Short-baseline Neutrino Research Articles

Scintillation light in SBND: simulation, reconstruction, and expected performance of the photon detection system

SBND is the near detector of the Short-Baseline Neutrino program at Fermilab. Its location near to the Booster Neutrino Beam source and relatively large mass will allow the study of neutrino interactions on argon with unprecedented statistics. This paper describes the expected performance of the SBND photon detection system, using a simulated sample of beam neutrinos and cosmogenic particles. Its design is a dual readout concept combining a system of 120 photomultiplier tubes, used for triggering, with a system of 192 X-ARAPUCA devices, located behind the anode wire planes. Furthermore, covering the cathode plane with highly-reflective panels coated with a wavelength-shifting compound recovers part of the light emitted towards the cathode, where no optical detectors exist. We show how this new design provides a high light yield and a more uniform detection efficiency, an excellent timing resolution and an independent 3D-position reconstruction using only the scintillation light. Finally, the whole reconstruction chain is applied to recover the temporal structure of the beam spill, which is resolved with a resolution on the order of nanoseconds.

Decaying sterile neutrinos at short baselines

Long-standing anomalous experimental results from short-baseline neutrino experiments have persisted for decades. These results, when interpreted with one or more light sterile neutrinos, are inconsistent with numerous null results experimentally. However, if the sterile neutrino decays en route to the detector, this can mimic νμ→νe oscillation signals while avoiding many of these external constraints. We revisit this solution to the MiniBooNE and LSND puzzles in view of new data from the MicroBooNE experiment at Fermilab. Using MicroBooNE’s liquid-argon time-projection chamber search for an excess of νe in the Booster beam, we derive new limits in two models’ parameter spaces of interest; where the sterile neutrino decays (I) via mixing with the active neutrinos, or (II) via higher-dimensional operators. We also provide an updated, comprehensive fit to the MiniBooNE neutrino- and antineutrino-beam data, including appearance (νe) and disappearance (νμ) channels. Despite alleviating the tension with muon neutrino disappearance experiments, we find that the latest MicroBooNE analysis rules out the decaying sterile neutrino solution in a large portion of the parameter space at more than 99% CL. Published by the American Physical Society 2024

Short baseline neutrino anomalies at stopped pion experiments

Stopped-pion experiments that measure coherent elastic neutrino-nucleus scattering (CEνNS) are sensitive to sterile neutrinos via disappearance. Using timing and energy spectra to perform flavor decomposition, we show that the delayed electron neutrino component provides an independent test of short-baseline anomalies that hint at ~ eV-mass sterile neutrinos. Dedicated experiments will be sensitive to nearly the entire sterile neutrino parameter space consistent with short-baseline data.

Sensitivity to kaon decays to ALPs at fixed target experiments

We study the sensitivity of fixed target experiments to hadronically coupled axionlike particles (ALPs) produced in kaon decays, with a particular emphasis on current and upcoming Short-Baseline Neutrino (SBN) experiments. We demonstrate that below the kaon decay mass threshold (ma<mK−mπ) kaon decay is the dominant production mechanism for ALPs at neutrino experiments, larger by many orders of magnitude than production in pseudoscalar mixing. Such axions can be probed principally by the diphoton and dimuon final states. In the latter case, even if the axion does not couple to muons at tree level, such a coupling is induced by the renormalization group flow from the UV scale. We reinterpret prior results by CHARM and MicroBooNE through these channels and show that they constrain new areas of heavy axion parameter space. We also show projections of the sensitivity of the SBN experiment and Deep Underground Neutrino Experiment (DUNE) to axions through these channels, which reach up to a decade higher in the axion decay constant beyond existing constraints. DUNE projects to have a sensitivity competitive with other world-leading upcoming experiments. Published by the American Physical Society 2024

Gain stability of Hamamatsu R5912-MOD photomultipliers at low temperature

The Photon Detection System (PDS) is a crucial component of the ICARUS detector in the Short Baseline Neutrino (SBN) Program at Fermi National Accelerator Laboratory (FNAL). It consists of 360 PhotoMultiplier Tubes (PMTs) 8” Hamamatsu R5912-MOD and, since June 2020, it has been operating at the liquid Argon cryogenic temperature. During these years, the PMTs have shown gain losses as an aging effect. Using a climatic chamber at the INFN Sezione di Catania, we confirmed a stable gain for a single PMT 8” Hamamatsu R5912-MOD when operated at room temperature, and a persistent gain loss at temperatures around -70 °C, although this temperature is rather higher than that of the liquid Argon.

