Fraction Of Decay Research Articles

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.

00/00007 Low-temperature oxidation of coal studied using wire-mesh reactors with body steady-state and transient methods

Gamma-ray and Kα X-ray emissions have been measured from a very pure 209Po source containing less than 0.13% 208Po activity and no detectable 210Po (≤ 2 × 10−4%). The alpha-particle emission rate for this source has previously been determined. Data are presented that confirm alpha decay to the 205Pb excited level at 262.8 keV, with an alpha-particle emission probability (±standard uncertainty) of 0.00559±0.00008. The ratio of K-shell electron capture to total electron capture for the second forbidden unique electron capture decay to the 896.6 keV level in 209Bi was determined to be 0.594±0.018. The electron capture decay fraction was found to be 0.00454±0.00007, while the probabilities per decay for the 896.6, 262.8, and 260.5 keV gamma rays and the Bi Kα and Pb Kα X-rays were measured as 0.00445±0.00007, 0.00085±0.00002, 0.00254±0.00003, 0.00202±0.00005, and 0.00136±0.00005, respectively.

Business Cycles, Political Cycles and the Popularity of Canadian Governments, 1974–1998

AbstractThis article examines the popularity of Canadian governments between 1974 and 1998 as revealed by the monthly Gallup poll. Approval of each majority government in the 1974–1993 period underwent a cycle of honeymoon, decay and recovery. Underneath the cycle was a long-term downward trend. A simple politicoeconomic model accounts for a large fraction of long-term decay and helps explain the anti-government landslides of 1984 and 1993. But the model leaves inter-election popularity cycles largely unexplained. After 1993, the economy ceased to account for popularity and a wholly new, but apparently stable, electoral cycle emerged. The article concludes with speculation on causes of and contingency in electoral cycles.

Formation, excited state and electron transfer properties of the phenoxyl radical of 4,4′-thiodiphenol

The transient absorption bands ( λ max = 335, 500, 650–800 nm) formed on pulse radiolysis of N 2O-saturated basic aqueous solution of 4,4′-thiodiphenol (TDPH) are assigned to phenoxyl radical (TDP ⋅) formed on one-electron oxidation of phenoxide ion (TDP −) of TDPH. Specific one-electron oxidants (N ⋅ 3, I ⋅− 2, Br ⋅, CCl 3OO ⋅) also produced phenoxyl radicals with similar transient absorption spectrum. Phenoxyl radicals are able to undergo electron transfer reaction with N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD) with a bimolecular rate constant of 4.5 × 10 9 dm 3 mol −1 s −1. Pulse radiolysis of N 2-saturated TDPH in benzene showed absorption bands at 330, 500, 650–800 nm. The second-order decay of these bands was not affected by oxygen and anthracene, well-known triplet quenchers and the transient spectrum is assigned to phenoxyl radicals formed on fast decay of solute triplets with a G value of 0.29. Benzophenone triplet is able to undergo energy transfer with TDPH with a bimolecular rate constant of 6 × 10 9 dm 3 mol −1 s −1 and formed benzophenone ketyl radical ( λ = 545 nm) and phenoxyl radical (TDP ⋅, λ = 500 nm) on H ⋅ atom transfer from TDPH to benzophenone in an intermediate complex. The G value of phenoxyl radicals was determined to be 1.44. Picosecond laser flash photolysis of TDPH in acetonitrile failed to form any transient absorption in 450–900 nm region, supporting that only a small fraction of TDPH triplet decay to phenoxyls. Pulse radiolysis and picosecond laser flash photolysis studies indicate that the triplets of TDPH are highly unstable. The oxidation potential of TDP −/ TDP ⋅, H + couple is estimated to be between 0.265 and 1.03 V.

Binding-dependent disorder-order transition in PKI alpha: a fluorescence anisotropy study.

