Akesson, P.F.
hep-ex
Photoproduction
[2.0, 5.0]
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Measurement of the cross-section for the process gamma gamma --> p anti-p at s(ee)**(1/2) = 183-GeV - 189-GeV at LEP.

The OPAL collaboration Abbiendi, G. ; Ainsley, C. ; Akesson, P.F. ; et al.
Eur.Phys.J.C 28 (2003) 45-54, 2003.
Inspire Record 595836 DOI 10.17182/hepdata.48881

The exclusive production of proton-antiproton pairs in the collisions of two quasi-real photons had been studied using data taken at sqrt(s)_ee=183 GeV and 189 GeV with the OPAL detector at LEP. Results are presented for Ppbar invariant masses, W, in the range 2.15 W< <3.95 GeV. The cross-section measurements are compared with previous data and with recent analytic calculations based on the quark-diquark model.

3 data tables
Table 1

Cross section as a function of the invariant mass of the pbar-p pair.

Table 2

Cross section for two photon production of the pbar-p pair.

Table 3

Angular distributions in 3 W ranges.


Exclusive leptoproduction of rho0 mesons from hydrogen at intermediate virtual photon energies.

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akushevich, I. ; et al.
Eur.Phys.J.C 17 (2000) 389-398, 2000.
Inspire Record 526550 DOI 10.17182/hepdata.47010

Measurements of the cross section for exclusive virtual-photoproduction of rho^0 mesons from hydrogen are reported. The data were collected by the HERMES experiment using 27.5 GeV positrons incident on a hydrogen gas target in the HERA storage ring. The invariant mass W of the photon-nucleon system ranges from 4.0 to 6.0 GeV, while the negative squared four-momentum Q^2 of the virtual photon varies from 0.7 to 5.0 GeV^2. The present data together with most of the previous data at W > 4 GeV are well described by a model that infers the W-dependence of the cross section from the dependence on the Bjorken scaling variable x of the unpolarized structure function for deep-inelastic scattering. In addition, a model calculation based on Off-Forward Parton Distributions gives a fairly good account of the longitudinal component of the rho^0 production cross section for Q^2 > 2 GeV^2.

2 data tables
Table 1

Cross sections are corrected for radiative effects (which typically amount s to 18 PCT).

Table 2

Longitudinal cross sections. The listed uncertainties include both the total error on the measured RHO0 photoproduction cross sections and the error on theparametrization of R for W<7 GeV.