Publications

Liquid argon time projection chambers have emerged as a competitive technology for detecting solar neutrinos. The SoLAr collaboration was formed to explore argon detectors with pixelated light and charge readout, aiming for high detection efficiency and improved energy resolution. Building on the success of an initial prototype, we present results obtained with a second SoLAr prototype (V2), a 30 × 30 × 30 cm3 time projection chamber operated in a cryostat containing several hundred kilograms of liquid argon. We report measurements of cosmic-ray muons using both tracking and calorimetry from light and charge sensors, and we highlight the improved performance achieved through combined charge-and-light reconstruction. These results demonstrate the promise of dual-readout detectors and motivate future prototyping efforts toward kiloton-scale facilities.

The study of solar neutrinos presents significant opportunities in astrophysics, nuclear physics, and particle physics. However, the low-energy nature of these neutrinos introduces considerable challenges to isolate them from background events, requiring detectors with low-energy threshold, high spatial and energy resolutions, and low data rate. We present the study of solar neutrinos with a kiloton-scale liquid argon detector located underground, instrumented with a pixel readout using the Q-Pix technology. We explore the potential of using volume fiducialization, directional topological information, light signal coincidence, and pulse-shape discrimination to enhance solar neutrino sensitivity. We find that discriminating neutrino signals below 5 MeV is very difficult. However, we show that these methods are useful for the detection of solar neutrinos when external backgrounds are sufficiently understood and when the detector is built using low-background techniques. When building a workable background model for this study, we identify 𝛾 background from the cavern walls and from capture of 𝛼 particles in radon decay chains as both critical to solar neutrino sensitivity and significantly underconstrained by existing measurements. Finally, we highlight that the main advantage of the use of Q-Pix for solar neutrino studies lies in its ability to enable the continuous readout of all low-energy events with minimal data rates and manageable storage for further off-line analyses.

The novel SoLAr concept aims to extend sensitivities of liquid-argon neutrino detectors down to the MeV scale for next-generation detectors. SoLAr plans to accomplish this with a liquid-argon time projection chamber that employs an anode plane with dual charge and light readout, which enables precision matching of light and charge signals for data acquisition and reconstruction purposes. We present the results of a first demonstration of the SoLAr detector concept with a small-scale prototype detector integrating a pixel-based charge readout and silicon photomultipliers on a shared printed circuit board. We discuss the design of the prototype, and its operation and performance, highlighting the capability of such a detector design.

The interacting binary Eta Carinae remains one of the most enigmatic massive stars in our Galaxy despite over four centuries of observations. In this work, its light curve from the ultraviolet to the near-infrared is analysed using spatially resolved HST observations and intense monitoring at the La Plata Observatory, combined with previously published photometry. We have developed a method to separate the central stellar object in the ground-based images using HST photometry and applying it to the more numerous ground-based data, which supports the hypothesis that the central source is brightening faster than the almost-constant Homunculus. After detrending from long-term brightening, the light curve shows periodic orbital modulation (ΔV ∼ 0.6 mag) attributed to the wind-wind collision cavity as it sweeps around the primary star and it shows variable projected area to our line-of-sight. Two quasi-periodic components with time scales of 2-3 and 8-10 yr and low amplitude, ΔV < 0.2 mag, are superimposed on the brightening light-curve, being the only stellar component of variability found, which indicates minimal stellar instability. Moreover, the light curve analysis shows no evidence of `shell ejections’ at periastron. We propose that the long-term brightening of the stellar core is due to the dissipation of a dusty clump in front of the central star, which works like a natural coronagraph. Thus, the central stars appear to be more stable than previously thought since the dominant variability originates from a changing circumstellar medium. We predict that the brightening phase, due mainly to dust dissipation, will be completed around 2032 ± 4 yr, when the star will be brighter than in the 1600’s by up to ΔV ∼ 1 mag.

