Search

This paper reports the first differential measurement of the charged-current interaction cross section of ${\nu }_{\mu }$ on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment’s off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be $\sigma =(0.95\pm 0.08(\text{stat})\pm 0.06(\text{det syst})\pm 0.04(\text{model syst})\pm 0.08(\text{flux}))\times {10}^{-38}{\mathrm{cm}}^2/\mathrm{n}$.

The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearance and disappearance channels. A sample of electron neutrino candidates at Super-Kamiokande in which a pion decay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses. Through combined analyses of these five samples, simultaneous measurements of four oscillation parameters, $|\mathrm{\Delta }{m}_{32}^2|$, ${\sin }^2{\theta }_{23}$, ${\sin }^2{\theta }_{13}$, and ${\delta }_{\mathrm{CP}}$ and of the mass ordering are made. A set of studies of simulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interaction model uncertainty. Multiple oscillation analyses are performed, and frequentist and Bayesian intervals are presented for combinations of the oscillation parameters with and without the inclusion of reactor constraints on ${\sin }^2{\theta }_{13}$. When combined with reactor measurements, the hypothesis of $CP$ conservation (${\delta }_{\mathrm{CP}}=0$ or $\pi$) is excluded at 90% confidence level. The 90% confidence region for ${\delta }_{\mathrm{CP}}$ is $[-2.95,-0.44]$ ($[-1.47,-1.27]$) for normal (inverted) ordering. The central values and 68% confidence intervals for the other oscillation parameters for normal (inverted) ordering are $\mathrm{\Delta }{m}_{32}^2=2.54\pm 0.08(2.51\pm 0.08)\times {10}^{-3}{\mathrm{eV}}^2/c^4$ and ${\sin }^2{\theta }_{23}=0.55_{-0.09}^{+0.05}$ ($0.55_{-0.08}^{+0.05}$), compatible with maximal mixing. In the Bayesian analysis, the data weakly prefer normal ordering (Bayes factor 3.7) and the upper octant for ${\sin }^2{\theta }_{23}$ (Bayes factor 2.4).

Measurements of electrons from ${\nu }_e$ interactions are crucial for the Deep Underground Neutrino Experiment (DUNE) neutrino oscillation program, as well as searches for physics beyond the standard model, supernova neutrino detection, and solar neutrino measurements. This article describes the selection and reconstruction of low-energy (Michel) electrons in the ProtoDUNE-SP detector. ProtoDUNE-SP is one of the prototypes for the DUNE far detector, built and operated at CERN as a charged particle test beam experiment. A sample of low-energy electrons produced by the decay of cosmic muons is selected with a purity of 95%. This sample is used to calibrate the low-energy electron energy scale with two techniques. An electron energy calibration based on a cosmic ray muon sample uses calibration constants derived from measured and simulated cosmic ray muon events. Another calibration technique makes use of the theoretically well-understood Michel electron energy spectrum to convert reconstructed charge to electron energy. In addition, the effects of detector response to low-energy electron energy scale and its resolution including readout electronics threshold effects are quantified. Finally, the relation between the theoretical and reconstructed low-energy electron energy spectra is derived, and the energy resolution is characterized. The low-energy electron selection presented here accounts for about 75% of the total electron deposited energy. After the addition of lost energy using a Monte Carlo simulation, the energy resolution improves from about 40% to 25% at 50 MeV. These results are used to validate the expected capabilities of the DUNE far detector to reconstruct low-energy electrons.

This paper reports on the search for heavy neutrinos with masses in the range $140<M_N<493\mathrm{MeV}/{\mathrm{c}}^2$ using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are $N\to {\ell }_{\alpha }^{\pm }{\pi }^{\mp }$ and $N\to {\ell }_{\alpha }^{+}{\ell }_{\beta }^{-}\stackrel{(-)}{\nu }(\alpha ,\beta =e,\mu )$. A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavored currents ($U_e^2$, $U_{\mu }^2$, $U_{\tau }^2$) as a function of the heavy neutrino mass, e.g., $U_e^2<{10}^{-9}$ at 90% C.L. for a mass of $390\mathrm{MeV}/{\mathrm{c}}^2$. These constraints are competitive with previous experiments.

