High-mass diffraction and Regge behavior of total cross sections

We consider a modified two-component model of particle production in which diffractive excitation into high mass states gives a contribution to K^±p, π^±p and pp total cross sections of sufficient magnitude and with the proper associated threshold to be a possible explanation of deviations of σ_tot from Regge pole model fits at Serpukhov energies. We present tests of the model. for K⁺p scattering by extrapolating σ_tot to National Accelerator Laboratory energies and by calculating the high mass diffraction contribution to the forward peak in inclusive reactions. The consistency of this scheme is discussed in relation to the pomeron intercept and the form of the triple-pomeron coupling.     

Raman scattering in Ag-intercalated TiS2

Ag-intercalated TiS₂ has been investigated using electron diffraction and Raman scattering. The energies of the E_g-1 and A_1g modes in 1T-TiS₂ at 300 K were found to be 232 and 336 cm^-1, respectively. In Ag_0.3TiS₂, at an ambient temperature of 4.2 K, modes were observed at 207, 239, 277, 311, and 347 cm^-1. Three of these modes have been associated with the formation of a superlattice at low temperatures. The superlattice formation was observed by electron diffraction and is attributed to an ordering of the silver atoms at interlayer interstices.     

Soft π−p and pp elastic scattering in the energy range 30 to 345 GeV

Differential cross sections for π^?p and pp elastic scattering have been measured at incident momenta ranging from 30 to 345 GeV and in the t range 0.002 (GeV/c)² ? |t| ? 0.04 (GeV/c)². From the analysis of the data, the ratio ? (t = 0) of the real to the imaginary parts of the forward scattering amplitude was determined together with the logarithmic slope b of the diffraction cone.The results on the real parts confirm the validity of the forward dispersion relations at high energies. Using the dispersion relations, it was shown that the experimental data on ?_{π?p(t = 0)} require a continuous rise of the total πp cross sections, at least up to the energy of 2000 GeV, thus revealing a close similarity in high-energy behaviour of πp and pp interactions.The results on the slope parameters from this experiment together with the analysis of the available world data demonstrate that the existing experimental data are consistent with the hypothesis of a universal shrinkage of the hadronic diffraction cone at high energies. The value of the asymptotic shrinkage parameter α_p^′ was found to be independent of the kind of the incident hadron and of the momentum transfer in the t range |t| ? 0.2 (GeV/c)² : 2α_{p^′ = ± 3 (GeV/c)^?2}.     

The accuracy of semiclassical approximations in extracting spectroscopic information from direct transfer reactions

The diffraction model amplitude for transfer reactions, previously developed by the author, is extended to energies below the Coulomb barrier. In this way, the spectroscopic factors for various transitions in the reaction ²⁰⁸Pb(d, p)²⁰⁹Pb are extracted. Comparison is made between our results and the predictions of the zero-range DWBA treatment, and good agreement is obtained. The observed cross sections at θ_L = 135° for various incident energies are also correctly reproduced within our treatment.     

Interaction potentials for diffraction of a He atom by a NaCl(001) surface

There exist two quite different sets of experimental results for the He-NaCl(001) interaction potential, inferred from bound-state resonance measurements of associated ⁴He-NaCl(001) bound-state energies E_n: Frankl's group has found a lowest bound-state energy E₀ ≈ −4.1 meV, whereas Benedek's group has found evidence of a deeper interaction potential well, with E₀≈ −7.2 meV. Furthermore, there are strong physical arguments for the existence of the deeper well. In the present paper, interaction potentials, based on empirical pairwise He-Na⁺ and He-Cl⁻ interactions, for diffraction of a He atom by a NaCl(001) surface are considered. Comparisons of close-coupling diffraction calculations with experimental data of Frankl's group are made, and values of the empirical parameters are inferred. On the basis of these comparisons, it is concluded that the lowest bound state proposed by Benedek's group is absent, and that the correct bound-state energies are those proposed by Frankl's group.     

