On the instanton-induced portion of the nucleon strangeness

We calculate the instanton contribution to the proton strangeness in an MIT bag enriched by the presence of a dilute instanton liquid. The evaluation is based on the expression of the nucleon matrix elements of bilinear strange-quark operators in terms of a model valence nucleon state and the interactions producing quark–antiquark fluctuations on top of that valence state. Our method combines use of the the evolution operator containing a strangeness source and the Feynman–Hellmann theorem. It enables one to evaluate the strangeness in different Lorentz channels in essentially the same way. Only the scalar channel is found to be affected by the interaction induced by the random instanton liquid. Received: 12 February 1999 / Published online: 30 June 1999     

On chemical equilibrium in nuclear collisions

The data on average hadron multiplicities in central A+A collisions measured at CERN SPS are analysed with the ideal hadron gas model. It is shown that the full chemical equilibrium version of the model fails to describe the experimental results. The agreement of the data with the off–equilibrium version allowing for partial strangeness saturation is significantly better. The chemical freeze–out temperature of about 180 MeV seems to be independent of the system size (from S+S to Pb+Pb) and in agreement with that extracted in , and collisions. The strangeness suppression is discussed at both hadron and valence quark level. It is found that the hadronic strangeness saturation factor increases from about 0.45 for interactions to about 0.7 for central A+A collisions with no significant change from S+S to Pb+Pb collisions indicating that the strangeness enhancement in heavy ion collisions cannot be fully attributed to the increased system size. The quark strangeness suppression factor is found to be about 0.2 for elementary collisions and about 0.4 for heavy ion collisions independently of collision energy and type of colliding system. Received: 31 October 1997 / Published online: 26 February 1998     

CP-violation in the production of $\tau$-leptons at TESLA with beam polarization

We study the prospects of discovering CP-violation in the production of leptons in the reaction at TESLA, an e ⁺ e ^- linear collider with center-of-mass energies of 500 or even 800 GeV. Non-vanishing expectation values of certain correlations between the momenta of the decay products of the two leptons would signal the presence of CP-violation beyond the standard model. We study how longitudinal beam polarization of the electron and positron beams will enhance these correlations. We find that T-odd and T-even vector correlations are well suited for the measurements of the real and imaginary parts of the electric dipole form factors. We expect measurements of the real part with a precision of roughly 10^-20 e cm and of the imaginary part of 10^-17 Received: 13 June 2002 / Revised version: 17 October 2002 / Published online: 20 December 2002     

Parity Violation in Electron Quasi-Elastic Scattering

Parity violating electron scattering on a nucleus in the quasi-elastic region is investigated within a relativistic single particle model from ²⁰⁸Pb and with the incident electron energy up to 1 GeV. We discuss the effect of nucleon electromagnetic form factors by comparing the standard Sachs form factors with the parameterized form recently adjusted to the world data. The effect of the strangeness is also investigated through the recent results of the strangeness form factors, and we separately calculate the asymmetries of longitudinal and transverse response functions.     

Core polarization effects on C4 form factors of sd-shell nuclei

Coulomb form factors of C4 transitions in even-even N = Z sd-shell nuclei ( ²⁰Ne, ²⁴Mg, ²⁸Si and ³²S) are discussed taking into account higher-energy configurations outside the sd-shell model space which are called core polarization effects. Higher configurations are taken into account through a microscopic theory, which allows particle-hole excitations from the 1s and 1p shells core orbits and also from the 2s1d-shell orbits to the higher allowed orbits with excitations up to 4 ω. The effect of core polarization is found essential in both the transition strengths and momentum transfer dependence of form factors, and gives a remarkably good agreement with the measured data with no adjustable parameters. The calculations are based on the Wildenthal interaction for the sd-shell model space and on the modified surface delta interaction (MSDI) for the core polarization effects. Received: 24 January 2002 / Accepted: 29 July 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: baguniv@uruklink.net Communicated by P. Schuck     

