Interpretation of multifrequency transient EPR spectra of the P 700 + A0Q K − state in photosystem I complexes with a sequential correlated radical pair model: Wild type versus A0 mutants

Transient electron paramagnetic resonance (TR-EPR) spectra of the electron-hole pair state P ₇₀₀ ⁺ A₀Q _K ^? in photosystem I are numerically calculated. Parameter variation concerns mainly the exchange integralJ of the precursor spin pair state P ₇₀₀ ⁺ A ₀ ^? Q_K and its lifetime τ. A prominent emissive feature in the high-field region (P ₇₀₀ ⁺ part) of the EPR spectrum turns out to be diminished with increasing lifetime τ of the precursor pair state in the case of positive exchange couplingJ>0 (ferromagnetic type). Correspondingly, the emissive feature becomes more pronounced with increasing lifetime τ in the case of negative exchange couplingJ<0 (antiferromagnetic type). These results can be used to interpret the changes in the pattern observed in TR-EPR spectra comparing wild-type and specific A₀ mutants. The central ligating amino acid residue to the A₀ chlorophyll cofactor is mutated from native methionine (M) to leucine (L) in either the PsaA or the PsaB branch. Changes are observed only for the A-side mutant: M688L(PsaA). They are consistent with the following parameters in the precursor pair P ₇₀₀ ⁺ A ₀ ^? :J≈0.5÷1.0 mT and τ=1.5÷2 ns (as compared to τ～0.05 ns in the wild type).     

Partial-wave analysis of the (KKK) system in the reaction K−p→K−K−K+p at 10 and 16 GeV/c

The reaction K^?p→K^?K^?K⁺p is shown to have properties similar to those of the diffractive reaction K^?p→K^?π^?π⁺p. This is true, at least in first approximation, for (a) the energy dependence of the cross sections, (b) the shape of the three meson spectra and (c) the differential cross sections dσ/dt_pp which have the same slope for the same mass of the three-meson system. Furthermore, the partial-wave composition of the (KKK) system is similar to that of the (Kππ) system, both systems being produced mostly in unnatural spin-parity states by natural parity exchange. In the KKK system, the J^P = 1⁺ state with S-wave decay into Kø(1020) is dominant, (72 ± 11) % of all events with (KKK) masses below 2 GeV.     

Meson-photon transition form factors and resonance cross-sections in e+e− collisions

Meson-photon-photon transition form factors for S-, P-, and D-wave states are calculated, the meson being treated as a non-relativistic heavy-quark-antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J^p = 0⁻, 0⁺, 1⁺, 2⁺, and 2⁻ in electron-positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for χ_c1, η_c(2S), and η_b(1S) within reach of LEP.With minor modifications to incorporate SU(3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e⁺e⁻ cross sections for 1⁺ states do not vanish at low Q², the Landau-Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.     

Weak Neutrino-Lepton Annihilation into Hadrons

An exploratory study of weak neutrino-lepton annihilation into hadrons, v̄_l + l → hadrons is presented. Simple cross-section estimates indicate processes of this type may be observable in a large bubble chamber. We discuss the information one could hope to obtain from such experiments. General formulas for amplitudes and cross sections are given for v̄_l + l → hadrons assuming a point-like V – A interaction. To establish tests of the V – A interaction, we recalculate the annihilation amplitudes assuming a point-like scalar-pseudoscalar or tensor-pseudotensor interaction. The extension to theories with intermediate vector bosons is sketched. We discuss the connection between v̄_l + l → hadrons and e⁺e⁻ → hadrons implied by the conserved vector current hypothesis. We note that in v̄_l + l → rH, K⋆(890), A₁, B creation (these reactions enjoy comparatively large cross sections) the leptonic as well as hadronic couplings of these J = 1 , I = 1/2 or 1 mesons could be determined. A related possibility is the direct creation of new heavy charged J = 1 mesons. The normal J = 1 resonance region could be explored with neutrino energies of the order 500–2000 GeV. For this, and for higher-energy work, a TeV proton accelerator is clearly necessary.     

Coherent A2− production of nuclei observed in the K−KS0 decay channel at 17.2 GeV/c

We have studied A₂^? production by π^? on a nuclear target in the K^?K_S⁰ decay channel, where the A₂^? is observed above a small background at 17.2 GeV/c incident momentum. Direct confirmation of coherent A₂ (J^P = 2⁺) production has been found.     

Analysis of the B 0(+) → J/ΨD 0(+) decays

We analyze B ⁰⁽⁺⁾ → J/ΨD ⁰⁽⁺⁾ decays by considering the contributions of annihilation diagrams. For each diagram, we calculate the branching ratios for various parameters X _A , which have played a significant role in our results. These parameters have been concluded from the divergence integrals in hard-scattering kernels. Here, we have considered three effective variables, including: Λ(225, 500 MeV), ρ _A (0, 1, 1/2), and φ _A . It is found that the most of the obtained data are placed in the experimental range at Λ = 225 MeV and Λ = 500 MeV for B ⁺ → J/ΨD ⁺ and B ⁰ → J/ΨD ⁰, respectively.     

