Determination Of Neutrino Mass Hierarchy Research Articles

Study of quantum decoherence at the Protvino to ORCA experiment

Protvino to ORCA (oscillation research with cosmics in the abyss) (P2O) is an upcoming neutrino oscillation experiment with a very long baseline of 2595 km. Because of the substantial baseline, this experiment provides a unique opportunity to study the Earth matter effects over very large distances. This makes it a suitable experiment to investigate the environmental decoherence in neutrino oscillations, where the neutrino system could interact with a stochastic environment and lead to a loss in the coherence of neutrino states. In this work, we consider an open quantum system framework to simulate the neutrino oscillations in the P2O experiment and obtain bounds on the decoherence parameters in different phenomenological models. Here, we also consider that the decoherence parameter Γ depends on neutrino energy Eν as Γjk(Eν)=Γ0(EνE0)n. Furthermore, assuming the presence of decoherence in nature, we study the effect of it on the determination of neutrino mass hierarchy and CP violation at the P2O experiment. Published by the American Physical Society 2024

Statistical Issues on the Neutrino Mass Hierarchy with Δχ2

The neutrino mass hierarchy determination (ν MHD) is one of the main goals of the major current and future neutrino experiments. The statistical analysis usually proceeds from a standard method, a single-dimensional estimator 1D−Δχ2 that shows some drawbacks and concerns, together with a debatable strategy. The drawbacks and considerations of the standard method will be explained through the following three main issues. The first issue corresponds to the limited power of the standard method. The Δχ2 estimator provides us with different results when different simulation procedures were used. Regarding the second issue, when χminNH2 and χminIH2 are drawn in a 2D map, their strong positive correlation manifests χ2 as a bidimensional variable, instead of a single-dimensional estimator. The overlapping between the χ2 distributions of the two hypotheses leads to an experiment sensitivity reduction. The third issue corresponds to the robustness of the standard method. When the JUNO sensitivity is obtained using different procedures, either with Δχ2 as one-dimensional or χ2 as two-dimensional estimator, the experimental sensitivity varies with the different values of the atmospheric mass, the input parameter. We computed the oscillation of Δχ2¯ with the input parameter values, Δm2input. The MH significance using the standard method, Δχ2, strongly depends on the values of the parameter Δm2input. Consequently, the experiment sensitivity depends on the precision of the atmospheric mass. This evaluation of the standard method confirms the drawbacks.

KM3NeT sensitivity to low energy astrophysical neutrinos

KM3NeT, a new generation of neutrino telescope, is currently being deployed in the Mediterranean Sea. While its two sites, ORCA and ARCA, were respectively designed for the determination of neutrino mass hierarchy and high-energy neutrino astronomy, this contribution presents a study of the detection potential of KM3NeT in the MeV-GeV energy range. At these low energies, the data rate is dominated by low-energy atmospheric muons and environmental noise due to bioluminescence and K-40 decay. The goal of this study is to characterize the environmental noise in order to optimize the selection of low-energy neutrino interactions and increase the sensitivity of KM3NeT to transient astrophysical phenomena, such as close-by core-collapse supernovae, solar flares, and extragalactic transients. In this contribution, we will study how using data science tools might improve the sensitivity of KM3NeT in these low-energy neutrino searches. We will first introduce the data sets and the different variables used to characterize KM3NeT’s response to the environmental noise. We will then compare the efficiency of various tools in identifying different components in the environmental noise and in disentangling low-energy neutrino interactions from the background events. We will conclude with the implication of low-energy neutrinos for future astrophysical transient searches.

Physics potential of the combined sensitivity of T2K-II, NOνA extension, and JUNO

Leptonic \textit{CP} violation search, neutrino mass hierarchy determination, and the precision measurement of oscillation parameters for a unitary test of the leptonic mixing matrix are among the major targets of the ongoing and future neutrino oscillation experiments. The work explores the physics reach for these targets by around 2027, when the third generation of the neutrino experiments starts operation, with a combined sensitivity of three experiments: T2K-II, NO$\nu$A extension, and JUNO. It is shown that a joint analysis of these three experiments can conclusively determine the neutrino mass hierarchy. Also, at certain values of \emph{true} \dcp, it provides closely around a $5\sigma$ confidence level (C.L.) to exclude \textit{CP}-conserving values and more than a $50\%$ fractional region of \emph{true} $\delta_{\text{CP}}$ values can be explored with a statistic significance of at least a $3\sigma$ C.L. Besides, the joint analysis can provide unprecedented precision measurements of the atmospheric neutrino oscillation parameters and a great offer to solve the $\theta_{23}$ octant degeneracy in the case of nonmaximal mixing.

