RadPhi TechNote
radphi-2000-501
May 15, 2000
The Radphi experiment uses a beryllium disk as a photoproduction target. During 1999 commissioning we ran with a target thickness of 2.6cm and found that the experiment could sustain rates up to 5•10/s. For the main physics run in Y2000 several additional target disks have been fabricated in case we need them. Assuming that the requested radiator of 3•10
rad.len. is installed we will have sufficient flexibility in terms of beam current to consider either increasing or decreasing our target thickness, in steps of 1.3cm. Increasing the target thickness diminishes our sensitivity to detector backgrounds not associated with the target, eg. beam halo, but eventually it begins to limit the angular resolution for showers reconstructed in the lead glass. One also has to be concerned about loss in efficiency due to conversions of final-state photons inside the target. Decreasing our target thickness to 1.3cm can also be considered if it would lead to a significant improvement in efficiency. This note reports the results of a study of all of these effects, and concludes that the target thickness of 2.6cm is close to optimum.