Exchange,production and decay of the Z meson (JPC = 2−−)

Recent high-statistics data for π^?p→ω⁰n indicate the presence of an amplitude with exchange quantum numbers in the series J^PC = 2^?? 4^??,… Previous phenomenological and theoretical estimates of reggeised Z exchange J^PC = 2^??) are shown to be in good agreement with data. Implications for observing the exchange of its EXD partner (the much sought A₁) and other unnatural parity states are discussed with reference to a with a quark model estimate of its branching ratio, we predict the cross section for production of the Z and its subsequent decay into ωπ. The prospects for a partial-wave analysis of the ωπ enhancement observed at 1700 MeV are discussed.     

Deexcitation of Cd 53P1 atoms in collisions with ground state atoms and molecules

Collisions of excited Cd 5³P₁ atoms were investigated using atomic fluorescence spectroscopy. Cadmium vapor, together with a quenching gas, was irradiated in a quartz fluorescence vessel with Cd 3261 Å resonance radiation and the intensity of the resulting resonance fluorescence was monitored in relation to the gas pressures. The experiments yielded the following cross sections Q₁₀ (in A²) for collisional transfer 5³P₁→5³P₀: CdAr=2×10^?3, CdN₂=8.0, CdH₂=7.0, CdCO=15.6. The cross sections Q for collisional deexcitation to the ground state (quenching) in A² are CdN₂ = 2.6×10^?2, CdH₂ = 11.0, CdCO = 3.4, CdCO₂ = 26.     

Evidence that absorption in the π+ π− π− system in nuclear matter is stronger in the JP = 0− than in the JP = 1+ state

In the reaction π^? + A → π⁺π^?π^? + A at 15.1 GeV/c the coherently produced 3π mass spectrum has a broad peak around 1.1 GeV which consists mainly of a J^P = 1⁺ state and of a smaller fraction of 0^-. Comparing the observed dependence of the production of these diffractive states on the atomic weight A of the target nuclei with the optical model, we have studied the absorption of the produced states in nuclear matter. We have found the following values of the absorption cross-sections: σ₂(0^-) = 49_?7⁺⁹ mb and σ₂(1⁺) = 15.8_?1.3^+1.5 mb.     

Comparing the p̅p → K − K + and p̅p → π−π+ reactions

A partial wave amplitude analysis of LEAR data on differential cross sections and analyzing powers of p?p → K ^? K ⁺ has been performed in the range p _lab = 360 ? 1000 MeV/c, and compared to the results from the same observables for p?p → π^?π⁺. Contrary to other analyses we see no compelling evidence of resonance behavior in our amplitudes. However, as we discuss, the resulting amplitudes are not unique since a third observable remains to be measured for both reactions. Another remarkable result is that for p?p → K ^? K ⁺ all our solutions in the momentum interval below 900 MeV/c, only partial wave amplitudes including J _max = 2 are necessary. This upper limit on the angular momentum is smaller than J _max = 3 which is required for the data of the reaction p?p → π^?π⁺ in the same momentum interval. This finding is consistent with a model analysis for data above 1 GeV/c. Annihilation models with short range baryon exchange give too small J ≥ 2 amplitudes and final state ππ and K?K interactions are presumably very important.     

Isotope effect in electron capture by protons into the 2S-state of hydrogen

We have investigated the isotope effect for electron capture into the 2S-state of hydrogen in close collisions for the processes H⁺ in H₂ and H⁺ in D₂. The differential cross sections and transition probabilities P_2S obtained for capture into H(2S) as a function of energy at a fixed angle of θ = 1° exhibit distinctive features, but no apparent isotope effects are detected.     

A partial-wave analysis of the neutral 3π system produced in the reaction π−p → (π+π−π0) n at 12 and 15 GeV/c

Data on the charge-exchange reaction π^?p → (π⁺π^?π⁰)n have been taken at beam momenta of 12 and 15 GeV/c, using the CERN Omega Multiparticle Spectrometer. A partial-wave analysis has been made of the (3π)⁰ system. We observe both natural and unnatural spin-parity production. The natural parity states can be identified with established resonances. In addition a natural spin-parity enhancement is observed at a mass of about 2 GeV/c² with J^P = 4⁺ preferred. We have called this effect the A₂¹ (2030). The unnatural spin-parity production found is consistent with reggeized Deck model predictions. No unambiguous A₁ or A₃ production is observed.     

