Constituent gluons and a new mechanism for radiative weak decays of hyperons

An effective quark-gluon-photon operator is considered as the mechanism for radiative weak decays of hyperons. The coefficient function is unsuppressed by GIM cancellations, suggesting a significant decay rate, and a substantial amount of parity violation (large decay asymmetry) is expected. Attempted model calculations confirm this last feature but fail to provide an adequate absolute decay rate.     

THE ΔS=l WEAK RADIATIVE DECAYS OF HYPERONS

We calculate the rates and asymmetry parameters of radiative hyperon decays based on the hybrid structure of hyperons.We exploit an effective Hamiltonian derived from a penguin-Like Feynman diagram. We also consider a model of a static mean gluon field. A plausible recoil effect is taken into account in the final results. The resultant asymmetry parameters are reasonably consistent with data.     

Neutrino masses from three-particle decays

The purely leptonic decays of the tau and the radiative decay of the pion provide determinations of the tau neutrino and muon neutrino masses, respectively. The shift of the energy at which the tau decay spectrum attains its maximum and the forward-backward ratio are both large enough to determine tau neutrino masses of about 100 MeV. The photon endpoint energy and partially integrated differential decay rate in pion decay are sensitive to a neutrino mass as small as 100 keV. Thus, the present bounds on neutrino masses can be significantly improved.     

Suppression factors for vector-meson-dominance couplings implied by duality

It is noted that recent experiments on φ decays indicate a suppression of the radiative decay by about a factor of 3 less than the vector-meson-dominance model predictions. FESR's on pion compton scattering amplitudes with identical t-channels but different direct channel resonances are shown to relate radiative decays of A₂ and ω. This again leads to a suppression factor of 3 to 4 for the A₂ radiative decay relative to the VMD prediction.     

Search for direct CP violation in nonleptonic decays of charged Xi and lambda hyperons

A search for direct CP violation in the nonleptonic decays of hyperons has been performed. In comparing the product of the decay parameters, alpha(Xi)alpha(Lambda), in terms of an asymmetry parameter, A(XiLambda), between hyperons and antihyperons in the charged Xi-->Lambdapi and Lambda-->ppi decay sequence, we found no evidence of direct CP violation. The parameter A(XiLambda) was measured to be 0.012+/-0.014.     

Measuring the photon polarization in B -->Kpipigamma

We propose a way of measuring the photon polarization in radiative B decays into K resonance states decaying to Kpipi, which can test the standard model and probe new physics. The photon polarization is shown to be measured by the up-down asymmetry of the photon direction relative to the Kpipi decay plane in the K resonance rest frame. The integrated asymmetry in K1(1400)-->Kpipi, calculated to be 0.34 plus/minus 0.05 in the standard model, is measurable at currently operating B factories.     

Pion decays and the pion electromagnetic form factor in a σ-model with quarks

We study in the one-loop approximation the decays of the pion and the pion electromagnetic form factor at low q² in the framework of a σ-model with quarks. The theory has a free parameters the quark and σ masses and the results are very insensitive to their values. We get good approximation for all processes considered except for the ratio of the axial to the vector form factor that appear in the electronic radiative decay of the charged pion. The reason is probably that our model includes the pion-pion interaction only in the isoscalar s-wave at the one-loop level.     

Radiative corrections to semileptonic decays of charged hyperons

We have studied the radiative corrections to the lepton energy spectrum in semileptonic hyperon decays. The calculation is performed relativistically for the baryons as well as for the leptons, under the assumption of the effective current-current interaction of the V-?A type for the baryonic part. We obtain the explicit formula of radiative corrections to the lepton energy spectrum which we can exactly evaluate in case of charged hyperon decays. Numerical values of the radiative corrections to the decays rate and the shape of the lepton energy spectrum are also given for some decay modes. It is shown that the spectral shape is little affected by the radiative corrections.     

Search for CP violation in the decay B0-->D*+/-D-/+

We report a search for CP-violating asymmetry in B0-->D(*+/-)D-/+ decays. The analysis employs two methods of B0 reconstruction: full and partial. In the full reconstruction method all daughter particles of the B0 are required to be detected; the partial reconstruction technique requires a fully reconstructed D- and only a slow pion from the D(*+)-->D0pi(+)(slow) decay. From a fit to the distribution of the time interval corresponding to the distance between two B meson decay points we calculate the CP-violating parameters and find the significance of nonzero CP asymmetry to be 2.7 standard deviations.     

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     

Relations between inclusive decay rates of heavy baryons

The dependence of inclusive weak decay rates of heavy hadrons on the flavors of spectator light quarks is revisited with application to decays of charmed and b hyperons. It is pointed out that the differences in the semileptonic decay rates, the differences in the Cabibbo-suppressed decay rates of the charmed hyperons, and the splitting of the total decay rates of the b hyperons are all related to the differences in the lifetimes of the charmed hyperons independently of poor knowledge of hadronic matrix elements. The approximations used in these relations are the applicability of the expansion in the inverse of the charmed quark mass and the flavor SU(3) symmetry.     