Neutrino CP measurement in the presence of RG running with mismatched momentum transfers

The neutrino mixing parameters are expected to have renormalization group (RG) running effect in the presence of new physics. If the momentum transfers at production and detection mismatch with each other, the oscillation probabilities are generally modified and become dependent on not just the neutrino energy but also the momentum transfer. Even in the limit of vanishing baseline, the transition probability for the appearance channel is interestingly not zero. This would significantly affect the sensitivity of the genuine leptonic Dirac CP phase. We further explore the possibility of combining the long- and short-baseline neutrino experiments to constrain such RG running effect for the purpose of guaranteeing the CP measurement. To simulate the double dependence on the neutrino energy and momentum transfer, we extend the usual o simulation of fixed baseline experiments and use a two-dimensional χ2 analysis to obtain sensitivities. Published by the American Physical Society 2024

Light detection and cosmic rejection in the ICARUS LArTPC at Fermilab

The ICARUS-T600 detector is a 760-ton Liquid Argon Time Projection Chamber (LArTPC) currently operating at Fermilab as the Far Detector in the Short Baseline Neutrino (SBN) program. The SBN program is composed of three LArTPCs with a central goal of testing the sterile neutrino hypothesis. After operating for 3-years in the Gran Sasso Underground Laboratory, the ICARUS detector was shipped to CERN where it was outfitted with 360 8” Photomultiplier Tubes (PMTs) for a new optical detection system. The PMT system detects fast scintillation light from charged particles interacting in the Liquid Argon, generating the trigger signal for the full detector and allows 3D reconstruction of events. Now operating at shallow depth, the detector is exposed to a high flux of cosmic rays that can fake neutrino interactions. To mitigate this effect a Cosmic Ray Tagger (CRT) and a 3-meter-thick concrete were installed. Precise timing information from both the PMT and CRT subsystems can help to identify whether an interaction originated from inside or outside of the ICARUS cryostat. This paper reviews a method for cosmogenic background reduction and timing calibration of the CRT and PMT light detection systems in ICARUS.

First Measurement of η Meson Production in Neutrino Interactions on Argon with MicroBooNE.

We present a measurement of η production from neutrino interactions on argon with the MicroBooNE detector. The modeling of resonant neutrino interactions on argon is a critical aspect of the neutrino oscillation physics program being carried out by the DUNE and Short Baseline Neutrino programs. η production in neutrino interactions provides a powerful new probe of resonant interactions, complementary to pion channels, and is particularly suited to the study of higher-order resonances beyond the Δ(1232). We measure a flux-integrated cross section for neutrino-induced η production on argon of 3.22±0.84(stat)±0.86(syst) 10^{-41} cm^{2}/nucleon. By demonstrating the successful reconstruction of the two photons resulting from η production, this analysis enables a novel calibration technique for electromagnetic showers in GeV accelerator neutrino experiments.

JLab spectral functions of argon in nuwro and their implications for MicroBooNE

The Short-Baseline Neutrino program in Fermilab aims to resolve the nature of the low-energy excess events observed in LSND and MiniBooNE, and analyze with unprecedented precision neutrino interactions with argon. These studies require a reliable estimate of neutrino cross sections, in particular for charged current quasielastic scattering (CCQE). Here, we report updates of the uro Monte Carlo generator that, most notably, bring the state-of-the-art spectral functions to model the ground state properties of the argon nucleus, and improve the accuracy of the cross sections at low energies by accounting for the effects of the nuclear Coulomb potential. We discuss these developments in the context of electron and neutrino interactions, by comparing updated uro predictions to experimental data from Jefferson Laboratory Hall A and MicroBooNE. The MicroBooNE CCQE-dominated data are described with the χ2 per degree of freedom of 0.7, compared with 1.0 in the local Fermi gas model. The largest improvement is observed for the angular distributions of the produced protons, where the χ2 reduces nearly by half. Being obtained using the axial form factor parametrization from MINERvA, our results indicate a consistency between the CCQE measurements in MINERvA and MicroBooNE. Published by the American Physical Society 2024

Status and perspectives of the ICARUS experiment at the Fermilab Short Baseline Neutrino program

