Two-particle,two-hole Jπ=0+ states in 40Ca

Excited J^π=0⁺ states in ⁴⁰Ca have been identified by the observation of L=0 angular distributions in the ³⁸Ar(τ, n) ⁴⁰Ca reaction. Strong transitions are observed to the ground state, the known 2p–2h at 9.38 (T=1) and 11.98 MeV (T=2), and to states at 8.28 and 10.65 MeV. The strongest excited-state transition is to the 8.28 MeV state, which we identify as the 2p–2h T=0 state. The J^π=0⁺ state at 7.30 MeV which has been suggested as the 2p–2h T=0 state is not observed.     

Structure of 0+ states in 18O

Analysis of spectroscopic factors obtained in single-nucleon transfer reactions leading to and from ¹⁸O yields two different sets of wave functions for the first three O⁺ states. One set of wave functions is in agreement with ¹⁶O(t, p)¹⁸O data for the three states-the other set is not. The wave functions that agree with the experimental data have the majority of the $\text{(s}\text{1}\text{2}\text{)}{}^2$ strength in the third O⁺ state.     

Wave functions of 0+ states in 42Ca

Ratios of cross sections in ⁴¹Ca(d,p) and ³⁸Ar(⁶Li,d) leading to 0⁺ states of ⁴²Ca allow determination of the coefficients in wave functions of the type a(2p)+b(4p?2h) + c(6p?4h), and an independent evaluation of the intrinsic amplitude for (sd)²(fp)² and (fp)⁴ α transfer.     

Role of 2p-2h states in weak 0+−0− transitions in A = 16 nuclei

Muon-capture and β-decay rates for the transitions ¹⁶O(0⁺, ground) (a3) ¹⁶N(0^?, 120 keV) are calculated to second order in perturbation theory. With a one-boson-exchange residual interaction, reasonable agreement to the decay rates Λ_μ and Λ_β can be achieved, but only if meson-exchange corrections are incorporated in the transition operator. These corrections strongly influence the time-like part of the axial-vector current.     

Shell model study of 0+ states in 40Ca

Low-lying positive parity levels of calcium-40 are discussed in the framework of the shell model. An inert ³²S core is assumed, and $\text{Od}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{Of}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ are taken as active orbits. As effective interactions we assumed those used by Federman and Pittel. Effect of many-particle and many-hole configurations up to 8p–8h states are shown to be important even for the very low-lying 0⁺ states.     

Low-lying 0+ states 16O via parity-mixed hartree-fock calculations

A Hartree-Fock calculation with parity-mixed orbitals is used in an effort to describe the ground state and O⁺ excited state of ¹⁶O. Parity projection and orthogonality between the ground state and the excited state are imposed as constraints in the variational procedure. It is found that there exists a stable ground state with parity-mixed orbitals. However, the only non spurious excited state which orthogonal to the ground state does not contain parity-mixing.     

Structure of 0+ states of 28Si and particle-hole conjugation

Full sd-shell calculations for the 0⁺ states of ²⁸Si have been performed in the SU(3) basis so that the intrinsic deformation of the shell model states can be deduced by inspection. The shell model Hamiltonian is decomposed in a symmetric part H_S and an antisymmetric part H_A with respect to particle-hole conjugation. It is shown that the splitting of prolate and oblate states is due to the spin-orbit part of H_A. The different prediction for ²⁸Si obtained with Kuo and with Preedom-Wildenthal matrix elements can be attributed to the difference in a single parameter: the strength of the spin-orbit part of H_A.     

High-resolution study of E0 internal pair decay of excited 0+ states in 58,60,62Ni

The recently developed magnetic plus Si(Li)-Si(Li) sum-coincidence technique is employed to measure E0 internal-pair-formation (IPF) branching ratios of excited 0⁺ states in ^58,60,62Ni. The $\text{X(}\text{E}\text{0}\text{E}\text{2}\text{)}$ values are obtained for a new 0⁺₄ state in ⁶⁰Ni at 3588.0 keV, for the 0⁺₂ and 0⁺₃ states at 2942.3 keV and 3530.9 keV in ⁵⁸Ni, for the corresponding states at 2284.8 keV and 3318.3 keV in ⁶⁰Ni, and for the 0⁺₂ state in ⁶²Ni at 2048.4 keV. The results are combined with the available lifetimes of these states to extract the monopole strengths ?²(0⁺_i ? 0⁺₁). The results and the nature of the 0⁺ states are discussed.     

Electromagnetic decay of excited 0+ states in 64, 66, 68Zn

The E0 and E2 transitions depopulating the excited 0⁺ states in ^64,66,68Zn are investigated. Several methods of γ-ray, conversion-electron and internal-pair spectrometry are employed, including a new time measurement technique. A total of 5 E0 transitions are observed and the monopole strengths ρ²(0_i⁺ → 0_i⁺) for most of them are extracted. The results and the nature of the excited 0⁺ states are discussed in terms of several nuclear models.     

