Testing the nature of the Λ(1520)-resonance in proton-induced production

The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of the pp → pK⁺K^-p and pp → pK⁺π⁰π⁰Λ reactions. In particular, we show that the ratio between the π⁰π⁰Λ and K^-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at Jülich or the developing CSR facility at Lanzhou.     

Structure of quantum-mechanical relativistic two-body interactions for spinning particles

Relativistic constraint mechanics yields consistent systems of coupled Dirac equations for pairs of spinning particles. We explicitly connect these equations to the Bethe-Salpeter equation of quantum field theory and to the interactions of classical Fokker-Tetrode dynamics (and hence to classical relativistic field theory) to obtain versions of these equations governed by systems of (possibly noncoulombic) relativistic potentials whose detailed structures contain important relativistic effects like correct Darwin interactions. We recast the defining pair of Dirac equations in a number of equivalent but important forms—“external potential,” Sazdjian, hyperbolic, and Breit— and examine their interconnection. Since the potentials in these equations are no more singular than — 1/4r² we are able to solve appropriate versions of them nonperturbatively for the qˉq system to obtain a very good fit to the entire meson spectrum and for the e ⁺ e ⁻ system to calculate the positronium spectrum of QED correct through order α ⁴ .     

New results for the production of Λ and Σhyperons in antineutrino scattering from protons

We obtain total and differential cross-sections for the strangeness changing charged current reactions ˉ + p → Λ + L ⁺ and ˉ + p → Σ⁰ + L ⁺ , where L is a charged lepton, either an electron, muon or tau. We do this by making use of the standard dipole form factors normally used and of the new form factors recently obtained from recoil proton measurements in electron-proton electromagnetic scattering. We also obtain the contributions of the individual form factors to the total and differential cross-sections for both sets of form factors. We find that the differential and total cross-sections for Λ production change only slightly between the two sets of form factors but that the differential and total cross-sections change substantially for Σ⁰ production. We discuss the possibility of distinguishing between the two cases for the experiments planned by the MINERν A Collaboration.     

Crystal electric field next to a hydrogen-like interstitial— µ+ in PrNi5

Muon spin rotation measurements of the temperature dependence and the anisotropy of the μ⁺ Knight shift in single crystals of the crystal electric field singlet ground state system PrNi₅ reveal pronounced deviations from a linear scaling of the Knight shift with the bulk magnetic susceptibility atT≤50 K. They are explained by a μ⁺ induced modification of the atomic susceptibility of neighboring Pr³⁺ ions. From the Knight shift anisotropy atT> 50 K it is determined that the implanted μ⁺ occupy a single intersitial site, namely the 6i site (0.5, 0, 0.21±0.02). Using this site information, good model fits to the measured data are obtained assuming a μ⁺ induced perturbation of the crystal electric field at the Pr³⁺ ions next to the μ⁺. Apparently, the presence of the μ⁺ leads to a lowering of the local symmetry, causing a lifting of the degeneracy and a pronounced rearrangement of the low lying crystal electric field levels for these ions.     

Registration of hydrogen-like leptonic bound states ( e-μ+) and ( e+μ-) in reactions of high-energy scattering of polarized electrons and positrons by nuclei with Z ～ 100 and analysis of CPT invariance

The cross-sections for the reactions of muonium (anti-muonium) production in the high-energy electron (positron) scattering by nuclei e ^-(e ⁺) + Z↦Z + M ⁰(ˉM) + μ^-(μ⁺) are calculated in dependence on energy and polarization of the initial electron (positron) and polarization of the final μ^-(μ⁺)-meson. Since this is a coherent phenomenon the cross-sections are proportional to Z². For Z ∼ 100, due to the factor Z², the cross-sections are large enough to be measured at the energies available for the HERA Collider at DESY. The results are discussed in connection with a test of CPT invariance. Received: 24 September 2002 / Accepted: 12 March 2003 / Published online: 27 May 2003     

