Λ and Λ production in K+p interactions at 32 GeV/c

A study of the inclusive and semi-inclusive Λ and $\text{Λ}$ production in K⁺p interactions at 32 GeV/c is presented. The inclusive cross sections for Λ and $\text{Λ}$ amount to 0.78 ± 0.05 and 0.42 ± 0.04 mb thus showing a remarkable growth between 16 and 32 GeV/c with a factor of 1.7 for Λ and 2.8 for $\text{Λ}$. Target and beam fragmentation processes are found to be dominant for Λ and $\text{Λ}$ production respectively with the following lower limits for the corresponding cross sections: $\text{σ(p}\text{→}\text{K}{}^{\mathrm{+}}\text{?) > 0.5}\text{mb}$ and $\text{σ(K}{}^{\mathrm{+}}\text{→}\text{p}\text{?}\text{) > 0.3}\text{mb}$. Although the early scaling conditions are fulfilled for the Λ production in the target fragmentation region, and $\text{Λ}$ production in the beam fragmentation region, scaling is not observed between 16 and 32 GeV/c in the x and p_T² Feynman variables. The Λ production is found to be very similar in the K⁺p inclusive reaction at 32 GeV/c and in the semi-inclusive reaction $\text{K}{}^{\mathrm{?}}\text{p}\text{→ Λ}\text{K}\text{K}\text{X}$ at the same energy. The $\text{Λ}\text{Λ}$ pair production cross section increases significantly in K⁺p interactions from 16 to 32 GeV/c where it reaches the value $\text{σ}{}_{\mathrm{<mtext>\Lambda </mtext><mtext>\Lambda </mtext>}}\text{= 47 ± 11 μ}\text{b}$. The cross sections for Λ or $\text{Λ}$ produced in association with an identified proton are also given and discussed.     

Hall to drift mobility ratio in Ga1−xAlxAs alloys

Hall concentration measurements as a function of temperature ($\text{750 ? T ? 77}\text{K}$) on n-type epitaxial layers of Ga_1?xAl_xAs in the composition range $\text{0 ? x ? 0.78}$, have been used to evaluate the composite dependence of the Hall to drift mobility ratio in this alloy at 300 K. This ratio is found to be close to unity for alloy compositions $\text{0 ? x ? 0.25}$ and $\text{0.6 ? x ? 0.78}$, but attains a maximum value of 3.8 at x = 0.42 due to the multiconduction Hall effect.     

High pT π0 production from αα and αp collisions at the CERN ISR

The invariant cross sections for π⁰ meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of $\text{7}\text{GeV}\text{c}$ and $\text{8}\text{GeV}\text{c}$, respectively. These measurements are compared with π⁰ production in pp collisions at the same values of $\text{s}\text{/}$nucleon, and the variation of the nuclear A-dependence with p_T is determined.     

Isomers in the N = 83 nucleus 149Dy

Energy levels in the N = 83 nucleus ¹⁴⁹Dy were studied by the reaction ¹⁵²Gd(α, 7n) at 106 MeV bombarding energy using in-beam γ-ray spectroscopy methods. The measurements identified three isomers in this nucleus, at 1073 keV (13 ± 3 ns), at 2700±150keV (5 μs < T_{$\text{1}\text{2}$} < 0.5 s), and above 3.5 MeV (50 ± 15 ns). The low-lying isomer is interpreted as i_{$\text{13}\text{2}$}. The configuration $\text{27}\text{2}$^?(πh_{$\text{11}\text{2}$}²)₁₀₊ ×vf_{$\text{7}\text{2}$} is suggested for the state at 2.7 MeV.     

Heavy-quark production by hadrons: Gluon jet fragmentation versus fusion

We show that at $\text{p}\text{p}$ collider energies heavy quarks are dominantly produced by the fragmentation of gluon jets into $\text{Q}\text{Q}$ with Q = c,b. This is because the underlying gg → gg jet cross section exceeds the fusion process $\text{gg → Q}\text{Q}$ by over two orders of magnitude. We compute the perturbative contribution to the gluon fragmentation from 2 → 3 processes such as gg $\text{→ gQ}\text{Q}$. We point out the observable consequences for single-lepton production and same-opposite charge dileptons. In particular, the observed production of dileptons with large p_T and low effective mass is explained.     

