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Walter Winter

Publications and source records attributed to Walter Winter.

At least 127 records · Page 7Linked to original sources
arXiv2008

Optimizing the greenfield Beta-beam

We perform a comprehensive and detailed comparison of the physics reach of Beta-beam neutrino experiments between two pairs of plausible source ions, (8B, 8Li) and (18Ne, 6He). We study the optimal choices for the baseline, boost factor, and luminosity. We take a 50 kton iron calorimeter, a la ICAL@INO, as the far detector. We follow two complementary approaches for our study: (i) Fixing the number of useful ion decays and boost factor of the beam, and optimizing for the sensitivity reach between the two pairs of ions as a function of the baseline. (ii) Matching the shape of the spectrum between the two pairs of ions, and studying the requirements for baseline, boost factor, and luminosity. We find that for each pair of ions there are two baselines with very good sensitivity reaches: a short baseline with $L [km]/ γ\simeq 2.6$ (8B+8Li) and $L [km]/γ\simeq 0.8$ (18Ne+6He), and a long ``magic'' baseline. For $γ\sim 500$, one would optimally use 18Ne and 6He at the short baseline for CP violation, 8B and 8Li at the magic baseline for the mass hierarchy, and either 18Ne and 6He at the short baseline or 8B and 8Li at the magic baseline for the $\sin^22θ_{13}$ discovery.

hep-ex↗
arXiv2008

Minimal Neutrino Beta Beam for Large theta_13

We discuss the minimum requirements for a neutrino beta beam if theta_13 is discovered by an upcoming reactor experiment, such as Double Chooz or Daya Bay. We require that both neutrino mass hierarchy and leptonic CP violation can be measured to competitive precisions with a single-baseline experiment in the entire remaining theta_13 range. We find that for very high isotope production rates, such as they might be possible using a production ring, a (B,Li) beta beam with a gamma as low as 60 could already be sufficient to perform all of these measurements. If only the often used nominal source luminosities can be achieved, for example, a (Ne,He) beta beam from Fermilab to a possibly existing water Cherenkov detector at Homestake with gamma \sim 190-350 (depending on the Double Chooz best-fit) could outperform practically any other beam technology including wide-band beam and neutrino factory.

hep-ph↗
arXiv2008

Neutrino factory optimization for non-standard interactions

We study the optimization of a neutrino factory with respect to non-standard neutral current neutrino interactions, and compare the results to those obtained without non-standard interactions. We discuss the muon energy, baselines, and oscillation channels as degrees of freedom. Our conclusions are based on both analytical calculations and on a full numerical simulation of the neutrino factory setup proposed by the international design study (IDS-NF). We consider all possible non-standard parameters, and include their complex phases. We identify the impact of the different parameters on the golden, silver, and disappearance channels. We come to the conclusion that, even in the presence of non-standard interactions, the performance of the neutrino factory hardly profits from a silver channel detector, unless the muon energy is significantly increased compared to the IDS-NF setup. Apart from the dispensable silver channel detector, we demonstrate that the IDS-NF setup is close to optimal even if non-standard interactions are considered. We find that one very long baseline is a key component in the search for non-standard interactions, in particular for |ε^m_{μτ}| and |ε^m_{ττ}|.

hep-ph↗
arXiv2008

Group space scan of flavor symmetries for nearly tribimaximal lepton mixing

We present a systematic group space scan of discrete Abelian flavor symmetries for lepton mass models that produce nearly tribimaximal lepton mixing. In our models, small neutrino masses are generated by the type-I seesaw mechanism. The lepton mass matrices emerge from higher-dimension operators via the Froggatt-Nielsen mechanism and are predicted as powers of a single expansion parameter εthat is of the order of the Cabibbo angle θ_C\simeq 0.2. We focus on solutions that can give close to tribimaximal lepton mixing with a very small reactor angle θ_{13}\approx 0 and find several thousand explicit such models that provide an excellent fit to current neutrino data. The models are rather general in the sense that large leptonic mixings can come from the charged leptons and/or neutrinos. Moreover, in the neutrino sector, both left- and right-handed neutrinos can mix maximally. We also find a new relation θ_{13}\lesssimε^3 for the reactor angle and a new sum rule θ_{23}\approxπ/4+ε/\sqrt{2} for the atmospheric angle, allowing the models to be tested in future neutrino oscillation experiments.

