Electromagnetic form factors of hyperons in a relativistic quark model

The relativistically covariant constituent quark model developed by the Bonn group is used to compute the EM form factors of strange baryons. We present form-factor results for the ground-state and some excited hyperons. The computed magnetic moments agree well with the experimental values and the magnetic form factors follow a dipole $Q^2$ dependence.Comment: 4 pages, 1 figure, Proceedings for NSTAR '04 conference in Grenoble, France, March 24-27, 2004 (World Scientific

The Leading Particle Effect from Heavy-Quark Recombination

The leading particle effect in charm hadroproduction is an enhancement of the cross section for a charmed hadron D in the forward direction of the beam when the beam hadron has a valence parton in common with the D. The large D+/D- asymmetry observed by the E791 experiment is an example of this phenomenon. We show that the heavy-quark recombination mechanism provides an economical explanation for this effect. In particular, the D+/D- asymmetry can be fit reasonably well using a single parameter whose value is consistent with a recent determination from charm photoproduction.Comment: Revtex file, 4 pages, 3 figure

Clustering in light nuclei in fragmentation above 1 A GeV

The relativistic invariant approach is applied to analyzing the 3.3 A GeV $^{22}$Ne fragmentation in a nuclear track emulsion. New results on few-body dissociations have been obtained from the emulsion exposures to 2.1 A GeV $^{14}$N and 1.2 A GeV $^{9}$Be nuclei. It can be asserted that the use of the invariant approach is an effective means of obtaining conclusions about the behavior of systems involving a few He nuclei at a relative energy close to 1 MeV per nucleon. The first observations of fragmentation of 1.2 A GeV $^{8}$B and $^{9}$C nuclei in emulsion are described. The presented results allow one to justify the development of few-body aspects of nuclear astrophysics.Comment: 7 pages, 8 figures, 3 tables, Nuclear Physics in Astrophysics-2, 16-20 May, 2005 (ATOMKI), Debrecen, Hungar

Topology of "white" stars in relativistic fragmentation of light nuclei

In the present paper, experimental observations of the multifragmentation processes of light relativistic nuclei carried out by means of emulsions are reviewed. Events of the type of "white" stars in which the dissociation of relativistic nuclei is not accompanied by the production of mesons and the target-nucleus fragments are considered. A distinctive feature of the charge topology in the dissociation of the Ne, Mg, Si, and S nuclei is an almost total suppression of the binary splitting of nuclei to fragments with charges higher than 2. The growth of the nuclear fragmentation degree is revealed in an increase in the multiplicity of singly and doubly charged fragments with decreasing charge of the non-excited part of the fragmenting nucleus. The processes of dissociation of stable Li, Be, B, C, N, and O isotopes to charged fragments were used to study special features of the formation of systems consisting of the lightest $\alpha$, d, and t nuclei. Clustering in form of the $^3$He nucleus can be detected in "white" stars via the dissociation of neutron-deficient Be, B, C, and N isotopes.Comment: 20 pages, 3 figures, 9 tables, conference: Conference on Physics of Fundamental Interactions, Moscow, Russia, 1-5 Mar 2004.(Author's translation

Leading Effects in Hadroproductions of Lambda_c and D From Constituent Quark-Diquark Cascade Picture

We discuss the hadroproductions of Lambda_c, Lambda_c bar, D and D bar in the framework of the constituent quark-diquark cascade model taking into account the valence quark annihilation. The spectra of Lambda_c and Lambda_c bar in pA, Sigma^-A and pi^-A collisions are well explained by the model using the values of parameters used in hadroproductions of D and D bar. It is shown that the role of valence diquark in the incident baryon is important for D bar productions as well as for Lambda_c production.Comment: 11 pages, 5 figures, v2:some explanations added, references added, typos corrected, v3: top margin change

"Tomography" of the cluster structure of light nuclei via relativistic dissociation

These lecture notes present the capabilities of relativistic nuclear physics for the development of the physics of nuclear clusters. Nuclear track emulsion continues to be an effective technique for pilot studies that allows one, in particular, to study the cluster dissociation of a wide variety of light relativistic nuclei within a common approach. Despite the fact that the capabilities of the relativistic fragmentation for the study of nuclear clustering were recognized quite a long time ago, electronic experiments have not been able to come closer to an integrated analysis of ensembles of relativistic fragments. The continued pause in the investigation of the "fine" structure of relativistic fragmentation has led to resumption of regular exposures of nuclear emulsions in beams of light nuclei produced for the first time at the Nuclotron of the Joint Institute for Nuclear Research (JINR, Dubna). To date, an analysis of the peripheral interactions of relativistic isotopes of beryllium, boron, carbon and nitrogen, including radioactive ones, with nuclei of the emulsion composition, has been performed, which allows the clustering pattern to be presented for a whole family of light nuclei.Comment: ISBN 978-3-319-01076-2. 55 pages, 28 figure

