Scintillation light detection in the long-drift ProtoDUNE-DP liquid argon TPC

Abstract

ProtoDUNE-DP is a 6 × 6 × 6 m 3 liquid argon time-projection-chamber (LArTPC) operated at the Neutrino Platform at CERN in 2019-2020 as a prototype of the DUNE Far Detector. DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. The light signal in these detectors is crucial to provide precise timing capabilities. In ProtoDUNE-DP, scintillation light produced by cosmic muons in the LArTPC is collected by the photomultiplier tubes (PMTs) placed up to 7 m away from the point of interaction. The scintillation light production and propagation processes are analyzed and compared to simulations, improving the understanding of some liquid argon properties. ProtoDUNE Dual Phase detectorThe Deep Underground Neutrino Experiment (DUNE) aims to address key questions in neutrino physics and astroparticle physics [1, 2, 3]. DUNE will consist of a near detector placed at Fermilab close to the production point of the muon neutrino beam of the Long-Baseline Neutrino Facility (LBNF), and four 17 kt liquid argon time-projection chambers (LArTPCs) as the far detector in the Sanford Underground Research Facility (SURF) at 1300 km from Fermilab [4].The ProtoDUNE Dual Phase (DP) detector [5,6] operated at the CERN Neutrino Platform in 2019-2020 to demonstrate the LArTPC DP technology at large scale as a possibility for the DUNE far detector. ProtoDUNE-DP has an active volume of 6×6×6 m 3 corresponding to a total LAr mass of 750 t, being the largest DP LArTPC ever operated. In ProtoDUNE-DP the argon ionization creates electrons which drift vertically thanks to an electric field. The ionization charge is then extracted, amplified, and detected in gaseous argon above the liquid surface, allowing a good signal to noise ratio and a fine spatial resolution. The scintillation light signal is collected by a photon detection system (PDS) to provide a trigger, and to determine precisely the event time, with possibility to perform calorimetric measurements and particle identification. Two Cosmic Ray Tagger (CRT) planes were added to opposite walls of the ProtoDUNE-DP cryostat to trigger on muon-tracks passing through both CRTs.The PDS of ProtoDUNE-DP [7] is formed of 36 8-inch cryogenic PMTs, R5912-02MOD from Hamamatsu [8,9], placed below the cathode grid. As the PMTs are not sensitive to 127-nm light, a wavelength shifter is placed to convert this light to the PMT wavelength detection range. A light calibration system (LCS) is installed to obtain an equalized PMT response [10]. A dedicated light acquisition and calibration software was developed for ProtoDUNE-DP [11].