Long-baseline Accelerator Research Articles

Fuzzy dark matter and nonstandard neutrino interactions

We discuss novel ways in which neutrino oscillation experiments can probe dark matter. In particular, we focus on interactions between neutrinos and ultra-light ("fuzzy") dark matter particles with masses of order $10^{-22}$ eV. It has been shown previously that such dark matter candidates are phenomenologically successful and might help ameliorate the tension between predicted and observed small scale structures in the Universe. We argue that coherent forward scattering of neutrinos on fuzzy dark matter particles can significantly alter neutrino oscillation probabilities. These effects could be observable in current and future experiments. We set new limits on fuzzy dark matter interacting with neutrinos using T2K and solar neutrino data, and we estimate the sensitivity of reactor neutrino experiments and of future long-baseline accelerator experiments. These results are based on detailed simulations in GLoBES. We allow the dark matter particle to be either a scalar or a vector boson. In the latter case, we find potentially interesting connections to models addressing various $B$ physics anomalies.

Recent results from the T2K experiment

Recent results of the analysis of 2:23×1021 POT data collected by the T2K long-baseline neutrino accelerator experiment are presented in this paper. It is shown that T2K is able to constrain the CP-violating phase δCP in the lepton sector with 2σ significance. Nearest plans for improving the sensitivity to δCP are also given.

Precision neutrino experiments vs the Littlest Seesaw

We study to what extent upcoming precision neutrino oscillation experiments will be able to exclude one of the most predictive models of neutrino mass and mixing: the Littlest Seesaw. We show that this model provides a good fit to current data, predicting eight observables from two input parameters, and provide new assessments of its predictions and their correlations. We then assess the ability to exclude this model using simulations of upcoming neutrino oscillation experiments including the medium-distance reactor experiments JUNO and RENO-50 and the long-baseline accelerator experiments DUNE and T2HK. We find that an accurate determination of the currently least well measured parameters, namely the atmospheric and solar angles and the CP phase δ, provide crucial independent tests of the model. For θ13 and the two mass-squared differences, however, the model’s exclusion requires a combination of measurements coming from a varied experimental programme. Our results show that the synergy and complementarity of future experiments will play a vital role in efficiently discriminating between predictive models of neutrino flavour, and hence, towards advancing our understanding of neutrino oscillations in the context of the flavour puzzle of the Standard Model.

Long-baseline neutrino accelerator experiments: results and prospects

Recent results from long-baseline neutrino experiments are presented. Prospects for determining the mass hierarchy and observing CP violation in neutrino oscillations are discussed.

Sterile neutrino oscillations: the global picture

Abstract Neutrino oscillations involving eV-scale neutrino mass states are investigated in the context of global neutrino oscillation data including short and long-baseline accelerator, reactor, and radioactive source experiments, as well as atmospheric and solar neutrinos. We consider sterile neutrino mass schemes involving one or two mass-squared differences at the eV2 scale denoted by 3+1, 3+2, and 1+3+1. We discuss the hints for eV-scale neutrinos from $ \mathop{{{v_e}}}\limits^{{\left( - \right)}} $ disappearance (reactor and Gallium anomalies) and $ \mathop{{{v_{\mu }}}}\limits^{{\left( - \right)}}\to \mathop{{{v_e}}}\limits^{{\left( - \right)}} $ appearance (LSND and MiniBooNE) searches, and we present constraints on sterile neutrino mixing from $ \mathop{{{v_{\mu }}}}\limits^{{\left( - \right)}} $ and neutral-current disappearance data. An explanation of all hints in terms of oscillations suffers from severe tension between appearance and disappearance data. The best compatibility is obtained in the 1+3+1 scheme with a p-value of 0.2% and exceedingly worse compatibilities in the 3+1 and 3+2 schemes.

Identifying the neutrino mass ordering with INO and NOvA

The relatively large value of $\theta_{13}$ established recently by the Daya Bay reactor experiment opens the possibility to determine the neutrino mass ordering with experiments currently under construction. We investigate synergies between the NOvA long-baseline accelerator experiment with atmospheric neutrino data from the India-based Neutrino Observatory (INO). We identify the requirements on energy and direction reconstruction and detector mass for INO necessary for a significant sensitivity. If neutrino energy and direction reconstruction at the level of 10% and 10 degree can be achieved by INO a determination of the neutrino mass ordering seems possible around 2020.

