Neutrino Oscillation Analysis Research Articles

Combined analysis of νμ disappearance and νμ→νe appearance in MINOS using accelerator and atmospheric neutrinos.

We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the ν(μ) disappearance and ν(e) appearance data using the three-flavor formalism. We measure |Δm(32)(2)| = [2.28-2.46] × 10(-3) eV(2) (68% C.L.) and sin(2)θ(23) = 0.35-0.65 (90% C.L.) in the normal hierarchy, and |Δm(32)(2)| = [2.32-2.53] × 10(-3) eV(2) (68% C.L.) and sin(2)θ(23) = 0.34-0.67 (90% C.L.) in the inverted hierarchy. The data also constrain δ(CP), the θ(23} octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.

Measurement of the intrinsic electron neutrino component in the T2K neutrino beam with the ND280 detector

The T2K experiment has reported the first observation of the appearance of electron neutrinos in a muon neutrino beam. The main and irreducible background to the appearance signal comes from the presence in the neutrino beam of a small intrinsic component of electron neutrinos originating from muon and kaon decays. In T2K, this component is expected to represent 1.2% of the total neutrino flux. A measurement of this component using the near detector (ND280), located 280 m from the target, is presented. The charged current interactions of electron neutrinos are selected by combining the particle identification capabilities of both the time projection chambers and electromagnetic calorimeters of ND280. The measured ratio between the observed electron neutrino beam component and the prediction is 1.01+-0.10 providing a direct confirmation of the neutrino fluxes and neutrino cross section modeling used for T2K neutrino oscillation analyses. Electron neutrinos coming from muons and kaons decay are also separately measured, resulting in a ratio with respect to the prediction of 0.68+-0.30 and 1.10+-0.14, respectively.

Three flavour analysis of neutrino oscillations with MINOS, and sterile neutrinos in MINOS+

Three flavour analysis of neutrino oscillations with MINOS, and sterile neutrinos in MINOS+

Accelerated event-by-event neutrino oscillation reweighting with matter effects on a GPU

Oscillation probability calculations are becoming increasingly CPU intensive in modern neutrino oscillation analyses. The independency of reweighting individual events in a Monte Carlo sample lends itself to parallel implementation on a graphics processing unit. The library Prob3++ was ported to the GPU using the CUDA C API, allowing for large scale parallelized calculations of neutrino oscillation probabilities through matter of constant density, decreasing the execution time by 2 orders of magnitude when compared to performance on a single CPU.

Neutrino factory near detector

The neutrino factory is a facility for future precision studies of neutrino oscillations. A so-called near detector is essential for reaching the required precision for a neutrino oscillation analysis. The main task of the near detector is to measure the flux of the neutrino beam. Such a high intensity neutrino source like a neutrino factory provides also the opportunity for precision studies of various neutrino interaction processes in the near detector. We discuss the design concepts of such a detector. Results of simulations of a high resolution scintillating fiber tracker show that such a detector is capable of determining the neutrino flux normalization with an uncertainty of less than 1% by measuring pure leptonic interactions. Reconstruction of the neutrino energy in each event and a flux estimation based on the shapes of the neutrino energy spectra are discussed. A full setup of the near detector, consisting of a high granularity vertex detector, high resolution tracker, and muon catcher is also presented. Finally, a method to extrapolate the measured near detector flux to the far detector is shown, demonstrating that it is able to extract the correct values of ${\ensuremath{\theta}}_{13}$ and the $CP$ violation phase $\ensuremath{\delta}$ without any significant bias and with high accuracy.

Combined analysis of all three phases of solar neutrino data from the Sudbury Neutrino Observatory

We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 \pm 0.16(stat.)+0.11-0.13(syst.))\times10^6 cm^{-2}s^{-1}. A two-flavor neutrino oscillation analysis yielded \Deltam^2_{21} = (5.6^{+1.9}_{-1.4})\times10^{-5} eV^2 and tan^2{\theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded \Deltam^2_{21} = (7.41^{+0.21}_{-0.19})\times10^{-5} eV^2, tan^2{\theta}_{12} = 0.446^{+0.030}_{-0.029}, and sin^2{\theta}_{13} = (2.5^{+1.8}_{-1.5})\times10^{-2}. This implied an upper bound of sin^2{\theta}_{13} < 0.053 at the 95% confidence level (C.L.).

Are light sterile neutrinos preferred or disfavored by cosmology?

We find that the viability of a cosmological model that incorporates 2 sterile neutrinos with masses around 1 eV each, as favored by global neutrino oscillation analyses including short baseline results, is significantly dependent on the choice of datasets included in the analysis and the ability to control the systematic uncertainties associated with these datasets. Our analysis includes a variety of cosmological probes including the cosmic microwave background (WMAP7+SPT), Hubble constant (HST), galaxy power spectrum (SDSS-DR7), and supernova distances (SDSS and Union2 compilations). In the joint observational analysis, our sterile neutrino model is equally favored as a LCDM model when using the MLCS light curve fitter for the supernova measurements, and strongly disfavored by the data at \Delta\chi^2 ~ 18 when using the SALT2 fitter. When excluding the supernova measurements, the sterile neutrino model is disfavored by the other datasets at \Delta\chi^2 ~ 12, and at best becomes mildly disfavored at \Delta\chi^2 ~ 3 when allowing for curvature, evolving dark energy, additional relativistic species, running of the spectral index, and freedom in the primordial helium abundance. No single additional parameter accounts for most of this effect. Therefore, if laboratory experiments continue to favor a scenario with roughly eV mass sterile neutrinos, and if this becomes decisively disfavored by cosmology, then a more exotic cosmological model than explored here may become necessary.