Ligand design and preparation, photophysical properties, and device performance of an encapsulated-type pseudo-tris(heteroleptic) iridium(iii) emitter

The organic molecule 2-(1-phenyl-1-(pyridin-2-yl)ethyl)-6-(3-(1-phenyl-1-(pyridin-2-yl)ethyl)phenyl)pyridine (H3L) has been designed, prepared, and employed to synthesize the encapsulated-type pseudo-tris(heteroleptic) iridium(III) derivative Ir(κ6-fac-C,C′,C″-fac-N,N′,N″-L). Its formation takes place as a result of the coordination of the heterocycles to the iridium center and the ortho-CH bond activation of the phenyl groups. Dimer [Ir(μ-Cl)(η4-COD)]2 is suitable for the preparation of this compound of class [Ir(9h)] (9h = 9-electron donor hexadentate ligand), but Ir(acac)3 is a more appropriate starting material. Reactions were carried out in 1-phenylethanol. In contrast to the latter, 2-ethoxyethanol promotes the metal carbonylation, inhibiting the full coordination of H3L. Complex Ir(κ6-fac-C,C′,C″-fac-N,N′,N″-L) is a phosphorescent emitter upon photoexcitation, which has been employed to fabricate four yellow emitting devices with 1931 CIE (x:y) ∼ (0.52:0.48) and a maximum wavelength at 576 nm. These devices display luminous efficacies, external quantum efficiencies, and power efficacies at 600 cd m–2, which lie in the ranges 21.4–31.3 cd A–1, 7.8–11.3%, and 10.2–14.1 lm W1–, respectively, depending on the device configuration

Anisotropic Collective Flow of Lambda Hyperons Produced in C + C Collisions at 4.2 AGeV/c

Features of anisotropic collective flow and spectral temperatures have been determined for lambda hyperons emitted from C + C collisions, at incident momentum of 4.2 AGeV/c, measured using the Propane Bubble Chamber of JINR at Dubna. Moreover, characteristics of protons and of negative pions, emitted from those collisions, have been determined and provided for comparison. The directed and elliptic flows of lambdas both agree in sign with the corresponding flows of protons. Parameters of the directed and elliptic flows for lambdas agree further, within errors, with the corresponding parameters for the co-produced protons. This contrasts an earlier finding by the E895 Collaboration of the directed flow being significantly weaker for lambdas than protons, in the much heavier Au + Au system, at comparable incident momentum. Particle spectral temperatures in the C + C collisions have been determined focusing independently on either center-of-mass energy, transverse energy or transverse momentum distributions. For either protons or negative pions, the temperatures were found to be approximately the same, no matter whether the emission of those particles was associated with lambda production or not. Results of the measurements have been compared to the results of simulations within the Quark-Gluon String Model.Comment: 25 pages, 5 figures, submitted to Nuclear Physics A; in revision, the discussion of results has been expanded and some deficiencies of figures and text have been correcte

Alignment in Gamma-Hadron Families of Cosmic Rays

Alignment of main fluxes of energy in a target plane is found in families of cosmic ray particles detected in deep lead X-ray chambers. The fraction of events with alignment is unexpectedly large for families with high energy and large number of hadrons. This can be considered as evidence for the existence of coplanar scattering of secondary particles in interaction of particles with superhigh energy, $E_0 > 10^{16}$ eV. Data analysis suggests that production of most aligned groups occurs low above the chamber and is characterized by a coplanar scattering and quasiscaling spectrum of secondaries in the fragmentation region. The most elaborated hypothesis for explanation of alignment is related to the quark-gluon string rupture. However, the problem of theoretical interpretation of our results still remains open.Comment: 15 pages, 2 tables, 6 figures (not included), Stanford University preprint SU-ITP-94-2

Prompt atmospheric neutrinos and muons: dependence on the gluon distribution function

We compute the next-to-leading order QCD predictions for the vertical flux of atmospheric muons and neutrinos from decays of charmed particles, for different PDF's (MRS-R1, MRS-R2, CTEQ-4M and MRST) and different extrapolations of these at small partonic momentum fraction x. We find that the predicted fluxes vary up to almost two orders of magnitude at the largest energies studied, depending on the chosen extrapolation of the PDF's. We show that the spectral index of the atmospheric leptonic fluxes depends linearly on the slope of the gluon distribution function at very small x. This suggests the possibility of obtaining some bounds on this slope in ``neutrino telescopes'', at values of x not reachable at colliders, provided the spectral index of atmospheric leptonic fluxes could be determined.Comment: 20 pages including 8 figure