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First R'n'D and Physics Results with a Novel Opaque Neutrino Detector

Periodic Reporting for period 1 - LORD (First R'n'D and Physics Results with a Novel Opaque Neutrino Detector)

Reporting period: 2016-09-01 to 2018-08-31

This project dealt with developing a new technique to detect elusive particles, such as neutrinos, and rare decays in the context of particle physics. Neutrinos interact with ordinary matter extremely weakly, hence massive detectors are used to observe their passage. One class of such detectors relies on large volumes filled with a so-called organic liquid scintillator (LS), a material that emits visible light when some energy gets deposited into it. The main limitation of a LS detector is that the scintillation light is detected far away from the place where the primary interaction takes place, hence the image that one gets of the interaction is somehow blurred. That is, it is extremely difficult to disentangle if there was just one, or multiple interactions happening at the same time. Analogously, it is difficult to identify the type of particle interacting in the detector. This issue is currently limiting our capability to tag and reject background events, hence to fully exploit the LS technology for the next generation of detectors involved in the search for rare processes.

The goal of this project was to introduce a new approach to collect the scintillation light meant to improve the spatial resolution with which the particle interaction could be imaged. That is, to improve the signal-to-background discrimination in a LS detector.

The importance of this goal lies in basic science. Neutrinos have proved to be a rich source of information about the understating of our universe during the last 70 years, but many unknowns concerning their nature are yet to be solved. Advancing the detection technology is therefore the only viable way to improve our comprehension of this elusive particle.
The work performed within this project revolved around designing, simulating, and testing a new particle detection technology based on organic liquid scintillator (LS). The design of a detector prototype was conceived and optimized by means of Montecarlo simulations. The capabilities of the new detection technique were assessed for different type of particle interactions and different energy ranges, in order to identify the expected performance of a real experiment.
The simulation activity helped to identify the regime in which the proposed detection technique is expected to overcome the performance of state-of-the-art detectors. The experimental validation (still ongoing at the moment of reporting) was designed to test all the critical aspects of the new technology.
State-of-the-art particle detectors based on organic liquid scintillator (LS) are currently limited by poor spatial resolution, which prevents to reconstruct the ionization pattern generated by charged particle present in the final state of rare processes. LS technology has many advantages, such as (1) being easily scalable, that is, no need for expensive cryostats or strong electric fields in the detection volume; (2) being versatile, since new interactions can be endowed by loading the LS with heavy metals; and (3) being well suited for electron-gamma discrimination at low energy thanks to the LS low photofraction. However, despite all these advantages, poor spatial resolution is currently limiting the application of LS technology to future low background experiments.

The detection technology developed in this project goes beyond the state of the art by dramatically improving the spatial resolution of LS detectors, hence allowing to fully disentangle the energy depositions of final state particles produced in elusive interactions. This feature is pivotal to discriminate between signal and background processes, and is expected to play a major role in the design of future experiments studying rare processes in the quest to advance our understanding of the fundamental laws of physics.

The main achievement of this action was to have a viable solution for all the aspects of the new detection technique, to have a complete understanding of its physics reach, and to seed its experimental validation which is currently ongoing.

This project is expected to have an impact primarily in terms of basic science. Namely, to have future particle detectors targeting rare processes employing the technique developed in this project to improve their background rejection capability, hence boosting their sensitivity to the detection of new physics.
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