Coulomb dissociation of incident 16O at 4.5 GeV/c

Projectile multifragment breakup of ¹⁶O, ²C and ⁷Li at energies 3.0–4.5 A-GeV is studied by means of the Weizsäcker-Williams method. The fragmentation channels of the ¹⁶O projectile at 4.5 A-GeV are investigated and compared with that of ¹⁶O at 200 A-GeV. The events characterized by N _h=0 and the events due to both Coulomb and diffraction dissociation have been selected and analyzed as a function of impact parameter. Also, the dependence of the electromagnetic dissociation cross-section on incident energy and the charge of projectile and target is found.     

Study of complex impedance spectroscopic properties of the KFeP2O7 compound

The KFeP₂O₇ compound was prepared by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction. The AC electrical conductivity and the dielectric relaxation properties of this compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 200 Hz–5 MHz and 553–699 K, respectively. Both impedance and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies Eg?=?0.94 (3)?eV and Egb?=?0.89 (1)?eV. The grain-and-grain boundary conductivities at 573 K are 1.07?×?10^?4 and 1.16?×?10^?5 (Ω^?1 cm^?1). The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation describes the same mechanism at various temperatures. The near value of the activation energies obtained from the equivalent circuit, conductivity data, and analysis of M″ confirms that the transport is through ion hopping mechanism.     

Semiclassical theory of analysing powers for polarised heavy-ion elastic scattering

A unified semiclassical theory of analysing powers of all ranks for polarised heavy-ion elastic scattering from a spin-zero target at energies above the Coulomb barrier is presented. Illustration is provided for by specialising to the two interactions, spin-orbit and tensor. The present approach recovers the phenomenological result, obtained by taking the difference of the nuclear overlap between unpolarised and aligned projectiles (shape-effect model), which successfully explained the structureless pattern of rank-2 observables for aligned ⁷Li + ⁵⁸Ni at E_lab ～ 20 MeV. Deviations observed for ⁷Li + ¹²C (oscillations) are interpreted as due to interference between diffraction (positive-angle) and negative-angle scattering terms.     

Vector analyzing power of π+7Li scattering in the region of the Δ33 resonance

Within Glauber diffraction theory, the vector analyzing power iT ₁₁ is calculated at three energies of positively charged pions, 134, 164, and 194 MeV, incident to ⁷Li nuclei. These energy values lie in the region of the Δ₃₃ resonance in π^± N interaction, the resonance maximum being at 180 MeV. The calculation of iT ₁₁ was performed with several model ⁷Li wave functions, including the αt-cluster and shell-model ones. The properties of π⁺⁷Li scattering are found to be sensitive to the structural features of the target nucleus. A comparison of the results of the calculations with experimental data shows that the wave functions in question and the potentials used to calculate them are quite appropriate.     

Two-photon exchange in p⊆)p→ℓ+ℓ−X and a comparison with QCD

A thorough study of lepton-pair production from two-photon annihilation in p?)p collisions is presented. The differential cross section is calculated over a large range of energies (27?√s?800 GeV as a function of the dilepton mass M as well as the dilepton transverse momentum Q_T and the Feynman variable x_F. No kinematical approximations (such as the equivalent photon approximation) are made. For Q_T ≈ 0 the two-photon mechanism represents an important fraction of the pp→e⁺e^?X cross section already at ISR energies, whereas at ISABELLE energies it dramatically dominates in the interval 0?Q_T?1 GeV. At ISR energies these conclusions follow from a direct comparison of the two-photon contribution with pp→e⁺e^?X data. For the ISABELLE energy range the expected O(α_s) QCD contribution to pp→?⁺?^?X, corrected for soft gluon radiation to all orders (in leading bilogarithmic approximation), was taken as a reference. At larger Q_T and ISR energies the γγ contribution is negligible, whereas at √s = 800 GeV γγ/QCD? 10–20% almost everywhere. Furthermore, two-photon candidate events from the ISR are shown to be in reasonable agreement with theory. A decomposition of the γγ cross section into contributions from both proton vertices being elastic, inelastic and of mixed configuration is given. The results provide important clues for a future isolation of the two-photon mechanism.     