Can the Hidden Phase in ΔS=1 Weak Radiative Decays of Hyperons Be Determined

In detail we analyse possible ways for measuring the hidden phase in ΔS=1 weak, radiative decays of hyperons and have found that any measurement on the kinematic quantities of the decays cannot determine the phase. The only possibility is to measure the CP non-invariannce in decays, even though it is very difficult. Our analysis is fully model-independent.     

Intermediate energy bremsstrahlung and the structure of free and bound hadrons: Radiative pion proton scattering,pion decay and muon capture

Experimental data on pion-proton bremsstrahlung, radiative pion decay and radiative muon capture are reviewed to demonstrate that the study of intermediate energy bremsstrahlung processes can reveal additional information on hadron structure inaccessible in their non-radiative counterparts.Dedicated to the memory of M. Gmitro.     

Search for finite-mass neutrinos in the decay π+→μ+vμ

If neutrinos possess non-zero mass, pion decay might have small decay branches to neutrino states with large masses. We have searched for such branches in the decay of pions produced at the Indiana University Cyclotron. The energy spectrum of decay muons shows no evidence for such neutrino branches and if these decays do exist, their branching ratios must be less than 10^?2 to 10^?3 for neutrino masses in the ranFge 7–33 MeV.     

Amplitude and trace reduction using Weyl-Van der Waerden spinors: Pion pair decay π+ → e+e−e+νe

Feynman diagram calculations are considerably simpler in the framework of Weyl-Van der Waerden spinors than in the standard formalism. We collect the basic formulae and illustrate the method by a few examples. We study pion pair decay in considerable detail and find that the long-standing ambiguity in determining the ratio of axial vector to vector structure term that hampered pion radiative decay can be resolved in the pair decay.     

Constant-Cutoff Approach to Strangeness Dependence in Radiative Decays of Hyperons

We suggest a quantum stabilization method forthe SU(2) -model, based on the constant-cutofflimit of the cutoff quantization method developed byBalakrishna et al., which avoids the difficulties with the usual soliton boundary conditions pointedout by Iwasaki and Ohyama. We investigate the baryonnumber B = 1 sector of the model and show that after thecollective-coordinate quantization it admits a stable soliton solution which depends on asingle dimensional arbitrary constant. We then study theradiative decays of J = 3+/2 baryonsusing the constant-cutoff approach to the SU(3)collective treatment of the Skyrme model for hyperons. Thus weinvestigate the radiative hyperon decays and thevariation of the decay widths with strangeness, showingthat the present results are in qualitative agreementwith the results obtained using the complete Skyrmemodel.     

Measurement of the CP-violation parameter sin2φ1 with a new tagging method at the Υ(5S) resonance

We report a measurement of the CP-violation parameter sin2φ1 at the Υ(5S) resonance using a new tagging method, called "B-π tagging." In Υ(5S) decays containing a neutral B meson, a charged B, and a charged pion, the neutral B is reconstructed in the J/ψK(S)(0) CP-eigenstate decay channel. The initial flavor of the neutral B meson at the moment of the Υ(5S) decay is opposite to that of the charged B and may thus be inferred from the charge of the pion without reconstructing the charged B. From the asymmetry between B-π(+) and B-π(-) tagged J/ψK(S)(0) yields, we determine sin2φ1=0.57±0.58(stat)±0.06(syst). The results are based on 121 fb(-1) of data recorded by the Belle detector at the KEKB e(+)e(-) collider.     

Sum rules for radiative quarkonium decays from short-range interactions

Sum rules previously derived for proton decay are extended and applied to treat effects of bound states spectroscopy on radiative quarkonium decays. The transition involves boson (photon or pion) emission followed by quark annihilation. Sum rules for the contributions from different intermediate bound states are derived by using closure and the assumptions (1) that the boson emission is described by a plane wave or multipole operator which satisfies a wave equation, and (2) that the annihilation depends on the bound state wave function or its derivative at the origin.     

Measurement of polarized target asymmetry on γn→π−p around the second resonance region

The polarized target asymmetry for γn→π^?p was measured over the second resonance region from 0.55 to 0.9 GeV at pion c.m. angles between 60° and 120°. A double-arm spectrometer was used with a deuterated butanol target to detect both the pion and the proton, thus considerably improving the data quality. Including the new data in the amplitude analysis, the radiative decay widths of three resonances were determined more accurately than before. The results are compared with various quark models.     

Pion-Muon Asymmetry Revisited

Long ago an unexpected and unexplainable phenomena was observed. The distribution of muons from positive pion decay at rest was anisotropic with an excess in the backward direction relative to the direction of the proton beam from which it was produced. Although this effect was observed by several different groups with pions produced by different means and detected by different methods, the result was not accepted by the physics community, because it is in direct conflict with a large set of other experiments indicating that the pion is a pseudoscalar particle. It is possible to satisfy both sets of experiments if helicity-zero vector particles exist and the pion is such a particle. Helicity-zero vector particles have direction but no net spin. For the neutral pion to be a vector particle requires an additional modification to conventional theory as discussed herein. An experiment is proposed which can prove that the asymmetry in the distribution of muons from pion decay is a genuine physical effect because the asymmetry can be modified in a controllable manner. A positive result will also prove that the pion is not a pseudoscalar particle.