The DEAP-3600 experiment is searching for weakly interacting massive particles dark matter with a $3.3\times 10^3\text{kg}$ single phase liquid argon (LAr) target, located 2.1 km underground at SNOLAB. The experimental signature of dark matter interactions is kilo electron volt–scale ${}^{40}\mathrm{Ar}$ nuclear recoils producing 128 nm LAr scintillation photons observed by photomultiplier tubes. The largest backgrounds in DEAP-3600 are electronic recoils (ERs) induced by $\beta$ and $\gamma$ rays originating from internal and external radioactivity in the detector material. A background model of the ER interactions in DEAP-3600 was developed and is described in this work. The model is based on several components which are expected from radioisotopes in the LAr, from ex situ material assay measurements, and from dedicated independent in situ analyses. This prior information is used in a Bayesian fit of the ER components to a 247.2 d dataset to model the radioactivity in the surrounding detector materials. Pulse-shape discrimination separates ER and NR events. However, detailed knowledge of the ER background and activity of detector components sets valuable constraints on NR backgrounds including neutrons and alphas. In addition, the activity of ${}^{42}\mathrm{Ar}$ in LAr in DEAP-3600 is determined by measuring the daughter decay of ${}^{42}\mathrm{K}$. This cosmogenically activated trace isotope is a relevant background at higher energies for other rare event searches using atmospheric argon, e.g., DarkSide-20k, GERDA, or LEGEND. The specific activity of ${}^{42}\mathrm{Ar}$ in the atmosphere is found to be $40.4\pm 5.9\mu \mathrm{Bq}/\mathrm{kg}$ of argon.

We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below $20\mathrm{GeV}/c^2$ using a target of low-radioactivity argon with a 6786.0 kg d exposure. The data were obtained using the DarkSide-50 apparatus at Laboratori Nazionali del Gran Sasso. The analysis is based on the ionization signal, for which the DarkSide-50 time projection chamber is fully efficient at $0.1\mathrm{keV}\text{ee}$. The observed rate in the detector at $0.5\mathrm{keV}\text{ee}$ is about $1.5\mathrm{event}/\mathrm{keV}\text{ee}/\mathrm{kg}/\mathrm{d}$ and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above $1.8\mathrm{GeV}/c^2$ for the spin-independent cross section of dark matter WIMPs on nucleons, extending the exclusion region for dark matter below previous limits in the range $1.8–6\mathrm{GeV}/c^2$.

Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but $CPT$ violation and nonstandard interactions can violate this symmetry. In this work we report the measurements of ${\sin }^2{\theta }_{23}$ and $\mathrm{\Delta }{m}_{32}^2$ independently for neutrinos and antineutrinos. The aforementioned symmetry violation would manifest as an inconsistency in the neutrino and antineutrino oscillation parameters. The analysis discussed here uses a total of $1.97\times {10}^{21}$ and $1.63\times {10}^{21}$ protons on target taken with a neutrino and antineutrino beam respectively, and benefits from improved flux and cross section models, new near-detector samples and more than double the data reducing the overall uncertainty of the result. No significant deviation is observed, consistent with the standard neutrino oscillation picture.

We report on the first search for nuclear ultraheavy dark matter (UHDM) in a dual-phase liquid argon time projection chamber using the DarkSide-50 experiment. Unlike conventional weakly interacting massive particles, a nuclear UHDM model may be composed of many dark nucleons and scatter numerous times while passing through the detector. Accounting for energy loss through the Earth’s overburden, we apply selection criteria optimized for multiscatter event topologies using the 532-day low-radiation campaign of the DarkSide-50 detector. Excluded limits on the UHDM-nucleon scattering cross section for dark nucleon masses of $m_{\chi }=10,50,100,500\mathrm{GeV}/{\mathrm{c}}^2$ are presented.

We report the measurements of the single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using $5.56\times {10}^{20}$ protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model-dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at 0.6 GeV, is measured to be $\sigma =(11.76\pm 0.44(\mathrm{stat})\pm 2.39(\mathrm{syst}))\times {10}^{-40}{\mathrm{cm}}^2{\text{nucleon}}^{-1}$. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.

This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise $5.8\times {10}^{20}$ and $6.3\times {10}^{20}$ protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference, and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects.