Coupled-channels analysis of energy-dependent isospin violation in the 12C(d, α)10B(1.74 MeV,T = 1) reaction

We have studied the isospin non-conserving ¹²C(d, α)¹⁰B(1.74 MeV, 0⁺, T= 1) reaction at several incident energies of 9 ≦ E_d ≦ 16 MeV in terms of a coupled-channels method. The reaction processes involved in the present analysis are the successive single-nucleon pick-up processes as well as the inelastic scattering of deuterons from ¹²C. It is assumed that the isospin violation should occur in the intermediate mirror cluster states of ³He + ¹¹B and t + ¹¹C, due to the Coulomb interaction. The calculation reproduces fairly well the observed features of the reaction, i.e. the decreasing cross section with increasing incident energy, and the variation of the angular distribution. We also note that the calculation shows the energy-dependent localization of isospin violation in the angular momentum space, i.e. a specifically narrow localization at the lower incident energies studied and its broadening at the higher energies. This fact is associated with the variation of the angular distribution from a forward-backward symmetry at the lower incident energies to a forward peak at the higher energies.     

The proton optical-model potential near the Coulomb barrier

Proton elastic scattering data from ¹⁹⁷Au, ²⁰⁸Pb and ²⁰⁹Bi at energies near the Coulomb barrier are analyzed. The energy dependences of the real volume and imaginary surface-derivative potential depths V_R and W_SF of a local optical-model potential with fixed geometric parameters are found to be much more rapid than at higher energies. The strong energy dependence of V_Rnear the Coulomb barrier is explained in terms of the non-locality of the nucleon-nucleus interaction.     

The 12C(α, γ)16O reaction and stellar helium burning

The cross section for the reaction ¹²C(α, γ)¹⁶O has been measured for a range of c.m. energies extending from 1.41 MeV to 2.94 MeV, by using ¹²C targets of high isotopic purity, large NaI(T1) crystals, and the time-of-flight technique for the suppression of prompt neutron background and time-independent background. Gamma-ray angular distributions were measured at c.m. energies of 2.18, 2.42, 2.56 and 2.83 MeV. By means of theoretical fits, which include the coherent effects of the 1^? states of ¹⁶O at 7.12 MeV, 9.60 MeV, and those at higher energies, the electric-dipole portion of the cross section at astrophysically relevant energies has been determined. A three-level R-matrix parametrization of the data yields an S-factor at E_c.m. = 0.3 MeV, S(0.3 MeV) = 0.14^+0.14_?0.12 MeV · b. A “hybrid” R-matrix optical-m parameterization yields S(0.3 MeV) = 0.08^+0.05_?0.04 MeV · b. This S-factor is of crucial importance in determining the abundances of ¹²C and ¹⁶O at the end of helium burning in stars.     

Total reaction cross section for 12C + 16O below the Coulomb barrier

The energy dependence of the total reaction cross section, σ(E), for ¹²C + ¹⁶O has been measured over the range E_c.m. = 4–12 MeV, by detecting γ-rays from the various possible residual nuclei with two large NaI(Tl) detectors placed close to the target. This technique for measuring total reaction cross sections was explored in some detail and shown to yield reliable values for σ(E). Although the principal emphasis of this work was placed on obtaining reliable cross sections, a preliminary study has been made of the suitability of various methods for extrapolating the cross section to still lower energies. The statistical model provides a good fit with a reasonable value for the strength function, 〈γ²〉/〈D〉 = 6.8 × 10^?2, over the range E_c.m. = 6.5–12 MeV, but predicts cross sections which are much too large for E_c.m. < 6.5 MeV. Optical model fits at low energies are especially sensitive to the radius and diffuseness of the imaginary component of the potential and, since these are still poorly known at present, such extrapolations may be wrong by orders of magnitude. A simple barrier penetration model gives a moderately good fit to the data and seems to provide the safest extrapolation to lower energies at the present time. It is clear, however, that our knowledge of the heavy-ion reaction mechanism at low energies is incomplete, and that cross-section measurements at still lower energies are needed to establish the correct procedure for extrapolating heavy-ion reaction cross sections to low energies.     

