Technical_Note

Abstract
The main component of the PANDA Barrel DIRC detector are 2:4m long synthetic fused silica
("quartz") bars with a rectangular cross section which are used as radiators and light guides. The
Cherenkov photons produced by a charged particle traversing the bar are reflected internally many
times before they reach the readout end of the bar. To guarantee a sufficiently high resolution of
the detector, these bars have to meet tight optical and mechanical specifications. Autocollimator
measurements on prototype bars of different manufacturers have been performed to very precisely
determine the squareness and parallelism of the bars. This method has been employed to see which
of the bars can meet the specifications and would be adequate to be used for the detector. So
far, bars by Lytkarino, Zeiss, Heraeus, InSync and Zygo have been measured. Furthermore the
measuring method ought to be applied in the future for quality assurance of the detector bars.
The measuring method and the results are described in this note.

The final version of the PANDA Barrel DIRC was distributed to the collaboration for review on April 12, 2017.
This short document summarizes the changes compared to the September 2016 version and provides an executive summary of the outcome of the 2016 beam test at CERN and of the decision in favor of the narrow bars with spherical lenses as baseline design for the PANDA Barrel DIRC.
The latest version of the TDR was uploaded to the publication forum at https://panda.gsi.de/publication/re-tdr-2016-001.