Potential impact of sub-structure on the determination of neutrino mass hierarchy at medium-baseline reactor neutrino oscillation experiments

In the past decade, the precise measurement of the lastly known neutrino mixing angle theta _{13} has enabled the resolution of neutrino mass hierarch (MH) at medium-baseline reactor neutrino oscillation (MBRO) experiments. Recent calculations of the reactor neutrino flux predict percent-level sub-structures in the bar{nu }_e spectrum due to Coulomb effects in beta decay. Such fine structure in the reactor spectrum has been an issue of concern for efforts to determine the neutrino MH for the MBRO approach, the concern being that the sub-dominant oscillation pattern used to discriminate different hierarchies will be obscured by fine structure. The energy resolutions of current reactor experiments are not sufficient to measure such fine structure, and therefore the size and location in energy of these predicted discontinuities has not been confirmed experimentally. There has been speculation that a near detector is required with sufficient energy resolution to resolve the fine structure. This article studies the impact of fine structure on the resolution of MH, based on predicted reactor neutrino spectra, using the measured spectrum from Daya Bay as a reference. We also investigate how a near detector could improve the sensitivity of neutrino MH resolution based on various assumptions of near detector energy resolution.

Research on the measurement of connecting bars’ axial force of JUNO central detector

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy and precisely measure oscillation parameters and study the solar neutrino, supernova neutrino, geo-neutrino, etc. JUNO’s central detector (CD) has 20 kilo-ton liquid scintillator as target mass, which is contained by a huge acrylic sphere with the inner diameter of 35.4 m, and the acrylic sphere is supported by a stainless steel structure through 590 connecting bars. Part of the connecting bars bear pull force and the other bars bear push force. There is a direct relationship between the stress of connecting bars and that of acrylic sphere. For the installation process of the CD, the pretightening force and axial force of the connecting bars should be monitored with accuracy, and for the filling process and running condition, the precise measurement of axial force can indicate the safety of structure of the CD. Statistical method was used to evaluate the performance of measurement schemes, and 4-fiber Bragg grating measurement scheme was determined to be the final scheme, which can get the measurement uncertainty better than 0.7 kN. Performance of different measurement schemes are discussed in detail, and some related finite element analysis and evaluation method are also introduced in this paper.

Developing the radium measurement system for the water Cherenkov detector of the Jiangmen Underground Neutrino Observatory

The Jiangmen Underground Neutrino Observatory is proposed to determine neutrino mass hierarchy using a 20 ktonne liquid scintillator detector. Strict radio-purity requirements have been put forward for all the components of the detector. According to the MC simulation results, the radon dissolved in the water Cherenkov detector should be below 200 mBq/m3. Radium, the progenitor of radon, should also be taken seriously into account. In order to measure the radium concentration in water, a radium measurement system, which consists of a radium extraction system, a radon emanation chamber and a radon concentration measurement system, has been developed. In this paper, the updated radon concentration in gas measurement system with a one-day-measurement sensitivity of ∼5 mBq/m3, the detail of the development of the radium concentration in water measurement system with a sensitivity of ∼23 mBq/m3 as well as the measurement results of Daya Bay water samples will be presented.

Progress of Veto Detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kiloton liquid scintillator detector with neutrino mass hierarchy determination as primary physics goal. The other measurements, including precise neutrino oscillation parameters, solar neutrino, geo-neutrino, supernova neutrinos and the diffuse supernova neutrinos background, will be performed at the same time. The detector will be built in a 700 meter deep underground laboratory. A multi-eto detector, composed of a Top Tracker and a Water Cherenkov, will be installed for cosmic muon detection and background reduction. The Top Tracker detector is placed above the central detector, and is composed of three layers of scintillating strips. The outer part of the Central Detector is filled with water and equipped with about 2400 MCP-PMTs (20 inches) to form the Water Cherenkov detector used for muon tagging. Thanks to the Veto detector, the cosmic muon induced fast neutron background can be reduced to a level of about 0.06/day.