The SoLAr concept introduces a novel liquid-argon neutrino detector technology to enhance sensitivity in the MeV energy range, broadening the scope to include solar and supernovae neutrinos. This technology is based on a monolithic light-charge pixel-based readout, offering a low energy threshold, exceptional energy resolution (approximately 7%), and effective background rejection through pulse-shape discrimination. The primary objective is to observe solar neutrinos in a 10-kiloton-scale detector, ultimately leading to precise measurements of the 8B flux, improved solar neutrino mixing parameters, and the first observation of the hep neutrino flux. It is also a timely technology choice for the DUNE “Module of Opportunity”, which could serve as a next-generation multi-purpose observatory for neutrinos from the MeV to the GeV range. A staged prototyping program is in progress to validate the viability of this detector concept, with a prospect to build a medium-sized demonstrator in the Boulby Underground Laboratory. Here, we present preliminary results from the prototype run in July 2023, showcasing cosmic muon tracks detected for the first time with an integrated light and charge readout.

SoLAr is a new concept for a liquid-argon neutrino detector technology to extend the sensitivities of these devices to the MeV energy range - expanding the physics reach of these next-generation detectors to include solar neutrinos. We propose this novel concept to significantly improve the precision on solar neutrino mixing parameters and to observe the “hep branch” of the proton-proton fusion chain. The SoLAr detector will achieve flavour-tagging of solar neutrinos in liquid argon. The SoLAr technology will be based on the concept of monolithic light-charge pixel-based readout which addresses the main requirements for such a detector: a low energy threshold with excellent energy resolution (approximately 7%) and background rejection through pulse-shape discrimination. The SoLAr concept is also timely as a possible technology choice for the DUNE “Module of Opportunity”, which could serve as a next-generation multi-purpose observatory for neutrinos from the MeV to the GeV range. The goal of SoLAr is to observe solar neutrinos in a 10 ton-scale detector and to demonstrate that the required background suppression and energy resolution can be achieved. SoLAr will pave the way for a precise measurement of the 8-B flux, an improved precision on solar neutrino mixing parameters, and ultimately lead to the first observation of hep neutrinos in the DUNE Module of Opportunity.

This thesis presents a study of low-energy solar neutrino detection using large-scale Liquid-Argon Time Projection Chambers (LArTPCs), focussing on novel pixelated readout technologies. Solar neutrinos offer a unique probe of fundamental neutrino properties and solar physics, but their detection in the MeV range is challenged by backgrounds. We investigate two complementary technologies: SoLAr, which integrates LArPix-based pixelated charge collection with Silicon Photomultipliers (SiPMs) in a hybrid anode design for simultaneous charge and light detection; and Q-Pix, a triggerless pixelated readout architecture based on charge integrate-reset circuits with local clocks, where Reset Time Differences encode ionisation waveforms via time-to-charge conversion. Two SoLAr prototypes were developed and operated, demonstrating VUV-sensitive SiPM performance in liquid argon and accurate charge-light signal matching with a charge detection threshold of ∼ 100 keV. We also implement a complete simulation and reconstruction framework, incorporating realistic detector geometry, electron transport, readout response, and detailed signal and background models, including intrinsic argon and radon progeny, as well as site-specific γ-ray and neutron fluxes. For Q-Pix, we demonstrate that with a pixel size of 4 × 4 mm² and a reset threshold of 1 fC (∼ 0.1475 MeV), full-scale operation produces data volumes below 1 PB per 10 ktonne−year. For SoLAr, assuming a shielded DUNE-like detector and 100 ktonne−year exposure, we project uncertainties of 0.90 × 10⁻⁵ eV² on Δm²₂₁ and 0.033 on sin² θ₁₂, improving to 0.46 × 10⁻⁵ eV² and 0.025 with 400 ktonne−year. At this higher exposure, we also obtain a day–night flux asymmetry at the level of (−5.6 ± 3.6) %. Combining Monte Carlo modelling, hardware validation, and advanced reconstruction techniques, this work establishes a path toward next-generation kilotonne-scale LArTPCs as observatories for precision solar neutrino physics.