The conformational flexibility of peptidyl ligands may be an essential element of many peptide-macromolecular interactions. Consequently, the alpha-carbonyl backbone flexibility of the 8 kDa protein kinase inhibitor (PKI alpha) peptide of cAMP-dependent protein kinase (cAPK) free in solution and bound to cAPK was assessed by time-resolved fluorescence anisotropy. Specifically, three full-length, single-site PKI alpha mutants (V3C, S28C, and S59C) were prepared, and fluorescein iodoacetamide (FI) was selectively conjugated to the side chains of each substituted cysteine. The time-resolved anisotropy decay profiles of the labeled mutants were well fit to a model-free nonassociative biexponential equation. Free in solution, the three labeled proteins had very similar anisotropy decays arising primarily from local alpha-carbonyl backbone movements. Only a small fraction of the anisotropy decay was associated with slower, whole-body tumbling, confirming that PKI alpha is highly disordered at all three locations. Complexation of the mutants with the catalytic (C) subunit of cAPK decreased the rate of whole-body tumbling for all three mutants. The effects on the rapid decay processes, however, were dependent upon the site of conjugation. The anisotropy decay profiles of both FI-V3C- and FI-S28C-PKI alpha were associated with significantly reduced contributions from the fast decay processes, while that of FI-S59C-PKI alpha was largely unaffected by binding to the C-subunit. The results suggest that the cAPK-binding domain of PKI alpha extends from the its N-terminus to residues beyond Ser28 but does not include the segment around Ser59, which is still part of a highly flexible domain when bound to the C-subunit.

Electric giant resonances in 40Ca and 48Ca probed with electron and proton scattering coincidence experiments

Excitation and particle decay of electric giant resonances in 40Ca and 48Ca are studied with electron and proton beams. Recent results of a 48Ca(e,e′n) measurement performed at the S-DALINAC in Darmstadt with kinematics that selectively populate electric monopole, dipole and quadrupole excitations are presented. The extracted B(E1) strength distribution is in good agreement with photo nuclear data and the predictions of microscopic calculations. The summed B(E2+E0) strength distribution, however disagrees with the result of these calculations. The neutron emission of the giant dipole resonance in 48Ca shows a large fraction of direct decay to 47Ca hole states. In addition, isoscalar giant monopole resonance strength in 40Ca was extracted from (e,e′α 0) and (e,e′α 1) angular correlations. A study of the quadrupole strength in the α 0 decay channel of 40Ca with a (p,p′α) coincidence measurement reiterates the unsolved discrepancy between results from electromagnetic and hadronic probes.

Looking for exotic multiquark states in nonleptonic B decays

Recent data on inclusive B decays into charmonium states taken by the CLEO collaboration suggest that a sizeable fraction of the nonleptonic decays may consist of the $J/\psi \Lambda \overline p$ three body final state, corresponding to a distinct enhancement in the inclusive $J/\psi$ momentum distribution. The kinematical boundary of this structure corresponds to the case where the $J/\psi$ recoils nearly monoenergetically in the B rest system against a partner having mass of $\simeq$ 2 GeV. This may allow the observation of a $\Lambda-\overline p $ bound state near or just below threshold; i.e., strange baryonium, even if the production rate is small. Using a phase space approach to the B meson decay, we study the $J/\psi$ momentum distribution and the effect of baryonium formation. We also discuss the possible observation of pentaquarks and hadronically-bound $J/\psi$ by the observation of monoenergetic baryons in these decays.

Polystyrene local dynamics in dilute solution: Temperature and solvent dependence of C-D vector correlation function shape

Variable temperature 2H-NMR T 1 experiments were performed on backbone deuterated atactic polystyrene in four solvents at two Larmor frequencies. Temperature-frequency superposition, which is consistent with experimental results for many other polymers, cannot describe our data. This indicates that the shape of the correlation function for C-D vector reorientation is temperature dependent. A modified log X 2 distribution of relaxation times, i.e., a delta function plus a log X 2 distribution, was used to fit the experimental data. These fits are consistent with literature 13 C T 1 and NOE data. As polystyrene local dynamics slow down by a factor of 5, the FWHM of the log X 2 distribution increases from 0.8 to 1.1 decades. Solvent identity does not play a major role in determining the shape of the correlation function. The fraction of the correlation function decay caused by librational motion was determined to be 0.28. The quantity was compared for series of polymers and found to correlate with the size of the side group.