Study of the radon removal and detection for JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose underground experiment with primary physics goal the neutrino mass hierarchy determination. For the sake of suppressing the radioactivity from the surrounding rocks and tagging the cosmic muons, the central detector is surrounded by a water Cherenkov detector. Therefore, the strict requirements are put forward for intrinsic radioactivity in water, i.e., the radon concentration should be less than 0.2 Bq/m3. In order to monitor the radon concentration in water, a high sensitivity detector has been developed. The degassing membrane device and the micro-bubble generator were installed in the JUNO prototype water system to study the radon removal in water.

The measurement of liquid scintillator nonlinear response and intrinsic energy resolution

For Jiangmen Underground Neutrino Observatory the requirements < 1 % energy scale uncertainty and 3 % at 1 MeV energy resolution are crucial in order to determine neutrino mass hierarchy. In this study, we focus on non-linearity due to ionization quenching and intrinsic energy resolution of the liquid scintillator. To measure them a small-scale laboratory setup was developed and the measurement of Birk’s quenching constant kB = 0.0196 ± 0.0019 (stat) ± 0.0030 (syst) cm/MeV was provided. With the assumption of negligible light collection term, intrinsic energy resolution term was determined: vint(50keV) ≈ 0.02 ± 0.005. This value is comparable with the statistical term of JUNO, therefore the effect could significantly contribute into the total energy resolution at this energy. Further studies should be directed toward accurate estimation of light collection effects.

Thermal reliability analysis of the central detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy, precisely measure oscillation parameters and study solar neutrinos, supernova neutrinos and geo-neutrinos, etc. The central detector (CD) of JUNO has 20,000 tons liquid scintillator as target mass, which contains inside a huge acrylic sphere with inner diameter of 35.4 m, supported by a stainless steel structure. The whole structure of CD will be installed inside a cylindrical water pool, and the acrylic sphere will be submerged in the center of water pool. The operating temperature of CD is designed to be 21 °C as long as over 20 years, which is determined by the mechanical requirement of the structure and physics consideration. For this operating temperature, a special cooling system will be used to maintain the temperature inside the water pool. The main structure of CD is composed of acrylic and stainless steel, and they have much different thermal expansion coefficients, strengths and life times. Change in temperature may affect the safety of CD. As part of reliability analysis, the effect of cooling system failure on the CD is considered, and finite element method is used in our thermal calculation. In this article, the temperature fields before and after cooling system failure are calculated and analyzed, and the temperatures of different locations of water pool after cooling system failure are compared and discussed in detail.

On the possibility to determine neutrino mass hierarchy via supernova neutrinos with short-time characteristics * * Supported in part by the National Natural Science Foundation of China (11504276, 11547310) (J.J. and Y.W.), by the National Recruitment Program for Young Professionals and the CAS Center for Excellence in Particle Physics (S.Z.)

In this paper, we investigate whether it is possible to determine the neutrino mass hierarchy via a high-statistics and real-time observation of supernova neutrinos with short-time characteristics. The essential idea is to utilize distinct times-of-flight for different neutrino mass eigenstates from a core-collapse supernova to the Earth, which may significantly change the time distribution of neutrino events in the future huge water-Cherenkov and liquid-scintillator detectors. For illustration, we consider two different scenarios. The first case is the neutronization burst of emitted in the first tens of milliseconds of a core-collapse supernova, while the second case is the black hole formation during the accretion phase for which neutrino signals are expected to be abruptly terminated. In the latter scenario, it turns out only when the supernova is at a distance of a few Mpc and the fiducial mass of the detector is at the level of gigaton, might we be able to discriminate between normal and inverted neutrino mass hierarchies. In the former scenario, the probability for such a discrimination is even less due to a poor statistics.

