Oscillation Parameter Space Research Articles

The Stereo search for a sterile neutrino at the ILL reactor with full data sample

During the last decades, several parameters describing the neutrino oscillation phenomenon have been characterized thanks to reactor neutrino experiments, in particular the precise measurement of the last-to-be-measured mixing angle θ 13. Following a reactor antineutrino flux re-estimation in 2011, a 6% deficit between observed and predicted reactor antineutrino fluxes, known as the Reactor Antineutrino Anomaly, has been observed. The Reactor Antineutrino Anomaly could be explained by an oscillation toward an additional non-interacting, (thus “sterile”) neutrino. The parameters that best explain the RAA are a mixing angle value of sin2 (2θnew ) = 0.17 and a mass splitting value of . Additionally, a discrepancy between the measured and predicted antineutrino energy spectrum taking the form of an excess of events around 5 MeV has been observed by several reactor neutrino experiments. This discrepancy has yet to be fully understood but could be caused by incorrect predictions of the neutrino spectra. The STEREO experiment, located at Institut Laue-Langevin in Grenoble (France), was designed to test the above mentioned oscillation hypothesis independently of shape and rate predictions. The segmented detector, located at ∼10 m of a compact reactor core, allows for a measurement of the antineutrino energy spectrum at various baselines, sensitive to the oscillation toward a sterile neutrino that would distort the spectrum differently at each baseline. The experiment could also help to disentangle isotopic contributions to the neutrino energy spectrum by providing a measurement of the spectrum shape and rate originating from a core with highly enriched (93%)235U. The experiment took data between November 2016 and November 2020. This talk will present the latest limits set in the oscillation parameter space with the full data sample, amounting to 334 (544) days of reactor-on (off), as well as the updated rate and spectrum shape measurements.

First Search for Short-Baseline Neutrino Oscillations at HFIR with PROSPECT.

This Letter reports the first scientific results from the observation of antineutrinos emitted by fission products of ^{235}U at the High Flux Isotope Reactor. PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, consists of a segmented 4ton ^{6}Li-doped liquid scintillator detector covering a baseline range of 7-9m from the reactor and operating under less than 1m water equivalent overburden. Data collected during 33 live days of reactor operation at a nominal power of 85MW yield a detection of 25 461±283 (stat) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5σ statistical significance within 2h of on-surface reactor-on data taking. A reactor model independent analysis of the inverse beta decay prompt energy spectrum as a function of baseline constrains significant portions of the previously allowed sterile neutrino oscillation parameter space at 95%confidence level and disfavors the best fit of the reactor antineutrino anomaly at 2.2σ confidence level.

Prospects of light sterile neutrino oscillation and CP violation searches at the Fermilab Short Baseline Neutrino Facility

We investigate the ability of the Short Baseline Neutrino (SBN) experimental program at Fermilab to test the globally-allowed (3+$N$) sterile neutrino oscillation parameter space. We explicitly consider the globally-allowed parameter space for the (3+1), (3+2), and (3+3) sterile neutrino oscillation scenarios. We find that SBN can probe with $5\sigma$ sensitivity more than 85\%, 95\% and 55\% of the parameter space currently allowed at 99\% confidence level for the (3+1), (3+2) and (3+3) scenarios, respectively. In the case of the (3+2) and (3+3) scenarios, CP-violating phases appear in the oscillation probability terms, leading to observable differences in the appearance probabilities of neutrinos and antineutrinos. We explore SBN's sensitivity to those phases for the (3+2) scenario through the currently planned neutrino beam running, and investigate potential improvements through additional antineutrino beam running. We show that, if antineutrino exposure is considered, for maximal values of the (3+2) CP-violating phase $\phi_{54}$, SBN could be the first experiment to directly observe $\sim 2\sigma$ hints of CP violation associated with an extended lepton sector.

