Comparison of two experiments on radiative neutron decay

Over 10 years ago we proposed an experiment on measuring the characteristics of radiative neutron decay in papers [1, 2]. At the same time we had published the theoretical spectrum of radiative gamma quanta, calculated within the framework of the electroweak interactions, on the basis of which we proposed the methodology for the future experiment [3, 4]. However, because we were denied beam time on the intensive cold neutron beam at ILL (Grenoble, France) for a number of years, we could only conduct the experiment in 2005 on the newly opened FRMII reactor of Technical University of Muenchen. The main result of this experiment was the discovery of radiative neutron decay and the measurement of its relative intensity B.R. = (3.2 ± 1.6) × 10⁻³ with C.L. = 99.7% for radiative gamma quanta with energy over 35 kev [5, 6]. Over a year after our first announcement about the results of the conducted experiment, “Nature” [7] published a letter asserting that its authors have also measured the branching ratio of radiative neutron decay B.R. = (3.13 ± 0.34) × 10⁻³ with c.l. = 68% and gamma quanta energy from 15 to 340 kev. This article aims to compare these two experiments. It is shown that the use of strong magnetic fields in the NIST (Washington, USA) experiment methodology not only prevents any exact measurement of the branching ratio and identification of radiative neutron decay events, but also makes registration of ordinary neutron decay events impossible.     

Observation of radiative leptonic decay of the tau lepton

Using 4.68 fb(-1) of e(+)e(-) annihilation data collected with the CLEO II detector at the Cornell Electron Storage Ring, we have studied tau radiative decays tau(-)-->nu(tau)&mgr;(-)nu;(&mgr;)gamma and tau(-)-->nu(tau)e(-)nu;(e)gamma. For a 10 MeV minimum photon energy in the tau rest frame, the branching fraction for radiative tau decay to a muon or electron is measured to be (3.61+/-0.16+/-0. 35)x10(-3) or (1.75+/-0.06+/-0.17)x10(-2), respectively. The branching fractions are in agreement with standard model theoretical predictions.     

Finite temperature radiative corrections to neutron decay and related processes

We present a detailed calculation of the radiative corrections at finite temperature to the processes nν ? pe, ne ? pν. and n ? peν. The temperature range considered is approximately 100 keV to 3 MeV, which is the range relevant for nucleosynthesis calculations. Photon absorption and emission, photonic corrections to the vertex and fermion wave-function renormalizations, as well as the correction to the electron “mass” are calculated explicitly. It is shown that infrared divergences are only cancelled when absorption and induced photon emission are included. We analyze the effect of these processes on the various reaction rates, and discuss the effects of these corrections on the calculated helium abundance in the universe.     

Observation of the radiative decay D0-->phigamma

We report the observation of the decay D0-->phigamma with a statistical significance of 5.4sigma in 78.1 fb(-1) of data collected by the Belle experiment at the KEKB e+e- collider. This is the first observation of a flavor-changing radiative decay of a charmed meson. The Cabibbo- and color-suppressed decays D0-->phipi(0), phieta are also observed for the first time. We measure branching fractions B(D0-->phigamma)=[2.60(+0.70)(-0.61)(stat)+0.15-0.17(syst)] x 10(-5), B(D0-->phipi(0))=[8.01+/-0.26(stat)+/-0.47(syst)] x 10(-4), and B(D0-->phieta)=[1.48+/-0.47(stat)+/-0.09(syst)] x 10(-4).     