Reactor neutrino spectral distortions play little role in mass hierarchy experiments

The Coulomb enhancement of low energy electrons in nuclear beta decay generates sharp cutoffs in the accompanying antineutrino spectrum at the beta decay endpoint energies. It has been conjectured that these features will interfere with measuring the effect of a neutrino mass hierarchy on an oscillated nuclear reactor antineutrino spectrum. These sawtooth-like features will appear in detailed reactor antineutrino spectra, with characteristic energy scales similar to the oscillation period critical to neutrino mass hierarchy determination near a 53 km baseline. However, these sawtooth-like distortions are found to contribute at a magnitude of only a few percent relative to the mass hierarchy-dependent oscillation pattern in Fourier space. In the Fourier cosine and sine transforms, the features that encode a neutrino mass hierarchy dominate by over sixteen (thirty-three) times in prominence to the maximal contribution of the sawtooth-like distortions from the detailed energy spectrum, given $3.2\%/\sqrt{E_\mathrm{vis.}/\mathrm{MeV}}$ (perfect) detector energy resolution. The effect of these distortions is shown to be negligible even when the uncertainties in the reactor spectrum, oscillation parameters, and counting statistics are considered. This result is shown to hold even when the opposite hierarchy oscillation patterns are nearly degenerate in energy space, if energy response nonlinearities are controlled to below 0.5\%. Therefore with accurate knowledge of detector energy response, the sawtooth-like features in reactor antineutrino spectra will not significantly impede neutrino mass hierarchy measurements using reactor antineutrinos.

On possibility of determining neutrino mass hierarchy by the charged-current and neutral-current events of supernova neutrinos in scintillation detectors

One of the unresolved mysteries in neutrino physics is the neutrino mass hierarchy. We present a new method to determine neutrino mass hierarchy by comparing the events of inverse beta decays (IBD), {bar{nu }}_e + prightarrow n + e^+, and neutral current (NC) interactions, nu ({overline{nu }}) + prightarrow nu ({overline{nu }}) + p, of supernova neutrinos from accretion and cooling phases in scintillation detectors. Supernova neutrino flavor conversions depend on the neutrino mass hierarchy. On account of Mikheyev–Smirnov–Wolfenstein effects, the full swap of the {bar{nu }}_e flux with the {bar{nu }}_x (x=mu ,~tau ) one occurs in the inverted hierarchy, while such a swap does not occur in the normal hierarchy. In consequence, the ratio of high energy IBD events to NC events for the inverted hierarchy is higher than in the normal hierarchy. Since the luminosity of {bar{nu }}_e is larger than that of nu _x in accretion phase while the luminosity of {bar{nu }}_e becomes smaller than that of nu _x in cooling phase, we calculate this ratio for both accretion and cooling phases. By analyzing the change of this event ratio from accretion phase to cooling phase, one can determine the neutrino mass hierarchy.

Towards a reconstruction of Supernova Neutrino Spectra in JUNO

Observation of supernovae (SN) through their neutrino emission is a fundamental point to understand both SN dynamics and neutrino physical properties. JUNO is a 20kton liquid scintillator detector, under construction in Jiangmen, China. The main aim of the experiment is to determine neutrino mass hierarchy by precisely measuring the energy spectrum of reactor electron antineutrinos. However due to its properties, JUNO has the capability of detecting a high statistics of SN events too. Existing data from SN neutrino consists only of 24 events coming from the SN 1987A,the detection of a SN burst in JUNO at ~ 10kpc will yield ~ 5x103 inverse beta decay (IBD) events from electron antineutrinos, about 1500 from proton elastic scattering (pES) above the threshold of 0.2 MeV, about 400 from electron elastic scattering (eES), plus several hundreds on other CC and NC interaction channels from all neutrino species.

Neutrino Physics and Astrophysics with the JUNO Detector

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton liquid scintillator multi-purpose underground detector, under construction near the Chinese city of Jiangmen, with data collection expected to start in 2021. The main goal of the experiment is the neutrino mass hierarchy determination, with more than three sigma significance, and the high-precision neutrino oscillation parameter measurements, detecting electron anti-neutrinos emitted from two nearby (baseline of about 53 km) nuclear power plants. Besides, the unprecedented liquid scintillator-type detector performance in target mass, energy resolution, energy calibration precision, and low-energy threshold features a rich physics program for the detection of low-energy astrophysical neutrinos, such as galactic core-collapse supernova neutrinos, solar neutrinos, and geo-neutrinos.

