20Ne + n → 21Ne(T = 32) resonances

$\text{T =}\text{3}\text{2}$ resonances in ²¹Ne have been studied in measurements of the total neutron cross section of ²⁰Ne using the 190 m neutron time-of-flight facility of the Karlsruhe Isochronous Cyclotron. The high time-of-flight resolution of 6.6 ps/m enabled the study of sharp $\text{T =}\text{3}\text{2}$ resonances in ²¹Ne with an effective energy resolution of up to 4000. Five $\text{T =}\text{case3}\text{2}$ levels have been observed as sharp resonances allowing the precise determination of total width Λ, partial decay with Λ_no and resonance energy E_R. The c.m. resonance parameters of the first $\text{T =}\text{3}\text{2}$ state in ²¹Ne are E_R = 2098.6 ± 0.3 keV, Λ = 2.2 ± 0.5 keV and Λ_no = 0.21 ± 0.05 keV. Upper limits for the partial decay widths are deduced for those $\text{T =}\text{3}\text{2}$ levels which do not appear as resonance anomalies. A search for additional $\text{T =}\text{3}\text{2}$ states was undertaken. The resonance energies are discussed in the framework of the isbobaric mass multiplet equation. The decay widths are compared with shell-model predictions of isospin mixing and the systematics of isospin-non-conserving particle decays.     

Non-perturbative QCD effects explain the ΔI = 12 rule in the chiral limit

It is shown that in the chiral limit, the enhancement of the $\text{ΔI=}\text{1}\text{2}$ transitions for mesons is explained by the large size of non-perturbative QCD matrix elements. For $\text{〈}\text{s}\text{s〉 = 〈}\text{u}\text{u〉}$ we obtain ∣M(K_S⁰ → 2π⁰) ∣ =(5.2±0.6) × 10^?7m_K in excellent agreement with experiment.     

The Ã1A″ ← X̃1A′ electronic transition in formyl chloride,CHClO

The ultraviolet absorption spectrum of formyl chloride has been recorded under conditions of modest resolution, 0.75 nm/mm, and long pathlengths, 96 m. The 314- to 269-nm spectrum proved to have well-defined vibrational fine structure and was assigned to the electron promotion, $\text{n → π}{}^1$. A comparison of the spectra of CHClO at 25 and ?78°C with CDClO led to the assignments: pseudo-origin, ν₂, ν₄, ν₅, and ν₆; $\text{32754.7}\text{32775.3}$, $\text{1153.8}\text{1092.0}$, $\text{633.6}\text{633.4}$, $\text{306.3}\text{303.1}$, and $\text{779.5}\text{566.5}\text{cm}{}^{\mathrm{?1}}$ for $\text{CHClO}\text{CDClO}$, respectively. A fit of the 6⁰, 6², 6³, and 6⁵ levels to those generated from a Gaussian-quadratic model potential yielded a barrier height of 1608.8 cm^?1 and an out-of-plane angle of 48.6° for the $\text{A}\text{?}$ state.     

A t-channel isospin analysis of the chew-low plot for NN → N(Nπ) interactions at 5.7 GeV/c

A new approach to the t-channel isospin analysis of ZN → Z′(Nπ) reactions is presented. This approach, useful for $\text{Z = N,}\text{N}\text{, K}{}^{\mathrm{?}}$ when only five independent sets of data are availables, is used to analyse data of $\text{N}\text{N →}\text{N}\text{(Nπ)}$ reactions obtained in a $\text{p}\text{p →}\text{N}\text{N}\text{π}$ experiment at $\text{5.7}\text{GeV}\text{/c}\text{and a}\text{p}\text{d →}\text{N}\text{Nπp}{}_{\mathrm{s}}$ experiment at 5.5 GeV/c. the t behaviour of the different isospin exchange amplitudes, suggests their exchange mechanism production. The mass spectrum, M_πN, of the contributions produced by exchanged isospin I_ex = 1, shows enhancements corresponding to N(1490) N(1670) and Δ(1230) isobars, while the mass spectrum for I_ex = 0 presents only a large bump at ～1350 MeV commonly identified as N¹(1400).     