Measurement of molecular hydrogen densities by resonance fluorescence

Using a pulsed capilary discharge through helium as a light source fluorescence within the Lyman bands (transitionX ¹ ∑ _g ⁺ →B ¹ ∑ _u ⁺ of molecular hydrogen and deuterium has been investigated. Selecting a narrow spectral range (width ≈ 8 ?) from the continuum radiation with a spectrometer, lines in the wavelength range from 1060 ? to 1110 ? have been excited having a vibrational quantum number υ″=0 in the lower state, and ≦υ′≦4 in the upper state. The fluorescence intensity has been measured as a function of υ′ and of the hydrogen density. Agreement with calculations has been found to be within ±30%. The method at present allows the determination of densities between 10¹⁰ and 10¹⁵ molecules per cm³ with a temporal resolution of 1μs and with a spacial resolution of 0.1 cm³     

Autosolitons in electron-hole plasma in p-Ge

The self-organization of an electron-hole plasma (EHP) heated by an electric field in pure p-Ge samples at T = 77 K has been studied experimentally. The derived current-voltage characteristics (CVCs) and the distributions of the electric field and IR emission of the hot carriers along the samples show that the segments of a steep rise or the S-shaped segments of the CVCs in samples with n-p junctions are related to the formation of longitudinal thermal-diffusion autosolitons (AS_‖); as a result, thin (d = 2–20 μm in diameter), melted-through current channels appear. Such AS_‖ are formed at high EHP densities (n ≥ 1 × 10¹⁶ cm⁻³), when the electron-hole scattering is dominant, and at electron temperatures T _e = (2–4.5)T ₀ (T ₀ is the lattice temperature). The saturation segments and the N-shaped segments in the CVCs are attributable to the generation of transverse thermal-diffusion high-field autosolitons (AS_⊥) in the form of narrow strata with electric field strengths = 1–20 kV cm⁻¹. High-field AS_⊥ are formed at EHP densities n = 5 × 10¹³−1 × 10¹⁶ cm⁻³, when the electron-phonon scattering is dominant, and at electron temperatures T _e ∼ Θ ≥ 5T ₀ (Θ is the Debye temperature). The generated longitudinal and transverse autosolitons have high temperatures (T _e ≥ 1000 K) and reduced carrier densities and can exist simultaneously in different parts of the sample. Original Russian Text ? M.N. Vinoslavskiĭ, P.A. Belevskii, A.V. Kravchenko, 2006, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 129, No. 3, pp. 477–492.     

Subthreshold ϕ-meson production and medium effects in proton-nucleus reactions

Within the spectral function approach, we study the direct production and decay via the dikaon (dimuon) channel of ϕ mesons in the interactions of 2.4-and 2.7-GeV protons with light and medium target nuclei. It is shown that the K ⁺ K ⁻ (μ⁺ μ⁻) invariant-mass distribution consists of the two components, which correspond to the ϕ decay “outside” and “inside” the target nucleus. The first (narrow) component has the free ϕ width, while the second (broad) component is distorted by the nuclear matter owing to resonance-nucleon scattering and a possible in-medium modification of the kaons and ρ meson at finite baryon density. The relative strength of the “inside” and “outside” components is analyzed in different scenarios for the ϕ width and momentum cut. It is demonstrated that the width of the resulting dimuon invariant-mass distribution on medium nuclei is larger than the free ϕ width by a factor of about 2 if the total ϕ in-medium width is used and the respective cutoff for the ϕ three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the ϕ in-medium properties owing to the strong absorption of the K ⁻ in the surrounding nuclear matter. On the other hand, because of the distortion of the K ⁺ and K ⁻ on their way out of the target nucleus mainly due to the hadronic kaon potentials, the latter distribution is broadened and shifted to higher invariant masses, which means that the measurement of such broadening would give additional evidence for the modification of the kaon and antikaon properties in the nuclear medium. The text was submitted by the author in English.     

New data on the p + N → [Σ0K+] + N reaction at E p= 70 GeV and the search for exotic baryons

New data for the diffractive reaction p+N→ [Σ⁰ K ⁺] +N at E _p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous study of this reaction. In the mass spectrum M(Σ⁰ K ⁺) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark baryon with hidden strangeness |qqqsˉs>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P ² _T < 0.01 GeV². The possibility of the Coulomb production mechanism for X(1810) is discussed. Received: 28 April 1999     

Multiquark picture for Σ (1620)

