Neutrino Mass Hierarchy Research Articles

Parallelized JUNO simulation software based on SNiPER

The Jiangmen Underground Neutrino Observatory (JUNO) is a neutrino experiment to determine the neutrino mass hierarchy. It has a central detector used for neutrino detection, which consists of a spherical acrylic vessel containing a 20 kt liquid scintillator (LS) and about 18,000 20-inch photomultiplier tubes (PMTs) to collect light from LS. Around the central detector, there is a water pool to provide shielding from background radioactivity. The outer water pool is also equipped with about 2000 PMTs to measure cosmic ray muons by detecting Cherenkov light.As one of the important parts in JUNO offline software, the serial simulation framework is developed based on SNiPER. It manages physics generator, detector simulation, event mixing and digitization. However, Geant4 based detector simulation of such a large detector is time-consuming and challenging. It is necessary to take full advantages of parallel computing to speed up simulation. Starting from version 10.0, Geant4 supports event-level parallelism. Even though this is based on pthread, it can be extended with other libraries such as Intel TBB and MPI. Therefore it is possible to parallelize JUNO simulation framework by integrating Geant4 and SNiPER.In this paper, our progress in developing parallelized simulation software is presented. The SNiPER framework can run in sequential mode, Intel TBB mode or other modes. The SNiPER task component is in charge of the event loop, which is like a simplified application manager. Two types of tasks are introduced in the simulation framework, one is a global task and another is a worker task. The global task will run only once to initialize detector geometry and physics processes before any other tasks spawned. Later it is accessed by other tasks passively. The worker tasks will be spawned after the global task is done. In each worker task, a Geant4 run manager is invoked to do the real simulation. In this way the simulation framework and the underlying TBB have been decoupled. Finally, the software performance of parallelized JUNO simulation software is also presented.

A vertex reconstruction algorithm in the central detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is designed to study neutrino mass hierarchy and measure three of the neutrino oscillation parameters with high precision using reactor antineutrinos. It is also able to study many other physical phenomena, including supernova neutrinos, solar neutrinos, geo-neutrinos, atmosphere neutrinos, and so forth. The central detector of JUNO contains 20,000 tons of liquid scintillator (LS) and about 18,000 20-inch photomultiplier tubes (PMTs), which is the largest liquid scintillator one under construction in the world up today. The energy resolution is expected to be 3%/√E(MeV). To meet the requirements of the experiment, an algorithm of vertex reconstruction, which takes into account time and charge information of PMTs, has been developed by deploying the maximum likelihood method and well understanding the complicated optical processes in the liquid scintillator.

Study on the radon removal for the water system of Jiangmen Underground Neutrino Observatory

The Jiangmen Underground Neutrino Observatory (JUNO), a 20-kton multipurpose underground liquid scintillator detector, was proposed with the determination of the neutrino mass hierarchy as a primary physics goal. To veto the cosmogenic background and shield the central detector from the environmental radioactivity, a multi-veto system, which consists of a water Cherenkov detector and a top tracker detector, is required. In order to keep the water quality good and remove the radon from water, an ultrapure water system, a radon removal system and radon concentration measurement system have been designed.

Breaking flavor democracy with symmetric perturbations

Flavor democracy broken in the fermion mass matrix by means of small perturbations can give rise to hierarchical fermion masses. We study the breaking of the S3L×S3R symmetry associated with democratic mass matrices to a smaller exchange symmetry S2L×S2R in the charged lepton, up and down quark sectors. An additional breaking of the S2L×S2R symmetry is necessary for the down quark mass matrix, which yields arbitrary perturbations in that sector. On the other hand, we require the neutrino mass matrix to be diagonal at the leading order, with the perturbations left arbitrary due to the absence of any guiding symmetry. We show that the interplay between these two kinds of perturbations reproduces the quark and lepton mass and mixing observables for either hierarchy of neutrino masses.

