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First light and tracks in WA105 at CERN

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First light and tracks in WA105 at CERN

On June 21st the WA105 prototype detector saw its first tracks from cosmic rays. This is an important step towards the futur giant neutrino detector DUNE !

The aim of the DUNE detector is the study of the difference between neutrinos and anti-neutrinos, looking for an asymmetry which could shed light on the absence of anti-matter in our Universe !

The WA105 detector is a demonstrator whose aim is to direct and validate the technologies that will be used for DUNE. LAPP actively participates to the WA105 project on various items : mechanics, automatism, simulation, data analysis. WA105 is an international collaboration with 14 institutes, among which 4 IN2P3 laboratories (APC, LPHNE, IPNL, LAPP) and the IRFU at CEA.

This detector is based on a time projection chamber and contains 5 tonnes (3000 litres) of liquid argon at -185°C. The passage of charged particles is detected through the emitted light and electron production in the argon. On the contrary to other such detectors, WA105 also contains a small fraction of argon gaz above the liquid : this is a 2 phase detector. With this design electrons drift thanks to an electric field up to the gaseous phase and are multiplied in this phase to provide an amplified signal, allowing the 3D tracks reconstruction.

Fig. 1 : WA105 3x1x1 detector when inserted in the cryostat.

In order to work at -185°C the detector is placed in a giant cryostat with 1m thick walls (Fig. 1). After some tuning period the first particles were observed by detecting in coincidence the scintillation light and collecting the electrons on the anode planes after amplification in the gaz. Figure 2 shows the first track from a cosmic ray.

Fig. 2 : First track from a cosmic ray

This large cryostat anticipates those under construction at CERN for the future generation of liquid argon detectors called ProtoDUNE. These detectors will serve as demonstrators for the validation of all technological and scientific aspects before the construction of the 10 kilo-tonne modules foreseen for DUNE.

The next steps for the WA105 project are the data acquisition and analysis and the construction of the next demonstrator, called ProtoDUNE-DP (Double Phase) at CERN, with 200 000 liquid argon litres. This detector will be placed in a beam of charged particles and is expected collect data at the end of 2018.

Contact : Dominique Duchesneau