Lifetime measurements of levels in 34Ar: Isoscalar and isovector matrix elements for E2 analogue transitions

Mean lifetimes have been measured for the low-lying levels in ³⁴Ar(T_z = ? 1) excited by the bombardment of ³He-implanted Au targets with a beam of 80 MeV ³²S. The lifetimes determined by fitting Doppler-broadened γ-ray lineshapes are as follows (E_x in keV, τ in fs): 2091, 460 ± 60; 3288, 280 ± 50; 3871, > 270 and 4128, 1301⁺¹⁷⁰_?130. The resulting transition matrix elements for the 2⁺₁ → 0⁺₁ and 2⁺₂ → 0⁺₁ transitions are compared with those for the analogue transitions in ³⁴S (T_z = + 1) and ³⁴Cl(T_z = 0) to determine the isoscalar and isovector components. The component values are compared with theoretical calculations and with values of the ratio of neutron to proton matrix elements determined by inelastic scattering with strongly interacting probes.     

Excited states of 10B from the 6Li(α, γ) and 9Be(p, γ) reactions

Excitation functions for the (α, γ) and (p, γ) reactions leading to ¹⁰B have been measured at θ = 0° in the energy range from E_x = 6.7 to 7.6 MeV. Two resonances corresponding to levels at 6.88 and 7.44 MeV are observed. Branching ratios extracted from γ-ray spectra are the same in both reactions for the 6.88 MeV (1^?, T = 0 + 1) level, but different at 7.44 MeV. The T = 0 + 1 level at 7.44 MeV (Γ = 90±10keV) is assigned 2^? or 2⁺ from its strong branch to the 3⁺ ground state. We find no evidence for a second isospin mixed 1^? state.     

Analysis of the K S K S system from the reaction π − p → K S K S n at 40 GeV

On the basis of experimental data from the 6-m spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow), an amplitude analysis of 40 553 events of the reaction π ^? p → K _S K _S n induced by a negatively charged pion of energy 40 GeV is performed over a broad momentumtransfer range by using a new procedure. The results for |t| > 0.1 GeV² are obtained for the first time. In particular, resonances of mass 1700 and 1900 MeV and width 120 MeV are discovered in the D ₊ wave (there were no such resonances for |t| < 0.1 GeV²). In the region of low momentum transfers, the S wave exhibits a structure that lies in the mass region around 1370 MeV and which requires three resonances for its explanation. Two of these (that of mass 1234 ± 6 MeV and width 47 ± 33 MeV and that of mass 1478 ± 6 MeV and width 119 ± 10 MeV) were found in the studies of A. Etkin et al. [Phys. Rev. D 25, 2446 (1982)] and O.N. Baloshin et al. {Yad. Fiz. 43, 1487 (1986) [Phys. At. Nucl. 43, 959 (1986)]}. The third has a mass of 1389 ± 9 MeV and a width of 30 ± 24 MeV. At high momentum transfers, the S wave is found to feature resonances that have the following parameters: M = 1328 ± 8 MeV and Γ = 237 ± 20 MeV, M = 1440 ± 6 MeV and Γ = 121 ± 15 MeV, and M = 1776 ± 15 MeV and Γ = 250 ± 30 MeV. For the D ₀ wave, it is found that, in addition to the well-known resonances f ₂, a ₂, and f′ ₂, there appear the following resonances in this wave: a resonance of mass 2005 ± 12 MeV and width 209 ± 32 MeV and a resonance of mass 2270 ± 12 MeV and width 90 ± 29 MeV at low |t| and a resonance of mass 1659 ± 6 and width 152 ± 18 and a resonance of mass 2200 ± 13 MeV and width 91 ± 62 MeV at high |t|.     

First observation ofΩ * resonances

In a experiment at the CERN SPS charged hyperon beam using incident Ξ^?, we have obtained evidence for the production of two Ω^* resonances decaying into Ξ^?π⁺ K ^?, with the following parameters:M ₁=2251±12,Γ ₁=48±20 MeV/c², 78 ±23 events, andM ₂=2284±12,Γ ₂=26±23 MeV/c² 45±10 events. The first state is also observed as a 4.2σ effect in a subsample which contains an additionalK ⁺ orK ⁰ in the final state. Production cross sections and branching ratios to Ξ^* K ^? and Ξ^? K ^* are presented.     

ESR study of vanadyl ion in tripotassium citrate

ESR spectra of VO²⁺ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 2.001 ± 0.001, g_y = 1.997 ± 0.001, g_z = 1.945 ± 0.001, A_x = (49.0 ± 1) × 10⁻⁴ cm⁻¹, A_y = (66.8 ± 1) × 10⁻⁴ cm⁻¹ and A_z = (168.4 ± 1) × 10⁻⁴ cm⁻¹. The covalency and Fermi contact terms are evaluated and compared with those of other lattices.     

