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Walter Winter

Publications and source records attributed to Walter Winter.

At least 145 records · Page 8Linked to original sources
arXiv2006

Neutrino Factory and Beta Beam Experiment

I summarize the current understanding of the neutrino oscillation physics with a neutrino factory and a beta beam, where I emphasize more recent phenomenological developments.

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arXiv2005

Testing mass-varying neutrinos with reactor experiments

We propose that reactor experiments could be used to constrain the environment dependence of neutrino mass and mixing parameters, which could be induced due to an acceleron coupling to matter fields. There are several short-baseline reactor experiment projects with different fractions of air and earth matter along the neutrino path. Moreover, the short baselines, in principle, allow the physical change of the material between source and detector. Hence, such experiments offer the possibility for a direct comparison of oscillations in air and matter. We demonstrate that for $\sin^2 2 θ_{13} \gtrsim 0.04$, two reactor experiments (one air, one matter) with baselines of at least 1.5 km can constrain any oscillation effect which is different in air and matter at the level of a few per cent. Furthermore, we find that using the same experiment while physically moving the material between source and detector improves systematics.

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arXiv2005

What would it take to determine the neutrino mass hierarchy if $θ_{13}$ were too small?

We discuss the experimental requirements for a mass hierarchy measurement for $θ_{13}=0$ using muon neutrino disappearance. We find that a specially optimized neutrino factory at $L \simeq 6 \,000 \, \mathrm{km}$ could do this measurement using extreme luminosities. In particular, we do not require charge identification for this purpose. In order to measure the mass hierarchy for more adequate luminosities, we explore the capabilities of low energy narrow band off-axis beams, which have relatively more events at low energies. We find that, in this case, the energy resolution of the detector quickly becomes the limiting factor of the measurement, and significantly affects the baseline optimization for determining the mass hierarchy.

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arXiv2005

Damping signatures in future neutrino oscillation experiments

We discuss the phenomenology of damping signatures in the neutrino oscillation probabilities, where either the oscillating terms or the probabilities can be damped. This approach is a possibility for tests of non-oscillation effects in future neutrino oscillation experiments, where we mainly focus on reactor and long-baseline experiments. We extensively motivate different damping signatures due to small corrections by neutrino decoherence, neutrino decay, oscillations into sterile neutrinos, or other mechanisms, and classify these signatures according to their energy (spectral) dependencies. We demonstrate, at the example of short baseline reactor experiments, that damping can severely alter the interpretation of results, e.g., it could fake a value of $\sin(2θ_{13})$ smaller than the one provided by Nature. In addition, we demonstrate how a neutrino factory could constrain different damping models with emphasis on how these different models could be distinguished, i.e., how easily the actual non-oscillation effects could be identified. We find that the damping models cluster in different categories, which can be much better distinguished from each other than models within the same cluster.

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arXiv2005

Direct test of the MSW effect by the solar appearance term in beam experiments

We discuss if one can verify the MSW effect in neutrino oscillations at a high confidence level in long-baseline experiments. We demonstrate that for long enough baselines at neutrino factories, the matter effect sensitivity is, as opposed to the mass hierarchy sensitivity, not suppressed by $\sin^2 2 θ_{13}$ because it is driven by the solar oscillations in the appearance probability. Furthermore, we show that for the parameter independent direct verification of the MSW effect at long-baseline experiments, a neutrino factory with a baseline of at least 6000 km is needed. For superbeams, we do not find a $5σ$ discovery potential of the MSW effect independent of $\sin^2 2 θ_{13}$. We finally summarize different methods to test the MSW effect.

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arXiv2004

From parameter space constraints to the precision determination of the leptonic Dirac CP phase

We discuss the precision determination of the leptonic Dirac CP phase $δ_{CP}$ in neutrino oscillation experiments, where we apply the concept of ``CP coverage''. We demonstrate that this approach carries more information than a conventional CP violation measurement, since it also describes the exclusion of parameter regions. This will be very useful for next-generation long baseline experiments where for sizable $\sin^2 2 θ_{13}$ first constraints on $δ_{CP}$ can be obtained. As the most sophisticated experimental setup, we analyze neutrino factories, where we illustrate the major difficulties in their analysis. In addition, we compare their potential to the one of superbeam upgrades and next-generation experiments, which also includes a discussion of synergy effects. We find a strong dependence on the yet unknown true values of $\sin^2 2 θ_{13}$ and $δ_{CP}$, as well as a strong, non-Gaussian dependence on the confidence level. A systematic understanding of the complicated parameter dependence will be given. In addition, it is shown that comparisons of experiments and synergy discussions do in general not allow for an unbiased judgment if they are only performed at selected points in parameter space. Therefore, we present our results in dependence of the yet unknown true values of $\sin^2 2 θ_{13}$ and $δ_{CP}$. Finally we show that for $δ_{CP}$ precision measurements there exist simple strategies including superbeams, reactor experiments, superbeam upgrades, and neutrino factories, where the crucial discriminator is $\sin^2 2 θ_{13} \sim 10^{-2}$.

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arXiv2004

Three-flavor analysis of long-baseline experiments

We compare the analysis of existing and future neutrino oscillation long-baseline experiments, where we point out that the analysis of future experiments actually implies a 12-dimensional parameter space. Within the three-flavor neutrino oscillation framework, six of these parameters are the fit parameters, and six are the simulated parameters. This high-dimensional parameter space requires the condensation of information and the definition of performance indicators for the purpose needed. As the most sophisticated example for such an indicator, we choose the precision of the leptonic CP phase, and discuss some of the complications of its computation and interpretation.

