Enhancing MeV physics at DarkSide-20k



The next challenges in neutrino and direct Dark Matter (DM) searches will require increasingly massive detectors, and increasingly complex, to cover a wide range of scientific goals.  The involved energy range extends from a few tens of eV induced by low mass WIMPs and neutrinos via coherent scattering, to solar neutrinos and neutrinoless double beta decay (~MeV scale), Supernova neutrinos (~10 MeV), and accelerator neutrinos (~GeV).  Experiments specifically designed for DM searches have the potential to explore the energy range up to Supernova neutrinos. Among them, DarkSide-20k is the next generation of Liquid Argon (LAr) Time Projection Chamber (TPC), which will be running at LNGS (Italy) from 2024. 
The former DarkSide detector (DarkSide-50 filled with 50 kg LAr) has been in operation since 2013 at LNGS and set the world's best limit for WIMPs with masses in the few GeV/c2 range. For higher mass WIMPs, DarkSide-50 has demonstrated the LAr extraordinary and unique potential in searching for WIMPs in a zero-background regime. These features will allow an unprecedented research with DarkSide-20k that will be filled with 50 tons of LAr, so an active mass 1000 times greater than that of DarkSide-50. In addition, DarkSide-20k will benefit from an improved detector design and especially from the use of new generation photosensors, Silicon Photomultipliers (SiPM), customly developed by the DarkSide Collaboration with FBK, with low dark count rate and high radiopurity. 
The aim of this project is to enhance the DarkSide sensitivity to solar and Supernova (SN) neutrinos. Specifically,the two goals are: 
1) the development of an almost real-time analysis, capable to identify low energy pulses, and to buffer their time and charge information in a time window of a few tens of seconds, to completely contain the SN signal but minimizing the amount of stored data.
2) the development of algorithms to exploit the directional signature of solar neutrinos, in order to improve background discrimination and to enhance the day-night asymmetry signature, leading to improved precision each component of the spectrum.
Neutrinos from the core-collapse SN are expected to be observed by DarkSide as a burst of low-energy events distributed over a time window of O(10 s). The proposal is to exploit an averaged event response template for applying an online matched-filter to the acquired waveforms. The matched-filter is the one that maximizes the signal-to-background ratio, and consequently the identification of physics events. The variables of interest that will be stored are the signal peak time and height of the filtered pulse, through a FIFO-like storage, for about 10 times the duration of a core-collapse SN. At the same time, the proposed approach will be used to constrain the background, which will be subtracted from the window containing the SN burst. The net result is the time evolution of the SN signal and the charge spectrum of the recoiled events. The application of this approach must be done at the data acquisition level, after dedicated studies on simulated data to evaluate the efficiency of pulse identification and to optimize the algorithm.
Electronic tracks, induced by MeV solar neutrino interactions via Elastic Scattering in LAr, have mm-cm scale length. In the DarkSide TPCs, ionization electrons are drifted to the gas phase, on the top of the TPC, where they are extracted and accelerated in order to produce a light pulse (S2) via electroluminescence. The time evolution of the S2 signal is expected to depend on the electronic recoil track orientation: ionization electrons from tracks orthogonal to the drift field reach the gas pocket at the same time and induce simultaneous S2 signals; in contrast, tracks parallel to the field induce longer signals, as the electrons at the two vertices of the track are delayed by a time proportional to the track length. Track orientation with respect to the Earth-Sun direction as a signature for solar neutrinos will be assessed by analysing DS-50 calibration data acquired with a 22Na source. Directional information is expected when looking at Compton electrons and considering the correlation of the S2 shape with the source position. The DS-20k sensitivity to solar neutrinos on the directional signature will then be evaluated.
In order to cope with the limitations imposed by the triggerless acquisition of DarkSide-20k, mainly dictated by computing resources in terms of storage and computing power, one possibility is to explore the development of algorithms, based on Artificial Intelligence (AI), that are fast enough to be used at the online level and capable of identifying and isolating channels and portions of waveforms of interest to the particular physics being studied. One possible development of the thesis is the contribution to the development of such algorithms and the evaluation of their performance on the two MeV physics channels mentioned above.

Contacts : tonazzoatapc.in2p3.fr (Alessandra Tonazzo), Davide Franco

Spcial application procedure via the CSC call https://doctorat.u-paris.fr/china-scholarship-council-at-up/?lang=en


Davide Franco, Alessandra Tonazzo






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