A theoretical model for the interacting upper states of the ν1, ν3, 2ν2, ν2 + ν4, and 2ν4 bands in methane

The effective vibration-rotation Hamiltonians complete to fourth order in the Amat-Nielsen scheme for the upper states of the ν₁, ν₃, 2ν₂, ν₂ + ν₄, and 2ν₄ bands in methane are reviewed, and the major vibration-rotation interactions (H₃₀, $\text{H}\text{?}{}_{40}$, $\text{H}\text{?}{}_{21}$, $\text{H}{}_{31}$, $\text{H}\text{?}{}_{22}$) connecting the different vibrational states are discussed. Explicit matrix elements in a basis of harmonic oscillator-symmetric rotor basis functions are given for the purely vibrational terms and for the vibration-rotation interactions. Expressions for spectral intensities of infrared and Raman spectra are presented, and the selection rules and transition moment matrix elements are stated. A computer program is described which, incorporating all these features, can be used for prediction of infrared and Raman spectra and for determination of molecular constants from observed spectra by a least-squares routine. As an example the program is applied to the 2ν₄ isotropic Raman spectrum of ¹²CH₄, leading to a very good agreement between the experimental and calculated spectra.     

The Ã1B2-X̃1A1 two-photon fluorescence excitation spectrum of 1,3-difluorobenzene

The $\text{A}\text{?}{}^1\text{B}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ system of 1,3-difluorobenzene has been observed using the technique of two-photon fluorescence excitation obtained with a pulsed dye laser. Calibration was achieved by a combination of the neon optogalvanic spectrum and etalon fringes. In circular, compared to linear, polarization the bands divide into two groups, those which are B₂-A₁ and which retain their intensity with circular polarization, and those which are A₁-A₁ and lose about 60% of their intensity under the same conditions. These two kinds of bands also show characteristic rotational contours. All of the A₁-A₁ bands whose assignments are established obtain their intensity through vibronic interaction in which the vibration ν′₂₅ (ν′₁₄ in the Wilson numbering) mixes the $\text{A}\text{?}$ with, presumably, the $\text{X}\text{?}$ state. There is an important Fermi resonance between the 9¹ and 10¹11¹ levels. Parts of the one-photon absorption spectrum have been photographed to identify sequences associated with the 0₀⁰ band for comparison with those observed in the two-photon spectrum, and to search for bands involving odd quanta of b₂ vibrations, including ν′₂₅ (ν′₁₄); none was found.     

Vibrational spectra and force constants of symmetric tops: Rovibrational analysis of 2ν6 and 2ν6 − ν6 of H3Si35Cl and H3Si37Cl,and a new method for the determination of A0 and DK0

The gas-phase ir spectra of monoisotopic H₃Si³⁵Cl [35] and H₃Si³⁷Cl [37] in the 2ν₆ region near 1300 cm^?1 have been studied with a resolution of 0.05 cm^?1. A total of 467 and 1206 lines have been assigned for [35] and [37], respectively, and analyzed by a least-squares procedure, σ(J, K) ～ 6 × 10^?3cm^?1, to yield three parameters for the 2ν₆⁰ and six for the 2ν₆^±2 states for both isotopomers. In the ν₆ region $\text{32}\text{47}$ and $\text{127}\text{150}$ lines have been assigned to the hot bands 2ν₆⁰ ? ν₆^±1 and 2ν₆^±2 ? ν₆^±1 of [35] and [37], respectively. While a hot band 2ν_t⁰ ? ν_t^±1 does not provide any information above that available from ν_t^±1 and 2ν_t⁰, a hot band 2ν_t^±2 ? ν_t^±1 may supply extra data concerning the ground state. A new method for the evaluation of A₀ and D_K⁰ from combination differences of ν_t^±1, 2ν_t^±2, and 2ν_t^±2 ? ν_t^±1 of a symmetric top with C_3v symmetry is presented. Application to [35] and [37] yielded A₀ of 2.8447(5) and 2.8437(3) cm^?1, and D_K⁰ of 2.12(20) and 2.38(9) × 10^?5 cm^?1, respectively.     