Measurement of the D0, D+ and Ds+ meson lifetimes at √s = 10.58 GeV

We have measured the lifetimes of the D⁰, D⁺ and D_s⁺ mesons with data from the CLEO detector. We find τ_D⁰ = (5.0 ± 0.7 ± 0.4) × 10⁻¹³s, τ_D⁺ = (11.4 ± 1.6 ± 0.7) × 10⁻¹³s and τ_Ds⁺ = (4.7 ± 2.2 ± 0.5) × 10⁻¹³s, giving lifetime ratios τ_D⁺/τ_D⁰ = 2.3 ± 0.5 and τ_Ds⁺/τ_D⁰ = 0.9 ± 0.5.     

The structure ofT=1 levels inA=14 nuclei

States in¹⁴C, populated via the¹¹B(α, p) reaction at 14 MeV bombarding energy, were investigated with the Doppler Shift Attenuation Method (DSAM). The analysis ofpγ coincidence spectra taken in a Ge(Li) detector at 0? and 120? with the particle detector near 0? with respect to the beam direction yielded the following lifetimes and lifetime limits for the states at 6.09, 6.59, 7.01 and 7.34 MeV, respectively, <20 fs, <1,200 fs, <7 fs and 160±60 fs. Shell model calculations using the MSDI and an empirical interaction fitted to nuclear states in 1p and 2s 1d shell nuclei, are shown to account very well for the experimental levels andγ-transition rates of 5 different multipolarities. The structure of the (J ^*,T)=(2⁺, 1) levels is discussed in the light of the experimentally observed T_z-dependence of the 2⁺, 1→0⁺, 1E2 matrix elements.     

The quadrupole moment of 26Mg as a test of shell-model interactions

The static quadrupole moment Q_21⁺, and the B(E2; 0₁⁺ → 2⁺₁) value of the first excited state of²⁶Mg have been measured using the reorientation effect in Coulomb excitation of ²⁶Mg projectiles. It is found that Q_21⁺ = ?13.6±3.0 (?9.5±3.0) e ·fm² and B(E2; 0⁺₁ → 2⁺₁) = 322±16 (328±16) e² ·fm⁴ for constructive (destructive) interference from higher states. The result for Q₂ clearly differentiates among several alternative effective interactions which have been used in shell-model calculations.     

ESR study of vanadyl ion in trisodium citrate pentahydrate

ESR study of VO²⁺ doped trisodium citrate pentahydrate is undertaken at room temperature. The observed spectra are correlated with the available crystal structure data and are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 1.998 ± 0.001, g_y = 1.992 ± 0.001, g_z = 1.934 ± 0.001, A_x = (70.0 ± 1) × 10^-4cm^-1, A_y = (66.6 ± 1) × 10^-4cm^-1 and A_z = (175.4 ± 1) × 10^-4cm^-1. The covalency and Fermi contact parameters are evaluated and compared with those of VO²⁺ in other lattices.     

Image potential eigenstates and resonances on the (110) surfaces of noble metals: Energies and lifetimes

The energies and lifetimes of the image potential resonances at the ? point on the Cu(110), Ag(110), and Au(110) surfaces are studied, and the energies of the image potential states on the Pd(110) surface are analyzed. It is shown that every quantum number n corresponds to a pair of image potential states (resonances) n ⁺ and n ^? at the ? point. The average energy of a pair of eigenstates (resonances) at n ≥ 2 is well described by the formula ē _n = (E _n+ + E _n?) = E ₀ ? (0.85 eV)/(n + δ)², where δ is the quantum defect, E ₀ = (1/2m _e )(?π/a)², and a is the lattice parameter. The splitting energy of a pair of eigenstates (resonances) obeys the law ΔE _n = E _n+ — E _n? ∝ n ^?3. The lifetimes τ _n± of image potential resonances are proportional to n ³.     

Spectral resonances which become eigenvalues

The stationary Schrödinger equation is ? _x ² φ + λV(x)φ=zφ for φ∈?²(R ⁺,dx). If the potential is bounded below, singular only atx=0, negative on some compact interval and behaves likeV(x)～1/x ^μ asx→∞ with 2≧μ>0, then the system admits shape resonances which continuously become eigenvalues as λ increases. Here λ>0 and for μ=2 a sufficiently large λ is required. Exponential bounds are obtained on Im(z) as λ approaches a threshold. The group velocity near threshold is also estimated.     

Inclusive φ-meson production in 93 and 63 GeV hadron interactions

The inclusive reactions h+p→φ+X, (h=π^±,,K^±,p^±), are studied for 0?x_F?0.3 and p⊥ ? 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp_⊥² anddσ/dx_F are presented and are compared with predictions of the naive parton model.     