The ICARUS collaboration has employed the 760 t T600 detector in a successful three-year physics run at the underground LNGS laboratory, performing a sensitive search for LSND-like anomalous νe appearance in the CERN Neutrino to Gran Sasso beam, which contributed to the constraints on the allowed neutrino oscillation parameters to a narrow region around Δm2 ∼ 1 eV2. After a significant overhaul at CERN, the T600 detector has been installed at Fermilab. In 2020 the cryogenic commissioning began with detector cool down, liquid Argon filling and recirculation. ICARUS then started its operation collecting the first neutrino events from the Booster Neutrino Beam (BNB) and the Neutrinos at the Main Injector (NuMI) beam off-axis, which were used to test the ICARUS event selection, reconstruction and analysis algorithms. ICARUS successfully completed its commissioning phase in June 2022, moving then to data taking for neutrino oscillation physics, aiming at first to either confirm or refute the claim by Neutrino-4 short-baseline reactor. ICARUS will also jointly search for evidence of sterile neutrinos together with the Short-Baseline Near Detector, within the Fermilab Short-Baseline Neutrino program experiment, and will perform measurements of neutrino cross sections with both beams and several Beyond Standard Model searches with the NuMI beam. In this paper, the main technical achievements of the ICARUS detector subsystems (Time Projection Chambers, Light Detection System, Cosmic Ray Tagger, Trigger and Data Acquisition) obtained with both BNB and NuMI neutrino beams during the commissioning phase, will be presented in terms of the overall detector performance and capability to select and reconstruct neutrino events.

A plastic scintillation muon veto for sub-Kelvin temperatures

Rare-event search experiments located on-surface, such as short-baseline reactor neutrino experiments, are often limited by muon-induced background events. Highly efficient muon vetos are essential to reduce the detector background and to reach the sensitivity goals. We demonstrate the feasibility of deploying organic plastic scintillators at sub-Kelvin temperatures. For the NUCLEUS experiment, we developed a cryogenic muon veto equipped with wavelength shifting fibers and a silicon photo multiplier operating inside a dilution refrigerator. The achievable compactness of cryostat-internal integration is a key factor in keeping the muon rate to a minimum while maximizing coverage. The thermal and light output properties of a plastic scintillation detector were examined. We report first data on the thermal conductivity and heat capacity of the polystyrene-based scintillator UPS-923A over a wide range of temperatures extending below one Kelvin. The light output was measured down to 0.8 K and observed to increase by a factor of 1.61 ± 0.05 compared to 300 K. The development of an organic plastic scintillation muon veto operating in sub-Kelvin temperature environments opens new perspectives for rare-event searches with cryogenic detectors at sites lacking substantial overburden.

Time calibration and synchronization of the scintillation light detection system in ICARUS-T600

The ICARUS-T600 Liquid Argon (LAr) Time Projection Chamber (TPC) is presently taking data in the Short Baseline Neutrino (SBN) program at Fermilab (U.S.A.) to search for a possible LSND-like sterile neutrino signal at Δm 2 ≈ 1 eV2 with the Booster Neutrino Beam (BNB). A light detection system, based on 360 large area Photo-Multiplier Tubes (PMTs), has been realized for ICARUS-T600 to detect VUV photons produced by the passage of ionizing particles in LAr. This system is fundamental for the TPC operation, providing an efficient trigger and contributing to the 3D reconstruction of events. Moreover, since the detector is exposed to a huge flux of cosmic rays due to its shallow depths installation, the light detection system allows for the time reconstruction of events, contributing to the identification and to the selection of genuine neutrino interactions. The correct time reconstruction of events requires the precise knowledge of the delay of each PMT channel and a good synchronization of recording electronics, this last based on fast sampling digitizers. To achieve a time resolution better than 1 ns, we perform three consecutive timing corrections deployed at different stages of the optical data flow. Results demonstrate the capability of the ICARUS-T600 light detection system to allow a precise reconstruction of the temporal evolution of each event occurring in the detector and the association of neutrino events with the bunched structure of BNB.