Production of direct single electrons in proton-nucleus collisions at 13 GeV/c

Direct production of single electrons in proton-nucleus collisions at 13 GeV/c has been measured. A rising $\text{e}\text{π}$ ratio with decreasing p_T above the 10^?4 level is observed for low p_T single electrons. The source of the rising $\text{e}\text{π}$ ratio at low $\text{e}\text{π}$ ratio at low p_T is discussed in connection with the low mass dielectron continuum below the ? mass region.     

On the interaction of cesium with cleaved GaAs(110) and Ge(111) surfaces: Work function measurements and adsorption site model

The work function of UHV cleaved p-Ge(111) and n-GaAs(110) surfaces has been measured in dependence of the Cs coverage. At very low coverages θ < 0.001 the decrease of the contact potential difference is extremely steep. For GaAs the initial slope of the CPD versus coverage curve amounts to ?740 eV for Ge to ?130 eV per monolayer. Up to the saturation coverage the curves exhibit straight line segments with breaks at distinct coverages. Breaks are found for GaAs at approximately $\text{1}\text{12}$, $\text{1}\text{6}$, and $\text{1}\text{3}$ of a monolayer, for Ge at about $\text{1}\text{12}$, $\text{1}\text{4}$, $\text{1}\text{2}$, and $\text{3}\text{4}$. A new model is developed to explain this behaviour. It is based on the assumption of specific adsorption sites for the Cs atoms at the surfaces. With this model the experimental results, including the breaks, may be described in the whole coverage range from θ = 0.03 up to the saturation. Furthermore the dipole moments derived from the straight line segments are in excellent agreement with those values calculated for different surface molecules between the adsorbed cesium and substrate atoms at the specific adsorption sites.     

Elementary excitations in quadrupolar systems

We consider $\text{S ?}\text{3}\text{2}$ isotropic quadrupolar ordered systems and derive elementary excitations at low temperature. A Holstein-Primakoff type transformation and a linear approximation are used. For $\text{S =}\text{3}\text{2}$, the spectrum is made of four degenerate acoustic branches. For S ? 2, only two degenerate branches satisfy the Goldstone theorem: they describe Δm = ± 1 excitations similar to librons in molecular crystals. The two degenerate branches describing Δm = ± 2 excitations have a gap at k = 0 although the hamiltonian is isotropic. For a special $\text{S =}\text{3}\text{2}$ cubic hamiltonian, a Goldstone mode is found in the spectrum and related to a continuous degeneracy of the ground state. A comparison between $\text{S =}\text{1}\text{2}$ dipolar and $\text{S =}\text{3}\text{2}$ quadrupolar systems is presented.     

Surface self-diffusion on Ni(110): Temperature dependence and directional anisotropy

The surface self-diffusion coefficients, D_s, on a Ni(110) crystal are measured by a mass transfer technique in [1$\text{1}$0] and [001] directions in the temperature range 773–1573 K. The surface cleanliness was checked by Auger electron spectroscopy. LEED investigations showed that the sinusoidal surface profile consisted of (110) terraces and monatomic steps. The temperature dependence of D_s can be expressed by $\text{D}{}_{\mathrm{s}}\text{[1}\text{1}\text{0] = 0.009}\text{exp}\text{(}\text{?17.5}\text{kcal}\text{mole}\text{· RT)}$ and $\text{D}{}_{\mathrm{<mtext>s</mtext>}}\text{[001] = 470}\text{exp}\text{(}\text{?45}\text{kcal}\text{mole}\text{· RT)}$ at temperatures below 1150 K. Theoretical values for the activation energies of surface migration were calculated in the framework of the pairwise interaction model. Together with an estimate for the formation energy of adatoms of $\text{16.3}\text{kcal}\text{mole}$, one obtains for the activation energy of surface self-diffusion 17 and $\text{51 kcal}\text{mole}$ for [1$\text{1}$0] and [001] direction, respectively. At T > 1150 K the anisotropy in D_s begins to vanish. Surface diffusion in [1$\text{1}$0] direction at T < 1150 K is most likely taking place by a simple adatom hopping process. Circumstantial evidence indicates that diffusion in [001] direction does not occur by a simple hopping process but by a more complex mechanism involving higher energy surface diffusion states. This isotropic process is suggested to take place for both directions at T < 1150 K.     