Alpha-particle and electron capture decay of 209Po

Gamma-ray and Kα X-ray emissions have been measured from a very pure 209Po source containing less than 0.13% 208Po activity and no detectable 210Po (≤ 2 × 10 −4%). The alpha-particle emission rate for this source has previously been determined. Data are presented that confirm alpha decay to the 205Pb excited level at 262.8 keV, with an alpha-particle emission probability (±standard uncertainty) of 0.00559±0.00008. The ratio of K-shell electron capture to total electron capture for the second forbidden unique electron capture decay to the 896.6 keV level in 209Bi was determined to be 0.594±0.018. The electron capture decay fraction was found to be 0.00454±0.00007, while the probabilities per decay for the 896.6, 262.8, and 260.5 keV gamma rays and the Bi Kα and Pb Kα X-rays were measured as 0.00445±0.00007, 0.00085±0.00002, 0.00254±0.00003, 0.00202±0.00005, and 0.00136±0.00005, respectively.

Inclusive decays of B mesons to charmonium.

We have used the CLEO-II detector at the Cornell Electron Storage Ringe (CESR) to study the inclusive production of charmonium mesons in a sample of 2.15 million {ital B{bar B}} events. We find inclusive branching fractions of (1.12{plus_minus}0.04{plus_minus}0.06)% for {ital B}{r_arrow}{ital J}/{psi}{ital X}, (0.34{plus_minus}0.04{plus_minus}0.03)% for {ital B}{r_arrow}{psi}{prime}{ital X}, and (0.40{plus_minus}0.06{plus_minus}0.04)% for {ital B}{r_arrow}{chi}{sub {ital c}1}{ital X}. We also find some evidence for the inclusive production of {chi}{sub {ital c}2}, and set an upper limit for the branching fraction of the inclusive decay {ital B}{r_arrow}{eta}{sub {ital c}}{ital X} of 0.9% at 90% confidence level. Momentum spectra for inclusive {ital J}/{psi}, {psi}{prime}, and {chi}{sub {ital c}1} production are presented. These measurements are compared to theoretical calculations.

A model-independent determination of the inclusive semileptonic decay fraction of B meson

Abstract With the ARGUS detector at the e+ e− storage ring DORIS II, we have determined decay fraction and electron momentum spectrum of the inclusive decay mode B → ev X. Using lepton tags from the second B meson in 209000 Γ(4S)→B decays, we could determine the momentum spectrum for all momenta Pe > 0.6 GeV/c. Including the small extrapolation to Pe > 0, we find the model-independent decay fraction Br(B→evX) = (9.6 ± 0.5 ± 0.4)%. Adding D meson tags, our result is (9.7 ± 0.5 ± 0.4)%.

Delayed isomeric state in 205Pb and its implications for 4πα liquid scintillation spectrometry of 209Po

Asays of 209Po by 4πα liquid scintillation (LS) measurements are confounded by an α-transition to a 2.3 keV ( J π = 1 2 − ) level in 205Pb which was previously unknown to be a delayed isomeric state. The level is believed to be populated by a substantial fraction of the total 209Po decay (∼80%), and presumably decays predominantly by internal conversion. The resulting conversion electrons from this delayed isomeric transition were identified in LS spectra. The lifetime is inferred to be at least several times 10 −5 s, although it may very well be substantially longer lived by orders of magnitude. The implications of these findings for routine measurements of 209Po by LS are discussed. Suggested experiments to precisely determine the lifetime of the state are also proposed.

Studies of the metastable decay of met-cars: The vanadium and niobium systems

The decay fractions and metastable decomposition channels were measured for V m C + n and Nb m C + n clusters using a reflectron time-of-flight mass spectrometer. These measurements for the V m C + n clusters reveal stable (8, 12) and (8, 13) met-car species. However, under the present experimental conditions, the Nb m C + n clusters display dominantly cubic structures, but the decay fraction and metastable decomposition measurements also show the presence of a stable (8, 12) species in the parent cluster spectrum. This evidence indicates that cubic structures and met-cars are being formed simultaneously for the niobium system.

The semileptonic decay fraction ofB-mesons in the light of interfering amplitudes

Consequences of the interference between spectator amplitudes for the lifetimes and semileptonic decay fractions of B^0 and B^+ mesons are discussed. Assuming duality and constructive interference between spectator amplitudes we are able to explain the low experimental value for the semileptonic decay fraction of $B$ mesons. Extracting these amplitudes from a fit to 11 exclusive hadronic B decay fractions we find a_1 = 1.05 +/- 0.03 +/- 0.10, a_2 =+0.227 +/ 0.012 +/- 0.022, an inclusive semileptonic decay fraction of (11.2 +/- 0.5 +/- 1.7), and a lifetime ratio tau(B^+) / tau(B^0) = 0.83 +/- 0.01 +/- 0.01.

