Bound-state effects in $\mu^{+}e^{-} \to \gamma \gamma$ and $\bar{B}^{0}_{s} \to \gamma \gamma$ decays

J.O. Eeg; K. Kumericki; I. Picek

doi:doi:10.1007/s100520000471

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2023 Impact factor 4.2

Particles and Fields

Eur. Phys. J. C 17, 163-168
DOI 10.1007/s100520000471

Bound-state effects in $\mu^{+}e^{-} \to \gamma \gamma$ and $\bar{B}^{0}_{s} \to \gamma \gamma$ decays

J.O. Eeg¹ - K. Kumericki² - I. Picek²

¹ Department of Physics, University of Oslo, 0316 Oslo, Norway
² Department of Physics, Faculty of Science, University of Zagreb, P.O.B. 331, 10002 Zagreb, Croatia

Received: 7 April 2000 / Revised version: 10 May 2000 /
Published online: 9 August 2000 - © Springer-Verlag 2000

Abstract
We demonstrate that in the double-radiative decays of heavy-light QED and QCD atoms, $\mu^{+} e^{-} \rightarrow \gamma\gamma$ and $\bar{B}^{0}_{s} \rightarrow\gamma\gamma$ , there is a contribution coming from operators that vanish on the free-quark mass shell. This off-shell effect is suppressed with respect to the effect of the well-known flavour-changing magnetic-moment operator by the bound-state binding factor. Accordingly, the negligible off-shellness of the weakly bound QED atoms becomes important for strongly bound QCD atoms. We present this effect in two different model approaches to QCD, one of them enabling us to keep close contact to the related effect in QED.