hep-ph↗
arXiv2007

The Seesaw Mechanism in Quark-Lepton Complementarity

We systematically construct realistic mass matrices for the type-I seesaw mechanism out of more than 20 trillion possibilities. We use only very generic assumptions from extended quark-lepton complementarity, i.e., the leptonic mixing angles between flavor and mass eigenstates are either maximal, or parameterized by a single small quantity epsilon that is of the order of the Cabibbo angle epsilon theta_C. The small quantity epsilon also describes all fermion mass hierarchies. We show that special cases often considered in the literature, such as having a symmetric Dirac mass matrix or small mixing among charged leptons, constitute only a tiny fraction of our possibilities. Moreover, we find that in most cases the spectrum of right-handed neutrino masses is only mildly hierarchical. As a result, we provide for the charged leptons and neutrinos a selected list of 1981 qualitatively different Yukawa coupling matrices (or textures) that are parameterized by the Cabibbo angle and allow for a perfect fit to current data. In addition, we also briefly show how the textures could be generated in explicit models from flavor symmetries.

hep-ph↗
arXiv2007

Physics and Performance Evaluation Group

We summarize the objectives and results of the ``international scoping study of a future neutrino factory and superbeam facility'' (ISS) physics working group. Furthermore, we discuss how the ISS study should develop into a neutrino factory design study (IDS-NF) from the point of view of physics and performance evaluation.

hep-ph↗
arXiv2007

Neutrino Oscillation Observables from Mass Matrix Structure

We present a systematic procedure to establish a connection between complex neutrino mass matrix textures and experimental observables, including the Dirac CP phase. In addition, we illustrate how future experimental measurements affect the selection of textures in the (theta_13,delta_CP)-plane. For the mixing angles, we use generic assumptions motivated by quark-lepton complementarity. We allow for any combination between U_l and U_nu, as well as we average over all present complex phases. We find that individual textures lead to very different distributions of the observables, such as to large or small leptonic CP violation. In addition, we find that the extended quark-lepton complementarity approach motivates future precision measurements of delta_CP at the level of theta_C \simeq 11 degrees.

hep-ph↗
arXiv2007

Systematic Parameter Space Search of Extended Quark-Lepton Complementarity

We systematically investigate the parameter space of neutrino and charged lepton mass matrices for textures motivated by an extended quark-lepton complementarity. As the basic hypothesis, we postulate that all mixing angles in U_l and U_nu be either maximal or described by powers of a single small quantity epsilon ~ theta_C. All mass hierarchies are described by this epsilon as well. In this study, we do not assume specific forms for U_l and U_nu, such as large mixing coming from the neutrino sector only. We perform a systematic scan of the 262,144 generated mixing matrices for being compatible with current experimental data, and find a sample of 2,468 possibilities. We then analyze and classify the effective charged lepton and neutrino mass textures, where we especially focus on a subset of models getting under pressure for small theta_13. In addition, we predict the mixing angle distributions from our sample of all valid textures, and study the robustness of this prediction. We also demonstrate how our procedure can be extended to predictions of the Dirac and Majorana phases in U_PMNS. For instance, we find that CP conservation in neutrino oscillations is preferred, and we can impose a lower bound on the mixing matrix element for neutrinoless double beta decay.