In this work we report on a new QCD sum rule analysis to predict masses of the excited baryon states (e.g. Σ (1620) and Λ (1405)) by using multiquark interpolating fields ((qˉq)(qqq)). For the Σ (1620) we consider the ˉKN, πΣ, and πΛ (I = 1) multiquark interpolating fields. The calculated mass from those multiquark states is about 1.592 GeV. For the Λ (1405) we first show the result using the π⁺Σ⁻+π⁰Σ⁰+π⁻Σ⁺ (I = 0) multiquark interpolating field, and compare the calculated mass to that of our previous result using the π⁰Σ⁰ multiquark state. We then show that the mass 1.405 GeV is well reproduced when using the ˉKN (I = 0) multiquark state. The uncertainties in our sum rules are also discussed. Received: 7 September 1998 / Revised version: 5 January 2000     

Structural features of aluminium alloy 1441 irradiated by Ar+ ions

Using electron microscopy it was found that irradiation of clad cold-worked specimens made of commercial aluminium-lithium alloy 1441 by the Ar ⁺ ions of energy 40 keV at low doses of irradiation (10¹⁵ cm⁻², irradiation time 1 s, T < 70 °C) and ion-current density of about 100 μA/cm² results in the transformation of the cellular structure formed in the alloy under deformation. As the dose of irradiation is increased up to 10¹⁶ cm⁻², a transition from a cellular to a subgrain structure close to a polygonal one is observed. The efficiency of the process is increased with ion-current density. Furthermore, under ion irradiation at increased ion-current densities, the β′(Al ₃ Zr) and Al ₈ Fe ₂ Si particles present in the deformed alloy dissolve, and disperse particles of a new Al ₂ LiMg phase of platelet shape are formed. The changes in the dislocation structure and phase composition in alloy 1441 are observed several seconds after irradiation not only in the surface layer adjacent to the ion incorporation band but also through the thickness of the specimen tens of thousands times greater than ion projective ranges. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–81, February, 2007.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

Target fragmentation in pp, ep and γp collisions at high energies

We calculate target fragmentation in pp→nX and γp→nX reactions in the meson cloud picture of the nucleon. The pp→nX reaction is used to fix the pnπ⁺ form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small x _Bj electroproduction of forward neutrons at HERA. Here the qˉq dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the hadronic reaction. For deep inelastic events (Q ² > 10 GeV²) screening is weaker but still present at large Q ². The signature for this absorptive rescattering is a shift of the dσ/dE_n distribution to higher neutron energies for photofragmentation. Received: 12 June 1999 / Revised version: 12 October 1999     

a 0 + (980)-resonance production in the reaction pp → dπ + η close to the K\bar K threshold

The reaction pp → dπ ⁺ η has been measured at a beam energy of T _p = 2.65 GeV (p _p = 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ ⁺ pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ ⁺(nπ) events. The differential cross section d ⁴ σ/dΩ_d dΩ _π ⁺ dp _d dp _π ⁺ for the reaction pp → dπ ⁺ η has been determined model independently for two regions of phase space. Employing a dynamical model for the a ₀ ⁺ production allows one then to deduce a total cross section of σ(pp → da ₀ ⁺ → dπ ⁺ η) = 1.1 ± 0.3_stat ± 0.7_syst μb for the production of π ⁺ η via the scalar a ₀ ⁺ (980) resonance and σ(pp → dπ ⁺ η) = 3.5 ± 0.3_stat ± 1.0_syst μb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction , the ratio of the total cross sections is , which is in agreement with branching ratios in the literature. The text was submitted by the authors in English.     

Viscous flow of magnetic vortices and rapid relaxation of magnetization in YBaCuO ceramics

The viscous flow of magnetic vortices in granular YBaCuO ceramics of various granule sizes is investigated using the microwave absorption method (f=80 MHz) in the range of varying magnetic fields H=±1500 Oe and of temperatures T=77 to 95 K. The conditions for the formation and melting of the vortex lattice, as well as the transition of the high-temperature superconductor (HTSC) state from the irreversibility region to the region of the viscous flow of magnetic vortices, are considered. The rapid magnetic relaxation times in the range τ=72 to 111 ms are determined from the magnetization relaxation in the HTSC materials under investigation depending on the granule size d, which varies from 1 to 30 μm. The experimental results on the variation of the relaxation time τ from 77 to 120 ms in a ceramic exposed to fast neutrons with various fluences (Φ=10¹⁶ to 10¹⁹ cm⁻²) are considered. The depinning process is analyzed; it occurs in the form of a thermally assisted flux flow in the range of low activation energies. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 6, 2001, pp. 968–973. Original Russian Text Copyright ? 2001 by Chashchin.     

