Spherically confined two-electron atoms immersed in Debye plasma

The effect of spatial confinement in the presence of plasma environment on the dipole allowed transition properties for the first five helium-like atoms (He through C⁴⁺) is studied. The Debye screening describes the effect of plasma. Additionally, the effect of a spatial confinement (as, for example, it is in the case of atoms surrounded by liquid helium) is described by locating the atom in the center of a spherical box. Time-dependent variation perturbation theory is applied to estimate the orbital energies, polarizabilities, transition energies, oscillator strengths, and transition probabilities. The effect of spatial confinement in the plasma environment shows interesting features. The decrease of the radius of confinement exerts pressure within the system and produces instability in the energy values ultimately ionizing the system. The ionization pressures at different plasma screenings are estimated. The ionization pressure at zero Debye screening for helium agrees with existing data.     

The influence of Debye plasma on the ground state energies of exotic systems

The effect of plasma environment on the ground state energies of exotic systems ppμ, ddμ and ttμ has been analyzed within a generalized three-body formalism using multi-term correlated basis sets. The Debye screening model of the plasma has been adopted for such a study. The binding energies of p with pμ, d with dμ and t with tμ have been estimated for a range of values of the Debye screening parameters. The systems tend toward instability for increased screening. The effect of particle correlation has been investigated in detail and is found to play an important role for the stability in these systems.     

Lepton and pion pair production in γγ collisions measured near the threshold at DCI

This paper reports a complete analysis of data taken at DCI to measure lepton and pion pair production close to the threshold in two-photon processes: e⁺e⁻→e⁺e⁻(e⁺e⁻, μ⁺μ⁻,π⁺π⁻). Preliminary results have been previously published including one-half of the total statistics. Final results presented here are in good agreement with QED for lepton pair production. The measured cross section for pion pair production is twice as large as that expected from Born terms only — a two standard deviation effect.     

Exotic clustering in Ce and Nd isotopes

We propose exotic binary cluster models for the intermediate mass nuclei ^146,148,150Ce and ^{148,150,152,154}Nd. The optimum choice of cluster and core is determined by joint consideration of the penetrability for exotic cluster emission, the deviations of cluster and core binding energies from underlying liquid drop values and the Q-values for breakup. It is noticeable that the core neutron number selected in this way is at or near the N = 82 shell closure. We use a standard form of the cluster-core potential to calculate the energies and wave functions of states in the ground 0⁺, 2⁺, 4⁺, … and lowest lying negative parity 1⁻, 3⁻, 5⁻, … bands. The theoretical spectra and electromagnetic properties are compared with measurements, and their general trends are reproduced satisfactorily.     

Fourth-generation signatures in D0-;D̄0 mixing and rare D decays

We study the effects of a fourth generation on D⁰-D̄⁰ mixing and the rare decays D⁰→μ⁺μ⁻, D→ℓ⁺ℓ ⁻X (where X is nonstrange), D→πℓ⁺ℓ⁻ and D→ϱγ (orωγ). D⁰-D̄⁰ mixing can be as large as the experimental limit of 0.5%. The fourth generation can enhance the branching ratios for the rare decays by several orders of magnitude: it can be as large as 10⁻⁹ for the decays D⁰→μ⁺μ⁻, D→ℓ⁺ℓ⁻X and D→πℓ⁺ℓ⁻. The long-distance contribution to the radiative decays is estimated to be ∼ 10⁻⁸ and is shown to be dominant in the three-generation model. The fourth generation can bring this branching ratio up to ∼ 10⁻⁶.     

A search for πNN bound systems

The d(π⁺, π⁻)T⁺⁺⁺ and the d(π⁻, π⁺) T⁻ reactions were studied at an incident pion energy of 260 MeV. Outgoing negative pions were detected at 35° and 55° in the first reaction, and the positive pions at 45° in the second. Indications for structures corresponding to a (π⁺pp) system with a mass of 2003.0±1.0 MeV and a (π⁻nn) system with a mass of 200.1±1.5 MeV were observed with marginal statistical significance. Upper limits for the cross sections are obtained.     

Search for rare φ decays in π+π−γ final state

A search for φ radiative decays has been performed using a data sample of about 2.0 million φ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From the selected e⁺e⁻→π⁺π⁻γ events the following results were obtained:B(φ→f₀(980)γ)<1×10⁻⁴ for destructive andB(φ→f₀(980)γ)<7×10⁻⁴ for constructive interference with the Bremsstrahlung process respectively,B(φ→γ→π⁺π⁻γ)<3×10⁻⁵ for E_γ>20 MeV,B(φ→ργ)<7×10⁻⁴. From the selected e⁺e⁻→μ⁺μ⁻γ eventsB(φ→μ⁺μ⁻γ)=(2.3±1.0)×10⁻⁵ has been obtained for E_γ>20 MeV. The upper limit on the P,CP-violating decay η→π⁺π⁻ has also been placed:B(η→π⁺π⁻)<9×10⁻⁴. All upper limits are at 90% C.L.     