We report an updated measurement of the ${\nu }_{\mu }$-induced, and the first measurement of the ${\overline{\nu }}_{\mu }$-induced coherent charged pion production cross section on ${}^{12}\mathrm{C}$ nuclei in the Tokai-to-Kamioka experiment. This is measured in a restricted region of the final-state phase space for which $p_{\mu ,\pi }>0.2\mathrm{GeV}$, $\cos ({\theta }_{\mu })>0.8$ and $\cos ({\theta }_{\pi })>0.6$, and at a mean (anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured ${\nu }_{\mu }$ charged current coherent pion production flux-averaged cross section on ${}^{12}\mathrm{C}$ is $(2.98\pm 0.37(\mathrm{stat})\pm 0.31(\mathrm{syst}{)}_{-0.00}^{+0.49}({\mathrm{Q}}^2\text{model}))\times {10}^{-40}{\mathrm{cm}}^2$. The new measurement of the ${\overline{\nu }}_{\mu }$-induced cross section on ${}^{12}\mathrm{C}$ is $(3.05\pm 0.71(\mathrm{stat})\pm 0.39(\mathrm{syst}{)}_{-0.00}^{+0.74}({\mathrm{Q}}^2\text{model}))\times {10}^{-40}{\mathrm{cm}}^2$. The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions.

This paper reports the first simultaneous measurement of the double differential muon neutrino charged-current cross section on oxygen and carbon without pions in the final state as a function of the outgoing muon kinematics, made at the ND280 off-axis near detector of the T2K experiment. The ratio of the oxygen and carbon cross sections is also provided to help validate various models’ ability to extrapolate between carbon and oxygen nuclear targets, as is required in T2K oscillation analyses. The data are taken using a neutrino beam with an energy spectrum peaked at 0.6 GeV. The extracted measurement is compared with the prediction from different Monte Carlo neutrino-nucleus interaction event generators, showing particular model separation for very forward-going muons. Overall, of the models tested, the result is best described using local Fermi gas descriptions of the nuclear ground state with RPA suppression.

DEAP-3600 is a single-phase liquid argon detector aiming to directly detect weakly interacting massive particles (WIMPs), located at SNOLAB (Sudbury, Canada). After analyzing data taken during the first year of operation, a null result was used to place an upper bound on the WIMP-nucleon, spin-independent, isoscalar cross section. This study reinterprets this result within a nonrelativistic effective field theory framework and further examines how various possible substructures in the local dark matter halo may affect these constraints. Such substructures are hinted at by kinematic structures in the local stellar distribution observed by the Gaia satellite and other recent astronomical surveys. These include the Gaia Sausage (or Enceladus), as well as a number of distinct streams identified in recent studies. Limits are presented for the coupling strength of the effective contact interaction operators ${\mathcal{O}}_1$, ${\mathcal{O}}_3$, ${\mathcal{O}}_5$, ${\mathcal{O}}_8$, and ${\mathcal{O}}_{11}$, considering isoscalar, isovector, and xenonphobic scenarios, as well as the specific operators corresponding to millicharge, magnetic dipole, electric dipole, and anapole interactions. The effects of halo substructures on each of these operators are explored as well, showing that the ${\mathcal{O}}_5$ and ${\mathcal{O}}_8$ operators are particularly sensitive to the velocity distribution, even at dark matter masses above $100\mathrm{GeV}/c^2$.

The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to $7\mathrm{GeV}/\mathrm{c}$. We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and $7\mathrm{GeV}/\mathrm{c}$ beam runs. The selection efficiency is 1% and the sample purity 92%. The initial energies of the selected kaon candidates encompass the expected energy range of kaons originating from proton decay events in DUNE (below $\sim 200\mathrm{MeV}$). In addition, we demonstrate the capability of this detector technology to discriminate between kaons and other particles such as protons and muons, and provide a comprehensive description of their energy loss in liquid argon, which shows good agreement with the simulation. These results pave the way for future proton decay searches at DUNE.

Dark matter with Planck-scale mass ($\simeq {10}^{19}\mathrm{GeV}/c^2$) arises in well-motivated theories and could be produced by several cosmological mechanisms. A search for multiscatter signals from supermassive dark matter was performed with a blind analysis of data collected over a 813 d live time with DEAP-3600, a 3.3 t single-phase liquid argon-based detector at SNOLAB. No candidate signals were observed, leading to the first direct detection constraints on Planck-scale mass dark matter. Leading limits constrain dark matter masses between $8.3\times {10}^6$ and $1.2\times {10}^{19}\mathrm{GeV}/c^2$, and ${}^{40}\mathrm{Ar}$-scattering cross sections between $1.0\times {10}^{-23}$ and $2.4\times {10}^{-18}{\mathrm{cm}}^2$. These results are interpreted as constraints on composite dark matter models with two different nucleon-to-nuclear cross section scalings.