Leptonic CP violation and leptogenesis in minimal supersymmetric SU(4)c×SU(2)L×SU(2)R

We consider a supersymmetric SU(4)$_c \times$SU(2)$_L \times$SU(2)$_R$ model with a minimal number of Higgs multiplets and Dirac and Majorana $CP$-violating phases in the neutrino flavor mixing matrix. The model incorporates the charged fermion masses and quark mixings, and uses type I seesaw to explain the solar and atmospheric neutrino oscillations. With the neutrino oscillation data of two mass squared differences and three flavor mixing angles, we employ thermal leptogenesis and the observed baryon asymmetry to find the allowed regions for the Dirac and Majorana phases. For a normal neutrino mass hierarchy, we find that the observed baryon asymmetry can be reproduced by a Dirac phase of around $\delta_{CP}=3 \pi/2$, which is strongly indicated by the recent T2K and NO$\nu$A data. For the case of inverted neutrino mass hierarchy, the predicted baryon asymmetry is not compatible with the observed value.

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.

Exploring neutrino mass and mass hierarchy in the scenario of vacuum energy interacting with cold dark matter**Supported by National Natural Science Foundation of China (11522540, 11690021), the Top-Notch Young Talents Program of China and the Provincial Department of Education of Liaoning (L2012087)

We investigate the constraints on total neutrino mass in the scenario of vacuum energy interacting with cold dark matter. We focus on two typical interaction forms, i.e., Q = βH ρc and Q = βH ρΛ. To avoid the occurrence of large-scale instability in interacting dark energy cosmology, we adopt the parameterized post-Friedmann approach to calculate the perturbation evolution of dark energy. We employ observational data, including the Planck cosmic microwave background temperature and polarization data, baryon acoustic oscillation data, a JLA sample of type Ia supernovae observation, direct measurement of the Hubble constant, and redshift space distortion data. We find that, compared with those in the ΛCDM model, much looser constraints on Σmν are obtained in the Q = βH ρc model, whereas slightly tighter constraints are obtained in the Q = βH ρΛ model. Consideration of the possible mass hierarchies of neutrinos reveals that the smallest upper limit of Σmν appears in the degenerate hierarchy case. By comparing the values of , we find that the normal hierarchy case is favored over the inverted one. In particular, we find that the difference in the Q = βH ρc model. In addition, we find that β = 0 is consistent with the current observations in the Q = βH ρc model, and β < 0 is favored at more than the 1 σ level in the Q = βH ρΛ model.

Revisiting the A4 model for leptons in light of NuFIT 3.2

We revisit the $A_4$ model for leptons in light of new result of NuFIT 3.2. We introduce a new flavon $\eta$ transforming as $A_4$ singlet $1'$ or $1"$ which couples to both charged leptons and neutrinos in next-leading order operators. The model consists of the five parameters: the lightest neutrino mass $m_1$, the vacuum expectation value of $\eta$ and three CP violating phases after inputting the experimental values of $\Delta m_{\rm atm}^2$ and $\Delta m_{\rm sol}^2$. The model with the $1"$ singlet flavon gives the prediction of $\sin^2 \theta_{12}$ around the best fit of NuFIT 3.2 while keeping near the maximal mixing of $\theta_{23}$. Inputting the experimental mixing angles with the $1\,\sigma$ error-bar, the Dirac CP violating phase is clearly predicted to be $|\delta_\text{CP}|=50^\circ- 120^\circ$, which will be tested by the precise observed value in the future. In order to get the best fit value $\sin^2\theta_{23}=0.538$, the sum of three neutrino masses is predicted to be larger than $90\,$meV. The cosmological observation for the sum of neutrino masses will also provide a crucial test of our predictions. It is remarked that the model is consistent with the experimental data only for the normal hierarchy of neutrino masses.

