Two photon annihilation into baryon anti-baryon pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard gamma gamma -> q qbar subprocess and form factors describing the soft q qbar -> B Bbar transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called B Bbar distribution amplitudes. A characteristic feature of the handbag mechanism is the absence of isospin-two components in the final state, which in combination with flavor symmetry provides relations among the form factors for the members of the lowest-lying baryon octet. Assuming dominance of the handbag contribution, we can describe current experimental data with form factors of plausible size, and predict the cross sections of presently unmeasured B Bbar channels.

Note:

20 pages latex, 4 figures. v2: minor clarifications, references updated Report-no: WU B 02-06, NORDITA-2002-15 HE

photon photon: annihilation
baryon: pair production
baryon: photoproduction
scattering amplitude: factorization
quark: pair production
form factor: energy dependence
momentum spectrum: parton
moment
Feynman graph: higher-order
symmetry: SU(3)

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