We have measured the scintillation and ionization yield of recoiling nuclei in liquid argon as a function of applied electric field by exposing a dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy pulsed narrow band neutron beam produced at the Notre Dame Institute for Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged to detect and identify neutrons scattered in the TPC and to select the energy of the recoiling nuclei. We report measurements of the scintillation yields for nuclear recoils with energies from 10.3 to 57.3 keV and for median applied electric fields from 0 to $970\mathrm{V}/\mathrm{cm}$. For the ionization yields, we report measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to $486\mathrm{V}/\mathrm{cm}$. We also report the observation of an anticorrelation between scintillation and ionization from nuclear recoils, which is similar to the anticorrelation between scintillation and ionization from electron recoils. Assuming that the energy loss partitions into excitons and ion pairs from ${}^{83m}\mathrm{Kr}$ internal conversion electrons is comparable to that from ${}^{207}\mathrm{Bi}$ conversion electrons, we obtained the numbers of excitons ($N_{\text{ex}}$) and ion pairs ($N_{\mathrm{i}}$) and their ratio ($N_{\text{ex}}/N_{\mathrm{i}}$) produced by nuclear recoils from 16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in LAr-TPC signals due to columnar recombination, a comparison of the light and charge yield of recoils parallel and perpendicular to the applied electric field is presented for the first time.

We report a measurement of the flux-integrated cross section for inclusive muon neutrino charged-current interactions on carbon. The double-differential measurements are given as a function of the muon momentum and angle. Relative to our previous publication on this topic, these results have an increased angular acceptance and higher statistics. The data sample presented here corresponds to $5.7\times {10}^{20}$ protons on target. The total flux-integrated cross section is measured to be $(6.950\pm 0.662)\times {10}^{-39}{\mathrm{cm}}^2{\text{nucleon}}^{-1}$ and is consistent with our simulation.

Neutrino- and antineutrino-oxygen neutral-current quasielasticlike interactions are measured at Super-Kamiokande using nuclear deexcitation $\gamma$ rays to identify signal-like interactions in data from a $14.94(16.35)\times {10}^{20}$ protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are $⟨{\sigma }_{\nu \text{−}\mathrm{NCQE}}⟩=1.70\pm 0.17(\mathrm{stat}.{)}_{-0.38}^{+0.51}(\mathrm{syst}.)\times {10}^{-38}{\mathrm{cm}}^2/\text{oxygen}$ with a flux-averaged energy of 0.82 GeV and $⟨{\sigma }_{\overline{\nu }\text{−}\mathrm{NCQE}}⟩=0.98\pm 0.16(\mathrm{stat}.{)}_{-0.19}^{+0.26}(\mathrm{syst}.)\times {10}^{-38}{\mathrm{cm}}^2/\text{oxygen}$ with a flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.

Dark matter detection experiments using liquid argon rely on a precise characterization of the ionization response to nuclear recoils, especially in the keV energy range relevant for light dark matter interactions. In this work, we present a comprehensive analysis that combines new measurements from the ReD setup, part of the DarkSide experimental program, with calibration data from DarkSide-50, as well as results from the ARIS and SCENE experiments. These combined datasets enable improved constraints on atomic screening effects in the modeling of the ionization response of liquid argon to nuclear recoils. The analysis is performed within the Thomas-Imel recombination framework adopted in previous DarkSide studies, and is here further constrained by the inclusion of ReD data, which allow the screening function to be determined from calibration measurements. By including the updated ionization model into the DarkSide-50 analysis framework, we obtain stronger exclusion limits on low-mass weakly interacting massive particle (WIMP) interactions, setting new world-leading constraints in the $1–3\mathrm{GeV}/{\mathrm{c}}^2$ WIMP mass range. Finally, we recast the sensitivity projections for the upcoming DarkSide-20k detector, demonstrating a significantly enhanced discovery potential for low-mass dark matter candidates.

Dark matter elastic scattering off nuclei can result in the excitation and ionization of the recoiling atom through the so-called Migdal effect. The energy deposition from the ionization electron adds to the energy deposited by the recoiling nuclear system and allows for the detection of interactions of sub-$\mathrm{GeV}/{\mathrm{c}}^2$ mass dark matter. We present new constraints for sub-$\mathrm{GeV}/{\mathrm{c}}^2$ dark matter using the dual-phase liquid argon time projection chamber of the DarkSide-50 experiment with an exposure of $(12306\pm 184)\mathrm{kg}\mathrm{d}$. The analysis is based on the ionization signal alone and significantly enhances the sensitivity of DarkSide-50, enabling sensitivity to dark matter with masses down to $40\mathrm{MeV}/c^2$. Furthermore, it sets the most stringent upper limit on the spin independent dark matter nucleon cross section for masses below $3.6\mathrm{GeV}/c^2$.