0+ states and E0 and E2 transition rates in even Sn nuclei

0⁺ states and their depopulating E0 and E2 transitions have been studied in ^112–124Sn. Several methods of γ-ray and electron spectrometry have been employed, including special coincidence techniques for lifetime, conversion electron and double Coulomb excitation measurements. For ^114–118Sn the E2 transition probabilities from the first excited 0⁺states (0₂⁺) are about 20 W.u., which is compatible with a vibrational two-phonon character. Also the E0 transition probabilities from these states are within a factor of two from the vibrational values. For the second excited 0⁺ states (0₃⁺) the corresponding E2 and E0 transition probabilities are considerably smaller. A total of 12 E0 transitions have been observed. The 0₃⁺ → 0₂⁺ transition is observed in ^114–120Sn and has in ¹¹⁶Sn a reduced transition probability 1–2 orders of magnitude larger than those of the groundstate E0 transitions, which indicates that the 0₃⁺ and 0₂⁺ states are strong mixtures of components with different 〈r²〉. The 0⁺ states in ¹¹⁶Sn are discussed as possible rotational band heads associated with a deformation β₂ ≈ 0.2. The Coulomb excitation cross section of the 0₂⁺ state is found to be sensitive to an interference term including matrix elements with the 2₂⁺ state. The relative sign of this term has been determined.     

Absolute frequency measurements of the 0002-0000, 2001-0000, and 1201-0000 bands of N2O by heterodyne spectroscopy

The absolute frequencies of 39 lines in the 00⁰2-00⁰0, 20⁰1-00⁰0, and 12⁰1-00⁰0 bands of N₂O in the range 4300–4800 cm^?1 have been measured by heterodyne frequency techniques. The lines were each measured in Doppler-limited absorption, with a color-center laser as a tunable probe of the N₂O and two stabilized CO₂ lasers as reference frequencies. New rovibrational constants have been fitted to these measurements. Tables of calculated transition frequencies are given, with estimated absolute uncertainties as small as 10^?4 cm^?1. The pressure shifts of four lines have been measured, and the values fall within the range of 0 to ?2 MHz/kPa (0 to ?0.2 MHz/Torr).     

The isospin forbidden 1− → 0+ transition in 40Ca

The isospin forbidden transition 1^? (6.95 MeV) → 0⁺ (g.s.) in ⁴⁰Ca is explained within a model that mixes isospin through single-particle energy differences and the two-body Coulomb interaction. There is no need to introduce an isospin non-conserving part of the nucleon-nucleon interaction to explain this anomalously fast transition.     

On the nature of 0+ mesons

It is shown that the I=0 s-wave ππ scattering amplitude near KK? threshold can be parametrized in terms of a wide resonance, that is, the S¹ may have a large partial width into ππ. All the 0⁺ mesons may have large widthsf.     

Wave functions of 0+ levels in 38Ca

A simple model of the first three 0⁺ levels in ³⁸Ca gives a good account of the excitation energies and (³He, n) cross sections. The hamiltonian derived is reasonable and the mixing is similar to that needed for other nearby nuclei.     

Strong sequential transfer processes in 0+ → 0+ (p,t) reactions on Pb isotopes

A marked difference of experimental analyzing powers $\text{A (θ)}\text{for}{}^{208}\text{Pb}\text{(}\text{p}\text{,}\text{t}\text{)}{}^{206}\text{Pb}\text{(0}{}_{\mathrm{<mtext>g</mtext>}}{}^{\mathrm{+}}\text{and}\text{0}{}_2{}^{\mathrm{+}}\text{)}$ reaction is explained by considering sequential transfer as wesses as well as the one-step process. The calculated A(0θ) for the 0₂⁺ state is very sensitive to the wave functions employed. An enhancement of the cross sections for the ground-state transitions of three Pb isotopes is found to be due to sequential transfer processes.     

Search for direct CP violating charge asymmetries in K±→π±π+π- and K±→π±π0π0 decays

A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes A_g=(g⁺-g^-)/(g⁺+g^-) in K^±→π^±π⁺π^- and K^±→π^±π⁰π⁰ decays by the NA48/2 experiment at CERN SPS is presented. A new technique of asymmetry measurement involving simultaneous K⁺ and K^- beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be A^c _g=(-1.5±2.2)×10^-4 with 3.11×10⁹K^±→π^±π⁺π^- decays, and Aⁿ _g=(1.8±1.8)×10^-4 with 9.13×10⁷K^±→π^±π⁰π⁰ decays. The precision of the results is limited mainly by the size of the data sample.     

K0πand K*0Σ+ photoproduction off the proton

The exclusive reactions γp → K ^*0Σ⁺(1189) and γp → K ⁰π⁰Σ⁺(1189) , leading to the p 4π⁰ final state, have been measured with a tagged photon beam for incident energies from threshold up to 2.5GeV. The experiment has been performed at the tagged photon facility of the ELSA accelerator (Bonn). The Crystal Barrel and TAPS detectors were combined to a photon detector system of almost 4π geometrical acceptance. Differential and total cross-sections are reported. At energies close to the threshold, a flat angular distribution has been observed for the reaction γp → K ⁰π⁰Σ⁺ suggesting dominant s -channel production. Σ^*(1385) and higher-lying hyperon states have been observed. An enhancement in the forward direction in the angular distributions of the reaction γp → K ^*0Σ⁺ indicates a t -channel exchange contribution to the reaction mechanism. The experimental data are in reasonable agreement with recent theoretical predictions.     

Search for the exotic Θ+ resonance in the NOMAD experiment

A search for exotic Θ⁺ baryon via Θ⁺→p+K⁰ _S decay mode in the NOMAD ν_μN data is reported. The special background generation procedure was developed. The proton identification criteria are tuned to maximize the sensitivity to the Θ⁺ signal as a function of x_F which allows to study the Θ⁺ production mechanism. We do not observe any evidence for the Θ⁺ state in the NOMAD data. We provide an upper limit on Θ⁺ production rate at 90% CL as 2.13×10^-3 per neutrino interaction. PACS 13.15.+g; 13.60.Le; 13.87.Fh; 14.40.Ev