First results of the KM3NeT/ARCA detector

The KM3NeT collaboration started to build a multi-km3neutrino telescope in the Mediterranean Sea. The telescope is composed of two parts: the ARCA detector, optimised for searches for high energy neutrino sources in the Universe, and ORCA, for the determination of the mass hierarchy of neutrinos. ARCA is under construction at the Capo Passero site, Italy, 80 km offshore at a depth of 3500 m while ORCA is located in the Toulon area, France, 40 km offshore at a depth of 2500 m. The basic detection element of the KM3NeT detector is the Digital Optical Module. The module is a pressure resistant glass sphere, containing 31 photo-multiplier tubes. Eighteen modules are arranged in the detection unit, a vertical structure anchored on the sea floor. The detection units are deployed on the sea bed to form a three-dimensional array of optical modules to detect Cherenkov light produced by neutrino-induced muons. In these proceedings preliminary results obtained with the first two detection units of ARCA are presented. The capability to select and reconstruct atmospheric muons is discussed. The dependence of the muon flux with the sea depth is derived, showing that the detector is well calibrated and the systematics are kept under control.

Confronting the DAMPE excess with the scotogenic type-II seesaw model

The DArk Matter Particle Explorer (DAMPE) has observed a tentative peak at E ∼ 1.4 TeV in the cosmic-ray electron spectrum. In this paper, we interpret this excess in the scotogenic type-II seesaw model. This model extends the canonical type-II seesaw model with dark matter (DM) candidates and a loop-induced vacuum expectation value of the triplet scalars, vΔ, resulting in small neutrino masses naturally even for TeV scale triplet scalars. Assuming a nearby DM subhalo, the DAMPE excess can be explained by DM annihilating into a pair of triplet scalars which subsequently decay to charged lepton final states. Spectrum fitting of the DAMPE excess indicates it potentially favors the inverted neutrino mass hierarchy. We also discuss how to evade associated neutrino flux in our model.

Status and perspectives of the JUNO experiment

The JUNO (Jiangmen Underground Neutrino Observatory), a 20 kton multi-purpose underground liquid scintillator detector, has been proposed and approved for realization in the south of China. After an intense design phase, the overall concept of the structure of the detector has been finalized, paving the way towards the construction of the several components and subsystems, which will compose it. Meanwhile, the excavation of the site which will host the experiment has been started and is rapidly progressing. The main physics target of JUNO is the determination of the neutrino mass hierarchy, which will be accessible through the measurement of the pattern of antineutrino spectrum from two high power nuclear complexes under installation 53 km away from the experimental site. In this work I describe the broad physics capabilities of the experiment, which include in addition to the crucial measure of the neutrino hierarchy the high precision determination of three oscillation parameters, as well as a rich astroparticle program, and I illustrate the main technical characteristics of the detector.

Geometric phase and neutrino mass hierarchy problem

We study the geometric phase for neutrinos at various man-made facilities, such as the reactor and accelerator neutrino experiments. The analysis is done for the three flavor neutrino scenario, in the presence of matter and for general, noncyclic paths. The geometric phase is seen to be sensitive to the CP violating phase in the leptonic sector and the sign ambiguity in . We find that for neutrino experimental facilities where the geometric phase can complete one cycle, all the phase curves corresponding to different values of CP violating phase, converge to a single point, called the cluster point. There are two distinct cluster points for positive and negative signs of Δ31. Thus, the geometric phase can contribute to our understanding of the neutrino mass hierarchy problem.

Fermion masses and mixings and dark matter constraints in a model with radiative seesaw mechanism

We formulate a predictive model of fermion masses and mixings based on a Δ(27) family symmetry. In the quark sector the model leads to the viable mixing inspired texture where the Cabibbo angle comes from the down quark sector and the other angles come from both up and down quark sectors. In the lepton sector the model generates a predictive structure for charged leptons and, after radiative seesaw, an effective neutrino mass matrix with only one real and one complex parameter. We carry out a detailed analysis of the predictions in the lepton sector, where the model is only viable for inverted neutrino mass hierarchy, predicting a strict correlation between θ23 and θ13. We show a benchmark point that leads to the best-fit values of θ12, θ13, predicting a specific sin2θ23 ≃ 0.51 (within the 3σ range), a leptonic CP-violating Dirac phase δ ≃ 281.6° and for neutrinoless double-beta decay mee ≃ 41.3 meV. We turn then to an analysis of the dark matter candidates in the model, which are stabilized by an unbroken ℤ2 symmetry. We discuss the possibility of scalar dark matter, which can generate the observed abundance through the Higgs portal by the standard WIMP mechanism. An interesting possibility arises if the lightest heavy Majorana neutrino is the lightest ℤ2-odd particle. The model can produce a viable fermionic dark matter candidate, but only as a feebly interacting massive particle (FIMP), with the smallness of the coupling to the visible sector protected by a symmetry and directly related to the smallness of the light neutrino masses.

