arXiv subjects

C. Frigerio Martins

Publications and source records attributed to C. Frigerio Martins.

7 recordsLinked to original sources

arXiv2026

Energy, vertex, and time response of a LiquidO detector with an opaque-scintillator target to Compton-tagged electrons

LiquidO detectors confine scintillation light near its point of production by stochastic scattering in an opaque medium and collect it with a lattice of wavelength-shifting (WLS) fibers. The elementary signal of such a detector is the point-like sub-MeV energy deposition, yet the response to that signal at the center of the detector volume has not been measured against an event-by-event ground truth. To close this gap, we couple BPULSE, a 4-liter prototype LiquidO detector, to a Compton-coincidence calibration setup that selects electron recoils of known energy on a constrained beam axis. The prototype is a 160 mm cube of opaque scintillator with 64 WLS fibers in alternating orthogonal layers at a 20 mm pitch, read out by silicon photomultipliers. Compton scatters of collimated gamma-ray beams from $^{137}$Cs and $^{60}$Co sources are tagged by a NaI(Tl) spectrometer. For 373.4 keV electrons, tagged from $90^{\circ}$ scatters of the $^{137}$Cs beam, the detector collects $19.04 \pm 0.07$ photoelectrons (p.e.). Across four operating points, the two sources at two scattering angles, it responds linearly at $48.3 \pm 1.5$ p.e./MeV. The energy resolution of $(23.4 \pm 0.4)\%$ matches the Poisson statistics of the detected photoelectrons. Collection at both fiber ends and larger sensors would raise the light yield of this target to an estimated 108-124 p.e./MeV. Center-of-mass reconstruction locates each recoil to the width of the delivered 20 mm beam spot, which bounds the intrinsic localization of the detector from above. The arrival time response sets a lower bound of 1.5 ns on the single-scatter start time at the observed $\approx 19$ p.e. light level. This single-scatter response is the building block for reconstructing multi-site events. It constrains the light collection, confinement, and timing models on which reconstruction in future LiquidO detectors will rest.

physics.ins-det↗

arXiv2026

Muon tracking in a LiquidO opaque scintillator detector

LiquidO is an innovative radiation detector concept. The core idea is to exploit stochastic light confinement in a highly scattering medium to self-segment the detector volume. In this paper, we demonstrate event-by-event muon tracking in a LiquidO opaque scintillator detector prototype. The detector consists of a 30 mm cubic scintillator volume instrumented with 64 wavelength-shifting fibres arranged in an 8$\times$8 grid with a 3.2 mm pitch and read out by silicon photomultipliers. A wax-based opaque scintillator with a scattering length of approximately 0.5 mm is used. The tracking performance of this LiquidO detector is characterised with cosmic-ray muons and the position resolution is demonstrated to be 450 $μ$m per row of fibres. These results highlight the potential of LiquidO opaque scintillator detectors to achieve fine spatial resolution, enabling precise particle tracking and imaging.

physics.ins-det↗

arXiv2025

COCOA: a compact Compton camera for astrophysical observation of MeV-scale gamma rays

COCOA (COmpact COmpton cAmera) is a next-generation gamma-ray telescope designed for astrophysical observations in the MeV energy range. The detector comprises a scatterer volume employing the LiquidO detection technology and an array of scintillating crystals acting as absorber. Surrounding plastic scintillator panels serve as a veto system for charged particles. The detector's compact, scalable design enables flexible deployment on microsatellites or high-altitude balloons. Gamma rays at MeV energies have not been well explored historically (the so-called "MeV gap") and COCOA has the potential to improve the sensitivity in this energy band.

astro-ph.IM↗

arXiv2025

The Stochastic Light Confinement of LiquidO

Light-based detectors have been widely used in fundamental research and industry since their inception in the 1930s. The energy particles deposit in these detectors is converted to optical signals via the Cherenkov and scintillation mechanisms that are then propagated through transparent media to photosensors placed typically on the detector's periphery, sometimes up to tens of metres away. LiquidO is a new technique pioneering the use of opaque media to stochastically confine light around each energy deposition while collecting it with an array of fibres that thread the medium. This approach preserves topological event information otherwise lost in the conventional approach, enabling real-time imaging down to the MeV scale. Our article demonstrates LiquidO's imaging principle with a ten-litre prototype, revealing successful light confinement of 90% of the detected light within a 5 cm radius sphere, using a custom opaque scintillator with a scattering length on the order of a few millimetres. These high-resolution imaging capabilities unlock opportunities in fundamental physics research and applications beyond. The absolute amount of light detected is also studied, including possible data-driven extrapolations to LiquidO-based detectors beyond prototyping limitations. Additionally, LiquidO's timing capabilities are explored through its ability to distinguish Cherenkov light from a slow scintillator.

physics.ins-det↗

arXiv2022

Neutrino Physics with an Opaque Detector

In 1956 Reines & Cowan discovered the neutrino using a liquid scintillator detector. The neutrinos interacted with the scintillator, producing light that propagated across transparent volumes to surrounding photo-sensors. This approach has remained one of the most widespread and successful neutrino detection technologies used since. This article introduces a concept that breaks with the conventional paradigm of transparency by confining and collecting light near its creation point with an opaque scintillator and a dense array of optical fibres. This technique, called LiquidO, can provide high-resolution imaging to enable efficient identification of individual particles event-by-event. A natural affinity for adding dopants at high concentrations is provided by the use of an opaque medium. With these and other capabilities, the potential of our detector concept to unlock opportunities in neutrino physics is presented here, alongside the results of the first experimental validation.

physics.ins-det↗

arXiv2010

The dark matter density at the Sun's location

We derive the value of the dark matter density at the Sun's location (rho_0) without globally mass-modeling the Galaxy. The proposed method relies on the local equation of centrifugal equilibrium and is independent of i) the shape of the dark matter density profile, ii) knowledge of the rotation curve from the galaxy center out to the virial radius, and iii) the uncertainties and the non-uniqueness of the bulge/disk/dark halo mass decomposition. The result can be obtained in analytic form. It explicitly includes the dependence on the relevant observational quantities and takes their uncertainties into account. By adopting the reference, state-of-the-art values for these, we find rho_0 = 0.43(11)(10)GeV/cm3, where the quoted uncertainties are respectively due to the uncertainty in the slope of the circular-velocity at the Sun location and the ratio between this radius and the length scale of the stellar exponential thin disk. We obtain a reliable estimate of rho_0, that, in addition, is ready to take into account any future change/improvement in the measures of the observational quantities it depends on.

astro-ph.GA↗

arXiv2009

A constant dark matter halo surface density in galaxies

We confirm and extend the recent finding that the central surface density r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co-added rotation curves of about 1000 spiral galaxies, mass models of individual dwarf irregular and spiral galaxies of late and early types with high-quality rotation curves and, galaxy-galaxy weak lensing signals from a sample of spiral and elliptical galaxies, we find that log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the observed kinematics of Local Group dwarf spheroidal galaxies are consistent with this value. Our results are obtained for galactic systems spanning over 14 magnitudes, belonging to different Hubble Types, and whose mass profiles have been determined by several independent methods. In the same objects, the approximate constancy of rho_0*r_0 is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including rho_0 and central stellar surface density.

astro-ph.CO↗