The 370-nm electronic spectrum of tropolone: Evidence from single vibronic level fluorescence spectra regarding the assignment of some vibrational fundamentals in the X̃ and à states

Single vibronic level fluorescence (SVLF) spectra of tropolone from vibronic levels in the $\text{A}\text{?}{}^1\text{B}{}_2$ electronic state, in combination with recently reported supersonic jet spectra, have enabled the assigning of many absorption bands in the region of 0₀⁰ which had previously been impossible. Some of the complexity in these bands has been shown to be due to a large Duschinsky effect involving the two lowest b₁ vibrations, ν₂₅ and ν₂₆. It has been shown that these vibrations have wavenumbers of 176 and 110 cm^?1, respectively, in the $\text{X}\text{?}$ state, and 172 and 39 cm^?1 in the $\text{A}\text{?}$ state. This last value shows how unresistent the molecule is in the $\text{A}\text{?}$ state to out-of-plane bending in the region of the five-membered ring. Other aspects of the vibrational complexity are due to the effect of ν′₂₆ in increasing the barrier to tunnelling of the hydrogen-bonding proton in the $\text{A}\text{?}$ state contrasting with very little effect of ν″₂₆ in the $\text{X}\text{?}$ state.     

The 16O + p → 17F (T = 32) resonances at Ep = 11.26,12.71 and 14.57 MeV

Excitation functions for ¹⁶O+p reactions have been measured with high energy resolution in the region of the first, second and seventh $\text{T =}\text{3}\text{2}$ resonances in ¹⁷F at extreme backward angles. The observed resonance shapes have been analyzed with a single-level resonance formula taking the off-resonance spin-flip amplitude into account. The resonance parameters of the ¹⁷F first $\text{T =}\text{3}\text{2}$ state studied with special emphasis are E_x = 11193.3 ± 2.3 keV, Γ = 200 ± 40 eV and Γ_p0 = 19 ± 3 eV. This result and other results are compared with previous studies and theoretical predictions. The comparison with data of the mirror nucleus ¹⁷O is discussed with respect to the observed charge asymmetry of the isospin-forbidden particle decay widths.     

On the optimality of axiomatic constraints for π0π0 scattering: The case of the lower bounds

We construct a nine-parameter family of π⁰π⁰ → π⁰π⁰ amplitudes F(s, t) such that (i) all the analyticity and unitarity conditions used in the derivation bounds are satisfied; (ii) F(s, t) can assume negative values in the unphysical region. Within this set, we minimize the values of $\text{F(}\text{4}\text{3}\text{,}\text{4}\text{3}\text{)}$ and of the scattering length a⁰⁰ = F(4, 0). Our best results are $\text{F(}\text{4}\text{4}\text{,}\text{4}\text{3}\text{) = -1.69}\text{and}\text{α}{}^{00}\text{= -0.88}$, whereas the best present lowers bounds are $\text{F(}\text{4}\text{3}\text{,}\text{4}\text{3}\text{) > -8.2}\text{and}\text{α}{}^{00}\text{> -1.65}$.     

Zeros of the π+π− → π+π− amplitude

Recent data on the reaction $\text{p}\text{p}\text{→ π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ show four conspicuous dips in the angular distribution at fixed values of ν = t?u. The conjecture is made that the channel π^?π⁺ → π^?π⁺ has zeros at the same ν values. Using data of the CERN-Munich group, one can follow the zeros through the whole Mandelstam plane. The zeros pass through the intersections of s and t channel poles, as the Veneziano model predicts; however, away from these intersections, they propagate in a fashion systematically quite different from Veneziano's ansatz.     