On the radiative pion decay

A reanalysis of the radiative pion decay together with the calculation of the radiative corrections within chiral perturbation theory (CHPT) is performed. The amplitude of this decay contains an inner Bremsstrahlung contribution and a structure-dependent part, which are both accessible in experiments. In order to obtain a reliable estimate of the hadronic contributions we combine the CHPT result with a large-N_c expansion and experimental data on other decays, which makes it possible to determine the occurring coupling constants. PACS  13.20.Cz; 12.39.Fe     

Observation of the radiative kaon decay K − → µ−π0γν

Using data collected with the ISTRA+ spectrometer during the 2001 run of the U-70 proton synchrotron in Protvino, the first observation of the radiative kaon decay K ⁻ → μ⁻π⁰γν is reported. The ratio Br(K _μ3γ, 5 < E*_γ < 30 MeV)/Br(K _μ3) is found to be [0.270 ± 0.029(stat.) ± 0.026(syst.)]% and the ratio Br(K _μ3γ, 30 < E*_γ < 60 MeV)/Br(K _μ3) = [0.0448 ± 0.0068(stat.) ± 0.0099(syst.)]%. These ratios are consistent with the theoretical predictions 0.21 and 0.047%, respectively. The measured angular distribution asymmetry for the region 5 < E*_γ < 30 MeV, A(cos ϑ*_μγ) = 0.093 ± 0.141, is two standard deviations away from the theoretical prediction of 0.354. The measured asymmetry in the T-odd variable ξ = p_γ · (p_μ × p_π)/m _K ³ is −0.03 ± 0.13. The text was submitted by the authors in English.     

Weak radiative decay of baryons

The decay amplitudes and asymmetry parameters for weak radiative decay of baryons are calculated in both pole model and quark model. It is demonstrated that both models give the same results and the results satisfy the symmetry relations we have derived recently. The agreement of the theoretical prediction with the presently measured decay rates and asymmetry is quite good in view of uncertainty in the calculation.     

Perturbation-induced radiative decay of solitons

New results concerning emission of radiation (quasi-linear waves) from kinks described by various versions of a perturbed sine-Gordon equation are presented. Considered physical problems pertain to condensed matter physics and nonlinear optics. In perticular, intensities of Swihart wave emission from a fluxon in a long dc driven Josephson junction, and of spin wave emission from a domain wall in a weak ferromagnet driven by external constant magnetic field are calculated. A general estimate for an exponentially small intensity of emission from a kink oscillating near a bottom of an effective potential wall is obtained. A system of coupled double sine-Gordon equations describing a double DNA helix is briefly investigated. It is demonstrated that a collision of a bi-kink (a bound state of two 2Π-kinks belonging to different subsystems) with a 4Π-kink belonging to either subsystem may result in excitation of large-amplitude internal oscillations of both the colliding solitons, and the rate of radiative damping of those oscillations is found. At last, radiative effects accompanying motion of a stimulated-Raman-scattering soliton in a dissipative medium are studied.     

Form factors in the radiative pion decay

We perform an analysis of the form factors that rule the structure-dependent amplitude in radiative pion decay. The resonance contributions to π→eν_eγ decays are computed through the proper construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions 〈VVP〉 and 〈VAP〉, and by demanding the smoothening of the form factors at high transfer of momentum. A comparison between theoretical and experimental determination of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic uncertainties, the search for new physics in this process is not feasible. PACS 11.15.Pg; 12.38.-t; 12.39.Fe     

On the massive Dirac neutrino radiative decay

The presence of right-handed currents and left-right mixing contributes to the neutrino radiative decay amplitude a term that is directly proportional to the charged lepton mass. This has led to the suggestion that observable decays of relic neutrinos might occur in the left-right model or the mirror model. Explicit calculations in these models are carried out including a careful analysis of the origin of neutrino mass, here assumed to be a Dirac mass. It is found that the amplitude is proportional to the neutrino mass and thus too small to be of interest. A brief comment on the neutrino magnetic moment in anSU(2) _L ×U(1) _Y model, which contains an iso-singlet charged scalar η⁺, is also presented.     

On the stimulated radiative decay of metastable states

I discuss the possibility of observing stimulated gamma emission by direct transition from long-lived metastable states of isomer nuclei, considering the effects of surplus emission-line broadening, so-called “laser lethargy,” and so on. A scenario and the configuration of an eventual experiment are presented.