arXiv subjects

S. Y. Tsai

Publications and source records attributed to S. Y. Tsai.

8 recordsLinked to original sources

arXiv2006

A Wave-Packet View of Neutrino Oscillation and Pion Decay

Kinematical aspects of pion decay $π\to μν$ is studied, with neutrino mixing taken into account. An attempt is made to derive the transition probability for such a sequence of processes: a $π^+$ produced at $(\vec{x}_π,t_π)$ with momentum $\vec{p}_π$ decays into a $μ^+$ and a $ν_μ$ somewhere in space-time and then the $μ^+$ is detected at $(\vec{x}_μ,t_μ)$ with momentum $\vec{p}_μ$ and a $ν_α$ (a neutrino with flavor $α= e$, $μ$, $...$) is detected at $(\vec{x}_ν,t_ν)$ with momentum $\vec{p}_ν$. It is shown that (1) if all the particles involved are treated as plane-waves, the energy-momentum conservation would eliminate the neutrino oscillating terms, leaving each mass-eigenstate to contribute separately to the transition probability; (2) if one treats all the particles involved as wave-packets, the neutrino oscillating terms would appear and would be multiplied by two suppression factors, which result from distinction in velocity and in energy between the two interfering neutrino mass-eigenstates. An approximate treatment which takes account of the two complementary features, each of the particles involved propagates along its classical trajectory on the one hand and energies and momenta of the particles involved are conserved during the decay on the other hand, is proposed and similarity and difference between our approach and that of Dolgov et al. are discussed.

hep-ph↗

arXiv2002

CP, T and CPT Violations in the K^0 - bar{K^0} System -- Present Status --

Possible violation of CP, T and CPT symmetries in the K^0 - bar{K^0} system is studied in a way as phenomenological and comprehensive as possible. For this purpose, we first introduce parameters which represent violation of these symmetries in mixing parameters and decay amplitudes in a convenient and well-defined way and, treating these parameters as small, derive formulas which relate them to the experimentally measured quantities. We then perform numerical analyses to derive constraints to these symmetry-violating parameters, with the latest data reported by KTeV Collaboration, NA48 Collaboration and CPLEAR Collaboration, along with those compiled by Particle Data Group, used as inputs. The result obtained by CPLEAR Collaboration from an unconstrained fit to a time-dependent leptonic asymmetry, aided by the Bell-Steinberger relation, enables us to determine or constrain most of the parameters separately. It is shown among the other things that (1) CP and T symmetries are violated definitively at least at the level of 10^{-4} in 2 pi decays, (2) CP and T symmetries are violated at least at the level of 10^{-3} in the K^0 - bar{K^0} mixing, and (3) CPT symmetry is at present tested to the level of 10^{-5} at the utmost.

hep-ph↗

arXiv2000

How do Neutrinos Propagate ? - Wave-Packet Treatment of Neutrino Oscillation

The wave-packet treatment of neutrino oscillation developed previously is extended to the case in which momentum distribution functions are taken to be a Gaussian form with both central values and dispersions depending on the mass eigenstates of the neutrinos. It is shown among other things that the velocity of the neutrino wave packets does not in general agree with what one would expect classically and that relativistic neutrinos emitted from pions nevertheless do follow, to a good approximation, the classical trajectory.

hep-ph↗

arXiv2000

CP,T and/or CPT Violations in the K0-K0bar System --Implications of the KTeV,NA48 and CPLEAR Results

Possible violation of CP, T and/or CPT symmetries in the $\ko$-$\kob$ system is studied from a phenomenological point of view. For this purpose, we first introduce parameters which represent violation of these symmetries in mixing parameters and decay amplitudes in a convenient and well-defined way and, treating these parameters as small, derive formulas which relate them to the experimentally measured quantities. We then perform numerical analyses, with the aid of the Bell-Steinberger relation, to derive constraints to these symmetry-violating parameters, firstly paying particular attention to the results reported by KTeV Collaboration and NA48 Collaboration, and then with the results reported by CPLEAR Collaboration as well taken into account. A case study, in which either CPT symmetry or T symmetry is assumed, is also carried out. It is demonstrated that CP and T symmetries are violated definitively at the level of 10^{-4} in $2π$ decays and presumably at the level of 10^{-3} in the $\ko-\kob$ mixing, and that the Bell-Steinberger relation helps us to establish CP and T violations being definitively present in the $\ko-\kob$ mixing and to test CPT symmetry to a level of 10^{-4} ~ 10^{-5}.

hep-ph↗

arXiv1999

Direct CP, T and/or CPT violations in the K^0-\bar{K^0} system - Implications of the recent KTeV results on $2π$ decays -

The recent results on the CP violating parameters Re(e'/e) and Δϕ= ϕ_{00}-ϕ_{+-} reported by the KTeV Collaboration are analyzed with a view to constrain CP, T and CPT violations in a decay process. Combining with some relevant data compiled by the Particle Data Group, we find Re(e_2-e_0) = (0.85 +- 3.11)*10^{-4} and Im(e_2-e_0) = (3.2 +- 0.7)*10^{-4}, where Re(e_I) and Im(e_I) represent respectively CP/CPT and CP/T violations in decay of K^0 and \bar{K^0} into a 2πstate with isospin I.

hep-ph↗

arXiv1999

More on Parametrization Relevant to Describe Violation of CP, T and CPT Symmetries in the $K^0-\bar{K^0}$ System

To study violation of CP, T and/or CPT symmetries in the $K^0-\bar{K^0}$ systems, one has to parametrize the relevant mixing parameters and decay amplitudes in such a way that each parameter represents violation of these symmetries in a well-defined way. Parametrization is of course not unique and is always subject to phase ambiguities. We discuss these problems with freedom associated with rephasing of final (or intermediate) as well as initial states taken into account. We present a fully rephasing-invariant parametrization and a particular rephasing-dependent parametrization, and give a couple of comments related to these and other possible parametrizations.

hep-ph↗

arXiv1998

Physics Involved in Neutrino Oscillation

Neutrino oscillation is discussed with emphases placed more on its conceptual aspects. After reviewing the two conventional formulations, referred to here as the same-energy prescription and the same-momentum prescription, wave packet treatments are developed for each of these two prescriptions. Both wave packets localized in space and those in time are considered, and, by invoking relativistic kinematics as well, the necessary conditions for oscillation to occur are derived, which appear to have a form more well-defined and quantitative than what have been noted before. Some phenomenological implications suggested by the wave packet treatments are briefly mentioned. Finally, as a possible third prescription, the same-velocity prescription is given.

hep-ph↗

arXiv1998

Further Study on Possible Violation of CP, T and CPT Symmetries in the $K^0$-$\bar{K^0}$ System --- Remarks and Results ---

We demonstrate how one may identify or constrain possible violation of $CP$, $T$ and $CPT$ symmetries in the $K^0$-$\bar{K^0}$ system in a way as phenomenological and comprehensive as possibie. For this purpose, we first introduce parameters which represent violation of these symmetries in mixing parameters and decay amplitudes in a well-defined way. After discussing some characteristics of these parameters, we derive formulae which relate them to the experimentally measured quantities. We then carry out a numerical analysis with the help of the Bell-Steinberger relation to derive constraints to these violating parameters from available experimental data. Finally, we compare our parametrization and procedure of analysis with those employed in the recent literature.

hep-ph↗