New Clues about light sterile neutrinos: preference for models with damping effects in global fits

This article reports global fits of short-baseline neutrino data to oscillation models involving light sterile neutrinos. In the commonly-used 3+1 plane wave model, there is a well-known 4.9σ tension between data sets sensitive to appearance versus disappearance of neutrinos. We find that models that damp the oscillation prediction for the reactor data sets, especially at low energy, substantially improve the fits and reduce the tension. We consider two such scenarios. The first scenario introduces the quantum mechanical wavepacket effect that accounts for the source size in reactor experiments into the 3+1 model. We find that inclusion of the wavepacket effect greatly improves the overall fit compared to a three-neutrino model by ∆χ2/dof = 61.1/4 (7.1σ improvement) with best-fit ∆m2 = 1.4 eV2 and wavepacket length of 67 fm. The internal tension is reduced to 3.4σ. If reactor-data only is fit, then the wavepacket preferred length is 91 fm (> 20 fm at 99% CL). The second model introduces oscillations involving sterile flavor and allows the decay of the heaviest, mostly sterile mass state, ν4. This model introduces a damping term similar to the wavepacket effect, but across all experiments. Compared to a three-neutrino fit, this has a ∆χ2/dof = 60.6/4 (7σ improvement) with preferred ∆m2 = 1.4 eV2 and decay Γ = 0.35 eV. The internal tension is reduced to 3.7σ.For many years, the reactor event rates have been observed to have structure that deviates from prediction. Community discussion has focused on an excess compared to prediction observed at 5 MeV; however, other deviations are apparent. This structure has L dependence that is well-fit by the damped models. Before assuming this points to new physics, we urge closer examination of systematic effects that could lead to this L dependence.

ICARUS at the Fermilab Short-Baseline Neutrino program: initial operation

The ICARUS collaboration employed the 760-ton T600 detector in a successful 3-year physics run at the underground LNGS laboratory, performing a sensitive search for LSND-like anomalous nu _e appearance in the CERN Neutrino to Gran Sasso beam, which contributed to the constraints on the allowed neutrino oscillation parameters to a narrow region around 1 eV^2. After a significant overhaul at CERN, the T600 detector has been installed at Fermilab. In 2020 the cryogenic commissioning began with detector cool down, liquid argon filling and recirculation. ICARUS then started its operations collecting the first neutrino events from the booster neutrino beam (BNB) and the Neutrinos at the Main Injector (NuMI) beam off-axis, which were used to test the ICARUS event selection, reconstruction and analysis algorithms. ICARUS successfully completed its commissioning phase in June 2022. The first goal of the ICARUS data taking will be a study to either confirm or refute the claim by Neutrino-4 short-baseline reactor experiment. ICARUS will also perform measurement of neutrino cross sections with the NuMI beam and several Beyond Standard Model searches. After the first year of operations, ICARUS will search for evidence of sterile neutrinos jointly with the Short-Baseline Near Detector, within the Short-Baseline Neutrino program. In this paper, the main activities carried out during the overhauling and installation phases are highlighted. Preliminary technical results from the ICARUS commissioning data with the BNB and NuMI beams are presented both in terms of performance of all ICARUS subsystems and of capability to select and reconstruct neutrino events.

Inspection of the detection cross section dependence of the Gallium Anomaly

We discuss in detail the dependence of the Gallium Anomaly on the detection cross section. We provide updated values of the size of the Gallium Anomaly and find that its significance is larger than about 5σ for all the detection cross section models. We discuss the dependence of the Gallium Anomaly on the assumed value of the half life of Ge71, which determines the cross sections of the transitions from the ground state of Ga71 to the ground state of Ge71. We show that a value of the Ge71 half life which is larger than the standard one can reduce or even solve the Gallium Anomaly. Considering the short-baseline neutrino oscillation interpretation of the Gallium Anomaly, we show that a value of the Ge71 half life which is larger than the standard one can reduce the tension with the results of other experiments. Since the standard value of the Ge71 half life was measured in 1985, we advocate the importance of new measurements with modern technique and apparatus for a better assessment of the Gallium Anomaly.

Flux-integrated semiexclusive cross sections for charged-current quasielastic and neutral-current elastic neutrino scattering off Ar40 and a sterile neutrino oscillation study

Flux-integrated semiexclusive differential cross sections for charged-current quasielastic and neutral-current elastic neutrino scattering on argon are analyzed. The cross sections are calculated using the relativistic distorted-wave impulse approximation with values of the nucleon axial mass ${M}_{A}=1\text{ }\text{ }\mathrm{GeV}$ and 1.2 GeV. The elastic scattering cross sections are also computed for different strange quark contributions to the neutral-current axial form factor. The flux-integrated differential cross sections as functions of reconstructed neutrino energy are evaluated for the far detector of the SBN experiment. The effects of the short baseline neutrino oscillations are taken into account in a $3+1$ framework. We found that cross sections depend on oscillation parameters and the ratio of the measured and predicted cross sections can be used in a sterile neutrino oscillation study.

