Atmospheric Neutrino Oscillations Research Articles

Analytical description of CP violation in oscillations of atmospheric neutrinos traversing the Earth

Flavour oscillations of sub-GeV atmospheric neutrinos and antineutrinos, traversing different distances inside the Earth, are a promising source of information on the leptonic CP phase δ. In that energy range, the oscillations are very fast, far beyond the resolution of modern neutrino detectors. However, the necessary averaging over the experimentally typical energy and azimuthal angle bins does not wash out the CP violation effects. In this paper we derive very accurate analytic compact expressions for the averaged oscillations probabilities. Assuming spherically symmetric Earth, the averaged oscillation probabilities are described in terms of two analytically calculable effective parameters. Based on those expressions, we estimate maximal magnitude of CP-violation effects in such measurements and propose optimal observables best suited to determine the value of the CP phase in the PMNS mixing matrix.

Earth tomography with atmospheric neutrino oscillations

The study of the flux of atmospheric neutrino crossing the Earth can provide useful information not only on the matter density of the different layers that make up the planet but also on their chemical composition. The key phenomenon that makes this possible is flavor oscillations and their dependence on the electron density along the neutrino baseline. To extract the relevant information, we simulate the energy and azimuth angle distribution of events produced in a generic neutrino telescope by atmospheric neutrinos passing through the deepest parts of the Earth. Changes in the densities of the outer core and the mantle are implemented by varying the location of the boundary between these layers so that the restrictions on the mass of and the moment of inertia of the Earth are both satisfied. This allows us to examine the effect of simultaneous changes in composition and density of the outer core, unlikely other works on the subject, where only one of these quantities was varied.

First simulation study of trackless events in the INO-ICAL detector to probe the sensitivity to atmospheric neutrino oscillation parameters

The proposed India-based Neutrino Observatory will host a 50 kton magnetized iron calorimeter (ICAL) with resistive plate chambers as its active detector element. Its primary focus is to study charged-current interactions of atmospheric muon neutrinos via the reconstruction of muons in the detector. We present the first study of the energy and direction reconstruction of the final state lepton and hadrons produced in charged current interactions of atmospheric electron neutrinos at ICAL and the sensitivity of these events to neutrino oscillation parameters $\theta_{23}$ and $\Delta m_{32}^2$. However, the signatures of these events are similar to those from neutral-current interactions and charged-current muon neutrino events in which the muon track is not reconstructed. On including the entire set of events that do not produce a muon track, we find that reasonably good sensitivity to $\theta_{23}$ is obtained, with a relative $1\sigma$ precision of 15% on the mixing parameter $\sin^2\theta_{23}$, which decreases to 21%, when systematic uncertainties are considered.

Enhancing sensitivity to non-standard neutrino interactions at INO combining muon and hadron information

In this paper, we explore the impact of flavor violating neutral current non-standard interaction (NSI) parameter varepsilon _{mu tau } in the oscillation of atmospheric neutrinos and antineutrinos separately using the 50 kt magnetized ICAL detector at INO. We find that due to non-zero varepsilon _{mu tau }, nu _mu rightarrow nu _mu and {bar{nu }}_mu rightarrow {bar{nu }}_mu transition probabilities get modified substantially at higher energies and longer baselines, where vacuum oscillation dominates. We demonstrate for the first time that by adding the hadron energy information along with the muon energy and muon direction in each event, the sensitivity of ICAL to the NSI parameter varepsilon _{mu tau } can be enhanced significantly. The most optimistic bound on varepsilon _{mu tau } that we obtain is -,,0.01< varepsilon _{mu tau } < 0.01 at 90% C.L. using 500 ktcdot yr exposure and considering E_mu , cos theta _mu , and E'_{mathrm{had}} as observables in their ranges of [1, 21] GeV, [− 1, 1], and [0, 25] GeV, respectively. We discuss for the first time the importance of the charge identification capability of the ICAL detector to have better constraints on varepsilon _{mu tau }. We also study the impact of non-zero varepsilon _{mu tau } on mass hierarchy determination and precision measurement of oscillation parameters.