Electroexcitation of 58ni: A sutdy of the fragmentation of the magnetic dipole strength

The distribution of the magnetic dipole strength in ⁵⁸Ni in the excitation energy range E_x = 6–15 MeV has been studied with high resolution inelastic electron scattering. Altogether 47 J^π = 1⁺ states have been determined. The summed Ml strength is Σ B(M1)↑ = 16.9_−3.3^+4.6μN². A shell model calculation including 1p-1h excitations is used to discuss the fragmentation, the summed strength and the relative importance of spin versus orbital magnetism. By comparison with inelastic proton scattering and charge exchange reactions the isospin structure of the M l strength distribution is analysed.     

Electroweak corrections to muon pair production in electron-positron annihilation at high energy

The lowest-order radiative corrections to the reaction e⁺ + e⁻ → μ⁺ + μ⁻ are analyzed in the standard SU(2) × U(1) electroweak theory. The virtual corrections are calculated in the on-shell renormalization scheme. The masses of the recently discovered Z-boson and W-boson are used to fix the weak coupling constants. The decay width of the Z-boson is also taken into account. By including the cross section of hard photon emission, various kinds of distribution are obtained both analytically and numerically. The magnitude of the effective axial vector coupling is confirmed to be quite different from that previously taken in the calculations within QED. This difference, which is due to the genuine electroweak corrections, reaches about 10% in angular distribution at the energy around the Z-boson mass, even if the reasonable effect of a hard photon is included.     

A study of K−π+ scattering in the reaction K−p→K−π+n at 11 GeV/c

Results from a high statistics study of the reaction K⁻p→K⁻π⁺n are presented. These results are based on data obtained with an 11 GeV/c beam using the LASS spectrometer at SLAC. The mass dependence of the spherical harmonic moments provides clear evidence for the production of the complete leading orbitally excited K¹ series up through J^P = 5⁻. These moments are used to perform an energy independent partial wave analysis of the K⁻π⁺ system from threshold to 2.6 GeV/c² using a t-dependent parametrization of the production amplitudes. The amplitudes corroborate the leading K¹(892), K₂¹(1430), K₃¹(1780), K₄¹(2060), and K₅¹(2380) resonances observed directly in the moments, and also provide new evidence for underlying states. The 0⁺ amplitude contains the K₀¹(1350) and a second 0⁺K¹(1950) at higher mass. The 1⁻K¹(1790) seen earlier two and three-body analyses is confirmed, and evidence is provided for suppressed K⁻π⁺ decay mode of a second 1⁻ state, the K¹(1410), which has been seen in earlier three-body analyses.     

Probing the violation of equivalence principle at a muon storage ring via neutrino oscillation

We examine the possible tests of violation of the gravitational equivalence principle (VEP) at a muon storage ring via neutrino oscillation experiments. If the gravitational interactions of the neutrinos are not diagonal in the flavour basis and the gravitational interaction eigenstates have different couplings to the gravitational field, this leads to the neutrino oscillation. If one starts with μ⁺ beam then appearance of τ^±, e⁺ and μ⁻ in the final state are the signals for neutrino oscillation. We have estimated the number of μ⁻ events in this scenario in ν_μ–N deep inelastic scattering. Final state lepton energy distribution can be used to distinguish the VEP scenario from the others. A large area of VEP parameter space can be explored at a future muon storage ring facility with moderate beam energy.     

Investigation of the reaction e+e− → ηπ+π− in the energy range up to 1.4 GeV

The reaction e⁺e⁻ → ηπ⁺π⁻ has been studied with the Neutral Detector in the CM energy range 1.05–1.40 GeV at VEPP-2M. At the maximum energy the cross section exceeds the prediction of the vector dominance with one ϱ(770). The following upper limits for the electron width times branching ratio into ηπ⁺π⁻ have been obtained for a resonance with a mass of 1.28 GeV and width of 0.08 GeV observed with the Omega-spectrometer at CERN: Λ_ee·B_ηππ < 9 eV, and for a ϱ′(1250) with a mass of 1.26 GeV and width of 0.125 GeV: Λ_ee·B_ηππ < 14 eV at 90% confidence level.     

Limits on a lepton-number violating process from e+e− collisions

If a new hypothetical particle induces a lepton-number violating process, it could also affect the reactions e⁺e⁻→μ⁺μ⁻ and e⁺e⁻→τ⁺τ⁻ through the t-channel exchange of the particle. A fit of the cross sections and forward-backward asymmetries measured by experiments at PEP and PETRA yields the 90% confidence level limits on the coupling of the partile: G_eμ < 0.119G_F and G_eτ < 0.085G_F, where G_F is the Fermi coupling constant. These limits exclude certain regions of couplings allowed by other lepton-number violating searches.     