Implications of lepton flavor violation on long baseline neutrino oscillation experiments

Nonstandard neutrino interactions (NSIs), the subleading effects in the flavor transitions of neutrinos, play a crucial role in the determination of the various unknowns in neutrino oscillations, such as neutrino mass hierarchy, the Dirac $CP$ violating phase, and the octant of the atmospheric mixing angle. In this work, we focus on the possible implications of lepton flavor violating (LFV) NSIs, which generally affect the neutrino propagation, on the determination of these unknown oscillation parameters. We study the effect of these NSIs on the physics potential of the currently running and upcoming long-baseline experiments, i.e., T2K, $\mathrm{NO}\ensuremath{\nu}\mathrm{A}$, and DUNE. We also check the allowed oscillation parameter space in the presence of LFV NSIs.

Neutrino oscillation physics potential of the T2K experiment

The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle $\theta_{13}$ have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal $\sin^22\theta_{23}$, the octant of $\theta_{23}$, and the mass hierarchy, in addition to the measurements of $\delta_{CP}$, $\sin^2\theta_{23}$, and $\Delta m^2_{32}$, for various combinations of $\nu$-mode and \(\bar{\nu}\)-mode data-taking. With an exposure of $7.8\times10^{21}$~protons-on-target, T2K can achieve 1-$\sigma$ resolution of 0.050(0.054) on $\sin^2\theta_{23}$ and $0.040(0.045)\times10^{-3}~\rm{eV}^2$ on $\Delta m^2_{32}$ for 100\%(50\%) neutrino beam mode running assuming $\sin^2\theta_{23}=0.5$ and $\Delta m^2_{32} = 2.4\times10^{-3}$ eV$^2$. T2K will have sensitivity to the CP-violating phase $\delta_{\rm{CP}}$ at 90\% C.L. or better over a significant range. For example, if $\sin^22\theta_{23}$ is maximal (i.e $\theta_{23}$=$45^\circ$) the range is $-115^\circ<\delta_{\rm{CP}}<-60^\circ$ for normal hierarchy and $+50^\circ<\delta_{\rm{CP}}<+130^\circ$ for inverted hierarchy. When T2K data is combined with data from the NO$\nu$A experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero $\delta_{CP}$ is substantially increased compared to if each experiment is analyzed alone.

Experimental parameters for a reactor antineutrino experiment at very short baselines

Reactor antineutrinos are used to study neutrino oscillation, search for signatures of non-standard neutrino interactions, and to monitor reactor operation for safeguard applications. The flux and energy spectrum of reactor antineutrinos can be predicted from the decays of the nuclear fission products. A comparison of recent reactor calculations with past measurements at baselines of 10-100m suggests a 5.7% deficit. Precision measurements of reactor antineutrinos at very short baselines O(1-10 m) can be used to probe this anomaly and search for possible oscillations into sterile neutrino species. This paper studies the experimental requirements for a new reactor antineutrino measurement at very short baselines and calculates the sensitivity of various scenarios. We conclude that an experiment at a typical research reactor provides 5{\sigma} discovery potential for the favored oscillation parameter space with 3 years of data collection.

Precision measurement of the 7Be solar neutrino flux and its day-night asymmetry with Borexino

Borexino measures the 7Be solar neutrino flux on 740 live days of data-taking to be 46±1.5+1.6−1.5 events/(day · 100 tons) which corresponds to an equivalent unoscillated flux on Earth of (3.11±0.10+0.11−0.10)·109sec −1 cm−2. This result excludes the no-oscillation hypothesis at 5 σ and provides a precise measurement of the survival probability Pee in the vacuum dominated oscillation regime Pee = 0.51±0.07. Borexino also measures the day-night asymmetry of the 7Be neutrino rate with a total error of 1.4% and finds it to be consistent with zero. This result is in agreement with the MSW-LMA hypothesis and disfavours at more than 8.5 σ the so-called LOW region of the oscillation parameter space.