Analysis of π N → K Λ and KN → π Λ using fixed-t dispersion relations,fesr and duality

A simultaneous analysis of low-energy (W ? 2 GeV) data for the reactions π^?p→ K^OΛ and K^?p → π^OΛ has been made using the hypothesis of two-component duality combined with fixed-t dispersion relations. Results are presented for the $\text{?}{}^1\text{Λπ}$ and $\text{N}{}^1\text{Λ}\text{K}$ couplings. The low-energy amplitudes are used to evaluate FESR integrals and lead to large EXD breaking for the $\text{K}{}_{\mathrm{<mtext>V</mtext>}}{}^1\text{?}\text{K}{}_{\mathrm{<mtext>T</mtext>}}{}^1$ helicity flip amplitudes.     

Study of the Kππ system produced in K−p → KππN reactions at 14.3 GeV/c

We have studied the $\text{K}\text{ππ}$ system in the 14.3 GeV/c reactions K^?p → K^?π⁺π^?p, $\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{K}{}^0\text{π}{}^{\mathrm{?}}\text{π}{}^0\text{and}\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{K}{}^0\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{n}$. The data have been obtained from a 500 000 picture exposure of the CERN 2m HBC. The first two final states are dominated by Q-production in the Kππ system; there is also an L-signal at M (Kππ) ～ 1.75 GeV. The reaction cross sections are compared to K^?p data at other energies. We discuss the Kππ mass dependence of the diffractive production slope. Evidence is presented for a Q^?p versus Q⁺p differential cross section cross-over around |t| = 0.17 GeV². A t-channel isospin analysis for the $\text{KN}\text{→}\text{K}\text{1(890)π}\text{N}$ channels in the Q-region shows that the I = 1 exchange amplitude is $\text{? 10\%}$ of the dominant I = 0 exchange amplitude. The Kππ decay distributions indicate a predominant J^P = 1⁺ state in the Q-region, and an important J^P = 2^? contribution in the L-region. We find neither s-channel nor t-channel helicity conservation at the meson vertex in the Q- or L-regions. The Kπ angular correlation moments within the Kππ diffractive system are characteristic of Kπ elastic scattering, suggesting a π-exchange Deck-type production mechanism. There is evidence for a Kf⁰ and κπ contribution (where κ is the J^P(Kπ) = 0⁺ state) to the diffractive Kππ system. A fit to the $\text{K}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{and}\text{K}{}^0\text{π}{}^{\mathrm{?}}\text{π}{}^0$ Dalitz-plot distributions for the Q-re gion indicates that the ratio of $\text{K}\text{?}\text{to K}{}^1\text{π}$ decay amplitudes decreases with increasing Kππ mass.     

A numerical estimate of deviations from the exponential decay law for the transition 2P12→1S12 in hydrogen

The deviations from the exponential decay law of the $\text{2}\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states of the Dirac hydrogen atom with respect to the transition $\text{2}\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→1}\text{S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ are numerically estimated. We find |a₀(t) ? exp(?λt)|?2.5 × 10^?4 for all t, where a₀(t) is the “exact” decay amplitude and λ is a complex constant such that (2Re λ)^?1 is the “natural lifetime” of the $\text{2}\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states with respect to the spontaneous transition to $\text{1}\text{S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$.     

Some studies of T = 32 states in 17F

Measurements have been made of some parameters of the second and sixth $\text{T =}\text{3}\text{2}$ states in ¹⁷F. For the second state, the resonance energy was found to be E_p = 12.707 ± 0.001 MeV (E_n = 12.550±0.001 MeV), which agrees with and improves on the accuracy of earlier work. For the sixth $\text{T =}\text{3}\text{2}$ state, at E_p = 14.435 MeV, the γ-decay was determined to be predominantly γ₀ with a branch to the first excited state of Γ(γ₁)/Γ(γ₀) ≦ 0.14. Together with other work, this determines J^π to be $\text{3}\text{2}{}^{\mathrm{?}}$. The capture strength is found to be (2J + 1)Γ_pΓ_γ/Γ = 11.4 ± 2.6 eV.     