Atmospheric neutrino oscillation analysis with external constraints in Super-Kamiokande I-IV

An analysis of atmospheric neutrino data from all four run periods of \superk optimized for sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for $\Delta m^2_{32}$, $\sin^2 \theta_{23}$, $\sin^2 \theta_{13}$ and $\delta_{CP}$ are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses based on atmospheric neutrino data alone. Additional constraints from reactor data on $\theta_{13}$ and from published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.5% and 94.5% based on the combined result.

Muon tracking with the fastest light in the JUNO central detector

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment designed to measure the neutrino mass hierarchy using a central detector (CD), which contains 20 kton liquid scintillator (LS) surrounded by about 18,000 photomultiplier tubes (PMTs), located 700~m underground. The rate of cosmic muons reaching the JUNO detector is about 3~Hz and the muon induced neutrons and isotopes are major backgrounds for the neutrino detection. Reconstruction of the muon trajectory in the detector is crucial for the study and rejection of those backgrounds. This paper will introduce the muon tracking algorithm in the JUNO CD, with a least squares method of PMTs' first hit time (FHT). Correction of the FHT for each PMT was found to be important to reduce the reconstruction bias. The spatial resolution and angular resolution are better than 3~cm and 0.4~degree, respectively, and the tracking efficiency is greater than 90\% up to 16~m far from the detector center.

A highly predictive A4 flavor 3-3-1 model with radiative inverse seesaw mechanism

We build a highly predictive 3-3-1 model, where the field content is extended by including several SU(3)L scalar singlets and six right handed Majorana neutrinos. In our model the gauge symmetry is supplemented by the discrete group, which allows to get a very good description of the low energy fermion flavor data. In the model under consideration, the discrete group is broken at very high energy scale down to the preserved Z2 discrete symmetry, thus generating the observed pattern of SM fermion masses and mixing angles and allowing the implementation of the loop level inverse seesaw mechanism for the generation of the light active neutrino masses, respectively. The obtained values for the physical observables in the quark sector agree with the experimental data, whereas those ones for the lepton sector also do, only for the case of inverted neutrino mass spectrum. The normal neutrino mass hierarchy scenario of the model is ruled out by the neutrino oscillation experimental data. We find an effective Majorana neutrino mass parameter of neutrinoless double beta decay of mee = 46.9 meV, a leptonic Dirac CP violating phase of −81.37° and a Jarlskog invariant of about 10−2 for the inverted neutrino mass hierarchy. The preserved Z2 symmetry allows for a stable scalar dark matter candidate.

Prediction on neutrino Dirac and Majorana phases and absolute mass scale from the CKM matrix