hep-ph↗
arXiv2007

Systematic Model Building Based on Quark-Lepton Complementarity Assumptions

In this talk, we present a procedure to systematically generate a large number of valid mass matrix textures from very generic assumptions. Compared to plain anarchy arguments, we postulate some structure for the theory, such as a possible connection between quarks and leptons, and a mechanism to generate flavor structure. We illustrate how this parameter space can be used to test the exclusion power of future experiments, and we point out that one can systematically generate embeddings in Z_N product flavor symmetry groups.

hep-ph↗
arXiv2007

Future precision neutrino experiments and their theoretical implications

Future neutrino oscillation measurement focus, at first priority, on the discovery of sin^2(2 theta_13) describing the coupling between solar and atmospheric oscillations. In this talk, we briefly discuss the prospects to measure sin^2(2 theta_13) by future reactor and beam experiments, and we illustrate the usefulness of these measurements (and their precision) from the theoretical point of view with an example.

hep-ph↗
arXiv2007

New features in the simulation of neutrino oscillation experiments with GLoBES 3.0

We present Version 3.0 of the GLoBES (``General Long Baseline Experiment Simulator'') software, which is a simulation tool for short- and long-baseline neutrino oscillation experiments. As a new feature, GLoBES 3.0 allows for user-defined systematical errors, which can also be used to simulate experiments with multiple discrete sources and detectors. In addition, the combination with external information, such as from different experiment classes, is simplified. As far as the probability calculation is concerned, GLoBES now provides an interface for the inclusion of non-standard physics without re-compilation of the software. The set of experiment prototypes coming with GLoBES has been updated. For example, built-in fluxes are now provided for the simulation of beta beams.

hep-ph↗
arXiv2007

Upgraded experiments with super neutrino beams: Reach versus Exposure

We introduce exposure as a means to making balanced comparisons of the sensitivities of long-baseline neutrino experiments to a nonzero θ_{13}, to CP violation and to the neutrino mass hierarchy. We illustrate its use by comparing the sensitivities of possible upgrades of superbeam experiments, namely NOvA*, T2KK and experiments with wide band beams. For the proposed exposures, we find the best nominal CP violation performance for T2KK. For equal exposures, a wide band beam experiment has the best mass hierarchy performance. The physics concept on which NOvA* is based has the best potential for discovering CP violation only for exposures above a threshold value.

hep-ph↗
arXiv2007

Neutrino Factory Superbeam

We discuss the optimization of a neutrino factory for large \sin^2 2 θ_{13}, where we assume minimum effort on the accelerator side. This implies that we use low muon energies for the price of an optimized detection system. We demonstrate that such a neutrino factory performs excellent if combined with the electron neutrino appearance channel. Instead of the platinum channel operated with the muon neutrinos from the muon decays, we propose to use the initial superbeam from the decaying pions and kaons, which might be utilized at little extra effort. Since we assume out-of-phase bunches arriving at the same detector, we do not require electron charge identification. In addition, we can choose the proton energy such that we obtain a synergistic spectrum peaking at lower energies. We find that both the superbeam and the neutrino factory beam should used at the identical baseline to reduce matter density uncertainties, possibly with the same detector. This effectively makes the configuration a single experiment, which we call ``neutrino factory superbeam''. We demonstrate that this experiment outperforms a low-energy neutrino factory or a wide band beam alone beyond a simple addition of statistics.

hep-ph↗
arXiv2007

Non-standard Hamiltonian effects on neutrino oscillations

We investigate non-standard Hamiltonian effects on neutrino oscillations, which are effective additional contributions to the vacuum or matter Hamiltonian. Since these effects can enter in either flavor or mass basis, we develop an understanding of the difference between these bases representing the underlying theoretical model. In particular, the simplest of these effects are classified as ``pure'' flavor or mass effects, where the appearance of such a ``pure'' effect can be quite plausible as a leading non-standard contribution from theoretical models. Compared to earlier studies investigating particular effects, we aim for a top-down classification of a possible ``new physics'' signature at future long-baseline neutrino oscillation precision experiments. We develop a general framework for such effects with two neutrino flavors and discuss the extension to three neutrino flavors, as well as we demonstrate the challenges for a neutrino factory to distinguish the theoretical origin of these effects with a numerical example. We find how the precision measurement of neutrino oscillation parameters can be altered by non-standard effects alone (not including non-standard interactions in the creation and detection processes) and that the non-standard effects on Hamiltonian level can be distinguished from other non-standard effects (such as neutrino decoherence and decay) if we consider specific imprint of the effects on the energy spectra of several different oscillation channels at a neutrino factory.