Rising dσdt probes pp diffraction mechanisms

The s-dependence of $\text{d}\text{σ}\text{d}\text{t}$ at fixed t reveals important features of the underlying mechanism. In particular, it can clarify the origin of the structure near t = ?1.2 in high-energy pp elastic scattering. If this structure comes from destructive interference between two terms of different energy dependence (e.g. between single and double pomeron exchanges), the plot of ln $\text{d}\text{σ}\text{d}\text{t}$versus ln s in the interference region will show an inflexion or dip; $\text{d}\text{σ}\text{d}\text{t}$ may even rise with increasing s through a limited interval. Other mechanisms have no such feature. We give illustrations and stress the interest of measurements in the NAL and ISR momentum range.     

Asymptotic freedom,light quarks and the origin of the ΔT = 12 rule in the non-leptonic decays of strange particles

A dynamical mechanism for the $\text{ΔT =}\text{1}\text{2}$ rule in the non-leptonic decays of strange particles is considered. The weak interactions are described within the Weinberg-Salam model while the strong interactions are assumed to be mediated by the exchange of an octet of colour vector gluons. It is shown that the effect of the strong interactions gives rise to new operators in the effective Hamiltonian of weak interactions which contain both left- and right-handed fermions. These operators satisfy the $\text{ΔT =}\text{1}\text{2}$ rule, and estimates within the relativistic quark model indicate that their contribution dominates the physical amplitudes of the K → 2π, 3π decays.     

An upper limit to the cross section for the reaction νμe−→νμe− at SPS energies

Candidates for the purely leptonic process $\text{ν}{}_{\mathrm{\mu }}\text{e}{}^{\mathrm{?}}\text{→}\text{ν}{}_{\mathrm{\mu }}\text{e}{}^{\mathrm{?}}$ have been searched for in the bubble chamber Gargamelle exposed to the CERN-SPS antineutrino wide-band beam. No single e^?, of energy greater than 1 GeV, was found in a total of 230 000 pictures, corresponding to 7400 charged current events. This leads to an upper limit for the observed cross section of $\text{σ}{}_{\mathrm{<mtext>obs</mtext>}}\text{< 1.6 × 10}{}^{\mathrm{?42}}\text{(}\text{E}{}_{\mathrm{\nu }}{}^{\mathrm{?}}\text{GeV}\text{)}$ cm² (90% C.L.). Interpretation of this value in terms of the standard W Weinberg-Salam model yields an upper limit to the mixing parameter sin²θ_W < 0.39 at 90% C.L.     

Construction of a unitary analytic amplitude for the scattering of spin-12 particles

We study the existence, the uniqueness and the construction of unitary analytic amplitudes for $\text{spin}\text{1}\text{2}\text{?}\text{1}\text{2}$ scattering, in the framework previously introduced by Atkinson-Mahoux-Ynduráin for spin 0-0, and $\text{spin}\text{0?}\text{1}\text{2}$ scattering.     

Quadrupole moment of the 5−2, 134 keV state in 197Hg

The quadrupole interaction for the $\text{5}{}^{\mathrm{?}}\text{2}\text{, 134}\text{keV}$ state of ¹⁹⁷Hg in solid Hg was observed by the e^?-γ time differential perturbed angular correlation method. The quadrupole coupling constant ν_Q=126 (2) MHz is derived. By comparison with experimental quadrupole coupling constants for ¹⁹⁹Hg in Hg and HgCl₂ as well as for ²⁰¹Hg in HgCl₂ the quadrupole moment of the $\text{5}{}^{\mathrm{?}}\text{2}\text{, 134}\text{keV}$ state in ¹⁹⁷Hg is related to that of the ²⁰¹Hg ground state, which is known. The value $\text{Q(}{}^{197}\text{Hg}\text{,}\text{5}{}^{\mathrm{?}}\text{2}\text{, 134}\text{keV}\text{)=0.47(6)}\text{b}$ is deduced. This value is not in agreement with the assumption of a $\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ shell-model configuration for the 134 keV state. It is consistent with an interpretation of the $\text{5}{}^{\mathrm{?}}\text{2}$ level in terms of the core coupling model of de Shalit.