Search results for "Mixing"
showing 10 items of 795 documents
Equilibrium properties of self-interacting neutrinos in the quasi-particle approach
2004
In this work a neutrino gas in equilibrium is studied both at T=0 and at finite temperature. Neutrinos are treated as massive Dirac quasi-particles with two generations. We include self-interactions among the neutrinos via neutral currents, as well as the interaction with a background of matter. To obtain the equilibrium properties we use Wigner function techniques. To account for corrections beyond the Hartree approximation, we also introduce correlation functions. We prove that, under the quasi-particle approximation, these correlation functions can be expressed as products of Wigner functions. We analyze the main properties of the neutrino eigenmodes in the medium, such as effective mass…
Lifetime measurement in 195Po
2009
The lifetime of the 17/2+ yrast state in 195Po has been measured using the recoil distance Doppler-shift technique to be $ \tau$ = 43(11) ps. The lifetime was extracted from the singles $ \gamma$ -ray spectra obtained by using the recoil-decay tagging method. The present work provides more information of the coupling schemes, shapes and configuration mixing in neutron-deficient odd-mass Po nuclei.
Relativistic Wigner function approach to neutrino propagation in matter
1999
In this work we study the propagation of massive Dirac neutrinos in matter with flavor mixing, using statistical techniques based on Relativistic Wigner Functions. First, we consider neutrinos in equilibrium within the Hartree approximation, and obtain the corresponding relativistic dispersion relations and effective masses. After this, we analyze the same system out of equilibrium. We verify that, under the appropiate physical conditions, the well known equations for the MSW effect are recovered. The techniques we used here appear as an alternative to describe neutrino properties and transport equations in a consistent way.
A finite number of regular rotational bands in the superdeformed well of 143Eu
1995
Abstract The number of excited superdeformed bands in 143 Eu is measured by use of the Fluctuation Analysis Method. Between 10 and 40 rotational bands, displaying typical rotational energy correlations over two consecutive transitions, are populated within a rather narrow range in transition energy, E γ ≈ 1300–1500 keV. These numbers are close to the values found for normally deformed nuclei and agree with microscopic cranking + band mixing calculations for the specific superdeformed nucleus, which predict the onset of rotational damping to occur at the excitation energy U 0 = 1.3–1.6 MeV above the yrast line.
Even harmonics generation in plasma as a new tool of current evolution diagnostics
2005
It is shown that using even harmonics of a test wave it is possible to diagnose the fast time evolution of the current density.
Constraints on an additional Z′ gauge boson versus the W, the top and the Higgs masses
1990
Abstract We analyse the restrictions on the mass and the mixing of an additional Z′ gauge boson that follow from the recent LEP measurements taking into account standard model (SM) radiative corrections. We find that these restrictions depend sharply on the assumed values for the SM structural parameters, the most important of which are M w and m top . The constraints become stronger for lighter W and heavier top.
Chiral loops and VMD in the V→PPγ decays
2002
Abstract We evaluate radiative decays of ρ and ω going to two neutral mesons, π0π0 and π0η. We use the sequential vector decay mechanisms in addition to chiral loops and ρ–ω mixing. The chiral loops are obtained using elements of UχPT successfully applied in the study of meson–meson interactions up to 1.2 GeV. The chiral loops are found very important in the case of the ρ→π0π0γ decay and small in the other cases. A good agreement with present measurements of ρ→π0π0γ and ω→π0π0γ is obtained and predictions are made for the other decays where the rates obtained are rather small.
Only three flavours
1998
Abstract It is shown that it is possible to account for all the experimental indications for neutrino oscillations with just three flavours. In particular we suggest that the atmospheric neutrino anomaly and the LSND result can be explained by the same mass difference and mixing. Possible implications and future test of the resulting mass and mixing pattern are given.
Estimation of bounds for left-right mixing from nuclear double beta decay processes
1993
Abstract Nuclear matrix elements, extracted from a systematic calculation of neutrinoless double beta decay rates for 0 + g.s →o + g.s transitions in 76 Ge, 82 Se, 128 Te, 130 Te and 136 Xe, have been used to compute bounds on the left-right mixing angle ζ of the weak currents. The parameters of the nuclear model have been fixed by calculating the corresponding two-neutrino double beta decay half lives. The present analysis favours a mixing of the order of |tanξ| −3 which is to be compared with those obtained in muon decay (|tan ξ | ⩽ 0.035) and in supernova (|tan ξ | ⩽ 10 −5 ) analysis. It shows that nuclear structure calculations yield estimates on ξ which complement the existing data.
Collectivity and Configuration Mixing inPb186,188andPo194
2006
Lifetimes of prolate intruder states in {sup 186}Pb and oblate intruder states in {sup 194}Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in {sup 188}Pb up to the 8{sup +} state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters vertical bar {beta}{sub 2} vertical bar =0.29(5) and vertical bar {beta}{sub 2} vertical bar =0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes.