TA-POS-2016-052

The PANDA detector [1] at the new, unique international accelerator facility FAIR, is designed to measure reactions induced by high intensity antiproton beams impinging on hydrogen as well as on nuclear targets, enabling a rich program of hadron physics in the charm quark sector. Hadronic particle identification in the region surrounding the interaction point will be performed with a Barrel DIRC, inspired by the successes of the BaBar DIRC [2]. The main task of the Barrel DIRC is to separate charged pions and kaons with > 3 for polar angles between 22 and 140 and particle momenta up to 3.5 GeV/c. In the baseline design long radiators (240 cm), surrounding the beam pipe at a radial distance of 47.6 cm, have on one end a highly reflective mirror and on the other end a lens system focussing the Cherenkov light into an expansion volume (EV). The EV directs the light from the radiator bars on to the photon detection plane. In test beams at GSI, pions with a momentum of 1.7 GeV/c hit the radiator coupled to a 30 cm-deep expansion prism, both made from synthetic fused silica, and with a 35 array of XP85012 [3] Microchannel-Plate PMTs (MCP-PMTs), comprising a total of 960 pixels, see Fig. 1.

The photon time of arrival and the time-over-threshold were measured by TDCs on a total of 24 trigger and readout boards (TRB3) [4]. An example of observed Cherenkov images is shown in Fig. 2. Further detailed studies were performed, in particular of wide radiator plates in combination with a variety of focusing optics, see Fig. 3, in a secondary hadron/lepton beam at the T9 beam line area of the CERN proton synchrotron. Wide plate radiators are of particular interest, due to significant fabrication cost reduction compared to narrow bars. The primary goal of the CERN beam test in 2015 was the experimental validation of the PID performance of the wide plate geometry using a time-based imaging reconstruction approach.

We present performance studies of the Barrel DIRC design for PANDA, based on test beam data at GSI and CERN, with the use of fast and finely segmented photon detectors, exploring the shape of radiator bars and lens systems to focus the Cherenkov photons. The results will form the basis for the Technical Design Report, expected to be completed by mid-2016.


References
[1] PANDA Collaboration, Physics Performance Report (arXiv:0903.3905v1), 2009.
[2] I. Adam, et al., Nucl. Instr. and Meth. A 538 (2005) 281.
[3] https://www.photonis.com/uploads/datasheet/pd/PLANACON-8x8-datasheet.pdf
[4] C. Ugur, et al., IEEE Nordic-MediterraneanWorkshop on Time to Digital Converters, 2013, DOI: 10.1109/NoMeTDC.2013.6658234.