Precision measurement of the7Be solar neutrino flux and its day-night asymmetry with Borexino

Borexino measures the 7Be solar neutrino flux on 740 live days of data-taking to be 46±1.5+1.6−1.5 events/(day · 100 tons) which corresponds to an equivalent unoscillated flux on Earth of (3.11±0.10+0.11−0.10)·109sec −1 cm−2. This result excludes the no-oscillation hypothesis at 5 σ and provides a precise measurement of the survival probability Pee in the vacuum dominated oscillation regime Pee = 0.51±0.07. Borexino also measures the day-night asymmetry of the 7Be neutrino rate with a total error of 1.4% and finds it to be consistent with zero. This result is in agreement with the MSW-LMA hypothesis and disfavours at more than 8.5 σ the so-called LOW region of the oscillation parameter space.

Sterile neutrino search with kaon decay at rest

Monoenergetic muon neutrinos (235.5 MeV) from positive kaon decay-at-rest are considered as a source for an electron neutrino appearance search. In combination with a liquid argon time projection chamber based detector, such a source could provide discovery-level sensitivity to the neutrino oscillation parameter space indicative of a sterile neutrino. Current and future intense >3 GeV kinetic energy proton facilities around the world can be employed for this experimental concept.

3+1and3+2sterile neutrino fits

We present the results of fits of short-baseline neutrino-oscillation data in $3+1$ and $3+2$ neutrino-mixing schemes. In spite of the presence of a tension in the interpretation of the data, $3+1$ neutrino mixing is attractive for its simplicity and for the natural correspondence of one new entity (a sterile neutrino) with a new effect (short-baseline oscillations). The allowed regions in the oscillation parameter space can be tested in near-future experiments. In the framework of $3+2$ neutrino mixing, there is less tension in the interpretation of the data, at the price of introducing a second sterile neutrino. Moreover, the improvement of the parameter goodness of fit is mainly a statistical effect due to an increase in the number of parameters. The $CP$ violation in short-baseline experiments allowed in $3+2$ neutrino mixing can explain the positive ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}$ signal and the negative ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}$ measurement in the MiniBooNE experiment. For the $CP$-violating phase, we obtained two minima of the marginal ${\ensuremath{\chi}}^{2}$ close to the two values where $CP$ violation is maximal.

Mass varying neutrinos in supernovae

We study the consequences on the neutrino oscillation parameter space, mixing angle (${tan}^{2}\ensuremath{\theta}$), and vacuum mass difference ($\ensuremath{\Delta}{m}_{0}^{2}$) when mass varying neutrino (MaVaN) models are assumed in a supernova environment. We consider electronic to sterile channels ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{s}$ and ${\overline{\ensuremath{\nu}}}_{e}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{s}$ in two-flavor scenario. In a given model of MaVaN mechanism, we induce a position-dependent effective mass difference, $\ensuremath{\Delta}{\stackrel{\texttildelow{}}{m}}^{2}(r)$, where $r$ is the distance from the supernova core, that changes the neutrino and antineutrino flavor conversion probabilities. We study the constraints on the mixing angle and vacuum mass difference coming from r-process and the SN1987A data. Our result is the appearance of a new exclusion region for very small mixing angles, ${tan}^{2}\ensuremath{\theta}={10}^{\ensuremath{-}6}--{10}^{\ensuremath{-}2}$, and small vacuum mass difference, $\ensuremath{\Delta}{m}_{0}^{2}=1--20\text{ }\text{ }{\mathrm{eV}}^{2}$, due the MaVaN mechanism.