In the type-I seesaw model, the lepton-flavor-mixing matrix (Pontecorvo-Maki-Nakagawa-Sakata matrix) and the quark-flavor-mixing matrix [Cabibbo-Kobayashi-Maskawa (CKM) matrix] may be connected implicitly through a relation between the neutrino Dirac Yukawa coupling ${Y}_{D}$ and the quark Yukawa couplings. In this paper, we study whether ${Y}_{D}$ can satisfy---in the flavor basis where the charged lepton Yukawa and right-handed neutrino Majorana mass matrices are diagonal---the relation ${Y}_{D}\ensuremath{\propto}\mathrm{diag}({y}_{d},{y}_{s},{y}_{b}){V}_{\mathrm{CKM}}^{T}$ or ${Y}_{D}\ensuremath{\propto}\mathrm{diag}({y}_{u},{y}_{c},{y}_{t}){V}_{\mathrm{CKM}}^{*}$ without contradicting the current experimental data on quarks and neutrino oscillations. We search for sets of values of the neutrino Dirac $CP$ phase ${\ensuremath{\delta}}_{CP}$, Majorana phases ${\ensuremath{\alpha}}_{2}$, ${\ensuremath{\alpha}}_{3}$, and the lightest active neutrino mass that satisfy either of the above relations, with the normal or inverted hierarchy of neutrino masses. In performing the search, we consider renormalization group evolutions of the quark masses and CKM matrix and the propagation of their experimental errors along the evolutions. We find that only the former relation ${Y}_{D}\ensuremath{\propto}\mathrm{diag}({y}_{d},{y}_{s},{y}_{b}){V}_{\mathrm{CKM}}^{T}$ with the normal neutrino mass hierarchy holds, based on which we make predictions for ${\ensuremath{\delta}}_{CP}$, ${\ensuremath{\alpha}}_{2}$, ${\ensuremath{\alpha}}_{3}$, and the lightest active neutrino mass.

Leptonic flavor structure in the brane shifted extra dimensional seesaw mechanism

We discuss the leptonic flavor structure generated by a brane shifted extra dimensional seesaw model with a single right handed neutrino in the bulk. In contrast to previous works, no unitarity approximation for the 3 times 3 submatrix has been employed. This allows to study phenomenological signatures such as lepton flavor violating decays. A strong prediction of the model, assuming CP conservation, are the ratios of flavor violating charged lepton decay and Z decay branching ratios which are correlated with the neutrino mixing angles and the neutrino mass hierarchy. Furthermore, it is possible to obtain branching ratios for mu rightarrow e gamma close to the experimental bounds even with Yukawa couplings of order one.

Muon reconstruction with a geometrical model in JUNO

The Jiangmen Neutrino Underground Observatory (JUNO) is a 20 kton liquid scintillator detector currently under construction near Kaiping in China. The physics program focuses on the determination of the neutrino mass hierarchy with reactor anti-neutrinos. For this purpose, JUNO is located 650 m underground with a distance of 53 km to two nuclear power plants. As a result, it is exposed to a muon flux that requires a precise muon reconstruction to make a veto of cosmogenic backgrounds viable. Established muon tracking algorithms use time residuals to a track hypothesis. We developed an alternative muon tracking algorithm that utilizes the geometrical shape of the fastest light. It models the full shape of the first, direct light produced along the muon track. From the intersection with the spherical PMT array, the track parameters are extracted with a likelihood fit. The algorithm finds a selection of PMTs based on their first hit times and charges. Subsequently, it fits on timing information only. On a sample of through-going muons with a full simulation of readout electronics, we report a spatial resolution of 20 cm of distance from the detector's center and an angular resolution of 1.6̂ over the whole detector. Additionally, a dead time estimation is performed to measure the impact of the muon veto. Including the step of waveform reconstruction on top of the track reconstruction, a loss in exposure of only 4% can be achieved compared to the case of a perfect tracking algorithm. When including only the PMT time resolution, but no further electronics simulation and waveform reconstruction, the exposure loss is only 1%.

Exploring collider aspects of a neutrinophilic Higgs doublet model in multilepton channels

We consider a neutrinophilic Higgs scenario where the Standard Model is extended by one additional Higgs doublet and three generations of singlet right-handed Majorana neutrinos. Light neutrino masses are generated through mixing with the heavy neutrinos via Type-I seesaw mechanism when the neutrinophilic Higgs gets a vacuum expectation value (VEV). The Dirac neutrino Yukawa coupling in this scenario can be sizable compared to those in the canonical Type-I seesaw mechanism owing to the small neutrinophilic Higgs VEV giving rise to interesting phenomenological consequences. We have explored various signal regions likely to provide a hint of such a scenario at the LHC as well as at future $e^+e^-$ colliders. We have also highlighted the consequences of light neutrino mass hierarchies in collider phenomenology that can complement the findings of neutrino oscillation experiments.