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arXiv2004

Understanding CP phase-dependent measurements at neutrino superbeams in terms of bi-rate graphs

We discuss the impact of the true value of the CP phase on the mass hierarchy, CP violation, and CP precision measurements at neutrino superbeams and related experiments. We we use a complete statistical experiment simulation including spectral information, systematics, correlations, and degeneracies to produce the results. However, since it is very complicated to understand the results in terms of a complete experiment simulation, we show the corresponding bi-rate graphs as useful tools to investigate the CP phase-dependencies qualitatively. Unlike bi-probability graphs, which are based upon oscillation probabilities, bi-rate graphs use the total event rates of two measurements simultaneously as a function of the CP phase. Since they allow error bars for direct quantitative estimates, they can be used for a direct comparison with a complete statistical experiment simulation. We find that one can describe the CP phase dependencies of the mentioned measurements at neutrino superbeam setups, as well as one can understand the role of the $\mathrm{sgn} (Δm_{31}^2)$-degeneracy. As one of the most interesting results, we discuss the dependence of the CP precision measurement as a function of the CP phase itself, which leads to ``CP patterns''. It turns out that this dependence is rather strong, which means that one has to be careful when one is comparing the CP precisions of different experiments.

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arXiv2004

Is there maximal mixing in the lepton sector?

We discuss the potential of long-baseline neutrino oscillation experiments to determine deviations from maximal ν_μ-ν_τmixing. We compare the obtainable sensitivities to predictions from neutrino mass models and to the size of quantum corrections. We find that the theoretical expectations for deviations are typically well within experimental reach.

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arXiv2003

Resolving degeneracies for different values of $θ_{13}$

We discuss options to resolve correlations and degeneracies with combinations of future neutrino long-baseline experiments. We use a logarithmic scale of $\sin^2 2 θ_{13}$ as a representation for a systematical classification of the experiments.

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arXiv2003

The role of matter density uncertainties in the analysis of future neutrino factory experiments

Matter density uncertainties can affect the measurements of the neutrino oscillation parameters at future neutrino factory experiments, such as the measurements of the mixing parameters $θ_{13}$ and $\deltacp$. We compare different matter density uncertainty models and discuss the possibility to include the matter density uncertainties in a complete statistical analysis. Furthermore, we systematically study in which measurements and where in the parameter space matter density uncertainties are most relevant. We illustrate this discussion with examples that show the effects as functions of different magnitudes of the matter density uncertainties. We find that matter density uncertainties are especially relevant for large $\stheta \gtrsim 10^{-3}$. Within the KamLAND-allowed range, they are most relevant for the precision measurements of $\stheta$ and $\deltacp$, but less relevant for ``binary'' measurements, such as for the sign of $\ldm$, the sensitivity to $\stheta$, or the sensitivity to maximal CP violation. In addition, we demonstrate that knowing the matter density along a specific baseline better than to about 1% precision means that all measurements will become almost independent of the matter density uncertainties.

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arXiv2003

Neutrino Factories and the "Magic" Baseline

We show that for a neutrino factory baseline of $L \sim 7300 km - 7 600 km$ a ``clean'' measurement of $\sin^2 2 θ_{13}$ becomes possible, which is almost unaffected by parameter degeneracies. We call this baseline "magic" baseline, because its length only depends on the matter density profile. For a complete analysis, we demonstrate that the combination of the magic baseline with a baseline of 3000 km is the ideal solution to perform equally well for the $\sin^2 2 θ_{13}$, sign of $Δm_{31}^2$, and CP violation sensitivities. Especially, this combination can very successfully resolve parameter degeneracies even below $\sin^2 2 θ_{13} < 10^{-4}$.

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arXiv2003

Tomography of the Earth's Core Using Supernova Neutrinos

We investigate the possibility to use the neutrinos coming from a future galactic supernova explosion to perform neutrino oscillation tomography of the Earth's core. We propose to use existing or planned detectors, resulting in an additional payoff. Provided that all of the discussed uncertainties can be reduced as expected, we find that the average matter densities of the Earth's inner and outer cores could be measured with a precision competitive with geophysics. However, since seismic waves are more sensitive to matter density jumps than average matter densities, neutrino physics would give partly complementary information.

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arXiv2002

Quark and Lepton Mass Patterns and the Absolute Neutrino Mass Scale

We investigate what could be learned about the absolute scale of neutrino masses from comparisons among the patterns within quark and lepton mass hierarchies. First, we observe that the existing information on neutrino masses fits quite well to the unexplained, but apparently present regularities in the quark and charged lepton sectors. Second, we discuss several possible mass patterns, pointing out that this quite generally leads towards hierarchical neutrino mass patterns especially disfavoring the vacuum solution.

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arXiv2002

Superbeams versus Neutrino Factories

We compare the physics potential of planned superbeams with the one of neutrino factories. Therefore, the experimental setups as well as the most relevant uncertainties and errors are considered on the same footing as much as possible. We use an improved analysis including the full parameter correlations, as well as statistical, systematical, and degeneracy errors. Especially, degeneracies have so far not been taken into account in a numerical analysis. We furthermore include external input, such as improved knowledge of the solar oscillation parameters from the KamLAND experiment. This allows us to determine the limiting uncertainties in all cases. For a specific comparison, we choose two representatives of each class: For the superbeam, we take the first conceivable setup, namely the JHF to SuperKamiokande experiment, as well as, on a longer time scale, the JHF to HyperKamiokande experiment. For the neutrino factory, we choose an initially conceivable setup and an advanced machine. We determine the potential to measure the small mixing angle sin^2 2 theta_{13}, the sign of Delta m^2_{31}, and the leptonic CP phase $\deltacp$, which also implies that we compare the limitations of the different setups. We find interesting results, such as the complete loss of the sensitivity to the sign of Delta m^2_{31} due to degeneracies in many cases.

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