Experimental results on diffractive one-pion production at the CERN ISR

New experimental results are reported on diffractive dissociation of protons into (nπ⁺) in proton-proton collisions at a centre-of-mass energy of $\text{s}\text{= 45}\text{GeV}$. The data were obtained using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. We have searched for resonance contributions and found peaks at mass values of 1.5 GeV, 1.65 GeV, and 2.1 GeV. A dip in $\text{d}\text{σ}\text{d}\text{t}$ is observed at low t and low mass; it is most pronounced for events with neutrons emitted at 90° in the Gottfried-Jackson frame. The correlation between mass and slope depends strongly on θ_J. The cross section of the channel pp → pnπ⁺ is 400 ± 110 μb at $\text{s}\text{= 45}\text{GeV}$, giving an energy dependence of s^?0.30±0.07 for isospin exchange zero in this channel.     

Inclusive π0 production at the CERN p-p̄ collider

Inclusive π⁰ production has been measured at the CERN pp? collider, $\text{s}\text{=540}\text{GeV}$, for 90° production angle and in a range of transverse momenta between 1.5 and 4.5 GeV/c. The invariant production cross section is larger than that measured at $\text{s}\text{= 53}\text{GeV}$ for p-p collisions. The production of μ mesons aand of direct photons is also investigated.     

Photoproduction of charm and beauty

The photoproduction of charm and beauty are reexamined within QCD. In addition to the photon-gluon amalgamation mechanism, $\text{q}$q → b$\text{b}$ or c$\text{c}$ is also examined. It turns out that for beauty production at SPS photon beams, the $\text{q}$q → b$\text{b}$ mechanism is dominant over γ-g amalgamation for Buras-Gaemers gluon distributions. The possibility of experimental measurement is briefly discussed.     

Observation of pure quadrupole resonance in zinc metal

We report the first observation of nuclear quadrupole resonance (NQR) in Zn metal. A resonance line, which under the assumption of axial symmetry (η=0) corresponds to the $\text{|M| =}\text{3}\text{2}\text{?}\text{5}\text{2}$ transition in the $\text{I =}\text{5}\text{2}$ ground state of ⁶⁷Zn, has been found at v = 4.086(2) MHz at 4.2K. This yields (for η=0) a quadrupole coupling constant of $\text{e}{}^2\text{qQ}\text{h}\text{= 13.620(8)}$MHz, which is the most accurate value currently available.     

Analysis of the high-temperature spin-glass susceptibility: Determination of the local magnetic exchange

New measurements are reported of the magnetic susceptibility above the freezing temperature T_f for noble-metal spin-glasses with $\text{1}\text{2}$ to 6 at.% Fe or Mn. The susceptibility for T_f<T?5 T_f is not Curie-Weiss, but local magnetic correlations manifest themselves and provide a key for the determination of the exchange interactions in spin-glasses. The exchange parameters J_n are resolved up to 5 neighbors for $\text{Au}$Fe, $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Pt}$Mn through a configuration ensemble calculation which includes atomic short range order.     

Structure factor for a Bose fluid

The structure factor is calculated for a Bose fluid using an expression for S(k), which is approximately valid for all values of k. Marked fluctuations appear for $\text{k = 2.15}\text{A}\text{?}{}^{-1}$, near the roton dip in E_k, and at $\text{k = 3.65}\text{A}\text{?}{}^{-1}$ near the dip in the second branch of E_k. Our calculations are indirectly a theoretical justification for the existence of a second branch in E_k. The results presented here agree fairly well with the experimental values for $\text{k >; 3.0}\text{A}\text{?}{}^{-1}$ along with a dip at $\text{k = 3.67}\text{A}\text{?}{}^{-1}$ which has not been reported earlier. It also suggests the existence of two waves, phonons and rotons, for $\text{k >; 3.0}\text{A}\text{?}{}^{-1}$.     

