arXiv subjects
Publications and source records attributed to Jean-Michel Levy.
Production and decay rates, polarization and differential distributions of decay products are calculated for a heavy neutrino produced in charged pseudoscalar meson decay and decaying itself in charged pseudoscalar and lepton or a lepton-antilepton pair of different flavours and a light SM like (anti)neutrino.
Some tension exists between present experimental data and models which comprise only the three light neutrino mass eigenstates necessary to explain solar and atmospheric oscillation results. Hence the revival of the idea that additional more massive states might enter the active neutrino superpositions produced and observed in charged current reactions. Such 'heavy' neutrinos with masses in the keV or MeV range might also be of interest as dark matter candidates. A state with mass larger than 1022 keV could decay into an $e^+ e^-$ pair and a light mass state, leaving an easily recognizable signature. The aim of this paper is to estimate the possible signal rate.
We review the kinematics of a neutrino beam in the idealized case where the parent mesons momenta are parallel, but without other approximation. This reveals several interesting features, in particular in the off-axis case, which are hidden by the approximations made in a previous treatment.
A wrong derivation of the phase of a propagating massive particle which has repeatedly appeared during the last years has the advantage of leading once more to the important question of the phase difference between the mass eigenstates constitutive of an oscillating neutrino described in the plane wave formalism. Serious errors of principle are pointed at in a number of simple calculations and the oscillation length is derived in a way which allows to show that the standard result can suffer but minute variations in the ultrarelativistic case.
The sample median is often used in statistical analyses of physical or astronomical data wherein a central value must be found from samples polluted by elements which do not belong to the population of interest or when the underlying probability law is such that the sample mean is useless for the stated purpose. Although it does not generally possesses the nice linearity properties of the mean, the median has advantages of its own, some of which are explored in this paper which elucidates analogies and differences between these two central value descriptors. Some elementary results are shown, most of which are certainly not new but not widely known either. It is observed that the moment and the quantile approaches to the description of a probability distribution are difficult to relate, but that when the quantile description is used, the sample median can be characterized very much in the same way as the sample mean; this opens the possibility of using it for estimation purposes beyond what is usually done. In order to relate the two approaches, a derivation is given of the asymptotic joint distribution of the mean and the median for a general continuous probability law.
The Lorentz transformation is entirely derived from length contraction, itself established through the known light-clock thought experiment . This makes the derivation accessible to beginning students once Eintein's two postulates have been admitted. The formula derived for the space part of the general rotation-free Lorentz transformation is very compact and allows for an easy derivation of the velocity and acceleration transformations. A possibly new and very simple relation is found between proper acceleration and acceleration in an inertial frame.
It is argued that systematically unbiassing estimators is not always justified and can be counter-productive. On the contrary, a general rule is given to build a (slightly) biased but consistent estimator which is always closer to the value being estimated than the unbiased estimator from which one has started.
Practical formulae are derived for the cross-section and polarization of the $τ$ lepton produced in deep-inelastic neutrino-nucleon scattering in the frame of the simple quark-parton model.
Forsaking the traditionnal hand-waving in the treatment of the motion, we show that the ultra-relativistic approximation and the equality of kinematical variables are unnecessary ingredients in the derivation of the oscillation length using plane waves, at least in a two flavor world. It ensues that the formula is valid as it is in the non relativistic regime, provided one uses the correct variable which is found to be momentum, not energy, and that the precise production kinematics is irrelevant. Consequences for the more complete treatments are briefly evoked.