Browsing by Author "Schwetz, Thomas"
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Item The Absolute Neutrino Mass Scale, Neutrino Mass Spectrum, Majorana CP-Violation and Neutrinoless Double-Beta Decay(2006-09-25T15:37:55Z) Pascoli, Silvia; Petcov, Serguey T.; Schwetz, Thomas; Physics; Elementary Particle TheoryAssuming 3-$\nu$ mixing, massive Majorana neutrinos and neutrinoless double-beta (\betabeta-) decay generated only by the (V-A) charged current weak interaction via the exchange of the three Majorana neutrinos, we briefly review the predictions for the effective Majorana mass $\meff$ in \betabeta-decay and reanalyse the physics potential of future \betabeta-decay experiments to provide information on the type of neutrino mass spectrum, the absolute scale of neutrino masses, and Majorana CP-violation in the lepton sector. Using as input the most recent experimental results on neutrino oscillation parameters and the prospective precision that can be achieved in future measurements of the latter, we perform a statistical analysis of a \betabeta-decay half-life measurement taking into account experimental and theoretical errors, as well as the uncertainty implied by the imprecise knowledge of the corresponding nuclear matrix element (NME). We show, in particular, how the possibility to dis...Item Can we learn something more on oscillations from atmospheric neutrinos?(2006-11-09T10:48:44Z) Schwetz, Thomas; Physics; Elementary Particle TheoryWe show that for long-baseline experiments using a Mt water Cerenkov detector atmospheric neutrino data provide a powerful method to resolve parameter degeneracies. In particular, the combination of long-baseline and atmospheric data increases significantly the sensitivity to the neutrino mass hierarchy and the octant of $\theta_{23}$. Furthermore, we discuss the possibility to use $\mu$-like atmospheric neutrino data from a big magnetized iron calorimeter to determine the neutrino mass hierarchy.Item Determining the Neutrino Mass Hierarchy with Atmospheric Neutrinos(2005) Petcov, Serguey T.; Schwetz, Thomas; Physics; Elementary Particle TheoryThe possibility to determine the type of neutrino mass hierarchy by studying atmospheric neutrino oscillations with a detector capable to distinguish between neutrino and antineutrino events, such as magnetized iron calorimeters, is considered. We discuss how the ability to distinguish between the neutrino mass spectrum with normal and inverted hierarchy depends on detector characteristics like neutrino energy and direction resolutions or charge miss-identification, and on the systematical uncertainties related to the atmospheric neutrino fluxes...Item Explaining LSND by a decaying sterile neutrino(2005) Palomares-Ruiz, Sergio; Pascoli, Silvia; Schwetz, Thomas; Physics; Elementary Particle TheoryWe 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 gm4 ~ few eV, g being the neutrino-scalar coupling and m4 the heavy neutrino mass, e.g. m4 in the range from 1 keV to 1 MeV and g ~ 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.Item Fermion masses and mixings in SO(10) models and the neutrino challenge to supersymmetric grand unified theories(2006-06-13T08:23:21Z) Bertolini, Stefano; Malinsky, Michal; Schwetz, Thomas; Physics; Elementary Particle TheoryWe present a detailed study of the quark and lepton mass spectra in a SO(10) framework with one 10_H and one \bar{126}_H Higgs representations in the Yukawa sector. We consider in full generality the interplay between type-I and type-II seesaws for neutrino masses. We first perform a \chi^2 fit of fermion masses independent on the detailed structure of the GUT Higgs potential and determine the regions in the parameter space that are preferred by the fermion mass sum rules. We then apply our study to the case of the minimal renormalizable SUSY SO(10) GUT with one 10_H, one \bar{126}_H, one 126_H, and one 210_H Higgs representations. By requiring that proton decay bounds are fulfilled we identify a very limited area in the parameter space where all fermion data are consistently reproduced. We find that in all cases gauge coupling unification in the supersymmetric scenario is severely affected by the presence of lighter than GUT (albeit B-L conserving) states. We then conclusively show that the minimal supersymmetric SO(10) scenario here considered is not consistent with data. The fit of neutrino masses with type-I and type-II seesaws within a renormalizable SO(10) framework strongly suggests a non-SUSY scenario for gauge unification.Item Global fits to neutrino oscillation data(2006-06-13T10:01:54Z) Schwetz, Thomas; Physics; Elementary Particle TheoryI 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 $\theta_{13}$ 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 $\Delta m^2_{21}$ and $\theta_{13}$ for the bound on $\theta_{13}$ and non-maximal