Measurement of the branching ratios for Kμ2+, Kπ2+, Ke3+ and Ke3+ decays using a magnetic spectrometer with streamer chambers

The momenta of ～30 000 charged particles from K⁺ decays were measured using a magnetic spectrometer with streamer chambers. The ratio R = Γ(K_π2⁺)/Γ(K_μ2⁺) = 0.3355 ± 0.0057 was obtained. Our values for the branching ratios are: (63.18±0.43)% for K_μ2⁺, (21.18±0.33)% for K_π2⁺, (3.33±0.51)% for K_μ3⁺, (4.99±0.54)% for K_e3⁺.     

A Monte Carlo method for quantum spins using boson world lines

A new Monte Carlo method is described for quantum (s= 1/2) spins which maps the spin model onto a model of hard-core bosons. The Hamiltonian is then broken up into kinetic and potential parts and the Trotter formula used to simulate the Bose system. The power of this mapping comes from the fact that, by letting the system evolve through unphysical spin states between imaginary time slices, the needed matrix elements have simple expressions. Specifically, for quantum Hamiltonians $$H = - \sum\limits_{i,j} {J_{i,j} (S_i^x S_j^x + S_i^y S_j^y ) + H_1 } $$ withH ₁ diagonal in thez components of the spins, we map the spins onto boson operators usingS ⁺=Ssux+iS^y→ψ ^?,S ^?=S^x?iS^y→ψ, andS ^z →n?1/2, withn=ψ ^?ψ Unfortunately, the mapping is not quite exact since one may create an unlimited number of bosons on any site while there are only two spin states per site. A large number of analytic calculations have been performed successfully by suppressing the unphysical statesn > 1 either energetically, as in ferromagnetic spin-wave calculations, or formally, as in Holstein-Primakoff or Dyson-Maleev transformations. In numerical simulations, however, one may do something much more simple; a termHC may be introduced into the Hamiltonian which projects out unphysical states. Formally,HC is zero for allowed states but infinite otherwise; alternatively,P _HC =exp(?? · HC) projects out states for any? > 0, giving unity for physical states but zero for unphysical ones. In practice, the analytic form ofHC is of no concern since it may be “hard-wired” into the algorithm to allow only hard-core states. The Hamiltonian becomes $$\begin{gathered} H = - \frac{1}{2}\sum\limits_{i,j} {J_{i,j} (S_i^ + S_j^ - + S_i^ - S_j^ + ) + H_I } \hfill \\ \to - \sum\limits_{< i,j > } {t_{i,j} } (\psi _i^\dag \psi _j + \psi _i^\dag \psi _i ) + H_I + HC \hfill \\ = T + H_I + HC \hfill \\ \end{gathered} $$ where the \(t_{i,j} = \tfrac{1}{2}J_{i,j} \) are the hopping coefficients for the bosons. The Trotter formula may now be used to approximate matrix elements:e ^-β·H =(e ^-Δτ·H ) ^L , whereβ=L·Δτ ande ^-Δτ·H ≈e ^-Δτ·T e ^-Δτ·HI e ^-Δτ·HC . Since we will use an occupation-number representation,H _I , will be diagonal and easily exponentiated. The hard-core projection operatorP _HC , again, will act only through the Monte Carlo moves which prohibit unphysical states. Only the exponential of the kinetic term remains to be evaluated. The factor exp(?Δτ · T) evolves the bosons between time slices as indistinguishable, free particles-without concern for physical/unphysical states nor for interactions among the particles—and so is easily expressed as a sum of products of single-particle propagators, as developed in any elementary quantum-mechanics text. The final picture, then, is one in which the indistinguishable particles evolve through imaginary time as though they are free, with interactions and the physical-state projector operating only everyΔτ. Sampling over permutations of world lines and performing the calculation on a lattice produces a relatively fast algorithm. The simulation generates configurations which are described byL lattice configurations on the various imaginary-time slices as well as the permutations that assign world lines from bosoms on one time slice to those on the next. Monte Carlo moves must both wiggle world lines around as well as reassign them. Any operator which is diagonal in the occupation-number representation may be measured in this simulation, even if it is a product of operators at different times. In addition, any operator, or product of such operators at different time slices, that conserves the boson number at each time slice can be measured. The resulting set of observables includes the energy, specific heat, and the parallel and transverse magnetizations and susceptibilities. To test the breakup, particularly the validiy of separating outHC with its infinite matrix elements, exact numerical calculations were carried out for small systems. It was found that in measuring the average value of an operatorA which has some nonzero matrix elements between physical and unphysical states, a dramatic improvement in convergence results if one projects out these elements-that is, the dependence of the estimator 〈P _HC ·A·P_HC〉 on the breakup parameterΔτ is much smaller than that for 〈A〉. To test the breakup further, we have studied spin-1/2 rings using Monte Carlo simulation, measuring both the energy and structure factor on 30-site rings for the XY model. The algorithm was also used to perform a Monte Carlo simulation of the quantum XY model in two dimensions on up to 15×16-site lattices. The specific-heat peak height saturates quickly with lattice size and is consistent with the value ofC _max=0.65 from previous extrapolations of exact results on small lattices. As a rough comparison of running times, this algorithm produced data of similar quality as a checkerboard decomposition in one-tenth of the time.     