Strain-induced photoreflectance spectra in the vicinity of the E 0 transition in GaAs/Si and InP/Si heterostructures

A study is reported of the structure of photoreflectance (PR) spectra in the vicinity of the E ₀ transition from thin (d=1–5 μm) n-GaAs and n-InP films (n=10¹⁶–10¹⁷ cm⁻³) grown epitaxially on Si(001) substrates. A quantitative analysis of the spectra involving multi-component fitting shows that the electronic optical transition from the {3/2;±1/2} subband provides a dominant contribution to the intermediate-field electromodulation component in both systems. The splitting observed in the GaAS/Si PR spectra near the main peak are accounted for not by the strain-induced valence-band splitting but rather by a spectral superposition of the intermediate-field component due to the {3/2;±1/2} subband with a low-energy excitonic component. The analytically established transition energy E ₀ ^3/2;±1/2 is used to calculate biaxial strains in epitaxial films. Fiz. Tverd. Tela (St. Petersburg) 41, 725–731 (April 1999)     

Probing the interactions of charmed mesons with nuclei in ¯p-induced reactions

We study the perspectives of resonant and nonresonant charmed-meson production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(3770),Ψ(4040) and Ψ(4160) on various nuclei, their propagation and decay to D,ˉD, D ^*,ˉD^*, D _s,ˉD_s in the medium and vacuum, respectively. The modifications of the open charm vector mesons in the nuclear medium are found to be rather moderate or even small such that dilepton spectroscopy will require an invariant mass resolution of a few MeV. Furthermore, the elastic and inelastic interactions of the open charm mesons in the medium are taken into account, which can be related to (u, d )-, s- or c-quark exchange with nucleons. It is found that by studying the D/ˉD ratio for low momenta in the laboratory ( ? 2 - 2.2 GeV/c) as a function of the target mass A stringent constraints on the c-quark exchange cross-section can be obtained. On the other hand, the ratios D ^- _s/D ⁺ _s as well as D/D ^- _s and D/D ⁺ _s at low momenta as a function of A will permit to fix independently the strength of the s-quark exchange reaction in D ^- _s N scattering. Received: 1 March 2002 / Accepted: 21 March 2002     

Meson exchange hyperon-nucleon interaction based on correlated ππ/K¯ exchange

We present a new model for the hyperon-nucleon (ΛN , ΣN interaction, derived within the meson exchange framework. The model incorporates the standard one-boson exchanges of the lowest pseudoscalar and vector meson multiplets with coupling constants fixed by SU(6) flavor symmetry relations. As a new feature, the contribution in the scalar-isoscalar (σ sector is derived from a microscopic model of correlated ππ and Kˉ exchange. The same model is also used to constrain the interaction resulting from the vector-isovector (ρ exchange channel. Additional short-ranged ingredients of the model in the scalar-isovector (a₀) and scalar-isospin-1/2 (κ channels are likewise viewed as arising from meson-meson correlations but are treated phenomenologically. With this model a satisfactory reproduction of the available hyperon-nucleon data is achieved.     

Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions

Antiproton proton annihilation reactions allow unique access to the moduli and phases of nucleon electromagnetic form factors in the time-like region. We present the helicity amplitudes for the unequal-mass single-photon reaction pˉ → l ⁺ l ^- in the s channel including the lepton mass. The relative signs of these amplitudes are determined using simple invariance properties. Helicity amplitudes for one-photon exchange annihilation reaction pˉ → Bˉ are also given, where B is any spin-one-half particle with structure. Crossing relations between the ep → ep scattering and the pˉ → l ⁺ l ^- annihilation channels are discussed and the crossing matrix for the helicity amplitudes is given. This matrix may be used to verify known expressions for the space-like helicity amplitudes due to one-photon exchange.     

Dilepton production from ρ-mesons in a quark-gluon plasma

Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π⁺-π⁻ annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma. Received: 8 September 1999 / Revised version: 22 October 1999