Investigation of neutrino oscillations in the T2k long-baseline accelerator experiment

High-sensitivity searches for transitions of muon neutrinos to electron neutrinos are the main task of the T2K (Tokai-to-Kamioka) second-generation long-baseline accelerator neutrino experiment. The present article is devoted to describing basic principles of T2K, surveying experimental apparatuses that it includes, and considering in detail the muon-range detector (SMRD) designed and manufactured by a group of physicists from the Institute of Nuclear Research (Russian Academy of Sciences, Moscow). The results of the first measurements with a neutrino beam are presented, and plans for the near future are discussed.

Evidence ofθ13>0from global neutrino data analysis

The neutrino mixing angle theta(13) is at the focus of current neutrino research. From a global analysis of the available oscillation data in a 3-neutrino framework, we previously reported [Phys. Rev. Lett. 101, 141801 (2008)] hints in favor of theta(13)>0 at the 90 % C.L. Such hints are consistent with the recent indications of nu(mu)-->nu(e) appearance in the T2K and MINOS long-baseline accelerator experiments. Our global analysis of all the available data currently provides >3 sigma evidence for nonzero theta(13), with 1-sigma ranges sin^2 theta(13) = 0.021+-0.007 or 0.025+-0.007, depending on reactor neutrino flux systematics. Updated ranges are also reported for the other 3-neutrino oscillation parameters (delta m^2, sin^2 theta(12)) and (Delta m^2, sin^2 theta(23)).

Minimal models with light sterile neutrinos

We study the constraints imposed by neutrino oscillation experiments on the minimal extensions of the Standard Model (SM) with n R gauge singlet fermions (“righthanded neutrinos”), that can account for neutrino masses. We consider the most general coupling of the new fields to the SM fields, in particular those that break lepton number and we do not assume any a priori hierarchy in the mass parameters. We proceed to analyze these models starting from the lowest level of complexity, defined by the number of extra fermionic degrees of freedom. The simplest choice that has enough free parameters in principle (i.e. two mass differences and two angles) to explain the confirmed solar and atmospheric oscillations corresponds to n R = 1. This minimal choice is shown to be excluded by data. The next-to-minimal choice corresponds to n R = 2. We perform a systematic study of the full parameter space in the limit of degenerate Majorana masses by requiring that at least two neutrino mass differences correspond to those established by solar and atmospheric oscillations. We identify several types of spectra that can fit long-baseline reactor and accelerator neutrino oscillation data, but fail in explaining solar and/or atmospheric data. The only two solutions that survive are the expected seesaw and quasi-Dirac regions, for which we set lower and upper bounds respectively on the Majorana mass scale. Solar data from neutral current measurements provide essential information to constrain the quasi-Dirac region. The possibility to accommodate the LSND/MiniBoone and reactor anomalies, and the implications for neutrinoless double-beta decay and tritium beta decay are briefly discussed.

Constraints onθ13from a three-flavor oscillation analysis of reactor antineutrinos at KamLAND

We present new constraints on the neutrino oscillation parameters $/textyen Delta m^{2}_{21}$, $/textyen theta_{12}$, and $/textyen theta_{13}$ from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of $3.49 \textyen times 10^{32}$ target-proton-year. Under the assumption of {\textyen it CPT} invariance, a two-flavor analysis (/textyen mbox{$\textyen theta_{13} = 0$}) of the KamLAND and solar data yields the best-fit values $\textyen tan^{2} \textyen theta_{12} = 0.444^{+0.036}_{-0.030}$ and $\textyen Delta m^{2}_{21} = 7.50^{+0.19}_{-0.20} \textyen times 10^{-5} ~ {\textyen rm eV}^{2}$; a three-flavor analysis with $\textyen theta_{13}$ as a free parameter yields the best-fit values $\textyen tan^{2} \textyen theta_{12} = 0.452^{+0.035}_{-0.033}$, $\textyen Delta m^{2}_{21} = 7.50^{+0.19}_{-0.20} \textyen times 10^{-5} ~ {\textyen rm eV}^{2}$, and $\textyen sin^{2} \textyen theta_{13} = 0.020^{+0.016}_{-0.016}$. This $\textyen theta_{13}$ interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global $\textyen theta_{13}$ analysis, incorporating the CHOOZ, atmospheric and accelerator data, which indicates $\textyen sin^{2} \textyen theta_{13} = 0.009^{+0.013}_{-0.007}$. A nonzero value is suggested, but only at the 79\textyen% C.L.

