Special Physics Department Seminar
Damian Goeldi
Graduate Student
University of Bern
Thursday, November 16, 2017

R&D Towards an Improved Concept of a Liquid Argon Time Projection Chamber

Liquid argon time projection chambers (LArTPCs) are ideally suited for future long-baseline neutrino experiments aiming to measure CP violation in the lepton sector, and determine the ordering of the three neutrino mass eigenstates. The far detectors of these experiments will have masses up to two orders of magnitude larger than contemporary designs, while the near detectors will have to cope with unprecedented beam intensities. This poses several challenges for the detector design. Large volumes result in longer drift distances and thus require higher drift voltages. Recent studies have shown the dielectric strength of LAr to be much lower than predicted by earlier work. This triggered an in-depth study of electric breakdowns in LAr by the Bern group. LArTPCs have used projective wire readouts for charge detection since their conception in 1977. However, wire readouts are notoriously fragile and therefore a limiting factor in the design of any large mass detectors. Furthermore, a wire readout also introduces intrinsic ambiguities in event reconstruction which will be problematic in the high-multiplicity environments of near detectors. To overcome these limitations, we are developing a pixelated charge readout for LArTPCs. Pixelated charge readout systems represent the single largest advancement in the sensitivity of LArTPCs, enabling true 3D tracking. They are mechanically robust and the direct 3D readout minimises reconstruction ambiguities, reducing event pile-up and improving background rejection. Due to their increased number of channels, pixelated charge readouts give raise to the need for novel readout electronics. The Bern group is testing new electronics in LArTPCs with cosmic rays. All the R&D performed at Bern is aimed towards a new fully-modular, pixelated LArTPC concept---ArgonCube---which is the proposed LAr component of the DUNE near detector. It will address the challenges described by splitting the detector volume into a number of small, self-contained, TPCs sharing a common cryostat. ArgonCube will require only moderate drift voltages, the charge will be read out by pixels and digitised in-situ by novel cold ADCs, and scintillation light will be contained, enabling more advanced triggers.