ZEUS Diffractive Physics Group
26 January 2000

Vector-Meson Photoproduction at High |t|
A Recently Proposed Model

J.A. Crittenden
P.I. Bonn

A brief summary of a recently proposed model for vector-meson photoproduction at high |t| was given. The model is based on the exchange of a new trajectory, related to f1 exchange, originally suggested in 1991 by Dorokhov and Kochelev in response to the spin crisis caused by the EMC measurements. The papers of Kochelev et al (hep-ph/9911480) and Oh et al (hep-ph/0001209) surmise that the Pomeron trajectory is related to the conformal anomaly of QCD and that the new trajectory is related to the QCD axial anomaly. The latter has a much weaker dependence on |t|, and so the prediction with both trajectories for the shape of the differential cross section matches the data we published in DESY 99-160 (and more recently in paper 499 contributed to EPS with the 1997 data) much better than the prediction for the Pomeron alone. The differing quantum numbers of the two trajectories result in different decay angular distributions. These predictions in hep-ph/0001209 for the spin-density matrix elements as a function of |t| are made in the Gottfried-Jackson frame, and can be compared to our 1997 results presented in EPS paper 499, though it is difficult to come to any clear conclusions at present. In response to a question posed during the meeting, Kochelev informed me afterwards that they have also begun calculating effects which may arise due to the dissociation of the proton.

Shortly after my talk Kochelev informed me that he and his colleagues have found an error in their calculation of the spin-density matrix elements. My transparencies have been modified to show only the corrected results.


Transparencies[html, Postscript (1.3 Mb)]
LANL Preprint hep-ph/0001209 [abs, src, ps, other]
LANL Preprint hep-ph/9911480 [abs, src, ps, other]
Kochelev note on helicity formalism [Postscript (275 kb)]
James A. Crittenden
2000-01-28