Beam monitoring and near detector requirements for a Neutrino factory or long-baseline beams

Neutrino Factory is a facility for future precision studies of neutrino oscillations. A so called near detector is essential for reaching the aimed precision of neutrino oscillation analysis. Main task of the near detector is to measure the flux of the neutrino beam. Such brilliant neutrino source like Neutrino Factory provides also opportunity for precision studies of various neutrino interaction processes in the near detector. We discuss design concepts of such a detector. Results of simulations of a high resolution scintillating fiber tracker show that it is capable to measure the neutrino flux through pure leptonic interactions with an uncertainty of less than 1%. A full set-up of the near detector consisting of high granularity vertex detector, high resolution tracker and muon catcher is also presented.

SNO and future solar neutrino experiments

The SNO Collaboration has completed a combined analysis of 8B solar neutrino data from all three phases of the project. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the sun of 5.25±0.16(stat.)−0.13+0.11(syst.)×106cm2s−1. A three-flavor neutrino oscillation analysis combining the SNO results with results of all other solar neutrino experiments and the KamLAND experiment yielded Δm212=(7.41−0.19+0.21)×10−5eV2, tan2θ12=0.446−0.029+0.030, and sin2θ13=(2.5−1.5+1.8)×10−2. The results of the SNO analysis will be presented, along with a discussion of future projects that will seek to study lower energy neutrinos to improve on our knowledge of the properties of neutrinos and the sun.

Final results from SNO

We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 ± 0.16(stat.)+0.11−0.13(syst.)) × 106cm−2s−1. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded Δm221 = (7.4l+0.21−0.19) × l0−5eV2, tan2 θ12 = 0.446+0.030−0.029, and sin2 θ13 = (2.5+1.8−1.5) × 10−2. This implied an upper bound of sin2 θ13 < 0.053 at the 95% confidence level (C.L.).

Stability analysis of collective neutrino oscillations in the supernova accretion phase with realistic energy and angle distributions

We revisit our previous results on the matter suppression of self-induced neutrino flavor conversions during a supernova (SN) accretion phase, performing a linearized stability analysis of the neutrino equations of motion, in the presence of realistic SN density profiles. In our previous numerical study, we used a simplified model based on an isotropic neutrino emission with a single typical energy. Here, we take into account realistic neutrino energy and angle distributions. We find that multienergy effects have a subleading impact in the flavor stability of the SN neutrino fluxes with respect to our previous single-energy results. Conversely, realistic forward-peaked neutrino angular distributions would enhance the matter suppression of the self-induced oscillations with respect to an isotropic neutrino emission. As a result, in our models for iron-core SNe, collective flavor conversions have a negligible impact on the characterization of the observable neutrino signal during the accretion phase. Instead, for a low-mass O-Ne-Mg core SN model, with lower matter density profile and less forward-peaked angular distributions, collective conversions are possible also at early times.

Scintillator R&D and construction of a prototype for the Double Chooz experiment

This is a contribution paper from the Double Chooz (DC) experiment to the special issue of Nuclear Physics B on the topics of neutrino oscillations, celebrating the recent Nobel prize to Profs. T. Kajita and A.B. McDonald.DC is a reactor neutrino experiment which measures the last neutrino mixing angle θ13. The DC group presented an indication of disappearance of the reactor neutrinos at a baseline of ∼1 km for the first time in 2011 and is improving the measurement of θ13. DC is a pioneering experiment of this research field. In accordance with the nature of this special issue, physics and history of the reactor-θ13 experiments, as well as the Double Chooz experiment and its neutrino oscillation analyses, are reviewed.

Impact of hierarchy upon the values of neutrino mixing parameters

A neutrino-oscillation analysis is performed of the more finely binned Super-K atmospheric, MINOS, and CHOOZ data in order to examine the impact of neutrino hierarchy in this data set upon the value of $\theta_{13}$ and the deviation of $\theta_{23}$ from maximal mixing. Exact oscillation probabilities are used, thus incorporating all powers of $\theta_{13}$ and $\epsilon :=\theta_{23}-\pi/4$. The extracted oscillation parameters are found to be dependent on the hierarchy, particularly for $\theta_{13}$. We find at 90% CL are $\Delta_{32} = 2.44^{+0.26}_{-0.20}$ and $2.48^{+0.25}_{-0.22}\times 10^{-3} {\rm eV}^2$, $\epsilon=\theta_{23}-\pi/4=0.06^{+0.06}_{-0.16}$ and $0.06^{+0.08}_{-0.17}$, and $\theta_{13}=-0.07^{+0.18}_{-0.11}$ and $-0.13^{+0.23}_{-0.16}$, for the normal and inverted hierarchy respectively. The inverted hierarchy is preferred at a statistically insignificant level of 0.3 $\sigma$.