Resistivity of dilute AlMg and AlMn between 0° and 100°C a generalized approach

We have measured the resistivity of $\text{Al}$Mg and $\text{Al}$Mn up to 0.5 at. % impurity concentration between 0° and 100°C. The results for the resistivity for both systems can be analysed within one generalized model in which spinfluctuations as well as changes in the electron-phonon interaction are considered. For $\text{Al}$Mn a calculation of the impurity contribution to d?/dT is attempted. For $\text{Al}$Mg there are indications that the superconducting T_c will increase with Mg concentration.     

Electrical resistance and magnetoresistance of amorphous alloys Gd67Co33 and Pd80Si20

In search for structural contributions to the low temperature anomaly we report high resolution resistance and magnetoresistance measurements ($\text{0.02}\text{K}\text{? T ? 20}\text{K}$) of amorphous splats of Gd₆₇Co₃₃ and Pd₈₀Si₂₀. For both alloys, the resistivity ?(H = 0, T) has a minimum at T ～ 10 K and increases with decreasing T. The ferromagnetic Gd₆₇Co₃₃ shows a strong negative field dependence of $\text{Δ?}\text{?(0)}$, saturating at H ～ 2T for T = 4.2 K but no measurable change in $\text{??}\text{?}\text{T}$ below 10 K is observed.The diamagnetic Pd₈₀Si₂₀ exhibits a positive field dependent magnetoresistance $\text{[Δ?}\text{?(0)]}\text{(}\text{H}\text{)}$ at low temperatures. Additionally, a field dependent part in $\text{??}\text{?}\text{T}$ is found which is probably due to paramagnetic impurities (～ 1 ppm Fe). However, there is also a field independent contribution in the amorphous state of Pd₈₀Si₂₀, which vanishes after crystallization. We attribute this to non-magnetic scattering induced by the disordered structure.     

Radiative decays of the Jψ and evidence for a new heavy resonance

The three photon final state produced in e⁺e^? collisions has been measured at the mass of the $\text{J}\text{ψ}$ resonance using the nonmagnetic part of the double arm spectrometer DASP. The decays $\text{J}\text{ψ}\text{→ ηγ, η'γ}$ and π^oγ were observed and their branching ratios are given. A four standard deviation signal was observed in the γγ mass spectrum at a mass of (2.83 ± 0.03) GeV. An upper limit is given for the direct decay $\text{J}\text{ψ}\text{→ 3γ}$.     

Ferroelectric lithium tantalate—III. Temperature dependence of the structure in the ferroelectric phase and the para-electric structure at 940°K

The neutron scattering from a single crystal of LiTaO₃ (Curie temperature 907°K) has been measured at 760, 820, 885 and 940°K, and has been remeasured at 298°K. Least squares structural refinement of the five data sets shows that as the temperature approaches T_c the oxygen atom approaches the position $\text{x,}\text{1}\text{3}\text{,}\text{1}\text{12}$, with respect to Ta at the origin, in space group R3c. The temperature variation of the oxygen y- and z-coordinates is very similar to that of the spontaneous polarization. The lithium atom position below T_c remains essentially invariant as a function of temperature. At T_c, the oxygen atom occupies the position $\text{x,}\text{1}\text{3}\text{,}\text{1}\text{12}$, the lithium atom becomes disordered and distributed over the positions $\text{00z}\text{and}\text{0, 0,}\text{1}\text{2}\text{-z}$, and the tan alum atom becomes located at an inversion center, in space group $\text{R}\text{3}\text{c}$. The lithium atom sites above T_c lie 0.374 Å on either side of the oxygen atom plane at $\text{z =}\text{1}\text{4}$.     

Analysis of topological cross sections in pp interactions at 22.4 GeVc

The multiplicity distribution for 11558 events in $\text{p}\text{p}$ interactions at 22.4 $\text{GeV}\text{c}$ was analyzed. The average charged multiplicity 〈n_ch〉 for inelastic events was found to be 4.69 ±0.05 and $\text{〈n}{}_{\mathrm{ch}}\text{〉}\text{D=2.04 ± 0.05}$. The early KNO scaling of normalized topological cross sections has been tested.