which is then used in the BS equation. Light pseudoscalar mesons then appear as (pseudo)Goldstone bosons of D$chi$SB, which is the key to the adequate description of the light sector, but the good modeling (in the low-momentum region only) of the gluon propagator has lead also to the successful reproduction of pseudoscalar decay constants and meson masses all the way up to the heavy quark regime. We have now shown that the coupled SD-BS approach is similarly successful in the description of two--photon processes of pseudoscalar mesons over a wide range of masses. The electromagnetic interactions are incorporated through a (generalized) impulse approximation employing a dressed quark-photon vertex satisfying the Ward-Takahashi identities of QED when quarks are dynamically dressed. Our approach then yields (in the chiral limit) the famous axial anomaly result for $pi^0ightarrowgammagamma$ amplitude exactly and analytically, independently of the details of the pion structure. This is crucial also for the off-shell extension of this process, namely for the $pi^0gamma^star ogamma$ amplitude. Although the dynamical dressing of the much heavier $c$-quarks is less important than the dressing of the light quarks, our results show that its consistent treatment is essential for the understanding of $eta_cightarrowgammagamma$ in the light of the rather low $gammagamma$-width from CLEO. While we do not question the accuracy of the non--relativistic description in the case of $eta_b$, it will certainly be interesting to see how well our approach does once the experimental data on $eta_b$ and $eta_b ightarrow gammagamma$ are available and compared with our results. After introducing into the bound--state approach employed above the parametrization of the effect of the {;it gluon}; axial anomaly, and so removing the ${;m U};_{; m A};{; m (1)};$ problem otherwise affecting the $eta$ and $eta^prime$, we also obtain reasonable results for ${; ar f};_{;eta_0};$ and ${; ar f};_{;eta_8};$, the $gammagamma$ decay constants of $eta_0$ and $eta_8$, $eta$ and $eta^prime$ two--photon decay widths, and for the mixing--independent $R$--ratio constructed from them.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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