RPC performance with HARDROC based readout

The proposed 51 kton magnetized Iron Calorimeter (ICAL) detector at India based Neutrino Observatory (INO) aims to investigate atmospheric neutrino oscillations. ICAL will use approximately 29000 glass-based Resistive Plate Chambers (RPCs) as active detector elements, that require millions of electronic channels to be read. Therefore, a multi-channel readout Application Specific Integrated Circuit (ASIC) named as HARDROC can be considered as a possible option. The ASIC is a 64 channel analog-digital front-end chip that can read negative fast and short input signals. Each of the HARDROC channels features a current sensitive pre-amplifier coupled to the triple-branch shaper stage and then 3 low offset discriminators. A comparative performance study of the RPC detector with HARDROC ASIC and with custom electronics, based on CAEN modules and HMC pre-amplifiers, was conducted. Measurements were made on a 30cm × 30cm glass RPC detector using the cosmic rays. The purpose of this work was to compare detector performance in terms of their strip detective efficiency and count rate.

Probing Beyond Standard Model Physics via Oscillations with IceCube DeepCore

For many years IceCube DeepCore has measured atmospheric neutrino interactions in the optically clear, deep ice at the South Pole. Analysing only three years of data has yielded the most precise measurements of the atmospheric neutrino oscillation parameters above 5 GeV. Measuring oscillations at these high energies, well above the tau-production threshold, and over extremely long baselines, provides strong constraints on new, Beyond Standard Model physics in a region of phase space uniquely accessed with atmospheric neutrinos. Here we report on the most recent searches for non-standard atmospheric neutrino oscillations with IceCube DeepCore.

Dependence of atmospheric muon flux on seawater depth measured with the first KM3NeT detection units

KM3NeT is a research infrastructure located in the Mediterranean Sea, that will consist of two deep-sea Cherenkov neutrino detectors. With one detector (ARCA), the KM3NeT Collaboration aims at identifying and studying TeV–PeV astrophysical neutrino sources. With the other detector (ORCA), the neutrino mass ordering will be determined by studying GeV-scale atmospheric neutrino oscillations. The first KM3NeT detection units were deployed at the Italian and French sites between 2015 and 2017. In this paper, a description of the detector is presented, together with a summary of the procedures used to calibrate the detector in-situ. Finally, the measurement of the atmospheric muon flux between 2232–3386 m seawater depth is obtained.

Atmospheric Neutrino and Proton Decay Results in Super-Kamiokande

Super-Kamiokande (SK) is a 50 kiloton water Cherenkov detector aiming for the detection of several physics such as solar, atmospheric, astrophysical neutrinos, proton decay, WIMP dark matter, etc. It has been running over 20 years since 1996, and achieved several remarkable outcomes in the field of the particle and astrophysics, one of which is the discovery of the neutrino oscillation, bringing the Nobel Prize in physics 2015. SK still accumulates a large number of neutrino events, and simultaneously the physic target and its sensitivity are extended along with the improvement of the analysis method, such as event reconstruction and background rejection. One of the strong motivations for the atmospheric neutrino oscillation measurement is to measure the mass ordering (hierarchy) between ½2 and ½3. The atmospheric neutrino is sensitive to the mass hierarchy with help of the matter effect which is given when passing through the Earth. We have performed a detailed analysis to discriminate small signature of the mass hierarchy due to the matter effect. Proton decay is a direct signature anticipated by the grand unified theory (GUT) which is the physics beyond the standard model. Though the major decay modes and GUT models are excluded by the past searches, the efforts to search a glimpse of the proton decay signal are being continued with better event reconstruction and analysis method. In this paper the recent results of the atmospheric neutrino measurement and proton decay search using the most updated dataset taken until 2017 spring are described.

Scalar Nonstandard Interactions in Neutrino Oscillation.

The scalar nonstandard interactions (NSI) can also introduce matter effect for neutrino oscillation in a medium. Especially the recent Borexino data prefer nonzero scalar NSI, η_{ee}=-0.16. In contrast to the conventional vector NSI, the scalar type contributes as a correction to the neutrino mass matrix rather than the matter potential. Consequently, the scalar matter effect is energy independent while the vector one scales linearly with neutrino energy. This leads to significantly different phenomenological consequences in reactor, solar, atmospheric, and accelerator neutrino oscillations. A synergy of different types of experiments, especially those with matter density variation, is necessary to identify the scalar NSI and guarantee the measurement of CP violation at accelerator experiments.