Strangeness enhancement and energy dependence in heavy ion collisions

The canonical statistical model analysis of strange and multistrange hadron production in central A–A relative to p–p/p–A collisions is presented over the energy range from GeV up to GeV. It is shown that the relative enhancement of strange particle yields from p–p/p–A to A–A collisions substantially increases with decreasing collision energy. It is largest at GeV, where the enhancement of and is of the order of 100, 20 and 3, respectively. In terms of the model these results are due to the canonical suppression of particle thermal phase space at lower energies, which increases with the strangeness content of the particle and with decreasing size of the collision fireball. The comparison of the model with existing data on the energy dependence of the kaon/pion ratio is also discussed. Received: 25 October 2001 / Published online: 5 July 2002     

Vector meson photoproduction at high-<Emphasis Type="Italic">t</Emphasis> and comparison to HERA data

We explore QCD calculations for the process where V is a vector meson, in the region and . We compare our calculations for the , and mesons with data from the ZEUS Collaboration at HERA and demonstrate that the BFKL approach is consistent with the data even for light mesons, whereas the two-gluon exchange approach is inadequate. We also predict the differential cross-sections for the and for which no data are currently available. Received: 23 May 2002 / Published online: 9 December 2002     

The controversial role of strangeness in the spin structure of the nucleon<Superscript>⋆</Superscript>

Although the strangeness content of the nucleon is small, it has played a major role in provoking puzzles and controversies in our understanding of the internal structure of the nucleon, particularly as concerns the spin structure. We recall the role of the strange polarization in precipitating the “spin crisis in the parton model” and discuss our present knowledge of the shape and sign of Δs(x) .     

Strangeness production and other recent results from Hall B at Jefferson Lab

Recent results using the CLAS detector at Jefferson Lab are discussed. We emphasize strangeness photo- and electro-production in the baryon resonance region between W = 1.6 and 2.3 GeV, where indications of s-channel structure are suggestive of high-mass baryon resonances coupling to kaons and hyperons in the final state. Other CLAS results, for the E _{1 +} /M _{1 +} transition form factor at the first -resonance, two-pion electroproduction, and photoproduction are also briefly mentioned.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.30.-a Decays of baryons - 13.30.Eg Hadronic decays - 13.40.-f Electromagnetic processes and properties - 13.60.-r Photon and charged-lepton interactions with hadronsR.A. Schumacher: For the CLAS Collaboration     

Polarization of strangeness Arizona muon

The longitudinal polarization of strangeness Arizona muon, namely, the 236 MeV/c ⁺ from the K^{+ +} v decay, has been measured to search for right-handed weak current in the strangeness changing process. The polarization has been determined to be –0.967±0.047.We are grateful to Professors T. Nishikawa, S. Ozaki, A. Kusumegi, and H. Sugawara of KEK for their encouragement and support during the course of this experiment. We are grateful to the operating crew of the KEK proton synchrotron and its experimental facilities for their cooperation during the experiment. This work is partially supported by the Grant-in-Aid of the Ministry of Education, Science and Culture.     

Strangeness production in nuclear matter and expansion dynamics

Thermodynamical properties of hot and dense nuclear matter are analyzed and compared for different equations of state (EoS). It is argued that the softest point of the equation of state and the strangeness separation on the phase boundary can manifest themselves in observables. The influence of the EoS and the order of the phase transition on the expansion dynamics of nuclear matter and strangeness excitation function is analyzed. It is shown that the bulk properties of the strangeness production in A-A collisions depend only weakly on the particular form of the EoS. The predictions of different models are related with experimental data on strangeness production.Received: 11 August 2003, Published online: 3 December 2003     

Strangeness −2 two-baryon systems

We derive strangeness −2 baryon–baryon interactions from a chiral constituent quark model including the full set of scalar mesons. The model has been tuned in the strangeness 0 and −1 two-baryon systems, providing parameter free predictions for the strangeness −2 case. We calculate elastic and inelastic NΞ and ΛΛ cross sections which are consistent with the existing experimental data. We also calculate the two-body scattering lengths for the different spin–isospin channels.     