Evidence for A JPC=4++ KK state at ∼2.2 GeV/c2 from K−p interactions at 11 GeV/c

Data from the reaction K⁻p→K⁻K⁺Λ at 11 GeV/c have been obtained in the LASS spectrometer at SLAC. A spherical harmonic moments analysis of the K⁻K⁺ system provides evidence for a rather narrow J^PC=4⁺⁺ state at ∼2.2 GeV/c². Relevant data from the reaction K⁻p→K⁰_sK⁰_sΛ in the present experiment are shown also, and comparisons made to results from MARK III and GAMS in this mass region.     

Production and fragmentation of the D10 meson in e+e− annihilations at √s=29 GeV

Neutral D¹ meson production in e⁺e⁻ annihilation at √s=29 GeV has been studied using the high resolution spectrometer. The decay of D¹⁰ into D⁰γ, where the D⁰ decays into K^−π+, has been observed. The production cross section in units of the point cross section is 0.63±0.22 for fractional energy Z⩾0.5. The fragmentation function is compared with that of the D¹⁺ meson measured in the same experiment.     

Observation of the leading K1 L-excitation series from JP = 1− through 5− in the reaction K− p → K− π+ n AT 11 GeV/c

High statistics data for the reaction K⁻p→K⁻π⁺n at 11 GeV/c have been obtained in the LASS spectrometer at SLAC. A spherical harmonic moments analysis provides clear evidence for the production of the complete leading orbitally excited K¹ series up through J^P = 5⁻. New measurements are made of the masses and widths of the 1⁻K¹(892), 2⁺K¹(1430 ), 3⁻ K¹(1780), and 4⁺ K¹(2060), and evidence is presented for the production of a new K¹ state at 2382 MeV/c² with spin-parity 5⁻.     

Indirect plasma inactivation by a low temperature atmospheric pressure plasma (LTAPP) system

The aim of this paper is to evaluate the inactivation effect of indirect low temperature plasma exposure at atmospheric pressure produced by the original Low Temperature Atmospheric Pressure Plasma (LTAPP) system. In this system, the low temperature plasma is generated using a high voltage power supply in oxygen at atmospheric pressure. The obtained survivor curves for Escherichia coli (G⁻), Bacillus subtilis (G⁺), Staphylococcus aureus (G⁺), Candida albicans (Yeast), and Saccharomyces cerevisiae (Yeast) showed that the LTAPP system could inactivate them. The optical microscope images of B. subtilis and S. cerevisiae treated have confirmed the inactivation effect of the LTAPP system.     

A search for decays of heavy neutrinos in the mass range 0.5–2.8 GeV

A search for decays of heavy neutrinos was conducted by the CHARM Collaboration in a prompt neutrino beam produced by dumping 400 GeV protons in a Cu target, and in the CERN wide-band neutrino beam produced by 400 GeV primary protons. No candidate event was found. In the beam-dump experiment heavy neutrinos have been assumed to be produced by mixing in charmed D meson decays. Neutrinos decaying into e⁺e⁻v_e, μ⁺e⁻v_μ, and μ⁺μ⁻v_μ were searched for. Limits of |U_ei|², |U_μi|² < 10⁻⁷ were obtained for neutrino masses around 1.5 GeV. In the wide-band experiment heavy neutrinos were assumed to be produced by neutral-current neutrino interactions in the CHARM calorimeter. Here a search was made for neutrinos decaying into a μ and hadrons. This experiment is sensitive to decays of neutrinos with mass in the range 0.5–2.8 GeV with limits of |U_μi|² < 3 × 10⁻⁴ for masses around 2.5 GeV. These measurements extend our previous results in the mass range 10–400 MeV.     

Time-dependent perturbation calculations for transition properties of two-electron atoms under Debye plasma

Systematic investigation have been performed for the dynamic polarizabilities, energy levels, oscillator strengths and transition probabilities for the first few members of helium isoelectronic series He, Li⁺,Be²⁺,B³⁺ and C⁴⁺ embedded in the Debye plasma. The effect of plasma is described by introducing an exponential screening (the Debye screening) to the nuclear Coulomb potential. Systematic trend is observed for all the properties under study with respect to increased screening. The ionization potential decreases with an increased screening and the number of bound excited states supported by the Debye screened potential is finite.     

Search for exotic decay modes of the ϒ(1S)

A search for two exotic decay modes of the ϒ(1S) meson has been made using the ARGUS detector at the e⁺e⁻ storage ring DORIS II at DESY. The first was ϒ(1S) decays into weakly interacting particles, for which an upper limit of 2.3% at the 90% CL on the branching ratio is found. The second mode was ϒ(1S)→γa, where a is a neutral particle with mass less than 1.5GeV/c², that either decays inside the detector or is sufficiently long-lived to escape detection. For short-lived particles a decaying into an e⁺e⁻ pair, upper limits on the BR(ϒ(1S)→γa) of 3.1 × 10⁻ at the 90% CL are found. The upper limit without restriction on the lifetime of a is found to be 1.3 × 10⁻³. Limits for other decay modes are also given.