arXiv subjects

Thomas Schwetz

Publications and source records attributed to Thomas Schwetz.

117 records · Page 7Linked to original sources

arXiv2006

Global fits to neutrino oscillation data

I summarize the determination of neutrino oscillation parameters within the three-flavor framework from world neutrino oscillation data with date of May 2006, including the first results from the MINOS long-baseline experiment. It is illustrated how the determination of the leading "solar" and "atmospheric" parameters, as well as the bound on $θ_{13}$ emerge from an interplay of various complementary data sets. Furthermore, I discuss possible implications of sub-leading three-flavor effects in present atmospheric neutrino data induced by $Δm^2_{21}$ and $θ_{13}$ for the bound on $θ_{13}$ and non-maximal values of $θ_{23}$, emphasizing, however, that these effects are not statistically significant at present. Finally, in view of the upcoming MiniBooNE results I briefly comment on the problem to reconcile the LSND signal.

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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

Neutrino oscillations: Current status and prospects

I summarize the status of neutrino oscillations from world neutrino oscillation data with date of October 2005. The results of a global analysis within the three-flavour framework are presented. Furthermore, a prospect on where we could stand in neutrino oscillations in ten years from now is given, based on a simulation of upcoming long-baseline accelerator and reactor experiments.

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arXiv2005

Explaining LSND by a decaying sterile neutrino

We propose an explanation of the LSND evidence for electron antineutrino appearance based on neutrino decay. We introduce a heavy neutrino, which is produced in pion and muon decays because of a small mixing with muon neutrinos, and then decays into a scalar particle and a light neutrino, predominantly of the electron type. We require values of $g m_4\sim$ few eV, $g$ being the neutrino--scalar coupling and $m_4$ the heavy neutrino mass, e.g. $m_4$ in the range from 1 keV to 1 MeV and $g \sim 10^{-6} - 10^{-3}$. Performing a fit to the LSND data as well as all relevant null-result experiments, we show that all data can be explained within this decay scenario. In the minimal version of the decay model, we predict a signal in the upcoming MiniBooNE experiment corresponding to a transition probability of the same order as seen in LSND. In addition, we show that extending our model to two nearly degenerate heavy neutrinos it is possible to introduce CP violation in the decay, which can lead to a suppression of the signal in MiniBooNE running in the neutrino mode. We briefly discuss signals in future neutrino oscillation experiments, we show that our scenario is compatible with bounds from laboratory experiments, and we comment on implications in astrophysics and cosmology.

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arXiv2005

Unitarity triangle test of the extra factor of two in particle oscillation phases

There are claims in the literature that in neutrino oscillations and oscillations of neutral kaons and B-mesons the oscillation phase differs from the standard one by a factor of two. We reconsider the arguments leading to this extra factor and investigate, in particular, the non-relativistic regime. We actually find that the very same arguments lead to an ambiguous phase and that the extra factor of two is a special case. We demonstrate that the unitarity triangle (UT) fit in the Standard Model with three families is a suitable means to discriminate between the standard oscillation phase and the phase with an extra factor of two. If $K_L - K_S$ and $B_{dH} - B_{dL}$ mass differences are extracted from the $K^0 - \bar K^0$ and $B_d^0 - \bar B_d^0$ data, respectively, with the extra factor of two in the oscillation phases, then the UT fit becomes significantly worse in comparison with the standard fit and the extra factor of two is disfavoured by the existing data at the level of more than 3 $σ$.

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arXiv2004

Precision spectroscopy with reactor anti-neutrinos

In this work we present an accurate parameterization of the anti-neutrino flux produced by the isotopes 235U, 239Pu and 241Pu in nuclear reactors. We determine the coefficients of this parameterization, as well as their covariance matrix, by performing a fit to spectra inferred from experimentally measured beta spectra. Subsequently we show that flux shape uncertainties play only a minor role in the KamLAND experiment, however, we find that future reactor neutrino experiments to measure the mixing angle $θ_{13}$ are sensitive to the fine details of the reactor neutrino spectra. Finally, we investigate the possibility to determine the isotopic composition in nuclear reactors through an anti-neutrino measurement. We find that with a 3 month exposure of a one ton detector the isotope fractions and the thermal reactor power can be determined at a few percent accuracy, which may open the possibility of an application for safeguard or non-proliferation objectives.

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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

Status of neutrino oscillations II: How to reconcile the LSND result?

We present an analysis of the global neutrino oscillation data including the LSND result in terms of four-neutrino mass schemes and a CPT violating three-neutrino framework. We find that the strong preference of oscillations into active neutrinos implied by recent solar+KamLAND as well as atmospheric neutrino data allows to rule out (2+2) mass schemes at 5.8$σ$, whereas (3+1) schemes are disfavoured at the 3.2$σ$ level by short-baseline experiments. The CPT violating scenario is disfavoured at 3.4$σ$ by KamLAND and atmospheric anti-neutrino data. We conclude that currently no convincing explanation for the LSND signal exists, and it remains a puzzle how to reconcile it with the other evidences for neutrino oscillations.

hep-ph↗

arXiv2003

Variations on KamLAND: likelihood analysis and frequentist confidence regions

In this letter the robustness of the first results from the KamLAND reactor neutrino experiment with respect to variations in the statistical analysis is considered. It is shown that an event-by-event based likelhood analysis provides a more powerful tool to extract information from the currently available data sample than a least-squares method based on energy binned data. Furthermore, a frequentist analysis of KamLAND data is performed. Confidence regions with correct coverage in the plane of the oscillation parameters are calculated by means of a Monte Carlo simulation. I find that the results of the usually adopted $χ^2$-cut approximation are in reasonable agreement with the exact confidence regions, however, quantitative differences are detected. Finally, although the current data is consistent with an energy independent flux suppression, a $\sim 2σ$ indication in favour of oscillations can be stated, implying quantum mechanical interference over distances of the order of 200 km.

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