Laser-induced effects for overlapping autoinoizing rydberg states of xenon

The effect of a laser field on the cross section of photoionization of an atom by probe radiation in the region of closely lying autoionizing resonances is studied theoretically. The cross sections in the region of the overlapping autoionizing Rydberg states 5p ⁵(² P _1/2)6d′ J = 1 and 5p ⁵(² P _1/2)8s′ J = 1 resonantly coupled with the discrete state 5p ⁵(² P _3/2)7p[1/2]₁ in the xenon atom are calculated. The behavior of the shape and position of resonances in relation to the frequency and intensity of laser radiation is studied.     

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.     

The (π, 2π) reaction and spin-isospin strength distribution in nuclei

We study pion production on nuclei within the distorted wave impulse approximation (DWIA) and using the local density approximation (LDA) for the treatment of possible nuclear spin-isospin mode enhancements. The scattering amplitude input is based on a one-nucleon mechanism since two-nucleon processes are here estimatedito be relatively unimportant. For discrete nuclear levels, we study differential and total (angle-integrated) cross sections for various pion-like levels (J^P = 0^?, 1⁺, 2^?,…; T = 1); these are also compared with non-pion-like excitations. The cross sections for discrete excitations are quite small. The inclusive cross sections, achieved by summing over all nuclear states, are considerably larger, of the order of 0.1–10 mb. We use the Fermi gas model to test the importance of the quasi-free peak for various incident pion momenta k, and to study the closure approximation for summing over nuclear levels when calculating inclusive cross sections. It is found that for k of the order of about twice the Fermi momentum most of the quasi-free peak region contributes to the nuclear excitations, and the use of closure is justified and practical. All cases are studied as a function of g', the Migdal spin-isospin parameter, and it is found that the dependence upon this parameter may range from changes of an order of magnitude to a factor of two over the range 0.4 ? g' ? 0.7.     

Effect of inelastic scattering processes on (p,t) reactions exciting the first 2+ states in Te,Sn and Cd isotopes

Differential cross sections of (p, t) reactions exciting the 2⁺₁ states in Te (A = 128 ? 120), Sn (116 and 114) and Cd (114 and 112) have been measured at E_p = 52 MeV. The observed differences of the angular distributions are interpreted by taking into account the two-step processes through inelastic scattering channels.     

A study of the 12N 2.43 MeV level

We have measured the differential cross sections for the reactions ¹²C(τ, τ′)¹²C(17.77 MeV 0⁺T=1) and ¹²C(τ, t)¹²N(2.43 MeV) at E_τ=44 MeV. The similar shapes of the angular distributions and the relative magnitudes of the cross sections suggest that the ¹²N 2.43 MeV level is the 0⁺T=1 analog to the ^q12C 17.77 MeV level. We have also studied the reaction ¹⁴N(p,t) ¹²N(2.43 MeV) at E_p=52 MeV. The strength with which this level is excited in this reaction is consistent with reasonable two-step calculations assuming the 2.43 MeV level to have J^π=0⁺.     

The (γ, p0) reactions in the giant dipole resonance region of 51V and 52Cr nuclei

The differential cross sections at 90° for the ⁵¹V(e, p₀)⁵⁰Ti and ⁵²Cr(e, p₀ + p₁)⁵¹V reactions have been measured over the giant dipole resonance region. These cross sections were used to obtain the differential cross sections of the ⁵¹V(γ, p₀)⁵⁰Ti and ⁵²Cr(γ, p₀ + p₁)⁵¹V reactions. The results show two peaks that appear at the same energies as the main peaks of the (γ, n) and (γ, p) cross section for both nuclei. The angular distributions of protons from the (e, p) reaction have also been measured at several points of the incident electron energy. The coefficients A₂ obtained by fitting with a series of Legendre polynomials, W(θ) = 1 + A₁P₁(cos θ)+A₂P₂(cos θ), varies with excitation energy. These results are discussed in terms of the direct-semidirect process considering isospin effects in the giant dipole resonance.     

Analysis of the 2ν3 band of 12CD3F at 5.06 μm recorded under high resolution

The 2ν₃(A₁) band of ¹²CD₃F near 5.06 μm has been recorded with a resolution of 20–24 × 10^?3 cm^?1. The value of the parameter (α^B ? α^A) for this band was found to be very small and, therefore, the K structure of the R(J) and P(J) manifolds was unresolved for J < 15 and only partially resolved for larger J values. The band was analyzed using standard techniques and values for the following constants determined: ν₀ = 1977.178(3) cm^?1, B″ = 0.68216(9) cm^?1, D″_J = 1.10(30) × 10^?6 cm^?1, α^B = (B″ ? B′) = 3.086(7) × 10^?3 cm^?1, and β^J = (D″_J ? D′_J) = ?3.24(11) × 10^?7 cm^?1. A value of α^A = (A″ ? A′) = 2.90(5) × 10^?3 cm^?1 has been obtained through band contour simulations of the R(J) and P(J) multiplets.