Significance of classically forbidden regions for short baseline neutrino experiments

Classically forbidden regions (CFRs) are common to both non-relativistic quantum mechanics, and to relativistic quantum field theory. It is known since 2001 that CFR contributes roughly sixteen percent of energy to the ground state of a simple harmonic oscillator (Adunas G. Z. et al., Gen. Relativ. Gravit., 33 (2001) 183). Similarly, quantum field theoretic arguments yield a non-zero amplitude for a massive particle to cross the light cone (that is, into the CFR). The signs of these amplitudes are opposite for fermions and antifermions. This has given rise to an erroneous conclusion that amplitude to cross the light cone is identically zero. This is true as long as a measurement does not reveal the considered object to be a particle or antiparticle. However, neutrino oscillation experiments do measure a neutrino ν, or an antineutrino . Here we show that in the context of neutrino oscillations these observations have the potential to resolve various short baseline anomalies for a sufficiently light lowest mass eigenstate. In addition, we make a concrete prediction for the upcoming results to be announced later this year by JSNS2.

Impact of wave packet separation in low-energy sterile neutrino searches

Light sterile neutrinos have been motivated by anomalies observed in short-baseline neutrino experiments.Among them, radioactive-source and reactor experiments have provided evidence and constraints, respectively, for electron neutrino disappearance compatible with an eV-scale neutrino. The results from these observations are seemingly in conflict. This letter brings into focus the assumption that the neutrino wave packet can be approximated as a plane wave, which is adopted in all analyses of such experiments. We demonstrate that the damping of oscillations, e.g., due to a finite wave packet size, solve the tension between these electron-flavor observations and constraints.

The light detection system of the ICARUS detector in the Short Baseline Neutrino program at Fermilab

The Short Baseline Neutrino (SBN) program at Fermilab is an extensive experimental programme aiming at searching for sterile neutrino(s) [1], whose existence is one of the fundamental open questions of neutrino physics. It employs three Liquid Argon Time Projection Chamber (LArTPC) detectors, called ICARUS, MicroBooNE and SBND, sampling the Booster Neutrino Beam (BNB) at different locations from its target. The SBN detectors, working near the Earth’s surface, are subjected to a substantial cosmic background, which can mimic genuine neutrino interactions. Thus, it is essential to distinguish the signals related to the neutrino beams from those induced by the cosmic rays. The light detection system is a vital part of LArTPCs, but its role is even more critical for surface-operating detectors like ICARUS. The ICARUS light detection system is based on 360 Photomultiplier Tubes (PMTs). Its main role is to provide an efficient trigger and contribute to the 3D reconstruction of detected events. The light detection system calibration and further trigger system improvements were performed for the final detector configuration during the detector commissioning at Fermilab. The trigger system effectively exploits the information given by the PMTs. To further increase that system’s efficiency in event filtering, an alternative method based on Convolutional Neural Network (CNN) has been developed. Simulation-based results show that this technique can reduce the cosmic background by up to 76% with a neutrino selection efficiency of 99%. However, to filter the real data cases, which are usually not identical to the simulated ones, this method was improved by applying Domain Adversarial Neural Network (DANN). The results prove that adversarial training through a DANN can alleviate the simulation bias, demonstrating the first successful application of DANN for CNN as an event classifier for a LArTPC.

The electronic set-up for the scintillation light detection system of ICARUS-SBN at Fermilab

The ICARUS-T600 Liquid Argon (LAr) Time Projection Chamber (TPC) is presently used as a far detector of the Short Baseline Neutrino (SBN) program at Fermilab (USA) to search for a possible sterile neutrino signal with the Booster Neutrino Beam (BNB). A light detection system, based on 360 Hamamatsu R5912-MOD Photo-Multiplier Tubes (PMTs), has been realized to detect vacuum ultraviolet (VUV) photons produced after the passage of ionizing particles in LAr. High performance electronics allows recording of the PMT signals and provides a fast discrimination for the exploitation of the scintillation light for trigger purposes. This system is fundamental for the TPC operation, contributing to the trigger system and for the 3D reconstruction of events.