hep-ph↗
arXiv2007

Physics with a very long neutrino factory baseline

We discuss the neutrino oscillation physics of a very long neutrino factory baseline over a broad range of lengths (between 6000 km and 9000 km), centered on the ``magic baseline'' ($\sim$ 7500 km) where correlations with the leptonic CP phase are suppressed by matter effects. Since the magic baseline depends only on the density, we study the impact of matter density profile effects and density uncertainties over this range, and the impact of detector locations off the optimal baseline. We find that the optimal constant density describing the physics over this entire baseline range is about 5% higher than the average matter density. This implies that the magic baseline is significantly shorter than previously inferred. However, while a single detector optimization requires fine-tuning of the (very long) baseline length, its combination with a near detector at a shorter baseline is much less sensitive to the far detector location and to uncertainties in the matter density. In addition, we point out different applications of this baseline which go beyond its excellent correlation and degeneracy resolution potential. We demonstrate that such a long baseline assists in the improvement of the $θ_{13}$ precision and in the resolution of the octant degeneracy. Moreover, we show that the neutrino data from such a baseline could be used to extract the matter density along the profile up to 0.24% at $1 σ$ for large $\sin^2 2 θ_{13}$, providing a useful discriminator between different geophysical models.

hep-ph↗
arXiv2006

How astrophysical neutrino sources could be used for early measurements of neutrino mass hierarchy and leptonic CP phase

We discuss the possible impact of astrophysical neutrino flux measurements at neutrino telescopes on the neutrino oscillation program of reactor experiments and neutrino beams. We consider neutrino fluxes from neutron sources, muon damped sources, and pion sources, where we parameterize the input from these sources in terms of the flux ratio $R=ϕ_μ/(ϕ_e+ϕ_τ)$ which can be extracted from the muon track to shower ratio in a neutrino telescope. While it is difficult to obtain any information from this ratio alone, we demonstrate that the dependence on the oscillation parameters is very complementary to the one of reactor experiments and neutrino beams. We find that for large values of $\sin^2 2 θ_{13}$, a measurement of R with a precision of about 20% or better may not only improve the measurement of the leptonic CP phase, but also help the determination of the mass hierarchy. In some cases, early information on $δ_{CP}$ may even be obtained from Double Chooz and an astrophysical flux alone without the help of superbeams. For small values of $\sin^2 2 θ_{13}$, we find that using the information from an astrophysical neutrino flux could eliminate the octant degeneracy better than reactor experiments and beams alone. Finally, we demonstrate that implementing an additional observable based on the electromagnetic to hadronic shower ratio at a neutrino telescope (such as at higher energies) could be especially beneficial for pion beam sources.

hep-ph↗
arXiv2006

Neutrino tomography - Learning about the Earth's interior using the propagation of neutrinos

Because the propagation of neutrinos is affected by the presence of Earth matter, it opens new possibilities to probe the Earth's interior. Different approaches range from techniques based upon the interaction of high energy (above TeV) neutrinos with Earth matter, to methods using the MSW effect on the neutrino oscillations of low energy (MeV to GeV) neutrinos. In principle, neutrinos from many different sources (sun, atmosphere, supernovae, beams etc.) can be used. In this talk, we summarize and compare different approaches with an emphasis on more recent developments. In addition, we point out other geophysical aspects relevant for neutrino oscillations.

physics.geo-ph↗