The sub-barrier fusion of40Ar with144,148,154Sm

The cross sections for production of evaporation residues (σ _er) and for fusion-fission (σ _ff) have been measured for⁴⁰Ar+^{144, 148, 154}Sm at sub-barrier energies by observation of x-ray emission from radioactive products and by direct,ΔE?E identification of fission fragments, respectively. These isotopes span the transition region from spherical (¹⁴⁴Sm) to strongly deformed (¹⁵⁴Sm) equilibrium shapes. The cross section for fusion,σ _fus=σ _er+σ _ff, is found to vary markedly at low energies with the isotope number and, hence, with the quadrupole collectivity of the target. The thresholds for fusion of¹⁴⁸Sm and¹⁴⁴Sm are, respectively, ～3.5 MeV and ～7 MeV (c.m.) higher than for fusion with¹⁵⁴Sm. These differences and the energy dependence of the fusion cross sections are discussed in terms of the effect of nuclear deformation on heavy-ion fusion. A comparative analysis of results for¹⁶O+Sm and⁴⁰Ar+Sm in terms of static deformation indicates thatσ _fus for the Ar+Sm system at very low energies is enhanced relative to the prediction for a one-dimensional barrier based on a fit toσ _fus for¹⁶O+Sm. This may be an indication that additional degrees of freedom (such as formation of a neck or fragment elongation) may be important for fusion with the larger projectile. At energies above the fusion barrier, values ofσ _fus for^{144, 148}Sm are nearly equal, but are significantly smaller than for¹⁵⁴Sm. This is in contrast to the results of previous experiments with¹⁶O projectiles in whichσ _fus (¹⁶O+¹⁴⁸Sm) andσ _fus (¹⁶O+¹⁵⁴Sm) were nearly equal above the barrier. These differences, observed for^{144, 148}Sm and¹⁵⁴Sm at energies above the barrier may reflect a new mechanism which is not encompassed by a static theory.     

Measurement of the elliptic flux of Z ⩾ 2 charged particles in collisions of relativistic nuclei with photoemulsion nuclei

The azimuthal asymmetry is measured for the emission of Z ≥ 2 particles from the interaction of ²²Ne, ²⁴Mg, ³²S, ⁵⁶Fe, ¹⁹⁷Au, and ²⁰⁷Pb nuclei with photoemulsion nuclei that is induced by semicentral collisions characterized by projectile energies in the range E _pr = 1.88–200 GeV per nucleon and by impact-parameter (b) values in the range 0.12 ≤ b/b _max ≤ 0.70. The results of these measurements are compared with the results of similar measurements for protons. It is found that, at a low energy of E _pr ≈ 2 GeV per nucleon, the ratio of the azimuthal-anisotropy coefficients v ₂ for Z ≥ 2 particles and protons is 6 ± 2, but that, for energies in the region E _pr ≥ 4 GeV per nucleon, the coefficients in question agree with each other. This may suggest that, at low energies, Z ≥ 2 particles are predominantly formed at an early stage of the development of a collective flow. For E _pr ≥ 4 GeV per nucleon, these particles are presumably formed at the stage of nuclear-matter expansion. Other possible explanations for the results of the observation of an elliptic flux of Z ≥ 2 particles are discussed.     

Searching for the Higgs at SLC and lep

We compute the cross section for the process e⁺e⁻ →Hff as a function of Higgs boson mass and of center-of-mass energies of M_z and beyond. We conclude that searches for a Higgs of mass less than 50 GeV are far more effective when carried out near the Z boson resonance that at any higher energy. However, a new window of Higgs boson masses extending from 50–107 GeV can be explored if and when e⁺e⁻ collisions can be studied with high luminosity at collision energies of 200 GeV. Collider energies at intermediate energies can play no useful role in the search for the Higgs.     

Muons in extensive air showers of energies E 0=1016.6–1019.8 eV

Data on muons with the threshold energy E _μ≈1.0×secθ GeV in extensive air showers of energies E ₀≥4×10¹⁶ eV measured on the Yakutsk and Akeno arrays are jointly analyzed. The results are compared with the calculations by the quark-gluon-string model with jets. It is shown that this model does not contradict the data measured for energies E ₀≤10¹⁸ eV on both arrays under the assumption that the primary particle composition differs from the composition where heavy nuclei dominate over protons. Experimental data for energies E ₀≥3×10¹⁸ eV indicate that the shower development differs from that predicted by the quark-gluon-string model with jets.