Исследование нейтринных осцилляций в ускорительных экспериментах с длинной базой

Исследование нейтринных осцилляций в ускорительных экспериментах с длинной базой

Relating the neutrino mixing angles to a lepton mass hierarchy

We propose two phenomenological scenarios of lepton mass matrices and show that either of them can exactly give rise to tan2θ13=me/(me+2mμ), tan2θ23=mμ/(me+mμ) and tan2θ12=(mem2+2mμm1)/(mem1+2mμm2) in the standard parametrization of lepton flavor mixing. The third relation, together with current experimental data, predicts a normal but weak hierarchy for the neutrino mass spectrum. We also obtain θ13≈2.8° for the smallest neutrino mixing angle and J≈1.1% for the Jarlskog invariant of leptonic CP violation, which will soon be tested in the long-baseline reactor and accelerator neutrino oscillation experiments. A seesaw realization of both scenarios is briefly discussed.

Bayesian constraints onϑ13from solar and KamLAND neutrino data

We present the results of a Bayesian analysis of solar and KamLAND neutrino data in the framework of three-neutrino mixing. We adopt two approaches for the prior probability distribution of the oscillation parameters $\ensuremath{\Delta}{m}_{21}^{2}$, ${sin}^{2}{\ensuremath{\vartheta}}_{12}$, ${sin}^{2}{\ensuremath{\vartheta}}_{13}$: (1) a traditional flat uninformative prior; and (2) an informative prior which describes the limits on ${sin}^{2}{\ensuremath{\vartheta}}_{13}$ obtained in atmospheric and long-baseline accelerator and reactor neutrino experiments. In both approaches, we present the allowed regions in the ${sin}^{2}{\ensuremath{\vartheta}}_{13}\mathrm{\text{\ensuremath{-}}}\ensuremath{\Delta}{m}_{21}^{2}$ and ${sin}^{2}{\ensuremath{\vartheta}}_{12}\mathrm{\text{\ensuremath{-}}}{sin}^{2}{\ensuremath{\vartheta}}_{13}$ planes, as well as the marginal posterior probability distribution of ${sin}^{2}{\ensuremath{\vartheta}}_{13}$. We confirm the $1.2\ensuremath{\sigma}$ hint of ${\ensuremath{\vartheta}}_{13}>0$ found in [G. Fogli et al., Phys. Rev. Lett. 101, 141801 (2008).] from the analysis of solar and KamLAND neutrino data. We found that the statistical significance of the hint is reduced to about $0.8\ensuremath{\sigma}$ by the constraints on ${sin}^{2}{\ensuremath{\vartheta}}_{13}$ coming from atmospheric and long-baseline accelerator and reactor neutrino data, in agreement with [T. Schwetz, M. Tortola, and J. W. F. Valle, New J. Phys. 10, 113011 (2008).].

Accelerator neutrino experiments: New results and perspectives

The current status of neutrino long-baseline accelerator experiments and new results obtained in these experiments are presented. Prospects for near-future program are also discussed.

Future possibilities with Fermilab neutrino beams

We will start with a brief overview of neutrino oscillation physics with emphasis on the remaining unanswered questions. Next, after mentioning near future reactor and accelerator experiments searching for a non zero θ13, we will introduce the plans for the next generation of long-baseline accelerator neutrino oscillation experiments. We will focus on experiments utilizing powerful (0.7 − 2.1 MW) Fermilab neutrino beams, either existing or in the design phase.