Infrared diode-laser spectrum of the CH3CN ν2 band: Analysis of local resonances with ν6±1 + 2ν8±2, ν4 + ν7±1 + ν8±1, ν4 + ν6±1, ν4 + ν7±1, and 2ν70 + ν8±1 states

Fifty-one sections of infrared diode-laser spectra of acetonitrile have been measured in the region from 2283.5 to 2235.7 cm^?1. About 450 transitions belonging to the ν₂ band have been assigned for K ≦ 7 and J ≦ 44. Anomalies found in the rotational structure have been proven to be due to five local resonances. Observed transition frequencies have been fitted by a least-squares method to a model which includes Fermi-type resonances (Δk = 0, Δ? = ± 3n) with ν₆^±1 + 2ν₈^±2 and ν₄ + ν₇^±1 + ν₈^±1 states, x, y-type Coriolis resonances (Δk = ±1, Δ? = ?3n ± 1) with ν₄ + ν₆^±1 and ν₄ + ν₇^±1 + ν₈^±1 states, and a centrifugal-distortion-type resonance (Δk = ±2, Δ? = ?3n ± 2) with a 2ν₇⁰ + ν₈^±1 state. The 11 × 11 dimensional energy matrix has been diagonalized in order to obtain the perturbed energy levels. The standard deviation for the fit is 1.075 × 10^?3 cm^?1. The molecular constants determined are also listed.     

Optical pumping of the metastable 53P0 level of ODD isotopes of cadmium

Metastable 5³P₀ atoms of ¹¹¹Cd and ¹¹³Cd are optically pumped in an atomic beam. Their magnetic resonances are observed with Landé factors g(³P₀, ¹¹¹ Cd) = (1.090±0.003) × 10^-3 and g(³P₀, ¹¹³Cd) = (1.143 ± 0.003) × 10^-3 which are 1.7 times larger than the g-factors of the 5¹S₀ ground state. This large difference arises from a slight mixing of the 5³P₀ level with the 5³P₁ and 5¹P₁ levels through the hyperfine interaction.     

Mößbauereffekt in Eisenstilben und FeCl2·H2O

Using Mößbauer effect measurements in the temperature range between 3 °K and 310 °K the magnetic fields at the nucleus in iron-stilbene, FeCl₂·H₂O and FeCl₃ are determined to beH _T=0=(250±10) kOe, (252±18) kOe and (468±10) kOe; a Néel-temperature ofT _N=(23±1) °K is measured for iron-stilbene. The electric quadrupole splittings atT=0 °K for iron-stilbene and FeCl₂ ·H ₂ O, ΔE=(+2.52±0.02) mm/sec and (+2.50±0.05) mm/sec, yield electric field gradients at the iron nucleus ofq _z=+9.7·10¹⁷ V/cm² and +9.6·10¹⁷ V/cm², whereq _z⊥H; Debyetemperatures of θ=162 °K and 188 °K are obtained. The energy of the excited 3d-electron levels in iron-stilbene is estimated to Δ₁=309 cm^?1 and Δ₂=618cm^?1 as deduced from the temperature dependence ofΔE. In contrast to the suggestion ofEuler andWillstaedt bivalence of the iron in ironstilbene is found; its composition is shown to be 4(FeCl₂ ·H ₂O)·stilbene.     

Low temperature EPR study of the “impurity” resonances in (TCNQ)- and (TCNQ)-2 salts

The so-called “impurity” resonances in polycrystalline Li⁺ (TCNQ)^-, Cu⁺ (TCNQ)^- and Cu⁺ (TCNQ)^-₂ have been studied at liquid helium-temperatures. The Li⁺ (TCNQ)^- resonance is partially resolved at low microwave powers with g_⊥ = 2.0025 ± 0.0005 and g_∥ = 2.008 ± 0.001. Itis found that the (TCNQ) and (TCNQ)^-₂ complexes give characteristics spectra. The possible origin of these resonances is discussed.     

An su (6)w fit to the negative parity baryon decay rates

We present a least squares fit to the experimental data on decays of negative parity baryon resonances into a pseudoscalar meson and either a J^P = 1/2⁺ stable baryon or a J^P = 3/2⁺ decuplet member. We find that the s-waves and d-waves are separately in good agreement with the predictions of SU (6)_w ⊗ O(2)_Lz. Predictions are given regarding several as yet unobserved decay processes, and for those which concern hitherto undetected resonances, their possible detection is discussed.