Momentum transfer theory of ion transport under the influence of resonant charge transfer collisions: the case of argon and neon ions in parent gases

Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). It was shown that, not surprisingly, RCT collisions may be represented as a special case of elastic scattering. Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar+Ar ⁺ collisions by making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne+Ne ⁺ integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models. Received 16 June 2002 / Received in final form 2nd August 2002 Published online 24 September 2002 RID="a" ID="a"e-mail: vrhovac@phy.bg.ac.yu RID="b" ID="b"e-mail: zoran@phy.bg.ac.yu     

On the mass,width and coupling constants of the <Emphasis Type="Italic">f</Emphasis><Subscript><Emphasis Type="Italic">0</Emphasis></Subscript>(980)

Using the pole approach we determine the mass and width of the f ₀ (980); in particular, we analyze the possibility that two nearby poles are associated to it. We restrict our analysis to a neighborhood of the resonance, using data for the phase shift and inelasticity, and the invariant mass spectrum of the decays. The formalism we use is based on unitarity and a generalized ver sion of the Breit-Wigner parameterization. We find that a single pole describes the f ₀ (980), the precise position depending upon the data used. As a byproduct, values for the and coupling constants are obtained. Received: 6 June 2002 / Revised version: 21 October 2002 / Published online: 3 March 2003     

Rare decay B\rightarrow X_sl^+l^- in a CP spontaneously broken two-Higgs doublet model

The Higgs boson mass spectrum and couplings of the neutral Higgs bosons to the fermions are worked out in a CP spontaneously broken two-Higgs doublet model in the large case. The differential branching ratio, forward-backward asymmetry, CP asymmetry and lepton polarization for are computed. It is shown that the effects of neutral Higgs bosons are quite significant when is large. Especially, the CP violating normal polarization can be as large as several percents. Received: 15 October 2001 / Revised version: 5 March 2002 / Published online: 26 July 2002     

A new intrinsic defect in amorphous SiO2: Twofold coordinated silicon

The well known optical absorption band at 5.03 eV (the “B₂ band”) and luminescence band at 4.3 eV in amorphous SiO₂ are due to singlet-to-singlet transitions, while the luminescence band at 2.65 eV - due to triplet-to-singlet transitions in a silicon-related intrinsic defect. This defect occurs both in the bulk and on the surface. Luminescence polarization data indicate C_2v symmetry. The most probable model for this center is a silicon atom with only two neighboring oxygens. Such defects form a separate class of valence alternation defects, characteristic for amorphous materials having atoms in tetrahedral coordination.     

Charm of small-x neutrino deep-inelastic scattering

Due to the weak-current nonconservation, the diffractive excitation of the charm and strangeness dominates the longitudinal structure function F _L (x, Q ²) of a neutrino DIS at a small Bjorken x. Quantitative predictions based on the color dipole BFKL approach are given for this effect in the kinematical range of the CCFR/NuTeV experiment. The relevance of our findings to the experimental tests of PCAC is discussed. The text was submitted by the authors in English.     

A study of quasielastic neutrino interactions ν μ n → μ− p in the NOMAD experiment

In this note, we present preliminary results on the study of the quasielastic reaction ν _μ n → μ⁻ p using the full set of NOMAD neutrino data. We perform a measurement of the total cross section of this process, normalizing to deep-inelastic scattering events selected from the same data sample. The measured cross section is found to be about 20% smaller than the world average of previous bubble chamber experiments. The analysis is still in progress since it is important to estimate the systematic uncertainties. for the NOMAD Collaboration The text was submitted by the authors in English.     

\Lambda, \bar{\Lambda} polarization and spin transfer in lepton deep-inelastic scattering

The flavor and helicity distributions of the and hyperons for both valence and sea quarks are calculated in a perturbative QCD (pQCD) based model. We relate these quark distributions to the fragmentation functions of and , and calculate the z-dependence of the longitudinal spin transfer to and in lepton deep-inelastic scattering (DIS). It is shown that the spin transfer to the is compatible with the first HERMES results at DESY, and further tests are suggested. We also make predictions for the z-dependence of the and longitudinal polarizations in neutrino (antineutrino) DIS processes. We investigate the sea contribution to the fragmentation functions, and we test a possible scenario where the sea quarks in (or the sea antiquarks in ) are negatively polarized, whereas the sea antiquarks in the (or the sea quarks in ) are positively polarized. The asymmetry of the polarized fragmentation functions of the sea quarks and antiquarks to and provides a way to understand the different behavior between the and spin transfers observed in the recent E665 experiment at FNAL. Received: 5 April 2000 / Published online: 26 July 2000