A model-independent determination of the inclusive semileptonic decay fraction of B mesons

With the ARGUS detector at the e +e - storage ring DORIS II, we have determined decay fraction and electron momentum spectrum of the inclusive decay mode B → eνX. Usinng lepton tags from the second B meson. in 209 000 γ(4 S) → B B decays, we could determine the spectrum for all electron momenta p e > 0.6 GeV/ c . Including the small extrapolation to p e > 0, we find the model-independent decay fraction B(B → eνX) = (9.6 ± 0.5 ± 0.4)%. Adding D meson tags, our result is (9.7 ± 0.5 ± 0.4)%.

Kaons in flavour taggedB decays

Using the ARGUS detector at thee+e− storage ring DORIS II, flavour-dependent kaon production inB meson decays has been studied. Using the leptons as flavour tags, it has been possible to separately measure the multiplicities ofK+,K− andKs0 in inclusiveB decays and in semileptonicB decays. The kaon production in semileptonicB decays was further used to estimate the ratio of charmed decays over all decays, and thus also the fraction of charmlessB decays.

Measurements of Z 0 → heavy flavours at LEP

The LEP experiments have studied the decays of the Z 0 to heavy quarks by exploiting their semi-leptonic decays, characteristic decay topology and lifetime, and by identifying inclusive and exclusive production of heavy flavoured hadrons. The emphasis here is placed on the measurement of the fraction of hadronic decays containing b or c quark decays to leptons, for which the LEP average values are: Γ b b Γ had × B(b→1)=0.0239±0.0007±0.0007 Γ c c Γ had × B(c→1)=0.0161±0.0015±0.0014 where the first error is statistical and the second systematic. The average partial widths derived from these measurements are: Γ b b =355±9±10±18( BR)MeV Γ c c =292±29±18( BR)MeV where systematic errors are dominated by the uncertainty in the semi-leptonic branching ratio. These results are in good agreement with the standard model expectations Γ b b = 378 MeV and Γ c c = 297 MeV , but the experimental accuracy is at present insufficient to confront detailed predictions such as the variation with top quark mass.

Negative-pion trapping by a metastable state in liquid helium.

We have found a long-lived metastable state of stopped ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ in liquid helium by measuring the time spectra of two different delayed products: (i) protons emitted after ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ absorption by $^{4}\mathrm{He}$ nuclei and (ii) 70-MeV electrons originating from free ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{e}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\nu}}_{\mathit{e}}$\ifmmode\bar\else\textasciimacron\fi{} decay. The lifetime and fraction of delayed ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ absorption obtained by using the emitted protons are 7.26\ifmmode\pm\else\textpm\fi{}0.12 nsec and 1.66\ifmmode\pm\else\textpm\fi{}0.05%, respectively. The free-decay fraction of a pion in liquid helium was obtained to be 0.64\ifmmode\pm\else\textpm\fi{}0.03% from this result, which is consistent with the observed free-${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ decay fraction. These results imply that 2.30\ifmmode\pm\else\textpm\fi{}0.07% of stopped ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ are trapped in the metastable state which have an overall lifetime of 10.1\ifmmode\pm\else\textpm\fi{}0.2 nsec. The same experimental and analysis were performed for stopped ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ in liquid neon, where no evidence for trapping was found.

An unmixed 17 keV neutrino

We argue that the observation of the kink in the electron energy spectrum in β decay does not necessarily imply mixing amongst the neutrinos. We have constructed a model in which the kink occurs because the neutron can also β decay into an isosinglet neutrino (with a Dirac mass of 17 keV) via a new interaction mediated by spin zero, Q=− 1 3 leptoquarks with a mass of 100–1000 GeV. Our model can be tested by modest improvements in the measurement of the longitudinal polarisation of electrons in β decay and in the branching fraction of the pion decay to electron. Astrophysical and cosmological implications of this new interaction of neutrinos are also discussed.

A measurement of the inclusive semileptonic decay fraction of charmed hadrons

Using the ARGUS detector at the DORIS-II storage ring at DESY, we have measured the inclusive semileptonic branching ratio of charmed hadrons produced in e +e − annihilition at =10 GeV to be BR(c→ev eX)=(9.8±0.9± 0.5 0.6)% and BR(c→ μv μ X)=(8.6±1.7± 0.7 0.8)%.