The design of the small prototype for the central detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy, precisely measure oscillation parameters and study solar neutrinos, supernova neutrinos and geo-neutrinos. The JUNO Central Detector 20 kton liquid scintillator target mass is contained by a huge acrylic sphere with a 35.4 m inner diameter, supported by a stainless steel structure, and the sphere is eventually submerged in pure water. Before the JUNO Central Detector is built, a small prototype has been designed and static loading experiments will be carried out to verify the consistency of the finite-element calculations and static loading experiments and test the subsystems performances, such as the monitoring system and liquid scintillator filling system. The small prototype is composed of an acrylic sphere with a 3 m inner diameter and an aluminum alloy support structure. In this article, the structure of the small prototype is briefly described. A detailed simulation study using finite element analysis is conducted to account for liquid-filled condition, temperature variation and existence of high load (due to vacuum pumping) and demonstrate a satisfying mechanical performance of the small prototype. The experimental plan about the prototype on the basis of the simulation will also be mentioned.

Mass hierarchy and CP -phase sensitivity of ORCA using the Fermilab neutrino beam

We explore neutrino mass hierarchy determination and CP-phase measurement using multi-megaton water Cherenkov detector KM3NeT-Oscillation Research with Cosmics in the Abyss (ORCA) in the Mediterranean sea receiving neutrino beam from the Fermilab Long Baseline Neutrino Facility (LBNF) over 6900 km baseline. We find that with the proposed beam luminosity of $1.2\times 10^{21}$ proton-on-target per year, it will be possible to determine mass hierarchy at $\gtrsim 4\,\sigma$ confidence level within 1 year in the neutrino mode alone. A combined 1 year in neutrino and 1 year in antineutrino mode can determine hierarchy at $\gtrsim 6\,\sigma$ confidence level. We also find that a non-zero CP-phase can be detected with up to $\sim 1.8\,\sigma$ significance after 10 years of data taking. We explore degeneracy of neutrino oscillation parameters and uncertainties in detection efficiencies affecting the results.

The Application of SNiPER to the JUNO Simulation

The JUNO (Jiangmen Underground Neutrino Observatory) is a multipurpose neutrino experiment which is designed to determine neutrino mass hierarchy and precisely measure oscillation parameters. As one of the important systems, the JUNO offline software is being developed using the SNiPER software. In this proceeding, we focus on the requirements of JUNO simulation and present the working solution based on the SNiPER.The JUNO simulation framework is in charge of managing event data, detector geometries and materials, physics processes, simulation truth information etc. It glues physics generator, detector simulation and electronics simulation modules together to achieve a full simulation chain. In the implementation of the framework, many attractive characteristics of the SNiPER have been used, such as dynamic loading, flexible flow control, multiple event management and Python binding. Furthermore, additional efforts have been made to make both detector and electronics simulation flexible enough to accommodate and optimize different detector designs.For the Geant4-based detector simulation, each sub-detector component is implemented as a SNiPER tool which is a dynamically loadable and configurable plugin. So it is possible to select the detector configuration at runtime. The framework provides the event loop to drive the detector simulation and interacts with the Geant4 which is implemented as a passive service. All levels of user actions are wrapped into different customizable tools, so that user functions can be easily extended by just adding new tools. The electronics simulation has been implemented by following an event driven scheme. The SNiPER task component is used to simulate data processing steps in the electronics modules. The electronics and trigger are synchronized by triggered events containing possible physics signals.The JUNO simulation software has been released and is being used by the JUNO collaboration to do detector design optimization, event reconstruction algorithm development and physics sensitivity studies.

Effect of systematics in the T2HK, T2HKK, and DUNE experiments

T2HK and T2HKK are the proposed extensions of the of T2K experiments in Japan and DUNE is the future long-baseline program of Fermilab. All these three experiments will use extremely high beam power and large detector volumes to observe neutrino oscillation. Because of the large statistics, these experiments will be highly sensitive to systematics. Thus a small change in the systematics can cause a significant change in their sensitivities. To understand this, we do a comparative study of T2HK, T2HKK and DUNE with respect to their systematic errors. Specifically we study the effect of the systematics in the determination of neutrino mass hierarchy, octant of the mixing angle $\theta_{23}$ and $\delta_{CP}$ in the standard three flavor scenario and also analyze the role of systematic uncertainties in constraining the parameters of the nonstandard interactions in neutrino propagation. Taking the overall systematics for signal and background normalization, we quantify how the sensitivities of these experiments change if the systematics are varied from $1\%$ to $7\%$.