Reconciling results of LSND, MiniBooNE and other experiments with soft decoherence

We propose an explanation of the LSND signal via quantum-decoherence of the mass states, which leads to damping of the interference terms in the oscillation probabilities. The decoherence parameters as well as their energy dependence are chosen in such a way that the damping affects only oscillations with the large (atmospheric) $\Delta m^2$ and rapidly decreases with the neutrino energy. This allows us to reconcile the positive LSND signal with MiniBooNE and other null-result experiments. The standard explanations of solar, atmospheric, KamLAND and MINOS data are not affected. No new particles, and in particular, no sterile neutrinos are needed. The LSND signal is controlled by the 1-3 mixing angle $\theta_{13}$ and, depending on the degree of damping, yields $0.0014 < \sin^2\theta_{13} < 0.034$ at $3\sigma$. The scenario can be tested at upcoming $\theta_{13}$ searches: while the comparison of near and far detector measurements at reactors should lead to a null-result a positive signal for $\theta_{13}$ is expected in long-baseline accelerator experiments. The proposed decoherence may partially explain the results of Gallium detector calibrations and it can strongly affect supernova neutrino signals.

Neutrino mixing sum rules and oscillation experiments

The neutrino mixing sum rule $\theta_{12} - \theta_{13}\cos(\delta) \approx \theta^\nu_{12}$ provides a possibility to explore the structure of the neutrino mass matrix in the presence of charged lepton corrections, since it relates the 1-2 mixing angle from the neutrino mass matrix, $\theta_{12}^\nu$, to observable parameters of the PMNS mixing matrix. The neutrino mixing sum rule holds if the charged lepton mixing angles are CKM-like, i.e., small and dominated by a 1-2 mixing, and for small 1-3 mixing in the neutrino mass matrix. These conditions hold in a wide class of well motivated flavour models. We apply this sum rule to present oscillation data, and we investigate the prospects of future neutrino facilities for exploring the sum rule by simulating various setups for long-baseline reactor and accelerator experiments. As explicit examples, we use the sum rule to test the hypotheses of tri-bimaximal and bimaximal neutrino mixing, where $\theta^\nu_{12}$ is predicted by $\sin^2(\theta^\nu_{12}) = 1/3$ or 1/2, respectively, although the neutrino mixing sum rule can be used to test any prediction for $\theta^\nu_{12}$.

Long-Baseline Accelerator Experiments in the United States

The status and future of long-baseline accelerator experiments in the United States is described. Discussed experiments will exploit the NuMI beamline, due to deliver the first neutrinos at the beginning of 2005. A short description of this flexible, high-intensity neutrino beamline at the Fermi National Laboratory is provided.

A method for detecting ν τ appearance in the spectra of quasielastic CC events

A method for detecting the transition ν μ→ν τ in long-baseline accelerator experiments, that consists in comparing the far-to-near ratios of the spectra of quasielastic CC events generated by high- and low-energy beams of muon neutrinos, is proposed. The test may be accessible to big water Cherenkov detectors and iron-scintillator calorimeters, and is limited by statistics rather than systematics. In the NuMI program with the MINOS detector, only the Δ m 2 values above some 4×10 −3 eV 2 can be probed.

A redetermination of the neutrino mass-squared difference in tri-maximal mixing with terrestrial matter effects

We re-fit for the neutrino mass-squared difference Δm 2 in the threefold maximal (i.e. tri-maximal) mixing scenario using recent CHOOZ and SUPER-K data, taking account of matter effects in the Earth. While matter effects have little influence on reactor experiments and proposed long-baseline accelerator experiments with L ≲ 1000 km, they are highly significant for atmospheric experiments, suppressing naturally ν e mixing and enhancing ν μ − ν τ mixing, so as to effectively remove the experimental distinction between threefold maximal and twofold maximal ν μ − ν τ mixing. Threefold maximal mixing is fully consistent with the CHOOZ and SUPER-K data and the best-fit value for the neutrino mass-squared difference is Δm 2≃(0.98± 0.30 0.23)×10 −3 eV 2.