Atmospheric neutrino oscillation analysis with subleading effects in Super-Kamiokande I, II, and III

We present a search for non-zero theta_{13} and deviations of sin^2 theta_{23} from 0.5 in the oscillations of atmospheric neutrino data from Super-Kamiokande -I, -II, and -III. No distortions of the neutrino flux consistent with non-zero theta_{13} are found and both neutrino mass hierarchy hypotheses are in agreement with the data. The data are best fit at Delta m^2 = 2.1 x 10^-3 eV^2, sin^2 theta_{13} = 0.0, and sin^2 theta_{23} =0.5. In the normal (inverted) hierarchy theta_{13} and Delta m^2 are constrained at the one-dimensional 90% C.L. to sin^2 theta_{13} < 0.04 (0.09) and 1.9 (1.7) x 10^-3 < Delta m^2 < 2.6 (2.7) x 10^-3 eV^2. The atmospheric mixing angle is within 0.407 <= sin^2 theta_{23} <= 0.583 at 90% C.L.

Atmospheric neutrinos and the implications to cosmic ray interactions

Atmospheric neutrinos have been used to study neutrino oscillations. Neutrino oscillation analyses with atmospheric neutrinos are discussed. With the increased statistics of the atmospheric neutrino data, it is more important to understand the atmospheric neutrino flux more accurately. Detailed calculations of the atmospheric neutrino fluxes calibrated by the atmospheric muon data show suggestions to the interaction of cosmic rays.

Super-Kamiokande atmospheric neutrino results

The recent results of the atmospheric neutrino measurements and neutrino oscillation analysis from Super-Kamiokande are presented. The Super-Kamiokande detector is observing the atmospheric neutrinos in the wide energy range from 0.1 GeV to 10 TeV. The data are fully consistent with two flavor νµ ↔ ντ oscillation scheme. We slightly improved the oscillation analysis method, which gives more stringent constraint on the oscillation parameters. The searches are made for the tau neutrino signal from νµ ↔ ντ oscillation and the effect of non-zero θ13 mixing angle. The preliminary result of Super-Kamiokande II data will be also mentioned.

10,000 Standard Solar Models: A Monte Carlo Simulation

We have evolved 10,000 solar models using 21 input parameters that are randomly drawn for each model from separate probability distributions for every parameter. We use the results of these models to determine the theoretical uncertainties in the predicted surface helium abundance, the profile of the sound speed versus radius, the profile of the density versus radius, the depth of the solar convective zone, the eight principal solar neutrino fluxes, and the fractions of nuclear reactions that occur in the CNO cycle or in the three branches of the p-p chains. We also determine the correlation coefficients of the neutrino fluxes for use in analysis of solar neutrino oscillations. Our calculations include the most accurate available input parameters, including radiative opacity, equation of state, and nuclear cross sections. We incorporate both the recently determined heavy element abundances recommended by Asplund et al. and the older (higher) heavy element abundances recommended by Grevesse & Sauval. We present best estimates of many characteristics of the standard solar model for both sets of recommended heavy element compositions.

Physics of Massive Neutrinos

I summarize the present status of global analyses of neutrino oscillations, including the most recent KamLAND and K2K data, as well as the latest solar and atmospheric neutrino fluxes. I give the allowed ranges of the three--flavour oscillation parameters from the current worlds' global neutrino data sample, their best fit values and discuss the small parameters DeltaM_solar/DeltaM_atm and sin^2 theta_13, which characterize the strength of CP violation in neutrino oscillations. I briefly discuss neutrinoless double beta decay and the LSND neutrino oscillation hint, as well as the robustness of the neutrino oscillation results in the presence of non-standard physics.

K2K far detector analysis

The far detector analysis for ν μ disappearance in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment is presented. The data used for this analysis is 8.9 × 10 19 protons on target (POT). A total of 107 events are observed in the far detector, Super-Kamiokande (SK), while 151 −10 +12 are expected without ν μ oscillation. Spectral distortion of the reconstructed neutrino energy (E ν ) is also observed, and it is consistent with ν μ − ν τ oscillation. The two-flavor ν μ − ν τ oscillation analysis is evaluated. We obtain an allowed region which is consistent with SK atmospheric neutrino oscillation analysis results. The probability to observe our results from a statistical fluctuation is 0.005% (4.0 σ ) in the case of no oscillation.

Recent results from K2K

The result for ν μ oscillation analysis in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment are presented. The data used for this analysis is 8.9 × 1019 protons on target (POT). A total of 107 events are observed in the far detector, Super-Kamiokande (SK), while 151 −10 +12 expected if ν μ oscillation is not assumed. The spectrum distortion of the reconstructed neutrino energy (Eν) is also observed, and it is consistent with the ν μ − ν τ oscillation. The two-flavor ν μ - ν τ oscillation analysis is evaluated. We obtained the allowed region which is consistent with SK atmospheric neutrino oscillation analysis results. The probability to get these results without neutrino oscillation is 0.005% (4.0σ).