Atmospheric neutrino oscillation analysis with improved event reconstruction in Super-Kamiokande IV

A new event reconstruction algorithm based on a maximum likelihood method has been developed for Super-Kamiokande. Its improved kinematic and particle identification capabilities enable the analysis of atmospheric neutrino data in a detector volume 32% larger than previous analyses and increases sensitivity to the neutrino mass hierarchy. Analysis of a 253.9 kton-year exposure of the Super-Kamiokande IV atmospheric neutrino data has yielded a weak preference for the normal hierarchy, disfavoring the inverted hierarchy at 74% assuming oscillations at the best fit of the analysis.

Neutrino mass matrix in a gauge group SU(2)L × U(1)e × U(1)μ × U(1)τ

The electroweak unification group [Formula: see text] in which each fermion multiplet has its own [Formula: see text] factor was proposed in 1986 to get the neutrino mass matrix. In this paper, the gauge group [Formula: see text] is restricted to lepton section only, leaving quark multiplets as in the Standard Model. In addition to lepton multiplets [Formula: see text], [Formula: see text] and [Formula: see text], there are three [Formula: see text] singlet right-handed neutrinos [Formula: see text]’s. With the breaking of [Formula: see text] to [Formula: see text], the right-handed neutrinos acquire heavy Majorana masses. Three heavy right-handed neutrinos [Formula: see text]’s are available to generate a [Formula: see text] nondiagonal neutrino mass matrix in terms of three Yukawa couplings [Formula: see text], [Formula: see text], [Formula: see text] of the Higgs scalar doublet to [Formula: see text], [Formula: see text], [Formula: see text] with [Formula: see text], [Formula: see text] and [Formula: see text], respectively. Three Yukawa couplings can be arranged and expressed in terms of masses [Formula: see text], [Formula: see text], [Formula: see text] in three different ways to obtain the results of interest for Case 1: [Formula: see text]; Case 2: [Formula: see text]; Case 3: [Formula: see text]. The results obtained for the three cases are compared with the experimental data from neutrino oscillations. Cases 1 and 2 are relevant for solar neutrino oscillations whereas Case 3 is relevant for atmospheric neutrino oscillations.

Dynamical generation of neutrino mass scales

In this letter we present a simple scenario where the mass scales associated to atmospheric and solar neutrino oscillations are obtained through the dynamical generation of neutrino masses. The main idea is that the two different scales are the result of two independent mechanisms, namely a type-I seesaw generating the atmospheric scale and a radiative 1-loop process providing the solar one. A relation of the two scales, reminiscent of the so-called sequential dominance, is thus obtained.

Tau neutrinos in IceCube, KM3NeT and the Pierre Auger Observatory

In 2018, the IceCube collaboration reported evidence for the identification of a blazar as an astrophysical neutrino source. That evidence is briefly summarised here before focusing on the prospects of tau neutrino physics in IceCube, both at high energies (astrophysical neutrinos) and at lower energies (atmospheric neutrino oscillations). In addition, future neutrino detectors such as KM3NeT and the IceCube Upgrade and their tau neutrino physics potential are discussed. Finally, the detection mechanism for high-energy (tau) neutrinos in the Pierre Auger Observatory and the resulting flux upper limits are presented.

The Antares And Km3Net Neutrino Telescopes: Status And Outlook For Acoustic Studies

The ANTARES detector has been operating continuously since 2007 in the Mediterranean Sea, demonstrating the feasibility of an undersea neutrino telescope. Its superior angular resolution in the reconstruction of neutrino events of all flavors results in unprecedented sensitivity for neutrino source searches in the southern sky at TeV energies, so that valuable constraints can be set on the origin of the cosmic neutrino flux discovered by theIceCube detector. The next generation KM3NeT neutrino telescope is now under construction, featuring two detectors with the same technology but different granularity: ARCA designed to search for high energy (TeV-PeV) cosmic neutrinos and ORCA designed to study atmospheric neutrino oscillations at the GeV scale, focusing on the determination of the neutrino mass hierarchy. Both detectors use acoustic devices for positioning calibration, and provide testbeds for acoustic neutrino detection.

