Triplet Asymmetry Calculation

Richard Jones
Sergey Chatrchyan
Hrachya Hakobyan
started Nov 20, 2003
last updated

The goal is to establish a method for measuring the polarization of a GeV-scale photon beam in a plane-polarization basis. The method should be based upon a process with a large physics asymmetry, for which the theoretical uncertainties on the asymmetry are small. Atomic pair production has a large asymmetry but its theoretical calculation is complicated by the dominance of the low-q2 part of the cross section where the nuclear charge is partially screened by atomic electrons. This can be taken into account by using the atomic form-factor, but that assumes that the scattering is elastic and fails to take into account atomic excitations that take place during the scattering process. One way to avoid the complications of atomic physics is to select the kinematics of pair production from a free electron and then detect the recoil electron in the final state. If the recoil electron is detected with sufficient momentum then the final-state interactions will be weak, and the process can be calculated from QED.

To our knowledge, so far no complete QED calculation of this process that takes polarization into account has been published. We undertake to carry out a numerical calculation ourselves, at tree level QED, and publish the results. As a check, we want to compare our results with published results that should be good approximations for some range of kinematics.

Table of Contents

What kinematics should we use to describe the process?

[RTJ] Nov 16, 2003
[HH] Dec 4, 2003

Does the calculation lead to a practical result?

[HH] Dec 4, 2003
[RTJ] Dec 8, 2003

Do we agree on the shape of the unpolarized cross section?

[RTJ] Dec 8, 2003



[1] "Workshop on Polarized Photon Polarimetry", W.J. Briscoe, M. Khandaker, and B. Wojtsekhowski, CLAS-NOTE 98-018 (1998) pdf
[2] "Exact Evaluation of Triplet Photoproduction", I. Endo and T. Kobayashi, Nucl. Instr. Meth. A328 (1993) 517-521.
[3] "Measuring Linear Polarization of Real Photons", Y.P. Peresunko, V.F. Bodyshev and E.A. Vinokurov, Fizika B8 (1999) 101-106. pdf
[3] "Triplet Production by Linearly Polarized Photons", I.V. Akushevich, H. Anlauf, E.A. Kuraev, P.G. Ratcliffe and B.G. Shaikhatdenov, (1999) 1-13. pdf

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