Neutrino oscillation parameter sampling with MonteCUBES

We present MonteCUBES (“Monte Carlo Utility Based Experiment Simulator”), a software package designed to sample the neutrino oscillation parameter space through Markov Chain Monte Carlo algorithms. MonteCUBES makes use of the GLoBES software so that the existing experiment definitions for GLoBES, describing long baseline and reactor experiments, can be used with MonteCUBES. MonteCUBES consists of two main parts: The first is a C library, written as a plug-in for GLoBES, implementing the Markov Chain Monte Carlo algorithm to sample the parameter space. The second part is a user-friendly graphical Matlab interface to easily read, analyze, plot and export the results of the parameter space sampling. Program summary Program title: MonteCUBES (Monte Carlo Utility Based Experiment Simulator) Catalogue identifier: AEFJ_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFJ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence No. of lines in distributed program, including test data, etc.: 69 634 No. of bytes in distributed program, including test data, etc.: 3 980 776 Distribution format: tar.gz Programming language: C Computer: MonteCUBES builds and installs on 32 bit and 64 bit Linux systems where GLoBES is installed Operating system: 32 bit and 64 bit Linux RAM: Typically a few MBs Classification: 11.1 External routines: GLoBES [1,2] and routines/libraries used by GLoBES Subprograms used: Cat Id ADZI_v1_0, Title GLoBES, Reference CPC 177 (2007) 439 Nature of problem: Since neutrino masses do not appear in the standard model of particle physics, many models of neutrino masses also induce other types of new physics, which could affect the outcome of neutrino oscillation experiments. In general, these new physics imply high-dimensional parameter spaces that are difficult to explore using classical methods such as multi-dimensional projections and minimizations, such as those used in GLoBES [1,2]. Solution method: MonteCUBES is written as a plug-in to the GLoBES software [1,2] and provides the necessary methods to perform Markov Chain Monte Carlo sampling of the parameter space. This allows an efficient sampling of the parameter space and has a complexity which does not grow exponentially with the parameter space dimension. The integration of the MonteCUBES package with the GLoBES software makes sure that the experimental definitions already in use by the community can also be used with MonteCUBES, while also lowering the learning threshold for users who already know GLoBES. Additional comments: A Matlab GUI for interpretation of results is included in the distribution. Running time: The typical running time varies depending on the dimensionality of the parameter space, the complexity of the experiment, and how well the parameter space should be sampled. The running time for our simulations [3] with 15 free parameters at a Neutrino Factory with O ( 10 6 ) samples varied from a few hours to tens of hours.

Mass varying neutrinos in the Sun

In this work we study the phenomenological consequences of the dependence of mass varying neutrinos on the neutrino density in the Sun, which we precisely compute in each point along the neutrino trajectory. We find that a generic characteristic of these scenarios is that they establish a connection between the effective Δ m 2 in the Sun and the absolute neutrino mass scale. This does not lead to any new allowed region in the oscillation parameter space. On the contrary, due to this effect, the description of solar neutrino data worsens for large absolute mass. As a consequence a lower bound on the level of degeneracy can be derived from the combined analysis of the solar and KamLAND data. In particular this implies that the analysis favours normal over inverted mass orderings. These results, in combination with a positive independent determination of the absolute neutrino mass, can be used as a test of these scenarios together with a precise determination of the energy dependence of the survival probability of solar neutrinos, in particular for low energies.

KamLAND, terrestrial heat sources and neutrino oscillations

We comment on the first indication of geo-neutrino events from KamLAND and on the prospects for understanding Earth energetics. Practically all models of terrestrial heat production are consistent with data within the presently limited statistics, the fully radiogenic model being closer to the observed value (≈9 geo-events). In a few years KamLAND should collect sufficient data for a clear evidence of geo-neutrinos, however discrimination among models requires a detector with the class and size of KamLAND far away from nuclear reactors. We also remark that the event ratio from thorium and uranium decay chains is well fixed N(Th)/N(U)≃0.25, a constraint that can be useful for determining neutrino oscillation parameters. We show that a full spectral analysis, including this constraint, further reduces the oscillation parameter space compared to an analysis with an energy threshold Evis>2.6 MeV.