E- discrimination at high energy in the JUNO detector

Cosmic Ray and neutrino oscillation physics can be studied by using atmospheric neutrinos. JUNO (Jiangmen Underground Neutrino Observatory) is a large liquid scintillator detector with low energy detection threshold and excellent energy resolution. The detector performances allow the atmospheric neutrino oscillation measurements. In this work, a discrimination algorithm for different reaction channels of neutrino-nucleon interactions in the JUNO liquid scintillator, in the GeV/sub-GeV energy region, is presented. The atmospheric neutrino flux is taken as reference, considering $\mathop {{v_\mu }}\limits^{( - )} $ and $\mathop {{v_e}}\limits^{( - )} $. The different temporal behaviour of the classes of events have been exploited to build a timeprofile-based discrimination algorithm. The results show a good selection power for $\mathop {{v_e}}\limits^{( - )} $ CC events, while the $\mathop {{v_\mu }}\limits^{( - )} $ CC component suffers of an important contamination from NC events at low energy, which is under study. Preliminary results are presented.

Unitarity bounds of astrophysical neutrinos

The flavor composition of astrophysical neutrinos observed at neutrino telescopes is related to the initial composition at their sources via oscillation-averaged flavor transitions. If the time evolution of the neutrino flavor states is unitary, the probability of neutrinos changing flavor is solely determined by the unitary mixing matrix that relates the neutrino flavor and propagation eigenstates. In this paper we derive general bounds on the flavor composition of TeV-PeV astrophysical neutrinos based on unitarity constraints. These bounds are useful for studying the flavor composition of high-energy neutrinos, where energy-dependent nonstandard flavor mixing can dominate over the standard mixing observed in accelerator, reactor, and atmospheric neutrino oscillations.

Neutrino astronomy and oscillation research in the Mediterranean: ANTARES and KM3NeT

Abstract ANTARES , the underwater neutrino telescope in the Northern Hemisphere, has been continuously operating since 2007 in the Mediterranean Sea. The transparency of the water allows for a very good angular resolution in the reconstruction of interactions from neutrinos of all flavours. This results in unprecedented sensitivity for neutrino source searches in the Southern Sky at TeV energies, so that valuable constraints can be set on the origin of the cosmic neutrino flux discovered by the IceCube detector. Building on the successful experience of ANTARES the next generation KM3NeT neutrino telescope is now under construction in the Mediterranean Sea to significantly boost the sensitivity. Two detectors with the same technology but different granularity are under construction at two sites and will focus on high energy cosmic neutrinos (ARCA with Gton instrumented volume, offshore Capo Passero, Italy) and on atmospheric neutrinos at low energies down to a few GeV to address atmospheric neutrino oscillations (ORCA with Mtons instrumented volume, offshore Toulon, France). The basic KM3NeT detection element, the Digital Optical Module (DOM), houses 31 three-inch PMTs inside a 17 inch glass sphere. This multi-PMT concept allows for an accurate measurement of the light intensity (photon counting) and offers directional information with an almost isotropic field of view, at a reduced cost. This contribution will provide an overview on the newest results from ANTARES and an outlook towards the construction plan and exciting science potential of KM3NeT.

KM3NeT: Next-generation neutrino telescope in the Mediterranean Sea

Abstract The successes of the ANTARES detector have demonstrated the feasibility and value of deep sea neutrino telescopes , as well as their versatility through Earth and Sea sciences. KM3NeT is a distributed undersea research infrastructure in the Mediterranean Sea that will host a network of next-generation neutrino telescopes. With the ORCA telescope at the KM3NeT-Fr site, the main objective is to determine the neutrinos mass hierarchy by studying atmospheric neutrino oscillations . The ARCA telescope at the KM3NeT-It site will allow for high energy neutrino astronomy . The telescopes consist of a regular 3D array of Digital Optical Modules, each composed of 31 photomultipliers, equally spaced along flexible lines anchored on the seabed. This multi-photomultipliers concept yields a factor three increase in photocathode area, compared to a design with a single 10 inch photomultiplier, leading to a significant cost reduction. Moreover, this concept allows for an accurate measurement of the light intensity and offers directional information with an almost isotropic field of view. A detailed overview of the detectors, their construction status and their physics program will be presented. The calibration techniques will be discussed, with an emphasis on time calibration, water properties and positioning measurements.

Measurement of the tau neutrino cross section in atmospheric neutrino oscillations with Super-Kamiokande

Using 5326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47±0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau appearance with a significance level of 4.6σ. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be (0.94±0.20)×10−38 cm2. The measurement is consistent with the Standard Model prediction, agreeing to within 1.5σ.9 MoreReceived 27 November 2017DOI:https://doi.org/10.1103/PhysRevD.98.052006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNeutrino oscillationsPhysical SystemsNeutrinosParticles & Fields

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.