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Search Results: 1 - 10 of 117915 matches for " T. Schwetz "
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Testing the statistical compatibility of independent data sets
M. Maltoni,T. Schwetz
Physics , 2003, DOI: 10.1103/PhysRevD.68.033020
Abstract: We discuss a goodness-of-fit method which tests the compatibility between statistically independent data sets. The method gives sensible results even in cases where the chi^2-minima of the individual data sets are very low or when several parameters are fitted to a large number of data points. In particular, it avoids the problem that a possible disagreement between data sets becomes diluted by data points which are insensitive to the crucial parameters. A formal derivation of the probability distribution function for the proposed test statistic is given, based on standard theorems of statistics. The application of the method is illustrated on data from neutrino oscillation experiments, and its complementarity to the standard goodness-of-fit is discussed.
Elastic neutrino - electron scattering and potential effects of magnetic and electric dipole moments
W. Grimus,T. Schwetz
Physics , 2000, DOI: 10.1016/S0550-3213(00)00451-X
Abstract: We consider elastic neutrino - electron scattering of solar neutrinos with magnetic moments and electric dipole moments, where the solar neutrino state at the scattering site is determined by the evolution in matter and solar magnetic fields of the initial electron neutrino state. We present the general cross section for an arbitrary superposition of active and sterile neutrino types with positive and negative helicities, with particular emphasis on the effect of transverse polarization, which gives rise to an azimuthal asymmetry as a function of the recoil electron momentum. Within our physically motivated approximation, we perform a general CP analysis and show that in the 1-Dirac and 2-Majorana neutrino cases no CP-violating effects are present, which means that it is not possible to distinguish between magnetic and electric dipole moments in these cases. We also study the consequences of neutrino energy averaging on the cross section and stress that in the 2-Majorana neutrino case this averaging leads to a suppression of the transverse neutrino polarization effects.
Elastic $νe^-$ scattering of solar neutrinos with electromagnetic moments
W. Grimus,T. Schwetz
Physics , 2000, DOI: 10.1016/S0920-5632(01)01077-5
Abstract: We consider the azimuthal asymmetry of the recoil electrons in elastic $\nu e^-$ scattering of solar neutrinos, which can arise if neutrinos have electromagnetic moments and there is a large solar magnetic field. We show that using this effect it is not possible to distinguish between magnetic and electric dipole moment in the 1-Dirac and 2-Majorana neutrino cases and that averaging over neutrino energy is important and suppresses the azimuthal asymmetry in the 2-Majorana case.
4-Neutrino mass schemes and the likelihood of (3+1)-mass spectra
W. Grimus,T. Schwetz
Physics , 2001, DOI: 10.1007/s100520100646
Abstract: We examine the (3+1)-class of 4-neutrino mass spectra within a rigorous statistical analysis based on the Bayesian approach to probability. The data of the Bugey, CDHS and KARMEN experiments are combined by using a likelihood function. Our statistical approach allows us to incorporate solar and atmospheric neutrino data and also the result of the CHOOZ experiment via inequalities which involve elements of the neutrino mixing matrix and are derived from these data. For any short-baseline $\Delta m^2$ we calculate a bound on the LSND transition amplitude $A_{\mu;e}$ and find that, in the $\Delta m^2$--$A_{\mu;e}$ plane, there is no overlap between the 99% CL region allowed by the latest LSND analysis and the region allowed by our bound on $A_{\mu;e}$ at 95% CL; there are some small overlap regions if we take the bound at 99% CL. Therefore, we conclude that, with the existing data, the (3+1)-neutrino mass spectra are not very likely. However, treating the (2+2)-spectra with our method, we find that they are well compatible with all data.
Precision measurement of solar neutrino oscillation parameters by a long-baseline reactor neutrino experiment in Europe
S. T. Petcov,T. Schwetz
Physics , 2006, DOI: 10.1016/j.physletb.2006.09.063
Abstract: We 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.
Determining the Neutrino Mass Hierarchy with Atmospheric Neutrinos
S. T. Petcov,T. Schwetz
Physics , 2005, DOI: 10.1016/j.nuclphysb.2006.01.020
Abstract: The 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. We show also how the neutrino mass hierarchy determination depends on the true values of $\theta_{13}$ and $\theta_{23}$, as well as on the type of the true hierarchy. We find that for $\mu$-like events, an accurate reconstruction of the energy and direction of the neutrino greatly improves the sensitivity to the type of neutrino mass spectrum. For $\sin^22\theta_{13} \cong 0.1$ and a precision of 5% in the reconstruction of the neutrino energy and $5^\circ$ in the neutrino direction, the type of neutrino mass hierarchy can be identified at the 2$\sigma$ C.L. with approximately 200 events. For resolutions of 15% for the neutrino energy and $15^\circ$ for the neutrino direction roughly one order of magnitude larger event numbers are required. For a detector capable to distinguish between $\nu_e$ and $\bar\nu_e$ induced events the requirements on energy and direction resolutions are, in general, less demanding than for a detector with muon charge identification.
R2D2 - a symmetric measurement of reactor neutrinos free of systematical errors
P. Huber,M. Lindner,T. Schwetz
Physics , 2004, DOI: 10.1088/1126-6708/2005/02/029
Abstract: We discuss a symmetric setup for a reactor neutrino oscillation experiment consisting of two reactors separated by about 1 km, and two symmetrically placed detectors, one close to each reactor. We show that such a configuration allows a determination of $\sin^22\theta_{13}$ which is essentially free of systematical errors, if it is possible to separate the contributions of the two reactors in each detector sufficiently. This can be achieved either by considering data when in an alternating way only one reactor is running or by directional sensitivity obtained from the neutron displacement in the detector.
A 4-neutrino model with a Higgs triplet
W. Grimus,R. Pfeiffer,T. Schwetz
Physics , 1999, DOI: 10.1007/s100520000255
Abstract: We take as a starting point the Gelmini -- Roncadelli model enlarged by a term with explicit lepton number violation in the Higgs potential and add a neutrino singlet field coupled via a scalar doublet to the usual leptons. This scenario allows us to take into account all three present indications in favour of neutrino oscillations provided by the solar, atmospheric and LSND neutrino oscillation experiments. Furthermore, it suggests a model which reproduces naturally one of the two 4-neutrino mass spectra favoured by the data. In this model the solar neutrino problem is solved by large mixing MSW \nu_e\to\nu_\tau transitions and the atmospheric neutrino problem by transitions of \nu_\mu into a sterile neutrino.
Resolving parameter degeneracies in long-baseline experiments by atmospheric neutrino data
P. Huber,M. Maltoni,T. Schwetz
Physics , 2005, DOI: 10.1103/PhysRevD.71.053006
Abstract: In 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.
Neutrino Mixing Sum Rules and Oscillation Experiments
Antusch, S.;Huber, P.;King, S. F.;Schwetz, T.
High Energy Physics - Phenomenology , 2007, DOI: 10.1088/1126-6708/2007/04/060
Abstract: 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 $\theta^\nu_{12}$.
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