values of $\theta_{23}$, 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.Item Neutrino oscillations: Current status and prospects(2005) Schwetz, Thomas; Physics; Elementary Particle TheoryI 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.Item Physics potential of the CERN-MEMPHYS neutrino oscillation project(2006-04-19T10:33:48Z) Campagne, Jean-Eric; Maltoni, Michele; Mezzetto, Mauro; Schwetz, Thomas; Physics; Elementary Particle TheoryWe consider the physics potential of CERN based neutrino oscillation experiments consisting of a Beta Beam (BB) and a Super Beam (SPL) sending neutrinos to MEMPHYS, a 440 kt water Cerenkov detector at Frejus, at a distance of 130 km from CERN. The $\theta_{13}$ discovery reach and the sensitivity to CP violation are investigated, including a detailed discussion of parameter degeneracies and systematical errors. For BB and SPL sensitivities similar to the ones of the phase II of the T2K experiment (T2HK) are obtained, where the results for the CERN-MEMPHYS experiments are less affected by systematical uncertainties. We point out that by a combination of data from BB and SPL a measurement with antineutrinos is not necessary and hence the same physics results can be obtained within about half of the measurement time compared to one single experiment. Furthermore, it is shown how including data from atmospheric neutrinos in the MEMPHYS detector allows to resolve parameter degeneracies and, in particular, provides sensitivity to the neutrino mass hierarchy and the octant of $\theta_{23}$.Item Precision measurement of solar neutrino oscillation parameters by a long-baseline reactor neutrino experiment in Europe(2006-07-26T08:30:19Z) Petcov, Serguey T.; Schwetz, Thomas; Physics; Elementary Particle TheoryWe consider the determination of the solar neutrino oscillation parameters $\Delta m^2_{21}$ and $\theta_{12}$ by studying oscillations of reactor anti-neutrinos emitted by nuclear power plants (located mainly in France) with a detector installed in the Frejus underground laboratory. The performances of a water Cerenkov detector of 147 kt fiducial mass doped with 0.1% of Gadolinium (MEMPHYS-Gd) and of a 50 kt scale liquid scintillator detector (LENA) are compared. In both cases 3$\sigma$ uncertainties below 3% on $\Delta m^2_{21}$ and of about 20% on $\sin^2\theta_{12}$ can be obtained after one year of data taking. The Gadolinium doped Super-Kamiokande detector (SK-Gd) in Japan can reach a similar precision if the SK/MEMPHYS fiducial mass ratio of 1 to 7 is compensated by a longer SK-Gd data taking time. Several years of reactor neutrino data collected by MEMPHYS-Gd or LENA would allow a determination of $\Delta m^2_{21}$ and $\sin^2\theta_{12}$ with uncertainties of approximately 1% and 10% at 3$\sigma$, respectively. These accuracies are comparable to those that can be reached in the measurement of the atmospheric neutrino oscillation parameters $\Delta m^2_{31}$ and $\sin^2\theta_{23}$ in long-baseline superbeam experiments.Item Resolving parameter degeneracies in long-baseline experiments by atmospheric neutrino data(2005) Huber, Patrick; Maltoni, Michele; Schwetz, Thomas; Physics; Elementary Particle TheoryIn this work we show that the physics reach of a long-baseline (LBL) neutrino oscillation experiment based on a superbeam and a megaton water Cherenkov detector can be significantly increased if the LBL data are combined with data from atmospheric neutrinos (ATM) provided by the same detector. ATM data are sensitive to the octant of $\theta_{23}$ and to the type of the neutrino mass hierarchy, mainly through three-flavor effects in e-like events. This allows to resolve the so-called $\theta_{23}$- and sign($\Delta m^2_{31}$)-parameter degeneracies in LBL data. As a consequence it becomes possible to distinguish the normal from the inverted neutrino mass ordering at $2\sigma$ CL from a combined LBL+ATM analysis if $\sin^2 2\theta_{13} \gtrsim 0.02$. The potential to identify the true values of $\sin^2 2\theta_{13}$ and the CP-phase $\delta_{cp}$ is significantly increased through the lifting of the degeneracies. These claims are supported by a detailed simulation of the T2K (phase II) LBL experiment combined with a full three-flavor analysis of ATM data in the HyperKamiokande detector.Item Testing mass-varying neutrinos with reactor experiments(2005) Schwetz, Thomas; Winter, Walter; Physics; Elementary Particle TheoryWe 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...Item Unitary triangle test of the extra factor of two in particle oscillation phases(2005) Bilenky, Samoil M.; Grimus, Walter; Schwetz, Thomas; Physics; Elementary Particle TheoryThere 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 KL - KS and BdH -BdL mass differences are extracted from the K0- ¯K0 and B0 d - ¯B0 d 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 sigma.