Simulation Study of Photon-to-Digital Converter (PDC) Timing Specifications for LoLX Experiment

The Light only Liquid Xenon (LoLX) experiment is a prototype detector aimed to study liquid xenon (LXe) light properties and various photodetection technologies. LoLX is also aimed to quantify LXe's time resolution as a potential scintillator for 10~ps time-of-flight (TOF) PET. Another key goal of LoLX is to perform a time-based separation of Cerenkov and scintillation photons for new background rejection methods in LXe experiments. To achieve this separation, LoLX is set to be equipped with photon-to-digital converters (PDCs), a photosensor type that provides a timestamp for each observed photon. To guide the PDC design, we explore requirements for time-based Cerenkov separation. We use a PDC simulator, whose input is the light information from the Geant4-based LoLX simulation model, and evaluate the separation quality against time-to-digital converter (TDC) parameters. Simulation results with TDC parameters offer possible configurations supporting a good separation. Compared with the current filter-based approach, simulations show Cerenkov separation level increases from 54% to 71% when using PDC and time-based separation. With the current photon time profile of LoLX simulation, the results also show 71% separation is achievable with just 4 TDCs per PDC. These simulation results will lead to a specification guide for the PDC as well as expected results to compare against future PDC-based experimental measurements. In the longer term, the overall LoLX results will assist large LXe-based experiments and motivate the assembly of a LXe-based TOF-PET demonstrator system.Comment: 5 pages, 7 figure

Scintillation detectors with silicon photomultiplier readout in a dilution refrigerator at temperatures down to 0.2 K

We are developing a novel high-brightness atomic beam, comprised of a two-body exotic atom called muonium (M = μ + + e -), for next-generation atomic physics and gravitational interaction measurements. This M source originates from a thin sheet of superfluid helium (SFHe), hence diagnostics and later measurements require a detection system which is operational in a dilution cryostat at temperatures below 1 K. In this paper, we describe the operation and characterization of silicon photomultipliers (SiPMs) at ultra-low temperatures in SFHe targets. We show the temperature dependence of the signal shape, breakdown voltage, and single photon detection efficiency, concluding that single photon detection with SiPMs below 0.85 K is feasible. Furthermore, we show the development of segmented scintillation detectors, where 16 channels at 1.7 K and one channel at 170 mK were commissioned using a muon beam.ISSN:1748-022

First Demonstration of a Pixelated Charge Readout for Single-Phase Liquid Argon Time Projection Chambers

Liquid Argon Time Projection Chambers (LArTPCs) have been selected for the future long-baseline Deep Underground Neutrino Experiment (DUNE). To allow LArTPCs to operate in the high-multiplicity near detector environment of DUNE, a new charge readout technology is required. Traditional charge readout technologies introduce intrinsic ambiguities, combined with a slow detector response, these ambiguities have limited the performance of LArTPCs, until now. Here, we present a novel pixelated charge readout that enables the full 3D tracking capabilities of LArTPCs. We characterise the signal to noise ratio of charge readout chain, to be about 14, and demonstrate track reconstruction on 3D space points produced by the pixel readout. This pixelated charge readout makes LArTPCs a viable option for the DUNE near detector complex.Traditional charge readout technologies of single-phase Liquid Argon Time projection Chambers (LArTPCs) based on projective wire readout introduce intrinsic ambiguities in event reconstruction. Combined with the slow response inherent in LArTPC detectors, reconstruction ambiguities have limited their performance, until now. Here, we present a proof of principle of a pixelated charge readout that enables the full 3D tracking capabilities of LArTPCs. We characterize the signal-to-noise ratio of charge readout chain to be about 14, and demonstrate track reconstruction on 3D space points produced by the pixel readout. This pixelated charge readout makes LArTPCs a viable option for high-multiplicity environments

Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO

Abstract Liquid xenon time projection chambers are promising detectors to search for neutrinoless double beta decay (0 $$\nu \beta \beta$$ ν β β ), due to their response uniformity, monolithic sensitive volume, scalability to large target masses, and suitability for extremely low background operations. The nEXO collaboration has designed a tonne-scale time projection chamber that aims to search for 0 $$\nu \beta \beta$$ ν β β of $$^{136}$$ 136 Xe with projected half-life sensitivity of $$1.35\times 10^{28}$$ 1.35 × 10 28  yr. To reach this sensitivity, the design goal for nEXO is $$\le$$ ≤ 1% energy resolution at the decay Q-value ( $$2458.07\pm 0.31$$ 2458.07 ± 0.31  keV). Reaching this resolution requires the efficient collection of both the ionization and scintillation produced in the detector. The nEXO design employs Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm scintillation light of liquid xenon. This paper reports on the characterization of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3 SiPMs specifically designed for nEXO, as well as new measurements on new test samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters (MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct crosstalk, correlated avalanches and photon detection efficiency were measured as a function of the applied over voltage and wavelength at liquid xenon temperature (163 K). The results from this study are used to provide updated estimates of the achievable energy resolution at the decay Q-value for the nEXO design

Laser excitation of the 1s-hyperfine transition in muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen (μp) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with 2×10-4 relative accuracy. In the proposed experiment, the μp atom undergoes a laser excitation from the singlet hyperfine state to the triplet hyperfine state, then is quenched back to the singlet state by an inelastic collision with a H2 molecule. The resulting increase of kinetic energy after the collisional deexcitation is used as a signature of a successful laser transition between hyperfine states. In this paper, we calculate the combined probability that a μp atom initially in the singlet hyperfine state undergoes a laser excitation to the triplet state followed by a collisional-induced deexcitation back to the singlet state. This combined probability has been computed using the optical Bloch equations including the inelastic and elastic collisions. Omitting the decoherence effects caused by the laser bandwidth and collisions would overestimate the transition probability by more than a factor of two in the experimental conditions. Moreover, we also account for Doppler effects and provide the matrix element, the saturation fluence, the elastic and inelastic collision rates for the singlet and triplet states, and the resonance linewidth. This calculation thus quantifies one of the key unknowns of the HFS experiment, leading to a precise definition of the requirements for the laser system and to an optimization of the hydrogen gas target where μp is formed and the laser spectroscopy will occur.ISSN:2542-465

Diffusion of muonic hydrogen in hydrogen gas and the measurement of the 1 s hyperfine splitting of muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen (μp) with 1 ppm accuracy by means of pulsed laser spectroscopy. In the proposed experiment, the μp atom is excited by a laser pulse from the singlet to the triplet hyperfine sub-levels, and is quenched back to the singlet state by an inelastic collision with a H₂ molecule. The resulting increase of kinetic energy after this cycle modifies the μp atom diffusion in the hydrogen gas and the arrival time of the μp atoms at the target walls. This laser-induced modification of the arrival times is used to expose the atomic transition. In this paper we present the simulation of the μp diffusion in the H₂ gas which is at the core of the experimental scheme. These simulations have been implemented with the Geant4 framework by introducing various low-energy processes including the motion of the H₂ molecules, i.e. the effects related with the hydrogen target temperature. The simulations have been used to optimize the hydrogen target parameters (pressure, temperatures and thickness) and to estimate signal and background rates. These rates allow to estimate the maximum time needed to find the resonance and the statistical accuracy of the spectroscopy experiment.ISSN:2666-936