On the differential cross section and the slope of vector meson electroproduction

Vector-meson electroproduction from generalized vector dominance

“…The modification of the vector-meson electroproduction cross-section resulting from the inclusion of off-diagonal transitions of the diffraction-dissociation type was investigated in [16]. For definiteness, in [16], the calculation of vectormeson production was based on a spectrum of an infinite series of vector-meson states coupled to the photon in a manner that assures duality to quark-antiquark production in e + e − annihilation. Under the fairly general assumption of a power law for the diffraction-dissociation amplitudes (at zero t) in terms of the ratios of the masses of the diffractively produced vector states…”

“…For destructive interference among neighbouring vector-meson states, incorporated in [16] through an alternating-sign series of vector-meson states, one finds…”

“…Concerning sum rule (1): it is unaffected by the introduction of off-diagonal terms, since the initial photon remains, when passing from the left-hand side to right-hand side of (1). In relation (2), offdiagonal terms with destructively interfering amplitudes imply multiplication of each σ V p by a specific correction factor somewhat smaller than unity [16]. The result (9) (or rather the underlying amplitude) with the constraint (10) in [16] was obtained by straightforward summation of an alternating series.…”

“…In relation (2), offdiagonal terms with destructively interfering amplitudes imply multiplication of each σ V p by a specific correction factor somewhat smaller than unity [16]. The result (9) (or rather the underlying amplitude) with the constraint (10) in [16] was obtained by straightforward summation of an alternating series. In view of the ensuing extension to longitudinal photons, we note that the transverse amplitude may, to a good approximation, be represented by a sum of dipole terms 5 by combining neighbouring terms in the series.…”

The total virtual photoabsorption cross section, deeply virtual Compton scattering and vector-meson production

“…The unpolarized cross section, however, was predicted [14,36] to only decrease as 1/Q 2 in strong disagreement with presentday experimental results that require an asymptotic behavior approximately as 1/Q 6 . A revival [37] of off-diagonal GVD [38] implied a 1/Q 4 dependence for the unpolarized cross section that in fact was found [37] to be consistent with the experimental data up to around Q 2 ≤ 20 GeV 2 available at the time, including the ratio of R L/T . Since the traditional vector-dominance approach relies on (soft) Pomeron exchange, it is unable to describe the strong W dependence observed for sufficiently large values of Q 2 + M 2 V .…”