Three-flavor solar neutrino oscillations with terrestrial neutrino constraints

We present an updated analysis of the current solar neutrino data in terms of three-flavor oscillations, including the additional constraints coming from terrestrial neutrino oscillation searches at the CHOOZ (reactor), Super-Kamiokande (atmospheric), and KEK-to-Kamioka (accelerator) experiments. The best fit is reached for the subcase of two-family mixing, and the additional admixture with the third neutrino is severely limited. We discuss the relevant features of the globally allowed regions in the oscillation parameter space, as well as their impact on the amplitude of possible CP-violation effects at future accelerator experiments and on the reconstruction accuracy of the mass-mixing oscillation parameters at the KamLAND reactor experiment.

Erratum: Supernova neutrino oscillations: A simple analytical approach [Phys. Rev. D65, 073008 (2002)

Analyses of observable supernova neutrino oscillation effects require the calculation of the electron (anti)neutrino survival probability P_ee along a given supernova matter density profile. We propose a simple analytical prescription for P_ee, based on a double-exponential form for the crossing probability and on the concept of maximum violation of adiabaticity. In the case of two-flavor transitions, the prescription is shown to reproduce accurately, in the whole neutrino oscillation parameter space, the results of exact numerical calculations for generic (realistic or power-law) profiles. The analytical approach is then generalized to cover three-flavor transitions with (direct or inverse) mass spectrum hierarchy, and to incorporate Earth matter effects. Compact analytical expressions, explicitly showing the symmetry properties of P_ee, are provided for practical calculations.

Supernova neutrino oscillations: A simple analytical approach

Analyses of observable supernova neutrino oscillation effects require the calculation of the electron (anti)neutrino survival probability ${P}_{\mathrm{ee}}$ along a given supernova matter density profile. We propose a simple analytical prescription for ${P}_{\mathrm{ee}},$ based on a double-exponential form for the crossing probability and on the concept of maximum violation of adiabaticity. In the case of two-flavor transitions, the prescription is shown to reproduce accurately, in the whole neutrino oscillation parameter space, the results of exact numerical calculations for generic (realistic or power-law) profiles. The analytical approach is then generalized to cover three-flavor transitions with (direct or inverse) mass spectrum hierarchy, and to incorporate Earth matter effects. Compact analytical expressions, explicitly showing the symmetry properties of ${P}_{\mathrm{ee}},$ are provided for practical calculations.

CONSTRAINTS ON NEUTRINO OSCILLATION PARAMETERS FROM TIME/ENERGY DEPENDENCE OF SOLAR 8B NEUTRINO FLUX

A search for neutrino oscillation is presented using time variations and energy dependence of the observed reduction of the solar neutrino flux. No significant time variation or energy dependence has been found in 1117 days of solar neutrino data taken with the Super-Kamiokande experiment. This constrains the two-neutrino oscillation parameter space independently of the model dependence of the solar neutrino flux. The combination of Super-Kamiokande's data of the day-night variation, energy dependence and flux results in two allowed regions at 95% C.L.

Status of the MINOS experiment

MINOS is designed to explore the neutrino oscillation parameter space favored by the SuperKamiokande Experiment. Presented is a description of MINOS and the status of the effort at this time.

Long-baseline study of the leading neutrino oscillation at a neutrino factory

Within the framework of three-flavor neutrino oscillations, we consider the physics potential of ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}$ appearance and ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}$ survival measurements at a neutrino factory for a leading oscillation scale $\ensuremath{\delta}{m}^{2}\ensuremath{\sim}3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3} {\mathrm{eV}}^{2}.$ Event rates are evaluated versus baseline and stored muon energy, and optimal values discussed. Over a sizable region of oscillation parameter space, matter effects would enable the sign of $\ensuremath{\delta}{m}^{2}$ to be determined from a comparison of ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}$ with ${\overline{\ensuremath{\nu}}}_{e}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ event rates and energy distributions. It is important, therefore, that both positive and negative muons can be stored in the ring. Measurements of the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}$ survival spectrum could determine the magnitude of $\ensuremath{\delta}{m}^{2}$ and the leading oscillation amplitude with a precision of $\mathcal{O} (1%\ensuremath{-}2%).$